松本 歩

In gallium arsenide (GaAs) semiconductor devices, wafer warpage caused by backside electrode stress complicates wafer handling during subsequent processing and affects device characteristics. Warpage has been primarily attributed to a high-stress nickel–gallium–arsenide (Ni3GaAs) reaction layer that forms at the interface between the electroless Ni–P plating film and the GaAs substrate during annealing at 240 °C for 1 h. In this study, the crystallinity of the Ni3GaAs layer and its lattice-matching state with the GaAs substrate were investigated using transmission electron microscopy. Ni3GaAs grew epitaxially, with its (0-111) plane aligned with the GaAs(001) plane, and four differently oriented microtwin crystals coexisted. Each microtwin crystal exhibited a columnar morphology approximately 10 nm in width and was aligned along the [001] GaAs direction. Ni3GaAs crystals were lattice-matched to the (220) and (2–20) planes perpendicular to the GaAs(001) surface and exhibited 0.8% compression and 3.3% elongation in the Ni3GaAs [01-12] and [2-110] directions, respectively, resulting in an average tensile strain of 1.3%. This strain was identified as the cause of wafer warpage. These findings clarify the microstructure and lattice strain characteristics of the Ni3GaAs alloy layer, contributing to a better understanding of crystal growth at the Ni3GaAs/GaAs interface and informing optimization strategies for GaAs device manufacturing.

This study represents the first use of porous silicon as a substrate in underwater LIBS for detecting dissolved elements.