Improved Ohmic Contacts in Openings
Original Publication Date: 1987-Jun-01
Included in the Prior Art Database: 2005-Feb-01
According to the standard process, a phosphate silicate glass (PSG) layer is deposited during the low pressure chemical vapor deposition (LPCVD) process, both on the active face as well as onto the backside of the wafer. After the contact holes have been opened, a boron ion implantation followed by an annealing operation at high temperature is completed while the PSG layer on the backside is used as a source for the next wafer and causes undesired phosphorous diffusion into the contacts. This, in turn, causes a depletion of the boron concentration and even an inversion of the type of conductivity of the substrate and provides more resistive contacts. In order to avoid this problem while performing a photo-engraving step to form the contacts, an etching step has been added between the resist exposition and development steps.