阅读说明：本技术 一种mos栅控晶闸管及其制造方法 (MOS grid-controlled thyristor and manufacturing method thereof ) 是由 陈万军 张舒逸 刘超 张波 于 2020-12-14 设计创作，主要内容包括：本发明涉及功率半导体技术领域,具体的说是适用于脉冲功率领域的一种MOS栅控晶闸管及其制造方法。本发明主要通过改进常规MOS栅控晶闸管的器件结构,使之具有常关特性,同时与避免了其应用于脉冲功率领域时因栅介质击穿导致的脉冲系统发生失效的问题,即在简化驱动电路的同时提升脉冲系统可靠性。(The invention relates to the technical field of power semiconductors, in particular to an MOS (metal oxide semiconductor) grid-controlled thyristor and a manufacturing method thereof, which are suitable for the field of pulse power. The invention mainly improves the device structure of the conventional MOS grid-controlled thyristor, so that the MOS grid-controlled thyristor has normally-off characteristics, and simultaneously avoids the problem of failure of a pulse system caused by gate dielectric breakdown when the MOS grid-controlled thyristor is applied to the field of pulse power, namely, the reliability of the pulse system is improved while a driving circuit is simplified.)

1. A MOS grid-controlled thyristor comprises an anode structure consisting of an anode (10) and anode metal (11) positioned at the bottom of the anode (10), a drift region (1) positioned at the top of the anode structure, a gate structure positioned at the top of the drift region (1) and a cathode structure; the drift region (1) is provided with a P-type well region (4), and an N-type well region (5) is arranged on the upper layer of the P-type well region (4); the upper layer of the N-type well region (5) is provided with a P-type source region (6); the grid structure is contacted with one end of the top of the P-type well region (4), the grid structure comprises a grid oxide layer (2), polycrystalline silicon (3) positioned on the upper surface of the grid oxide layer (2) and grid metal (9) positioned on the upper surface of the polycrystalline silicon (3), and the bottom of the grid oxide layer (2) is simultaneously contacted with the upper surface of the N-type drift region (1), the upper surface of part of the P-type well region (4), the upper surface of part of the N-type well region (5) and the upper surface of part of the P-type source region (6); the grid metal (9) is in contact with part of the polycrystalline silicon (3), extends to the other end of the top of the P-type well region (4) along the upper part of the cathode structure, and is in contact with the upper surface of the P-type well region (4) on one side far away from the polycrystalline silicon (3); the cathode structure comprises cathode metal (8), and the cathode metal (8) is in contact with the upper surfaces of part of the P-type source region (6) and part of the N-type well region (5); the gate oxide layer (2), the polycrystalline silicon (3) and the cathode metal (8) are completely isolated by an insulating medium layer (7); the cathode metal (8) and the grid metal (9) are completely isolated by an insulating medium layer (7).

2. A manufacturing method of a MOS grid-controlled thyristor is characterized by comprising the following steps:

the first step is as follows: a substrate silicon wafer is adopted to manufacture a junction terminal, and an N-type drift region (1) is formed;

the second step is that: growing a gate oxide layer (2) on the upper surface of the N-type drift region (1) through thermal oxidation, depositing polycrystalline silicon (3) on the surface of the gate oxide layer (2), and etching;

the third step: forming a P-type well region (4) on the upper surface of the N-type drift region (1) by ion implantation and junction pushing by adopting a polysilicon self-alignment technology;

the fourth step: injecting N-type impurities into the P-type well region (4) to form an N-type well region (5);

the fifth step: injecting P-type impurities into the N-type well region (5) to form a P-type source region (6);

and a sixth step: depositing a BPSG insulating medium layer (7) on the surface of the device, and etching an ohmic contact hole, wherein the insulating medium layer (7) completely covers the upper surface and the side surface of the polysilicon (3);

the seventh step: depositing a first layer of metal on the front surface of the device and etching the first layer of metal to form cathode metal (8);

eighth step: depositing a BPSG insulating medium layer (7) on the surface of the device, and etching an ohmic contact hole, wherein the insulating medium layer (7) completely covers the upper surface and the side surface of the cathode metal (8);

the ninth step: depositing a second layer of metal on the front surface of the device to form a gate metal (9);

the tenth step: depositing a passivation layer;

the eleventh step: thinning and polishing the lower surface of the N-type drift region (1), implanting ions and activating to form an anode region (10);

the twelfth step: and back gold, and depositing anode metal (11) at the bottom of the anode region (10) to form an anode.

