A double-sided thinning process for hard and brittle semiconductor substrates based on ultrafast laser

Abstract

The application discloses a kind of based on hard and brittle semiconductor substrate double-face thinning process of ultrafast laser.This process is first by ion implantation or chemical solution to wafer double face is activated treatment, softens surface layer material to reduce processing difficulty;Subsequently wafer is fixed in laser modification chamber, through dynamic circulation etching solution synchronously updates solution in chamber and removes laser by-product;Then utilize two ultrafast laser respectively to wafer upper and lower surface is scanned synchronously, first stage adopts nonlinear path to realize double-face high-efficiency thinning, second stage is switched to linear parallel path and adjusts wafer direction, completes the morphology regulation of microstructure and double-face precision finishing;Finally through double-face chemical mechanical polishing (CMP) removal balance, obtains target thinning and atomic level flat surface.This process is through double-face collaborative processing and dynamic etching liquid control, with high efficiency, low damage and high precision advantage, suitable for silicon carbide, gallium nitride and other hard and brittle semiconductor material's large-scale thinning manufacturing.

Description

Technical Field

[0001] This invention belongs to the field of laser-assisted processing technology, specifically relating to a double-sided thinning process for hard and brittle semiconductor substrates based on ultrafast lasers. Background Technology

[0002] As semiconductor devices continue to evolve towards miniaturization and high integration, wafer thinning technology has become a crucial step in advanced packaging and device manufacturing. For hard and brittle semiconductor materials such as silicon carbide (SiC) and gallium nitride (GaN), the wafers formed after ingot cutting often have subsurface defects, and their thickness is insufficient to meet the requirements of subsequent processes such as photolithography. Therefore, thinning processes are needed to reduce the wafer thickness by 50-100 μm. However, traditional thinning techniques face significant challenges when processing such high-hardness materials: while mechanical grinding can achieve rapid thinning, the intense friction between the grinding wheel and sharp corners easily leads to subsurface damage and microcracks, and the grinding wheel suffers severe wear; while single-sided laser thinning technology can reduce the introduction of damage, its processing efficiency is low, and the deposition byproducts generated by the laser are difficult to remove in real time, easily interfering with subsequent laser processing and leading to decreased process stability.

[0003] In existing technologies, single-sided laser thinning relies on multiple cleaning passes and parameter adjustments to maintain processing accuracy, which limits overall efficiency and makes it impossible to process both sides of the wafer simultaneously, leading to uneven stress distribution and warping risks. In addition, surface residues after laser processing (such as amorphous layers) need to be removed through additional chemical etching or polishing steps, further increasing process complexity and cost.

[0004] To address the aforementioned problems, this invention proposes a double-sided thinning process for hard and brittle semiconductor substrates based on ultrafast lasers. Through a synergistic design of simultaneous double-sided scanning, dynamic etchant circulation, and staged path optimization, it achieves efficient and low-damage thinning. The process first softens the wafer surface layer through ion implantation or chemical activation, reducing the energy requirements for subsequent laser processing. Then, ultrafast lasers are used to simultaneously perform nonlinear path roughing and linear path finishing on both sides, combined with a dynamically updated etchant to remove laser byproducts in real time, avoiding surface contamination. Finally, atomically flat surfaces are achieved through double-sided chemical mechanical polishing (CMP). Compared to traditional processes, this method effectively improves thinning efficiency, providing a reliable solution for the high-precision manufacturing of hard and brittle semiconductor materials. Summary of the Invention

[0005] (I) Purpose of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a double-sided thinning process for hard and brittle semiconductor substrates based on ultrafast lasers, which aims to improve the efficiency and quality of the wafer thinning process.

[0007] (II) Technical Solution

[0008] The present invention is achieved through the following technical solution.

[0009] (1) Double-sided activation treatment is performed on the hard and brittle semiconductor wafer. Under high temperature conditions, the surface material on both sides is softened by ion implantation technology or chemical solution immersion.

[0010] (2) The activated wafer is fixed in the positioning device of the laser-modified chamber, and the chamber is equipped with a liquid delivery device and a filtration device to maintain the concentration stability by dynamically circulating and updating the etching solution.

[0011] (3) Turn on ultrafast laser 1 and ultrafast laser 2 to scan the upper and lower surfaces of the wafer simultaneously; First stage thinning: ultrafast laser 1 scans the upper surface with a non-linear path, and ultrafast laser 2 scans the lower surface simultaneously with a non-linear path; until the thinning depth on both sides reaches 40±0.5μm; Second stage thinning: adjust the laser energy density, rotate the wafer 90° using the positioning device, and switch ultrafast laser 1 and ultrafast laser 2 to linear parallel path scanning until the thinning depth on both sides reaches 4±0.5μm;

[0012] (4) The thinned wafer is subjected to double-sided chemical mechanical polishing (CMP) to finally achieve an atomically flat surface with a total thinning amount of 100±0.5μm and a surface roughness Ra<1nm.

