There are different requirements for the production process and the final product of SiC-SiC wafer bonding. The manufacturing of devices that are sensitive to high temperature processing – due to broadened doping profiles and induced thermal stresses – requires room temperature bonding with high bond strength, while for electrical devices, it is mandatory that the bonding interface with a thin amorphous layer is oxide-free.[1] Reduced complexity of processes is also an important point for the final production. Hence, the goal of this work was to perform and characterize direct bonding of SiC-SiC without any added/deposited bonding layer. This type of bonded SiC wafers can be used for power electronics such as for the fabrication of traction inverter for automotive applications, DC/DC converter, on board charger or charging station.[2] For the wafer bonding processes standard 100 mm 4H SiC wafers were bonded with their Si-terminated faces in order to fabricate oxide-free bonds. The wafer bonding process was performed using the EVG ComBond® system: first the native oxides from both wafer surfaces were removed using an ion beam sputtering process, followed by the transfer of both wafers to the bonding process station operated in ultra-high vacuum (UHV) to significantly retard the oxidation process. Finally, the bonding process was performed at room temperature (RT). The goal of this study was to demonstrate the feasibility of the bonding process and to gain insight on the surface chemistry after activation. The investigations covered three areas: incoming inspection of the original wafer, characterization of activated single wafer and analysis of bonded wafer pairs. The focus was on compositional, chemical, mechanical and morphological analysis of the surfaces and of the bonded interfaces. In the case of single wafers, the focus of the incoming inspection was on whether the wafers fulfill the requirements of wafer bonding, and on the characterization of activated wafers to measure the surface modifications. Atomic force microscopy (AFM), white light interferometry (WLI) and spectroscopic ellipsometry (SE) were used to determine the surface roughness, the wafer topography and the surface layer structure, respectively. All three parameters are essential for successful RT SiC-SiC wafer bonding. The change of the surface chemistry was investigated by angle resolved x-ray photoelectron spectroscopy (AR-XPS). The quality of the bonded wafers and the bonding energy were verified using scanning acoustic microscopy (SAM) measurements (Fig. 1) as well as the Maszara blade test. Furthermore, cross-section transmission electron microscopy (X-TEM) showed a bonding interface with a thin amorphous layer and no noticeable additional oxygen containing layer (Fig. 2). In order to gain quantitative elemental distributions of oxygen and argon, energy dispersive x-ray spectroscopy (EDXS) was applied. The work reported is a demonstration of the capability of the different characterization methods regarding SiC-SiC wafer bonding. Future work will focus on the investigation of the bonded interface characteristics in the function of the bonding process parameters and the annealing conditions. [1] F. Mu, M. Fujino, T. Suga, Y. Takahashi, H. Nakazawa and K. Iguchi, "Wafer bonding of SiC-SiC and SiC-Si by modified surface activated bonding method" 2015 International Conference on Electronics Packaging and iMAPS All Asia Conference (ICEP-IAAC), Kyoto, Japan, 2015, pp. 542-545, doi: 10.1109/ICEP-IAAC.2015.7111073. [2] Tsunenobu Kimoto, "Material science and device physics in SiC technology for high-voltage power devices" Jpn. J. Appl. Phys. 54 040103 (2015), doi: 10.7567/JJAP.54.040103. Figure 1

In this study, the feasibility of oxide-free room temperature wafer bonding process was demonstrated for 4H-SiC wafers with in situ surface oxide removal. The investigations covered three areas: incoming metrology of the original wafer, characterization of activated single wafer and analysis of bonded wafer pairs. The focus was on compositional, chemical, mechanical and morphological analysis of the surfaces and of the bonded interfaces. Incoming wafers were inspected whether they fulfill the requirements of wafer bonding, and activated wafers were characterized to measure the surface modifications. The quality of the bonded wafers and the bonding energy were verified using scanning acoustic microscopy measurements as well as the Maszara blade test. Furthermore, cross-section transmission electron microscopy was used to investigate the amorphous layer at the bonding interface. The work reported is a demonstration of the capability of different characterization methods regarding SiC-SiC wafer bonding.

We utilize indium fin oxide (ITO) as a material for direct bonding of Si wafers at low temperatures and without any pretreatment in order to create junctions of Si-ITO//ITO-Si. Transparent conducive oxides combine good conductivity with high optical transparency, rendering them ideal for joining III-V materials with Si based technology, e.g. to fabricate optoelectronic devices like light emitting diodes or solar cells. We found that bonded wafers did not display macroscopic defects and exhibit a bonding energy greater than 1 J/m(2) determined by double cantilever beam test. This bonding strength is high enough to bear further front-of-line processing like backside grinding. The bonding interface was investigated by means of transmission electron microscopy to gain insight into the bonding mechanism. We observed that the bonding mechanism proceeds through grain growth of the ITO layers across the original bonding interface upon annealing above the crystallization temperature of ITO. To explore other factors which could influence the obtained wafer bonds, ITO layers were deposited on Si wafers and characterized before and after annealing by atomic force microscopy, scanning electron microscopy and X-Ray crystallography.

Silver nanoparticles have been generated in aqueous buffer solution using a water-soluble silicon phthalocyanine sensitizer. Red light illumination (660 nm LED) was performed under aerobic conditions at ambient temperature in the presence of TEOA as a reductant. Structural characterization of the Ag nanoparticles formed was carried out by transmission electron microscopy (TEM). The resulting silver particles, depending on irradiation time and choice of procedure, were found to have a spheric shape and a narrow size distribution of 5-10 nm.

In this work, we show that the room-temperature photoluminescence intensity from Ge ion-bombarded (GIB) epitaxial Ge on Si quantum dots (QD) can be improved by their vertical stacking. We stress that the growth of GIB-QD multilayers is more demanding compared to all-crystalline epitaxial QDs, as a consequence of local amorphous regions within the GIB-QDs required during their genesis. We show that in spite of those amorphous regions, for accurately chosen growth temperatures of the Si spacer layers separating the GIB-QD layers, multiple GIB-QD layers can be stacked without detrimental break-down of epitaxial growth. Compared to a single GIB-QD layer, we observe a 650% increase in PL intensity for an eleven-layer GIB-QD stack, indicating that such multilayers are promising candidates as gain material for all-group-IV nano-photonic lasers.