阅读说明：本技术 用于在垂直功率器件中减小接触注入物向外扩散的氧***的Si层 (Si layer for oxygen insertion to reduce contact implant out-diffusion in vertical power devices ) 是由 M.波茨尔 O.布兰克 T.菲尔 B.格勒 R.哈瑟 S.里奥曼 A.梅瑟 M.罗施 于 2019-08-08 设计创作，主要内容包括：用于在垂直功率器件中减小接触注入物向外扩散的氧插入的Si层。一种半导体器件包括：延伸到Si衬底中的栅沟槽；在Si衬底中的本体区，该本体区包括沿栅沟槽的侧壁延伸的沟道区；在本体区上方、在Si衬底中的源区；延伸到Si衬底中并且通过源区的一部分和本体区的一部分与栅沟槽分离的接触沟槽，该接触沟槽填充有导电材料，该导电材料接触在接触沟槽的侧壁处的源区和在接触沟槽的底部处的高掺杂本体接触区；以及沿接触沟槽的侧壁形成并且被设置在高掺杂本体接触区和沟道区之间的扩散阻挡结构，该扩散阻挡结构包括Si和氧掺杂Si的交替层。(An oxygen-inserted Si layer for reducing contact implant out-diffusion in vertical power devices. A semiconductor device includes: a gate trench extending into the Si substrate; a body region in the Si substrate, the body region including a channel region extending along a sidewall of the gate trench; a source region in the Si substrate over the body region; a contact trench extending into the Si substrate and separated from the gate trench by a portion of the source region and a portion of the body region, the contact trench being filled with a conductive material contacting the source region at sidewalls of the contact trench and the highly doped body contact region at a bottom of the contact trench; and a diffusion barrier structure formed along sidewalls of the contact trench and disposed between the highly doped body contact region and the channel region, the diffusion barrier structure comprising alternating layers of Si and oxygen-doped Si.)

1. A semiconductor device, comprising:

a gate trench extending into the Si substrate;

a body region in the Si substrate, the body region comprising a channel region extending along a sidewall of the gate trench;

a source region in the Si substrate over the body region;

a contact trench extending into the Si substrate and separated from the gate trench by a portion of the source region and a portion of the body region, the contact trench filled with a conductive material that contacts the source region at sidewalls of the contact trench and a highly doped body contact region at a bottom of the contact trench; and

a diffusion barrier structure formed along sidewalls of the contact trench and disposed between the highly doped body contact region and the channel region, the diffusion barrier structure comprising alternating layers of Si and oxygen-doped Si.

2. The semiconductor device of claim 1, wherein the diffusion barrier structure extends along a bottom of the contact trench.

3. The semiconductor device of claim 1 wherein the highly doped body contact region is laterally confined only by the diffusion barrier structure, which is not at the bottom of the contact trench.

4. The semiconductor device of claim 1, wherein the conductive material filling the contact trench may extend onto the front major surface of the Si substrate beyond the diffusion barrier structure and in a direction towards the gate trench.

5. The semiconductor device of claim 1, wherein the diffusion barrier structure comprises a blanket layer of Si epitaxially grown on the alternating layers of Si and oxygen-doped Si.

6. A method of manufacturing a semiconductor device, the method comprising:

forming a gate trench extending into the Si substrate;

forming a contact trench extending into the Si substrate and separated from the gate trench;

forming a highly doped body contact region in the Si substrate at the bottom of the contact trench;

forming a diffusion barrier structure along sidewalls of the contact trench, the diffusion barrier structure comprising alternating layers of Si and oxygen-doped Si;

forming a body region in the Si substrate, the body region including a channel region extending along a sidewall of the gate trench;

forming a source region in the Si substrate over the body region; and

the contact trench is filled with a conductive material that contacts the source region at the sidewalls of the contact trench and the highly doped body contact region at the bottom of the contact trench.

7. The method of claim 6, wherein forming the diffusion barrier structure comprises:

epitaxially growing the alternating layers of Si and oxygen-doped Si on sidewalls and bottom of the contact trench prior to filling the contact trench with the conductive material.

8. The method of claim 7, further comprising:

epitaxially growing a Si cap layer on the alternating layers of Si and oxygen-doped Si.

9. The method of claim 7, wherein forming the highly doped body contact region comprises:

implanting dopant species into the alternating layers of Si and oxygen-doped Si at the bottom of the contact trench; and

annealing the Si substrate to activate the implanted dopant species.

10. The method of claim 7, further comprising:

removing the alternating layers of Si and oxygen-doped Si from at least a portion of the bottom of the contact trench.

