Determination of the possible magnitude of the charging effect in a SCALPEL mask membrane

Previously, we theoretically investigated the charging of free standing die lectric thin films irradiated by 100 keV electrons and formulated kinetic e quations describing the dynamic process [M. Mkrtchyan et al., Microelectron . Eng. 46, 233 (1999)]. It was shown that in the currently used SCALPEL(R) masks comprising a 1000-Angstrom-thick amorphous SiNx film supported by a g rillage of Si struts, the membrane charging could be significant and might have an adverse effect on the system performance. The membrane charging, se nsitive to both the conductivity and the geometry of conductive path, can b e regulated in a straightforward manner by tailoring both of them; for inst ance, by applying a top surface conductive layer (TSCL) with an appropriate thickness and doping level. Here we discuss the results obtained on the ba sis of our charging model modified to be applicable to the case of a SiNx m embrane with a TSCL (e.g., a 10-nm-thick amorphous Si or poly-Si film doped by boron). The results presented demonstrate that this modification of the membrane is sufficient to avoid the adverse effect of the mask-membrane ch arging. The required structure can be generated simply by regulating the ga s hows in the low-pressure chemical vapor deposition process to produce a t hin final layer of a:Si or poly-Si which can be doped during or after depos ition. (C) 1999 American Vacuum Society. [S0734-211X(99)12406-5].