Technical Field

The invention relates to the technical field of power semiconductors, in particular to an MOS (metal oxide semiconductor) grid-controlled thyristor and a manufacturing method thereof, which are suitable for the field of pulse power.

Background

In pulse power systems, energy is often compressed over a time width by an energy storage system and by power semiconductor switches, resulting in transient high power pulses. For current pulses, it is generally required to have a large rising edge di/dt and peak current. The power semiconductor switch is used as a key device in a power pulse system, determines the output power of the system, and therefore, corresponding requirements are provided for the peak current and the di/dt capacity of the power semiconductor switch.

Conventional MOS Control Thyristors (MOS-Control Thyristors, MCTs) have the characteristics of high current density, high switching speed, low conduction voltage drop, and the like, and are very suitable for being applied to the field of power pulses. However, since the conventional MCT is a normally-on device, a negative voltage needs to be applied to the gate to maintain the blocking state, so that the driving circuit thereof is complicated and it is not favorable for improving the reliability of the system. On this basis, a MOS-controlled thyristor (CS-MCT) having a Cathode short-circuit structure is proposed, which introduces a Cathode short-circuit region, compared to a conventional MCT. When the device is blocked in the forward direction, the cathode short-circuit region provides a hole extraction path, so that the device can realize the forward blocking under the zero bias of the grid, has normally-off characteristics and is beneficial to simplifying a driving circuit. Meanwhile, the CS-MCT can be triggered at a smaller conduction current, so that the CS-MCT has a smaller conduction resistance in a larger current range. However, when the conventional MCT and CS-MCT are in pulse discharge, due to the large di/dt, large induced electromotive force is generated on parasitic inductance from the cathode of the device to ground, and the potential difference between two ends of a gate capacitor is increased, which easily causes breakdown of a gate oxide layer, and causes failure of a pulse system.

Disclosure of Invention

The invention aims to enable the MOS control thyristor to have normally-off characteristic, and simultaneously avoid the problem that a pulse system fails due to gate dielectric breakdown when the MOS control thyristor is applied to the field of pulse power, namely, the reliability of the pulse system is improved while a driving circuit is simplified.

The technical scheme of the invention is as follows: a MOS grid-controlled thyristor comprises a cellular structure, a drift region 1, a grid structure and a cathode structure, wherein the cellular structure comprises an anode 10 and an anode metal 11 positioned at the bottom of the anode 10; the N-type drift region 1 is provided with a P-type well region 4, and an N-type well region 5 is arranged on the upper layer of the P-type well region 4; the upper layer of the N-type well region 5 is provided with a P-type source region 6; the grid structure is contacted with one end of the top of the P-type well region 4, and comprises a grid oxide layer 2, polycrystalline silicon 3 positioned on the upper surface of the grid oxide layer and grid metal 9; the bottom of the gate oxide layer 2 is simultaneously contacted with the upper surface of the N-type drift region 1, the upper surface of part of the P-type well region 4, the upper surface of part of the N-type well region 5 and the upper surface of part of the P-type source region 6; the grid metal 9 is contacted with the upper surface of part of the polysilicon 3, extends to one side far away from the polysilicon 3, and is contacted with the upper surface of part of the P-type well region 4 at one side far away from the polysilicon 3; the cathode structure comprises cathode metal 8, and the cathode metal 8 is in contact with the upper surface of part of the P-type source region 6 and the upper surface of part of the N-type well region 5; the gate oxide layer 2, the polycrystalline silicon 3 and the cathode metal 8 are completely isolated by an insulating medium layer 7; the cathode metal 8 and the cathode metal 9 are completely separated by the insulating medium layer 7.

