A method for improving the preparation of 300mm lightly doped substrates with ultra-thick thickness epitaxial edge defects

Abstract

This invention discloses a method for preparing a 300mm lightly doped substrate with improved edge defects in ultra-thick epitaxial layers, comprising the following steps: S1. Growing a silicon oxide thin film on the back side of the 300mm substrate after double-sided polishing and before final polishing; S2. Performing ring etching on the edge region of the silicon oxide thin film. This method effectively prevents the reaction between the substrate back side near the edge and the growth gas during epitaxial layer growth, thus preventing the formation of silicon noise at the back edge and avoiding adhesion between the substrate and the susceptor, thereby improving the quality of the substrate back edge.

Description

Technical Field

[0001] This invention belongs to the field of silicon substrate processing technology, specifically relating to a method for preparing a 300mm lightly doped substrate to improve edge defects in ultra-thick epitaxial layers. Background Technology

[0002] With the booming development of integrated circuit technology in new energy vehicles, high-speed rail, photovoltaics, and industry, the market demand for high-voltage power semiconductor devices is increasing. Simultaneously, in the manufacturing of high-voltage power devices, as the production cost of 300mm large-diameter substrates decreases, the substrate type will inevitably shift towards 300mm large-diameter substrates. These 300mm large-diameter substrates focus more on improving edge defects to increase substrate utilization. However, the impact on power semiconductor quality mainly comes from three aspects: first, design capabilities based on system know-how; second, differences in front-end processes, i.e., differences in the process level of substrate manufacturing; and third, differences in back-end processes, i.e., differences in chip packaging process level.

[0003] In the substrate manufacturing process, considering flatness issues, 300mm substrates generally require double-sided polishing and final polishing. Furthermore, substrates used in high-voltage power devices often require the growth of ultra-thick epitaxial layers (THK > 40μm) to improve device withstand voltage. However, during the growth of ultra-thick epitaxial layers, the long time required causes the growth gases TCS (trichlorosilane) and H2 to diffuse to the edges of the substrate's back side, creating defects. In severe cases, this can cause adhesion between the substrate's back edge and the susceptor of the epitaxial machine. This not only increases the risk of fragmentation during unloading but also leads to a bridging-like defect at the substrate edges. Figure 1 As shown, this affects the quality of the epitaxial wafer, and in severe cases, it can even cause cracks in the epitaxial wafer.

[0004] On the other hand, in existing technologies, for substrates heavily doped with As (arsenic) and P (phosphorus) (generally referring to resistivity <0.5 ohm·cm), a high-temperature epitaxial growth stage is performed. To prevent the outward diffusion of the dopant, a layer with a thickness of [thickness missing] is often deposited on the back side of the substrate before final polishing. The thin film (i.e., the back seal film) is typically made of silicon oxide, silicon nitride, polysilicon, etc. If the film is uneven at the edge of the substrate back side, or if it is not completely removed and there are residues, the thinner areas or areas not covered by the film will easily lead to substrate exposure (the thinner areas may also be exposed due to pre-epitaxy treatment or other reasons such as scratches). During the growth of the epitaxial layer, growth gas will be induced to grow along the exposed substrate at its location, while in other areas, the growth gas cannot be deposited due to the presence of the back seal film. This forms a root-like defect, different from the aforementioned Bridging-like defect, namely a Silicon Nodule. Figures 2-3 As shown, a back seal film is generally not required for lightly doped substrates. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a 300mm lightly doped substrate to improve edge defects in ultra-thick epitaxial layers, thereby overcoming the shortcomings of the prior art.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for fabricating a 300mm substrate with improved edge defects in ultra-thick epitaxial layers includes the following steps:

[0008] S1. A silicon oxide thin film is grown on the back side of a 300mm substrate after double-sided polishing and before final polishing;

[0009] S2. Perform ring etching on the edge region of the silicon oxide film.

[0010] Preferably, the substrate has a thickness of 700-800 mm, and the epitaxial layer thickness of the epitaxial wafer made from the substrate is >40 μm;

[0011] The thickness of the silicon oxide film in step S1 is

[0012] Preferably, the ring etching area in step S2 includes the chamfered area on the back side of the substrate and the outermost edge area in the back side plane, and the ring etching width is 0.1 to 1 mm.

