Some Factors Affecting Hillock Formation due to PECVD Processing of Sputtered Al-4% Cu-1% Si Films

Abstract

This paper discusses deposition parameter effects and subsequent heating on certain properties of sputtered A1-4 a/o Cu-1 a/o Si films. Emphasis was placed on developing a process yielding metal films resistant to hillock growth during the deposition of passivating films in a plasma-enhanced chemical vapor deposition (PECVD) reactor at relatively high (400°C) temperatures. The films were made in a commercial sputtering system which did not provide a means to heat sink the Si substrates. In contrast to most earlier reports, film smoothness and morphological stability increased with decreasing substrate deposition temperatures. Films deposited onto substrates pre-heated to ~200°C increased their average roughness from ~25 to ~320 Å during the PECVD process, resulting in hillock heights up to 5000 Å. By contrast, films deposited onto non pre-heated substrates underwent a roughness increase from ~20 to ~80 Å with PECVD processing to yield maximum hillock heights of ~500 Å. This difference is attributed to substrate heating by the deposition process and the absence of heat sinking which leads to an estimated 150-200°C increase in effective deposition temperature above the nominal values; such films, when reheated to 400°C, lack sufficient compressive stresses to produce large hillocks. Reductions in both grain size and preferred orientation were also found to enhance film stability. © 1991, The Electrochemical Society, Inc. All rights reserved.