阅读说明：本技术 半导体装置及制造方法 (Semiconductor device and method of manufacturing the same ) 是由 吉田崇一 于 2020-02-20 设计创作，主要内容包括：提供一种半导体装置,其具备半导体基板和设置在半导体基板的上表面的上方的发射电极,半导体基板具有：第一导电型的漂移区；第二导电型的基区,其设置在漂移区与半导体基板的上表面之间；第二导电型的接触区,其设置在基区与半导体基板的上表面之间,并且掺杂浓度高于基区的掺杂浓度；沟槽接触部,其连接于发射电极,并且以贯穿接触区的方式设置,且为导电材料；以及第二导电型的高浓度插塞区,其与沟槽接触部的底部接触地设置,并且掺杂浓度高于接触区的掺杂浓度。(Provided is a semiconductor device comprising a semiconductor substrate and an emitter electrode provided above the upper surface of the semiconductor substrate, wherein the semiconductor substrate comprises: a drift region of a first conductivity type; a base region of a second conductivity type provided between the drift region and the upper surface of the semiconductor substrate; a contact region of a second conductivity type, which is provided between the base region and the upper surface of the semiconductor substrate and has a doping concentration higher than that of the base region; a trench contact portion connected to the emitter electrode, disposed in a manner of penetrating the contact region, and made of a conductive material; and a high concentration plug region of the second conductivity type disposed in contact with the bottom of the trench contact portion and having a doping concentration higher than that of the contact region.)

1. A semiconductor device is characterized by comprising a semiconductor substrate and an emitter electrode provided above the upper surface of the semiconductor substrate,

the semiconductor substrate has:

a drift region of a first conductivity type;

a base region of a second conductivity type provided between the drift region and an upper surface of the semiconductor substrate;

a contact region of a second conductivity type provided between the base region and the upper surface of the semiconductor substrate and having a doping concentration higher than that of the base region;

a trench contact portion connected to the emitter electrode, disposed in a manner of penetrating the contact region, and made of a conductive material; and

a high concentration plug region of a second conductivity type disposed in contact with a bottom of the trench contact portion and having a doping concentration higher than that of the contact region.

2. The semiconductor device according to claim 1,

in the depth direction of the semiconductor substrate, the thickness of the high concentration plug region is smaller than that of the contact region.

3. The semiconductor device according to claim 2,

the lower end of the high concentration plug region is disposed at a position closer to the upper side than the lower end of the base region.

4. The semiconductor device according to any one of claims 1 to 3,

the semiconductor substrate further having an emitter region of the first conductivity type disposed between the base region and an upper surface of the semiconductor substrate and having a doping concentration higher than a doping concentration of the drift region,

the contact region is disposed to a position deeper than the emission region.

5. The semiconductor device according to any one of claims 1 to 4,

the semiconductor substrate has:

a plurality of trench portions provided from an upper surface of the semiconductor substrate to the drift region; and

a mesa portion sandwiched by two groove portions among the plurality of groove portions,

the semiconductor device has a transistor portion and a diode portion,

the transistor portion has a boundary portion in contact with the diode portion,

the trench contact portion and the high concentration plug region are provided in the mesa portion of the boundary portion.

6. The semiconductor device according to claim 5,

the trench contact portion and the high concentration plug region are also provided in the transistor portion other than the boundary portion.

7. The semiconductor device according to claim 5 or 6,

the trench contact portion and the high concentration plug region are also provided in the diode portion.

8. The semiconductor device according to any one of claims 5 to 7,

the groove portion has a conductive portion and an interlayer insulating film provided between the conductive portion and the emitter electrode,

the emitter electrode is in contact with an upper surface of the mesa portion.

9. A method of manufacturing, characterized in that,

a method for manufacturing a semiconductor device having a semiconductor substrate having a drift region of a first conductivity type,

the manufacturing method comprises the following steps:

a step of forming a base region of a second conductivity type, which is disposed between the drift region and the upper surface of the semiconductor substrate, and a contact region of the second conductivity type, which is disposed between the base region and the upper surface of the semiconductor substrate and has a doping concentration higher than that of the base region;

a step of forming a contact trench penetrating the contact region on an upper surface of the semiconductor substrate;

a step of forming a high concentration plug region of a second conductivity type, the high concentration plug region being in contact with a bottom of the contact trench and having a doping concentration higher than that of the contact region; and

and a step of forming a trench contact portion by providing a conductive material in the contact trench.

10. The manufacturing method according to claim 9,

the manufacturing method includes the steps of forming an interlayer insulating film inside the contact trench and on the upper surface of the semiconductor substrate, and etching back the interlayer insulating film on the upper surface of the semiconductor substrate.

Technical Field

The present invention relates to a semiconductor device and a method of manufacturing the same.

Background

Conventionally, semiconductor devices provided with transistors such as Insulated Gate Bipolar Transistors (IGBTs) are known (for example, see patent documents 1 to 3).

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2010-147381

Patent document 2: japanese laid-open patent publication No. 2012-156564

Patent document 3: japanese patent laid-open No. 2010-147380

Technical problem

The semiconductor device preferably has a small loss.

In order to solve the above problem, a first embodiment of the present invention provides a semiconductor device including a semiconductor substrate, and the semiconductor device may include an emitter electrode provided above an upper surface of the semiconductor substrate. The semiconductor substrate may have a drift region of a first conductivity type. The semiconductor substrate may have a base region of the second conductivity type disposed between the drift region and the upper surface of the semiconductor substrate. The semiconductor substrate may have a contact region of the second conductivity type disposed between the base region and the upper surface of the semiconductor substrate and having a doping concentration higher than that of the base region. The semiconductor substrate may have a trench contact portion connected to the emitter electrode and disposed in a manner of penetrating the contact region and being a conductive material. The semiconductor substrate may have a high concentration plug region of the second conductivity type disposed in contact with a bottom of the trench contact and having a doping concentration higher than that of the contact region.

The thickness of the high concentration plug region may be smaller than the thickness of the contact region in the depth direction of the semiconductor substrate.

The lower end of the high concentration plug region may be disposed above the lower end of the base region.

The semiconductor substrate may have an emitter region of the first conductivity type, which is disposed between the base region and the upper surface of the semiconductor substrate and has a doping concentration higher than that of the drift region. The contact region may be disposed to be deeper than the emitter region.

