A method for manufacturing a silicon dioxide inclined table structure and its application

Abstract

The present invention discloses a method for manufacturing a silicon dioxide inclined mesa structure and its application. The slope top and bottom of the silicon dioxide inclined mesa structure have a small angle of 1 to 15°, and the middle has a large angle of 15 to 60°. It is a kind of inclined mesa structure with a small top and a large bottom and a rounded and smooth edge morphology. The structure is formed by peeling off the silicon dioxide film using a double-layer glue process. The method for manufacturing the silicon dioxide inclined mesa structure provided by the present invention can be applied in scenarios including but not limited to the following three aspects: 1. It is used as an insulating dielectric layer to thicken the electrical isolation between metal layers of various types of devices; 2. It is used as an etching mask to be used for inclined angle etching of SiC materials; 3. It is used as a passivation dielectric layer to be used in the inclined field plate terminal structure of power devices made of materials such as SiC or GaN.

Description

Technical Field

[0001] The invention belongs to the field of semiconductor process technology, in particular to the field of semiconductor power electronic device process technology, and in particular relates to a method for manufacturing a silicon dioxide inclined mesa structure and an application thereof. Background Art

[0002] Silicon dioxide (SiO2) thin film material is a dielectric film with excellent physical and chemical properties. It has the advantages of excellent dielectric properties, low loss and good material stability. It is one of the most widely used materials in semiconductor micro-processing technology. It can be used as an etching mask for semiconductor materials, surface passivation for semiconductor devices, and dielectric isolation between metal layers. It is widely used. Therefore, the preparation and patterning process of silicon dioxide thin film is a very important and basic process technology in semiconductor micro-processing technology. There are many methods for preparing silicon dioxide thin film. It can be grown by various types of chemical vapor deposition (CVD) equipment (such as PECVD, ICPCVD and LPCVD, etc.), or by physical vapor deposition equipment such as magnetron sputtering. For Si or SiC materials, silicon dioxide thin film can also be grown on the surface by thermal oxidation. The patterning process of silicon dioxide thin film usually adopts plasma dry etching process (such as RIE, ICP etching) or wet etching process (such as BOE or HF solution wet etching).

[0003] For the dry etching process of SiO2, due to the anisotropy of the dry etching process and the etching selectivity ratio of the SiO2 etching process using a photoresist mask is usually greater than 1, the SiO2 etching morphology obtained by dry etching using RIE or ICP equipment is generally steep. The steep SiO2 etching morphology is not as advantageous as the SiO2 morphology with an inclined angle in some device process scenarios. For example, in the application scenario of thickened metal interlayer dielectric isolation, the steep SiO2 opening morphology will cause the step coverage of the upper thickened metal to deteriorate, and when using SiO2 as a mask to etch SiC materials, the steep SiO2 mask morphology is prone to cause etching micro-grooves at the bottom corners of the SiC etching process. Finally, when making the device field plate terminal structure, the voltage resistance efficiency obtained by the steep SiO2 morphology is not as high as that of the SiO2 morphology with a small angle.

[0004] If a wet etching process is used to etch SiO2 thin film, due to the isotropy of the wet etching process and the lateral drilling effect of the corrosive solution, the etching angle of the SiO2 etched morphology obtained by the wet process will be smaller than that of the dry process, and the sidewall etching angle is generally between 20 and 45°. In their article published in TED in 2008, Hiyoshi et al. of the Kimoto research group in Japan used this method to produce a SiO2 inclined table with a morphology of approximately 1 / 4 arc and used it to etch a SiC inclined table with an arc shape. However, the inherent disadvantage of the wet etching process is that it is more difficult to control the process and the process repeatability and uniformity are poor. Especially when the line width of the photolithography pattern is small, there is a great risk of random photoresist falling when using a wet process to etch SiO2, which will cause the SiO2 in the area that should not be etched to be etched away in the same way, resulting in irreversible process losses. In addition, the BOE or HF solution used in wet etching will corrode certain metals, which limits its application scope in the scenario of thickening the dielectric isolation between metal layers of devices.

