Oxygen reactive ion etching mechanisms of organic and organosilicon polymers

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Abstract
The oxygen reactive ion etching characteristics of a silyl novolac polymer and an organic novolac polymer were investigated as a function of pressure, self-bias voltage, power density, radio frequency (rf) frequency, and other system variables. For each etching condition, sheath thickness measurements were used as a diagnostic to estimate the flux and average bombardment energy of ions and the energetic neutral products of charge transfer collisions. The estimated flux allows the observed etching rate to be converted into a yield per bombarding particle. The trends for the etching rate as a function of pressure and other system variables were found to reflect a single trend for the yield as a function of the average bombardment energy. The yield of the organic novolac is proportional to the bombardment energy and is equal to 12 carbon atoms per 100 eV. The silicon atom yield of the organosilicon novolac is equal to the sputtering yield of SiO2 as predicted by the steady-state model of organosilicon polymer etching. The selectivity in bilayer lithographic schemes (the ratio of the organic to organosilicon etching rates) increases as the bombardment energy decreases because the SiO2 sputtering yield is negligible for bombardment energies less than 50 eV.

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