Laser-chemical composite surface planarization process based on laser stripping sheet

Abstract

The invention discloses a laser-chemical composite surface planarization process based on a laser stripping sheet. The method comprises the following steps: firstly, carrying out surface scanning on the surface of a wafer subjected to laser-ultrasonic stripping by adopting femtosecond laser, thinning the wafer to a first target thickness through an ultra-short pulse cold working mechanism, and optimizing the sharp corner fluctuation of the surface at the same time; then immersing the wafer into a hydrofluoric acid-nitric acid mixed solution containing a platinum / iridium catalyst, accurately etching the residual sharp corner by utilizing a selective catalytic reaction of a contact point of a catalyst plate and the wafer, and feeding back and adjusting processing parameters in real time through a morphology monitoring module and an infrared thermal imaging system; and finally, thinning to the required thickness by adopting chemical mechanical polishing, and obtaining an atomic-scale flat surface. According to the technology, through the synergistic effect of laser pre-thinning and chemical etching, the problems that a traditional grinding technology is low in efficiency and large in material consumption are solved, and the technology has the advantages of being efficient, low in damage, high in precision and the like and is suitable for surface treatment of hard semiconductor wafers 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 laser-chemical composite surface planarization process based on a laser peeling sheet. Background Art

[0002] With the progress of semiconductor manufacturing technology, the laser stealth processing combined with the ultrasonic-assisted peeling process has gradually become the mainstream technology in wafer manufacturing due to its advantages such as high efficiency and low stress. This technology forms a stealth cutting layer inside the wafer through laser, and then uses ultrasonic waves to achieve precise separation of materials. It is especially suitable for brittle materials such as silicon carbide and gallium nitride, and can significantly reduce the problems of edge cracks and chipping. However, after separation, this process will form undulating sharp corners with a height of 40 - 50 μm on the wafer surface, and these sharp corners need to be completely removed through subsequent thinning and planarization processes to meet the strict requirements of surface flatness for processes such as lithography and coating.

[0003] Currently, the industrial process chain mainly relies on mechanical grinding and chemical mechanical polishing (CMP) to process such surface defects. Traditional mechanical grinding gradually thins the wafer and reduces the height of the sharp corners through rough grinding and fine grinding, but the high hardness and uneven distribution in the sharp corner area lead to serious grinding wheel wear, low processing efficiency, and easy introduction of subsurface damage and microcracks. In addition, alternative solutions such as chemical etching or laser polishing are difficult to balance efficiency and surface quality due to their isotropic etching characteristics or thermal damage problems, further restricting their applications.

[0004] In view of the above problems, the present invention proposes a laser-chemical composite surface planarization process. This process reduces the height of the sharp corners and the amount of material removal through femtosecond laser pre-thinning, combines catalytic selective etching technology to precisely remove the remaining sharp corners, and finally uses CMP to achieve atomic-level surface flatness. The cold processing characteristics of femtosecond laser avoid thermal damage, catalytic etching selectively removes the sharp corner area through local reactions, and CMP only needs to remove a micron-level allowance to complete the fine repair. Compared with traditional processes, this method significantly reduces grinding wheel wear and processing time, and at the same time avoids subsurface damage, providing an efficient and reliable solution for the manufacture of high-precision semiconductor devices. Summary of the Invention

[0005] (1) Objects of the Invention

[0006] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a laser-chemical composite surface planarization process based on a laser peeling sheet, aiming to effectively remove the sharp corner undulations of the laser peeling sheet and improve processing efficiency.

[0007] (2) Technical Solutions

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

[0009] (1) Pretreat the surface of the semiconductor wafer after laser stealth machining combined with ultrasonic-assisted separation. The wafer surface has undulating sharp corners with a size of 40 - 50 μm;

[0010] (2) Use femtosecond laser to perform multi-pass surface scanning on the wafer surface, reduce the wafer thickness from the initial 425 ± 25 μm to 380 ± 5 μm, and reduce the surface sharp corner undulation to 15 - 20 μm;

[0011] (3) Immerse the wafer processed in step (2) into a chemical etching solution containing a catalyst, utilize the selective catalytic reaction at the contact points between the catalyst plate and the wafer surface to precisely remove the sharp corner area, and monitor the wafer surface temperature in real time through an infrared thermal imager to avoid local over-etching caused by reaction heat release until the surface sharp corners are completely removed and the surface roughness Ra ≤ 0.1 μm;

[0012] (4) Perform chemical mechanical polishing (CMP) on the wafer processed in step (3) to obtain an atomically flat surface with the target thinned thickness.

