ANALYSES OF THE CHEMICAL TOPOGRAPHY OF SILICON DIOXIDE CONTACT HOLES ETCHED IN A HIGH-DENSITY PLASMA SOURCE

High aspect ratio sub-half-micron contacts were etched in SiO2 using a high density C2F6 plasma generated by an inductively coupled, low pre ssure reactor. Process development studies have shown that high aspect ratio contact holes can be open in thick dielectric layers with a goo d selectivity to the underlying silicon. Minimization of reactive ion etching lag is obtained by using high bias power conditions, which on the other hand induce a degradation of the photoresist, described as a graphitization of the resist. The degradation induces considerable ro ughness at the edges of the resist structures which leads to the creat ion of striations in the silicon dioxide as the pattern transfer in th e SiO2 proceeds. X-ray photoelectron spectroscopy (XPS) studies have a llowed analysis of high aspect ratio SiO2 contact holes. Using appropr iate flood gun conditions, a complete separation of the XPS peaks orig inating from the resist mask and from the fluorocarbon polymer deposit ed on the bottom of the contact holes is possible. The XPS analyses sh ow, in particular, that the fluorination of the polymers on the bottom of the contact holes strongly increases with the aspect ratio of the contact hole, and that the fluorination of the polymers deposited on t he contact hole sidewalls Is even greater. (C) 1997 American Vacuum So ciety.