OXYGEN MAGNETICALLY ENHANCED REACTIVE ION ETCHING OF SILYLATED RESIST PATTERNS

One of the critical steps in top-surface imaging lithographic processes such as diffusion enhanced silylated resist DESIRE is the dry development, i.e., the anisotropic oxygen plasma etching of the nonsilylated resist selective with respect to silylated resist. In this article the etch characteristics of the DESIRE process in a magnetically enhanced reactive ion etching etcher are described. The application of a magnetic field is shown to increase both the etch rate and the etch selectivity. The dependency of etch rates, etch selectivity, linewidth and residue formation on magnetic field, radio-frequency (rf) power, oxygen pressure, and flow are reported. The expected linewidth variation with varying etch selectivity, due to sloped silicon profiles in the resist, is observed when the selectivity variation is due to varying rf power or oxygen flow. However, it is not observed when the selectivity variation is due to varying magnetic field. An explanation is given. The etch rate of silylated resist is shown to be dependent on the properties of the thin SiO2 top layer formed during oxygen etching, which is dependent both on etching and on silylation conditions.