11. The method of claim 10, wherein removing the alternating layers of Si and oxygen-doped Si from at least a portion of the bottom of the contact trench comprises:

epitaxially growing a Si cap layer on the alternating layers of Si and oxygen-doped Si;

depositing a conformal spacer oxide on the Si cap layer;

anisotropically etching the conformal spacer oxide to expose a diffusion barrier structure at a bottom of the contact trench;

etching away the exposed diffusion barrier structure at the bottom of the contact trench; and

removing the conformal spacer oxide after etching away the exposed diffusion barrier structure at the bottom of the contact trench.

12. The method of claim 6, wherein forming the diffusion barrier structure comprises:

epitaxially growing the alternating layers of Si and oxygen-doped Si only on the sidewalls, but not on the bottom, of the contact trench prior to filling the contact trench with the conductive material.

13. The method of claim 12, further comprising:

epitaxially growing a Si cap layer on the alternating layers of Si and oxygen-doped Si.

14. The method of claim 12, wherein forming the highly doped body contact region comprises:

implanting dopant species into the bottom of the contact trench, the bottom of the contact trench being free of the alternating layers of Si and oxygen-doped Si; and

annealing the Si substrate to activate the implanted dopant species.

15. The method of claim 6, further comprising:

etching back an insulating layer formed on the front main surface of the Si substrate before filling the contact trench with the conductive material, such that the insulating layer has an opening that is aligned with the contact trench and is wider than a combined width of the contact trench and the diffusion barrier structure.

16. The method of claim 15, wherein filling the contact trench with the conductive material comprises:

depositing the conductive material in the contact trench and in an opening formed in the insulating layer such that the conductive material extends onto the front major surface of the Si substrate beyond the diffusion barrier structure and in a direction toward the gate trench.

17. The method of claim 6, wherein forming the diffusion barrier structure comprises:

epitaxially growing the alternating layers of Si and oxygen-doped Si on the sidewalls and bottom of the contact trench prior to forming the body region and the source region.

18. The method of claim 17, further comprising:

epitaxially growing a Si cap layer on the alternating layers of Si and oxygen-doped Si before forming the body regions and the source regions.

19. The method of claim 17, further comprising:

removing the alternating layers of Si and oxygen-doped Si from at least a portion of the bottom of the contact trench.

20. The method of claim 19, wherein removing the alternating layers of Si and oxygen-doped Si from at least a portion of the bottom of the contact trench comprises:

epitaxially growing a Si cap layer on the alternating layers of Si and oxygen-doped Si;

depositing a conformal spacer oxide on the Si cap layer;

anisotropically etching the conformal spacer oxide to expose a diffusion barrier structure at a bottom of the contact trench;

etching away the exposed diffusion barrier structure at the bottom of the contact trench; and

removing the conformal spacer oxide after etching away the exposed diffusion barrier structure at the bottom of the contact trench.

21. The method of claim 6, wherein forming the diffusion barrier structure comprises:

forming a sacrificial insulating layer at the bottom of the contact trench before forming the body region and the source region;

after forming the sacrificial insulating layer, epitaxially growing alternating layers of the Si and oxygen-doped Si on sidewalls of the contact trench;

after epitaxially growing the alternating layers of Si and oxygen-doped Si, the sacrificial insulating layer is removed from the bottom of the contact trench.

22. The method of claim 6, further comprising:

filling the contact trench with a sacrificial plug material after forming the diffusion barrier structure and before forming the source and body regions;

forming the source region and the body region in the Si substrate after filling the contact trench with the sacrificial plug material;

removing the sacrificial plug material after forming the source region and the body region;

implanting dopant species into the bottom of the contact trench after removing the sacrificial plug material and before filling the contact trench with the conductive material; and

annealing the Si substrate to activate the implanted dopant species to form the highly doped body contact region.

Background

As the dimensions of trench-based transistors shrink, the impact of highly doped source/body contacts on the net body doping near the channel region becomes more important. The Vth (threshold voltage) and RonA (on-state resistance) of the device increase for a wider lateral distribution of source/body contact diffusion with doping levels 2-3 orders of magnitude higher than the body doping. Increasing the distance between the source/body contact and the channel region causes the body to be depleted at high drain voltages, which may result in high DIBL (drain induced barrier reduction). Furthermore, the process window variation for both trench width and contact width, as well as contact misalignment, must become smaller to avoid these adverse effects (higher Vth, higher RonA, and higher DIBL).

Therefore, it is desirable to better control the lateral out-diffusion of the source/body contact doping.

