semiconductor devices

Abstract

The present invention discloses a semiconductor device, wherein the front side of the channel region is formed with device units arranged according to a first step, each device unit including a trench gate passing through the channel region; an optimization structure for optimizing the body diode is also formed on the front side of the channel region, including: a second trench electrode structure provided in some or all of the device units, wherein in the device unit provided with the second trench electrode structure, the second trench electrode structure is located on at least one side of the trench gate. The second trench of the second trench electrode structure passes through the channel region, and the side of the second trench is spaced apart from the adjacent front electrode region. The top of the second conductive material layer of the second trench electrode structure is connected to the first front electrode connected to the front electrode region and the channel region, and the gate conductive material layer of the trench gate is connected to the gate. Without increasing the width of the trench gate and without changing the first step, the second trench electrode structure is used to adjust the width of the channel region and thereby optimize the performance of the body diode.

Description

Technical Field

[0001] The present invention relates to a semiconductor integrated circuit, and in particular to a semiconductor device. Background Art

[0002] like Figure 1 The figure shows the structure of an existing super junction (SJ) MOSFET. Taking an N-type device as an example, the existing super junction MOSFET (SJ-MOSFET) includes:

[0003] To reduce the resistance of the heavily N-type doped semiconductor substrate 101, it is generally desirable to make the doping concentration of the semiconductor substrate 101 as high as possible and the thickness of the semiconductor substrate 101 as thin as possible. A thinner semiconductor substrate 101 also reduces thermal resistance and is beneficial for heat dissipation of power devices. After thinning, the semiconductor substrate 101 serves as a drain region.

[0004] The N-type doped drift region 102 is typically formed of an epitaxial layer. P-pillars 105 are also formed in the drift region 102. The N-pillars formed by the drift region 102 between the P-pillars 105 and the P-pillars 105 are arranged alternately to form a superjunction structure. By utilizing the lateral depletion of the P-pillars 105 and the drift region 102, the doping concentration of the drift region 102 can be significantly increased without reducing the breakdown voltage, thereby reducing the resistance of the drift region 102. The sum of the width of the P-pillars 105 and the distance between the P-pillars 105 is called the pitch of the SJ-MOSFET. Generally, the lower the pitch, the more pronounced the lateral depletion effect, the further the doping concentration of the drift region 102 can be increased, and the lower the device's specific on-resistance. Reducing the pitch provides a direction for optimizing the SJ-MOSFET.

[0005] The trench gate includes a gate dielectric layer 103 formed on the inner surface of the gate trench and a gate conductive material layer 104 filled therein. The gate dielectric layer 103 is usually made of an oxide layer such as silicon dioxide. The thickness of the oxide layer determines the withstand voltage of the gate. The typical thickness is The gate conductive material layer 104 is usually made of polysilicon.

[0006] The channel region 106 is a P-type doped region. The doping concentration of the channel region 106 determines the threshold voltage of the device. The channel region 106 is usually formed by ion implantation.

[0007] The N-type heavily doped source region 107 is usually formed by ion implantation, usually using arsenic implantation, with an implantation energy between 40 and 100 keV and an implantation dose between 1e15 and 1e16 / cm 2 between;

[0008] The source region 107 is connected to the source metal formed by the front metal layer 110 through the metal through hole 108.

[0009] The metal via 108 is usually filled with tungsten. To ensure that the metal via 108 forms a good ohmic contact with the channel region 106, a via injection layer 109 is provided. The via injection layer 109 is usually implanted with BF2, with an injection energy of 15 to 100 keV and an injection dose of 1e14 / cm 2 ~5e15 / cm 2 between.

[0010] Figure 1 In the structure shown, a body diode is formed between the channel region 106 and the drift region 102. When the body diode is forward biased, the channel region 106 injects holes into the drift region 102. Holes are minority carriers in the drift region 102 and need to be removed during the reverse recovery process. Therefore, to improve the reverse recovery performance of the body diode, it is necessary to reduce the amount of holes injected into the drift region 102 by the channel region 106. In the prior art, there are two main directions for optimizing the body diode of MOSFET:

[0011] 1. Reduce the dose of the via injection corresponding to the via injection layer 109. However, the via injection is to ensure that the metal via 108 can form a good ohmic contact with the channel region 106. Reducing the dose will easily lead to an increase in contact resistance and increase the risk of parasitic transistor conduction.

[0012] 2. Reduce the width of the channel region 106 within a pitch and make the width of the channel region 106 as small as possible; increasing the width of the gate trench helps optimize the body transistor, but this will increase the capacitance of the MOSFET, namely the gate-drain capacitance Cgd. Because the gate trench width increases, the overlapping area between the trench gate and the drift region 102 increases, so Cgd increases. Cgd, as the Miller capacitance, has a greater impact on the switching performance of the device. When Cgd increases, the switching speed will be reduced. Summary of the Invention

[0013] The technical problem to be solved by the present invention is to provide a semiconductor device that can improve the performance of the body diode and simultaneously improve the capacitance of the device, thereby increasing the switching speed of the device; and can further improve the performance of the body diode without reducing the contact resistance of the channel electrode of the device.

[0014] In order to solve the above technical problems, the present invention provides a semiconductor device comprising:

[0015] A channel region doped with the second conductivity type.

[0016] A drift region doped with a first conductive type is formed at the bottom of the channel region.

[0017] A back electrode region heavily doped with the first conductivity type is formed at the bottom of the drift region.

[0018] A plurality of device units connected in parallel are formed on the front side of the channel region, each of the device units comprising:

[0019] A trench gate comprises a gate trench, a gate dielectric layer formed on the inner surface of the gate trench, and a gate conductive material layer filled in the gate trench; the gate trench passes through the channel region, and the surface of the channel region covered by the side of the gate conductive material layer is used to form a conductive channel.

[0020] A front electrode region is heavily doped with a first conductivity type, and the front electrode region and the side surface of the trench gate are self-aligned.

