AVS 45th International Symposium
    Plasma Science and Technology Division Wednesday Sessions
       Session PS-WeM

Paper PS-WeM7
Silicon Oxidation Employing Negative Ion under Transformer Coupled RF Bias

Wednesday, November 4, 1998, 10:20 am, Room 318/319/320

Session: Plasma Damage
Presenter: H. Shindo, Tokai University, Japan
Authors: H. Shindo, Tokai University, Japan
T. Fujii, Tokai University, Japan
T. Koromogawa, Tokai University, Japan
Y. Horiike, Toyo University, Japan
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Directional silicon oxidation technique is highly required in various ULSI processes. Especially for trench isolation of memory cell, the oxidation should be directional but with low damage. For this purpose, a new method of negative ion assisted silicon oxidation has been experimentally studied employing a microwave O@sub 2@ plasma. A feasibility of directional silicon oxidation by negative ion was examined. The plasma produced in a 6 inch stainless-steel chamber was employed and the downstream plasma was mainly concerned because the negative ion was highly populated. Ion mass and energy analysis showed that the dominant negative ion was O @super -@ and its density was more than one order higher than O @sub 2@@super -@. The oxide film quality produced was analyzed by XPS, FTIR and ellipsometer. The oxidation depth under the positive DC biases without any local discharge showed a great voltage dependence, meaning a major role of negative ion O @super -@ for oxidation. While under the negative DC biases the oxidation was rather small but the fairly large amount of the sputtering was observed at the voltage as small as 50 V, indicating the high chemical reactivity of O @super -@. In conjunction with the sputtering, however, it was observed that the sputtering became remarkable in a condition of oxidation saturation. On a basis of the oxidation depth obtained under these DC biases, directional oxidation was examined under low frequency RF bias of 100 kHz with a transformer couple to apply the net positive voltage for negative ion. This directional oxidation was made employing a Si sample of line and space with SiO@sub 2@ mask. It was demonstrated that the directional oxidation of1500A depth was possible under the RF bias of 25 W with 10 minute.