[0013] Further, in step (1), the semiconductor wafer is one of single-crystal silicon carbide, single-crystal gallium nitride, or single-crystal diamond wafers;

[0014] Further, in step (2), the femtosecond laser has a wavelength of 343 - 1064 nm, a pulse width of 100 - 500 fs, an energy density of 2 - 15 J / cm 2 , a scanning speed of 50 - 1000 mm / s, adopts a Z-shaped or spiral progressive scanning path, the spacing between adjacent scanning paths is 50 - 80% of the laser spot diameter, and the spot overlap rate is controlled at 20 - 40%;

[0015] Further, in step (3), the chemical etching solution is a mixed solution of hydrofluoric acid and nitric acid with a volume ratio of 1:2 - 1:5. The catalyst plate is made of platinum or iridium metal, and has nano-scale grooves on its surface to enhance solution flow. The wafer and the catalyst plate move relative to each other in a coaxial rotation manner, and a contact pressure of 20 - 40 KPa is applied;

[0016] Further, in steps (3) and (4), a surface topography detection module is set up to monitor the sharp corner undulation height in real time through a white light interferometer, and feedback to adjust the femtosecond laser energy density or chemical etching time;

[0017] Further, in step (5), the chemical mechanical polishing adopts a combination of a polyurethane polishing pad and a silica colloidal polishing solution, the polishing temperature is maintained at 20 - 25 °C, an alkaline polishing solution with a pH of 9 - 11 is used, and the polishing pressure is 500 - 600 g·cm -2 .

[0018] (III) Beneficial Effects

[0019] The above technical solution of the present invention has the following beneficial technical effects:

[0020] (1) The femtosecond laser thinning removal / acute angle removal process proposed by the present invention can efficiently achieve the removal of the target thinning thickness, and at the same time significantly reduce the undulation degree of the peeling sheet.

[0021] (2) The selective catalytic acute angle removal process proposed by the present invention can achieve precise and controllable removal of the acute angle part with low consumable consumption.

[0022] (3) The dynamic working condition monitoring and parameter regulation process proposed by the present invention can adjust the processing parameters according to the acute angle removal situation to achieve low damage to the substrate and controllable removal of the acute angle. Description of the Drawings

[0023] Figure 1 It is a schematic process flow diagram of the semiconductor wafer processing of the present invention.

[0024] Figure 2 It is a cross-sectional morphology diagram of the original silicon carbide laser peeling sheet in Example 1.

[0025] Figure 3 It is a cross-sectional morphology diagram of the silicon carbide wafer obtained after femtosecond laser treatment in Example 1.

[0026] Figure 4 It is a surface morphology diagram of the silicon carbide wafer obtained after CMP treatment in Example 1. Detailed Embodiments

[0027] To make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the specific embodiments and with reference to the drawings. It should be understood that these descriptions are exemplary and not intended to limit the scope of the present invention.

[0028] Example 1:

[0029] (1) Pretreat the surface of the silicon carbide wafer after laser stealth processing combined with ultrasonic-assisted separation. The surface of the wafer has undulating acute angles of 40-60 μm.

[0030] (2) Perform surface scanning on the wafer surface with a femtosecond laser. The laser parameters are set as wavelength 343 nm, pulse width 209 fs, and energy density 4 J / cm 2, The scanning speed is 500 mm / s, and the Z-shaped scanning path is adopted. The spacing between adjacent scanning paths is 80% of the laser spot diameter, and the spot overlap rate is controlled at 40%. Through multi-pass scanning, the wafer thickness is thinned from the initial 450 μm to 380 ± 5 μm, and the surface corner undulation is reduced to 20 μm. A surface topography detection module is set up to monitor the corner undulation height in real time through a white light interferometer and feedback to adjust the femtosecond laser energy density.

[0031] (3) Immerse the wafer processed in step (2) into a chemical etching solution containing a catalyst. The chemical etching solution is a mixed solution of hydrofluoric acid and nitric acid with a volume ratio of 1:2. Utilize the selective catalytic reaction at the contact point between the catalyst plate and the wafer surface to precisely remove the corner area; the catalyst plate is made of platinum or iridium metal, and the surface is provided with nanoscale grooves to enhance the solution flow. The wafer and the catalyst plate move relative to each other in a coaxial rotation manner, and a contact pressure of 20 KPa is applied; set the surface topography detection module as in step (3), feedback to adjust the chemical etching time. In addition, monitor the wafer surface temperature in real time through an infrared thermal imager to avoid local over-etching caused by reaction heat release until the surface corners are completely removed and the surface roughness Ra ≤ 0.1 μm.