[0021] A body diode is formed by the channel region and the drift region between the front electrode region and the back electrode region.

[0022] The device units are arranged in a first step, where the first step is the sum of the width of the gate trenches and the spacing between the gate trenches.

[0023] The front electrode region is connected to a first front electrode composed of a front metal layer through a corresponding first through-hole on the top.

[0024] The gate conductive material layer is connected to the gate composed of the front metal layer through a corresponding second through hole on the top.

[0025] The bottom of the first through hole corresponding to the top of the front electrode region is also connected to the channel region.

[0026] The back surface of the back electrode region is connected to a back electrode composed of a back metal layer.

[0027] An optimization structure for optimizing the body diode is also formed on the front surface of the channel region, and the optimization structure includes:

[0028] The second trench electrode structure includes a second trench, a second dielectric layer formed on the inner surface of the second trench, and a second conductive material layer filled in the second trench.

[0029] The second trench electrode structure is provided in part or all of the device units. In the device unit provided with the second trench electrode structure, the second trench electrode structure is located on at least one side of the trench gate.

[0030] The second trench passes through the channel region, and a distance exists between a side surface of the second trench and the adjacent front electrode region.

[0031] The second conductive material layer is also connected to the first front electrode through the first through hole adjacent to the top of the front electrode region.

[0032] Without increasing the width of the trench gate and without changing the first step, the second trench electrode structure is used to adjust the width of the channel region along the width direction of the gate trench. The second trench electrode structure in the semiconductor device is set according to the requirements of the body diode. The more the number of the second trenches and the larger the width of the second trenches, the smaller the width of the channel region, and the better the performance of the body diode.

[0033] A further improvement is that the first through hole is an integral part of the optimized structure, the metal of the first through hole is a metal that can directly form an ohmic contact with the channel region, and the bottom of the first through hole does not form a second conductive type heavily doped through hole injection region to achieve ohmic contact between the first through hole and the channel region, so as to reduce the second conductive type doping amount in the channel region, thereby improving the performance of the body diode.

[0034] A further improvement is that the metal used in the first through hole includes Al.

[0035] A further improvement is that each of the device units is provided with the second trench electrode structure.

[0036] A further improvement is that the second trench electrode structures provided in each of the device units are identical.

[0037] A further improvement is that one or more second trench electrode structures are provided between the trench gates.

[0038] A further improvement is that the gate trench and the second trench have a process structure formed simultaneously using the same process.

[0039] A further improvement is that the width of the second trench is greater than or equal to the width of the gate trench.

[0040] A further improvement is that the distance between the gate trench and the second trench is greater than or equal to the distance between the second trenches.

[0041] A further improvement is that the gate dielectric layer and the second dielectric layer are made of the same material and are formed simultaneously.

[0042] The gate conductive material layer and the second conductive material layer are made of the same material and are formed at the same time.

[0043] A further improvement is that the gate conductive material is a polysilicon gate heavily doped with the first conductivity type.

[0044] A further improvement is that, in the width direction of the gate trench, the trench gate and the second trench electrode structure divide the channel region into a first channel segment and a second channel segment.

[0045] The first channel segment is located between the gate trench and the second trench or between two gate trenches, and the second channel segment is located between the second trenches.

[0046] The doping concentration of the first channel segment is set according to the threshold voltage requirement.

[0047] The second channel segment is a component of the optimized structure, and the doping concentration of the second channel segment is lower than the doping concentration of the first channel segment, so as to reduce the second conductivity type doping amount of the channel region, thereby improving the performance of the body diode.

[0048] A further improvement is that the optimized structure also includes a first bottom doped region doped with the first conductive type located at the bottom of the second channel segment, and the first bottom doped region is used to block the second conductive type charges in the second channel segment from being injected into the drift region, thereby improving the performance of the body diode.

[0049] A further improvement is that the second conductive type doping impurities of the second channel segment are global ion implanted impurities or photolithography defined selective ion implanted impurities.

[0050] The second conductivity type doping impurities of the first channel segment include photolithographically defined selective ion implantation impurities.

[0051] The photomask for photolithographic definition of the first channel segment adopts the photomask for the front electrode region, or the photomask for photolithographic definition of the first channel segment and the photomask for the front electrode region are independent of each other.

[0052] A further improvement is that the semiconductor device is a super junction device, and a super junction structure is formed in the drift region.

[0053] A further improvement is that the semiconductor device includes a MOSFET, the front electrode region is a source region, the back electrode region is a drain region, the first front electrode is a source electrode, and the back electrode is a drain electrode.

[0054] A further improvement is that the semiconductor device includes a reverse conducting IGBT, and the reverse conducting IGBT includes an IGBT and a fast recovery diode.

[0055] A collector region heavily doped with the second conductivity type is formed at the bottom of the drift region, and the back surface of the collector region is also connected to the back surface electrode.

[0056] The front electrode region is the emitter region of the IGBT and the anode region of the fast recovery diode, the first front electrode serves as the emitter of the IGBT and the anode of the fast recovery diode, the back electrode region serves as the cathode region of the fast recovery diode, and the back electrode serves as the collector of the IGBT and the cathode of the fast recovery diode.

[0057] A further improvement is that a buffer layer doped with the first conductive type is formed on the back of the drift region, the doping concentration of the buffer layer is greater than the doping concentration of the drift region, the buffer layer is located between the collector region and the drift region and is used to achieve field cutoff of the IGBT.

[0058] A further improvement is that the semiconductor device is an N-type device, the first conductivity type is N-type, and the second conductivity type is P-type; or the semiconductor device is a P-type device, the first conductivity type is P-type, and the second conductivity type is N-type.