[0005] Therefore, considering the process repeatability and stability, it is usually hoped to use dry etching process to obtain SiO2 structure with smaller etching angle, which requires improvement of traditional dry etching process. According to public reports, Tang Longjuan and others from the Institute of Semiconductors of the Chinese Academy of Sciences disclosed a method of making inclined sidewall silicon dioxide structure by photolithography and dry etching. The main steps are: 1. Clean the substrate; 2. Deposit silicon dioxide film on the substrate; 3. Apply photoresist on the substrate with thin film deposited and perform photolithography; 4. Thin the photoresist; 5. Harden the film at high temperature; 6. Perform RIE dry etching on the substrate after photolithography to obtain inclined silicon dioxide sidewall morphology. The author obtained a silicon dioxide inclined terrace structure with an angle between 40 and 70 degrees and a thickness of about 1.5μm by this method. In addition, the photoresist reflow technology can also be used to etch SiO2 materials at a smaller angle. The characteristics of the photoresist reflow technology are as follows: 1. Use photoresist directly as a mask for etching SiO2 materials; 2. Reduce the angle of the edge of the photoresist by reflowing the photoresist at a high temperature; 3. Dry-etch the SiO2 covered with photoresist, and obtain a SiO2 inclined table structure with a smaller inclination angle through the pattern transfer during the etching process. The two methods mentioned above have similarities. They both use high temperature to bake the photoresist to reduce the angle morphology of the photoresist mask, and finally transfer the small angle morphology to the SiO2 film through the pattern transfer during the etching process. Although the preparation of the SiO2 inclined table structure can be achieved, the high temperature baking process used in the above method will cause the photoresist to be carbonized, which will make the subsequent degumming process more difficult, and the residual photoresist cannot be completely removed by simply cleaning with acetone. Whether it is cleaning with concentrated sulfuric acid + hydrogen peroxide or removing the glue with a plasma degumming machine, it cannot be implemented in some device application scenarios because it will damage the existing device process structure. If the baking temperature of the photoresist is lowered, although it is beneficial to the subsequent degumming process, the obtained SiO2 etching angle will also be steeper. For example, the patent application of Tang Longjuan and others mentioned that when the photoresist baking temperature is 120°C, the obtained SiO2 etching angle is only 60-70°, which cannot meet the use requirements of related application scenarios.

[0006] Based on the above discussion, it can be seen that the existing process methods for forming the inclined mesa structure of silicon dioxide have their own shortcomings. Therefore, in order to further simplify the process, improve the morphology, enhance the adaptability of application scenarios and improve the process stability, new process methods for making SiO2 inclined mesa structures need to be further developed. Summary of the invention

[0007] In view of this, the present invention provides a method for preparing a silicon dioxide inclined mesa structure and its application. The method can realize the preparation of the silicon dioxide inclined mesa structure without a high-temperature baking process, which provides convenience for subsequent degumming. The silicon dioxide inclined mesa structure prepared by the present invention can be used for the insulating layer of various semiconductor devices, the etching mask of SiC materials, and the terminal structure of power devices made of materials such as SiC or GaN, and has broad application prospects.

[0008] To achieve this purpose, the present invention adopts the following technical scheme: a method for manufacturing a silicon dioxide inclined mesa structure, wherein the top and bottom of the slope of the silicon dioxide inclined mesa structure both have a small angle of 1 to 15°, and the middle has a large angle of 15 to 60°, and the silicon dioxide inclined mesa structure is a kind of inclined mesa structure with a small top and a large bottom and a rounded and smooth edge morphology; the silicon dioxide inclined mesa structure is formed by peeling off a silicon dioxide film with a film thickness of 0.5 to 5 μm using a double-layer glue process, and the process is as follows:

[0009] S1: Spin-coat a pad-thickness glue layer A with a thickness of 1 to 5 μm on the sample;

[0010] S2: Continue to spin-coat a photolithography exposure glue layer B with a thickness of 0.5 to 5 μm on the pad thick glue layer A;

[0011] S3: performing photolithography and development on a double-layered adhesive layer consisting of a pad thick adhesive layer A and a photolithography exposure adhesive layer B, wherein the developer simultaneously performs lateral etching on the pad thick adhesive layer A, and the pattern opening size of the pad thick adhesive layer A is larger than the opening size of the photolithography exposure adhesive layer B, thereby forming an inverted table opening structure on the double-layered adhesive layer structure;

[0012] S4: depositing SiO2 film by chemical vapor deposition equipment or magnetron sputtering equipment, the deposition temperature is between 25 and 200° C., forming a first portion of SiO2 film on the photolithography exposure layer B, and forming a second portion of SiO2 film in the double-layered layer inverted mesa opening pattern;

[0013] S5: Peel off the first part of the SiO2 film, and obtain a patterned silicon dioxide inclined terrace structure in the second part.

