Doping method for silicon carbide semiconductor devices

Abstract

The present application relates to a kind of doping methods suitable for silicon carbide semiconductor device.It is prepared in silicon carbide wafer with second conductive type doped region and first conductive type doped region, wherein, second conductive type doped region includes the second conductive type deep doped region formed by ion implantation and the second conductive type surface doped region formed by laser doping, the doping depth of second conductive type deep doped region in silicon carbide wafer is greater than the doping depth of second conductive type surface doped region in silicon carbide wafer and the doping depth of first conductive type doped region in silicon carbide wafer, second conductive type surface doped region is located above second conductive type deep doped region, and second conductive type surface doped region is adjacent to second conductive type deep doped region.The present application can reduce the number of ion implantation, avoid surface concentration drop, effectively realize the box type impurity distribution after doping, reduce the process difficulty, and improve the process precision.

Description

TECHNICAL FIELD

[0001] The present application relates to a doping method, in particular, a doping method suitable for silicon carbide semiconductor devices. BACKGROUND

[0002] Ion implantation is a key process for all SiC (silicon carbide) devices. Due to the extremely low diffusion constant of impurities in SiC, diffusion process cannot be used for doping as in silicon wafers, and in the activation annealing of implantation, the diffusion of most post-implantation impurities is so small that it can be ignored. Therefore, in order to achieve the box distribution of ion implantation, it is currently necessary to use a multi-stage implantation method.

[0003] Currently, N-type region ion implantation is mostly N and P ion implantation, and P-type region ion implantation is mostly Al ion implantation. Since the extraction of device electrodes requires the combination of heavily doped surface and metal to form ohmic contact, the post-implantation stage (high energy first and then low energy) will be implanted with low implantation energy (~25eV) to increase the surface doping concentration to 1×1019cm 19 -3 The above. However, due to the ion depth distribution in the implantation process, the highest peak cannot reach the surface of SiC, and there will be a certain concentration decrease on the implantation surface.

[0004] On the other hand, the total on-resistance of SiC MOSFET is composed of ohmic contact resistance, channel resistance, JFET resistance, drift region resistance, wafer body resistance, etc., and the size of the channel resistance is one of the key factors affecting the total on-resistance. In the process, the main factors affecting the channel length are layout line width and overlay accuracy. In order to avoid errors caused by photolithography, when using double implantation method, self-alignment process is mostly used to achieve the uniformity of device performance, which relies on the processing accuracy of hard mask to control the size of implantation area. Since the precise etching process of hard mask is difficult, it is very difficult to control the processing uniformity.

[0005] In the research of SiC doping, it has been reported that laser doping is used to replace ion implantation to achieve doping process, that is, high concentration doping is formed on the surface, and ohmic contact with electrode metal is successfully formed. However, since laser can only achieve surface heating, and the diffusion constant of Al in 4H-SiC is extremely low, the depth of laser doping is only about 200nm. In the current SiC power device, the doping depth of P-type needs to be greater than 500nm, therefore, the laser doping process is difficult to meet the doping requirements in SiC power devices. SUMMARY

[0006] ​The present application aims to overcome the deficiencies in the prior art, and provides a doping method suitable for silicon carbide semiconductor devices, which can reduce the number of ion implantation, avoid the surface concentration drop, effectively realize the box-type impurity distribution after doping, reduce the process difficulty, and improve the process precision.

[0007] According to the technical scheme provided by the present application, the doping method suitable for silicon carbide semiconductor devices provides a silicon carbide wafer with a first conductivity type; a second conductivity type doped region and a first conductivity type doped region located in the second conductivity type doped region are prepared in the silicon carbide wafer, wherein the second conductivity type doped region includes a second conductivity type deep doped region formed by ion implantation and a second conductivity type surface doped region formed by laser doping, the doping depth of the second conductivity type deep doped region in the silicon carbide wafer is greater than the doping depth of the second conductivity type surface doped region in the silicon carbide wafer and the doping depth of the first conductivity type doped region in the silicon carbide wafer, the second conductivity type surface doped region is located above the second conductivity type deep doped region, and the second conductivity type surface doped region is adjacent to the second conductivity type deep doped region.