The invention also provides a manufacturing method of the MOS grid-controlled thyristor, which comprises the following steps:

the first step is as follows: manufacturing a junction terminal by using a substrate silicon wafer to form an N-type drift region 1;

the second step is that: growing a gate oxide layer 2 on the upper surface of the N-type drift region 1 through thermal oxidation, depositing polycrystalline silicon 3 on the surface of the gate oxide layer 2, and etching;

the third step: forming a P-type well region 4 on the upper surface of the N-type drift region 1 by ion implantation and junction pushing by adopting a polysilicon self-alignment technology;

the fourth step: injecting N-type impurities into the P-type well region 4 to form an N-type well region 5;

the fifth step: injecting P-type impurities into the N-type well region 5 to form a P-type source region 6;

and a sixth step: depositing a BPSG insulating medium layer 7 on the surface of the device, and etching an ohmic contact hole, wherein the insulating medium layer 7 completely covers the upper surface and the side surface of the polysilicon 3;

the seventh step: depositing a first layer of metal on the front surface of the device and etching the first layer of metal to form cathode metal 8;

eighth step: depositing a BPSG insulating medium layer 7 on the surface of the device, and etching an ohmic contact hole, wherein the insulating medium layer 7 completely covers the upper surface and the side surface of the cathode metal 8;

the ninth step: depositing a second layer of metal on the front surface of the device to form a gate metal 9;

the tenth step: depositing a passivation layer;

the eleventh step: thinning and polishing the lower surface of the N-type drift region 1, implanting ions and activating to form an anode region 10;

the twelfth step: and back gold, and depositing anode metal 11 at the bottom of the anode region 10 to form an anode.

The MOS gate controlled thyristor has the advantages that compared with the conventional MOS controlled thyristor, the MOS gate controlled thyristor has a normally-off characteristic and is beneficial to simplifying a driving circuit. Meanwhile, the problem that a pulse system fails due to gate dielectric breakdown when the pulse power control circuit is applied to the field of pulse power is avoided, and the reliability of the system is improved.

Drawings

FIG. 1 is a schematic diagram of a conventional MCT;

FIG. 2 is a schematic structural diagram of a MOS-gated thyristor according to an embodiment;

FIG. 3 is a simulated comparison of forward blocking characteristics of a conventional MCT and an embodiment MOS-gated thyristor;

FIG. 4 is an equivalent circuit diagram of a MOS controlled thyristor under capacitive pulsed discharge conditions;

FIG. 5 shows partial threshold voltage V of NMOS in MOS-gated thyristor_THA simulation result graph which is changed along with the implantation dosage of the P-type trap region 4;

FIG. 6 is a graph comparing simulation results of potential differences across the gate-cathode of a conventional MCT and an embodiment MOS gated thyristor structure during pulsed discharge;

fig. 7 is a schematic diagram of forming an N-type drift region 1 by using a substrate silicon wafer in the process flow of the embodiment;

FIG. 8 is a schematic diagram of the process flow of an embodiment for fabricating a gate oxide layer 2 and polysilicon 3 on an N-type silicon wafer;

FIG. 9 is a schematic diagram of an embodiment of a process flow for forming P-well regions on an N-type silicon wafer;

FIG. 10 is a schematic diagram of an embodiment of a process flow for forming an N-well in a P-well;

FIG. 11 is a schematic diagram of a process flow of an embodiment for forming a P-type source region in an N-well region;

FIG. 12 is a schematic diagram of a first deposition of a BPSG layer in a process flow of an embodiment;

FIG. 13 is a schematic diagram of a process flow in an embodiment in which a first layer of metal is deposited and etched to form a cathode metal 8;

FIG. 14 is a schematic diagram of a second deposition of a BPSG layer and etching of contact holes in the process flow of an embodiment;

fig. 15 is a schematic diagram of a second layer of metal deposited to form the gate metal 9 in the process flow of the embodiment;

FIG. 16 is a schematic diagram of a P-type anode region formed on the back side of an N-type silicon wafer in the process flow of the embodiment;

fig. 17 is a schematic illustration of the deposition of anodic metal on the P-type anode region in the process flow of the embodiment.

