title: Improvement in thickness uniformity of thick SOI by numerically controlled local wet etching.
abstract: Silicon-on-insulator (SOI) wafers are promising semiconductor materials for high-speed LSIs, low-power-consumption electric devices and micro electro mechanical systems (MEMS). The thickness distribution of an SOI causes the variation of threshold voltage in electronic devices manufactured on the SOI wafer. The thickness distribution of a thin SOI, which is manufactured by applying a smart cut technique, is comparatively uniform. On the other hand, a thick SOI has a large thickness distribution because a bonded wafer is thinned by conventional grinding and polishing. For a thick SOI wafer with a thickness of 1 microm, it is required that the tolerance of thickness variation is less than 50 nm. However, improving the thickness uniformity of a thick SOI layer to a tolerance of +/- 5% is difficult by conventional machining because of the fundamental limitations of these techniques. We have developed numerically controlled local wet etching (NC-LWE) technique as a novel deterministic subaperture figuring and finishing technique, which utilizes a localized chemical reaction between the etchant and the surface of the workpiece. We demonstrated an improvement in the thickness distribution of a thick SOI by NC-LWE using an HF/HNO3 mixture, and thickness variation improved from 480 nm to 200 nm within a diameter of 170 mm.
authors.affiliation: Research Center for Ultra-precision Science and Technology, Graduate School of Engineering, Osaka University, Yamadaoka 2-1, Suita, Osaka 565-0871, Japan.
authors.forename: Kazuya
authors.initials: K
authors.lastname: Yamamura
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Ueda
authors.forename: Mao
authors.initials: M
authors.lastname: Hosoda
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Zettsu
mesh_terms: D003460:Crystallization / Q000379:methods*; D004553:Electric Conductivity; D046911:Macromolecular Substances / Q000737:chemistry; D008422:Materials Testing; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size; D012825:Silicon / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D046911:Macromolecular Substances; D012825:Silicon