Disclosure of Invention

According to an embodiment of a semiconductor device, the semiconductor device comprises: a gate trench extending into the Si substrate; a body region in the Si substrate, the body region including a channel region extending along a sidewall of the gate trench; a source region in the Si substrate over the body region; a contact trench extending into the Si substrate and separated from the gate trench by a portion of the source region and a portion of the body region, the contact trench being filled with a conductive material contacting the source region at sidewalls of the contact trench and the highly doped body contact region at a bottom of the contact trench; and a diffusion barrier structure formed along sidewalls of the contact trench and disposed between the highly doped body contact region and the channel region, the diffusion barrier structure comprising alternating layers of Si and oxygen-doped Si.

In an embodiment, the diffusion barrier structure may extend along the bottom of the contact trench.

Alone or in combination, the highly doped body contact region may be laterally confined only by the diffusion barrier structure, which is not at the bottom of the contact trench.

The conductive material filling the contact trenches may extend onto the front main surface of the Si substrate beyond the diffusion barrier structure and in a direction towards the gate trenches, either individually or in combination.

The diffusion barrier structure may comprise, either alone or in combination, a blanket layer of Si epitaxially grown on alternating layers of Si and oxygen-doped Si.

The Si substrate may comprise, alone or in combination, one or more Si epitaxial layers grown on a base Si substrate.

According to an embodiment of a method of manufacturing a semiconductor device, the method comprises: forming a gate trench extending into the Si substrate; forming a contact trench extending into the Si substrate and separated from the gate trench; forming a highly doped body contact region in the Si substrate at the bottom of the contact trench; forming a diffusion barrier structure along sidewalls of the contact trench, the diffusion barrier structure comprising alternating layers of Si and oxygen-doped Si; forming a body region in the Si substrate, the body region including a channel region extending along a sidewall of the gate trench; forming a source region in the Si substrate over the body region; and filling the contact trench with a conductive material that contacts the source region at the contact trench sidewalls and the highly doped body contact region at the bottom of the contact trench.

In an embodiment, forming the diffusion barrier structure may include epitaxially growing alternating layers of Si and oxygen-doped Si on sidewalls and a bottom of the contact trench prior to filling the contact trench with the conductive material.

The method may further comprise epitaxially growing a blanket layer of Si on the alternating layers of Si and oxygen-doped Si, either alone or in combination.

Separately or in combination, forming the highly doped body contact region may include implanting dopant species into the alternating layers of Si and oxygen-doped Si at the bottom of the contact trench, and annealing the Si substrate to activate the implanted dopant species.

Separately or in combination, the method may further include removing the alternating layers of Si and oxygen-doped Si from at least a portion of the bottom of the contact trench.

Removing the alternating layers of Si and oxygen-doped Si from at least a portion of the bottom of the contact trench, alone or in combination, may include: epitaxially growing a Si cap layer on the alternating layers of Si and oxygen-doped Si; depositing a conformal spacer oxide on the Si cap layer; anisotropically etching the conformal spacer oxide to expose the diffusion barrier structure at the bottom of the contact trench; etching away the exposed diffusion barrier structure at the bottom of the contact trench; and removing the conformal spacer oxide after etching away the exposed diffusion barrier structure at the bottom of the contact trench.

Separately or in combination, forming the diffusion barrier structure may include epitaxially growing alternating layers of Si and oxygen-doped Si only on the sidewalls, but not on the bottom, of the contact trench prior to filling the contact trench with the conductive material.

The method may further comprise epitaxially growing a blanket layer of Si on the alternating layers of Si and oxygen-doped Si, either alone or in combination.

Separately or in combination, forming the highly doped body contact region may include: implanting dopant species into a region of the bottom of the contact trench that is free of alternating layers of Si and oxygen-doped Si, and annealing the Si substrate to activate the implanted dopant species.

Separately or in combination, the method may further comprise, prior to filling the contact trench with the conductive material, etching back an insulating layer formed on the front main surface of the Si substrate such that the insulating layer has an opening aligned with the contact trench and wider than a combined width of the contact trench and the diffusion barrier structure.

Filling the contact trench with a conductive material may include, alone or in combination: a conductive material is deposited in the contact trench and in the opening formed in the insulating layer such that the conductive material extends onto the front major surface of the Si substrate beyond the diffusion barrier structure and in a direction towards the gate trench.

Forming the diffusion barrier structure may comprise, either alone or in combination, epitaxially growing alternating layers of Si and oxygen-doped Si on the sidewalls and bottom of the contact trench prior to forming the body and source regions.

Separately or in combination, the method may further comprise epitaxially growing a blanket layer of Si on the alternating layers of Si and oxygen-doped Si prior to forming the body and source regions.

Separately or in combination, the method may further include removing the alternating layers of Si and oxygen-doped Si from at least a portion of the bottom of the contact trench.

