Hard and brittle semiconductor substrate double-sided thinning process based on ultrafast laser

Abstract

The invention discloses a hard and brittle semiconductor substrate double-sided thinning process based on ultrafast laser. According to the process, firstly, the two faces of a wafer are activated through ion implantation or a chemical solution at a high temperature, and a surface layer material is softened to reduce the machining difficulty; then fixing the wafer in a laser modification chamber, synchronously updating the solution in the chamber by dynamically circulating the corrosive liquid, and removing laser by-products; then two beams of ultrafast laser are used for synchronously scanning the upper surface and the lower surface of the wafer respectively, in the first stage, double-face efficient thinning is achieved through a non-linear path, in the second stage, a linear parallel path is switched, the direction of the wafer is adjusted, and morphology regulation and control of the microstructure and double-face precise finishing are completed; and finally, the allowance is removed through double-sided chemical mechanical polishing (CMP), and the target thinning amount and the atomic-scale flat surface are obtained. The process has the advantages of high efficiency, low damage and high precision through double-sided collaborative processing and dynamic corrosive liquid control, and is suitable for large-scale thinning manufacturing of hard and brittle semiconductor materials such as silicon carbide and gallium nitride.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser-assisted processing, and particularly relates to a double-sided thinning process for hard and brittle semiconductor substrates based on ultrafast lasers. Background Art

[0002] With the continuous development of semiconductor devices towards miniaturization and high integration, wafer thinning technology has become a key link in advanced packaging and device manufacturing. For hard and brittle semiconductor materials such as silicon carbide (SiC) and gallium nitride (GaN), the cut wafers formed after ingot cutting will have subsurface defects, and the thickness is difficult to meet the requirements of subsequent processes such as lithography, and need to be thinned by about 50-100 μm through a thinning process. However, traditional thinning technologies face significant challenges when dealing with such high-hardness materials: although mechanical grinding can achieve rapid thinning, the intense friction between the grinding wheel and the sharp corner area easily leads to subsurface damage and microcracks, and the grinding wheel wears severely; while the single-sided laser thinning technology can reduce the introduction of damage, but the processing efficiency is low, and the deposition by-products generated by the laser action are difficult to remove in real time, which easily interferes with subsequent laser processing and leads to a decline in process stability.

[0003] In the prior art, single-sided laser thinning needs to rely on multiple cleaning and parameter adjustments to maintain processing accuracy, the overall efficiency is limited, and the two sides of the wafer cannot be processed synchronously, resulting in uneven stress distribution and warping risks. In addition, the surface residues (such as amorphous layers, etc.) after laser processing need to be removed through additional chemical etching or polishing steps, further increasing the process complexity and cost.

[0004] To address the above problems, the present invention proposes a double-sided thinning process for hard and brittle semiconductor substrates based on ultrafast lasers, which realizes the goals of high efficiency and low damage through the collaborative design of double-sided synchronous scanning, dynamic etching solution circulation, and phased path optimization. This process first softens the surface layer of the wafer through ion implantation or chemical activation to reduce the energy requirement for subsequent laser processing; then uses ultrafast lasers to perform non-linear path rough machining and linear path fine machining on both sides synchronously, and combines the dynamically updated etching solution to remove laser by-products in real time to avoid surface contamination; finally, achieves an atomically flat surface through double-sided chemical mechanical polishing (CMP). Compared with the traditional process, this method can effectively improve the thinning efficiency and provide a reliable solution for the high-precision manufacturing of hard and brittle semiconductor materials. Summary of the Invention

[0005] (I) Object of the Invention

[0006] Aiming at the deficiencies of the prior art, the object of the present invention is to provide a double-sided thinning process for hard and brittle semiconductor substrates based on ultrafast lasers, aiming to improve the efficiency and quality in the wafer thinning process.

[0007] (II) Technical Solution

[0008] The present invention is realized through the following technical solutions.

[0009] (1) Perform double-sided activation treatment on the hard and brittle semiconductor cutting wafer. Under high-temperature conditions, soften the double-sided surface layer materials through ion implantation technology or chemical solution immersion.

[0010] (2) Fix the activated wafer in the positioning device of the laser modification chamber. The chamber is equipped with a liquid feeding device and a suction filtration device, and maintain the concentration stability by dynamically circulating and updating the etching solution.

[0011] (3) Turn on the ultrafast laser 1 and the ultrafast laser 2, and synchronously scan the upper surface and the lower surface of the wafer respectively; The first-stage thinning: The ultrafast laser 1 scans the upper surface along a non-linear path, and the ultrafast laser 2 synchronously scans the lower surface along a non-linear path; Until the double-sided thinning depth reaches 40 ± 0.5 μm; The second-stage thinning: Adjust the laser energy density, rotate the wafer 90° through the positioning device, and the ultrafast laser 1 and the ultrafast laser 2 are switched to linear parallel paths for scanning until the double-sided thinning depth reaches 4 ± 0.5 μm.

[0012] (4) Perform double-sided chemical mechanical polishing (CMP) on the thinned wafer, and finally achieve an atomic-level flat surface with a total thinning amount of 100 ± 0.5 μm and a surface roughness Ra < 1 nm.

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

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

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

[0016] Furthermore, the etching solution in step (2) is a mixed solution of hydrofluoric acid, nitric acid, sulfuric acid and deionized water, and the volume ratios 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] Further, in the first-stage scanning of step (3), the non-linear scanning path is one or a combination of two of a spiral progressive path or a staggered 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 / cm 2 , and the scanning speed is 50 - 1000 mm / s.

