Effect of Laser Slicing on Stress and Wafer Shape of 4H-SiC Substrates

doi:10.16553/j.cnki.issn1000-985x.2025.0225

Abstract

Abstract: Under the background of the rapid development of third-generation semiconductors and the growing demand for large-size， low-warp 8-inch （1 inch=2.54 cm） 4H-SiC substrates， the traditional multi-wire sawing suffers from large material loss and limited capability in precisely controlling residual stress and wafer shape. However， the existing laser slicing studies are mostly focused on small-size or semi-insulating 4H-SiC， and a systematic understanding of the correlation among process parameters， residual stress， and wafer shape for conductive 8-inch 4° off-axis ingots under engineering conditions is still lacking. In this work， the 8-inch conductive N-type 4° off-axis 4H-SiC ingots are used as the research object. Internal modification is introduced by 1 064 nm picosecond laser irradiation combined with ultrasonic slicing， while the scanning speed （50~400 mm/s） is systematically varied. By means of SEM/TEM/SAED， Raman depth profiling， high-resolution XRD combined with the Stoney equation， lattice stress analysis and full-aperture wafer-shape measurements， a multi-scale evaluation chain is established from the microscopic modified layer to the macroscopic warp of the whole wafer. This paper clarifies the nucleation and propagation mechanism of SiC cracks along the ［11 $2 ˉ$ 0］ crystallographic direction induced by picosecond laser irradiation， and reveals influence of laser scanning speed on the slicing efficiency， stress distribution and wafer shape quality of 8-inch SiC substrates from both micro- and macro-perspectives. The paper provides theoretical support and process-optimization pathways for high-quality laser slicing fabrication of 8-inch 4H-SiC wafers， and offers a reference research idea for achieving controllable wafer shape tuning of SiC substrates based on laser-modified layers.

Key words: 4H-SiC wafer; picosecond laser slicing; equivalent residual stress; wafer shape; Warp

CLC Number:

O786

HU Haolin, LI Qizhi, SHE Wenjing, ZOU Xing, LU Zhitao, CHEN Gang, WANG Yingde, WAN Yuxi. Effect of Laser Slicing on Stress and Wafer Shape of 4H-SiC Substrates[J]. Journal of Synthetic Crystals, 2026, 55(3): 378-386.

Figures/Tables 4

Fig.1 Schematic diagrams of 8-inch 4H-SiC ingot and internal laser modification geometry. （a） Schematic diagram of laser incident from C-face and generating equally spaced modified sites inside the ingot；（b） schematic diagram of 4° off-axis 4H-SiC microscopic step structure， where modified sites are aligned along ［112ˉ0］ direction and tilted by about 4° with respect to physical horizontal plane

Fig.2 Microstructural characterization of laser-modified layer and crack network. （a） Cross-sectional SEM image prepared along ［112ˉ0］ direction at a scanning speed of v=300?mm/s without ultrasonic slicing；（b） magnified view of boxed region in Fig.2 （a）；（c） low-magnification TEM image of wafer cross-section （single-pulse energy increased to 50 μJ）；（d） high-magnification TEM image of interface between modified layer （region A） and unmodified substrate （region B）；（e） selected-area electron diffraction （SAED） pattern from region A；（f） SAED pattern from region B；（g） cross-sectional SEM image of substrate after ultrasonic slicing with modified surface facing upward；（h） micro-Raman spectra acquired on cross-section with modified surface facing upward at distances of 0， 1.3， 2.6， 3.9 and 10 μm from surface

Fig.3 Characterization of the average curvature radius based on XRD. （a） Schematic diagram of X-ray diffraction geometry；（b） on modified surface of each separated wafer， several radial positions R are selected from center to edge with a fixed step， and δ is measured point by point；（c） mechanical schematic diagram based on Stoney model； variation of sample δ-δˉ with radial coordinate R at 200~400 mm/s （d） and 50~100 mm/s （e）. The dashed lines are linear fits used to extract average curvature radius Rafter

Fig.4 Variation of curvature， equivalent average biaxial stress and wafer shape under different scanning speeds. （a） Variation of Rafter of separated wafers along ［112ˉ0］ direction and equivalent average biaxial stress?σeff calculated from Stoney equation with scanning speed v；（b） representative in-plane stress distribution maps obtained using a lattice stress analyzer；（c） variation of Warp index of 8-inch separated wafers with scanning speed v；（d） variation of Bow?index of 8-inch separated wafers with scanning speed v

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