Evaluation of unsaturated fluorocarbons for dielectric Etch applications

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2003.Includes bibliographical references (p. 175-183).The semiconductor industry is currently faced with the problem of the use and emissions of strong global warming compounds, known as perfluorocompounds (PFCs) for dielectric etch applications. The release of global warming compounds from this and other sources is suspected to result in changes in the earth's climate and weather patterns. Quantitative targets for emissions reduction set by the World Semiconductor Council (WSC) makes it urgent to find a solution to this issue. A long-term means of approaching this problem is to find and develop alternative chemistries that are more environmentally benign without sacrificing performance. Several classes of chemistries have been investigated to date, including hydrofluorocarbons (HFCs), iodofluorocarbons (IFCs), and NF3/hydrocarbons. One class of chemistries that have shown considerable promise is the unsaturated fluorocarbons (UFCs). The research documented herein uses the UFCs to assess etch process and emissions performance. Not only are these novel chemistries tested on conventional silicon dioxide films, but also on new low-k dielectrics that are likely candidates for future generation process flows. Emissions and process performance are reported for each of the different gases. The prospects for integration of some of these chemistries to next generation processes are good from both a process and emissions standpoint. The UFCs are not strong greenhouse gases as a result of their short atmospheric lifetimes (typically less than a day). Unlike many of the previous alternative chemistries studied, the emissions from UFCs are due to reformation of reactive products into strong global warming gases, specifically PFCs and HFCs, in the plasma environment. In this work, the formation of plasma effluents has been studied.(cont.) In this work, the formation of plasma effluents has been studied. These reformation products are not only a result of the reformation of reactive species from the breakup of the feed gas, but also a result of the interaction of the plasma with surfaces in the etch chamber, including the wafer being etched. Process performance has been assessed by performing cross-sectional scanning electron microscopy (SEM). Emissions data have been collected using Fourier transform infrared spectroscopy (FTIR). In-situ process monitoring methods such as optical emission spectroscopy (OES) and residual gas analysis (RGA) have been used in some experiments. Ex-situ studies of fluorocarbon deposited films have been performed using X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (TOF-SIMS). Screening experiments performed on an Applied Materials HDP high-density etch chamber showed that all of the UFCs in addition to a fluorinated ether were capable of process performance comparable to PFC based processes, such as C3F8. These studies showed that octafluorocyclopentene and hexafluoropropene processes result in greater than 70% emissions reduction compared to a C3F8-based reference process. Three isomers of C4F6 performed even better, with greater than 80% emissions reduction. Hexafluorobenzene based processes displayed the greatest silicon dioxide etch emissions reduction of 97% ...by Ritwik Chatterjee.Ph.D