Patent Application
20240038879
The present disclosure relates to a power semiconductor device with an insulated trench gate electrode, for instance to an insulated gate bipolar transistor (IGBT), and to a method of producing a power semiconductor device.
Documents U.S. Pat. No. 9,825,158 B2 and US 2020/0006539 A1 relate to an insulated gate bipolar transistor with an insulated trench gate electrode.
It has been found that hot carrier injection into the gate oxide is a typical trench degradation mechanism associated with the loss of long-term stability in trench IGBTs. Injected charge carriers can become trapped at the interface between the silicon semiconductor material and the trench oxide, especially at the trench bottom. During turn-off the current consists mostly of holes being displaced during the expansion of the depletion layer. Holes are accelerated towards the trench bottom by the high electric field in the depletion layer, especially during the overvoltage phase of hard turn-off switching events.
An object to be solved is to provide a power semiconductor device with improved long-term stability and to provide a method that allows to reliably produce such a device.
Exemplary embodiments of the disclosure address the above shortcomings, inter alia, for example a power semiconductor device according to claim 1 and a method according to claim 15. Further configurations and developments are the subject-matter of the dependent claims.
According to at least one embodiment of the power semiconductor device, the power semiconductor device comprises a semiconductor body extending in a vertical direction between an emitter side with an emitter electrode and a collector side opposite the emitter side. The power semiconductor device comprises a drift layer of a first conductivity type, a base layer of a second conductivity type different than the first conductivity type extending between the drift layer and the emitter side. The power semiconductor device further comprises a source region of the first conductivity type arranged on a side of the base layer facing away from the drift layer and at least one first trench extending from the emitter side into the drift layer wherein an insulated trench gate electrode extends into the first trench. The power semiconductor device further comprises at least one second trench extending from the emitter side into the drift layer wherein an electrically conductive layer extends into the second trench, the electrically conductive layer being electrically insulated from the base layer and the drift layer. The at least one second trench is arranged on a side of the at least one first trench facing away from the source region. A portion of the base layer arranged on a side of the at least one second trench facing away from the at least one first trench extends from the emitter side at least as deep in the vertical direction towards the collector side as the at least one second trench.
Contrary to the first trench, the second trench is electrically inactive and may also be referred to as a dummy trench. For example, electrically inactive means that there is no electrically conductive channel formed along the at least one second trench in an on-state of the power semiconductor device. For example, the at least one first trench is arranged between the source region and the at least one second trench, so that the second trench is separated from the source region via the first trench. It has been found that the portion of the base layer that extends comparably deep towards the collector side helps to significantly reduce the avalanche intensity near the first trench acting as active trench, for example compared to a design where the depth of the base layer is the same on both sides of the second trench.
If the doping concentration of the portion of the base layer does not abruptly decrease in vertical direction, for instance due to an implant tail of the dopants, the depth of the portion may be determined using that vertical position, where the doping concentration of the portion of the second conductivity type has decreased to the doping concentration of the dopants of the first conductivity type in the drift layer.
The first conductivity type may be n-type and the second conductivity type may be p-type or vice versa.
For example, a bottom of the trench directly adjoins the portion of the base layer in regions.
For example, the insulated trench gate electrode is electrically insulated from at least one of the semiconductor body and the electrically conductive layer. The electrically conductive layer is not in direct electrical contact with the at least one second trench, for instance.
During turn-off of the power semiconductor device, charge carriers, for instance holes in the case of a p-type base layer, may be extracted via the charge carrier extraction contact. In other words, the charge carrier extraction contact represents a plasma control feature that helps to further reduce the avalanche generation near the first trench.
It has been found that in the presence of the charge carrier extraction contact, a significant amount of injected holes may get diverted away from the first trench acting as active trench. Moreover, the second trench may electrostatically shield the active trench thereby protecting the first trench with the insulated trench gate electrode. The sub-region may be electrostatically screened by the first trench and the second trench which facilitates a controlled plasma extraction during a turn-off switching event without compromising the static losses too much. Consequently, a robust power semiconductor device with decreased degradation may be obtained without significant impact on the device performance.
The charge carrier extraction may be controlled via the electrical voltage applied to the charge carrier extraction contact. The applied voltage may correspond to the voltage at the emitter electrode or be different therefrom.
