Silicon carbide power das device with p-type variable doped base region and method of fabrication thereof

Abstract

The application provides a silicon carbide power DAS device with a P-type variable-doping base region and a preparation method thereof. The prepared silicon carbide power DAS device with the P-type variable-doping base region comprises a p+ epitaxial layer 1, a P-base region 2, an N+ substrate 3, a passivation layer 4, a back electrode 5 and a front electrode 6. The P-base region 2 uses a longitudinal variable-doping base region, the doping concentration of the P-base region at the P- / N+ junction can be reduced, the longitudinal uniformity of the base region electric field can be improved, and the avalanche opening speed of the device can be improved. Meanwhile, the doping concentration of the P-base region at the P+ / P- junction can be improved, the concentration gradient at the negative corner of the device can be reduced, the surface electric field can be inhibited, and the working reliability of the device can be improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of semiconductors, and particularly relates to a silicon carbide power DAS device with a P-type variable-doped base region and a preparation method thereof. BACKGROUND

[0002] DAS (Diode Avalanche Shaper) is a kind of semiconductor short-circuit switch diode, which has the characteristics of high efficiency, high reliability, long continuous working time and small volume, and is usually applied to UWB (Ultra Wide Band) pulse signal sources as a key device.

[0003] Due to the theoretical limit of silicon material, silicon-based DAS cannot meet the requirements of most several-kilovolt or even several-decades-kilovolt pulse systems. Silicon carbide material has higher band gap, saturation drift velocity, thermal conductivity, critical breakdown field and radiation resistance than silicon material, so that the performance of silicon carbide-based DAS devices is better than that of silicon-based DAS. In the pulse system with the same voltage level requirement, the number of silicon carbide-based DAS in series is much smaller than that of silicon-based DAS, which greatly saves the volume of the system; meanwhile, the reduction of the drift region thickness and the improvement of the saturation drift velocity can reduce the voltage rise time of the device, so that the silicon carbide-based DAS can work under high frequency and high speed conditions.

[0004] However, due to the limitation of the current preparation process of silicon carbide devices, the conventional silicon carbide-based DAS device with an N-type base region is difficult to prepare. The P-type base region in the prior art is purely etched with uniform doping, and in order to reduce the surface electric field, the base region of the device has a high doping concentration, so that the opening speed of the device is slow; at the same time, the limitation of the preparation process leads to the concentration of local electric field of the device, which increases the possibility of failure before work, and makes it difficult to fully exert the advantages of silicon carbide material, thereby limiting the performance of the DAS device. SUMMARY

[0005] In order to solve the above problems in the prior art, the application provides a silicon carbide power DAS device with a P-type variable-doped base region and a preparation method thereof. The technical problems to be solved by the application are solved by the following technical solutions.

[0006] In a first aspect, the application provides a silicon carbide power DAS device with a P-type variable-doped base region, which comprises:

[0007] a p+ epitaxial layer 1, a P-base region 2, an N+ substrate 3, a passivation layer 4, a back electrode 5 and a front electrode 6;

[0008] The P-base region 2 is located above the N+ substrate 3, and the doping concentration of the P-base region 2 is lower near the N+ substrate 3 than near the p+ epitaxial layer 1; the p+ epitaxial layer 1 is located above the P-base region 2, and the front electrode 6 is located above the p+ epitaxial layer 1; the p+ epitaxial layer 1, the P-base region 2 and the N+ substrate 3 are in a trapezoidal step structure; the passivation layer 4 wraps the trapezoidal step structure of the p+ epitaxial layer 1, the P-base region 2 and the N+ substrate 3 from top to bottom, and exposes the front electrode 6 on the upper surface of the trapezoidal step structure; the N+ substrate 3 is provided with a step surface, which makes the upper part of the N+ substrate 3 in a trapezoidal shape and the lower part in a rectangular shape; the back electrode 5 is located on the lower surface of the rectangular shape, and the passivation layer 4 wraps the upper part of the N+ substrate 3 and the step surface.

[0009] The doping concentration of the P-base region 2 increases from bottom to top in turn and changes in a gradient, and the doping concentration of the P-base region 2 is in a continuous change Gaussian distribution, and the metal for depositing the back electrode 5 and the front electrode 6 includes Ti and Ni.

[0010] Optionally, the N+ substrate 3 includes a first step surface and a second step surface, the first step surface is in contact with the lower surface of the P-base region 2, and the second step surface is located on both sides of the junction of the trapezoidal shape and the matrix; the passivation layer 4 wraps the N+ substrate 3 from top to bottom until the second step surface is completely wrapped, and exposes the part below the second step surface of the N+ substrate 3.

