By Georgy K. Vinogradov, Masaharu Takeda, FOI Corp., Kanagawa, Japan

Highly selective SiO₂ etching plasma processes increasingly are required in manufacturing of ultralarge scale integrated circuits, where deep etching of silicon oxide (oxide) layers involves fluorocarbon deposition. Such processes, based on unsaturated fluorocarbons like c-C₄F₈, C₄F₆ or C₅F₈, have been developed and widely used in recent years. Because of special mechanisms of plasma chemical etching [1-3], it is difficult to etch high aspect ratio contact (HARC) holes without etch-stop or microloading effects under the conditions of high selectivity. In practice, thus, there is only one type of 200/300mm plasma etcher for highly selective SiO₂ etch, especially for HARC holes: narrow-gap parallel-plate capacitive. This article presents a different approach to address the requirements of these processes.

Capacitive reactive ion etching (RIE) tools (also known as two-frequency capacitive plasma sources) have had a long, useful life in the industry. For more than three decades of semiconductor plasma processing, there were no competitive tools around for one basic reason: a requirement of low gas residence time. Since a wafer size determines two dimensions (x-y), the only way to provide low gas residence time is to decrease the discharge volume by shrinking the space or discharge gap (z) over a wafer stage. Yet another reason is that a parallel plate configuration is expedient for generating uniform RF bias sheath, crucial for a deep oxide etch.