Room temperature covalent bonds between bonded silicon oxide layers can be realized by forming surface and subsurface absorption layers followed by terminating outmost bonding surfaces with desired bonding groups prior to bonding. For example, by introducing fluorine into bonding oxide layers and NH2 groups onto surfaces of bonding oxide layers before bonding, bonding energy equivalent to silicon fracture energy (2500mJ∕m2) has been realized at room temperature after storage in air. Fluorine incorporation causes Si–O–Si ring breaking leading to fluorinated oxide formation with lower density, thus facilitating a higher diffusion rate of polymerization by-products and enhanced moisture absorptivity. Results indicate that by-products of the polymerization reaction between NH2 groups on mating surfaces appear to be more easily diffused and dispersed away from the bonding interface by the low density fluorinated oxide than are polymerization by-products of OH groups. This enhanced by-product removal results in covalent bonding at room temperature.
By introducing a nanometer-scale H trapping defective silicon layer on bonding surfaces, the bonding surface energy of bonded oxide-free, HF dipped, hydrophobic silicon wafers can reach a silicon fracture surface energy of 2500 mJ/m 2 at 300 to 400°C compared with 700°C conventionally achieved. Adding boron atoms on bonding surfaces can reduce the surface hydrogen release temperature but would not increase the bonding energy unless a defective layer is also formed. This indicates that, in order to achieve high bonding energy, the released hydrogen must be removed from the bonding interface. Many prebonding treatments are available for low-temperature hydrophobic wafer bonding including the formation of an amorphous silicon layer by As ϩ implantation, by B 2 H 6 or Ar plasma treatment, or by sputter deposition, followed by an HF dip and room temperature bonding in air. The interface amorphous layer may be recrystallized by annealing at elevated temperatures, e.g., at 450°C for As ϩ-implanted samples.
An oxide-free, covalently bonded interface of InP/silicon wafer pairs has been realized at low temperature by B2H6 plasma treatment of bonding surfaces in the reactive ion etch mode followed by a HF dip and room temperature bonding in air. The bonding energy reaches InP fracture surface energy of 630 mJ/m2 at 200 °C. A total B-doped amorphous layer of about 15 Å with peak concentration of ∼2×1020 cm−3 was detected at the bonding interface. The release of hydrogen at low temperature from B–H complexes and subsequent absorption of the atomic hydrogen by the amorphous layer at the bonding interface is most likely responsible for the enhanced bonding energy.
The purpose of this study is to investigate anomalous redistribution of beryllium (Be) in GaAs grown by molecular beam epitaxy (MBE). A concentration-dependent diffusion coefficient for Be is found from the substitutional-interstitial diffusion model. The importance of the generation of BeI from Ga point defects (vacancies or interstitials) in the diffusion process is also presented. Extremely rapid interstitial diffusion during growth, on the order of 30 μm in 1 h at 680 °C, has also been observed. This effect begins to occur for hole concentrations above 1019/cm3. Unintentional incorporation of Be into GaAs grown after closing the Be shutter is also presented. Consideration of the surface concentration of Be during MBE growth facilitates the explanation of this memory effect.
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