Silicon-on-insulator (SOI) wafers are important semiconductor substrates in high-performance devices. In accordance with device miniaturization requirements, ultrathin and highly uniform top silicon layers (SOI layers) are required. A novel method involving numerically controlled (NC) atmospheric-pressure plasma sacrificial oxidation using an electrode array system was developed for the effective fabrication of an ultrathin SOI layer with extremely high uniformity. Spatial resolution and oxidation properties are the key factors controlling ultraprecision machining. The controllability of plasma oxidation and the oxidation properties of the resulting experimental electrode array system were examined. The results demonstrated that the method improved the thickness uniformity of the SOI layer over one-sixth of the area of an 8-in. wafer area.
An array-type atmospheric-pressure radio-frequency (RF) plasma generator is proposed for high-precision and high-throughput numerically controlled (NC) processes. We propose the use of a metal-oxide-semiconductor field-effect transistor (MOSFET) circuit for direct RF switching to achieve plasma on–off control. We confirmed that this type of circuit works correctly using a MOSFET with a small parasitic capacitance between its source and gate. We examined the design method for the distance between adjacent electrodes, which corresponds to the parasitic capacitance between adjacent electrodes and is very important in the individual on–off control of each electrode. We developed a prototype array-type plasma generator apparatus with 19 electrodes and the same number of MOSFET circuits; we then confirmed that each electrode could control its plasma on–off state individually. We also demonstrated that the thickness uniformity of the surface Si layer of a silicon-on-insulator wafer could be processed to less than 1 nm peak to valley by the NC sacrificial oxidation method using the apparatus.
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