次世代半導体ガラス基板への微細レーザー加工を実現

In recent years, glass has attention as a core material for substrates and interposers due to its excellent highfrequency characteristics and coefficient of thermal expansion (CTE) similar to silicon. In such applications, it is necessary to create a large number of fine through-holes in the glass. Currently, these vias are drilled using ultrafast laser induced selective etching. However, this process involves the use of hydrofluoric acid (HF), a hazardous substance, which poses a significant issue. Consequently, a direct laser processing technique is highly anticipated. In this study, we report on the direct laser drilling of glass without the use of etching. Using an ultrashort-pulse laser with a wavelength of 257 nm, we successfully drilled fine holes in 100μ m-thick ENA1 glass. Laser processing was performed with a pulse energy of 4μ J and 200 shots, achieving hole formation with a pitch of 25μ m and a hole diameter of 6μ m. The aspect ratio of the holes was 16.7, and the time required to drill a single hole was 4 ms. Furthermore, to investigate which laser parameters are crucial for creating high-aspect-ratio holes in thicker ENA1 glass, we collected data on the relationship between pulse energy, number of pulse, and hole geometry. The results revealed that hole depth is limited by pulse energy. The aspect ratio does not change largely since higher pulse energy makes larger hole diameter in high pulse energy region.