Removing the alternating layers of Si and oxygen-doped Si from at least a portion of the bottom of the contact trench, alone or in combination, may include: epitaxially growing a Si cap layer on the alternating layers of Si and oxygen-doped Si; depositing a conformal spacer oxide on the Si cap layer; anisotropically etching the conformal spacer oxide to expose the diffusion barrier structure at the bottom of the contact trench; etching away the exposed diffusion barrier structure at the bottom of the contact trench; and removing the conformal spacer oxide after etching away the exposed diffusion barrier structure at the bottom of the contact trench.

Separately or in combination, forming the diffusion barrier structure may include: forming a sacrificial insulating layer at the bottom of the contact trench before forming the body region and the source region; after forming the sacrificial insulating layer, epitaxially growing alternating layers of Si and oxygen-doped Si on sidewalls of the contact trench; after epitaxially growing alternating layers of Si and oxygen-doped Si, the sacrificial insulating layer is removed from the bottom of the contact trench.

Individually or in combination, the method may further comprise: filling the contact trench with a sacrificial plug material after forming the diffusion barrier structure and before forming the source and body regions; forming a source region and a body region in the Si substrate after filling the contact trench with a sacrificial plug material; removing the sacrificial plug material after forming the source region and the body region; implanting dopant species into the bottom of the contact trench after removing the sacrificial plug material and before filling the contact trench with a conductive material; and annealing the Si substrate to activate the implanted dopant species to form a highly doped body contact region.

Those skilled in the art will recognize additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings.

Drawings

The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts. Features of the various illustrated embodiments may be combined unless they are mutually exclusive. Embodiments are depicted in the drawings and are detailed in the following description.

Fig. 1 illustrates a partial cross-sectional view of an embodiment of a trench-based semiconductor device having a diffusion barrier structure.

Fig. 2A to 2F illustrate respective cross-sectional views of the trench-based semiconductor device shown in fig. 1 during different stages of the fabrication process.

Fig. 3 illustrates a partial cross-sectional view of another embodiment of a trench-based semiconductor device having a diffusion barrier structure.

Fig. 4 illustrates a partial cross-sectional view of another embodiment of a trench-based semiconductor device having a diffusion barrier structure.

Fig. 5A to 5D illustrate respective cross-sectional views of embodiments omitting the diffusion barrier structure from at least a portion of the bottom of the contact trench.

Fig. 6A-6L illustrate respective partial cross-sectional views of a trench-based semiconductor device during different stages of the fabrication process, wherein a diffusion barrier structure is formed prior to the body and source regions of the device.

Detailed Description

Embodiments described herein control lateral out-diffusion of source/body contact doping of trench-based transistors, allowing narrower Vth, RonA, and DIBL distributions for given geometrical variations of highly doped source/body contacts and gate trenches, and/or allowing lateral spacing between the source/body contacts and the channel region of the device to be reduced for given Vth, RonA, and DIBL windows. Lateral out-diffusion of source/body contact doping is better controlled by interposing a diffusion barrier structure comprising alternating layers of Si and oxygen doped Si between the highly doped source/body contact and the channel region of the device. The oxygen-doped Si layer of the diffusion barrier structure limits lateral out-diffusion of the source/body contact doping, thereby controlling the lateral out-diffusion of the source/body contact doping in a direction towards the channel region. The diffusion barrier structure enables a narrower Vth distribution of, for example, a narrow trench MOSFET, or enables a smaller distance between the contact trench and the gate trench for a predetermined Vth distribution width. Embodiments of a semiconductor device having such a diffusion barrier structure, and corresponding manufacturing methods, are described in more detail below.

Fig. 1 illustrates a partial cross-sectional view of an embodiment of a trench-based semiconductor device 100. The semiconductor device 100 includes: one or more gate trenches 102 extending into the Si substrate 104. The Si substrate 104 may include one or more Si epitaxial layers grown on a base Si substrate. The gate electrode 106 disposed in each gate trench 102 is insulated from the surrounding semiconductor material by a gate dielectric 108. A field electrode 110 may be disposed in each gate trench 102 below a corresponding gate electrode 106 and insulated from the surrounding semiconductor material and gate electrode 106 by a field dielectric 112. The gate dielectric 108 and the field dielectric 112 may comprise the same or different materials and may have the same or different thicknesses. Alternatively, the field electrode 110 may be formed in a different trench separate from the gate trench 102 or omitted entirely, depending on the type of semiconductor device. The trench-based semiconductor device 100 may be a power semiconductor device such as a power MOSFET (metal oxide semiconductor field effect transistor), an IGBT (insulated gate bipolar transistor), or the like.

