ANGULAR-DEPENDENCE OF THE POLYSILICON ETCH RATE DURING DRY-ETCHING INSF6 AND CL-2

The angular dependence of the etch rate in reactive ion etching (RIE) and inductively coupled plasma (ICP) systems for polysilicon etching w ith SF6 and Cl-2 is determined using a recently developed direct measu rement method. The latter utilizes specially patterned silicon groove structures consisting of 7-10 mu m wide planar surfaces which form var ious angles with respect to the wafer normal. The structures are produ ced by highly anisotropic wet chemical etching of Si through a grating like mask pattern aligned along specific crystallographic orientations of the wafer which results in the development of planar surfaces of v arious 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 o nly standard Si wafers are used and the size of the pattern is only a few mu m the method is fully IC production compatible, which means tha t one can measure the angular dependence of the etch rate directly in production etching systems. The results for RIE of polysilicon with SF 6 show that the process becomes more isotropic with increasing pressur e. The angular dependence of the RIE and ICP polysilicon etch rates in Cl-2, atmosphere were found to vary with the substrate bias. Specific ally low substrate bias resulted in an under cosine distribution where as bias higher than 240-250 V led to over cosine distributions. (C) 19 97 American Vacuum Society.