Ultrathin Strained Si-on-Insulator and SiGe-on-Insulator Created using Low Temperature Wafer Bonding and Metastable Stop Layers

Abstract

A method for fabricating smooth, uniform thickness, low defect density, monocrystalline SiGe alloys and strained Si on any desired substrate was developed, allowing for the creation of SiGe-on-insulator and strained Si-on-insulator. After wafer bonding and layer transfer via either delamination by hydrogen implantation, or back side grinding and Si etching, a selective SiGe etch was used to remove excess material and expose a strained Si stop layer. Recent improvements made to the process include more robust stop layers, low temperature wafer bonding, and improved selective SiGe etching. A major improvement involves the use of metastable films that allow for thicker stop layers. Experimental data for threading and misfit dislocation density for metastable Si layers on virtual substrates is presented. Another improvement is the use of plasma activation prior to wafer bonding, allowing for strong low temperature bonding, while enabling metastable layers to retain their nonequilibrium strain state. Within the context of layer transfer followed by etching, a detailed analysis of SiGe selective etching stopping on strained Si was conducted. An etch consisting of nitric acid and dilute hydrofluoric acid was optimized to yield an acceptable selectively and etch rate, while not creating any pinholes in the exposed stop layer. © 2003 The Electrochemical Society. All rights reserved.