A method for non-destructive recycling of ultra-thin silicon nitride protective layer wafers for silicon / silicon carbide substrates and wafer structure

Abstract

The application discloses a kind of ultra-thin silicon nitride protective layer wafer lossless recycling method and wafer structure suitable for silicon / silicon carbide substrate, which deposits 10-20 angstrom ultra-thin silicon nitride barrier protective layer on the surface of silicon or silicon carbide polishing substrate, then deposits silicon oxide functional film on the surface of the protective layer to obtain silicon oxide dummy wafer. After use, long-term immersion etching with hydrofluoric acid is used, and the characteristics of the silicon nitride layer resistant to hydrofluoric acid corrosion are used to completely peel off the surface layer of the failed silicon oxide film while preventing the hydrofluoric acid from contacting the polishing surface of the substrate, achieving zero corrosion of the substrate. The regenerated wafer does not need chemical mechanical polishing repair and can directly re-deposit silicon oxide film to achieve multiple recycling. The application also provides a wafer structure composed of a polishing substrate, an ultra-thin silicon nitride barrier protective layer, and a silicon oxide functional film stack, which is suitable for 8-inch silicon wafers and 8-inch silicon carbide wafers.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor thin film technology and high-end wafer regeneration and reuse technology, specifically relating to a non-destructive recycling method and wafer structure for ultra-thin silicon nitride protective layer wafers adapted to silicon / silicon carbide substrates. Background Technology

[0002] In 8-inch semiconductor mass production fabs, silicon oxide dummy wafers are widely used in PECVD (Plasma Enhanced Chemical Vapor Deposition), LPCVD (Low Pressure Chemical Vapor Deposition), and oxidation diffusion equipment for cavity preheating, process verification, film thickness calibration, anomaly review, and process monitoring, making them an indispensable consumable on the production line. For a standardized 8-inch mass production line with a monthly capacity of 50,000 wafers, the monthly stable consumption of silicon oxide dummy wafers is approximately 400 wafers.

[0003] Currently, the industry-standard recycling method is to use hydrofluoric acid wet immersion to peel off the surface layer of failed silicon oxide film. This process presents a technical dilemma: insufficient immersion time results in excessive film residue, rendering the wafer unusable; while extending the immersion time for complete film removal corrodes the mirror-polished layer of the silicon or silicon carbide substrate, causing increased surface roughness, micro-pits, and loss of process accuracy. To repair the polished surface, traditional processes must add a chemical mechanical polishing step, which not only consumes polishing consumables, occupies machine capacity, and increases labor hours, but also continuously reduces the thickness of the wafer substrate, shortening the wafer's lifespan.

[0004] Existing silicon nitride barrier protection solutions typically employ films tens of nanometers thick, which severely interferes with the measurement accuracy of silicon oxide and is unsuitable for dummy wafer scenarios in process monitoring. Furthermore, no technical solution simultaneously addresses the batch, non-destructive regeneration requirements of both silicon and silicon carbide wafers. The procurement costs of 8-inch silicon wafers and 8-inch silicon carbide wafers differ significantly, and under traditional processes, both types of wafers are reused only 1-2 times. The frequent scrapping of silicon carbide wafers, in particular, results in extremely high consumable operating costs for mass production fabs. Summary of the Invention

[0005] This invention provides a method for the non-destructive recycling of ultrathin silicon nitride protective layer wafers adapted to silicon / silicon carbide substrates, comprising the following steps: S1, providing an 8-inch polished substrate, wherein the substrate is a double-sided polished silicon wafer or a polished silicon carbide wafer; S2, depositing an ultrathin silicon nitride barrier protective layer with a thickness of 10-20 Å on the polished surface of the substrate; S3, depositing a silicon oxide functional film on the surface of the ultrathin silicon nitride protective layer to prepare a silicon oxide dummy wafer for production line process calibration and machine monitoring; S4, after the wafer has been used, using a hydrofluoric acid wet etching process for a long time to completely remove the surface failure silicon oxide film; S5, isolating the silicon / silicon carbide substrate polished surface by the silicon nitride layer, achieving zero corrosion and zero damage to the substrate polished layer; S6, obtaining a non-destructive regenerated wafer after cleaning and drying, without the need for chemical mechanical polishing repair; S7, the regenerated wafer can be directly redeposited with a silicon oxide film, achieving multiple recycling and reuse.