According to at least one embodiment of the power semiconductor device, during operation of the power semiconductor device, the charge carrier extraction contact is electrically addressable separately from the emitter electrode. Thus, the applied voltage may be independent from the voltage at the emitter electrode. In other words, the charge carrier extraction contact and the emitter electrode are configured two separate contact elements. For example, the voltage applied to the charge carrier extraction contact is positive with respect to the emitter electrode or the same as the voltage at the emitter electrode. For example, the voltage at the charge carrier extraction contact differs for different states during operation. For example, a positive voltage during an on-state may prevent excessive charge charrier extraction. During an off-state or a switching into the off-state, the voltage at the charge carrier extraction contact may be negative with respect to emitter electrode in order to enhance the charge carrier extraction.
According to at least one embodiment of the power semiconductor device, the charge carrier extraction contact is electrically connected to the emitter electrode. Thus, the voltage at the charge carrier extraction contact corresponds to that of the voltage at the emitter electrode.
The impact of the second trench on the power semiconductor device may further be controlled via a voltage applied to the electrically conductive layer in the second trench.
According to at least one embodiment of the power semiconductor device, the electrically conductive layer is at the same voltage as the emitter electrode or at a positive voltage with respect to the emitter electrode during operation of the power semiconductor device. For example, the electrically conductive layer is at a voltage applied to the emitter electrode or at a voltage applied to the insulated trench gate electrode. However, the applied voltage may also differ from both the voltage at the insulated trench gate electrode and the voltage at the emitter electrode.
According to at least one embodiment of the power semiconductor device, the charge carrier extraction contact is subdivided into a plurality of segments. For example, the segments are arranged beside one another in a direction extending in parallel to a main extension direction of the at least one first trench. However, a single charge carrier contact without any segments may also be used.
For example, a proportion of the emitter side covered by the segments of the charge carrier extraction contact along a straight line extending in parallel to the main extension direction of the at least one first trench amounts to at least 0.1% or at least 10% or at least 30% and/or at most % or at most 80%.
According to at least one embodiment of the power semiconductor device, the sub-region and the source region are arranged laterally beside one another when seen onto the emitter side. In other words, there is no source region between the first trench and the second trench.
According to at least one embodiment of the power semiconductor device, an edge-to-edge distance between the at least one first trench and the at least one second trench is between 0.5 μm and 5 μm inclusive. It has been found that the percentage of the avalanche generation shared by the second trench reduces as the spacing between the first trench and the second trench increases. Thus, placing the second trench as close as possible to the first trench would be of advantage in terms of the protection of the first trench. However, a spacing which is too small may result in higher turn-off losses.
According to at least one embodiment of the power semiconductor device, the at least one first trench and the at least one second trench have the same depth in the vertical direction. Consequently, the at least one first trench and the at least one second trench may be produced in a common process step.
The term “same depth” also includes minor differences of the depth within fabrication tolerances. However, the depth of the first trench and the second trench may also differ from one another if appropriate.
According to at least one embodiment of the power semiconductor device, an enhancement layer of the first conductivity type is arranged in regions between the drift layer and the base layer, wherein the enhancement layer is more heavily doped than the drift layer.
For example, a maximum doping concentration of the enhancement layer is larger than a maximum doping concentration of the drift layer at least by a factor of 50 or a factor of 100.
The enhancement layer may act as a charge carrier barrier, thereby reducing the on-state losses.
According to at least one embodiment of the power semiconductor device, the enhancement layer is arranged between the at least one first trench and the at least one second trench. Thus, a part of the enhancement layer may also be present in the sub-region. By means of the enhancement layer placed in the sub-region between the first trench and the second trench, on-state losses via the charge carrier extraction contact may further be reduced. However, the sub-region between the first trench and the second trench may also be free of the enhancement layer.
According to at least one embodiment of the power semiconductor device, the portion extends below the at least one second trench towards the at least one first trench. For example, the second trench completely overlaps with the portion when seen in vertical direction. For example, the portion extends beyond the second trench when seen towards the first trench, but does not overlap with the charge carrier extraction contact when seen in vertical direction. The portion may extend even further towards the first trench. For example, the sub-region completely overlaps with the portion when seen in vertical direction. For example, the first trench overlaps with the portion when seen in vertical direction completely or at least in regions.
According to at least one embodiment of the power semiconductor device, the portion of the base layer extends in a cross-sectional view of the power semiconductor device in a lateral direction between two partial regions of the at least one second trench. The two partial regions may be formed by one contiguous second trench or by two separate second trenches. For example, the portions of the at least one second trench extend in parallel to one another, for instance spaced apart from one another in a direction running perpendicular to the main extension direction of the at least one first trench.