The semiconductor substrate may have a plurality of trench portions provided from an upper surface of the semiconductor substrate to the drift region. The semiconductor substrate may have a mesa portion sandwiched between two trench portions. The semiconductor device may have a transistor portion and a diode portion. The transistor portion may have a boundary portion in contact with the diode portion. A trench contact and a high concentration plug region may be provided in the mesa portion of the boundary portion.

The trench contact portion and the high concentration plug region may be provided in the transistor portion other than the boundary portion.

The trench contact portion and the high concentration plug region may be further provided at the diode portion.

The groove portion may have a conductive portion and an interlayer insulating film disposed between the conductive portion and the emitter electrode. The emitter electrode may be in contact with an upper surface of the mesa portion.

In a second embodiment of the present invention, there is provided a method for manufacturing a semiconductor device including a semiconductor substrate having a drift region of a first conductivity type. The manufacturing method may include a step of forming a base region of the second conductivity type, which is disposed between the drift region and the upper surface of the semiconductor substrate, and a contact region of the second conductivity type, which is disposed between the base region and the upper surface of the semiconductor substrate and has a doping concentration higher than that of the base region. The manufacturing method may include a step of forming a trench for contact penetrating a contact region on an upper surface of the semiconductor substrate. The manufacturing method may include a step of forming a high concentration plug region of the second conductivity type, which is in contact with the bottom of the contact trench and has a doping concentration higher than that of the contact region. The manufacturing method may include a step of forming a trench contact portion by disposing a conductive material inside the contact trench.

The manufacturing method may include a step of forming an interlayer insulating film on the inside of the contact trench and the upper surface of the semiconductor substrate and etching back the interlayer insulating film on the upper surface of the semiconductor substrate.

The above summary of the present invention does not include all the necessary features of the present invention. Moreover, a sub-combination of these feature groups can also be another invention.

Drawings

Fig. 1 is a plan view showing an example of a semiconductor device 100 according to an embodiment of the present invention.

Fig. 2A is an enlarged view of the area a in fig. 1.

Fig. 2B is a diagram showing another arrangement example of the cathode region 82 in a plan view.

Fig. 3 is a diagram showing one example of a section B-B in fig. 2A and 2B.

Fig. 4 is a perspective sectional view showing a structural example of the mesa portion 60.

Fig. 5 is a sectional view showing a structural example of the mesa portion 60.

Fig. 6 is a perspective sectional view showing a structural example of the table surface portion 61.

Fig. 7 is a perspective sectional view showing another configuration example of the table surface portion 61.

Fig. 8 is a sectional view showing a configuration example of an end portion of the active portion 120 in the X-axis direction.

Fig. 9 is an XZ sectional view showing an example of the mesa portion 62 included in the semiconductor device 100.

Fig. 10 is a diagram illustrating a part of the steps in the method for manufacturing the semiconductor device 100.

Fig. 11 is a diagram showing another example of the section B-B in fig. 2A and 2B.

Fig. 12 is a diagram comparing characteristics of the semiconductor device 100 of the example and the semiconductor device of the comparative example.

Fig. 13 is a diagram showing an example of hole density distribution in the depth direction of the diode portion 80 of the example and the comparative example.

Description of the symbols

10 … semiconductor substrate, 11 … well region, 12 … emitter region, 14 … base region, 15 … contact region, 16 … accumulation region, 18 … drift region, 20 … buffer region, 21 … upper surface, 22 … collector region, 23 … lower surface, 24 … collector, 29 … straight line portion, 30 … dummy trench portion, 31 … front end portion, 32 … dummy insulating film, 34 … dummy conductive portion, 38 … interlayer insulating film, 39 … straight line portion, 40 … gate trench portion, 41 … front end portion, 42 … gate insulating film, 44 … gate conductive portion, 52 … emitter electrode, 54 … trench contact portion, 55 … high concentration plug region, 56 … contact hole, … contact trench, 58 … boundary portion, 60,61,62 … mesa portion, 70 … transistor portion, 72 boundary portion, 78 … end portion region, 80 diode portion, 3681, … extension region, … edge structure portion, 100 … semiconductor device, 102 … edge, 112 … gate pad, 120 … active part, 130 … outer peripheral gate wiring, 131 … active side gate wiring, 202 … mask pattern, 204 … conductive material

Detailed Description

The present invention will be described below with reference to embodiments thereof, but the following embodiments do not limit the invention according to the claims. In addition, all combinations of the features described in the embodiments are not necessarily essential to the solution of the invention.

In this specification, one side in a direction parallel to the depth direction of the semiconductor substrate is referred to as "up", and the other side is referred to as "down". One of the two main surfaces of the substrate, layer, or other member is referred to as an upper surface, and the other surface is referred to as a lower surface. The directions of "up" and "down" are not limited to the direction of gravity or the direction when the semiconductor device is mounted.

In this specification, technical matters will be described using orthogonal coordinate axes of X, Y, and Z axes. The orthogonal axes are merely for specifying the relative positions of the components, and are not limited to specific directions. For example, the Z-axis is not limited to representing the height direction relative to the ground. Note that the + Z-axis direction and the-Z-axis direction are opposite directions to each other. When the positive and negative are not described and the Z-axis direction is described, the direction is parallel to the + Z axis and the-Z axis. In this specification, a case of viewing from the + Z axis direction is sometimes referred to as a plan view.

In the present specification, the term "identical" or "equal" may include a case where an error due to a manufacturing variation or the like is included. The error is, for example, within 10%.

In this specification, the conductive type of the impurity-doped region doped with an impurity is referred to as P-type or N-type. However, the conductivity type of each doped region may be opposite polarity. In the present specification, the term "P + type" or "N + type" means a higher doping concentration than P type or N type, and the term "P-type" or "N-type" means a lower doping concentration than P type or N type. In the present specification, the term "P + + type" or "N + + type" means that the doping concentration is higher than that of P + type or N + type.

In the present specification, the doping concentration refers to the concentration of an impurity activated as a donor or an acceptor. In this specification, the difference in the concentration of a donor and an acceptor may be referred to as a doping concentration. This concentration difference can be measured by a capacitance-voltage measurement method (CV method). In addition, the carrier concentration measured by the spreading resistance measurement method (SR method) may be used as the doping concentration. In addition, when the doping concentration profile has a peak, the peak may be the doping concentration in the region. In the case where the doping concentration in the region where the donor or the acceptor exists is almost uniform, the average value of the doping concentrations may be set as the doping concentration in the region. In addition, in this specification, the concentration of the dopant refers to the respective concentrations of the donor and the acceptor.