The trench-based semiconductor device 100 further comprises: a body region 114 formed in the Si substrate 104. The body regions 114 include channel regions 116, the channel regions 116 extending vertically along sidewalls 118 of the corresponding gate trenches 102. Semiconductor device 100 further includes a source region 120 formed in Si substrate 104 above body region 114. Vertical current flow through channel region 116 is controlled by applying a gate potential to gate electrode 106. A drain region or collector region (not shown) is formed below the drift region 122. Depending on the type of device, additional structures may be formed in drift region 122 and/or between drift region 122 and the drain/collector region. For example, in the case of an IGBT-type device, a charge compensation structure may be formed in drift region 122 and/or a field stop layer may be formed between drift region 122 and the drain/collector regions. Again, any type of semiconductor device having a trench gate may utilize the diffusion barrier teachings described herein.

The trench-based semiconductor device 100 further comprises: a contact trench 124 extending into the Si substrate 104. The contact trench 124 is separated from each adjacent gate trench 102 by a portion of the source region 120 and a portion of the body region 114. The contact trench 124 is filled with a conductive material 126 (such as doped polysilicon, metal, etc.), which conductive material 126 contacts the source region 120 at the sidewalls of the contact trench 124 and a highly doped body contact region 128 at the bottom of the contact trench 124. The conductive material 126 filling the contact trench 124 may extend onto the front major surface 130 of the Si substrate 104 beyond the diffusion barrier structure 132 and in a direction towards the gate trench 102 such that the conductive material 126 contacts the source region 120 along the front major surface 130 of the Si substrate 104 between the gate trench 102 and the diffusion barrier structure 132.

The highly doped body contact regions 128 at the bottom of the contact trenches 124 have the same doping type as the body regions 114, but at a higher concentration to provide a good ohmic contact with the conductive material 126 filling the contact trenches 124. For example, in the case of an n-channel device, the source regions 120 and the drift regions 122 are n-type doped, and the body regions 114, the channel regions 116 and the highly doped body contact regions 128 are p-type doped. Conversely, in the case of a p-channel device, the source regions 120 and the drift region 122 are p-type doped, and the body regions 114, the channel regions 116 and the highly doped body contact regions 128 are n-type doped.

In either case, the diffusion barrier structure 132 is formed at least along the sidewalls of the contact trench 124 and disposed between the highly doped body contact region 126 and the channel region 116. The diffusion barrier structure 132 may also extend along the bottom of the contact trench 124 (as shown in fig. 1), only along the sidewalls, or along only a portion of the sidewalls and bottom, as described in more detail later herein.

Diffusion barrier structure 132 comprises alternating layers of Si134 and oxygen-doped Si 136. The alternating layers of Si134 and oxygen-doped Si136 form oxygen-doped silicon regions grown by epitaxy. In an embodiment, the oxygen concentration of each oxygen-doped Si layer 136 is less than 5e14 cm-3. Each oxygen-doped Si layer 136 may have a thickness in the atomic range (e.g., one or several atomic thicknesses) or in the nanometer range to ensure sufficient crystal information for growing Si on the oxygen-doped Si layer 136. The alternating layers of Si134 and oxygen-doped Si136 may be achieved by epitaxially growing Si layers alternating with oxygen layers respectively adsorbed on the Si layer surfaces, e.g., having a certain limited thickness for the oxygen-doped Si layer 136 to ensure sufficient Si growth.

Fig. 1 provides an exploded view of the diffusion barrier structure 132, which diffusion barrier structure 132 may further include a Si buffer layer 138 between the Si substrate 104 and the alternating layers of Si134 and oxygen-doped Si136, and/or a capping layer 140 epitaxially grown on the alternating layers of Si134 and oxygen-doped Si 136. The Si buffer layer 138 may be relatively thin, for example, in the range of 2-5 nm thick. The Si buffer layer 138 may be grown after the implantation or etching step. Capping layer 140 provides high carrier mobility in this region of device 100. One or both of buffer layer 138 and capping layer 140 may be omitted. The oxygen-doped Si layer 136 of the diffusion barrier structure 132 limits the lateral out-diffusion of the source/body contact doping, thereby controlling the lateral out-diffusion of the source/body contact doping in a direction toward the channel region 116. The oxygen-doped Si layer 136 of the diffusion barrier structure 132 may also improve carrier mobility within the vertical channel region 116 of the device 100.

The oxygen-doped Si layer 136 of the diffusion barrier structure 132 may be formed by introducing a partial monolayer of oxygen into the Si lattice. The oxygen atoms are placed interstitially to minimize damage to the Si lattice. The Si atomic layer 134 separates adjacent partial monolayers 136 of oxygen. Alternating layers of Si134 and oxygen-doped Si136 may be formed by Si epitaxy with oxygen absorption at different steps. For example, the temperature and gas conditions may be controlled during the epitaxy process to form a partial oxygen monolayer 136. Oxygen may be introduced/incorporated between the epitaxial layers 134 of Si, for example, by controlling the introduction of an oxygen precursor into the epitaxial chamber. The resulting diffusion barrier structure 132 comprises a monolayer 136 alternating with a standard Si epitaxial layer 134 devoid of oxygen, the monolayer 136 comprising primarily Si but having a doping level or concentration level of oxygen. The diffusion barrier structure 132 may also include a Si cap layer 140 epitaxially grown on alternating layers of Si134 and oxygen-doped Si136, or the Si cap layer 140 may be omitted.