[0059] The semiconductor device of the present invention adopts trench gates in each device unit, and the trench gates are arranged in a first step cycle. A second trench electrode structure is provided in some or all of the device units. Unlike the top of the second conductive material layer of the trench gate, which is connected to the gate composed of the front metal layer, the top of the second conductive material layer of the second trench electrode structure is connected to the first front electrode composed of the front metal layer. The first front electrode is an electrode connected to the channel region and the front electrode region formed on the surface of the channel region and self-aligned with the side of the trench gate, such as the source of a MOSFET or the emitter of an IGBT. In this way, the channel is connected to the second trench electrode structure. The longitudinal cutting of the region can reduce the width of the channel region. The width of the channel region refers to the lateral width of the channel region along the width direction of the trench gate. The present invention utilizes the characteristic that the second trench electrode structure can reduce the width of the channel region. Finally, the second trench electrode structure is set according to the needs of the body diode and the total width of the channel region in the semiconductor device is set. Since the body diode is formed by the PN junction formed by the contact between the channel region and the drift region at the bottom, after the total width of the channel region is reduced, the minority carriers injected from the channel region to the drift region in the body diode will be reduced, and the reverse recovery characteristics of the body diode will be improved. Therefore, the performance of the body diode can be optimized. At the same time, unlike the trench gate, the top of the second trench electrode structure of the present invention is connected to the first front electrode. Therefore, by adding the second trench electrode structure, the depletion effect of the second trench electrode on the drift region will reduce the depletion effect of the trench gate on the drift region. Therefore, the parasitic capacitance of the gate and the back electrode formed between the trench gate and the drift region, such as the gate-drain capacitance Cgd of the MOSFET or the gate-collector capacitance Cgc of the IGBT, will be reduced. Cgd or Cgc, as the Miller capacitance of the device, has a greater impact on the switching performance of the device. Reducing Cgd or Cgc is beneficial to improving the switching speed of the device. In the prior art, the width of the channel region is reduced by simply increasing the width of the trench gate in the first step to improve the body diode. In the technical solution, the increase in the width of the trench gate will bring about the adverse effect of increasing the parasitic capacitance of the gate and the back electrode. Therefore, the present invention can not only improve the body diode performance but also improve the capacitance of the device at the same time, thereby improving the switching speed of the device.

[0060] In addition, the metal of the first through hole connected to the first front electrode can be further optimized so that the metal of the first through hole can directly form an ohmic contact with the bottom channel region, so that there is no need to form an additional second conductive type heavily doped through hole injection region at the contact position between the channel region and the first contact hole. Compared with the prior art that requires the formation of a second conductive type heavily doped through hole injection region at the bottom of the first through hole, the present invention can reduce the total amount of second conductive type doping in the channel region, thereby further reducing the amount of minority carriers injected from the channel region to the drift region in the body diode, so the performance of the body diode can be further optimized; at the same time, since the metal of the first through hole is specially set, it can still ensure the formation of an ohmic contact with the channel region, so it will not reduce the contact resistance of the channel electrode of the device. The channel electrode is the first front electrode, so the present invention can further improve the performance of the body diode without reducing the contact resistance of the channel electrode of the device.

[0061] In addition, in addition to using the second trench electrode structure to longitudinally divide the channel region and thus reduce the width of the channel region, the present invention can also control the number of second trench electrode structures to achieve the arrangement of two or more second trench electrode structures between some or all of the gate trenches. In this way, the channel region can be divided into a first channel segment located between the gate trench and the second trench and a second channel segment located between the second trenches. Since the second channel segment is not related to the threshold voltage, adjusting the doping concentration of the second channel segment does not affect the channel conduction performance. Therefore, the doping concentration of the second channel segment can independently control the doping concentration of the first channel segment. In this way, the total doping amount of the channel region can be further reduced by reducing the doping concentration of the second channel segment, thereby further reducing the amount of minority carriers injected from the channel region to the drift region in the body diode, so that the performance of the body diode can be further optimized.

[0062] In addition, the present invention can further set a first bottom doped region doped with the first conductive type at the bottom of the second channel segment, which can further reduce the amount of minority carriers injected from the channel region to the drift region in the body diode without affecting the threshold voltage of the device, so that the performance of the body diode can be further optimized.

[0063] Except for the different connection relationship between the second trench electrode structure and the trench gate of the present invention and the top front electrode, the two can adopt corresponding process structures and be formed simultaneously using the same process. Therefore, the present invention does not increase additional process costs and has the advantages of simple process and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0065] Figure 1 It is a schematic diagram of the structure of an existing super junction MOSFET;

[0066] Figure 2 is a schematic structural diagram of a semiconductor device according to a first embodiment of the present invention;

[0067] Figure 3 is a schematic structural diagram of a semiconductor device according to a second embodiment of the present invention;

[0068] Figure 4 is a schematic structural diagram of a semiconductor device according to a third embodiment of the present invention;

[0069] Figure 5 FIG. 4 is a schematic structural diagram of a semiconductor device according to a fourth embodiment of the present invention. DETAILED DESCRIPTION

[0070] A semiconductor device according to a first embodiment of the present invention:

[0071] like Figure 2 FIG. 1 is a schematic structural diagram of a semiconductor device according to a first embodiment of the present invention. The semiconductor device according to the first embodiment of the present invention is a MOSFET, comprising:

[0072] A channel region 6 doped with the second conductivity type.

[0073] A drift region 2 doped with the first conductivity type is formed at the bottom of the channel region 6 .

[0074] In the first embodiment of the present invention, the drift region 2 is formed of a semiconductor epitaxial layer such as a silicon epitaxial layer.

[0075] The semiconductor device is a superjunction device, with a superjunction structure formed in the drift region 2. The superjunction structure includes second-conductivity-type pillars 5 formed in the drift region 2, with the drift region 2 between the second-conductivity-type pillars 5 forming first-conductivity-type pillars. The superjunction structure can improve the withstand voltage of the semiconductor device and simultaneously improve the doping concentration of the drift region 2. In other embodiments, the superjunction structure may not be provided in the drift region 2. In this way, the device achieves withstand voltage directly through the drift region 2 during reverse bias.

