The structural changes that accommodate wafer splitting after hydrogen implantation of silicon and the transfer of split layers to a handle substrate were investigated using triple axis x-ray diffraction, to monitor the strain in the implanted layer, and atomic force microscopy. Silicon substrates (004) were implanted with a hydrogen dose that ranged from 5×1015 cm−2 to 8×1016 cm−2 and energies of either 30 kV or 140 kV. The changes in the implanted layer properties were investigated after annealing at 150–300°C for short times. For annealing temperatures up to 150°C, the strain-induced implant profile did not change appreciably nor did the surface roughness increase, indicating that, for these implant conditions, the implant is stable. Annealing at 200°C or higher for 10 min or more led to increased surface roughness and a change to the implant profile, although blister formation did not occur. Higher surface roughness is not conducive to successful wafer bonding, so these measurements helped to determine the annealing sequence that is appropriate for bonding. In this case, hydrophobic bonded wafers were successfully fabricated with the transferred layer showing similar structural properties as a thin epitaxial film of the same thickness. The use of x-ray scattering for this technique can be easily transferred to other materials for which other techniques, such as infrared absorption, have not been developed.
As part of a series of wafer bonding experiments, the exfoliation/blistering of ion-implanted Cd 0.96 Zn 0.04 Te substrates was investigated as a function of postimplantation annealing conditions. (211) Cd 0.96 Zn 0.04 Te samples were implanted either with hydrogen (5 ϫ 10 16 cm Ϫ2 ; 40-200 keV) or co-implanted with boron (1 ϫ 10 15 cm Ϫ2 ; 147 keV) and hydrogen (1-5 ϫ 10 16 cm Ϫ2 ; 40 keV) at intended implant temperatures of 253 K or 77 K. Silicon reference samples were simultaneously co-implanted. The change in the implant profile after annealing at low temperatures (Ͻ300°C) was monitored using high-resolution x-ray diffraction, atomic force microscopy (AFM), and optical microscopy. The samples implanted at the higher temperature did not show any evidence of blistering after annealing, although there was evidence of sample heating above 253 K during the implant. The samples implanted at 77 K blistered at temperatures ranging from 150°C to 300°C, depending on the hydrogen implant dose and the presence of the boron co-implant. The production of blisters under different implant and annealing conditions is consistent with nucleation of subsurface defects at lower temperature, followed by blistering/exfoliation at higher temperature. The surface roughness remained comparable to that of the as-implanted sample after the lower temperature anneal sequence, so this defect nucleation step is consistent with a wafer bond annealing step prior to exfoliation. Higher temperature anneals lead to exfoliation of all samples implanted at 77 K, although the blistering temperature (150-300°C) was a strong function of the implant conditions. The exfoliated layer thickness was 330 nm, in good agreement with the projected range. The "optimum" conditions based on our experimental data showed that implanting CdZnTe with H ϩ at 77 K and a dose of 5 ϫ 10 16 /cm 2 is compatible with developing high interfacial energy at the bonded interface during a low-temperature (150°C) anneal followed by layer exfoliation at higher (300°C) temperature.
We have successfully bonded (211) cadmium zinc telluride (CZT) substrates onto (001) Si substrates for subsequent epitaxial-layer deposition of mercury cadmium telluride device layers. Silicon-nitride intermediate layers were employed as they provide both low surface roughness, which is necessary for bonding, and low absorption in the 1-10-µm range. Prior to bonding, the SiN layers were activated using oxygen plasma. Transmission infrared (IR) imaging showed Ͼ70% bonded area of a 10 mm ϫ 10 mm CdZnTe substrate onto a Si substrate. After the initial bond, the structure was exposed to a low-temperature anneal (150°C) for extended periods of time (22 h) to increase the bond strength. This process was sufficient to produce a CdZnTe on silicon structure that was able to withstand subsequent chemical-mechanical polishing (CMP) of the CZT substrate. We also investigated CMP of the transferred CdZnTe to improve the surface for subsequent epitaxial deposition. A Br/ethylene glycol/methanol solution produced the lowest damage levels, as determined by triple axis x-ray diffraction (TAD) while a standard silica/NaOH treatment produced a surface with Ͻ0.5-nm root mean square (RMS) roughness.
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