Improvement of electrostatic damage resistance of photomasks with conductive ITO film fabricated using UAPS (UV-Assisted-Partial-Strip) method

The photomasks for contact-type lithography are vulnerable to electrostatic damage. In the present study, a conducting ITO material was introduced as a bridge between the chromium metal patterns to prevent electrostatic damage. The core of this research was to optimize the material and bridging structure to distribute the accumulated charges efficiently. On the other hand, when fabricating the bridging circuit, it is challengeable to deposit an ITO material without electrical disconnection due to the inevitable chromium undercut shape caused by isotropic etching during the wet etching process. A method called UV-Assisted-Partial-Strip (UAPS) was adopted in this study. UAPS induces a change in the solubility and erosion properties of resistance through irradiation with 365 nm light and optimization of the alkaline solution process. Focused ion beam-scanning electron microscopy confirmed that the conducting ITO film was deposited without electrical disconnection on the side of the chromium pattern over the entire area of the photomask. ITO thin film was optimized 20 nm-thick, 3.0 x 10(2) omega/ sheet resistance, and about 84% transmittance. The subsequent hand roller test and electrostatic discharge immunity test showed that the initiation voltage of the electrostatic melted-typed defect had been increased remarkably.

Automated summary

This study aimed to prevent electrostatic damage to contact-type lithography photomasks by using a conducting ITO material as a bridge between chromium metal patterns, optimizing the deposition process with a method called UV-Assisted-Partial-Strip (UAPS). The conducting ITO film was successfully deposited without electrical disconnection, increasing the initiation voltage of electrostatic defects.