The Effects of Damage on Hydrogen-Implant-Induced Thin-Film Separation from Bulk Silicon Carbide
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S.R. WILSON* * Motorola Inc.. Semiconductor Products Sector. Tempe, Arizona **Oak Ridge National Laboratory. Solid State Division. Oak Ridge. TN. 37831-6048 ABSTRACT Exfoliation of SiC by hydrogen implantation and subsequent annealing forms the basis for a thin-film separation process which. when combined with hydrophilic wafer bonding, can be exploited to produce silicon-carbide-on-insulator, SiCOI. SiC thin films produced by this process exhibit unacceptably high resistivity because defects generated by the implant neutralize electrical carriers. Separation occurs because of chemical interaction of hydrogen with dangling bonds within microvoids created by the implant, and physical stresses due to gas-pressure effects during post-implant anneal. Experimental results show that exfoliation of SiC is dependent upon the concentration of implanted hydrogen, but the damage generated by the implant approaches a point when exfoliation is, in fact, retarded. This is attributed to excessive damage at the projected range of the implant which inhibits physical processes of implantinduced cleaving. Damage is controlled independently of hydrogen dosage by elevating the temperature of the SiC during implant in order to promote dynamic annealing. The resulting decrease in damage is thought to promote growth of micro-cracks which form a continuous cleave. Channeled H_ implantation enhances the cleaving process while simultaneously minimizing residual damage within the separated film. It is shown that high-temperature irradiation and channeling each reduces the hydrogen fluence required to affect separation of a thin film and results in a lower concentration of defects. This increases the potential for
producing SiCOI which is sufficiently free of defects and, thus, more easily electrically activated. INTRODUCTION Hydrogen implantation through an oxide film followed by hydrophilic wafer bonding and a thermal cycle is a process developed to cleave a thin film of silicon-on-insulator (SOI).I The process has recently been applied to produce silicon carbide-on-insulator (SiCOI) films for 2 possible use as a wide bandgap semiconductor in power rf and switching devices. SiC thin films separated from bulk material using this process have measured too resistive, a condition attributed to damage in the SiC thin film caused by the hydrogen implant itself The experiments described in this work are motivated by the desire to understand the implant damage mechanisms in order to make the separation process more efficient and produce defect-free, lowresistivity SiC. The problem is illustrated in Figure 1 which shows a schematic of the hydrogen-implantinduced separation process and a channeled RBS spectrum of SiCOI (-500 nm) produced by this process. Backscattered counts from Si in the SiCOI (integrated over channels 540-640) measure 824 greater than similarly measured counts from virgin SiC. Calculating density using the RBS data, one measures 1.27 x1 0 2" displaced atoms/cm3. These vacancies have the potential to cause 33 Mat. Res. Soc. Symp. P
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