Method for controlling an n-type dopant concentration depth profile in bipolar transistor epitaxial layers

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 t on the n-type collector precursor region. Next, an undoped epitaxial layer of a thickness t 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 Si Ge epitaxial layer and a p-type in-situ doped Si Ge epitaxial layer between the undoped epitaxial layer and the p-type in-situ doped epitaxial base layer. Accumulation of the n-type dopant concentration in p-type epitaxial layers (such as the p-type in-situ doped epitaxial base layer or the p-type in-situ doped Si Ge epitaxial layer) that are formed subsequent to a non-p-type epitaxial layer (such as the undoped epitaxial layer or undoped Si Ge epitaxial layer, respectively) is controlled by manipulating the thickness ratio of t to t , while keeping the thickness of N-layer fixed at t (i.e. t +t ).