Downstream oxygen etching of low dielectric polymers using a microwave plasma.

摘要

As dictated by the International Technology Roadmap for Semiconductors, there is an immediate need to develop low dielectric materials for use in metalization schemes in integrated circuits. Low dielectric materials are needed in order to reduce resistance-capacitance time delays, cross-talk and power. This dissertation is focused on studying the etching characteristics of a family of low dielectric polymers, the parylenes. Three types of parylene are studied: parylene-N, parylene-C, and AF4. Parylene films on silicon substrates were etched in a downstream microwave oxygen plasma system. The goal was to characterize the chemical reactions that occurred on the parylene in an oxygen radical atmosphere. First, the effects of pressure and temperature on the etch characteristics of parylene-N were studied. X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy analyses were performed on the parylene films formation are key steps during the etch process. Next, a model was generated to describe the reactive species concentrations throughout the reactor volume, including the generation of oxygen radicals in the plasma cavity, their transport to the parylene surface, and their reaction with the parylene. The predicted results were compared to experimental etch data. Good agreement between the model and experimental data was achieved when a model consisting of data from Bell, the Joint Institute for Laboratory Astrophysics and cross-sections published by Cosby and an overall reaction order of 0.5 is compared. Other models included cross-sections published by Phelps and Lieberman. In order to further understand the etching process, the two other parylenes, parylene-C and AF-4, were etched and analyzed. The etching characteristics as a function of temperature are reported. X-ray photoelectron and infrared spectroscopic analysis of these films is also reported. The apparent activation energy for the etch process is approximately 7.0 kcal/mol for each polymer. The XPS and infrared analysis showed carbonyl formation and aromatic ring opening. Based on these analyses, it was determined that a possible rate-limiting step in the etching was the ring opening and that the primary etch products were carbon monoxide and carbon dioxide.