Detailed Description

The technical scheme of the invention is described in detail in the following with reference to the accompanying drawings and embodiments:

fig. 1 is a schematic structural diagram of a conventional MOS controlled thyristor, which has a parasitic thyristor structure, when a positive voltage is applied to a gate, an NMOS portion in the structure is turned on, and electrons are injected into a drift region through a channel, so that the parasitic thyristor is triggered to be turned on, and has a larger di/dt when turned on and a smaller conduction voltage drop when turned on. However, the conventional MOS control thyristor structure is a normally-on device, and when the MOS control thyristor structure is forward blocked, a negative voltage needs to be applied to the gate to form a PMOS channel as a hole extraction path to achieve a larger withstand voltage, so that a required control circuit is complicated, and the improvement of the reliability of the system is not facilitated.

Fig. 2 is a schematic structural diagram of a MOS-gated thyristor in the embodiment. Compared with the conventional MOS control thyristor, the structure of the invention has the gate metal 9, and the gate metal 9 is contacted with the upper surface of the part of the P-type well region 4 at one side far away from the polysilicon 3.

The MOS grid-controlled thyristor provided by the invention has the following working principle:

in the forward blocking state, when the gate is biased to zero, the structure provides a hole extraction path, and holes injected from the anode can be extracted through the P-type well region 4 to the gate metal 9 contacting with part of the upper surface of the P-type well region 4. Therefore, for the structure of the invention, the grid electrode does not need to be added with negative voltage when the positive direction is blocked, namely, the positive direction blocking can be realized under the zero bias of the grid electrode, thereby being beneficial to simplifying a control circuit and improving the reliability of a system. During pulse discharge, the cathode is grounded and a positive voltage is applied to the gate. For the present hairIn the structure, when positive voltage is applied to the gate, an NMOS (N-channel metal oxide semiconductor) consisting of a polysilicon 3, a gate oxide layer 2, an N-type well region 5, a P-type well region 4 and an N-type drift region 1 below the gate oxide layer 2 is turned on, and the threshold voltage of the NMOS is V_TH. Meanwhile, when the voltage on the grid electrode is gradually increased, the PN junction formed by the P-type well region 4 and the N-type well region 5 is conducted, and the conduction voltage drop is V_B(V_BAbout 0.7V, V_B＞V_TH). At this time, a bleed current is formed from the gate metal 9 to the cathode metal 8, and the potential between the gate and the cathode is clamped. Thus, there is more than V on the gate_BWhen the voltage is in the range of the gate voltage, a PN junction formed by the P-type well region 4 and the N-type well region 5 is conducted, so that the potential difference between the gate and the cathode is kept in a lower range, and the gate oxide layer is prevented from being broken down by the increased potential difference at two ends of the gate capacitor during pulse discharge. It is noted that the threshold voltage V of the NMOS portion of the device can be adjusted by properly adjusting the implantation dose of the P-type well region 4 within the range that does not affect the main characteristics of the device_THGet the value meeting the application requirement and meet V_TH<V_B。

Fig. 3 is a simulation comparison graph of the forward blocking characteristics of the conventional MOS-controlled thyristor and the example MOS-gated thyristor. It can be seen that the conventional MOS controlled thyristor needs to be applied with a negative gate voltage to maintain a large forward blocking voltage, and the structure of the present invention can withstand a forward blocking voltage equivalent to the positive blocking voltage under the gate zero bias.

