Process integration issues for advanced contact etch of a .25 μm BiCMOS application in manufacturing

The contact etch module for BiCMOS device is one of the most critical modules. The process window involves several steps, including insulator thickness and uniformity, photolithography, etch and post etch treatments used to make contact to the front end devices. Due to the topography of the BiCMOS structure, the etch process requires high selectivity of oxide to nitride at 20:1 and nitride to TiSi greater than 30:1. The highly polymerizing process requires chemicals such as C4F8 and CO. These chemicals have the tendency to cause etch stop if the process is not scrutinized frequently throughout all steps. After the etch, the post etch treatments are a critical component in removing the residues. Selecting the correct wet chemicals can improve the contact resistances significantly. This paper will examine the contact module process window for photolithography and etch and post etch treatments. It will illustrate how the yield was improved in a BiCMOS manufacturing environment.