[0013] Preferably, the growth of the silicon oxide thin film in step S1 is performed using a chemical vapor deposition method.

[0014] Preferably, the chemical vapor deposition method comprises the following steps:

[0015] A silicon oxide thin film was grown on the back side of a substrate under inert gas protection using SiH4 and O2 in a volume ratio of 1:(8-14) at normal atmospheric pressure and 400-500°C.

[0016] Preferably, step S2 uses a liquid phase or gas phase method for ring etching.

[0017] Preferably, the liquid phase ring etching step involves first covering the silicon oxide thin film layer on the back side of the substrate with an HF acid-resistant material, exposing only the area to be etched at the edge of the substrate, then immersing it in an HF solution with a mass percentage of 4-7% for 50-150 seconds, and finally removing the HF acid-resistant material.

[0018] Preferably, the vapor phase ring etching step involves first placing the substrate with the back side facing up, then covering the silicon oxide thin film layer on the back side of the substrate with an HF acid-resistant material, exposing only the area to be etched at the edge of the substrate, and then introducing HF gas for ring etching.

[0019] Therefore, the method of the present invention effectively prevents the reaction between the substrate back side near the edge and the growth gas during epitaxial layer growth, and also prevents the formation of silicon nodule at the back edge, thereby avoiding the phenomenon of substrate and sulfide sticking together and improving the quality of the back edge of the substrate. Attached Figure Description

[0020] Figure 1 These are photographs taken under a microscope showing defects at the back edge of a substrate after ultra-thick epitaxial deposition in existing technology.

[0021] Figures 2-3 These are photographs of defects in existing silicon nodule technology observed under microscopes of different magnifications.

[0022] Figure 4 This is a schematic diagram showing the locations of Silicon Nodule and Bridging-Like defects generated during epitaxy on a 300mm substrate.

[0023] Figure 5 This is a schematic diagram of the silicon oxide thin film growth and ring etching positions in this application;

[0024] Figure 6 This is a photograph taken under a microscope of the back edge of the substrate after ultra-thick epitaxial deposition using the method of this invention. Detailed Implementation

[0025] This invention provides a method for preparing a 300mm lightly doped substrate with improved edge defects in ultra-thick epitaxial layers, comprising the following steps:

[0026] S1. A silicon oxide thin film (LTO thin film) is grown on the back side of the substrate after double-sided polishing and before final polishing;

[0027] S2. Perform ring etching on the edge region of the silicon oxide film.

[0028] This application grows a silicon oxide thin film on the back side of a 300mm substrate after double-sided polishing and before final polishing. During subsequent epitaxy of this substrate, the silicon oxide thin film effectively prevents the deposition of growth gas at the edge of the substrate where it contacts the susceptor, further avoiding adhesion between the substrate and the susceptor and preventing bridging-like defects. However, in actual production, it has been found that for lightly doped large-size substrates such as 300mm substrates, slight scratches caused by the polishing effect of the epitaxial gas HCl or other reasons may occur during ultra-thickness epitaxy. This can lead to the removal of thinner areas of silicon oxide film at the wafer bevel, but the removal of the edge silicon oxide film is not complete, leaving a large portion of the silicon oxide film intact, resulting in silicon nodule defects. The locations of the aforementioned bridging-like and silicon nodule defects are shown below. Figure 4 As shown. Therefore, in order to prevent root-like defects during epitaxy, this application also performs ring etching on the edge region of the grown silicon oxide film to completely remove the film layer at the edge. In this way, there is no residual silicon oxide film to induce subsequent epitaxy. Even if a small amount of growth gas is deposited at the edge, root-like defects will not be formed, and there is no significant impact on the performance of the substrate and epitaxial wafer.

[0029] like Figure 5 As shown, the silicon oxide film grown on the back side of the substrate covers the back chamfer and the back plane. To prevent bridging defects, a silicon oxide film should be used to cover the contact area between the back side of the substrate and the substrate (near the edge of the back plane of the substrate). At the same time, to prevent silicon nodule defects, the silicon oxide film at the back chamfer of the substrate is removed (the silicon oxide film covering the substrate before etching is a film resistant to HF acid etching. During the etching process, the silicon oxide film covered by the HF acid resistant film is retained, while the exposed silicon oxide film is etched away by immersing it in HF acid, and then the HF acid resistant film is removed). The silicon oxide film with a width of approximately 0.01 to 0.09 mm at the edge of the back plane outside the connection with the substrate is also removed.

