In this paper, we report thin silicon shadow masks used for vacuum thermal evaporation (VTE) for manufacturing compact-size OLED (organic light emitting diodes) displays. Currently, the OLED displays attract many research attentions because of novel organic materials for emitting the light at relative low cost. The fabrication processes of OLED make use of shadow masks for thermal deposition of organic materials due to etching difficulties. The metal shadow masks are widely used because of easy access. However, the openings of the metal shadow masks are limited to vertical sidewall, which cause the rounded profile at the top surface of deposited organic layers. This may cause potential step coverage problem and non-uniform device efficiency. In order to overcome the deposition profile of organic materials, we propose to use thin silicon shadow masks. Due to the crystal orientation of (100) silicon wafers, the etched aperture slope of the silicon shadow mask has approximately 54 degree sidewalls. This slope increases the accepting angle of the openings around the edge that results in a better profile of deposited organic materials. The simulation model for deposition profile is based on basic physical equation. The simulation results show flat profile at the top surface by using silicon shadow masks with the wedged openings; which could overcome the potential problem listed above. The silicon shadow masks are fabricated by micromachining techniques and are used in the vacuum deposition of aluminum and organic polymers. The scanning electron microscopy (SEM) pictures of organic films and side profiles measured by alpha stepper will be applied to verify the simulation models and to optimize the deposition factor. We demonstrate that the thin silicon shadow masks can provide deposition advantages over traditional metal shadow masks in terms of deposition profiles of aluminum and organic layers for making OLED displays.