Double-pulse sequence laser-assisted in-situ chemical etching method for improving semiconductor thinning efficiency

Abstract

The invention discloses a double-pulse-sequence laser-assisted in-situ chemical etching method for improving semiconductor thinning efficiency. The method comprises the following steps: firstly, placing a semiconductor wafer in a prepared chemical etching solution; then the liquid level height is adjusted, and nanosecond and ultrafast laser multi-focus flat-topped light beams are modulated through a spatial light modulator; then performing first processing on the semiconductor material in the ablation liquid by using nanosecond laser to realize removal at a specific depth, and then performing second processing by using ultrafast laser to remove a defect layer introduced by the nanosecond laser and optimize the quality of the substrate; and finally, the semiconductor material is taken out, and atomic-scale flattening processing is carried out through chemical mechanical polishing. The method has the advantages of high efficiency, high repeatability, high controllability and the like, and the thinning efficiency and quality of the semiconductor substrate can be effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of laser-assisted processing, and in particular relates to a double-pulse sequence laser-assisted in-situ chemical etching method for improving semiconductor thinning efficiency. Background Art

[0002] With the development of semiconductor technology, the importance of efficient and high-quality thinning technology in semiconductor wafer processing has become increasingly prominent. Traditional wafer thinning methods mainly rely on mechanical grinding and chemical mechanical polishing (CMP). Although these technologies can provide a higher surface flatness, they still have significant deficiencies in thinning efficiency, material removal rate, and wafer surface micro-damage control. Especially for high-hardness and high-brittle materials (such as silicon carbide, gallium nitride, etc.), these traditional methods are prone to cause micro-crack propagation or sub-surface damage, thereby reducing the performance of the wafer.

[0003] Laser-assisted thinning technology has attracted widespread attention due to its high precision, high flexibility and non-contact processing characteristics. However, processing methods using a single laser source (such as nanosecond laser or femtosecond laser) have difficulty in achieving a balance between material removal rate and surface quality control. Nanosecond lasers have a high material removal capacity, but are prone to produce thermal effects and oxidative modification layers during processing; while ultrafast lasers can achieve high-precision micromachining, their removal efficiency is relatively low, and it is difficult to effectively process deeper modified areas. In addition, the synergy between existing laser technology and chemical etching has not yet been fully developed, especially the optimization issues in in-situ processing.

[0004] In response to the above technical bottlenecks, the present invention proposes a dual-pulse sequence laser-assisted in-situ chemical etching method, which combines the efficient ablation capability of nanosecond lasers and the precise processing characteristics of ultrafast lasers, and cooperates with chemical etching technology to achieve dual optimization of high efficiency and surface quality in the wafer thinning process. The multi-focus flat-top beam shaping of the laser through a spatial light modulator (SLM) can further improve the processing efficiency and uniformity. At the same time, the in-situ action of the chemical etching solution reduces the residual heat effect and negative impact of the oxidized modified layer that may be generated during laser processing. This composite method can not only significantly improve the wafer thinning efficiency, but also effectively reduce the damage to the wafer surface during the processing process, providing a new technical approach for the manufacture of high-performance semiconductor devices. Summary of the invention

[0005] (I) Purpose of the invention

[0006] In view of the deficiencies in the prior art, the object of the present invention is to provide a dual-pulse sequence laser-assisted in-situ chemical etching method for improving semiconductor thinning efficiency, aiming 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 solutions.

[0009] (1) Cleaning the surface of the semiconductor wafer after multi-wire cutting or laser stripping and setting it aside;

[0010] (2) preparing a chemical etching solution, adjusting the liquid level to a suitable level, and immersing the semiconductor wafer in the etching solution;

[0011] (3) shaping the outgoing beams of the nanosecond laser and the ultrafast laser by a spatial light modulator to form multi-focus flat-top beams respectively;

[0012] (4) turning on the nanosecond laser, setting the laser parameters, and performing the first ablation modification on the semiconductor wafer under the etching solution;

[0013] (5) After the nanosecond laser ablation modification is completed, the ultrafast laser parameters are set to perform secondary processing on the nanosecond modified area;

[0014] (6) After the ultrafast laser processing is completed, the wafer is removed from the etching solution and then subjected to chemical mechanical polishing (CMP). The wafer after CMP is the final finished product sample.

[0015] Furthermore, the chemical etching solution in step (2) is a mixed solution of HNO3 / HF / deionized water, the volume ratio of which is 1:1:3, and the liquid level is 5-15 mm;

[0016] Furthermore, in step (3), the number of multi-focal points is 30-300, and the flat-top beam profile is a square;

[0017] Furthermore, in step (4), the nanosecond laser parameters include laser pulse width, laser wavelength, laser power, pulse frequency, scanning speed, scanning spacing, and scanning times, and their values ​​are set to 1-100ns, 343nm, 5W-50W, 10-100KHz, 10mm / s-100mm / s, 10-20μm, and 1-10 times, respectively;

[0018] Furthermore, in step (5), the ultrafast laser parameters include laser pulse width, laser wavelength, laser power, pulse frequency, scanning speed, scanning spacing, and scanning times, and their values ​​are set to 200fs-400ps, 343-1064nm, 4W-10W, 100KHz-1 MHz, 20mm / s-50mm / s, 10-25μm, and 1-5 times, respectively.