Fig. 1 is a plan view showing an example of a semiconductor device 100 according to an embodiment of the present invention. Fig. 1 shows positions where the respective members are projected on the upper surface of the semiconductor substrate 10. In fig. 1, only a part of the components of the semiconductor device 100 is shown, and a part of the components is omitted.

The semiconductor device 100 includes a semiconductor substrate 10. The semiconductor substrate 10 is a substrate made of a semiconductor material such as silicon or a compound semiconductor. The semiconductor substrate 10 has an edge 102 in a plan view. In this specification, the term "in plan view" means a view from the upper surface side of the semiconductor substrate 10. The semiconductor substrate 10 of this example has two sets of end edges 102 facing each other in a plan view. In fig. 1, the X-axis and the Y-axis are parallel to a certain end edge 102. In addition, the Z-axis is perpendicular to the upper surface of the semiconductor substrate 10.

The semiconductor substrate 10 is provided with an active portion 120. The active portion 120 is a region in which a main current flows in the depth direction between the upper surface and the lower surface of the semiconductor substrate 10 when the semiconductor device 100 is controlled to be in an on state. Although the emitter electrode is provided above the active portion 120, it is omitted in fig. 1.

Transistor portion 70 including a transistor element such as an IGBT may be provided in active portion 120. The active portion 120 may further include a diode portion 80 including a diode element such as a freewheeling diode (FWD).

In fig. 1, a region where transistor portion 70 is arranged is denoted by "I", and a region where diode portion 80 is arranged is denoted by "F". Transistor portion 70 and diode portion 80 are arranged in parallel in a predetermined arrangement direction (X-axis direction in fig. 1). The transistor portions 70 and the diode portions 80 may be alternately arranged in parallel in the X-axis direction. In this specification, a direction perpendicular to the arrangement direction in a plan view may be referred to as an extending direction (Y-axis direction in fig. 1). The transistor portion 70 and the diode portion 80 may have long sides in the extending direction, respectively. That is, the length of the transistor portion 70 in the Y-axis direction is larger than the width in the X-axis direction. Likewise, the length of diode portion 80 in the Y-axis direction is larger than the width in the X-axis direction. The extending direction of the transistor portion 70 and the diode portion 80 may be the same as the longitudinal direction of the trench portion.

The diode portion 80 has an N + -type cathode region in a region in contact with the lower surface of the semiconductor substrate 10. In this specification, a region where the cathode region is provided is referred to as a diode portion 80. That is, the diode portion 80 is a region overlapping with the cathode region in a plan view. In the lower surface of the semiconductor substrate 10, a P + -type collector region may be provided in a region other than the cathode region. In this specification, the diode portion 80 may include an extension region 81 extending in the Y-axis direction to a gate wiring described later in the diode portion 80. A collector region is provided on the lower surface of the extension region 81.

The semiconductor device 100 may have one or more pads above the semiconductor substrate 10. The semiconductor device 100 of this example has a gate pad 112. The semiconductor device 100 may further include pads such as an anode pad, a cathode pad, and a current detection pad. Each pad is disposed near the end edge 102. The vicinity of the end edge 102 refers to an area between the end edge 102 and the emitter electrode when viewed from above. When the semiconductor device 100 is mounted, each pad may be connected to an external circuit through a wire such as a metal wire.

A gate voltage is applied to the gate pad 112. The gate pad 112 is electrically connected to the conductive portion of the gate trench portion of the active portion 120. The semiconductor device 100 includes a gate wiring connecting the gate pad 112 and the gate groove portion. In fig. 1, gate wirings are hatched with diagonal lines.

The gate wiring of this example includes an outer peripheral gate wiring 130 and an active-side gate wiring 131. In a plan view, the peripheral gate line 130 is disposed between the active portion 120 and the edge 102 of the semiconductor substrate 10. The outer peripheral gate line 130 of this example surrounds the active portion 120 in a plan view. A region surrounded by the outer peripheral gate line 130 in a plan view may be the active portion 120. In addition, the outer peripheral gate wiring 130 is connected to the gate pad 112. The outer peripheral gate line 130 is disposed above the semiconductor substrate 10. The outer peripheral gate wiring 130 may be a metal wiring.

The active-side gate wiring 131 is provided in the active portion 120. By providing the source-side gate wiring 131 in the active portion 120, variations in wiring length from the gate pad 112 to each region of the semiconductor substrate 10 can be reduced.

The active-side gate wiring 131 is connected to the gate trench portion of the active portion 120. The active-side gate wiring 131 is disposed above the semiconductor substrate 10. The active-side gate wiring 131 may be a wiring formed of a semiconductor such as polycrystalline silicon doped with impurities.

The active-side gate wiring 131 may be connected to the outer circumferential gate wiring 130. The active-side gate line 131 of this example is provided so as to extend from the outer peripheral gate line 130 on one side to the outer peripheral gate line 130 on the other side in the X-axis direction so as to cross the active portion 120 at substantially the center in the Y-axis direction.

The semiconductor device 100 may include a temperature sensing unit, not shown, which is a PN junction diode formed of polysilicon or the like, and/or a current detection unit, not shown, which simulates an operation of a transistor portion provided in the active portion 120.

The semiconductor device 100 of this example includes an edge termination structure portion 90 between the peripheral gate line 130 and the edge 102. The edge termination structure 90 alleviates electric field concentration on the upper surface side of the semiconductor substrate 10. The edge termination structure 90 has, for example, a guard ring and a field plate provided in a ring shape so as to surround the active portion 120, and has a structure in which a surface electric field is reduced and these are combined.

Fig. 2A is an enlarged view of the area a in fig. 1. Region a is a region including transistor portion 70, diode portion 80, and active-side gate wiring 131. In the semiconductor substrate 10 of this example, the gate trench portion 40, the dummy trench portion 30, the well region 11, the emitter region 12, the base region 14, and the contact region 15 are provided in contact with the upper surface of the semiconductor substrate 10. In addition, in the semiconductor substrate 10 of this example, the cathode region 82 and the collector region 22 are provided in contact with the lower surface of the semiconductor substrate 10.

