AlN-AlN Wafer Bonding and Its Thermal Characteristics

Abstract

Homogeneous bonding was successfully demonstrated on 150 mm Si wafers by face-to-face fusion bonding of two clean and smooth aluminum nitride (AlN) layers. Characterization result from XPS confirms the layer composition and reveals that approximately 5 nm of the layer surface was partially oxidized during processing. The as-bonded wafer pair is nearly void and particle free with a high bonding strength of 1263.0 mJ/m 2 , enabling it to withstand the subsequent process steps. In addition, the AlN-AlN bonded wafers appear to have the best heat dissipation capability when compared with other bonded wafers, which used SiO 2 or Al 2 O 3 as the bonding layer.Wafer bonding allows heterogeneous integration of two materials that have similar or very different lattice parameters and thermal properties, via an intermediate bonding layer or direct bonding. One of the most prominent applications of wafer bonding is silicon-oninsulator (SOI) (1-5), and it can also be extended to germanium-on-insulator (GOI) (6, 7) or other III-V groups integration (8,9). First direct bonded SOI was reported by Lasky et al. in 1986 (3). Since then, SOI fabricated from wafer bonding has been gaining ground from the conventional Si substrate in ultra-large scale integrations (ULSI) and microelectro-mechanical systems (MEMS) as the starting substrate (10), which benefits from its on-insulator structure. The "on-insulator" advantages make it possible to attain mechanical stability close to Si substrate and excellent electrostatic control, such as attenuated short-channel effects (11), reduced parasitic capacitance and absence of latchup (12). As the most common buried insulator material, SiO 2 has already shown extensive popularity in a couple of optical devices (13-15). However, the low thermal conductivity of SiO 2 (1.46 Wm −1 K −1 ) limits the heat dissipation efficiency and degrades the advantages of SOI. Also, the degraded heat dissipation path deteriorates its heat transfer efficiency to the underlying bulk Si layer, leading to severe self-heating effect. This effect is magnified further by device scaling for performance improvement, which constrains the applicability of SOI in electronics, especially in the cases where high temperature and power dissipation are expected. In order to address this problem, numerous efforts have been dedicated to exploring for novel buried insulator materials with high thermal conductivity. For example, Puurunen et al. had confirmed the possibility to utilize TiO 2 as the buried insulator in the formation of SOI by wafer bonding, whereas an Al 2 O 3 under-layer was required (16). Additionally, SOI formed through Al 2 O 3 -Al 2 O 3 wafer bonding was successfully demonstrated (4). This was 10.1149/06405.0141ecst ©The Electrochemical Society ECS Transactions, 64 (5) 141-148 (2014) 141 ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 169.230.243.252 Downloaded on 2015-04-06 to IP