[0008] When the second conductivity type doped region is prepared in the silicon carbide wafer, the required second conductivity type surface doped region is prepared by laser doping process first, and then the second conductivity type deep doped region is prepared by ion implantation process; or, the second conductivity type deep doped region is prepared by ion implantation process first, and then the required second conductivity type surface doped region is prepared by laser doping process.

[0009] The doping depth of the second conductivity type deep doped region in the silicon carbide wafer is greater than 500nm.

[0010] The first conductivity type doped region is prepared by laser doping process; the laser spot size when preparing the first conductivity type doped region is different from the laser spot size when preparing the second conductivity type surface doped region.

[0011] When preparing the second conductivity type surface doped region, a second conductivity type doped film layer is arranged on the silicon carbide wafer, and after laser irradiation on the second conductivity type doped film layer, a second conductivity type laser doped region can be obtained in the silicon carbide wafer, and the second conductivity type surface doped region can be prepared by using the second conductivity type laser doped region;

[0012] When preparing the second conductivity type deep doped region, a mask layer is arranged on the silicon carbide wafer, and after selective masking and etching of the mask layer, an ion implantation window penetrating through the mask layer can be obtained, and by using the mask layer and the ion implantation window, the second conductivity type deep doped region can be prepared in the silicon carbide wafer by ion implantation process.

[0013] In the laser doping process, the wavelength of the laser is 100nm-2000nm, and the power density is 0-100J / cm 2 .

[0014] When the first conductive type is N type, the second conductive type doping film layer comprises an aluminum film.

[0015] When the first conductive type is N type, the first conductive type doping film layer comprises a silicon nitride film layer or a phosphor silicon glass film layer.

[0016] When the first conductive type is N type, the second conductive type is P type; and when the first conductive type is P type, the second conductive type is N type.

[0017] The advantages of the present application are as follows: for a first conductive type silicon carbide wafer, a first conductive type doping region is prepared by a laser doping process; when a second conductive type doping region is prepared, a second conductive type surface doping region is prepared by a laser doping process, and a second conductive type deep doping region is prepared by an ion implantation process, thereby meeting the requirement of preparing a second conductive type doping region in a silicon carbide wafer, reducing the number of ion implantations, avoiding a decrease in surface concentration, and achieving a more ideal box-shaped impurity distribution.

[0018] Since the etching process of a high-precision hard mask in a traditional process is difficult and has high precision requirements, the doping process of the present application replaces a photolithography process to control the precision of the size of a doping region by using a laser processing device, thereby reducing the process difficulty and improving the process precision. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figures 1-8 A specific implementation process diagram of the present application is shown in the figure.

[0020] Figure 1 A schematic diagram of an N-type silicon carbide wafer of the present application is shown in the figure.

[0021] Figure 2 A schematic diagram of setting a P-type doping film layer on a silicon carbide wafer of the present application is shown in the figure.

[0022] Figure 3 A schematic diagram of preparing a P-type laser doping region by using a laser doping process of the present application is shown in the figure.

[0023] Figure 4 A schematic diagram of removing a P-type doping film layer of the present application is shown in the figure.

[0024] Figure 5 A schematic diagram of setting a mask layer on a silicon carbide wafer of the present application is shown in the figure.

[0025] Figure 6This is a schematic diagram of the P-type deeply doped region obtained according to the present invention.

[0026] Figure 7 This is a schematic diagram of the N-type doped film obtained in this invention.

[0027] Figure 8 This is a schematic diagram of the N-type doped region obtained according to the present invention.

[0028] Explanation of reference numerals in the attached figures: 1-Silicon carbide wafer, 2-P-type doped film, 3-P-type doped laser spot, 4-P-type laser doped region, 5-Mask layer, 6-Mask layer window, 7-P-type deep doped region, 8-N-type doped film, 9-N-type doped region, 10-N-type doped laser spot, and 11-P-type surface doped region. Detailed Implementation

[0029] The present invention will be further described below with reference to specific accompanying drawings and embodiments.