[0076] A back electrode region 1 heavily doped with the first conductivity type is formed at the bottom of the drift region 2. In the first embodiment of the present invention, the back electrode region 1 serves as a drain region.

[0077] A plurality of parallel device units are formed on the front surface of the channel region 6, each device unit including:

[0078] The trench gate includes a gate trench, a gate dielectric layer 3 formed on the inner surface of the gate trench, and a gate conductive material layer 4 filled in the gate trench; the gate trench passes through the channel region 6, and the surface of the channel region 6 covered by the side of the gate conductive material layer 4 is used to form a conductive channel. Figure 2The cross section in FIG is a cross section along the width direction of the gate trench, and the direction perpendicular to the width direction of the gate trench is the length direction of the gate trench, that is, the extension direction of the gate trench. The width of the channel region 6 is also the dimension along the width direction of the gate trench.

[0079] The front electrode region 7 is heavily doped with the first conductivity type, and the front electrode region 7 and the side of the trench gate are self-aligned. In the first embodiment of the present invention, the front electrode region 7 serves as a drain region. Figure 2 As shown, when the device is not conducting, the front electrode region 7 and the drift region 2 are isolated by the channel region 6. When the device is conducting, a conductive channel formed on the surface of the channel region 6, which is covered by the side of the gate conductive material layer 4, enables conduction between the front electrode region 7 and the drift region 2. The length of the conductive channel is the dimension along the side of the gate conductive material layer 4 from the front electrode region 7 to the drift region 2; the width of the conductive channel is the dimension along the length of the gate trench.

[0080] The body diode is formed by the channel region 6 and the drift region 2 between the front electrode region 7 and the back electrode region 1 .

[0081] Each device unit is arranged according to the first step, and the first step is the sum of the width of the gate trench and the spacing between the gate trenches. The step of the super junction structure is the sum of the width of a second conductive type column 5 and the width of a first conductive type column. In the first embodiment of the present invention, the step of the super junction structure is also equal to the first step. That is, in a super junction unit consisting of a second conductive type column 5 and an adjacent first conductive type column, a device unit is provided and a trench gate is also provided. In other embodiments, it is also possible that the step of the super junction structure is not equal to the first step.

[0082] The front electrode region 7 is connected to a first front electrode formed by a front metal layer 10 through a corresponding first through hole 11 on the top. In the first embodiment of the present invention, the first front electrode is a source.

[0083] The gate conductive material layer 4 is connected to the gate composed of the front metal layer 10 through a corresponding second through hole (not shown) at the top. Figure 2 Only the front metal layer 10 in the first front electrode formation region is shown, and the front metal layer 10 in the gate formation region is not shown.

[0084] The bottom of the first through hole 11 corresponding to the top of the front electrode region 7 is also connected to the channel region 6 .

[0085] The back surface of the back electrode region 1 is connected to a back electrode composed of a back metal layer (not shown). In the first embodiment of the present invention, the back electrode is a drain.

[0086] An optimization structure for optimizing the body diode is also formed on the front surface of the channel region 6. The optimization structure includes:

[0087] The second trench electrode structure includes a second trench, a second dielectric layer 3 a formed on the inner surface of the second trench, and a second conductive material layer 4 a filled in the second trench.

[0088] The second trench electrode structure is provided in part or all of the device units. In the device unit provided with the second trench electrode structure, the second trench electrode structure is located on at least one side of the trench gate.

[0089] The second trench passes through the channel region 6 , and a distance exists between a side surface of the second trench and the adjacent front electrode region 7 .

[0090] The second conductive material layer 4 a is also connected to the first front electrode through the first through hole 11 on the top of the adjacent front electrode region 7 .

[0091] Without increasing the width of the trench gate and without changing the first step, the second trench electrode structure is used to adjust the width of the channel region 6 along the width direction of the gate trench. The second trench electrode structure in the semiconductor device is set according to the requirements of the body diode. The more the number of second trenches and the larger the width of the second trenches, the smaller the width of the channel region 6, and the better the performance of the body diode.

[0092] In the first embodiment of the present invention, the first through hole 11 is a component of the optimized structure. The metal of the first through hole 11 is a metal that can directly form an ohmic contact with the channel region 6. The bottom of the first through hole 11 does not form a through hole injection region that is heavily doped with the second conductive type to achieve ohmic contact between the first through hole 11 and the channel region 6, so as to reduce the second conductive type doping amount in the channel region 6, thereby improving the performance of the body diode.

[0093] In the first embodiment of the present invention, the semiconductor device is an N-type device, wherein the first conductivity type is N-type and the second conductivity type is P-type. Thus, the channel region 6 is P-type doped, and the metal used in the first through hole 11 includes Al. Al can directly form an ohmic contact with the P-type doped channel region 6.

[0094] In other embodiments, the semiconductor device may be a P-type device, the first conductivity type may be P-type, and the second conductivity type may be N-type.

[0095] In the first embodiment of the present invention, each device unit is provided with a second trench electrode structure.

[0096] The second trench electrodes arranged in each device unit have the same structure. Figure 2 The structure of a device unit is shown in FIG. In the first step, a second trench electrode structure is provided on both sides of the trench gate. In some embodiments, other device unit structures of the semiconductor device can be used. Figure 2In some embodiments, other device unit structures of the semiconductor device can adopt different Figure 2 The device units shown, for example: some device units are not provided with the second trench electrode structure; or some device units are provided with second trench electrode structures different from two, for example: one or more than three second trench electrode structures.

[0097] In the first embodiment of the present invention, one or more second trench electrode structures are provided between each trench gate. Figure 2 In, when two Figure 2 When the device unit structures shown are spliced ​​together, two second trench electrode structures are provided between the two trench gates.

[0098] The gate trench and the second trench have a process structure formed simultaneously by using the same process.