[0014] Preferably, in step S1, the samples include but are not limited to Si, SiC and GaN.

[0015] Preferably, the pad thickness glue layer A adopts LOR series pad thickness glue, and the photolithography exposure glue layer B adopts AZ series photoresist.

[0016] The invention discloses an application of a silicon dioxide inclined mesa structure, wherein the silicon dioxide inclined mesa structure is used as an insulating dielectric layer between thickened metal layers of various types of semiconductor devices to achieve electrical isolation between metal layers and improve the step coverage of the upper metal at the SiO2 dielectric opening and to enhance its current carrying capacity.

[0017] An application of a silicon dioxide inclined mesa structure, wherein the silicon dioxide inclined mesa structure is used as an etching mask for inclined angle etching of SiC materials.

[0018] An application of a silicon dioxide inclined mesa structure, wherein the silicon dioxide inclined mesa structure is used for an inclined field plate terminal structure of a power device made of SiC or GaN material.

[0019] An application of a silicon dioxide inclined mesa structure, wherein the silicon dioxide inclined mesa structure is used to manufacture a silicon dioxide inclined mesa structure or an inclined mesa structure of other types of dielectric films, wherein the other types of dielectric films include but are not limited to SiN x film.

[0020] The beneficial effects of the present invention are as follows: the method for making the inclined silica mesa structure provided by the present invention can realize the making of the inclined silica mesa structure without high-temperature baking process, which provides convenience for subsequent degumming. The inclined silica mesa structure prepared by the present invention can be used for: 1. Applying the SiO2 inclined mesa structure to the device thickening metal layer isolation can improve the step coverage characteristics of its upper metal at the dielectric opening, thereby enhancing its flow capacity; 2. Applying the SiO2 inclined mesa structure to the inclined etching of SiC materials can avoid the generation of etching micro-grooves. If it is applied to the preparation of the inclined etching terminal, it can alleviate the edge field strength aggregation effect compared with the vertical etching terminal, and improve the voltage resistance of the device terminal; 3. Applying the SiO2 inclined mesa structure to the inclined field plate terminal structure of the power device of materials such as SiC or GaN, the voltage resistance efficiency of the inclined field plate terminal structure will be significantly improved compared with the traditional vertical or large-angle field plate terminal structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The process for manufacturing the silicon dioxide inclined mesa structure;

[0022] Figure 2 To adopt Figure 1 Scanning electron microscope (SEM) photo of the silicon dioxide tilted terrace structure actually produced in the process;

[0023] Figure 3 It is a cross-sectional schematic diagram of the gate and anode metal thickening structure of the semiconductor switch device in Example 1;

[0024] Figure 4 This is a scanning electron microscope (SEM) photograph of the inclined etching of SiC material using the silicon dioxide inclined terrace structure as a mask in Example 2;

[0025] Figure 5 The device withstand voltage simulation results of the SiC Schottky diode device with tilted field plate terminals at different angles in Example 3. DETAILED DESCRIPTION

[0026] A method for manufacturing a silicon dioxide inclined terrace structure and its application, wherein the top and bottom of the slope of the silicon dioxide inclined terrace structure have a small angle of 1 to 15 degrees, and the middle has a large angle of 15 to 60 degrees, forming a small top and large bottom inclined terrace structure with a rounded and smooth edge morphology; the structure is formed by peeling off the silicon dioxide film using a double-layer glue process, and the film thickness of the silicon dioxide film is between 0.5 and 5 μm. The process flow is as follows Figure 1 As shown, the silicon dioxide inclined table structure actually prepared by the above process method is as follows Figure 2 The method for making the inclined mesa structure of silicon dioxide provided by the present invention can be applied in the following three scenarios including but not limited to: 1. It is applied as an insulating dielectric layer to thicken the electrical isolation between metal layers of various types of devices; 2. It is applied as an etching mask to the inclined angle etching of SiC materials; 3. It is applied as a passivation dielectric layer to the inclined field plate terminal structure of power devices made of SiC or GaN.

[0027] In order to better understand the present invention, the content of the present invention will be further explained below in conjunction with specific embodiments, but the content of the present invention is not limited to the following embodiments. Those of ordinary skill in the art will appreciate that the embodiments described herein are to help readers understand the principles of the present invention, and should be understood that the protection scope of the present invention is not limited to such special statements and embodiments. Those of ordinary skill in the art can make various other various specific deformations and combinations that do not depart from the essence of the present invention based on these technical revelations disclosed by the present invention, and these deformations and combinations are still within the protection scope of the present invention.

