Relaxation of Strained SiGe on Insulator by Direct Wafer Bonding
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B8.22.1
Relaxation of Strained SiGe on Insulator by Direct Wafer Bonding Jer-shen Maa, Jong-Jan Lee, Douglas Tweet and Sheng Teng Hsu Sharp Laboratories of America, Camas, WA, 98607, USA ABSTRACT Strained SiGe was bonded to silicon dioxide by direct wafer bonding and Smart-cut technique. Strained SiGe with a graded 20%-30% Ge concentration was deposited by RTCVD on (100) Si to a thickness between 300nm to 350nm. H2+ for wafer splitting was implanted at an energy varied from 40 keV to 150 keV and a dose between 2.5E16 and 4.5E16 ions/cm2. SiGe relaxation was found to depend on wafer split temperature, and on post-split annealing temperature. SiGe relaxation of greater than 80% was observed after wafer splitting and annealing. Was it from gliding of a SiGe film weakly bonded to an oxide surface? In order to determine the relaxation mechanism, samples with different film structure were prepared. The films were then annealed at various temperatures. Some film showed a high degree of relaxation, and some showed minimal relaxation, depending mostly on hydrogen implant depth. The results indicated that the generation of dislocation is the possible cause of SiGe relaxation. INTRODUCTION Previous reported SiGe relaxation was mostly related to the SiGe virtual-substrate fabricated by a thick relaxed SiGe layer of constant Ge concentration on a thick layer of SiGe with graded Ge composition. The total SiGe thickness is on the order of several microns [1]. Relaxation of thinner SiGe film by hydrogen implantation and annealing was reported by several groups [2, 3]. Since hydrogen implantation has been successfully used to induce exfoliation of silicon for the fabrication of high-quality silicon-on-insulator (SOI) wafers using SmartCut process [4], and the hydrogen dose used for silicon exfoliation is higher than that required for film relaxation, it is essential to examine the relaxation of SiGe film from direct wafer bonding using SmartCut process. There are two possible mechanisms for SiGe relaxation after bonded to oxide surface: (1) After wafer splitting, the bonding energy between SiGe and oxide is weak, therefore gliding of SiGe layer, over a loosely bonded oxide surface may not be impossible. (2) Relaxation of SiGe on bulk Si substrate is related to the existence of dislocations. Hydrogen implanted into SiGe structure to the region slightly below the SiGe/Si interface can greatly enhance the relaxation of SiGe layer [2, 3]. This is believed from the dislocations generated in the defect zone formed by hydrogen implantation. In direct wafer bonding using SmartCut process, the hydrogen implanted region is on the top of the film after film transfer. This defect zone may also affect the relaxation of SiGe on SiO2 by enhancing the dislocation nucleation. These are two completely different mechanisms. It is essential to differentiate the cause and identify the true mechanism. These will be discussed in this paper.
B8.22.2
EXPERIMENTAL 6-inch P-type Si (100) wafers are used as substrates for SiGe deposition. Prior to depositi
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