[0099] The width of the second trench is greater than or equal to the width of the gate trench.

[0100] The distance between the gate trench and the second trench is greater than or equal to the distance between the second trenches.

[0101] The gate dielectric layer 3 and the second dielectric layer 3 a are made of the same material and are formed simultaneously. For example, both are oxide layers and are formed simultaneously through a thermal oxidation process.

[0102] The gate conductive material layer 4 and the second conductive material layer 4a are made of the same material and are formed simultaneously. In some embodiments, the gate conductive material is a polysilicon gate heavily doped with a first conductivity type.

[0103] In the semiconductor device of the first embodiment of the present invention, trench gates are used in each device unit, and the trench gates are arranged in a first step cycle. A second trench electrode structure is provided in part or all of the device units. Unlike the top of the second conductive material layer 4a of the trench gate, which is connected to the gate composed of the front metal layer 10, the top of the second conductive material layer 4a of the second trench electrode structure is connected to the first front electrode composed of the front metal layer 10. The first front electrode is an electrode connected to the channel region 6 and the front electrode region 7 formed on the surface of the channel region 6 and self-aligned with the side of the trench gate, i.e., the source of the MOSFET. In this way, the longitudinal direction of the channel region 6 is controlled by the second trench electrode structure. Cutting can reduce the width of the channel region 6. The width of the channel region 6 refers to the lateral width of the channel region 6 along the width direction of the trench gate. The first embodiment of the present invention utilizes the characteristic that the second trench electrode structure can reduce the width of the channel region 6. Finally, the second trench electrode structure is set according to the needs of the body diode and the total width of the channel region 6 in the semiconductor device is set. Since the body diode is formed by the PN junction formed by the contact between the channel region 6 and the drift region 2 at the bottom, after the total width of the channel region 6 is reduced, the minority carriers injected from the channel region 6 to the drift region 2 in the body diode will be reduced, and the reverse recovery characteristics of the body diode will be improved. Therefore, the performance of the body diode can be optimized. At the same time, unlike the trench gate, the top of the second trench electrode structure of the first embodiment of the present invention is connected to the first front electrode. Therefore, by adding the second trench electrode structure, the depletion effect of the second trench electrode on the drift region 2 will reduce the depletion effect of the trench gate on the drift region 2. Therefore, the parasitic capacitance of the gate and the back electrode formed between the trench gate and the drift region 2, such as the gate-drain capacitance Cgd of the MOSFET, will be reduced. Cgd, as the Miller capacitance of the device, has a greater impact on the switching performance of the device. Reducing Cgd is beneficial to improving the switching speed of the device. In the prior art, the body diode is improved by simply increasing the width of the trench gate in the first step to reduce the width of the channel region 6. The increase in the width of the trench gate will bring about the adverse effect of increasing the parasitic capacitance of the gate and the back electrode. Therefore, the first embodiment of the present invention can not only improve the body diode performance but also improve the capacitance of the device at the same time, thereby improving the switching speed of the device.

[0104] In addition, the first embodiment of the present invention further optimizes the metal of the first through hole 11 connected to the first front electrode, so that the metal of the first through hole 11 can directly form an ohmic contact with the bottom channel region 6, so that there is no need to form an additional second conductive type heavily doped through hole injection region at the contact position between the channel region 6 and the first contact hole. Compared with the prior art that requires the formation of a second conductive type heavily doped through hole injection region at the bottom of the first through hole 11, the first embodiment of the present invention can reduce the total amount of second conductive type doping in the channel region 6, thereby further reducing the amount of minority carriers injected from the channel region 6 to the drift region 2 in the body diode, so that the performance of the body diode can be further optimized; at the same time, since the metal of the first through hole 11 is specially set, it can still ensure that ohmic contact is formed between the channel region 6, so it will not reduce the contact resistance of the channel electrode of the device. The channel electrode is the first front electrode, so the first embodiment of the present invention can further improve the performance of the body diode without reducing the contact resistance of the channel electrode of the device.

[0105] The second trench electrode structure and the trench gate of the first embodiment of the present invention can be formed simultaneously using corresponding process structures and the same process, except for the different connection relationship with the top front electrode. Therefore, the first embodiment of the present invention does not increase additional process costs and has the advantages of simple process and low cost.

[0106] The semiconductor device according to the first embodiment of the present invention is further described below with reference to specific parameters:

[0107] In the first embodiment of the present invention, the semiconductor device is an N-type device and has a super junction structure, so the following description is based on an N-type super junction MOSFET.

[0108] Figure 1 In the superjunction structure of the existing superjunction MOSFET shown, the width of the P column, i.e., the second conductive type column 105, is 3 μm, the distance between the P columns is 4 μm, and the corresponding pitch of the superjunction structure is 7 microns; the first step corresponding to the device unit is equal to the step of the superjunction structure, and the first step includes a trench gate and a channel region 106 between the trench gates. The width of the trench gate is 1 micron, and the width of the channel region 106 in a first step is 6 microns.

[0109] And in Figure 2 In the first embodiment of the present invention, the super junction structure and Figure 1 The structures shown are the same, that is, the width of the P column, i.e., the second conductive type column 5, is 3 μm, the distance between the P columns is 4 μm, and the corresponding pitch of the super junction structure is 7 microns; the first step corresponding to the device unit is equal to the step of the super junction structure.

[0110] In the first step, in addition to the trench gate and channel region 6, two second trench electrode structures are also provided. If the width of the second trench is consistent with the width of the gate trench, then at 7 microns, the width of the channel region 6 will be reduced from the existing 6 microns to 4 microns, including three 1-micron trenches in the first step. Therefore, the width of the channel region 6 is reduced. The reduced width of the channel region 6 reduces the area of ​​holes injected when the parasitic body diode of the MOSFET is turned on, which helps improve the reverse recovery characteristics of the body diode. In a MOSFET, the first front electrode is the source, so the second trench electrode structure is also called a trench source structure, and the second trench is also called a source trench. In other embodiments, the width of the source trench, i.e., the second trench, can be wider than the width of the gate trench. For example, the width of the source trench can be 1.2μm, 1.5μm, or even 2.0μm. The wider the width of the source trench, the smaller the width of the channel region 6. The distances between the trenches can be the same, that is, the distances between the gate trench and the source trench are the same as the distances between the source trenches; more preferably, the distances between the source trenches are closer, which helps to further reduce the width of the channel region 6 within a Pitch.