[0006] Furthermore, the ultrathin silicon nitride layer is deposited using LPCVD or PECVD processes, with a film thickness uniformity error ≤ ±1 Å and no pinhole defects.

[0007] Furthermore, the hydrofluoric acid immersion time is not limited by the etching endpoint, and the immersion time can be extended arbitrarily according to the thickness of the silicon oxide film to ensure that the film is completely peeled off without any residue.

[0008] Furthermore, the thickness of the ultrathin silicon nitride protective layer is any one of 10 Å, 15 Å, or 20 Å.

[0009] Furthermore, the regenerated wafers can be stably recycled ≥ 5 times.

[0010] Furthermore, the method is also compatible with 8-inch silicon / silicon carbide substrates, with universal process parameters and production line equipment.

[0011] Furthermore, the present invention also provides an 8-inch silicon oxide dummy wafer structure that can be recycled without damage, which is composed of an 8-inch polished substrate, a 10-20 Å ultrathin silicon nitride barrier protective layer, and a silicon oxide functional film stacked sequentially from bottom to top; the polished substrate is a silicon substrate or a silicon carbide substrate.

[0012] Furthermore, the film thickness uniformity error of the ultrathin silicon nitride barrier protective layer is ≤±1Å, and there are no pinhole defects.

[0013] Furthermore, the ultrathin silicon nitride layer is deposited on the surface of a silicon carbide substrate using a PECVD process at a deposition temperature of 200–400°C, a radio frequency power of 100–300W, and reactant gases of SiH4 and NH3. The SiH4 flow rate is 50–200 sccm, the NH3 flow rate is 100–500 sccm, and the deposition pressure is 0.5–2 Torr. The density of the deposited silicon nitride film is higher than that of the silicon nitride film deposited using an LPCVD process, and it exhibits a lower corrosion rate under the same hydrofluoric acid immersion conditions.

[0014] Furthermore, the ultrathin silicon nitride protective layer has a thickness of 15 Å, is deposited using a PECVD process, and the Si-N bond density in the deposited silicon nitride film is ≥8.5 × 10⁻⁶. 22 cm⁻ 3 The residual stress of the film is ≤200MPa, and the corrosion rate of the silicon nitride film is ≤0.1Å / min after immersion in hydrofluoric acid.

[0015] Compared to traditional processes, this invention offers the following advantages: it completely avoids the dilemmas of hydrofluoric acid etching, allowing for thorough film removal over a long period with no silicon oxide residue, while fully protecting the substrate polishing layer and preventing microscopic corrosion and surface degradation; it completely eliminates the chemical mechanical polishing (CMP) regeneration process, saving polishing fluid and pad consumables, releasing CMP machine capacity, and reducing labor and equipment costs; the measurement error of the 10–20 Å ultrathin silicon nitride layer is less than 0.5%, not affecting silicon oxide film thickness, refractive index, or process calibration data, fully meeting mass production accuracy requirements; and it increases the wafer recycling rate from the traditional 1–2 times to over 5 times, significantly reducing the frequency of wafer scrapping. For silicon wafers, stable reuse ≥5 times can reduce new wafer purchases by over 60%, directly saving over RMB 25,000 per month in silicon wafer procurement and regeneration processing costs, and over RMB 300,000 annually. For silicon carbide wafers, this invention achieves zero corrosion, zero roughness degradation, and no thickness loss, enabling stable recycling ≥5 times. The cost of consumables per lifecycle is reduced by over 60%, completely eliminating the need for chemical mechanical polishing. This invention relies entirely on existing LPCVD / PECVD and hydrofluoric acid wet processing equipment, requiring no new equipment or process modifications to production lines. It is compatible with the batch regeneration of both silicon-based and silicon carbide-based silicon oxide dummy wafers. Detailed Implementation

[0016] The present invention will now be described in detail through specific embodiments. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0017] First Embodiment

[0018] This embodiment provides a method for non-destructive recycling of ultrathin silicon nitride protective layer wafers adapted to silicon substrates, and the corresponding wafer structure.