In addition, an emitter electrode 52 and an active-side gate wiring 131 are provided above the semiconductor substrate 10. The emitter electrode 52 is in contact with the emitter region 12, the contact region 15, and the base region 14 at the upper surface of the semiconductor substrate 10. The emitter electrode 52 is connected to the dummy conductive portion of the dummy groove portion 30. An interlayer insulating film may be provided between the emitter electrode 52 and the semiconductor substrate 10. The interlayer insulating film is provided with a contact hole for connecting the emitter electrode 52 and the semiconductor substrate 10.

An insulating film such as a thermally oxidized film is provided between the active-side gate wiring 131 and the semiconductor substrate 10. The active-side gate wiring 131 is connected to the gate conductive portion in the gate groove portion 40 on the upper surface of the semiconductor substrate 10. The active-side gate wiring 131 is not connected to the dummy conductive portion in the dummy trench portion 30. The gate trench portion 40 is provided to extend in the X-axis direction to a position below a gate wiring such as the active-side gate wiring 131. The gate conductive portion of the gate trench portion 40 is connected to the gate wiring.

A well region 11 is provided below the active-side gate wiring 131. The well region 11 is a region in which: the doping concentration thereof is higher than that of the base region 14, is formed in contact with the upper surface of the semiconductor substrate 10, and is formed to a position deeper than the bottom of the base region 14. The width of the well region 11 in the Y axis direction may be larger than the width of the active-side gate wiring 131 in the Y axis direction.

The transistor portion 70 is provided with a gate trench portion 40. The diode portion 80 is provided with a dummy groove portion 30. In the transistor portion 70, a dummy groove portion 30 may be provided. The gate trench portion 40 functions as a gate electrode to which a gate potential is applied in the transistor portion 70. An emitter potential is applied to the dummy trench portion 30.

The gate trench portion 40 and the dummy trench portion 30 have long sides in the Y-axis direction in a plan view. That is, the gate groove portion 40 and the dummy groove portion 30 are provided to extend in the Y-axis direction. The gate trench portion 40 and the dummy trench portion 30 may have a straight line portion parallel to the Y-axis direction.

The gate groove portion 40 and the dummy groove portion 30 are arranged at a predetermined interval in the X-axis direction. Note that the arrangement pattern of the gate trench portions 40 and the dummy trench portions 30 is not limited to the example of fig. 2A. The group including one or more gate trench portions 40 and the group including one or more dummy trench portions 30 may be alternately arranged along the X-axis direction.

The front ends of the two straight line portions of the at least one groove portion may be connected by a curved front end portion. In the example of fig. 2A, the gate trench portion 40 has two straight line portions 39 and one front end portion 41. The dummy groove portion 30 may similarly have two straight portions 29 and one tip portion 31. The dummy groove portion 30 may have only a straight portion. The tip of each trench portion in the Y axis direction may be disposed inside the well region 11. This can alleviate electric field concentration at the tip of the groove.

In this specification, a region of the semiconductor substrate 10 sandwiched by two straight line portions of the groove portion in the X-axis direction may be referred to as a mesa portion. The transistor portion 70 is provided with a mesa portion 60, and the diode portion 80 is provided with a mesa portion 61. The mesa portion is a region on the upper surface side of the semiconductor substrate 10 sandwiched between the groove portions with respect to the deepest bottom portion of the groove portion.

In each mesa portion, a P-type base region 14 is provided. The base region 14 is exposed at a part of the upper surface of the mesa portion. A contact region 15 and an emitter region 12 are provided on the upper surface of base region 14 of transistor portion 70. The contact region 15 of this example is of the P + type with a higher doping concentration than the doping concentration of the base region 14. The emitter region 12 of this example is of an N + type having a higher doping concentration than that of a drift region described later.

The emitter region 12 is provided on the upper surface of the semiconductor substrate 10 in contact with the gate trench portion 40. The emitter region 12 and the contact region 15 of this example are provided from one groove portion to the other groove portion with the mesa portion 60 therebetween. In the upper surface of the mesa portion 60 of this example, the contact regions 15 and the emitter regions 12 are alternately arranged in the Y-axis direction.

In another example, in the mesa portion 60, the contact region 15 and the emitter region 12 may also be arranged in stripes in the Y-axis direction. For example, the emitter regions 12 are provided in regions adjacent to the groove portions, and the contact region 15 is provided in a region sandwiched between the emitter regions 12. A base region 14 may be disposed on the upper surface of the mesa portion 60, and the base region 14 may sandwich a region in which the contact region 15 and the emitter region 12 are disposed in the Y-axis direction.

The emitter region 12 may not be provided in the mesa portion 61 of the diode portion 80. The base region 14 is provided on the upper surface of the mesa portion 61 in this example. The base region 14 may occupy more than half of the area of the upper surface of the mesa portion 61. A contact region 15 may be disposed on the upper surface of the mesa portion 61. The contact region 15 of the mesa portion 61 may be provided at a position overlapping with the end portion of the groove contact portion 54 in the Y-axis direction. The base region 14 may be provided on the upper surface of the mesa portion 61 so as to sandwich the contact region 15 in the Y-axis direction.

Each of the mesa portion 60 and the mesa portion 61 is provided with a trench contact portion 54. The trench contact portion 54 includes a contact trench (trench portion) formed from the upper surface of the semiconductor substrate 10 to the inside of the semiconductor substrate 10 and a conductive portion filled in the trench. The conductive portion may be formed of the same material as the emitter electrode 52 and be continuous with the emitter electrode 52, or may be formed of a material different from the emitter electrode 52.

The trench contact portion 54 penetrates the contact region 15 in the depth direction (Z-axis direction). That is, the volume of the contact region 15 is reduced by providing the trench contact portion 54. This can suppress hole injection from contact region 15 when the gate of transistor portion 70 is in the off state and the diode operates. Therefore, the reverse recovery loss in diode portion 80 can be reduced.

Further, by providing the trench contact portion 54, the contact area between the conductive portion and the semiconductor substrate 10 can be increased. Therefore, even if the widths of the mesa portion 60 and the mesa portion 61 in the X axis direction are made smaller, an increase in contact resistance between the emitter electrode 52 and the semiconductor substrate 10 can be suppressed.

The width of the trench contact portion 54 in the X-axis direction is smaller than the width of each mesa portion in the X-axis direction. Both ends of the groove contact portion 54 in the Y-axis direction may be provided in the contact regions 15 arranged at both ends in the Y-axis direction among the contact regions 15 of the respective mesa portions.

