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The Uniformity of SOI layer thickness is need to be within plus or minus 5%, because an increase of dispersion of the silicon layer thickness increases the characteristic variation of fully depleted SOI MOSFETs. The thickness range of the SOI layer is required to be smaller and smaller, since the thickness of the silicon layer keeps getting thinner and thinner with the miniaturization of MOSFETs. Thus, we attempted to make the thickness uniformity of SOI layer more uniform by numerically controlled (NC) sactificial oxidation using atmospheric-pressure plasma [1]. Figure 1 shows the procedure of numerically controlled sacrificial atmospheric-pressure plasma oxidation using array of electrodes. First of all, the thickness distribution of the silicon layer is measured by spectroscopic elipsometry, and the redundant thickness at each regions is calculated. Secondly, NC plasma oxidation is performed by controlling the plasma-on time of each electrode (Figs 1(a), (b)). The region of atmospheric- pressure plasma is localized around the electrodes, because the mean free path of a gas molecule is very short. Finally, the wafer is dipped into HF solution to reveal the uniform SOI layer (Figs 1(c), (d)).

An array of electrodes covering one-sixth of the area of an 8″ wafer was developed as a prototype system for NC sacrificial plasma oxidation. It was demonstrated that the system can be used for simultaneous NC processes by the individual control of the plasma-on time of each electrode.

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.

Deterministic machining processes, in which the removal distribution is programmed on the basis of surface figure error, are used for fabricating ultra-precision optics. In these processes, numerically controlled (NC) machining is performed by the dwell-time control of a small removal spot by controlling the scan speed of the work table. Although their accuracy is very high, their throughput is low because of the long path of a raster scan. Thus, we propose an array-type removal system that can control the dwell time to realise high-throughput deterministic machining. We focused on plasma-process-based deterministic methods, and NC sacrificial plasma oxidation was selected as the method for use in the prototype apparatus with an electrode array system. Using the system, the thickness range of the top silicon layer of a silicon-on-insulator wafer was successfully improved by the NC process, and it was demonstrated that the electrode array system can be used for deterministic machining.

Recently, silicon-on-insulator (SOI) metal–oxide–semiconductor field-effect transistors (MOSFETs) have attracted great interest from manufacturers of semiconductor devices because of their excellent electrical characteristics. According to International Technology Roadmap for Semiconductors 2007, a very uniform surface Si layer will be required in a few years; however, no production method has been identified. To achieve the required uniformity in surface Si layer thickness, a new method of numerically controlled sacrificial oxidation using atmospheric-pressure plasma was developed. This paper demonstrates a new electrode array system developed for rapid processing. A very uniform oxide with a peak-to-valley (PV) of 0.13 nm was obtained; the relationship of oxide thickness versus oxidation time is shown.