[0030] like Figure 8 As shown: In order to reduce the number of ion implantation times, avoid the decrease in surface concentration, effectively achieve the box-shaped impurity distribution after doping, reduce the process difficulty, and improve the process accuracy, taking an N-type silicon carbide wafer as an example, the present invention prepares a P-type doped region and an N-type doped region 9 located in the P-type doped region within the silicon carbide wafer 1. The P-type doped region includes a P-type deep doped region 7 formed by ion implantation and a P-type surface doped region 11 formed by laser doping. The doping depth of the P-type deep doped region 7 in the silicon carbide wafer 1 is greater than the doping depth of the P-type surface doped region 11 in the silicon carbide wafer 1 and the doping depth of the N-type doped region 9 in the silicon carbide wafer 1. The P-type surface doped region 11 is located above the P-type deep doped region 7 and is adjacent to the P-type deep doped region 7.

[0031] Specifically, the silicon carbide wafer 1 has an N-type conductivity. Other specific details regarding the silicon carbide wafer 1 can be selected as needed, and are well-known to those skilled in the art, so they will not be elaborated here. During doping, it is generally necessary to prepare a P-type doped region and an N-type doped region 9 within the silicon carbide wafer 1, wherein the N-type doped region 9 is located within the P-type doped region.

[0032] In the embodiment of the present application, the P-type doped region includes a P-type deep doped region 7 prepared by ion implantation and a P-type surface doped region 11 prepared by laser doping, and the doping depth of the P-type deep doped region 7 is greater than the doping depth of the P-type surface doped region 11 and the N-type doped region 9. Therefore, when the P-type surface doped region 11 is prepared by the laser doping process, the doping concentration of the surface is ensured, and the process requirements such as ohmic contact can be met. After the P-type deep doped region 7 is prepared by ion implantation, the P-type deep doped region 7 and the P-type surface doped region 11 have the same doping type, and the P-type deep doped region 7 and the P-type surface doped region 11 are adjacent, thereby solving the problem that the corresponding doping requirements cannot be met by diffusion doping in the existing silicon carbide wafer 1, effectively realizing the box-type impurity distribution after doping, and reducing the process difficulty.

[0033] In specific implementation, the doping depth of the P-type deep doped region in the silicon carbide wafer 1 is greater than 500 nm. The doping depth of the P-type surface doped region 11 can be the same as the doping depth of the N-type doped region 9, or the doping depth of the P-type surface doped region 11 can be different from the doping depth of the N-type doped region 9, which can be selected according to actual needs, and details are not described herein. In addition, the doping concentration relationship of the P-type surface doped region 11 and the P-type deep doped region 7 can be selected as needed, which is well known to those skilled in the art, and details are not described herein.

[0034] In the embodiment of the present application, in order to accurately control doping, the N-type doped region 9 is prepared by a laser doping process; the laser spot size when preparing the N-type doped region 9 is different from the laser spot size when preparing the P-type surface doped region 11, that is, the N-type doped region 9 is generally located on the corresponding surface of the silicon carbide wafer 1. In specific implementation, in the laser doping process, the wavelength of the laser is 100 nm to 2000 nm, the power density is 0-100 J / cm 2 .

[0035] Further, when the P-type doped region is prepared in the silicon carbide wafer 1, the P-type surface doped region 11 is first prepared by the laser doping process, and then the P-type deep doped region 7 is prepared by the ion implantation process, or the P-type deep doped region 7 is first prepared by the ion implantation process, and then the P-type surface doped region 11 is prepared by the laser doping process.

[0036] In the embodiment of the present application, when the P-type doped region is prepared, the specific order of the P-type surface doped region 11 and the P-type deep doped region 7 can be selected as needed. Of course, the order of the P-type doped region and the N-type doped region 9 can also be selected as needed, that is, the P-type doped region can be prepared first, and then the N-type doped region 9 is prepared, or the N-type doped region 9 can be prepared first, and then the P-type doped region is prepared, and the specific order can be selected as needed, and details are not described herein.

[0037] Furthermore, when preparing the P-type surface doped region 11, a P-type doped film layer 2 is provided on the silicon carbide wafer 1. After the P-type doped film layer 2 is irradiated with a laser, a P-type laser doped region 4 is obtained in the silicon carbide wafer 1, and the P-type surface doped region 11 can be prepared using the P-type laser doped region 4.