The groove contact portion 54 provided in the land portion 60 and the groove contact portion 54 provided in the land portion 61 may be the same length in the Y axis direction or may be different lengths. In the mesa portion 60, the trench contact portion 54 is disposed above each region of the contact region 15 and the emitter region 12. The contact region 15 and the emitter region 12 may be arranged in a range where the trench contact portion 54 is provided. The trench contact portion 54 of this example is not provided in the region of the mesa portion 60 corresponding to the base region 14 and the well region 11. In mesa portion 61, trench contact portion 54 is disposed above contact region 15 and base region 14. However, the trench contact portion 54 is not provided above the base region 14 sandwiched between the contact region 15 and the well region 11 in the mesa portion 61.

In the diode portion 80, an N + -type cathode region 82 is provided in a region in contact with the lower surface of the semiconductor substrate 10. In a region in contact with the lower surface of the semiconductor substrate 10, the collector region 22 is provided in a region where the cathode region 82 is not provided. The cathode region 82 is disposed apart from the well region 11 in the Y-axis direction. At least one of base region 14 and contact region 15 may be disposed between cathode region 82 and well region 11 in a plan view. In this example, the distance in the Y-axis direction between the cathode region 82 and the well region 11 is larger than the distance in the Y-axis direction between the trench contact portion 54 and the well region 11.

Fig. 2B is a diagram showing another arrangement example of the cathode region 82 in a plan view. The position of the end of the cathode region 82 in the Y axis direction in this example coincides with the position of the end of the trench contact portion 54. Since the extraction of carriers is facilitated by providing trench contact portion 54, it is easy to secure a withstand voltage even if cathode region 82 is brought close to well region 11.

The position of the end of the cathode region 82 in the Y axis direction may not coincide with the position of the end of the trench contact portion 54. The end portion of the cathode region 82 in the Y-axis direction may be disposed at a position overlapping the contact region 15. The end portion of the cathode region 82 in the Y axis direction may be disposed between the trench contact portion 54 and the well region 11.

Fig. 3 is a diagram showing one example of a section B-B in fig. 2A and 2B. The b-b cross section is the XZ plane through the contact zone 15. The semiconductor device 100 of this example has the semiconductor substrate 10, the emitter electrode 52, and the collector electrode 24 in this cross section.

The emitter electrode 52 may be in contact with the upper surface 21 of the semiconductor substrate 10 in each mesa portion. That is, no insulating film is provided between each mesa portion and the emitter electrode 52. The insulating film does not extend directly above the mesa portions but is buried in the trench portions. The emitter electrode 52 may be in contact with the upper surface 21 in a range including a plurality of mesa portions and a plurality of groove portions. With this configuration, even if the width of the mesa portion in the X-axis direction is made smaller, the contact area between the mesa portion and the emitter electrode 52 can be secured.

The collector electrode 24 may be provided on the entire lower surface 23 of the semiconductor substrate 10. The collector electrode 24 and the emitter electrode 52 may be formed of a metal material such as aluminum.

A P-type base region 14 is provided on the upper surface 21 side of the semiconductor substrate 10 in the cross section. In this cross section, on the upper surface 21 side of the semiconductor substrate 10 in the transistor portion 70, a P + -type contact region 15 and a P-type base region 14 are provided in this order from the upper surface 21 of the semiconductor substrate 10. In this cross section, a P-type base region 14 is provided on the upper surface 21 side of the semiconductor substrate 10 in the diode portion 80.

In each mesa portion, an N + -type accumulation region 16 having a higher doping concentration than that of the drift region 18 may be provided between the base region 14 and the drift region 18. The accumulation region 16 may not be provided in the mesa portion 61. By providing the accumulation region 16, the carrier Injection promotion effect (IE effect) can be enhanced, and the on voltage in the transistor portion 70 can be reduced.

In transistor portion 70 and diode portion 80, N-type drift region 18 is provided below base region 14. In transistor portion 70 and diode portion 80, N + -type buffer region 20 is provided below drift region 18.

The doping concentration of the buffer region 20 is higher than the doping concentration of the drift region 18. The buffer region 20 can function as a field stop layer that prevents a depletion layer spreading from the lower surface of the base region 14 from reaching the collector region 22 and the cathode region 82.

In the transistor portion 70, a P + -type collector region 22 is provided below the buffer region 20. In the diode portion 80, a cathode region 82 is provided below the buffer region 20.

One or more gate groove portions 40 and one or more dummy groove portions 30 are provided on the upper surface 21 side of the semiconductor substrate 10. Each trench portion is provided so as to penetrate the base region 14 from the upper surface 21 of the semiconductor substrate 10 and reach the drift region 18. In a region where at least one of the emitter region 12, the contact region 15, and the accumulation region 16 is provided, each trench portion also penetrates these regions to reach the drift region 18. The trench portion penetrating doped region is not limited to being manufactured in the order in which the trench portion is formed after the doped region is formed. After forming the trench portions, a structure in which the doped regions are formed between the trench portions is also included in the structure in which the trench portions penetrate the doped regions.

The gate groove portion 40 has a gate insulating film 42 and a gate conductive portion 44 provided on the upper surface 21 side of the semiconductor substrate 10. The gate insulating film 42 is provided so as to cover the inner wall of the gate groove portion 40. The gate insulating film 42 may be formed by oxidizing or nitriding a semiconductor of an inner wall of the gate trench portion 40. The gate conductive portion 44 is provided inside the gate groove portion 40 at a position inside the gate insulating film 42. That is, the gate insulating film 42 insulates the gate conductive portion 44 from the semiconductor substrate 10. The gate conductive portion 44 is formed of a conductive material such as polysilicon.

The gate conductive portion 44 includes a region facing the base region 14 with the gate insulating film 42 interposed therebetween. The gate conductive portion 44 is insulated from the emitter electrode 52 by the interlayer insulating film 38. The interlayer insulating film 38 is silicate glass such as PSG or PBSG. At least a part of the interlayer insulating film 38 may be disposed inside the gate trench. At least a part of the interlayer insulating film 38 may be provided above the upper surface 21 of the semiconductor substrate 10. If a predetermined voltage is applied to the gate conductive portion 44, a channel formed of an inversion layer of electrons is formed in a surface layer of an interface in the base region 14 in contact with the gate trench.

