AVS 46th International Symposium
    Plasma Science and Technology Division Tuesday Sessions
       Session PS-TuM

Paper PS-TuM4
Vacuum Beam Studies of Photoresist Etching Kinetics

Tuesday, October 26, 1999, 9:20 am, Room 609

Session: Plasma-Surface Interactions I
Presenter: F. Greer, University of California, Berkeley
Authors: F. Greer, University of California, Berkeley
J.W. Coburn, University of California, Berkeley
D.B. Graves, University of California, Berkeley
Correspondent: Click to Email
One factor limiting the development of reliable models of high density, low pressure oxide etch plasmas is the relatively poor understanding of the plasma-photoresist surface interactions. In particular, the relatively high rates of photoresist (PR) loss experienced in high density fluorocarbon plasmas is a significant problem. It has long been accepted that fluorine plays a key role in controlling the oxide to PR etch rate selectivity. The addition of hydrogen has been shown to improve this selectivity by scavenging fluorine from the tool. To develop reliable models of these etch tools, it is necessary to understand how this process occurs and to predict PR etch rates as a function of the neutral to ion flux ratio at the surface as well as the ion energy dependence. The neutral and ion compositions in practical etch systems are difficult to measure and control accurately; however, vacuum beam systems can probe the plasma-surface interactions of various samples by employing independent beams of both neutral and ionic species. The complicated chemistry of fluorocarbon plasmas is modeled with argon ions and independent neutral fluxes of hydrogen and fluorine atoms intersecting at the surface of a photoresist sample. We will present experimental evidence that the etch yield of photoresist (carbon atoms removed per incident argon ion) under these conditions is quite high compared to that of silicon and silicon dioxide. The presence of a simultaneous flux of hydrogen on the photoresist surface does not affect the etch yield measured despite the fact that HF does form during the etching process. In addition, the relative reactivity of hydrogen and fluorine atoms for abstraction of one another on the photoresist surface has been measured with modulated beam mass spectrometry with and without ion bombardment. These results are incorporated into a phenomenological model of the photoresist etching process.