[0111] Therefore, the second trench electrode structure of the first embodiment of the present invention can adjust the width of the channel region 6, thereby optimizing the performance of the body diode. Furthermore, because the second conductive material layer 4a of the second trench electrode structure of the first embodiment of the present invention is connected to the source, it can provide a shielding effect on the gate electrode, which is equivalent to reducing the effective overlap area between the trench gate and the drift region 2. It can also reduce Cgd, thereby improving the switching speed of the device. Therefore, compared with the prior art structure that improves the performance of the body diode by increasing the width of the trench gate, the first embodiment of the present invention not only overcomes the technical problem of increased Cgd caused by increasing the width of the trench gate, but also further reduces Cgd, thereby further improving the performance of the device.

[0112] In the first embodiment of the present invention, the first through-hole 11 is made of aluminum and is directly connected to the channel region 6 and the heavily doped source region 7. The source region 7 is heavily doped, so the first through-hole 11 and the source region 7 can form a good ohmic contact. The channel region 6 is P-type, and the epitaxial layer of the channel region 6 is typically a silicon epitaxial layer. The aluminum in the first through-hole 11 can form a good ohmic contact with the P-type silicon. This eliminates the need for through-hole (CT) implantation. Without CT implantation, the dose of P-type impurities is reduced, the number of injected holes is reduced, and the performance of the parasitic body diode is further improved.

[0113] Furthermore, the aluminum in the first through-hole 11 is also connected to the second conductive material layer 4a. In the first embodiment of the present invention, since the second conductive material layer 4a is also formed of polysilicon, it is also called source polysilicon (poly). The source poly is typically heavily N-type doped, which can also form a good ohmic contact.

[0114] In addition to improving the performance of the body diode, the absence of via implantation at the bottom of the first via 11 further reduces the uniformity of the threshold voltage (VTH), making the device more suitable for parallel applications. Furthermore, the absence of via implantation allows the distance between the first via 11 and the gate trench of the trench gate to be further reduced.

[0115] In the first embodiment of the present invention, the step of a super junction structure, namely the Pitch, is composed of the sum of the widths of a second conductive type column 5 and an adjacent first conductive type column; the first step of the device unit is the same as the step of the super junction structure. There are two second trenches, namely the source trenches, on the left and right next to the trench gate (gate-Trench), that is, there are two source trenches and one gate trench in one pitch. However, if the pitch of the super junction is further reduced to 5μm, or even 3μm; it becomes more difficult to realize two source trenches and one gate trench in one pitch, and it can be changed to have one source trench and one gate trench in one pitch; in this way, the gate trench can also be shielded by the source trench to reduce the Cgd capacitance. If the pitch of the super junction is large, three or even more source trenches and one gate trench can also be realized in one pitch.

[0116] A semiconductor device according to a second embodiment of the present invention:

[0117] like Figure 3 FIG. 1 is a schematic structural diagram of a semiconductor device according to a second embodiment of the present invention. The difference between the semiconductor device according to the second embodiment of the present invention and the semiconductor device according to the first embodiment of the present invention is that the semiconductor device according to the second embodiment of the present invention further has the following features:

[0118] In the width direction of the gate trench, the trench gate and the second trench electrode structure divide the channel region 6 into a first channel segment 6 b and a second channel segment 6 a .

[0119] The first channel section 6 b is located between the gate trench and the second trench or between two gate trenches, and the second channel section 6 a is located between the second trenches. Figure 3A device unit corresponding to the first step is also shown. Figure 3 The device units shown are arranged repeatedly, so that there are two second trenches between the two gate trenches. In this way, the channel region 6 between the two second trenches is the second channel segment 6a. Figure 3 Only half of the corresponding second channel segment 6a is shown on both the left and right sides, so that each device unit contains one second channel segment 6a. In other embodiments, the second channel segment 6a can be present only in some gate trenches. In this way, the area between the gate trenches without the second channel segment 6a is the first channel segment 6b. For example, when no second trench electrode structure is provided between two gate trenches or only one second trench electrode structure is provided, only the first channel segment 6b is provided between the two gate trenches.

[0120] Figure 3 The device cell shown includes one second channel segment 6a, i.e., one second channel segment 6a is provided between two trench gates. In other embodiments, the device cell including the second channel segment 6a may include more than two second channel segments 6a. In this case, the number of second trench electrode structures between the two trench gates is three or more.

[0121] The doping concentration of the first channel segment 6b is set according to the threshold voltage requirement. The second channel segment 6a does not affect the threshold voltage of the device, so the doping concentration of the second channel segment 6a is not limited by the threshold voltage requirement, allowing the doping concentration of the second channel segment 6a to be lower. As a component of the optimized structure, the doping concentration of the second channel segment 6a is lower than the doping concentration of the first channel segment 6b, thereby reducing the amount of the second conductivity type doping in the channel region 6, thereby improving the performance of the body diode.

[0122] In some embodiments, the second conductivity type dopant impurities of the second channel segment 6a are implanted across the board, saving a photomask and reducing process costs. Furthermore, the implanted impurities corresponding to the second channel segment 6a are also superimposed on the first channel segment 6b. In some embodiments, the second conductivity type dopant impurities of the second channel segment 6a can be implanted via selective ion implantation defined by photolithography. The photolithographic definition can prevent the implanted impurities corresponding to the second channel segment 6a from being superimposed on the first channel segment 6b.