The dummy trench portion 30 may have the same structure as the gate trench portion 40 in the cross section. The dummy groove portion 30 includes a dummy groove provided on the upper surface 21 side of the semiconductor substrate 10, a dummy insulating film 32, and a dummy conductive portion 34. The dummy insulating film 32 is provided so as to cover the inner wall of the dummy trench. The dummy conductive portion 34 is disposed inside the dummy trench and is disposed inside the dummy insulating film 32. The dummy insulating film 32 insulates the dummy conductive portion 34 from the semiconductor substrate 10. The dummy conductive portions 34 may be formed of the same material as the gate conductive portions 44. In this cross section, the dummy conductive portion 34 may be insulated from the emitter electrode 52 by the interlayer insulating film 38. The dummy conductive portion 34 may be connected to the emitter electrode 52 through a contact hole or the like provided in the interlayer insulating film 38 in a cross section different from that of fig. 3. At least a part of the interlayer insulating film 38 may be disposed inside the dummy trench. At least a part of the interlayer insulating film 38 may be provided on the upper surface 21 of the semiconductor substrate 10.

A trench contact 54 of conductive material is provided in at least one mesa. The trench contact 54 may be formed of the same material as the emitter electrode 52, or may be formed of a material such as tungsten. By forming the trench contact portion 54 from a material including tungsten, a fine trench contact portion 54 can be easily formed. The trench contact 54 is connected to the emitter electrode 52.

The trench contact portion 54 is provided so as to penetrate the contact region 15. That is, the trench contact portion 54 is provided from the upper surface 21 of the semiconductor substrate 10 to a position reaching the base region 14. The lower end of trench contact portion 54 may be disposed at the same position as the lower end of base region 14, or may be disposed below the lower end of base region 14. The trench contact 54 may penetrate the emitter region 12 in a different cross section than in fig. 3.

As described above, since the trench contact portion 54 penetrates the contact region 15, the contact region 15 becomes small. Therefore, injection of holes from the contact region 15 to the drift region 18 side can be suppressed.

A high concentration plug region 55 of P + + type having a higher doping concentration than that of the contact region 15 is provided in a region in contact with the bottom of the trench contact portion 54. The high concentration plug region 55 may cover the entire bottom surface of the trench contact 54. The doping concentration of the high concentration plug region 55 may be 2 times or more, 5 times or more, or 10 times or more the doping concentration of the contact region 15. By providing the high concentration plug region 55, the contact resistance between the trench contact portion 54 and the semiconductor substrate 10 can be reduced. In addition, holes are easily extracted from the semiconductor substrate 10 by the high concentration plug region 55 and the trench contact portion 54. Therefore, the reverse recovery loss can be further reduced. It is preferable that the thickness of the high concentration plug region 55 in the depth direction is smaller than the thickness of the contact region 15 in the depth direction.

Transistor portion 70 may have boundary portion 72 in contact with diode portion 80. The boundary portion 72 includes one or more mesa portions 60. The mesa portion 60 in the boundary portion 72 may have the same structure as the mesa portion 60 except for the boundary portion 72.

The trench contact portion 54 and the high concentration plug region 55 may be provided in the mesa portion 60 of the boundary portion 72. This can reduce the holes flowing from the contact region 15 of the boundary portion 72 to the diode portion 80. The trench contact portion 54 and the high concentration plug region 55 may be provided only at the boundary portion 72, or may be provided at a position other than the boundary portion 72.

The trench contact portion 54 and the high concentration plug region 55 may also be provided at the mesa portion 60 other than the boundary portion 72. The trench contact portion 54 and the high concentration plug region 55 may be provided on the entire mesa portion 60 of the transistor portion 70. The trench contact portion 54 and the high concentration plug region 55 may also be provided on the entire mesa portion 60 having the contact region 15 and the emitter region 12. This can reduce the number of holes flowing from the entire transistor portion 70 to the diode portion 80.

The trench contact portion 54 and the high concentration plug region 55 may also be provided at the diode portion 80. The trench contact portion 54 and the high concentration plug region 55 may be provided on the entire mesa portion 61 of the diode portion 80. The groove contact portion 54 provided in the mesa portion 61 may be formed to the same depth as the groove contact portion 54 provided in the mesa portion 60, or may be formed to a different depth from the groove contact portion 54 provided in the mesa portion 60. In the mesa portion 61, the trench contact portion 54 may also penetrate the contact region 15.

Fig. 4 is a perspective sectional view showing a structural example of the mesa portion 60. In fig. 4, the contact trench 57 in the trench contact portion 54 is shown, and the conductive material filled in the contact trench 57 is omitted.

The contact region 15 in this example is arranged to be deeper than the emitter region 12. As shown in fig. 4, the contact trench 57 is provided so as to penetrate the contact region 15 and the emitter region 12. When the emitter region 12 is provided at a position deeper than the contact region 15, the contact trench 57 may be provided at a position deeper than the lower end of the emitter region 12, or may be provided at a position shallower than the lower end of the emitter region 12.

A P + + type high concentration plug region 55 is provided in the bottom of the contact trench 57. The contact region 15, the emitter region 12, and the base region 14 may be exposed at the side surfaces of the contact trench 57. The high concentration plug region 55 may be exposed at the bottom surface of the contact trench 57. Trench contact 54 may contact region 15, emitter region 12, base region 14, and heavy plug region 55.

Fig. 5 is a sectional view showing a structural example of the mesa portion 60. In this example, the thickness of the high concentration plug region 55 is T1, the thickness of the contact region 15 is T2, the protrusion length of the contact trench 57 protruding downward from the lower end of the contact region 15 is T3, and the thickness of the base region 14 below the high concentration plug region 55 is T4 in the depth direction of the semiconductor substrate 10. The thickness or length of each component may take on the maximum value of the thickness or length of each component.

In this example, the thickness T1 of the high concentration plug region 55 is smaller than the thickness T2 of the contact region 15. The thickness T1 may be less than half the thickness T2, less than 1/4, or less than 1/10. This can suppress the injection of holes from the high concentration plug region 55. The product of the thickness T1 of the high concentration plug region 55 and the doping concentration of the high concentration plug region 55 may be smaller than the product of the thickness T2 of the contact region 15 and the doping concentration of the contact region 15.

The lower end of the high concentration plug region 55 is provided above the lower end of the base region 14. That is, the high concentration plug region 55 is provided in the base region 14, and does not contact the accumulation region 16 or the drift region 18. Thereby, the trench contact 54 is prevented from being connected to the N-type region through the high concentration plug region 55.

