Silicon Trench Oxidation in Downstream of Microwave Oxygen Plasma

Abstract

For one application of nonequilibrium oxygen plasma, low-temperature silicon trench oxidation is examined under the conditions of radio frequency bias as well as DC bias applications. The silicon oxidation has a very strong dependence on the substrate bias and is drastically reduced under the condition of no bias. The oxidation depth shows a maximum in a far downstream position from the microwave window. The silicon trench oxidation mapping clearly demonstrates that the maximum depth occurs along the line of the substrate bias of +20 V just above the plasma potential. In particular, silicon trench bottom oxidation is limited to higher radio frequency bias under the above conditions. It is concluded, for the reasons above, that the oxidation is due to the negative oxygen ions in downstream.

Spectroscopic and electrical characterization of oxygen microwave discharge used for downstream plasma oxidation of Si

“…25,26 However, in these plasma conditions where the substrate is floated in the plasma, the substrate sheath potential determined by the difference (V p À V f ) is positive. The positive ions are, thus, attracted to the substrate to avoid charge-up, 27 it was found that (V p À V f ) is about 20 V at Z 1 and about 10 V at Z 2 . Our findings suggest that not only the negative ions mediate the oxidation of silicon surface, but also the positive ions and eventually the atomic oxygen, especially when the substrate is unbiased.…”