[0028] Example 1

[0029] A semiconductor switch device, the front of which has two metal interconnect structures, a gate thickened metal layer and an anode thickened metal layer, for electrical signal extraction, and the cathode thickened metal is located on the back of the substrate. On the front of the device, in order to avoid electrical short circuit, the gate anode thickened metal layer is electrically isolated by SiO2 medium, wherein the SiO2 isolation medium needs to be etched at the anode ohmic contact position to open a window so that the anode ohmic contact and the thickened metal can effectively make electrical contact. The structural diagram is shown in the figure below. Figure 3As shown. Among them, the thickness of the gate thickened metal is 3 to 4 μm, the thickness of the SiO2 isolation medium is 2 to 3 μm, and the thickness of the anode thickened metal is 4 to 5 μm. In terms of technology, RIE / ICP plasma dry etching equipment is usually used to open windows for the above-mentioned SiO2 isolation medium, and the resulting window sidewalls are relatively steep structures. The steep SiO2 etching window opening process will cause the subsequent anode thickened metal covering the dielectric to have poor coverage characteristics at the step position, which will lead to a significant deterioration in the current flow capacity of the device anode. In order to improve the above-mentioned anode thickened metal step coverage, a feasible method is to reduce the etching angle morphology of the SiO2 layer below it at the anode window position, and the above goal can be easily achieved by using the method proposed in the present invention to produce a silicon dioxide inclined mesa structure.

[0030] Example 2

[0031] The silicon dioxide inclined terrace structure obtained by the manufacturing method of the present invention can be used to perform inclined small-angle etching on silicon carbide materials. The specific process implementation process is as follows:

[0032] 1. According to the attached Figure 1 The process flow shown in the figure makes a patterned silicon dioxide tilted terrace structure on a SiC sample and uses it as a mask for subsequent SiC material etching;

[0033] 2. Place the SiC sample with SiO2 patterned mask prepared in step 1 into an ICP plasma dry etching device, and dry-etch the SiC material using SF6 / O2 as etching gas;

[0034] 3. Use BOE wet etching method to remove the residual SiO2 mask and finally obtain the small-angle etching morphology of silicon carbide;

[0035] Figure 4 This is the scanning electron microscope (SEM) cross-sectional morphology of the sample after the SiC etching process in the above step 2 is completed. The SiC small-angle etching morphology obtained by the above process method can be applied to the production of SiC etching terminals. Since the etching angle is small, it will be able to significantly improve the field intensity concentration effect at the bottom corner of the etching, thereby effectively improving the etching process window of the device etching terminal.

[0036] Example 3

[0037] The silicon dioxide inclined mesa structure obtained by the manufacturing method of the present invention can be used as a passivation dielectric layer in the inclined field plate terminal structure of power devices made of materials such as SiC or GaN. The application of the present invention in this aspect is specifically described below using the inclined field plate terminal structure of a SiC Schottky diode device.

[0038] SiC Schottky diode device (SiC SBD), the SiC material structure from top to bottom is N- / N+ / substrate. N- is the drift layer, and its doping concentration is 5×10 15 cm -3 , with a thickness of 5 μm; N+ is a buffer layer with a doping concentration of 1×10 18 cm -3 , thickness is 2μm; substrate is N+ 4H-SiC intrinsic substrate, doping concentration is 5×10 18 cm -3 , thickness is 350μm.

[0039] The process flow of device preparation is as follows:

[0040] 1. Use RCA standard cleaning method to clean SiC samples;

[0041] 2. Deposit 150nm of Ni metal on the back of the sample and perform RTA high temperature annealing to form a back ohmic contact;

[0042] 3. According to the attached Figure 1 The process flow shown in the figure produces a patterned silicon dioxide tilted terrace structure on the front of the SiC sample, where the SiO2 pattern opening area is defined as the active area of ​​the SiC SBD device;

[0043] 4. The front Schottky metal is made on the front of the sample by photolithography stripping process. The Schottky metal can be made of metal Ni or metal Ti with a thickness of 150nm. The size of the Schottky metal pattern is 30μm larger than the size of the SiO2 pattern opening, and the metal extension part is normally covered on the inclined terrace structure of the silicon dioxide passivation medium.