[0011] In a second aspect, the application provides a preparation method of a silicon carbide power DAS device with a P-type variable-doping base region, which comprises the following steps:

[0012] Step 1: obtaining an N+ substrate 3;

[0013] Step 2: growing a P-base region 2 with a regular change in doping concentration on the surface of the N+ substrate region 3 by a CVD method;

[0014] Step 3: growing a P+ epitaxial layer 1 on the surface of the P-base region 2 by a CVD method;

[0015] Step 4: etching the outer peripheral edges of the P-base region 2, the P+ epitaxial layer 1 and part of the N+ substrate region 3, so that the P+ epitaxial layer 1, the P-base region 2 and the N+ substrate 3 are in a trapezoidal step structure, and etching a step surface on the N+ substrate 3, so that the upper part of the N+ substrate 3 is in a trapezoidal structure and the lower part is in a rectangular structure;

[0016] Step 5: etching part of the upper surface of the P+ epitaxial layer 1;

[0017] Step 6: growing a SiO2 passivation layer 4 on the step surface of the N+ substrate 3 from bottom to top, until the SiO2 passivation layer 4 wraps the etched part of the P+ epitaxial layer 1, the P-base region 2 and the step surface of the N+ substrate 3;

[0018] Step 7: depositing metal on the lower surface of the lower part of the rectangular structure of the N+ substrate 3 to form the back electrode 5, and depositing metal on the upper surface of the P+ epitaxial layer 1 to form the front electrode 6.

[0019] The growth temperature for growing the P- base region 2 is 1600-1900 ℃, the growth temperature for growing the P+ epitaxial layer 1 is 1600-1900 ℃, and the metal deposited in step 7 includes Ti and Ni;

[0020] The annealing temperature for annealing the back electrode 5 and the front electrode 6 is 400-1000 ℃. The doping concentration of the P- base region 2 changes regularly from low to high, and is in a gradient change or a continuous change of Gaussian distribution.

[0021] The beneficial effects of the present application are:

[0022] The present application provides a silicon carbide power DAS device with a P-type variable-doped base region and a preparation method thereof. The prepared silicon carbide power DAS device with a P-type variable-doped base region comprises a p+ epitaxial layer 1, a P- base region 2, an N+ substrate 3, a passivation layer 4, a back electrode 5, and a front electrode 6. The P- base region 2 uses a longitudinal variable-doped base region, which can reduce the doping concentration of the P- base region at the P- / N+ junction, improve the longitudinal uniformity of the base region electric field, and improve the avalanche opening speed of the device. At the same time, the doping concentration of the P- base region at the P+ / P- junction is increased, the concentration gradient at the negative corner of the device is reduced, the surface electric field is suppressed, and the working reliability of the device is improved.

[0023] The present application will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a schematic diagram of a silicon carbide power DAS device with a P-type variable-doped base region provided by an embodiment of the present application;

[0025] Figure 2 is a preparation flowchart of a silicon carbide power DAS device with a P-type variable-doped base region provided by an embodiment of the present application. DETAILED DESCRIPTION

[0026] The present application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0027] As shown in Figure 1 , the present application provides a silicon carbide power DAS device with a P-type variable-doped base region, which comprises:

[0028] a p+ epitaxial layer 1, a P- base region 2, an N+ substrate 3, a passivation layer 4, a back electrode 5, and a front electrode 6;

[0029] The P-base region 2 is located above the N+ substrate 3, the doping concentration of the P-base region 2 is lower near the N+ substrate 3 than near the p+ epitaxial layer 1, the p+ epitaxial layer 1 is located above the P-base region 2, and the front electrode 6 is located above the p+ epitaxial layer 1; the p+ epitaxial layer 1, the P-base region 2 and the N+ substrate 3 form a trapezoidal step structure; the passivation layer 4 wraps the trapezoidal step structure of the p+ epitaxial layer 1, the P-base region 2 and the N+ substrate 3 from top to bottom, and exposes the front electrode 6 on the upper surface of the trapezoidal step structure; the N+ substrate 3 is provided with a step surface, the step surface makes the upper part of the N+ substrate 3 form a trapezoid, and the lower part form a rectangle; the back electrode 5 is located on the lower surface of the rectangle, and the passivation layer 4 wraps the upper part of the N+ substrate 3 and the step surface.

[0030] The doping concentration of the P-base region 2 increases from bottom to top in turn and forms a gradient change, or the doping concentration of the P-base region 2 forms a continuous change Gaussian distribution. The metal for depositing the back electrode 5 and the front electrode 6 includes Ti and Ni.