[0019] The wafer structure of this embodiment, from top to bottom, includes: a surface silicon oxide functional film, an ultrathin silicon nitride barrier layer, and an 8-inch polished substrate. The 8-inch polished substrate is a double-sided polished silicon wafer. The ultrathin silicon nitride barrier layer is deposited on the polished surface of the substrate, with a thickness of 10–20 Å. The surface silicon oxide functional film is deposited on the surface of the ultrathin silicon nitride barrier layer.

[0020] The wafer recycling method of this embodiment includes the following steps.

[0021] Step 1: Provide an 8-inch double-sided polished silicon wafer as a substrate.

[0022] Step two involves depositing an ultrathin silicon nitride barrier layer with a thickness of 15 Å on the polished surface of the substrate using LPCVD technology. The film uniformity error is ≤ ±1 Å, and there are no pinhole defects. LPCVD is a low-temperature deposition process that does not damage the original polished mirror surface properties of the substrate.

[0023] Step 3: Deposit a 1000Å TEOS (tetraethyl orthosilicate) silicon oxide functional film on the surface of the ultrathin silicon nitride protective layer to prepare a silicon oxide dummy wafer that can be used for production line equipment calibration and process monitoring.

[0024] Step four: After the wafer has been used in the mass production process, it is immersed in a room-temperature hydrofluoric acid wet bath for 120 minutes. Hydrofluoric acid has a high etching selectivity for silicon oxide and almost no corrosion for silicon nitride, so it can be etched thoroughly for a long time, so that the failed silicon oxide film on the surface can be completely peeled off without any residue.

[0025] Step 5: Utilizing the silicon nitride layer's resistance to hydrofluoric acid corrosion, during the hydrofluoric acid immersion process, the silicon nitride layer completely isolates the hydrofluoric acid from contact with the polished surface of the silicon substrate, resulting in no corrosion, no roughness degradation, and no structural damage to the substrate.

[0026] Step six: After standard semiconductor cleaning and drying, a non-destructive regenerated wafer is obtained. AFM (Atomic Force Microscopy) inspection shows that the polished surface roughness is consistent with that of a new wafer, with no corrosion damage and no shift in film thickness reference, eliminating the need for chemical mechanical polishing repair.

[0027] Step 7: The regenerated wafer can be directly redeposited with a silicon oxide film, achieving stable reuse more than 5 times.

[0028] In other alternative solutions of this embodiment, the ultrathin silicon nitride layer can also be deposited using PECVD. The thickness of the ultrathin silicon nitride protective layer can be any of 10Å, 15Å, or 20Å. Within this thickness range, the protective performance of the film is stable, with no penetration or substrate damage from prolonged hydrofluoric acid etching, and the measurement error is controlled within 0.3%, fully meeting mass production process standards. The hydrofluoric acid immersion time is not limited by the etching endpoint and can be freely extended according to the thickness of the silicon oxide film, ensuring 100% residue-free peeling of the film. The method described in this embodiment relies entirely on existing LPCVD / PECVD equipment and hydrofluoric acid wet processing equipment, requiring no new equipment or modification of the production line process. It is compatible with the batch regeneration of both silicon-based and silicon carbide-based silicon oxide dummy wafers, with universal process parameters and production line equipment.

[0029] Second Embodiment

[0030] This embodiment provides a non-destructive recycling method for ultrathin silicon nitride protective layer wafers adapted to silicon carbide substrates, and the corresponding wafer structure. Based on the first embodiment, this embodiment optimizes the PECVD process parameters to address the material properties of the silicon carbide substrate, thereby obtaining a silicon nitride protective layer with higher density and stronger resistance to hydrofluoric acid corrosion.

[0031] The wafer structure of this embodiment, from top to bottom, includes: a surface silicon oxide functional film, an ultrathin silicon nitride barrier layer, and an 8-inch polished substrate. The 8-inch polished substrate is an 8-inch conductive silicon carbide polished wafer. The ultrathin silicon nitride barrier layer is deposited on the polished surface of the substrate, with a thickness of 15 Å. The surface silicon oxide functional film is deposited on the surface of the ultrathin silicon nitride barrier layer.