[0013] Furthermore, in step (1), the hard and brittle semiconductor wafer is one of single-crystal silicon carbide, single-crystal gallium nitride, or single-crystal diamond.

[0014] Furthermore, in step (1), the high temperature range is 50-100℃, the ion implantation activation treatment uses argon-oxygen mixed gas (volume ratio 3:1) plasma, the implantation energy is 20-200keV, and the treatment time is 5-20min; the chemical activation uses a mixed solution of hydrofluoric acid and hydrogen peroxide (volume ratio 1:4-1:8), and the soaking time is 5-10min.

[0015] Furthermore, in step (2), the positioning device includes a vacuum adsorption clamp with a positioning accuracy of ±0.1mm and a rotation angle error of ≤0.5°; the liquid delivery device has a flow rate of 50-200mL / min, and the negative pressure of the filtration device is maintained at 0.1-0.5MPa.

[0016] Further, in step (2), the etching solution is a mixed solution of hydrofluoric acid, nitric acid, sulfuric acid and deionized water, wherein the volume percentages of hydrofluoric acid, nitric acid, sulfuric acid and deionized water are 15-20 vol%, 30-40 vol%, 0-10 vol%, and 30-55 vol%, respectively.

[0017] Furthermore, in the first stage of scanning in step (3), the nonlinear scanning path is one or a combination of two of the following: a spiral progressive path or an interlaced grid path; the laser pulse width is 100 fs-50 ps; the wavelength is 343-1064 nm; and the energy density is 3-15 J / cm². 2 The scanning speed is 50-1000 mm / s.

[0018] Furthermore, in the second stage of scanning in step (3), the linear parallel path scanning spacing is 20-90% of the spot diameter, and the laser energy density is adjusted to 1-3 J / cm². 2 The scanning speed is 500-1000 mm / s.

[0019] Furthermore, the CMP in step (4) uses an alkaline polishing solution with a pH of 10-12, and the double-sided polishing pressure is 400-500 g·cm⁻¹. 2 Polishing temperature 20-25℃.

[0020] (III) Beneficial Effects

[0021] The above-described technical solution of the present invention has the following beneficial technical effects:

[0022] (1) The substrate double-sided activation process proposed in this invention can effectively reduce the difficulty of subsequent surface processing.

[0023] (2) The ultrafast laser double-sided synchronous modification process and composite path / multi-orientation scanning process proposed in this invention can effectively improve the wafer thinning efficiency, reduce the introduction of subsurface damage by controlling the microstructure morphology by polarization direction, and improve surface uniformity, which is beneficial to subsequent CMP processing.

[0024] (3) The in-situ removal process of modified by-products proposed in this invention can ensure the efficiency of laser modification and avoid the deposition products affecting the absorption rate of the substrate to laser. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the semiconductor wafer processing flow of the present invention.

[0026] Figure 2 This is a schematic diagram of the semiconductor wafer processing apparatus of the present invention.

[0027] Figure 3 The image shows the optical microstructure of the surface obtained after processing in Example 1.

[0028] Figure 4 The image shows the surface AFM morphology obtained after processing in Example 1. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention.

[0030] Example 1:

[0031] (1) Double-sided activation treatment is performed on the single-crystal silicon carbide dicing wafer. The silicon carbide double-sided surface material is softened by a mixed solution of hydrofluoric acid / hydrogen peroxide with a volume ratio of 1:4 at 50°C.

[0032] (2) The activated wafer is fixed in the positioning device of the laser-modified chamber. The positioning device includes a vacuum adsorption fixture with a positioning accuracy of ±0.1mm and a rotation angle error of ≤0.5°. The chamber is equipped with a liquid delivery device and a filtration device. The flow rate of the liquid delivery device is 50-200mL / min, and the negative pressure of the filtration device is maintained at 0.1-0.5Mpa. The etching solution is dynamically circulated to maintain the concentration stability. The etching solution is a mixed solution of hydrofluoric acid, nitric acid and deionized water, wherein the volume percentages of hydrofluoric acid, nitric acid, sulfuric acid and deionized water are 20vol%, 30vol%, 5vol% and 45vol%, respectively.