[0032] (4) Perform chemical mechanical polishing (CMP) on the wafer processed in step (3). Use an alkaline polishing solution with a pH of 10, a polishing pressure of 100 Pa, adopt a combination of a polyurethane polishing pad and a silica colloidal polishing solution, and maintain the polishing temperature at 25 °C to finally obtain an atomically flat surface with the target thinned thickness.

[0033] Test results: Figure 2 For the cross-sectional morphology of the silicon carbide peeling sheet described in step (1) of Example 1, it can be found that there are corners with undulations of 40 - 60 μm. Figure 3 For the cross-sectional morphology diagram of the silicon carbide wafer obtained after femtosecond laser treatment in Example 1, the corner undulation is reduced to within 20 μm. Figure 4 For the surface optical microscopic morphology after CMP treatment in Example 1, it can be found that the surface corners are completely removed and have good surface finish.

[0034] It should be understood that the above specific embodiments of the present invention are only used for exemplary illustration or explanation of the principle 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 changes and modification examples falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A laser-chemical composite surface planarization process based on a laser lift-off sheet, characterized in that It includes the following steps: (1) Pretreat the surface of the semiconductor wafer after laser stealth machining combined with ultrasonic-assisted separation. The wafer surface has undulating sharp corners with a size of 40 - 60 μm; (2) Use femtosecond laser to perform multi-pass surface scanning on the wafer surface, reduce the wafer thickness from the initial 425 ± 25 μm to 380 ± 5 μm, and reduce the undulation of the surface sharp corners to 15 - 20 μm; (3) Immerse the wafer processed in step (2) into a chemical etching solution containing a catalyst, and utilize the selective catalytic reaction at the contact points between the catalyst plate and the wafer surface to precisely remove the sharp corner areas. Meanwhile, use an infrared thermal imager to monitor the wafer surface temperature in real time to avoid local over-etching caused by reaction heat release until the surface sharp corners are completely removed and the surface roughness Ra ≤ 0.1 μm; (4) Perform chemical mechanical polishing (CMP) on the wafer processed in step (3) to obtain an atomically flat surface with the target thinning thickness.

2. The laser-chemical composite surface planarization process based on a laser lift-off sheet according to claim 1, wherein, In step (1), the semiconductor wafer is one of single-crystal silicon carbide, single-crystal gallium nitride or single-crystal diamond wafers.

3. A laser-chemical composite surface planarization process based on a laser peeling sheet according to claim 1, characterized in that In the step (2), the femtosecond laser has a wavelength of 343 - 1064 nm, a pulse width of 100 - 500 fs, an energy density of 2 - 15 J / cm 2 , a scanning speed of 50 - 1000 mm / s, and adopts a zigzag or spiral progressive scanning path. The spacing between adjacent scanning paths is 50 - 80% of the laser spot diameter, and the spot overlap rate is controlled at 20 - 40%.

4. A laser-chemical composite surface planarization process based on a laser lift-off sheet according to claim 1, characterized in that In step (3), the chemical etching solution is a mixed solution of hydrofluoric acid and nitric acid with a volume ratio of 1:2 - 1:

5. The catalyst plate is made of platinum or iridium metal, and the surface is provided with nanoscale grooves to enhance solution flow. The wafer and the catalyst plate move relative to each other in a coaxial rotation manner, and a contact pressure of 20 - 40 KPa is applied.

5. A laser-chemical composite surface planarization process based on a laser lift-off sheet according to claim 1, characterized in that, In steps (3) and (4), a surface topography detection module is set up to monitor the undulation height of the sharp corners in real time through a white light interferometer, and feedback to adjust the femtosecond laser energy density and the chemical etching time.

6. A laser-chemical composite surface planarization process based on a laser peeling sheet according to claim 1, characterized in that, In step (5), chemical mechanical polishing is carried out using a combination of a polyurethane polishing pad and a silica colloidal polishing liquid. The polishing temperature is maintained at 20 - 25 °C, an alkaline polishing liquid with a pH of 9 - 11 is used, and the polishing pressure is 500 - 600 g·cm -2 .

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