[0123] In some embodiments, the second conductivity type dopant impurities of the first channel segment 6b include photolithographically defined selective ion implanted impurities. In some preferred embodiments, the photomask for the front electrode region 7 is used between the photomask for the photolithographic definition of the first channel segment 6b, thereby eliminating the need for a separate photomask design and reducing process costs. In some embodiments, the photomask for the photolithographic definition of the first channel segment 6b and the photomask for the front electrode region 7 can also be independent of each other.

[0124] In the second embodiment of the present invention, in addition to using the second trench electrode structure to longitudinally divide the channel region 6 and thus reduce the width of the channel region 6, the present invention can also control the number of the second trench electrode structures to achieve the arrangement of two or more second trench electrode structures between some or all of the gate trenches. In this way, the channel region 6 can be divided into a first channel segment 6b located between the gate trench and the second trench and a second channel segment 6a located between the second trenches. Since the second channel segment 6a is not related to the threshold voltage, adjusting the doping concentration of the second channel segment 6a does not affect the channel conduction performance. Therefore, the doping concentration of the second channel segment 6a can independently control the doping concentration of the first channel segment 6b. In this way, the total doping amount of the channel region 6 can be further reduced by reducing the doping concentration of the second channel segment 6a, thereby further reducing the amount of minority carriers injected from the channel region 6 to the drift region 2 in the body diode, so that the performance of the body diode can be further optimized.

[0125] like Figure 3 As shown, in the second embodiment of the present invention, the second trench, i.e., the second channel segment 6a between the source trench Source trench and the Source trench, does not require VTH, so the dose can be made very low; while the gate trench, i.e., the first channel segment 6b between the Gate trench and the Source trench, requires VTH requirements and its dose needs to be increased to prevent punch-through.

[0126] In terms of process implementation, a mask or general injection can be used to realize the second channel segment 6a. Boron is usually injected. The injection energy is usually 40-100 keV and the injection dose is usually 1e12-5e12 cm 2 In the gate-source trench, between the gate trench and the source trench, another mask is used to increase the concentration to create the first channel segment 6b. Because the concentration of the first channel segment 6b needs to be increased only where the heavily doped source region 7 is located, in some embodiments, the first channel segment 6b can share a mask with the source region 7. Using this mask set, two implants are performed: one for the heavily N-type source region and the other for the P-type channel.

[0127] A semiconductor device according to a third embodiment of the present invention:

[0128] like Figure 4 FIG. 1 is a schematic structural diagram of a semiconductor device according to a third embodiment of the present invention. The difference between the semiconductor device according to the third embodiment of the present invention and the semiconductor device according to the second embodiment of the present invention is that the semiconductor device according to the third embodiment of the present invention further has the following features:

[0129] The optimized structure also includes a first bottom doped region 12 doped with the first conductivity type located at the bottom of the second channel segment 6a. The first bottom doped region 12 is used to block the second conductivity type charges in the second channel segment 6a from being injected into the drift region 2, thereby improving the performance of the body diode.

[0130] The third embodiment of the present invention can further set a first bottom doped region 12 doped with the first conductive type at the bottom of the second channel segment 6a, which can further reduce the amount of minority carriers injected from the channel region 6 to the drift region 2 in the body diode without affecting the threshold voltage of the device, so that the performance of the body diode can be further optimized.

[0131] like Figure 5 FIG. 4 is a schematic diagram of the structure of a semiconductor device according to a fourth embodiment of the present invention. Figure 3 The difference between the semiconductor device of the second embodiment of the present invention and the semiconductor device of the fourth embodiment of the present invention is that the semiconductor device of the fourth embodiment of the present invention is a reverse conducting IGBT (RC-IGBT).

[0132] The reverse conducting IGBT includes an IGBT and a fast recovery diode.

[0133] In the third embodiment of the present invention, in order to further reduce the injection of minority carriers from the body diode into the drift region 2, the following method can be adopted: an N-type doped first bottom doping region 12 is added below the first channel segment 6a. The function of the first bottom doping region 12 is to further prevent the first channel segment 6a from injecting holes into the drift region 2. In some embodiments, the first bottom doping region 12 is usually formed by ion implantation of phosphorus, the implantation energy is usually 60 to 300 keV, and the implantation dose is usually 1e12 / cm 2 ~1e13 / cm 2 between.

[0134] In the semiconductor device according to the fourth embodiment of the present invention:

[0135] A collector region 13 heavily doped with the second conductivity type is formed at the bottom of the drift region 2 , and the back surface of the collector region 13 is also connected to the back electrode.

[0136] The front electrode region 7 is the emitter region of the IGBT and the anode region of the fast recovery diode. The first front electrode serves as the emitter of the IGBT and the anode of the fast recovery diode. The back electrode region 15 serves as the cathode region of the fast recovery diode. The back electrode serves as the collector of the IGBT and the cathode of the fast recovery diode. Figure 5 In the figure, the back electrode area is represented by a mark 15 alone.

[0137] A buffer layer 14 doped with the first conductive type is formed on the back of the drift region 2 . The doping concentration of the buffer layer 14 is greater than that of the drift region 2 . The buffer layer 14 is located between the collector region 13 and the drift region 2 and is used to achieve field stop of the IGBT.

[0138] Figure 5 In the embodiment, no super junction structure is provided in the drift region 2. In other embodiments, a super junction structure may be provided in the drift region 2.

[0139] The present invention has been described in detail above by means of specific embodiments, but these do not constitute limitations of the present invention. Without departing from the principles of the present invention, those skilled in the art may make many variations and improvements, which should also be considered as the scope of protection of the present invention.