[0033] (3) Turn on ultrafast laser 1 and ultrafast laser 2 to simultaneously scan the upper and lower surfaces of the wafer, respectively; First stage thinning: ultrafast laser 1 scans the upper surface in a spiral progressive path, and ultrafast laser 2 also scans the lower surface synchronously in a spiral progressive path. The pulse width of both lasers is 209 fs, the wavelength is 1026 nm, and the energy density is 8 J / cm². 2 The scanning speed is 200 mm / s; until the thinning depth on both sides reaches 40 ± 0.5 μm; the second stage of thinning: the laser energy density is adjusted, the wafer is rotated 90° using a positioning device, and ultrafast laser 1 and ultrafast laser 2 are switched to linear parallel path scanning with a scanning interval of 60% of the spot diameter and the laser energy density adjusted to 2 J / cm. 2 The scanning speed is 500 mm / s until the double-sided thinning depth reaches 4 ± 0.5 μm.

[0034] (4) The thinned wafer is subjected to double-sided chemical mechanical polishing (CMP) using an alkaline polishing solution with a pH of 10-12 and a double-sided polishing pressure of 500 g·cm⁻¹. 2 The polishing temperature is 25℃, achieving an atomically flat surface with a total thinning amount of 100±0.5μm and a surface roughness Ra<1nm.

[0035] Test results: Figure 3 and Figure 4 The image shows the surface morphology of the silicon carbide wafer obtained after processing in Example 1. It can be seen that the surface has high gloss and flatness.

[0036] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A double-sided thinning process for hard and brittle semiconductor substrates based on ultrafast lasers, characterized in that, Includes the following steps: (1) Double-sided activation treatment is performed on hard and brittle semiconductor wafers. Under high temperature conditions, the surface materials on both sides are softened by ion implantation or chemical solution immersion. The high temperature range is 50-100℃. Ion implantation activation treatment uses argon-oxygen mixed gas plasma with a volume ratio of 3:1, with an implantation energy of 20-200 keV and a treatment time of 5-20 min. Chemical activation uses a mixed solution of hydrofluoric acid and hydrogen peroxide with a volume ratio of 1:4-1:8 and an immersion time of 5-10 min. (2) The activated wafer is fixed in the positioning device of the laser-modified chamber. The chamber is equipped with a liquid delivery device and a filtration device. The etching solution is dynamically circulated to maintain concentration stability. The etching solution is a mixed solution of hydrofluoric acid, nitric acid, sulfuric acid and deionized water, wherein the volume percentages of hydrofluoric acid, nitric acid, sulfuric acid and deionized water are 15-20 vol%, 30-40 vol%, 0-10 vol%, and 30-55 vol%, respectively. (3) Turn on ultrafast laser 1 and ultrafast laser 2 to scan the upper and lower surfaces of the wafer simultaneously; first stage of thinning: ultrafast laser 1 scans the upper surface with a nonlinear path, and ultrafast laser 2 scans the lower surface simultaneously with a nonlinear path; until the thinning depth on both sides reaches 40±0.5 μm; Second stage thinning: Adjust the laser energy density, rotate the wafer 90° using the positioning device, and switch ultrafast laser 1 and ultrafast laser 2 to linear parallel path scanning until the double-sided thinning depth reaches 4±0.5 μm; (4) The thinned wafer is subjected to double-sided chemical mechanical polishing (CMP) to finally achieve an atomically flat surface with a total thinning amount of 100±0.5 μm and a surface roughness Ra<1 nm.

2. The process according to claim 1, characterized in that: The hard and brittle semiconductor wafer mentioned in step (1) is one of single-crystal silicon carbide, single-crystal gallium nitride, or single-crystal diamond.

3. The process according to claim 1, characterized in that: The positioning device in step (2) includes a vacuum adsorption clamp with a positioning accuracy of ±0.1 mm and a rotation angle error of ≤0.5°; the flow rate of the liquid delivery device is 50-200 mL / min, and the negative pressure of the filtration device is maintained at 0.1-0.5 MPa.

4. The process according to claim 1, characterized in that: In the first stage of scanning in step (3), the nonlinear scanning path is one or a combination of two of the spiral progressive path or the staggered grid path, the laser pulse width is 100fs-50 ps, ​​the wavelength is 343-1064 nm, the energy density is 3-15 J / cm², and the scanning speed is 50-1000 mm / s.

5. The process according to claim 1, characterized in that: In the second stage of scanning in step (3), the linear parallel path scanning spacing is 20-90% of the spot diameter, the laser energy density is adjusted to 1-3 J / cm², and the scanning speed is 500-1000 mm / s.

6. The process according to claim 1, characterized in that: The CMP in step (4) uses an alkaline polishing solution with pH 10-12, a double-sided polishing pressure of 400-500 g·cm⁻², and a polishing temperature of 20-25℃.

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