AVS 58th Annual International Symposium and Exhibition
    Plasma Science and Technology Division Monday Sessions
       Session PS-MoM

Paper PS-MoM11
High-Aspect Silicon Trench Oxidation in Downstream of Surface-wave Oxygen Plasma

Monday, October 31, 2011, 11:40 am, Room 201

Session: Advanced FEOL / Gate Etching I
Presenter: Haruo Shindo, Tokai University, Japan
Authors: Y. Taniuchi, Tokai University, Japan
H. Shindo, Tokai University, Japan
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A low temperature and low damage silicon oxidation technique is highly required in various technology fields, such as in ULSI insulation layer formations, MEMS ( Micro-Electro-Mechanical System) processes and other material surface treatments. In particular, in ULSI, the shallow trench isolation (STI) technique is inevitable to realize further integrations. In this process, so-called, a liner oxidation, in which the trench bottom is directly oxidized, becomes more severe, as the trench aspect ratio is further increased with the integrations. In MEMS ( Micro-Electro-Mechanical System) processes, on the other hand, deep silicon trench etching with high aspect ratios is one of key technologies, and to realize a deep trench etching with a good directionality, a side wall passivation by the trench oxidation is inevitable. In this work, a silicon trench oxidation is investigated by employing a microwave oxygen plasma downstream under the condition of radio-frequency bias as well as the DC. In particular, the radio-frequency bias and the DC are superimposed and applied onto the substrate with the trench structure, and the oxidation rates at various portions of trench with the aspect ratio of 2 to 6 are examined as a function of the superimposed substrate bias. The oxidation depth shows a maximum in a very downstream of further position from the microwave window, indicating that the oxidation is due to negative oxygen ions. The silicon trench oxidation mapping, in which the oxidation film thickness is two-dimensionally plotted for the radio frequency bias and DC bias voltages, clearly demonstrates that the maximum is brought about along the line of the substrate bias of +20 V just above the plasma potential. In particular, the silicon trench bottom oxidation is just limited onto the higher radio frequency bias within the above condition. As for the dependence on the trench aspect ratio R, the oxidation at the trench bottom was attained 100 % of the trench top up to R=3, while at the trench bottom with R more than 4 it was only 60 %. The oxidation at the bottom of deep trench with the aspect ratio R= 6 was improved at the higher radio frequency bias. It is concluded that the oxidation is due to the negative oxygen ions in downstream.