Capabilities and Limitations of Plasma Polymerized Methylsilane (PPMS) All-Dry Lithography.

Abstract

In this paper we report the results of a feasibility study of manufacturability of processes using plasma polymerized methylsilane (PPMS) as both a single-layer and a bilayer resist in both negative and positive tone development modes. PPMS has shown great promise as the basis for an all dry lithographic process. The photosensitive polymer is deposited in a low power plasma of methylsilane gas and is comprised of a Si-Si bonded network. PPMS undergoes efficient photo-oxidative crosslinking upon exposure to 248 or 193nm light in air to form an oxide-like material (PPMSO). We have identified several structural differences of films deposited at different temperatures and have correlated those differences to the air stability and the photosensitivity of PPMS films. We have also examined the effect of laser pulse power and repetition rate on the efficiency of exposure and conclude that the rate of oxygen diffusion into the film limits the effectiveness of high laser power for increasing the throughput of an exposure tool. We have concluded that positive tone PPMS processing is not practical because of the slow diffusion of oxygen through the film, required for effective photo-oxidation of PPMS to occur.