KR-20260067795-A - Laser processing method for removing wafer surface hardened layer

KR20260067795AKR 20260067795 AKR20260067795 AKR 20260067795AKR-20260067795-A

Abstract

The laser processing method for removing a hardened layer on a wafer surface according to the present invention may include a lapping step for polishing the surface of a wafer to match the flatness and parallelism of a wafer cut to a predetermined thickness; a laser surface polishing step for removing a physically damaged layer formed on the surface of the wafer during the lapping step by irradiating a primary laser beam onto the wafer surface after the lapping step is completed; a trimming step for removing a hardened layer formed on the surface of the wafer during the laser surface polishing step by irradiating a secondary laser beam onto the wafer surface after the laser surface polishing step is completed; and a CMP step in which the surface of the wafer is chemically mechanically polished to control the roughness of the wafer surface and remove foreign substances after the trimming step is completed.

Inventors

김영국
조현호
김준호
최진영
정지훈
차병철

Assignees

한국생산기술연구원

Dates

Publication Date: 20260513
Application Date: 20241106

Claims (9)

A lapping step for polishing the surface of a wafer cut to a predetermined thickness to match the flatness and parallelism of the wafer; A laser surface polishing step of irradiating a primary laser beam onto the wafer surface after the above lapping step is completed to remove a physically damaged layer formed on the surface of the wafer during the above lapping step; A trimming step of irradiating a secondary laser beam onto the wafer surface where the laser surface polishing step is completed to remove the hardened layer formed on the wafer surface during the laser surface polishing step; and A laser processing method for removing a wafer surface hardened layer, comprising a CMP step in which the surface of the wafer is chemically mechanically polished to control the roughness of the wafer surface and remove foreign substances after the above trimming step is completed.
In paragraph 1, A laser processing method for removing a hardened wafer surface layer, wherein after the laser surface polishing step, the hardness of the wafer surface increases compared to before the laser surface polishing step, and after the trimming step, the hardness of the wafer surface decreases compared to before the laser surface polishing step.
In paragraph 1, A laser processing method for removing a wafer surface hardened layer, wherein in the trimming step, the secondary laser beam is irradiated with a lower power than the primary laser beam.
In paragraph 1, A laser processing method for removing a wafer surface hardened layer, wherein the pulse width of the laser irradiated in the laser surface polishing step and the trimming step is 1000 fs or less.
In paragraph 1, A laser processing method for removing a hardened layer on the surface of a wafer, wherein the wafer has a Mohs hardness of 9.3 or higher.
In paragraph 1, A laser processing method for removing a hardened wafer surface layer, wherein the wafer is SiC.
In paragraph 6, A laser processing method for removing a wafer surface hardened layer, wherein the secondary laser beam power in the trimming step is 5 W or less.
In Paragraph 7, A laser processing method for removing a wafer surface hardened layer, wherein the hardness of the wafer surface after trimming one or more times in the above trimming step is less than or equal to the hardness of the wafer surface prior to the above laser surface polishing step.
In Paragraph 7, A laser processing method for removing a hardened wafer surface layer, wherein the Vickers hardness of the wafer surface is 2100 Hv or less after trimming five or more times in the above trimming step.

Description

Laser processing method for removing wafer surface hardened layer The present invention relates to a laser processing method for removing a hardened layer on a wafer surface, and more specifically, to a process that replaces a conventional stock polishing process by irradiating a laser onto a wafer surface to polish a SiC surface without water and slurry, and can remove the hardened layer on the wafer surface, whose hardness has increased through laser surface polishing, by trimming. The SiC power semiconductor market is expected to experience continuous growth as it replaces Si devices in the automotive, energy, and ICT sectors. Since SiC wafers are approximately 10 to 15 times more expensive than Si wafers of the same size, improvements in the surface polishing process can generate high added value. SiC possesses an dielectric breakdown electric field strength about 10 times higher than Si, allowing it to withstand 10 times higher voltages, thereby enabling high output and miniaturization. Additionally, its thermal conductivity is about three times higher than Si, ensuring stability during heat generation such as high-speed charging and prolonged operation. Notably, while it exhibits excellent durability due to its high Mohs hardness, it has the disadvantage of being difficult to process. Figure 1 shows conventional SiC This is a schematic diagram of a wafer surface polishing process. As shown in FIG. 1, the process of polishing the surface of a wafer (W) mainly includes a lapping step for processing the thickness of the cut wafer (W) after cutting the wafer (W), a stock polishing step for removing a damaged layer on the surface of the wafer (W), and a CMP step for securing surface roughness. The lapping step takes about one hour to polish the surface of the wafer (W) to about 60 to 140 µm, the stock polishing step to remove the damaged layer formed on the surface of the wafer (W) takes about one to four hours to polish the surface of the wafer (W) to about 2 to 11 µm, and the CMP step to ensure surface roughness takes about one hour to polish the surface of the wafer (W) to about 1 to 2 µm. The stock polishing step proceeds by supplying a slurry containing an abrasive between the polishing pad and the wafer, and by rotating the work table so that the wafer surface and the slurry come into contact with the polishing pad, thereby polishing the surface of the wafer (W). As described above, the time required for the stock polishing step in the wafer surface polishing process accounts for a large proportion of the total wafer surface polishing process, and the slurry must be continuously supplied during the stock polishing step, and as the wafer (W) surface is subjected to pressure for a long time by the polishing head, the wafer (W) is stressed, increasing the possibility of defects occurring. To address this, if the stock polishing step is replaced with laser beam processing, the SiC wafer surface hardens at high temperatures during rapid polishing with high laser energy. Thermal hardening occurs on the SiC wafer due to direct laser processing, increasing surface hardness, which acts disadvantageously for subsequent machining processes (such as CMP). Therefore, research is needed on a laser processing method to solve the aforementioned problems, which reduces environmental pollution caused by mechanical and chemical polishing methods while simultaneously removing the hardened layer on the wafer surface. Figure 1 is a schematic diagram of a conventional SiC wafer surface polishing process. FIG. 2 is a schematic diagram of a device for removing a surface hardened layer of a wafer using a laser according to one embodiment of the present invention. FIG. 3 is a schematic diagram of a wafer surface hardening layer removal process using a laser according to one embodiment of the present invention. Figure 4 is a graph showing the polishing thickness (Step height) according to the number of laser surface polishing processes (Pass array) using a primary laser beam according to an embodiment of the present invention. Figure 5 is a graph showing Vickers hardness according to the number of laser surface polishing processes (pass array) using a primary laser beam according to one embodiment of the present invention. FIG. 6 is a graph showing the polishing thickness (Step height) according to the number of trimming passes using a secondary laser beam according to an embodiment of the present invention. Figure 7 is a graph showing Vickers hardness according to the number of trimming passes using a secondary laser beam according to one embodiment of the present invention. FIG. 8 is an example of SiC wafer processing according to a laser surface polishing process (Pass array) using a primary laser beam and a trimming process (Trimming Pass) using a secondary laser beam according to an embodiment of the present invention. Specific embodiments of the present invention will be described in detail below with reference to the dra