[0030] This application chooses to perform silicon oxide thin film deposition and ring etching after double-sided polishing and before final polishing. If deposition is performed after final polishing, it will cause damage to the polished surface. However, if deposition is performed before final polishing, the final polishing can remove the damage to the front side of the substrate caused by LTO deposition.

[0031] Therefore, the method of the present invention effectively prevents the reaction between the substrate back side near the edge and the growth gas during epitaxial layer growth, and also prevents the formation of silicon nodule at the back edge, thereby avoiding the phenomenon of substrate sticking to the contact position (Susceptor) and improving the quality of the back edge of the substrate.

[0032] This invention improves the morphology of a 300mm double-sided polished substrate after the thick epitaxial layer is grown, resulting in a significant improvement in the substrate edge morphology and thus enhancing the quality of the epitaxial wafer. Specifically... Figure 6 As shown (this product is derived from Example 1).

[0033] The epitaxial layer thickness of the ultra-thick epitaxial wafer described in this application is generally >40 μm, with a corresponding substrate thickness of approximately 700–800 mm, and the grown silicon oxide thin film thickness is preferably... If the silicon oxide film is too thick, it will increase costs and reduce production capacity; if it is too thin, it will be etched away by the vapor phase epitaxial gas during epitaxial deposition.

[0034] Preferably, the width of the ring etching in step S2 is 0.1 to 1 mm, including the chamfer on the back side of the substrate and the outermost edge area in the back plane.

[0035] Step S1: The growth of the silicon oxide thin film is preferably carried out by chemical vapor deposition. Further, the chemical vapor deposition method specifically includes the following steps: under the protection of an inert gas, using SiH4 and O2 with a volume ratio of 1:(8-14), a silicon oxide thin film is grown on the back side of the substrate at normal atmospheric pressure and 400-500°C.

[0036] Compared to thermal oxidation methods, the aforementioned chemical vapor deposition method requires lower temperatures, and compared to plasma chemical vapor deposition methods, it does not require special plasma equipment. Furthermore, the silicon oxide thin film deposited by this method not only has a faster growth rate but also achieves a density sufficient for subsequent epitaxial processes, while also offering higher throughput. The production process is also relatively safe due to its low temperature and ambient pressure.

[0037] Preferably, step S2 uses a liquid phase or gas phase method for ring etching.

[0038] Preferably, the liquid phase ring etching step involves first covering the silicon oxide film layer on the back of the substrate with an HF acid-resistant material, such as an HF acid-resistant film, exposing only the area to be etched at the edge of the substrate (the diameter of the covering film is generally slightly larger than the diameter of the horizontal plane on the back of the substrate; during etching, the HF acid will penetrate to the inner edge of the horizontal plane on the back of the substrate, etching away the silicon oxide film at the inner edge of the horizontal plane on the back of the substrate). Then, the substrate is immersed in an HF solution with a mass percentage of 4-7% for 50-150 seconds, and finally the acid-resistant film is removed.

[0039] Preferably, the vapor phase ring etching step involves first placing the substrate with the back side facing up, then covering the silicon oxide thin film layer on the back side of the substrate with an HF acid-resistant material such as a corrosion-resistant disc, exposing only the area to be etched at the edge of the substrate, and then introducing HF gas for ring etching.

[0040] Liquid phase etching is preferred, as the silicon oxide film obtained by liquid phase etching has a more regular edge compared to the gas phase.

[0041] Example 1

[0042] A lightly phosphorus-doped substrate (300 mm in diameter, with a back chamfer width of 0.9 mm) with a resistivity of 1–10 ohm·cm after double-sided polishing was used. Under nitrogen inert gas protection, a layer with a thickness of [missing information] was grown on the back side of the substrate using SiH4 and O2 in a volume ratio of 1:9 at normal atmospheric pressure and 430°C. A silicon oxide film was applied, and then an acid-resistant film with a diameter of 298.3 mm was used to cover the LTO layer on the back side of the substrate, exposing only the LTO at the edge of the substrate. The substrate was then immersed in a 5% HF solution for 100 seconds of etching. Finally, the acid-resistant film was removed. The measured ring etch width was approximately 0.95 mm (including the back chamfer width + in-plane etch width).