[0031] Reference Figure 1 The N+ substrate 3 of the present application includes a first step surface and a second step surface, the first step surface is in contact with the lower surface of the P-base region 2, the second step surface is located on both sides of the junction of the trapezoid and the matrix, the passivation layer 4 wraps the N+ substrate 3 from top to bottom until completely wrapping the second step surface, and exposes the part below the second step surface of the N+ substrate 3.

[0032] Principle explanation: It is worth mentioning that reducing the doping concentration of the P-base region at the P- / N+ junction reduces the slope of the electric field near the PN junction to the position change, so that the electric field near the PN junction is more uniform. Under the excitation of external signals, the high-field avalanche ionization region in the base region is larger; the carrier concentration accumulated in the base region is higher, and the rate of establishing the low-field region in the device is faster. Therefore, reducing the doping concentration of the P-base region at the P- / N+ junction can improve the switching rate of the DAS device. At the same time, increasing the doping concentration of the P-base region at the P+ / P- junction can reduce the concentration gradient at the negative bevel angle in the actual device, reduce the multiplication factor of the surface electric field and the bulk electric field at the negative bevel angle, and ensure the normal operation of the device and improve the reliability of the device operation.

[0033] The present application provides a silicon carbide power DAS device with a P-type variable-doping base region, which includes a p+ epitaxial layer 1, a P-base region 2, an N+ substrate 3, a passivation layer 4, a back electrode 5 and a front electrode 6; the P-base region 2 of the present application uses a longitudinal variable-doping base region, which can increase the doping concentration of the P-base region at the P+ / P- junction, reduce the concentration gradient at the negative angle of the device, suppress the surface electric field, and improve the working reliability of the device; at the same time, the doping concentration of the P-base region at the P- / N+ junction is reduced, the longitudinal uniformity of the base region electric field is improved, and the avalanche opening speed of the device is improved.

[0034] As Figure 2As shown, the application provides a preparation method of a silicon carbide power DAS device with a P-type variable-doping base region, which comprises the following steps:

[0035] Step 1: obtaining an N+ substrate 3;

[0036] Step 2: growing a P-base region 2 with a regularly changing doping concentration on the surface of the N+ substrate region 3 by a CVD method;

[0037] In the P-base region 2, the doping concentration regularly changes in a gradient or Gaussian distribution from low to high.

[0038] Step 3: growing a P+ epitaxial layer 1 on the surface of the P-base region 2 by a CVD method;

[0039] Step 4: etching the outer peripheral edge of the P-base region 2, the P+ epitaxial layer 1 and part of the N+ substrate region 3, so that the P+ epitaxial layer 1, the P-base region 2 and the N+ substrate 3 form a trapezoidal step structure, and etching the step surface of the N+ substrate 3, so that the upper part of the N+ substrate 3 forms a trapezoidal structure and the lower part forms a rectangular structure;

[0040] Step 5: etching part of the upper surface of the P+ epitaxial layer 1;

[0041] Step 6: growing a SiO2 passivation layer 4 on the step surface of the N+ substrate 3 from low to high, until the SiO2 passivation layer 4 wraps the etched part of the P+ epitaxial layer 1, the P-base region 2 and the step surface of the N+ substrate 3;

[0042] Step 7: depositing metal on the lower surface of the lower part of the rectangular structure of the N+ substrate 3 to form a back electrode 5, and depositing metal on the upper surface of the P+ epitaxial layer 1 to form a front electrode 6.

[0043] In the step 7, the growth temperature for growing the P-base region 2 is 1600-1900℃, the growth temperature for growing the P+ epitaxial layer 1 is 1600-1900℃, and the metal deposited in the step 7 includes Ti and Ni.

[0044] After the deposition of the metal to form the back electrode 5 and the front electrode 6, the preparation method provided by the application further comprises: performing annealing treatment on the back electrode 5 and the front electrode 6, and the annealing temperature is 400-1000℃.

[0045] The application provides a preparation method of a silicon carbide power DAS device with a P-type variable-doping base region, and the prepared silicon carbide power DAS device with the P-type variable-doping base region comprises a p+ epitaxial layer 1, a P-base region 2, an N+ substrate 3, a passivation layer 4, a back electrode 5 and a front electrode 6; the P-base region 2 uses a longitudinal variable-doping base region, the doping concentration of the P-base region at the P+ / P- junction can be improved, the concentration gradient at the negative angle of the device can be reduced, the surface electric field can be inhibited, and the working reliability of the device can be improved; meanwhile, the doping concentration of the P-base region at the P- / N+ junction can be reduced, the longitudinal uniformity of the base region electric field can be improved, and the avalanche opening speed of the device can be improved.

