AVS 59th Annual International Symposium and Exhibition
    Plasma Science and Technology Wednesday Sessions
       Session PS-WeM

Paper PS-WeM3
Evaluation of Chemistry Effects of Fluorcarbon Molecules for High Aspect Ratio Silicon Oxide Etch

Wednesday, October 31, 2012, 8:40 am, Room 25

Session: Advanced BEOL/Interconnect Etching
Presenter: C.M. Anderson, Air Liquide
Authors: C.M. Anderson, Air Liquide
R. Gupta, Air Liquide
C. Dussarrat, Air Liquide
Correspondent: Click to Email
For semiconductor dry etch applications, the evolution of chemistry selection has shifted away from fully saturated fluorocarbons towards molecules that exhibit increased selectivity of silicon oxide over mask and underlayer materials. Recent studies show that the presence of both H atoms and C=C bonds can improve selectivity while maintaining reasonable silicon oxide etch rate. The reason for this is linked to the behavior of molecule fragments in a plasma etch environment, wherein higher C:F ratios are favored. The intent of this work is to systematically study the role of gas molecule structure as it affects etching behavior, with the goal of finding an ideal candidate molecule to enable current and future processing requirements.This study will provide an extensive survey of etch chemistries in order to uncover the specific effects of H, C=C double bonds, F:C ratio, and molecule structure as they relate to etching performance. The model chemistries for this work include both cyclic- and linear-type structures. Using a RIE plasma etch tool, the performance of each molecule is studied on blanket wafers, measuring silicon oxide etch rate as well as selectivity to photoresist, silicon nitride, and amorphous carbon hardmask films. For selected conditions of optimized etch rate and PR selectivity, patterned wafer stacks are also etched and examined in cross-section SEM. Corresponding optical emission spectroscopy (OES) data is collected at the same time, showing qualitatively the relative densities of active species in the plasma during the etch process. In order to develop predictive tools to correlate etch performance to the molecule structure, we perform mass spec measurements of the gases by direct injection of the fluorocarbon gas, measuring the electron-impact fragmentation of each gas. Electron energies from 10-100 eV are recorded, and the relative abundance of each fragment species is plotted against the electron energy. It is found that this method gives a strong indication of a molecules propensity to deposit polymer films during an etch process. Further, the nature of the representative polymer film for each gas can be predicted from the fragmentation patterns, in terms of F:C ratio and C-F bonding as measured by XPS.As a result of this analytical work, several optimum etch molecules have been identified that exhibit excellent selectivity to both PR and a-C hardmask. These chemistries are currently being tested in commercial dielectric etch tools to validate performance.