Method of contact patterning of thin film transistors for embedded dram using a multi-layer hardmask

Abstract

An integrated circuit structure comprises one or more backend-of-line (BEOL) interconnects formed over a first ILD layer. An etch stop layer is over the one or more BEOL interconnects, the etch stop layer having a plurality of vias that are in contact with the one or more BEOL interconnects. An array of BEOL thin-film-transistors (TFTs) is over the etch stop layer, wherein adjacent ones of the BEOL TFTs are separated by isolation trench regions. The TFTs are aligned with at least one of the plurality of vias to connect to the one or more BEOL interconnects, wherein each of the BEOL TFTs comprise a bottom gate electrode, a gate dielectric layer over the bottom gate electrode, and an oxide-based semiconductor channel layer over the bottom gate electrode having source and drain regions therein. Contacts are formed over the source and drain regions of each of BEOL TFTs, wherein the contacts have a critical dimension of 35 nm or less, and wherein the BEOL TFTs have an absence of diluted hydro-fluoride (DHF).