Fig. 2A-2F illustrate respective cross-sectional views of the trench-based semiconductor device 100 shown in fig. 1 during different stages of a fabrication process.

Fig. 2A shows device 100 after forming gate trench 102, body region 114, and source region 120. Any common semiconductor fabrication process for forming the gate trenches, body regions and source regions may be used, such as, for example, trench masking and etching, trench filling, dopant implantation and activation (annealing), and the like.

Fig. 2B shows the device 100 after etching contact trenches 124 into the Si substrate 104 in the semiconductor mesa between adjacent gate trenches 102. Any common trench etch process may be used. For example, a hard mask/insulating layer 200, such as silicon oxide, may be formed on the front major surface 130 of the Si substrate 104 and patterned to form the opening 202. The exposed portions of the Si substrate 104 may then be isotropically etched to form contact trenches 124, the contact trenches 124 having a width (W1) greater than the width (W2) of the openings 202 in the hard mask 200.

Fig. 2C shows device 100 after epitaxial growth of diffusion barrier structures 132 on the sidewalls and bottom of contact trenches 124. Diffusion barrier structure 132 comprises alternating layers of Si134 and oxygen-doped Si 136. A Si cap layer 140 may be epitaxially grown on the alternating layers of Si134 and oxygen-doped Si 136. The Si cap layer 140 may be omitted. Diffusion barrier structure 132 may be doped in situ or thereafter with the same conductivity type as source region 120 to provide a good ohmic contact between source region 120 and conductive material 126 subsequently deposited in contact trench 124.

Fig. 2D shows the device 100 during implantation of the diffusion barrier structure 132 into the lower portion of the contact trench 124, which lower portion of the contact trench 124 has dopants 204 of the same conductivity type as the body region 114, to provide a good ohmic contact between the body region 114 and the conductive material 126 subsequently deposited in the contact trench 124. Activation of the implanted dopants 204 by annealing forms highly doped body contact regions 128 at the bottom of the contact trenches 124 that have the same doping type as the body regions 114, but at a higher concentration to provide good ohmic contact with the conductive material 126 subsequently deposited in the contact trenches 124. The oxygen-doped Si layer 136 of the diffusion barrier structure 132 limits the lateral out-diffusion of the source/body contact doping, thereby controlling the lateral out-diffusion of the source/body contact doping in a direction toward the channel region 116. In one embodiment, a diffusion barrier structure 132 is present at the bottom of the contact trench 124, as shown in fig. 2D. According to this embodiment, the oxygen doped Si layer 136 of the diffusion barrier structure 132 also limits the vertical out-diffusion of the source/body contact doping in the direction towards the drift region 122. In embodiments described in more detail later herein, the diffusion barrier structure 132 is partially or completely omitted from the bottom of the contact trench 124 and thus does not limit the vertical out-diffusion of the source/body contact doping.

Fig. 2E shows the device 100 after etching back the hard mask 200 to widen (W2') the opening 202 in the mask 200. Any standard dielectric etch back process may be used. The widened opening 202 in the hard mask 200 is aligned with the contact trench 124 and is wider than the combined width (W3) of the contact trench 124 and the diffusion barrier structure 132.

Fig. 2F shows the device after filling the contact trench 124 with a conductive material 126. The conductive material 126 contacts the source regions 120 at the sidewalls of the contact trenches 124 and the highly doped body contact regions 128 at the bottom of the contact trenches 124. The conductive material 126 may extend onto the front major surface 130 of the Si substrate 104 beyond the diffusion barrier structure 132 and in a direction towards the gate trench 102, e.g., if the opening 202 in the hard mask 200 was previously widened, as shown in fig. 2E.

Fig. 3 illustrates a partial cross-sectional view of another embodiment of a trench-based semiconductor device 300. The embodiment shown in fig. 3 is similar to the embodiment shown in fig. 1. In contrast, however, the body contact dopants implanted and activated in capping layer 140 of diffusion barrier structure 132 extend into source region 120 of device 300.