Fig. 4 is an equivalent circuit diagram of a MOS controlled thyristor under a capacitor pulse discharge condition. It can be seen that when the MOS controlled thyristor is turned on, a larger current rising edge di/dt will be at the parasitic inductance L from the cathode to the ground_CA larger induced voltage is generated. The voltage can charge and discharge the gate capacitor to cause voltage oscillation at two ends of a gate-cathode, and when the voltage fluctuation peak value is larger than the withstand voltage (V) of a gate dielectric_OXThe thickness of the gate oxide layer is 100nm corresponding to V_OXAbout 100V) can result in gate dielectric breakdown, causing the pulsed system to fail.

FIG. 5 shows partial threshold voltage V of NMOS in MOS-gated thyristor_THSimulation results varying with the implantation dose of the P-type well region 4. It can be seen that the junction push time is maintained in the P-type well region 4V is constant in temperature and is increased along with the increase of the implantation dose of the P-type well region 4_THThe implant dose of the P-type well region 4 is smaller, so as to satisfy V_TH<V_BThe design requirements of (2).

Fig. 6 is a comparison of simulation results of potential differences across the gate-cathode of the MOS-gated thyristor in the conventional MCT and the example, at the time of pulse discharge. It can be seen from the figure that for the conventional MCT the voltage oscillation across the gate-cathode is significant, with a maximum peak value of more than 150V, whereas for the structure of the invention the voltage oscillation across the gate-cathode is small, with a maximum peak value reduced by about 99% with respect to the conventional MCT. This is because the structure of the invention has more than V on the grid electrode during the pulse discharge process_B(V_BMuch less than V_OX) At the same time, a PN junction formed by the P-type well region 4 and the N-type well region 5 is turned on, and the potential difference between the gate and the cathode is kept in a low range. The conventional MCT structure has a large peak voltage swing across the gate-cathode due to the absence of a bleed path for the voltage on the gate. Therefore, the structure of the invention effectively reduces the voltage difference between two ends of the grid-cathode during pulse discharge, and greatly reduces the breakdown risk of the grid oxide layer. Therefore, the structure of the invention avoids the problems of device damage and system failure caused by breakdown of the gate oxide layer when the voltages at two ends of the gate capacitor of the MOS gate-controlled thyristor are overlarge.

Taking the schematic structure diagram of the device shown in fig. 2 as an example, the manufacturing method comprises the following steps:

the first step is as follows: manufacturing a junction terminal by using a substrate silicon wafer to form an N-type drift region 1;

the second step is that: growing a gate oxide layer 2 on the upper surface of the N-type drift region 1 through thermal oxidation, depositing polycrystalline silicon 3 on the surface of the gate oxide layer 2, and etching;

the third step: forming a P-type well region 4 on the upper surface of the N-type drift region 1 by ion implantation and junction pushing by adopting a polysilicon self-alignment technology;

the fourth step: injecting N-type impurities into the P-type well region 4 to form an N-type well region 5;

the fifth step: injecting P-type impurities into the N-type well region 5 to form a P-type source region 6;

and a sixth step: depositing a BPSG insulating medium layer 7 on the surface of the device, and etching an ohmic contact hole, wherein the insulating medium layer 7 completely covers the upper surface and the side surface of the polysilicon 3;

the seventh step: depositing a first layer of metal on the front surface of the device and etching the first layer of metal to form cathode metal 8;

eighth step: depositing a BPSG insulating medium layer 7 on the surface of the device, and etching an ohmic contact hole, wherein the insulating medium layer 7 finishes the upper surface and the side surface of a cathode metal 8;

the ninth step: depositing a second layer of metal on the front surface of the device to form a gate metal 9;

the tenth step: depositing a passivation layer;

the eleventh step: thinning and polishing the lower surface of the N-type drift region 1, implanting ions and activating to form an anode region 10;

the twelfth step: and back gold, and depositing anode metal 11 at the bottom of the anode region 10 to form an anode.

The core idea of the invention is that the device structure is improved, so that the device has normally-off characteristic compared with the conventional MOS control thyristor, and the simplification of a driving circuit is facilitated. Meanwhile, the problem that a pulse system fails due to gate dielectric breakdown when the pulse power control circuit is applied to the field of pulse power is avoided, and the reliability of the system is improved.