According to at least one embodiment of the power semiconductor device, the at least one second trench contiguously forms the two partial regions of the second trench. However, the two partial regions of the second trench may also be formed by two separate second trenches.
According to at least one embodiment of the power semiconductor device, the at least one second trench forms a closed loop enclosing the portion of the base layer when seen in the vertical direction. The portion of the base layer may be spaced apart from the closed loop in regions. For example, outside of the closed loop the base layer does not extend at least as deep in the vertical direction as the at least one second trench at any position.
According to at least one embodiment of the power semiconductor device, the two partial regions of the at least one second trench are arranged between two partial regions of the at least one first trench in a cross-sectional view of the power semiconductor device. For example, the portions of the at least one first trench extend in parallel to one another, for instance spaced apart from one another in a direction running perpendicular to the main extension direction of the at least one first trench. For example, the at least one first trench contiguously forms the two partial regions of the first trench. However, the two partial regions of the second trench may also be formed by two separate first trenches. For example, the at least one first trench forms a closed loop enclosing the at least one second trench, which may be formed as a closed loop, for instance.
According to at least one embodiment of the power semiconductor device, the power semiconductor device is a trench IGBT.
A trench IGBT (insulated gate bipolar transistor) comprises on an emitter side (also called source side) a source region (also called emitter layer) of a first conductivity type and a base layer (also called well layer) of a second conductivity type different than the first conductivity type. A contact in form of an emitter electrode (also called source electrode) contacts the source region and the base layer. An insulated trench gate electrode is arranged on the emitter side lateral to the source region and the base layer.
The inventive concept may be applied to different types of IGBTs such as conventional punch-through IGBTs, non-punch-through IGBTs (NPT-IGBTs), reverse-blocking IGBTs or reverse-conducting IGBTs. Furthermore, it may be applied to other power semiconductor devices with an insulated trench gate electrode.
The semiconductor body of the power semiconductor device may be based on silicon. However, other semiconductor materials may also be used, for example wide bandgap materials such as silicon carbide (SiC) or gallium nitride (GaN).
For example, the power semiconductor device is configured for operating at large electrical currents, for instance of at least hundred amperes and/or at large electrical voltages of at least 500 V.
Furthermore, a method of producing a power semiconductor device is specified. For example, the method may be used to produce the power semiconductor device described here. Features disclosed in connection with the power semiconductor device are also disclosed for the method, and vice versa.
According to at least one embodiment of the method, the method includes the steps of:
For example, the steps are performed in the indicated order. However, the order of steps may also vary. For example, step c) may be performed prior to step b) or together with step b) in one common step. Thus, the formation of the at least one second trench does not necessarily require an individual production step in addition to the step of forming the at least one first trench.
Further aspects of the disclosure will become apparent from the following description of the exemplary embodiments and figures. In the exemplary embodiments and figures similar or similarly acting constituent parts are provided with the same reference signs. Generally, only the differences with respect to the individual embodiments are described. Unless specified otherwise, the description of a part or aspect in one embodiment applies to a corresponding part or aspect in another embodiment as well.
In the Figures:
The elements illustrated in the figures and their size relationships among one another are not necessarily true to scale. Rather, individual elements or layer thicknesses may be represented with an exaggerated size for the sake of better representability and/or for the sake of better understanding.
A detail of a power semiconductor device 1 is illustrated in
The power semiconductor device 1 comprises a semiconductor body 2 extending in a vertical direction between an emitter side 21 with an emitter electrode 51 and a collector side 22 opposite the emitter side 21.
The power semiconductor device 1 comprises a drift layer 26 of a first conductivity type, a base layer 28 of a second conductivity type different than the first conductivity type extending between the drift layer 26 and the emitter side 21. A source region 29 of the first conductivity type is arranged on a side of the base layer 28 that faces away from the drift layer 26.
In the subsequent description of the exemplary embodiments the first conductivity type is n-type and the second conductivity type is p-type so that the base layer 28 is a p-type layer. However, the layers may also be inverted with respect to their conductivity type.
The power semiconductor device 1 comprises a first trench 3 and a second trench 4. The first trench 3 and the second trench 4 extend from the emitter side 21 into the drift layer 26. An insulated trench gate electrode 30 comprising a gate electrode layer 31 which is electrically conductive and a gate insulation layer 32 extends into the first trench 3. The gate electrode layer 31 is electrically insulated from the semiconductor body 2. During operation of the power semiconductor device 1 the first trench 3 represents an active trench at the potential level of the gate voltage.
