An Analysis of Edge Chipping in LiTaO₃ Wafer Grinding Using a Scratch Test and FEA Simulation

Abstract

Lithium tantalite (LiTaO3) is a representative multifunctional single-crystal material with electro-optical, acoustic, piezoelectric, pyroelectric, and nonlinear optical properties used as a substrate for surface acoustic wave (SAW) devices. To enhance SAW device performance, thinner LiTaO3 substrates with improved surface roughness are desired. Chemical mechanical polishing (CMP) is employed to achieve the desired surface roughness after grinding. However, the thinning process increases the risk of substrate fracture, especially at the edges, resulting in edge chipping. Edge chipping can lead to complete substrate failure during SAW device fabrication, requiring an effective wafer geometry to prevent it. The study utilizes scratch tests and finite element analysis (FEA) to identify the optimal edge shape (C-cut, trimmed, and thinned) for preventing edge chipping on LiTaO3 wafers. The C-cut edge refers to the rounding of the wafer’s edge, while the trimmed edge refers to the machining of the wafer’s edge to be perpendicular to the wafer surface. As a result of the scratch tests, we observed edge-chipping lengths of 115 and 227 μm on the C-cut and trimmed edges, respectively, while the thinned edge (half C-cut) resulted in complete wafer fracture. In the finite element analysis (FEA), edge-chipping lengths of 80, 120, and 150 μm were obtained on the C-cut, trimmed, and thinned edges (half C-cut), respectively. In conclusion, it has been confirmed that the C-cut, trimmed, and thinned edge shapes are effective in preventing edge chipping. However, considering that the C-cut edge shape becomes thinner through grinding, using the trimmed edge shape appears to be the most effective.

Keywords

• edge chipping
• finite element analysis (FEA)
• lithium tantalite (LiTaO₃)
• surface acoustic wave (SAW) device
• scratch test