[0046] The above is a further detailed description of the application in combination with specific preferred embodiments, and the specific implementation of the application cannot be limited to these descriptions. For ordinary skilled persons in the technical field of the application, some simple deductions or replacements can be made without departing from the concept of the application, and all of them shall be regarded as falling within the protection scope of the application.

Claims

1. A silicon carbide power DAS device having a P-type variable-doped base region, characterized by, Comprise: p+epitaxial layer (1), P-base region (2), N+substrate (3), passivation layer (4), back electrode (5) and front electrode (6); The P-base region (2) is located on the N+substrate (3), the doping concentration of the P-base region (2) near the N+substrate (3) side is lower than that near the p+epitaxial layer (1) side; The p+epitaxial layer (1) is located on the P-base region (2), and the front electrode (6) is located on the p+epitaxial layer (1); The p+epitaxial layer (1), P-base region (2) and N+substrate (3) are in trapezoidal step structure; The passivation layer (4) wraps the p+epitaxial layer (1), P-base region (2) and N+substrate (3) in trapezoidal step structure periphery from top to bottom, and exposes the front electrode (6) on the upper surface of the trapezoidal step structure; The N+substrate (3) is provided with a step surface, the step surface makes the upper part of the N+substrate (3) trapezoidal and the lower part rectangular; The back electrode (5) is located on the lower surface of the rectangle, and the passivation layer (4) wraps the upper part of the N+substrate (3) and the step surface; The doping concentration of the P-base region (2) increases from bottom to top in turn, which is gradient change or continuous change of Gaussian distribution.

2. The silicon carbide power DAS device with P-type variable-doped base region of claim 1, wherein, The metal deposited to form the back electrode (5) and the front electrode (6) comprises Ti and Ni.

3. The silicon carbide power DAS device with P-type variable-doped base region of claim 1, wherein, The N+substrate (3) comprises a first step surface and a second step surface, the first step surface is in contact with the lower surface of the P-base region (2), and the second step surface is located on both sides of the junction of the trapezoid and the matrix; The passivation layer (4) wraps the N+substrate (3) from top to bottom until it completely wraps the second step surface, exposing the part below the second step surface of the N+substrate (3).

4. A method for fabricating a silicon carbide power DAS device with a p-type variable doped base region, characterized in that, Preparation of a silicon carbide power DAS device with a P-type variable doping base region as claimed in any one of claims 1 to 3, the preparation method comprising: Step 1: obtaining an N+substrate (3); Step 2: growing a P-base region (2) with regular change of doping concentration on the surface of the N+substrate region (3) by CVD method; Step 3: growing a P+epitaxial layer (1) on the surface of the P-base region (2) by CVD method; Step 4: etching the outer peripheral edge of the P-base region (2), P+epitaxial layer (1) and part of the N+substrate region (3) to make the P+epitaxial layer (1), P-base region (2) and N+substrate (3) into trapezoidal step structure, and etching the step surface of the N+substrate (3) to make the upper part of the N+substrate (3) into trapezoidal structure and the lower part into rectangular structure; Step 5: etching part of the upper surface of the P+epitaxial layer (1); Step 6: growing a SiO2 passivation layer (4) on the step surface of the N+substrate (3) from bottom to top until the SiO2 passivation layer (4) wraps the etched part of the P+epitaxial layer (1), P-base region (2) and step surface of the N+substrate (3). Step 7: depositing metal on the lower surface of the lower part rectangular structure of the N+ substrate (3) to form a back electrode (5), and depositing metal on the upper surface of the P+ epitaxial layer (1) to form a front electrode (6); the doping concentration of the P- base region (2) is regularly changed to be sequentially increased from bottom to top, and is changed in a gradient or a continuous Gaussian distribution.

5. The method for fabricating a silicon carbide power DAS device with a p-type variable doped base region according to claim 4, characterized in that, The growth temperature for growing the P- base region (2) is 1600ºC ~ 1900ºC.

6. The method of producing a silicon carbide power DAS device with a P-type variable doped base region as defined in claim 4, wherein, The growth temperature for growing the P+ epitaxial layer (1) is 1600ºC ~ 1900ºC.

7. The method of producing a silicon carbide power DAS device with a P-type variable doped base region as defined in claim 4, wherein, The metal deposited in the step 7 includes Ti and Ni, and the preparation method further includes: The back electrode (5) and the front electrode (6) are subjected to annealing treatment, and the annealing temperature is 400ºC ~ 1000ºC.

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