[0019] (III) Beneficial effects

[0020] The above technical solution of the present invention has the following beneficial technical effects:

[0021] (1) The multi-focus flat-top beam shaping process proposed in the present invention can achieve high-efficiency material surface modification, improve the flatness of the modified surface, and reduce the introduction of sub-surface defects.

[0022] (2) The in-situ high-temperature chemical etching process proposed in the present invention can simultaneously remove the laser-modified amorphous / oxidation products, ensure the surface quality, and further improve the reaction efficiency under the laser thermal effect.

[0023] (3) The dual-pulse sequence modification process proposed in the present invention can first achieve efficient thinning and removal of a large area at a specific depth, and then further remove the defect layer introduced by the previous nanosecond laser through the fine processing characteristics of the ultrafast laser, and significantly optimize the surface quality of the substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the process flow of SiC wafer processing according to the present invention.

[0025] Figure 2 It is the comprehensive material removal rate of the silicon carbide wafer obtained in Example 1. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the present invention more clear, the present invention is further described in detail below in combination with specific implementation methods and with reference to the accompanying drawings. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention.

[0027] Embodiment 1:

[0028] (1) Clean the surface of the silicon carbide wafer after multi-wire cutting or laser stripping and set it aside for later use.

[0029] (2) preparing a chemical etching solution and adjusting a suitable liquid level, wherein the chemical etching solution is a mixed solution of HNO3 / HF / deionized water, wherein the volume ratio thereof is 1:1:3 and the liquid level is 15 mm, and then immersing the semiconductor wafer in the etching solution.

[0030] (3) The output beams of the nanosecond laser and the ultrafast laser are shaped by a spatial light modulator to form multi-focus flat-top beams, respectively, where the number of focuses is 30 and the flat-top beam profile is a square.

[0031] (4) Turn on the nanosecond laser and set the laser parameters, including laser pulse width, laser wavelength, laser power, pulse frequency, scanning speed, scanning spacing, and scanning times, with the values ​​being set to 8 ns, 343 nm, 20 W, 100 kHz, 10 mm / s, 10 μm, and 5 times, respectively, to perform the first ablation modification on the semiconductor wafer under the etching solution.

[0032] (5) After the nanosecond laser ablation modification is completed, the ultrafast laser parameters are set to 209 fs, 1064 nm, 4 W, 100 kHz, 20 mm / s, 20 μm, and 5 times, respectively, to perform secondary processing on the nanosecond modified area;

[0033] (6) After the ultrafast laser processing is completed, the wafer is removed from the etching solution and then subjected to chemical mechanical polishing (CMP). The wafer after CMP is the final finished product sample.

[0034] Test results: Figure 2 The comprehensive material removal rate of the silicon carbide wafer obtained in Example 1 shows that the double-pulse sequence laser + in-situ etching process after shaping can greatly improve the thinning efficiency of the silicon carbide material.

[0035] It should be understood that the above specific embodiments of the present invention are only used to illustrate or explain the principles of the present invention, and do not constitute a limitation of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. In addition, the appended claims of the present invention are intended to cover all changes and modifications that fall within the scope and boundaries of the appended claims, or the equivalent forms of such scope and boundaries.

Claims

1. A double pulse sequence laser assisted in-situ chemical etching method for improving semiconductor thinning efficiency, characterized in that The steps include: (1) Cleaning the surface of the semiconductor wafer after multi-wire cutting or laser stripping and setting it aside; (2) preparing a chemical etching solution, adjusting the liquid level to a suitable level, and immersing the semiconductor wafer in the etching solution; (3) shaping the outgoing beams of the nanosecond laser and the ultrafast laser by a spatial light modulator to form multi-focus flat-top beams respectively; (4) turning on the nanosecond laser, setting the laser parameters, and performing the first ablation modification on the semiconductor wafer under the etching solution; (5) After the nanosecond laser ablation modification is completed, the ultrafast laser parameters are set to perform secondary processing on the nanosecond modified area; (6) After the ultrafast laser processing is completed, the wafer is removed from the etching solution and then subjected to chemical mechanical polishing (CMP). The wafer after CMP is the final finished product sample.

2. A double pulse sequence laser assisted in-situ chemical etching method for improving semiconductor thinning efficiency according to claim 1, characterized in that: The chemical etching solution in step (2) is a mixed solution of HNO3 / HF / deionized water, with a volume ratio of 1:1:3 and a liquid level of 5-15 mm.

3. The double pulse sequence laser assisted in-situ chemical etching method for improving semiconductor thinning efficiency according to claim 1, characterized in that: The number of multi-focal points in step (3) is 30-300, and the flat-top beam profile is a square.

4. The double pulse sequence laser assisted in-situ chemical etching method for improving semiconductor thinning efficiency according to claim 1, characterized in that: The nanosecond laser parameters in step (4) include laser pulse width, laser wavelength, laser power, pulse frequency, scanning speed, scanning spacing, and scanning times, and their values ​​are set to 1-100ns, 343nm, 5W-50W, 10-100KHz, 10mm / s-100mm / s, 10-20μm, and 1-10 times, respectively.

5. The double pulse sequence laser assisted in-situ chemical etching method for improving semiconductor thinning efficiency according to claim 1, characterized in that: The ultrafast laser parameters in step (5) include laser pulse width, laser wavelength, laser power, pulse frequency, scanning speed, scanning spacing, and scanning times, and their values ​​are set to 200fs-400ps, 343-1064nm, 4W-10W, 100KHz-1 MHz, 20mm / s-50mm / s, 10-25μm, and 1-5 times, respectively.

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