Low temperature oxidation of silicon using a microwave plasma disk source

Abstract

A new reactor concept, referred to as a microwave plasma disk source, is implemented and is used as a source of negative oxygen ions for low temperature oxidation of silicon. Oxide growth rates of 1000 Å per hour, with only 100 W of absorbed power in the plasma, have been achieved on unheated silicon wafers in two configurations. In the first case, positively biased wafers are in actual contact with the plasma and in the second, the positively biased wafers are 15 cm downstream from the plasma ion source. In both cases the bias current density due to electrons and negative ions is on the order of 100 mA/cm2 and the plasma source electron density is on the order of 2×1012 cm−3. Oxide growth rates are correlated with plasma absorbed power, bias current, pressure, and plasma density. The reactor utilizes a single-mode, internally tuned resonant cavity that can be continuously operated over a wide range of gas flow and pressure (>10 to <10−3 Torr). The plasma disk source is scalable with frequency. In the present configuration, the excitation frequency is 2.45 GHz, the plasma disk diameter is 10 cm, and the disk thickness is 1.5 cm.