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ABSTRACT A new etching method for a single crystalline A1203(100) film grown on Si(100) by LPCVD and a sapphire wafer is established for the first time using Si ion-implantation and buffered hydrofluoric acid (HF+H20) chemical etchant to develop many applications of the SO structure. Line and space patterns of resist were transferred to sharp A1203 and Si patterns. An etching of 0. 12/mthick-A1203 films on Si substrates and sapphire wafers was observed very clearly. The etch rate is I00A/min under implanted conditions of 80kV and 3x10 15 cm- 2 .The implanted A1203 surfaces are investigated by SIMS and XPS. The change from A1203 to A1203SiO2 (aluminosilicate), which can be easily etched HF+H20, is considered to be a main reason, though bonds broken by implantation are also effective for this etching.

INTRODUCTION Si on insulator (SO) structures are of great interest not only for VLSI substrates but also for new structure devices such as a SOI-MOSFET of high voltage lateral and buried back gate for high temperature application I l. Many efforts for S0l structures have been done until now , and Recently SIMOX ( Separation by implanted oxygen ) and SDB ( Si direct bonding ) wafers are expected to be VLSI wafers instead of Si wafers for low power IC and power MOS IC 12 1. However, a heteroepitaxial growth to fabricate SOl structures is attractive method due to possibility of multilayer SOl and easy control of the thickness of the layers. By a heteroepitaxial growth method of an insulating layer of y -A1203 and Si film, we proposed an SOl structure of Si(100)/ A1203( 100)/ Si(100) 131. Moreover, a double SOt structure: Si( 100)/ A1203( 100)/Si(100) /A1203( 100)/Si(100) substrate, has been studied for sensor applications such as an etching stop layer due to the chemically stable property 14, 51 and a high-temperature pressure sensor 16, 71 as well as a MOS FET

devices 181. However, since the single crystalline A1203 including sapphire is very stable for chemical etchant, the chemical stability becomes a disadvantage for etching the material to fabricate a device. The A1203 films can not be etched by dilute HF at 20°C for 60 min and KOH (7mol/l) at 70°C for 60 min 141, and by dry etching with CCI4 gas. In this article, a new etching method for the single crystalline A1203 film grown by LPCVD (Low pressure chemical vapor deposition) and a sapphire wafer is established for the first time using Si ion-implantation and HF chemical etchant 267 Mat. Res. Soc. Symp. Proc. Vol. 396 ©1996 Materials Research Society

to develop potential applications of the SO[ structure. Ion implantation is a well-established tool in the fabrication of modern electronic devices. It introduces energetic charged atomic particles into a substrate for the purpose of changing the electrical, metallurgical, or chemical properties of the substrate. The etching properties and the implanted A1203 surfaces are investigated by Dektak thickness measurement, SIMS (Secondary Ion Mass Spectroscopy) and XPS (X-ray Photoelectron Spectroscopy). The mechanism of t