The protruding length T3 of the contact trench 57 is smaller than the thickness T4 of the base region 14. If the protrusion length T3 is increased, the distance between the high concentration plug region 55 and the drift region 18 (or the accumulation region 16) becomes shorter, and the withstand voltage is lowered. The projection length T3 may be less than half the thickness T4, or less than 1/4.

Further, if the thickness T1 of the high concentration plug region 55 is large, the distance between the high concentration plug region 55 and the drift region 18 (or the accumulation region 16) becomes short, and the withstand voltage is lowered. The thickness T1 may be less than half the thickness T4, less than 1/4, or less than 1/10.

Further, the width of the contact trench 57 in the X axis direction (i.e., the width of the trench contact portion 54) is W1, and the distance between the gate trench portion 40 and the contact trench 57 in the X axis direction is W2. That is, the width W2 is the width of the contact region 15. The width W1 may be equal to or more than half the width W2, or equal to or more than 1 time. By increasing the width W1, hole injection from the contact region 15 can be suppressed.

The high concentration plug region 55 may be formed by implanting P-type impurities into the contact trench 57 from above the upper surface 21 of the semiconductor substrate 10. At this time, P-type impurities are also implanted into the contact region 15 and the region of the emitter region 12 exposed on the side surface of the contact trench 57. The boundary portion 58 of the contact region 15 in contact with the contact trench 57 may have an impurity concentration higher than that of a region of the contact region 15 in contact with the gate trench portion 40. With this configuration, the contact resistance between the trench contact portion 54 and the contact region 15 can be further reduced. In addition, the P-type impurity concentration of the region of the emitter region 12 in contact with the contact trench 57 may be higher than the P-type impurity concentration of the region of the emitter region 12 in contact with the gate trench portion 40. The region of the emitter region 12 in contact with the contact trench 57 may also be inverted to P-type.

The width W2 is preferably set to a thickness such that the P-type impurity implanted from the contact trench 57 into the emitter region 12 does not reach the gate trench portion 40. The width W2 may be 0.2 μm or more, or may be 0.5 μm or more.

The step of forming the high concentration plug region 55 is preferably performed after forming the emitter region 12, the base region 14, the accumulation region 16, the contact region 15, and the respective trench portions. This can reduce the thermal history with respect to the high-concentration plug region 55 and the boundary portion 58. Therefore, the thickness T1 of the high concentration plug region 55 can be reduced, and the P-type impurity implanted into the boundary portion 58 can be suppressed from reaching the gate trench portion 40.

Fig. 6 is a perspective sectional view showing a structural example of the table surface portion 61. In fig. 6, the contact trench 57 in the trench contact portion 54 is shown, and the conductive material filled in the contact trench 57 is omitted.

As shown in fig. 6, the contact trench 57 is provided from the upper surface 21 of the semiconductor substrate 10 to the inside of the base region 14. The contact trench 57 may penetrate the contact region 15. A P + + type high concentration plug region 55 is provided in the bottom of the contact trench 57. The contact region 15 and the base region 14 may be exposed at the side surface of the contact trench 57. The high concentration plug region 55 may be exposed at the bottom surface of the contact trench 57. The trench contact 54 may contact the contact region 15, the base region 14, and the high concentration plug region 55.

Fig. 7 is a perspective sectional view showing another configuration example of the table surface portion 61. The mesa portion 61 of the present example has the same structure as the mesa portion 60 on the upper surface 21 of the semiconductor substrate 10. That is, in the mesa portion 61 of this example, the contact regions 15 and the emitter regions 12 are alternately arranged in the Y-axis direction. In this case, the contact trench 57 may be provided from the upper surface 21 of the semiconductor substrate 10 to the base region 14 through the contact region 15 and the emitter region 12.

Fig. 8 is a sectional view showing a configuration example of an end portion of the active portion 120 in the X-axis direction. The cross-section of fig. 8 is an XZ cross-section. The active portion 120 of this example surrounds the well region 11 in a plan view. Although the outer peripheral gate line 130 is provided above the well region 11, it is omitted in fig. 8.

The active portion 120 of this example has an end region 78 between the transistor portion 70 (or the diode portion 80) disposed at the outermost end in the X-axis direction and the well region 11. The gate trench portion 40 and the dummy trench portion 30 are not disposed in the end region 78. The base region 14 may be exposed at the upper surface 21 of the semiconductor substrate 10 in the end region 78.

More than one set of trench contacts 54 and heavy concentration plug regions 55 may be provided in the end region 78. In the end region 78 of this example, the plurality of sets of trench contact portions 54 and high concentration plug regions 55 are arranged at equal intervals in the X-axis direction. The trench contact 54 and the high concentration plug region 55 in the end region 78 may have the same structure as the trench contact 54 and the high concentration plug region 55 in the transistor portion 70. By providing the end region 78, carriers such as holes flowing from a region outside the active region 120 to the active region 120 can be extracted. This can suppress concentration of carriers on the mesa portion disposed at the end of the active portion 120.

Fig. 9 is an XZ sectional view showing an example of the mesa portion 62 included in the semiconductor device 100. Mesa portion 62 may be provided in transistor portion 70 or diode portion 80. The mesa portion 62 is a floating mesa electrically insulated from the emitter electrode 52 by the interlayer insulating film 38. By providing the mesa portion 62, extraction of carriers to the emitter electrode 52 can be suppressed, and the IE effect can be further improved. The trench contact 54 is not provided in the mesa portion 62.

Fig. 10 is a diagram illustrating a part of the steps in the method for manufacturing the semiconductor device 100. A process of forming the trench contact is shown in fig. 10. In fig. 10, the accumulation zone 16 is omitted. Before forming the trench contact portion, the contact region 15, the emitter region 12, the base region 14, the gate trench portion 40, and the dummy trench portion 30 are formed on the semiconductor substrate 10. In this example, the upper end of the gate conductive portion 44 of the gate groove portion 40 and the upper end of the dummy conductive portion 34 of the dummy groove portion 30 are disposed below the upper surface 21 of the semiconductor substrate 10.

In S1000, an interlayer insulating film 38 is formed above the conductive portion of each groove portion and on the upper surface 21 of the semiconductor substrate 10. As described above, since the conductive portion of each groove portion is disposed below the upper surface 21 of the semiconductor substrate 10, a part of the interlayer insulating film 38 is also formed on the conductive portion in each groove portion.