[0043] Epitaxy was performed on the above-treated substrate, and an untreated double-sided polished substrate was used as a control. The epitaxial thickness was 50 μm. The edge morphology of both substrates was observed under a microscope, and the results are as follows. Figure 1 and 4 As shown in the above images, the edge morphology of the epitaxial wafer is greatly improved after processing according to this application.

[0044] Example 2

[0045] A lightly phosphorus-doped substrate (300 mm in diameter, with a back chamfer width of 0.15 mm) with a resistivity of 1–10 ohm·cm after double-sided polishing was used. Under nitrogen inert gas protection, a layer with a thickness of [missing information] was grown on the back side of the substrate using SiH4 and O2 at a volume ratio of 1:12 at normal atmospheric pressure and 450°C. A silicon oxide film was applied, and then an acid-resistant film with a diameter of 299.8 mm was used to cover the LTO layer on the back side of the substrate, exposing only the LTO at the edge of the substrate. The substrate was then immersed in a 5% HF solution for 100 seconds of etching. Finally, the acid-resistant film was removed. The measured ring etch width was approximately 0.2 mm (including the back chamfer width + the in-plane etch width).

[0046] Example 3

[0047] A lightly phosphorus-doped substrate (300 mm in diameter, with a back chamfer width of 0.45 mm) with a resistivity of 1–10 ohm·cm after double-sided polishing was used. Under nitrogen inert gas protection, a layer with a thickness of [missing information] was grown on the back side of the substrate using SiH4 and O2 at a volume ratio of 1:14, at normal atmospheric pressure and 450°C. A silicon oxide film was applied, and then an acid-resistant film with a diameter of 299.2 mm was used to cover the LTO layer on the back side of the substrate, exposing only the LTO at the edge of the substrate. The substrate was then immersed in a 5% HF solution for 100 seconds of etching. Finally, the acid-resistant film was removed. The measured ring etch width was approximately 0.5 mm (including the back chamfer width + the in-plane etch width).

[0048] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. Thus, if these modifications and modifications of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include these modifications and modifications.

Claims

1. A method for preparing a 300mm lightly doped substrate with improved edge defects in ultra-thick epitaxial layers, characterized in that, Includes the following steps: S1. A silicon oxide thin film is grown on the back side of a 300mm thick substrate after double-sided polishing and before final polishing; the substrate thickness is 700-800mm, the epitaxial layer thickness of the epitaxial wafer fabricated from the substrate is >40μm, and the silicon oxide thin film thickness is... The substrate resistivity is 1–10 ohm·cm; the silicon oxide thin film is grown using chemical vapor deposition (CVD); the steps of the CVD method are as follows: A silicon oxide thin film was grown on the back side of a substrate under inert gas protection using SiH4 and O2 in a volume ratio of 1:(8-14) at normal atmospheric pressure and 400-500°C. S2. Perform ring etching on the edge region of the silicon oxide film; the ring etching region includes the chamfer on the back side of the substrate and the outermost edge region in the back plane, the ring etching width is 0.2 to 1 mm; the width of the outermost edge region in the back plane is 0.01 to 0.09 mm.

2. The method for preparing a 300mm lightly doped substrate with improved edge defects in ultra-thick epitaxial layers as described in claim 1, characterized in that, Step S2 involves ring etching using either liquid or gas phase methods.

3. The method for preparing a 300mm lightly doped substrate with improved edge defects in ultra-thick epitaxial layers as described in claim 2, characterized in that, The liquid phase ring etching step involves first covering the silicon oxide thin film layer on the back of the substrate with an HF acid-resistant material, exposing only the area to be etched at the edge of the substrate, then immersing it in an HF solution with a mass percentage of 4-7% for 50-150 seconds, and finally removing the HF acid-resistant material.

4. The method for preparing a 300mm lightly doped substrate with improved edge defects in ultra-thick epitaxial layers as described in claim 2, characterized in that, The vapor phase ring etching step involves first placing the substrate with the back side facing up, then covering the silicon oxide thin film layer on the back side of the substrate with an HF acid-resistant material, exposing only the area to be etched at the edge of the substrate, and then introducing HF gas for ring etching.

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