Method for laser-assisted chemical mechanical polishing of semiconductor wafer

Abstract

The invention discloses a method for laser-assisted chemical mechanical polishing of a semiconductor wafer. According to the method, a semiconductor wafer is firstly subjected to chemical pretreatment, and then heat treatment and ultraviolet irradiation are combined to optimize the surface conditions of the wafer. And outputting shaped flat-top laser by combining with a pulse laser, sequentially scanning the semiconductor wafer through a dual-wavelength laser sequence, and optimizing a modification effect by adopting a non-linear laser scanning path so as to realize a pretreatment process of the laser. And finally, performing chemical mechanical polishing on the wafer subjected to laser pretreatment so as to obtain a final finished product sample piece. The method has the advantages of being simple, efficient, high in repeatability and the like, and the efficiency and quality of subsequent chemical mechanical polishing of semiconductor wafers 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 method for laser-assisted chemical mechanical polishing of a semiconductor wafer. Background Art

[0002] In the field of semiconductor and advanced material processing, semiconductor materials such as silicon carbide have attracted widespread attention due to their special physical and chemical properties. This type of semiconductor has the advantages of high hardness, high thermal conductivity, good chemical stability and strong oxidation resistance, which makes it very suitable for manufacturing high-performance electronic devices, especially those working in high-frequency, high-power and high-temperature environments. However, the processing of hard and brittle semiconductors is very difficult, and conventional processing methods often cannot meet the requirements for material surface quality in the subsequent finishing process.

[0003] Chemical mechanical polishing (CMP) is a key technology used in the semiconductor industry to flatten the surface of wafers. Although CMP is a mature technology, due to the high hardness of semiconductor materials such as silicon carbide, polishing them using the CMP method faces many challenges. Due to the low removal rate and low efficiency of semiconductor wafers during the CMP polishing process, the polishing time is prolonged, which increases manufacturing costs and reduces production efficiency. Therefore, improving the removal rate of semiconductor wafers in CMP is a technical problem that urgently needs to be solved.

[0004] In response to the above problems, researchers have begun to try to use laser technology to improve the polishing effect of semiconductor wafers in recent years. As a high-energy-density light source, laser can produce microstructural changes on the surface of materials, thereby regulating the surface properties of materials. Among them, laser-assisted modification process is considered to be an effective method, which aims to change the surface state of semiconductor materials by using laser treatment before CMP, in order to improve the removal efficiency of CMP. Summary of the invention

[0005] (I) Purpose of the invention

[0006] The purpose of the present invention is to provide a new laser processing process for semiconductor wafers before chemical mechanical polishing by integrating and optimizing strategies such as wafer pretreatment, beam shaping, multi-wavelength compounding, and nonlinear scanning, in order to address the problems of uneven energy and unclear modification effect in the existing laser modification process during the processing.

[0007] (II) Technical solution

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

[0009] (1) First, the semiconductor wafer is placed in anhydrous ethanol for chemical pretreatment, the surface is cleaned and dried, and then placed in a muffle furnace to be heated in an oxygen atmosphere and the surface of the wafer is irradiated with ultraviolet light;

[0010] (2) Integrate the beam shaping device into the pulsed laser to convert the Gaussian spot output by the laser into a flat-top spot;

[0011] (3) placing the semiconductor wafer on a processing table and scanning the semiconductor wafer with two wavelengths of laser light respectively, wherein the two wavelengths of laser light act on the surface of the semiconductor wafer in the same processing path in succession at a set time interval;

[0012] (4) Pre-designing the nonlinear scanning paths of the two wavelength lasers through a program;

[0013] (5) starting the femtosecond laser, setting laser parameters, and starting laser modification processing on the semiconductor wafer;

[0014] (6) Performing chemical mechanical polishing on the semiconductor wafer after laser modification.

[0015] Furthermore, in step (1), the oxygen flow rate is 20-50 sccm, the heating temperature is 900-1100° C., the ultraviolet light wavelength is 200-350 nm, and the irradiation time is 20-40 min.

[0016] Furthermore, the pulse laser in step (2) is a femtosecond, picosecond or nanosecond laser.

[0017] Furthermore, in the step (3), the laser wavelength for the first scan is 350-400 nm, and the laser wavelength for the subsequent scan is 700 nm-1200 nm.

[0018] Furthermore, the scanning time interval in step (3) is 2-4s.

[0019] Furthermore, the nonlinear scanning path in step (4) is spiral or annular.

[0020] Furthermore, the laser parameters in step (5) include laser pulse width, laser power, pulse frequency, scanning speed, scanning spacing, and scanning times, and their values ​​are set to 50fs-10ns, 20W-40W, 100KHz-1 MHz, 100mm / s-1000mm / s, 20μm-100μm, and 5-20 times, respectively.

[0021] (III) Beneficial effects

[0022] The above technical solution of the present invention has the following beneficial technical effects:

[0023] (1) The heat treatment combined with the ultraviolet light irradiation semiconductor wafer process in the present invention can activate the surface of the semiconductor wafer, which is beneficial to the laser modification process.

[0024] (2) The beam shaping process of the present invention can increase the uniformity of the laser processing process, reduce local overheating and thermal stress concentration, and thus reduce the possibility of significant material damage.

