飞秒激光加工4H-SiC时用于深度精确晶圆切片的自聚焦控制
Self-Focusing Control for Depth-Precise Wafer Slicing of 4H-SiC in Femtosecond Laser Processing
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中文总结 AI 辅助
该研究针对4H-SiC晶圆飞秒激光切片的深度控制问题，结合实验与模拟揭示自聚焦行为与切片质量的关联，构建可加工性图为激光参数优化提供实用指导。
中文摘要 AI 辅助
4H-SiC作为第三代芯片材料，凭借优异的热导率和高击穿场强，能在电力电子应用中实现高功率密度和更高开关频率。随着芯片架构向三维及异质集成发展，机械和热设计空间收窄，良率风险增大。特别是先进封装要求中间工艺的晶圆减薄至<100μm，以缩短互连并控制热机械应力。飞秒激光切片用于4H-SiC晶圆，提供了一种非接触加工方法，可生产低缺陷的薄层，但强光学非线性掩盖了激光参数与切片质量的关系。本文结合实验、半经验分析模型和数值光线光学模拟，系统研究飞秒激光在4H-SiC切片中克尔效应诱导的自聚焦。研究表明，脉冲能量与加工深度的相互作用决定自聚焦行为，其与分离后的表面纹理参数和分离应力直接相关，从而将非线性光束传播与切片质量关联起来。基于该关系，在归一化辐照度背景下，定义了脉冲能量-自聚焦深度空间中的可加工性图。分析上，该模型将Marburger公式扩展至聚焦光束，用归一化辐照度替代功率比。光线光学模拟捕捉自聚焦点的几何特征，并通过实验观察验证。在物理定义的阈值内，该可加工性图直接将激光参数与分离应力和表面纹理指标关联，为超越试错法的深度控制提供实用指导。
英文摘要
4H-SiC has emerged as a third-generation chip material because its superior thermal conductivity and high breakdown field enable the material to achieve high power density and higher switching frequencies in power-electronics applications. As chip architectures evolve toward 3D and heterogeneous integration, the mechanical and thermal design space tightens while yield risks grow. In particular, advanced packages require mid-process wafer thinning to < 100 $μ$m to shorten interconnects and control thermo-mechanical stress. Femtosecond laser slicing for 4H-SiC wafers offers a non-contact processing approach to produce thin layers with low defects, while strong optical nonlinearities obscure the relationship between the laser parameters and the resulting slicing quality. Here, we systematically investigate Kerr-induced self-focusing using a femtosecond laser in 4H-SiC slicing by combining experiments, a semi-empirical analytical model, and numerical ray optics simulations. We demonstrate that the interplay between pulse energy and processing depth governs the self-focusing behavior, which directly correlates with post-separation surface texture parameters and separation stress, thereby linking nonlinear beam propagation to slicing quality. Based on this relationship, we define a processability map in the pulse energy with self-focusing depth space over a normalized irradiance background. Analytically, the model extends the Marburger formula to focused beams by replacing the power ratio with a normalized irradiance. Ray optics simulations capture the geometric features at the self-focusing point and are validated against experimental observations. Within physically defined thresholds, the processability map directly connects laser parameters to separation stress and surface texture metrics, providing practical guidance for depth control beyond trial-and-error.