In S1002, the interlayer insulating film 38 above the upper surface 21 of the semiconductor substrate 10 is etched back to be removed. Thereby, the interlayer insulating film 38 in each groove portion is left, and the upper surfaces of the mesa portions 60 and 61 are exposed.

In S1004, the contact trench 57 is formed by etching the upper surface 21 of the semiconductor substrate 10 after forming the mask pattern 202 on the upper surface 21 of the semiconductor substrate 10. The contact trench 57 penetrates the contact region 15.

In S1006, the high concentration plug region 55 in contact with the bottom of the contact trench 57 is formed. The high concentration plug region 55 may be formed by implanting the same P-type impurity as the contact region 15. In addition, the acceleration energy of the impurity ions in S1006 may be smaller than that when the impurity ions are implanted into the contact region 15. In addition, the heat treatment temperature in S1006 may be lower than the heat treatment temperature when the contact region 15 is formed. In addition, the heat treatment time in S1006 may be shorter than the heat treatment time when the contact region 15 is formed. In S1006, heat treatment may not be performed.

As an example, the P-type impurity is boron. As one example, the acceleration voltage of the impurity ions at the time of forming the contact region 15 may be above 100keV and below 140 keV. The implantation amount of impurity ions can be 1 × 10¹⁵(/cm²) Above and 5 × 10¹⁵(/cm²) The following. The heat treatment temperature can be above 950 ℃ and 1100 DEG CThe following. The heat treatment time may be 20 minutes or more and 40 minutes or less.

As one example, the acceleration voltage of the impurity ions at the time of forming the high concentration plug region 55 may be above 20keV and below 80 keV. The implantation amount of impurity ions can be 1 × 10¹⁵(/cm²) Above and 5 × 10¹⁵(/cm²) The following. The implantation amount of the impurity ions at the time of forming the high concentration plug region 55 may be smaller than that at the time of forming the contact region 15. However, since the thickness of the high concentration plug region 55 is small, the doping concentration per unit volume becomes high. The heat treatment temperature may be 800 ℃ or higher and 900 ℃ or lower. The heat treatment time when the high concentration plug region 55 is formed may be a time less than one tenth of the heat treatment time when the contact region 15 is formed. The heat treatment time when the high concentration plug region 55 is formed may be 5 seconds or more and 1 minute or less.

In S1008, a conductive material is formed inside the contact trench 57. In this example, a conductive material 204 is also formed over the mask pattern 202. The conductive material formed inside the contact trench 57 becomes the trench contact portion 54.

In S1010, the mask pattern 202 is removed. Thereby, the trench contact portion 54 can be formed. After the trench contact 54 is formed, the emitter electrode 52 is formed on the upper surface 21 of the semiconductor substrate 10. When the trench contact 54 is formed of the same material as the emitter electrode 52, the conductive material may be deposited after removing the mask pattern 202 in S1008.

After the formation of the high concentration plug region 55, it is preferable that no step is performed at a temperature higher than the heat treatment temperature at the time of the formation of the high concentration plug region 55. Thereby, the thickness of the high concentration plug region 55 can be controlled with high accuracy.

Fig. 11 is a diagram showing another example of the section B-B in fig. 2A and 2B. The structure of the interlayer insulating film 38 of the semiconductor device 100 of this example is different from that of the example shown in fig. 3. The other structure is the same as the example shown in fig. 3.

In this example, the interlayer insulating film 38 is provided above the upper surface 21 of the semiconductor substrate 10. The interlayer insulating film 38 is provided so as to cover each groove portion. That is, the width of the interlayer insulating film 38 in the X-axis direction is larger than the width of the groove portion. The interlayer insulating film 38 may be provided in each groove, or the interlayer insulating film 38 may not be provided.

Each of the mesa portion 60 and the mesa portion 61 has a portion not covered with the interlayer insulating film 38. The interlayer insulating film 38 may be provided with a contact hole 56 that exposes the mesa portion 60 and the mesa portion 61. The contact hole 56 may be provided to have a long side in the longitudinal direction (Y-axis direction) of each land 60.

The trench contact portion 54 of this example is provided on the upper surfaces of the mesa portion 60 and the mesa portion 61 exposed through the contact hole 56. The trench contact portion 54 may be formed by etching the upper surface of the semiconductor substrate 10 using the interlayer insulating film 38 provided with the contact hole 56 as a mask. At this time, in the upper surface 21 of the semiconductor substrate 10, the position of the opening portion of the contact hole 56 coincides with the position of the trench contact portion 54. In another example, the position of the opening portion of the contact hole 56 and the position of the trench contact portion 54 may not coincide.

Fig. 12 is a diagram comparing characteristics of the semiconductor device 100 of the example and the semiconductor device of the comparative example. Fig. 12 shows a waveform of a forward current If in the diode unit 80 and a waveform of an anode-cathode voltage Vr of the diode unit 80 when the transistor unit 70 is turned off. The semiconductor device of the comparative example has the same structure as the semiconductor device 100 except that the trench contact 54 is not provided.

As shown in fig. 12, in the semiconductor device 100 of the embodiment, the peak current Irp at the time of reverse recovery is smaller than that of the comparative example. Therefore, the semiconductor device 100 can reduce reverse recovery loss. This is considered to be because carrier injection from the contact region 15 is suppressed by providing the channel contact portion 54.

Fig. 13 is a diagram showing an example of hole density distribution in the depth direction in the diode portions 80 of the example and the comparative example. Fig. 13 shows the hole density of a region adjacent to the transistor portion 70 in the diode portion 80. As shown in fig. 13, it is understood that the hole density of the embodiment is reduced by providing the trench contact portion 54, particularly on the upper surface (positive electrode) side.

Although the present invention has been described above with reference to the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various changes and modifications can be added to the above embodiments. As is apparent from the description of the claims, the embodiments to which such changes and improvements are added can be included in the technical scope of the present invention.

It should be noted that the execution order of the respective processes such as actions, procedures, steps, and stages in the apparatus, system, program, and method shown in the claims, the specification, and the drawings may be implemented in any order unless "earlier", "in advance", or the like is specifically explicitly indicated, and in addition, the result of the previous process is not used in the subsequent process. Even if the description is made using "first", "next", and the like for convenience sake with respect to the operation flows in the claims, the description, and the drawings, it does not mean that the operations must be performed in this order.