Fig. 4 illustrates a partial cross-sectional view of another embodiment of a trench-based semiconductor device 400. The embodiment shown in fig. 4 is similar to the embodiment shown in fig. 1 and 3. However, differently, the diffusion barrier structure 132 is omitted from the bottom of the contact trench 124, and thus the vertical out-diffusion of the source/body contact doping is not limited. According to this embodiment, dopants out-diffused from the highly doped body contact regions 128 are directed vertically deeper into the drift region/Si substrate 122/104. The diffusion barrier structure 132 may be omitted from the bottom of the contact trench 132 by epitaxially growing alternating layers of Si134 and oxygen-doped Si136 only on the sidewalls of the contact trench 124, rather than on the bottom. For example, dielectric spacers (not shown) may be formed at the bottom of the contact trenches 124 to prevent epitaxial growth of the diffusion barrier structures 132 at the trench bottoms.

Fig. 5A-5D illustrate respective cross-sectional views of another embodiment omitting the diffusion barrier structure 132 from at least a portion of the bottom of the contact trench 124.

Fig. 5A shows the semiconductor device 500 after forming diffusion barrier structures 132 on the sidewalls and bottom of the contact trenches 124, e.g., as previously described herein in connection with fig. 2C. A conformal spacer oxide 502 is also deposited on the Si capping layer 140 of the diffusion barrier structure 132. If the capping layer 140 is omitted, the conformal spacer oxide 502 is deposited directly on the uppermost one of the alternating layers of Si134 and oxygen-doped Si136 of the diffusion barrier structure 132. In either case, any standard conformal spacer oxide, such as silicon oxide, may be used.

Fig. 5B shows the semiconductor device 500 during anisotropic etching of the conformal spacer oxide 502 from the top to expose the diffusion barrier structure 132 at the bottom of the contact trench 124. The anisotropic etch is represented by the downward arrows in fig. 5B. If a Si capping layer 140 is provided, the capping layer 140 will be exposed at the bottom of the contact trench 124. Otherwise, the uppermost of the alternating layers of Si134 and oxygen-doped Si136 will be exposed. The conformal spacer oxide 502 may be removed from the bottom of the contact trench 124 using any standard dielectric anisotropic etch process.

Fig. 5C shows the semiconductor device 500 during etching away the diffusion barrier 132 exposed at the bottom of the contact trench 124. The Si etch is represented by the downward arrow in fig. 5C. Any standard Si etch process may be used.

Fig. 5D shows the semiconductor device 500 after etching away the exposed diffusion barrier structure 132 at the bottom of the contact trench 124 and after removing the conformal spacer oxide 502. After etching away the exposed diffusion barrier structures 132 at the bottom of the contact trenches 124, the conformal oxide spacers 502 may be removed using any standard dielectric removal process (e.g., isotropic etching). Then, processing of the device 500 continues to form highly doped body contact regions at the bottom of the contact trenches 124, fill the contact trenches 124, and so on, e.g., as illustrated in fig. 2D-2F.

Fig. 6A-6L illustrate respective partial cross-sectional views of a trench-based semiconductor device 600 during different stages of the fabrication process, in which diffusion barrier structures 132 are formed prior to body regions 114 and source regions 120.

Fig. 6A shows the semiconductor device 500 after formation of the gate trench 102 in the Si substrate 104 and after formation of a hard mask/insulating layer 200, such as, for example, silicon oxide, on the front main surface 130 of the Si substrate 104. Any common semiconductor fabrication process for forming the gate trench and the hard mask may be used, such as, for example, trench masking and etching, dielectric deposition and/or thermal oxidation, and the like.

Fig. 6B shows the semiconductor device 600 after etching the contact trenches 124 into the Si substrate 104 between adjacent gate trenches 102. The contact trench 124 may be formed using any common trench etch process. For example, an opening 202 may be formed in the hard mask 200 on the front major surface 130 of the Si substrate 104, and the exposed portion of the Si substrate 104 may be isotropically etched to form a contact trench 124 that is wider than the opening 202 in the hard mask 200.

Fig. 6C shows semiconductor device 600 after epitaxial growth of diffusion barrier structures 132 on the sidewalls and bottom of contact trenches 124, e.g., as previously described herein in connection with fig. 2C. A Si cap layer 140 may be epitaxially grown on the alternating layers of Si134 and oxygen-doped Si 136. Alternatively, the Si capping layer 140 may be omitted.

Fig. 6D shows an alternative embodiment in which the diffusion barrier structure 132 is omitted from the bottom of the contact trench 124. The diffusion barrier structure 132 may be omitted partially or completely from the bottom of the contact trench 124. For example, the diffusion barrier structure 132 may be omitted from the bottom of the contact trench 124 by epitaxially growing alternating layers of Si134 and oxygen-doped Si136 only on the sidewalls of the contact trench 124, rather than on the bottom. Dielectric spacers may be formed at the bottom of the contact trench 124 to prevent epitaxial growth of the diffusion barrier structure 132 at the trench bottom.