[0032] The wafer recycling method of this embodiment includes the following steps.

[0033] Step 1: Provide an 8-inch conductive silicon carbide polished wafer as the substrate. This silicon carbide wafer is a mass-produced conductive silicon carbide polished wafer, priced at 4000-6500 yuan per piece.

[0034] Step two involves depositing an ultrathin silicon nitride barrier layer with a thickness of 15 Å on the polished substrate surface using PECVD. The deposition parameters are: deposition temperature 200–400℃, RF power 100–300W, reactant gases SiH4 and NH3, SiH4 flow rate 50–200 sccm, NH3 flow rate 100–500 sccm, and deposition pressure 0.5–2 Torr. The film uniformity error is ≤ ±1 Å, and there are no pinhole defects. PECVD is a low-temperature deposition process that does not damage the original polished mirror surface properties of the substrate. X-ray photoelectron spectroscopy (XPS) analysis is used to calculate the Si-N bond density by the ratio of the Si 2p and N 1s peak areas. The Si-N bond density in the deposited silicon nitride film is ≥ 8.5 × 10⁻⁶. 22 cm⁻ 3 The residual stress of the film is ≤200MPa, and the density is higher than that of silicon nitride films deposited by LPCVD process. It also has a lower corrosion rate under the same hydrofluoric acid immersion conditions.

[0035] Step 3: Deposit a silicon oxide functional film on the surface of the ultrathin silicon nitride protective layer to prepare a silicon oxide dummy wafer that can be used for production line equipment calibration and process monitoring.

[0036] Step four: After the wafer completes its mass production process, it is immersed in a room-temperature hydrofluoric acid wet bath. Hydrofluoric acid has a high etching selectivity for silicon oxide and almost no corrosion for silicon nitride. The immersion time is determined based on the thickness of the silicon oxide film to ensure complete removal of the failed silicon oxide film on the surface without residue. Testing showed that in this embodiment, after immersion in hydrofluoric acid for 600 minutes, the silicon nitride film corrosion rate was ≤0.1 Å / min, effectively protecting the silicon carbide substrate from damage during prolonged immersion.

[0037] Step five: Utilizing the silicon nitride layer's resistance to hydrofluoric acid corrosion, the silicon nitride layer completely isolates the hydrofluoric acid from contact with the polished surface of the silicon carbide substrate during the hydrofluoric acid immersion process. The polished mirror surface of the silicon carbide substrate is complete and defect-free, with no micro-corrosion pits, no roughness degradation, no thickness loss, and no parameter offset.

[0038] Step six: After standard semiconductor cleaning and drying, a non-destructive regenerated wafer is obtained, which does not require chemical mechanical polishing repair.

[0039] Step 7: The regenerated wafer can be directly redeposited with a silicon oxide film, enabling multiple cycles of reuse, with a stable reuse count of ≥5 times. Since the unit price of silicon carbide wafers is more than 20 times that of ordinary silicon wafers, this embodiment reduces the consumable cost of silicon carbide wafers per lifecycle by more than 60%, completely eliminating the expensive chemical mechanical polishing (CMP) precision polishing process.

[0040] In other optional embodiments of this example, the thickness of the ultrathin silicon nitride protective layer can be any of 10 Å, 15 Å, or 20 Å. Within this thickness range, the silicon nitride film deposited by the PECVD process exhibits stable protective performance, with no penetration or substrate damage even after prolonged hydrofluoric acid etching, and the measurement error is controlled within 0.3%, fully meeting mass production process standards. There are no process limitations on the hydrofluoric acid immersion time; the immersion time can be freely extended according to the thickness of the silicon oxide film, ensuring 100% residue-free peeling of the film. The method described in this embodiment relies entirely on existing PECVD equipment and hydrofluoric acid wet processing equipment, requiring no new equipment or modification of the production line process; the process parameters and production line equipment are universal.