The second trench 4 is arranged on a side of the first trench 3 facing away from the source region 29 and does not represent an active trench. An electrically conductive layer 41 extends into the second trench 4. The electrically conductive layer 41 is electrically insulated from the drift layer 26 and the base layer 28. The emitter electrode 51 is arranged at the emitter side 21. The first trench 3 and the second trench 4 may have the same depth, so that they can be formed in a common process step.
In the exemplary embodiment shown, the second trench 4 is electrically insulated from the insulated trench gate electrode 30 and is electrically connected to the emitter electrode 51.
However, the electrically conductive layer 41 may also be electrically separated from the emitter electrode 51. For example, the electrically conductive layer 41 is at the same voltage as the emitter electrode 51 or at a positive voltage with respect to the emitter electrode 51 during operation of the power semiconductor device 1. For example, the electrically conductive layer 41 is at the voltage applied to the emitter electrode or at the voltage applied to the insulated trench gate electrode 3. However, the applied voltage may also differ from both the voltage at the insulated trench gate electrode 3 and the voltage at the emitter electrode. A positive voltage applied to the electrically conductive layer 41 may provide an improved electrostatic shielding of the sub-region 6.
In the exemplary embodiment of
On a side of the second trench 4 that faces away from the first trench 3 the base layer 28 comprises a portion 281 having a depth d2 which is larger than or at least as large as a depth d1 of the second trench 4. For example, the portion 281 of the base layer 28 extends from the emitter side 21 deeper in the vertical direction towards the collector side 22 than the second trench 4. For example, the difference d2−d1 is between 0 μm and 5 μm inclusive. The portion 281 directly adjoins a bottom of the second trench 4 in regions.
A sub-region 6 of the power semiconductor device 1 extending between the first trench 3 and the second trench 4 comprises a charge carrier extraction contact 61 via which the base layer 28 is electrically connected.
The sub-region 6 and the source region 29 are arranged on opposite sides of the first trench 3, so that the sub-region 6 is free of a source region. In the exemplary embodiment shown, the charge carrier extraction contact 61 is electrically connected to the emitter electrode 51. Thus, during operation of the power semiconductor device 1 the charge carrier extraction contact 61 may be at the emitter voltage Ve.
However, during operation of the power semiconductor device 1, the charge carrier extraction contact 61 may also be electrically addressable separately from the emitter electrode 51. Thus, the applied voltage may be independent from the voltage at the emitter electrode 51. For example, the voltage applied to the charge carrier extraction contact 61 is positive with respect to the emitter electrode 51 or the same as the voltage at the emitter electrode 51. For example, the voltage at the charge carrier extraction contact 61 differs for different states during operation.
It has been found that the second trench 4 acting as a dummy trench together with the portion 281 of the base layer 28 that extends deeper towards the collector side 22 than the second trench 4 results in a significant reduction of the avalanche generation during the turn-off switching of the power semiconductor device 1. Degradation of the gate insulation layer 32 caused by hot carriers may be eliminated or at least reduced in this manner.
The reduced avalanche generation near the first trench 3 has been confirmed by simulations as illustrated in
As
The power semiconductor device 1 further comprises a collector layer 25. In an IGBT the collector layer 25 is of the second conductivity type. A collector electrode 52 is arranged on the collector side 22 of the power semiconductor device 1. The collector electrode 52 directly adjoins the collector layer 25. In the following figures only the upper part of the power semiconductor device 1 is shown in the cross-sectional views for the sake of easier representation.
The power semiconductor device 1 further comprises an optional enhancement layer 27 arranged between the drift layer 26 and the base layer 28 in regions. The enhancement layer 27 is a layer with a maximum doping concentration which is higher than the doping concentration of the drift layer 26 by at least a factor of 50. The enhancement layer 27 may act as a charge carrier barrier, for instance as a hole barrier for an n-type enhancement layer 27.
The enhancement layer 27 is also present in the sub-region 6 so that the enhancement layer 27 reduces the charge carrier extraction at the charge carrier extraction contact 61, thereby reducing the on-state losses.
The charge carrier extraction contact 61 still provides an additional escape path to the plasma during turn-off switching but at the same time limits the on-state losses due to the electrostatic screening of the sub-region 6 provided by the first trench 3 and the second trench 4.
