Abstract: Process for the formation of epitaxial layers with controlled n-type dopant concentration depth profiles for use in NPN bipolar transistors. The process includes first providing a semiconductor substrate (e.g. a [100]-oriented silicon wafer substrate) with an n-type collector precursor region formed on its surface, followed by forming an n-type (e.g. phosphorous or arsenic) in-situ doped epitaxial layer of a thickness t1 on the n-type collector precursor region. Next, an undoped epitaxial layer of a thickness t2 is formed on the n-type in-situ doped epitaxial layer. A p-type (e.g. boron) in-situ doped epitaxial base layer is subsequently formed on the undoped epitaxial layer. The process can also include the sequential formation of an undoped Si1−xGex epitaxial layer and a p-type in-situ doped Si1−xGex epitaxial layer between the undoped epitaxial layer and the p-type in-situ doped epitaxial base layer.

Abstract: A process for anisotropically etching a tungsten silicide or tungsten polycide structure. If the silicide/polycide film has an overlying oxide layer, the insulating layer is removed by a gas mixture composed of CHF.sub.3 and C.sub.2 F.sub.6. The WSi.sub.x silicide layer is then etched in a reactive ion etch using a gas mixture formed from Cl.sub.2 and C.sub.2 F.sub.6, with sufficient O.sub.2 added to control polymer formation and prevent undercutting of the silicide. The polysilicon layer is then etched using a gas mixture formed from Cl.sub.2 and C.sub.2 F.sub.6. The result is a highly anisotropic etch process which preserves the critical dimension of the etched structures. The etch parameters may be varied to produce a tapered sidewall profile for use in the formation of butted contacts without the need for a contact mask.