[0041] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for non-destructive recycling of ultrathin silicon nitride protective layer wafers adapted to silicon / silicon carbide substrates, characterized in that, Includes the following steps: S1. Provide an 8-inch polished substrate, wherein the substrate is a double-sided polished silicon wafer or a polished silicon carbide wafer; S2. Deposit an ultrathin silicon nitride barrier protective layer with a thickness of 10-20 Å on the polished surface of the substrate; S3. Deposit a silicon oxide functional film on the surface of the ultrathin silicon nitride protective layer to prepare a silicon oxide dummy wafer for production line process calibration and machine monitoring. S4. After the wafer is used, it is etched by long-term immersion in hydrofluoric acid to completely remove the surface failure silicon oxide film. S5. By isolating the silicon nitride layer from hydrofluoric acid contact with the silicon / silicon carbide substrate polishing surface, zero corrosion and zero damage to the substrate polishing layer are achieved. S6. After cleaning and drying, a damage-free regenerated wafer is obtained without the need for chemical mechanical polishing repair. S7. Regenerated wafers can be directly redeposited with silicon oxide films, enabling multiple cycles of reuse.

2. The method for non-destructive recycling of ultrathin silicon nitride protective layer wafers adapted to silicon / silicon carbide substrates according to claim 1, characterized in that: The ultrathin silicon nitride layer is deposited using LPCVD or PECVD processes, with a film thickness uniformity error of ≤±1Å and no pinhole defects.

3. The method for non-destructive recycling of ultrathin silicon nitride protective layer wafers adapted to silicon / silicon carbide substrates according to claim 1, characterized in that: The soaking time in hydrofluoric acid is not limited by the etching endpoint. The soaking time can be extended arbitrarily according to the thickness of the silicon oxide film to ensure that the film is completely peeled off without any residue.

4. The method for non-destructive recycling of ultrathin silicon nitride protective layer wafers adapted to silicon / silicon carbide substrates according to claim 1, characterized in that: The thickness of the ultrathin silicon nitride protective layer is any one of 10 Å, 15 Å, or 20 Å.

5. The method for non-destructive recycling of ultrathin silicon nitride protective layer wafers adapted to silicon / silicon carbide substrates according to claim 1, characterized in that: Regenerated wafers can be stably recycled ≥ 5 times.

6. The method for non-destructive recycling of ultrathin silicon nitride protective layer wafers adapted to silicon / silicon carbide substrates according to claim 1, characterized in that: The method is compatible with 8-inch silicon / silicon carbide substrates, and the process parameters and production line equipment are universal.

7. An 8-inch silicon dioxide dummy wafer structure that can be recycled without damage, characterized in that: It is composed of an 8-inch polished substrate, a 10-20 Å ultrathin silicon nitride barrier protective layer, and a silicon oxide functional film stacked sequentially from bottom to top; the polished substrate is a silicon substrate or a silicon carbide substrate.

8. The non-destructive, recyclable 8-inch silicon dioxide dummy wafer structure according to claim 7, characterized in that: The thickness uniformity error of the ultrathin silicon nitride barrier protective layer is ≤±1Å, and there are no pinhole defects.

9. The method for non-destructive recycling of ultrathin silicon nitride protective layer wafers adapted to silicon / silicon carbide substrates according to claim 2, characterized in that: The ultrathin silicon nitride layer is deposited on the surface of a silicon carbide substrate using a PECVD process. The deposition temperature is 200–400℃, the radio frequency power is 100–300W, the reaction gases are SiH4 and NH3, the SiH4 flow rate is 50–200 sccm, the NH3 flow rate is 100–500 sccm, and the deposition pressure is 0.5–2 Torr. The density of the deposited silicon nitride film is higher than that of the silicon nitride film deposited using the LPCVD process, and it has a lower corrosion rate under the same hydrofluoric acid immersion conditions.

10. The method for non-destructive recycling of ultrathin silicon nitride protective layer wafers adapted to silicon / silicon carbide substrates according to claim 9, characterized in that: The ultrathin silicon nitride protective layer has a thickness of 15 Å and is deposited using a PECVD process. The Si-N bond density in the deposited silicon nitride film is ≥8.5 × 10⁻⁶. 22 cm⁻ 3 The residual stress of the film is ≤200MPa, and the corrosion rate of the silicon nitride film is ≤0.1Å / min after immersion in hydrofluoric acid.