In one embodiment, a sacrificial insulating layer 602 is formed at the bottom of the contact trench 124. After the sacrificial insulating layer 602 is formed, alternating layers of Si134 and oxygen-doped Si136 are epitaxially grown only on the sidewalls of the contact trenches 132. After epitaxial growth of alternating layers of Si134 and oxygen doped Si136, the sacrificial insulating layer 602 is removed from the bottom of the contact trench 124.

In another embodiment, alternating layers of Si134 and oxygen-doped Si136 may be grown on the sidewalls and bottom of the contact trench 124 and then removed from some or all of the trench bottom, e.g., as previously described herein in connection with fig. 5A-5D.

Fig. 6E-6L illustrate portions of the diffusion barrier structure 132 disposed along the bottom of the contact trench 124, with dashed lines indicating that the diffusion barrier structure 132 may or may not be present at the bottom of the contact trench 124.

Fig. 6E shows the semiconductor device 600 after the contact trenches 124 are filled with a sacrificial plug material 604 (e.g., such as carbon or another material), which sacrificial plug material 604 may be selectively etched to the material of the hard mask 200 formed on the front major surface 130 of the Si substrate 104.

Fig. 6F shows the semiconductor device 600 after etching back the hard mask 200 followed by the formation of a screen oxide 606.

Fig. 6G shows semiconductor device 600 after formation of body regions 114 and source regions 120 in Si substrate 104, for example, by dopant implantation and dopant activation by annealing. Body region 114 and source region 120 are formed using dopants having opposite conductivity types. The dopants are implanted and then activated by annealing to form body regions 114 and source regions 120. The dopant implantation is represented by the downward arrow in fig. 6G. If the diffusion barrier structure 132 is omitted from the bottom of the contact trench 124, the dopant species may be implanted directly into the Si substrate 104 at the bottom of the contact trench 124, which is free of alternating layers of Si134 and oxygen-doped Si 136.

Fig. 6H shows the semiconductor device 600 after a mesa protection oxide 608 is deposited over the Si substrate 104.

Fig. 6I shows the semiconductor device 600 after the mesa protection oxide 608 is planarized and exposes a top surface 610 of the sacrificial plug material 604 in the contact trench 124. Any standard planarization process may be used, such as CMP (chemical mechanical polishing), for example.

Fig. 6J illustrates the semiconductor device 600 after the sacrificial plug material 604 is removed from the contact trenches 124. The process used to remove the sacrificial plug material 604 from the contact trench 124 depends on the type of plug material. For example, the process may involve wet and/or dry chemical etching.

Fig. 6K shows the semiconductor device 600 during the implantation of a dopant species 612 into the bottom of the contact trench 124. The dopant type (p-type or n-type) is the same as that of body region 114, but at a higher concentration to form an ohmic contact. The Si substrate 104 is annealed to activate the implanted dopant species 612, thereby forming highly doped body contact regions 128 at the bottom of the contact trenches 124. The oxygen-doped Si layer 136 of the diffusion barrier structure 132 limits at least lateral out-diffusion of the source/body contact doping in a direction toward the vertical channel region 116. The oxygen-doped Si layer 136 of the diffusion barrier structure 132 also limits the vertical out-diffusion of the source/body contact doping in a direction towards the drift region 122 if the diffusion barrier structure 132 is present at the bottom of the contact trench 124.

Fig. 6L shows the semiconductor device 600 after filling the contact trenches 124 with the conductive material 126. The conductive material 126 contacts the source regions 120 at the sidewalls of the contact trenches 124 and the highly doped body contact regions 128 at the bottom of the contact trenches 124. The conductive material 126 may extend onto the front major surface 130 of the Si substrate 104 beyond the diffusion barrier structure 132 and in a direction towards the gate trench 102, if the opening in the mesa protection oxide 608 is widened prior to depositing the conductive material 126, e.g., as shown in fig. 2E.

Spatially relative terms, such as "below," "lower," "over," "upper," and the like, are used for ease of description to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the device in addition to different orientations than those depicted in the figures. Furthermore, terms such as "first," "second," and the like, are also used to describe various elements, regions, sections, etc., and are also not intended to be limiting. Like terms refer to like elements throughout the specification.

As used herein, the terms "having," "containing," "including," "comprising," and the like are open-ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. The articles "a," "an," and "the" are intended to include the plural as well as the singular, unless the context clearly indicates otherwise.

With the above range of variations and applications in mind, it should be understood that the present invention is not limited by the foregoing description, nor is it limited by the accompanying drawings. Instead, the present invention is limited only by the following claims and their legal equivalents.