[0025] (3) The multi-wavelength composite process proposed in the present invention can realize the structural component reconstruction of the surface layer and the heat-affected zone respectively, further optimize the modified layer, and help improve the polishing effect of the subsequent CMP.

[0026] (4) The nonlinear laser scanning strategy proposed in the present invention can enable the laser to produce uniform energy distribution and photothermal effect on the silicon carbide surface, further regulating the modification effect and surface morphology. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic flow chart of the method for processing semiconductor wafers in the present invention.

[0028] Figure 2 This is a comparison chart of the average material removal rate (MRR) of the CMP solution obtained in Example 1 and the laser modification + CMP solution within 3 hours of polishing time.

[0029] Figure 3 This is the SEM effect picture of the SiC wafer surface polished by the laser modification + CMP scheme obtained in Example 1. DETAILED DESCRIPTION

[0030] 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.

[0031] Embodiment 1:

[0032] (1) A SiC wafer with a diameter of 5 cm was ultrasonically cleaned in anhydrous ethanol for 15 min, and then placed in a muffle furnace and heated in an oxygen atmosphere, wherein the oxygen flow rate was 20 sccm and the heating temperature was 1000°C. Simultaneously, 254 nm ultraviolet light was used to irradiate the wafer surface for 20 min.

[0033] (2) The beam shaping device is integrated into the femtosecond laser to convert the output Gaussian beam into a flat-top beam.

[0034] (3) The SiC wafer is placed on a processing table and scanned using two laser wavelengths. The first laser has a wavelength of 343 nm and the second laser has a wavelength of 1026 nm. The scanning time interval between the two laser wavelengths is 2 s, and the two lasers act on the surface of the SiC wafer in the same processing path.

[0035] (4) The scanning paths of the two wavelength lasers are set to a circular shape through the program.

[0036] (5) Start the femtosecond laser, set the laser pulse width, laser power, pulse frequency, scanning speed, scanning spacing, and scanning times to 230 fs, 20 W, 100 kHz, 100 mm / s, 50 μm, and 20 times, respectively, and start laser modification of the SiC wafer.

[0037] (6) The SiC wafer after laser modification is subjected to chemical mechanical polishing for 3 hours, and the polished sample is the final product.

[0038] Test results: Figure 2 The average material removal rate (MRR) of the CMP scheme and the laser modification + CMP scheme obtained in Example 1 within a polishing time of 3 hours. It can be seen that the MRR of the laser modification + CMP scheme is improved by about six times compared with the original CMP method.

[0039] Figure 3 The SEM renderings of the SiC wafer surfaces polished by the CMP scheme and the laser modification + CMP scheme obtained in Example 1 show that the wafer surface after the laser modification + CMP scheme has excellent surface smoothness and is free of defects such as holes and cracks.

[0040] 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 method for laser-assisted chemical mechanical polishing of a semiconductor wafer, characterized in that The steps include: (1) First, the semiconductor wafer is placed in anhydrous ethanol for chemical pretreatment, the surface is cleaned and dried, and then placed in a muffle furnace to be heated in an oxygen atmosphere and the surface of the wafer is irradiated with ultraviolet light; (2) Integrate the beam shaping device into the pulsed laser to convert the Gaussian spot output by the laser into a flat-top spot; (3) placing the semiconductor wafer on a processing table and scanning the semiconductor wafer with two wavelengths of laser light respectively, wherein the two wavelengths of laser light act on the surface of the semiconductor wafer in the same processing path in succession at a set time interval; (4) Pre-designing the nonlinear scanning paths of the two wavelength lasers through a program; (5) starting the femtosecond laser, setting laser parameters, and starting laser modification processing on the semiconductor wafer; (6) Performing chemical mechanical polishing on the semiconductor wafer after laser modification.

2. The method for laser-assisted chemical mechanical polishing of a semiconductor wafer according to claim 1, characterized in that: In the step (1), the oxygen flow rate is 20-50 sccm, the heating temperature is 900-1100° C., the ultraviolet light wavelength is 200-350 nm, and the irradiation time is 20-40 min.

3. The method for laser-assisted chemical mechanical polishing of a semiconductor wafer according to claim 1, characterized in that: The pulse laser in step (2) is a femtosecond, picosecond or nanosecond laser.

4. The method for laser-assisted chemical mechanical polishing of a semiconductor wafer according to claim 1, characterized in that: In the step (3), the laser wavelength for the first scan is 350-400 nm, and the laser wavelength for the second scan is 700 nm-1200 nm.

5. The method for laser-assisted chemical mechanical polishing of a semiconductor wafer according to claim 1, characterized in that: The scanning time interval in step (3) is 2-4s.

6. The method for laser-assisted chemical mechanical polishing of a semiconductor wafer according to claim 1, characterized in that: The nonlinear scanning path in step (4) is spiral or circular.

7. The method for laser-assisted chemical mechanical polishing of a semiconductor wafer according to claim 1, characterized in that: The laser parameters in step (5) include laser pulse width, laser power, pulse frequency, scanning speed, scanning spacing, and scanning times, and their values ​​are set to 50fs-10ns, 20W-40W, 100KHz-1 MHz, 100mm / s-1000mm / s, 20μm-100μm, and 5-20 times, respectively.

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