[0038] When preparing the P-type deep doped region 7, a mask layer 5 is provided on the silicon carbide wafer 1. After selectively masking and etching the mask layer 5, an ion implantation window 6 that penetrates the mask layer 5 can be obtained. Using the mask layer 5 and the ion implantation window 6, the P-type deep doped region 7 can be prepared in the silicon carbide wafer 1 by ion implantation process.

[0039] In this embodiment of the invention, when using laser doping, a P-type doped film layer 2 needs to be formed on the silicon carbide wafer 1. When the P-type doped film layer 2 is irradiated with a laser, a P-type surface doped layer 4 can be formed, and a P-type surface doped region 11 can be obtained using the P-type surface doped layer 4. In specific implementation, the P-type doped film layer 2 can be an aluminum film.

[0040] During ion implantation, a mask layer 5 is typically deposited on the silicon carbide wafer 1. The mask layer 5 can be made of commonly used materials, and etching techniques commonly employed in this field can be used to obtain the ion implantation window 6. The resulting P-type deeply doped region 7 corresponds to the ion implantation window 6.

[0041] like Figures 1-8 The diagram shown is a schematic representation of the doping process of the present invention. The specific process is described below.

[0042] like Figure 1 The diagram shown is a schematic representation of an N-conductivity silicon carbide wafer 1. Figure 2 As shown, a P-type doped film layer 2 is formed on a silicon carbide wafer 1. The P-type doped film layer 2 can be deposited on the silicon carbide wafer 1, and its thickness and other properties can be set as needed. The P-type doped film layer 2 can be an aluminum film. Figure 3 As shown, a laser doping process is performed on the P-type doped film layer 2. During the laser doping process, the P-type doped film layer 2 is irradiated by a P-type doping laser spot 3, thereby obtaining a P-type laser doped region 4 in the silicon carbide wafer 1. Generally, the P-type laser doped region 4 extends downward from the surface of the silicon carbide wafer 1. The position, doping depth, and doping concentration of the P-type laser doped region 4 can be selected as needed, which is well known to those skilled in the art and will not be described in detail here.

[0043] like Figure 4 The diagram shown is a schematic of the removal of the p-type doped film layer 2 using techniques commonly used in this field. Figure 5The diagram shows a sample of a silicon carbide wafer 1 with a mask layer 5, after which an ion implantation window 6 is obtained by etching the mask layer 5. Etching the mask layer 5 requires low etching precision, significantly reducing the complexity of the process. Figure 6 As shown, P-type impurity ions are implanted onto the silicon carbide wafer 1. The specific ion implantation process conditions are consistent with existing ion implantation processes and are well known to those skilled in the art. After P-type ion implantation, a P-type deep-doped region 7 can be prepared within the silicon carbide wafer 1. The doping depth of the P-type deep-doped region 7 is greater than that of the P-type laser-doped region 4. In cross-section, the length of the P-type deep-doped region 7 is less than the length of the P-type laser-doped region 4, and the P-type laser-doped region 7 is adjacent to the P-type laser-doped region 4.

[0044] like Figure 7 The diagram shows a schematic of the process after removing the mask layer 5 using techniques commonly used in this field and depositing an N-type doped film layer 8 on the silicon carbide wafer 1. The N-type doped film layer 8 can be a silicon nitride layer or a phosphosilicate glass film layer. Figure 8 As shown, this illustrates the application of laser doping technology to irradiate the N-type doped film layer 8. Specifically, the N-type doped laser spot 10 is used to irradiate the N-type doped film layer 8. The size of the N-type doped laser spot 10 is smaller than that of the P-type doped laser spot 3, thereby creating an N-type doped region 9 within the silicon carbide wafer 1. The N-type doped region 9 only partially covers the P-type laser doped region 4, while the remaining P-type laser doped region 4 forms the P-type surface doped region 11. The doping depth of the N-type doped region 9 can be greater than the doping depth of the P-type surface doped region 11, or the doping depth of the N-type doped region 9 can be less than or equal to the doping depth of the P-type surface doped region 11.

