Angular dependence of the polysilicon etch rate during dry etching in SF6 and Cl2

Abstract

The angular dependence of the etch rate in reactive ion etching (RIE) and inductively coupled plasma (ICP) systems for polysilicon etching with SF6 and Cl2 is determined using a recently developed direct measurement method. The latter utilizes specially patterned silicon groove structures consisting of 7–10 μm wide planar surfaces which form various angles with respect to the wafer normal. The structures are produced by highly anisotropic wet chemical etching of Si through a gratinglike mask pattern aligned along specific crystallographic orientations of the wafer which results in the development of planar surfaces of various orientations. These surfaces are then coated with the materials to be studied—polysilicon in this case. The deposited polysilicon is then etched under a variety of conditions in a RIE and an ICP reactor and the etch rates determined by interferometric measurements. Since only standard Si wafers are used and the size of the pattern is only a few μm the method is fully IC production compatible, which means that one can measure the angular dependence of the etch rate directly in production etching systems. The results for RIE of polysilicon with SF6 show that the process becomes more isotropic with increasing pressure. The angular dependence of the RIE and ICP polysilicon etch rates in Cl2 atmosphere were found to vary with the substrate bias. Specifically low substrate bias resulted in an under cosine distribution whereas bias higher than 240–250 V led to over cosine distributions.