Low Temperature Si Layer Transfer by Mechanical Ion-Cut*

Yonah Cho
(Professor Nathan W. Cheung)
(NSF) DMI-0088145 and (UC-SMART) SM-97-01

Recent developments in layer transfer processes for multi-material integration relies greatly on the “paste-and-cut” approach. Exemplified in both thermal ion-cut [1], mechanical ion-cut [2], and ELTRAN®[3] processes for SOI wafers, as well as laser liftoff transfer of GaN onto Si [4], the “paste-and-cut” approach consists of (1) the bonding of two materials' units and (2) separating the bonded system along a prescribed layer other than the bonded interface. Our work investigates a low temperature layer transfer process using a mechanical ion-cut process consisting of direct wafer bonding (Si/Si and Si/SiO2) and crack-initiated separation at the ion implantation region. Experimentally measured strengths of bonded Si/Si and Si/SiO2 interfaces, and of the hydrogen-implanted cut layer indicate that layer transfer occurs when the strength of bonding interface is greater than that of the implanted layer. In summary, the mechanical ion-cut renders three modes of separation depending on relative interface strengths. The schematics illustration of the three modes and corresponding images for the Si/SiO2 system are shown in Figure 1. The process temperature for partial mechanical transfer starts as low as 105°C for Si/Si and 170°C for Si/SiO2, compared to 400-600°C for the conventional thermal ion cut.

Figure 1: Schematic illustration of (a) three separation modes for an implanted Si-SiO2 pair and (b) images of corresponding separation surfaces.

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