[0045] After the above process steps, the desired P-type doped region and N-type doped region 9 can be prepared in the silicon carbide wafer 1. Of course, in specific implementation, the N-type doped region 9 can be prepared first, followed by the P-type doped region. When the silicon carbide wafer 1 is of the P-conductivity type, please refer to the above description for details, which are well known to those skilled in the art and will not be elaborated here.

[0046] In summary, N-type doped regions 9 are prepared by laser doping. When preparing P-type doped regions, P-type surface doped regions 11 can be prepared by laser doping, and P-type deep doped regions 7 can be prepared by ion implantation. This meets the requirement of preparing P-type doped regions within N-type silicon carbide wafers 1 and can effectively reduce the number of ion implantation cycles. When N-type doped regions 9 and P-type surface doped regions 11 are prepared by laser doping, the surface concentration decrease can be avoided, and a more ideal box-shaped impurity distribution can be achieved.

[0047] Since the etching process of high-precision hard mask in the traditional process is difficult, and the precision requirement is high, the doping process replaces the photolithography process by the laser processing equipment to control the precision of the doping area size, reduces the process difficulty, and improves the process precision.

Claims

1. A method of doping suitable for use in silicon carbide semiconductor devices, providing a silicon carbide wafer having a first conductivity type; characterized by: The silicon carbide wafer is internally provided with a second-conductivity-type doped region and a first-conductivity-type doped region in the second-conductivity-type doped region, wherein the second-conductivity-type doped region comprises a second-conductivity-type deep doped region formed by ion implantation and a second-conductivity-type surface doped region formed by laser doping, the doping depth of the second-conductivity-type deep doped region in the silicon carbide wafer is greater than the doping depth of the second-conductivity-type surface doped region in the silicon carbide wafer and the doping depth of the first-conductivity-type doped region in the silicon carbide wafer, the second-conductivity-type surface doped region is located above the second-conductivity-type deep doped region, and the second-conductivity-type surface doped region is adjacent to the second-conductivity-type deep doped region; In the preparation of the second-conductivity-type surface doped region, a second-conductivity-type doped film layer is arranged on the silicon carbide wafer, and after laser irradiation on the second-conductivity-type doped film layer, a second-conductivity-type laser doped region is obtained in the silicon carbide wafer, and the second-conductivity-type surface doped region is prepared by using the second-conductivity-type laser doped region; In the preparation of the second-conductivity-type deep doped region, a mask layer is arranged on the silicon carbide wafer, and after selective masking and etching of the mask layer, an ion implantation window penetrating through the mask layer is obtained, and the second-conductivity-type deep doped region is prepared in the silicon carbide wafer by using the mask layer and the ion implantation window through an ion implantation process; The doping depth of the second-conductivity-type deep doped region in the silicon carbide wafer is greater than 500 nm; The first-conductivity-type doped region is prepared by a laser doping process, and the laser spot size in the preparation of the first-conductivity-type doped region is different from the laser spot size in the preparation of the second-conductivity-type surface doped region.

2. The method of claim 1 wherein: In the preparation of the second-conductivity-type doped region in the silicon carbide wafer, the second-conductivity-type surface doped region is first prepared by a laser doping process, and then the second-conductivity-type deep doped region is prepared by an ion implantation process; or the second-conductivity-type deep doped region is first prepared by an ion implantation process, and then the second-conductivity-type surface doped region is prepared by a laser doping process.

3. The method of claim 1 wherein: In the laser doping process, the wavelength of the laser is 100 nm to 2000 nm, and the power density is 0-100 J / cm 2 .

4. The method of claim 1 wherein: When the first-conductivity-type is N-type, the second-conductivity-type doped film layer comprises an aluminum film.

5. The method of claim 1 wherein: the silicon carbide semiconductor device is a vertical junction barrier Schottky (VJBS) diode. In the preparation of the first-conductivity-type doped region, a first-conductivity-type doped film layer is arranged on the silicon carbide wafer, and when the first-conductivity-type is N-type, the first-conductivity-type doped film layer comprises a silicon nitride film layer or a phosphor silicon glass film layer.

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