Claims

1. A semiconductor device, characterized in that: include: a channel region doped with a second conductivity type; A drift region doped with a first conductive type is formed at the bottom of the channel region; A back electrode region heavily doped with the first conductivity type is formed at the bottom of the drift region; A plurality of device units connected in parallel are formed on the front side of the channel region, each of the device units comprising: A trench gate comprises a gate trench, a gate dielectric layer formed on the inner surface of the gate trench, and a gate conductive material layer filled in the gate trench; the gate trench passes through the channel region, and the surface of the channel region covered by the side of the gate conductive material layer is used to form a conductive channel; A front electrode region heavily doped with a first conductivity type, wherein the front electrode region and the side of the trench gate are self-aligned; A body diode is formed by the channel region and the drift region between the front electrode region and the back electrode region; The device units are arranged in a first step, wherein the first step is the sum of the width of the gate trench and the spacing between the gate trenches; The front electrode region is connected to a first front electrode composed of a front metal layer through a corresponding first through hole on the top; The gate conductive material layer is connected to the gate composed of the front metal layer through a second through hole corresponding to the top; The bottom of the first through hole corresponding to the top of the front electrode region is also connected to the channel region; The back surface of the back electrode region is connected to a back electrode composed of a back metal layer; An optimization structure for optimizing the body diode is also formed on the front surface of the channel region, and the optimization structure includes: a second trench electrode structure comprising a second trench, a second dielectric layer formed on an inner surface of the second trench, and a second conductive material layer filled in the second trench; The second trench electrode structure is provided in part or all of the device units, and in the device unit provided with the second trench electrode structure, the second trench electrode structure is located on at least one side of the trench gate; The second trench passes through the channel region, and a distance exists between a side surface of the second trench and the adjacent front electrode region; The second conductive material layer is also connected to the first front electrode through the first through hole adjacent to the top of the front electrode region; Without increasing the width of the trench gate and without changing the first step, the width of the channel region along the width direction of the gate trench is adjusted using the second trench electrode structure. The second trench electrode structure in the semiconductor device is configured according to the requirements of the body diode. The greater the number of second trenches and the greater the width of the second trenches, the smaller the width of the channel region, and the better the performance of the body diode. One or more second trench electrode structures are provided between each of the trench gates; In the width direction of the gate trench, the trench gate and the second trench electrode structure divide the channel region into a first channel segment and a second channel segment; The first channel segment is located between the gate trench and the second trench or between two gate trenches, and the second channel segment is located between the second trenches; The doping concentration of the first channel segment is set according to the threshold voltage requirement; The second channel segment is a component of the optimized structure, and the doping concentration of the second channel segment is lower than the doping concentration of the first channel segment, so as to reduce the second conductivity type doping amount of the channel region, thereby improving the performance of the body diode.

2. The semiconductor device according to claim 1, wherein: The first through hole is a component of the optimized structure. The metal of the first through hole is a metal that can directly form an ohmic contact with the channel region. The bottom of the first through hole does not form a through hole injection region that is heavily doped with the second conductive type to achieve ohmic contact between the first through hole and the channel region, so as to reduce the second conductive type doping amount in the channel region, thereby improving the performance of the body diode.

3. The semiconductor device according to claim 2, wherein: The metal used in the first through hole includes Al.

4. The semiconductor device according to claim 1, wherein: Each of the device units is provided with the second trench electrode structure.

5. The semiconductor device according to claim 4, wherein: The second trench electrode structures provided in each of the device units are identical.

6. The semiconductor device according to claim 5, wherein: The gate trench and the second trench have a process structure formed simultaneously by using the same process.

7. The semiconductor device according to claim 6, wherein: The width of the second trench is greater than or equal to the width of the gate trench.

8. The semiconductor device according to claim 7, wherein: The distance between the gate trench and the second trench is greater than or equal to the distance between the second trenches.

9. The semiconductor device according to claim 6, wherein: The gate dielectric layer and the second dielectric layer are made of the same material and are formed at the same time; The gate conductive material layer and the second conductive material layer are made of the same material and are formed at the same time.

10. The semiconductor device according to claim 9, wherein: The gate conductive material is a polysilicon gate heavily doped with a first conductivity type.

11. The semiconductor device according to claim 5, wherein: The optimized structure also includes a first bottom doped region doped with the first conductive type located at the bottom of the second channel segment, and the first bottom doped region is used to block the second conductive type charges in the second channel segment from being injected into the drift region, thereby improving the performance of the body diode.

12. The semiconductor device according to claim 5, wherein: The second conductive type doping impurities of the second channel segment are fully ion-implanted impurities or selectively ion-implanted impurities defined by photolithography; The second conductivity type doping impurities of the first channel segment include photolithographically defined selective ion implantation impurities; The photomask for photolithographic definition of the first channel segment adopts the photomask for the front electrode region, or the photomask for photolithographic definition of the first channel segment and the photomask for the front electrode region are independent of each other.

13. The semiconductor device according to claim 1, wherein: The semiconductor device is a super junction device, and a super junction structure is formed in the drift region.

14. The semiconductor device according to claim 1 or 13, wherein: The semiconductor device includes a MOSFET, the front electrode region is a source region, the back electrode region is a drain region, the first front electrode is a source electrode, and the back electrode is a drain electrode.

15. The semiconductor device according to claim 1 or 13, wherein: The semiconductor device includes a reverse conducting IGBT, and the reverse conducting IGBT includes an IGBT and a fast recovery diode; A collector region heavily doped with the second conductivity type is formed at the bottom of the drift region, and the back side of the collector region is also connected to the back side electrode; The front electrode region is the emitter region of the IGBT and the anode region of the fast recovery diode, the first front electrode serves as the emitter of the IGBT and the anode of the fast recovery diode, the back electrode region serves as the cathode region of the fast recovery diode, and the back electrode serves as the collector of the IGBT and the cathode of the fast recovery diode.

16. The semiconductor device according to claim 15, wherein: A buffer layer doped with a first conductive type is also formed on the back side of the drift region. The doping concentration of the buffer layer is greater than the doping concentration of the drift region. The buffer layer is located between the collector region and the drift region and is used to achieve field stop of the IGBT.

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