AVS 45th International Symposium
    Plasma Science and Technology Division Tuesday Sessions
       Session PS2-TuM

Invited Paper PS2-TuM3
Selective Oxide Etching in a High-Density Plasma Reactor: Gas Phase Chemistry

Tuesday, November 3, 1998, 9:00 am, Room 318/319/320

Session: Oxide Etching
Presenter: J.L. Cecchi, University of New Mexico
Authors: J.L. Cecchi, University of New Mexico
T.M. Bauer, University of New Mexico
A. Inoue, University of New Mexico
M.E. Littau, University of New Mexico
M.J. Sowa, University of New Mexico
Correspondent: Click to Email
Achieving a stable, reproducible selective oxide etch process in high-density plasma reactors continues to prove problematic, owing in large part to the complex chemistry on the wafer surface. The process relies upon polymerizing hydrofluorocarbon (HFC) feedstocks that produce simultaneous deposition and etching, which must be balanced to provide selectivity while avoiding etch stop. The process is further complicated by a preponderance of reactions occurring on internal surfaces, the composition and temperature of which may change in time. Much of this complexity is revealed in the gas phase chemistry that accompanies the selective oxide etch process, and in this paper, we explore the relationship between the gas phase chemistry and the etching characteristics. We measure the concentration of fluorocarbon precursors, including CF@sub 3@, CF@sub 2@, and CF, with wavelength-modulated diode laser spectroscopy. Atomic species concentrations are measured by optical emission spectroscopy and ion current is measured with a Langmuir probe. These measurements have been made in inductively coupled plasma (ICP) reactors using a variety of HFC feedstocks over a pressure range of 5 to 60 mTorr, ICP powers of 300 to 2500 W, wafer bias of 0 to 400 W, residence times from 0.1 to 1 s, and with varying distance between the ICP coil and the wafer. By exercising the reactor over this large range of parameter space, we are able to vary the concentrations of most gas phase species by over two orders of magnitude. We have analyzed our data with models which relate the polymer growth rate, oxide etch rate, and resist etch rate to the gas phase species concentrations. From this we are able to infer the role of the gas phase precursors, as well as extract kinetic parameters for the processes.