[0044] 5. Thicken the front side of the device with Al metal and the back side with Ag metal to facilitate wire bonding and packaging;

[0045] 6. Make a PI passivation layer on the front of the device to complete the entire device preparation process.

[0046] In order to verify the influence of the tilted field plate terminal on the withstand voltage performance of SiC SBD devices, the breakdown withstand voltage simulation of the device field plate terminal structure with different angles was carried out by device simulation software. The simulation results are shown in Figure 2. Figure 5As shown. It can be clearly seen that as the inclination angle of the field plate terminal decreases, the voltage withstand efficiency of the device terminal is constantly improving. The terminal efficiency corresponding to a 45° inclination angle is 68%; the terminal efficiency corresponding to a 26° inclination angle is 74%; the terminal efficiency corresponding to an 11° inclination angle is 88%; and the terminal efficiency corresponding to a 6° inclination angle is 96.5%. Therefore, the inclined field plate terminal structure prepared by the silicon dioxide inclined mesa structure manufacturing method proposed in the present invention will be able to significantly improve the breakdown voltage withstand efficiency of the device compared to the traditional large-angle or vertical field plate terminal.

Claims

1. A method for manufacturing a silicon dioxide inclined mesa structure, characterized in that: The top and bottom of the slope of the silicon dioxide inclined mesa structure both have a small angle of 1 to 15°, and the middle has a large angle of 15 to 60°. The silicon dioxide inclined mesa structure is a kind of inclined mesa structure with a small top and a large bottom and a rounded and smooth edge morphology. The silicon dioxide inclined mesa structure is formed by peeling off a silicon dioxide film with a film thickness of 0.5 to 5 μm using a double-layer glue process, and the process is as follows: S1: Spin-coat a pad-thickness glue layer A with a thickness of 1 to 5 μm on the sample; S2: Continue to spin-coat a photolithography exposure glue layer B with a thickness of 0.5 to 5 μm on the pad thick glue layer A; S3: performing photolithography and development on a double-layered adhesive layer consisting of a pad thick adhesive layer A and a photolithography exposure adhesive layer B, wherein the developer simultaneously performs lateral etching on the pad thick adhesive layer A, and the pattern opening size of the pad thick adhesive layer A is larger than the opening size of the photolithography exposure adhesive layer B, thereby forming an inverted table opening structure on the double-layered adhesive layer structure; S4: depositing SiO2 film by chemical vapor deposition equipment or magnetron sputtering equipment, the deposition temperature is between 25 and 200° C., forming a first portion of SiO2 film on the photolithography exposure layer B, and forming a second portion of SiO2 film in the double-layered layer inverted mesa opening pattern; S5: Peel off the first part of the SiO2 film, and obtain a patterned silicon dioxide inclined terrace structure in the second part.

2. The method for manufacturing a silicon dioxide inclined mesa structure according to claim 1, characterized in that: In the step S1, the sample includes Si, SiC or GaN.

3. The method for manufacturing a silicon dioxide inclined terrace structure according to claim 1, characterized in that: The pad thickness glue layer A adopts LOR series pad thickness glue, and the photolithography exposure glue layer B adopts AZ series photoresist.

4. An application of a silicon dioxide inclined table structure, characterized in that: The silicon dioxide inclined terrace structure is prepared according to the method described in claim 1, 2 or 3. The silicon dioxide inclined terrace structure is used as an insulating dielectric layer between thickened metal layers of various types of semiconductor devices to achieve electrical isolation between metal layers and improve the step coverage of the upper metal at the SiO2 dielectric opening and improve its current carrying capacity.

5. An application of a silicon dioxide inclined mesa structure, characterized in that: The silicon dioxide inclined terrace structure is prepared according to the method described in claim 1, 2 or 3, and the silicon dioxide inclined terrace structure is used as an etching mask for inclined angle etching of SiC materials.

6. An application of a silicon dioxide inclined mesa structure, characterized in that: The silicon dioxide inclined mesa structure is prepared according to the method described in claim 1, 2 or 3, and the silicon dioxide inclined mesa structure is used for the inclined field plate terminal structure of a power device made of SiC or GaN material.

7. An application of a silicon dioxide inclined mesa structure, characterized in that: The silicon dioxide inclined mesa structure is prepared according to the method described in claim 1, 2 or 3, and the silicon dioxide inclined mesa structure is used to prepare the inclined mesa structure of the SiNx film.

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