For example, typical maximum doping concentrations may be between 1*1012 cm−3 and 1*1014 cm−3 for an n− drift layer 26, 3*1016 cm−3 for an n enhancement layer 27, 1.5*1017 cm−3 for a p base layer 28, 5*1017 cm−3 for the portion 281 of the base layer 28 and 1*1019 cm−3 for a p+ contact portion 282 of the base layer 28.
As shown in
As
The portion 281 of the base layer 28 is located completely within the closed loop formed by the second trench 4 when seen in vertical direction.
However, the partial regions 39 of the first trench 3 and/or the partial regions 49 of the second trenches 4 may also be formed by separate trenches in other designs.
As shown in
For example, the number of segments 610 amounts to between 20 and 200 per millimeter in a direction parallel to the main extension direction L1. However, a single segment may also be used instead.
For example, the power semiconductor device 1 has a cell design providing a stripe trench IGBT with a length of between 0.5 and 3 mm along the main extension direction L1. A cell pitch c1, i.e. a center-to-center distance between adjacent power semiconductor devices 1 in a direction perpendicular to the main extension direction L1 as illustrated in
However, the proposed design may also apply for other power semiconductor devices and other design geometries.
The exemplary embodiment shown in
In departure therefrom, the power semiconductor device 1 the portion 281 extends below the second trench 4 in a direction towards the first trench 3. The second trench 4 completely overlaps with the portion when seen in vertical direction. For example, the portion 281 extends beyond the second trench 4 when seen towards the first trench 3, but does not overlap with the charge carrier extraction contact 61 when seen in vertical direction. This is illustrated using line 62 referring to the edge of the charge carrier extraction contact 61 at the side facing the second trench 4.
Unlike in the embodiment shown, the portion 281 may extend even further towards the first trench 3. For example, the sub-region 6 completely overlaps with the portion 281 when seen in vertical direction. In this case, the sub-region 281 may be completely of the second conductivity type. Alternatively, a part of the drift layer 26 and/or a part of the enhancement layer 27 may be located on a side of the portion 281 that faces the emitter side 21.
Furthermore, even the first trench 3 may overlap in regions or completely with the portion 281 when seen in vertical direction.
In a step S11 a semiconductor body 2 extending in a vertical direction between an emitter side 21 and a collector side 22 opposite the emitter side 21 is provided.
In a step S12 at least one first trench 3 extending from the emitter side 21 into the semiconductor body 2 is formed. This can be done by etching, for instance.
In a step S13 at least one second trench 4 extending from the emitter side 21 into semiconductor body 2 is formed. Unlike in the
In a step S14 an electrically conductive layer 41 extending into the at least one second trench 4 is formed. For example, the electrically conductive layer is deposited as a metallic layer, for instance by chemical vapor deposition (CVD) or physical vapor deposition (PVD).
For example, the power semiconductor device 1 produced in this way comprises an emitter electrode 51 at the emitter side 21, a drift layer 26 of a first conductivity type, a base layer 28 of a second conductivity type different than the first conductivity type extending between the drift layer 26 and the emitter side 21, a source region 29 of the first conductivity type arranged on a side of the base layer (28) facing away from the drift layer 26, and an insulated trench gate electrode 30 extending into the first trench 3. The at least one first trench 3 extends from the emitter side 21 into the drift layer 26. The at least one second trench 4 extends from the emitter side 21 into the drift layer 26, the at least one second trench 4 being arranged on a side of the at least one first trench 3 facing away from the source region 29. The electrically conductive layer 41 is electrically insulated from the base layer 28 and the drift layer 26. A portion 281 of the base layer 28 arranged on a side of the at least one second trench 4 facing away from the at least one first trench 3 extends from the emitter side 21 at least as deep in the vertical direction towards the collector side 22 as the at least one second trench 4. A sub-region 6 of the power semiconductor device 1 extending between the at least one first trench 3 and the at least one second trench 4 comprises a charge carrier extraction contact 61 electrically connected to the base layer 28.
The doping of the layers or portions of the semiconductor body 2 may be performed prior to or after at least one of steps S12 and S13.
This patent application claims the priority of European patent application 20216115.4, the disclosure content of which is hereby incorporated by reference.
The disclosure described herein is not restricted by the description given with reference to the exemplary embodiments. Rather, the disclosure encompasses any novel feature and any combination of features, including in particular any combination of features in the claims, even if this feature or this combination is not itself explicitly indicated in the claims or exemplary embodiments.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20216115.4 | Dec 2020 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/086590 | 12/17/2021 | WO |