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

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

[0020] (III) Beneficial effects

[0021] The above technical solutions of the present invention have the following beneficial technical effects:

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

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

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

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

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

[0027] Figure 3 is the surface optical microscopic morphology diagram obtained after the treatment in Example 1.

[0028] Figure 4 is the surface AFM morphology diagram obtained after the treatment in Example 1. Specific embodiments

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

[0030] Example 1:

[0031] (1) Perform double-sided activation treatment on a single-crystal silicon carbide cutting wafer. In an environment of 50 °C, soften the surface materials on both sides of the silicon carbide through a hydrofluoric acid / hydrogen peroxide mixed solution with a volume ratio of 1:4.

[0032] (2) Fix the activated wafer in the positioning device of the laser modification chamber. The positioning device includes a vacuum adsorption fixture with a positioning accuracy of ±0.1 mm and a rotation angle error of ≤0.5°. A liquid delivery device and a suction filtration device are installed in the chamber. The flow rate of the liquid delivery device is 50 - 200 mL / min, and the negative pressure of the suction filtration device is maintained at 0.1 - 0.5 Mpa. The etching solution is maintained at a stable concentration by dynamically circulating and updating it. The etching solution is a mixed solution of hydrofluoric acid, nitric acid, and deionized water, where the volume ratios of hydrofluoric acid, nitric acid, sulfuric acid, and deionized water are 20 vol%, 30 vol%, 5 vol%, and 45 vol% respectively.

[0033] (3) Turn on the ultrafast laser 1 and the ultrafast laser 2, and synchronously scan the upper surface and the lower surface of the wafer respectively; First-stage thinning: The ultrafast laser 1 scans the upper surface along a spiral progressive path, and the ultrafast laser 2 also synchronously scans the lower surface along a spiral progressive path. The pulse widths of both lasers are 209 fs, the wavelength is 1026 nm, and the energy density is 8 J / cm 2 , and the scanning speed is 200 mm / s; until the thinning depths on both sides reach 40 ± 0.5 μm; Second-stage thinning: Adjust the laser energy density, rotate the wafer 90° through the positioning device, and the ultrafast laser 1 and the ultrafast laser 2 are switched to linear parallel path scanning. The scanning pitch is 60% of the spot diameter, and the laser energy density is adjusted to 2 J / cm 2 , and the scanning speed is 500 mm / s until the thinning depths on both sides reach 4 ± 0.5 μm.

[0034] (4) Perform double-sided chemical mechanical polishing (CMP) on the thinned wafer. Use an alkaline polishing solution with a pH of 10 - 12, and the double-sided polishing pressure is 500 g·cm- 2 , and the polishing temperature is 25 °C to achieve an atomic-level flat surface with a total thinning amount of 100 ± 0.5 μm and a surface roughness Ra < 1 nm.

[0035] Test results: Figure 3 and Figure 4 is the surface morphology diagram of the silicon carbide wafer obtained after the treatment of Example 1. It can be found that the surface has high glossiness and flatness.

[0036] It should be understood that the above specific embodiments of the present invention are only for illustrative explanation or interpretation of the principles of the present invention, and do not constitute a limitation to the present invention. Therefore, any modifications, equivalent replacements, improvements, etc. made without departing from the spirit and scope of the present invention shall be included within the protection scope of the present invention. In addition, the appended claims of the present invention are intended to cover all variations and modifications that fall 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, It includes the following steps: (1) Perform double-sided activation treatment on the hard and brittle semiconductor cutting wafer. Under high-temperature conditions, soften the surface materials on both sides through ion implantation technology or chemical solution immersion; (2) Fix the activated wafer in the positioning device of the laser modification chamber. The chamber is equipped with a liquid delivery device and a suction filtration device, and the etching solution is dynamically circulated and updated to maintain concentration stability; (3) Turn on the ultrafast laser 1 and the ultrafast laser 2, and synchronously scan the upper surface and the lower surface of the wafer respectively; First-stage thinning: The ultrafast laser 1 scans the upper surface along a non-linear path, and the ultrafast laser 2 synchronously scans the lower surface along 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° through the positioning device, and the ultrafast laser 1 and the ultrafast laser 2 are switched to linear parallel paths for scanning until the thinning depth on both sides reaches 4±0.5μm; (4) Perform double-sided chemical mechanical polishing (CMP) on the thinned wafer, and finally achieve an atomic-level flat surface with a total thinning amount of 100±0.5μm and a surface roughness Ra<1nm.

2. The process according to claim 1, characterized in that: The hard and brittle semiconductor wafer 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: In step (1), the high-temperature range is 50-100°C. For ion implantation activation treatment, an argon-oxygen mixed gas (volume ratio 3:1) plasma is used, the implantation energy is 20-200keV, and the treatment time is 5-20min; for chemical activation, a mixed solution of hydrofluoric acid and hydrogen peroxide (volume ratio 1:4-1:8) is used, and the soaking time is 5-10min.

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

5. The process according to claim 1, characterized in that: In step (2), the etching solution is a mixed solution of hydrofluoric acid, nitric acid, sulfuric acid and deionized water, and the volume ratios of hydrofluoric acid, nitric acid, sulfuric acid and deionized water are 15-20vol%, 30-40vol%, 0-10vol% and 30-55vol% respectively.

6. The process according to claim 1, characterized in that: In the first-stage scanning of step (3), the non-linear scanning path is one or a combination of two of a spiral progressive path or an interleaved 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 / cm 2 , and the scanning speed is 50 - 1000 mm / s.

7. The process according to claim 1, characterized in that: In the second-stage scanning of step (3), the scanning pitch of the linear parallel path is 20-90% of the spot diameter, and the laser energy density is adjusted to 1-3 J / cm 2 , and the scanning speed is 500-1000 mm / s.

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

Images