Optimization of the Ion-Cut Process in Si and SiC
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Optimization of the Ion-Cut Process in Si and SiC O. W. Holland,* D. K. Thomas,* and R. B. Gregory** *Oak Ridge National Laboratory, Oak Ridge, TN 37831-6048 **Motorola Inc., Tempe, AZ 85284 ABSTRACT H+-implantation is the basis for an ion-cut process, which combines hydrophilic wafer bonding, to produce heterostructures over a wide range of materials. This process has been successfully applied in Si to produce a commercial silicon-on-insulator material. The efficacy of implantation to produce thin-film separation was studied by investigation of H+-induced exfoliation in Si and SiC. Experiments were done to isolate the effects of the hydrogen chemistry from that of implant damage. Damage is manipulated independently of H+ dosage by a variety of techniques ranging from elevated temperature irradiation to a two-step implantation scheme in Si, and the use of channeled-ion implantation in SiC. The results will demonstrate that such schemes can significantly reduce the critical dose for exfoliation. INTRODUCTION The ion-cut process utilizes both hydrogen implantation and wafer bonding [1] to form thinfilm heterostructures [2]. Stress generated by hydrogen implantation can cause physical separation within a solid at or near the range of the ions, Rp. Wafer bonding constrains this separation to occur laterally so that the bonded pair completely separates resulting in transfer of the superficial layer (i.e., the layer at the surface of the implanted wafer ahead of Rp). This transfer process forms the heterostructure and can be repeated using different materials to yield complex, multilayer structures. Ion-cut is presently used commercially to produce a silicon-oninsulator (SOI) heterostructure [3]. The utility of this process to produce thin-film heterostructures ultimately depends upon its economy and the quality of the transferred thin-films. Therefore, it is important to develop optimization schemes that reduce the critical hydrogen dose for affecting separation, and minimize the deleterious effects of ion-induced damage. This paper reports the development of several schemes for optimization of ion-cutting in Si and SiC. The technological importance of these materials is well known, and the ability to use them to form a heterostructure provides a tremendous tool for engineering materials. In particular, SiC is a wide band-gap semiconductor that is targeted to replace Si in high-power, high-temperature electronic applications. Ion-cutting may impact this development by making it possible to manufacture hybrid integrated circuits fabricated on a composite substrate containing both materials. EXPERIMENTAL PROCEDURE Irradiation was done with a raster-scanned beam of 60 keV H+-ions at an average current density of ~2 µamps/cm2. Random implants were nominally done with the sample normal tilted 7° relative to the incident ions, while no tilt was used for channeled-ion implantation. Samples were mounted on a holder that was resistively heated to achieve the desired implantation temperature. Si(100) wafers used in this study were
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