The Low-temperature Bonding Technology Based On An Amorphous Ge Interlayer And Its Application In GOI

Wafer bonding technique,in which the semiconductor junctions with different crystal structures or lattice constants can be formed by using this method,is playing an important role in micro electromechanical systems(MEMS),photoelectric devices,and high-performance silicon-on-linsulator(SOI)wafers.At present,a lot of methods,such as conventional hydrophilic bonding,HF-treated hydrophobic bonding,surface-activated bonding(SAB),plasma-assisted bonding,anodic bonding and the mediation layer bonding have been applied to form Si-based junctions.Nevertheless,because of the hydrophilic reaction during post annealing,an oxidation layer was formed at the bonded interface.The existence of the oxidation layer greatly limits the carrier transport across the bonded interface.The high vacuum surface activation bond and hydrophobic bond can realize the bonding without interfacial oxidation layer,but the cost of the harsh bonding conditions is too high.The shortcoming of the traditional mediation layer bonding method is obvious.Because the introduction of heterogeneous materials at the bonded interface,it produces a large number of defects in the interface.In this work,an amorphous Ge intermediate layer is introduced into the Si bonded interface to lower the annealing temperature and improve the bonding strength.Due to the loose properties of the amorphous germanium structure,a non-bubble bonding interface was obtained,and no oxide layer was found.The PN junctions and Ge/SiO2 bonded wafers are fabricated by low-temperature wafer bonding based on a thin amorphous Ge.The main works are summarized as follows:1.Ar ion bombardment and magnetron sputtering were used to form amorphous silicon on the surface of silicon wafer,and the surface morphology was studied.The structure and hydrophobic characteristics of HF-treated amorphous Si layer were used to realize Si/Si bonding.We found that the low-temperature wafer bonding based on Ar ion bombardment activation surface cannot be achieved without high-vacuum environment.The HF solution can give the surface hydrophobic properties of a-Si,but it also worsens the surface morphology of a-Si.The phenomenon of the solution with nitric acid and ammonia is more obvious.The introduction of a-Si layer helps to absorb the interface bubbles,then lower the annealing temperature.The hydrophobic bonding is very demanding on the surface morphology of the wafer.The surface of a-Si layer with the hydrophobic treatment cannot meet the bonding conditions,so the high-intensity bonding cannot be achieved.2.It is found that the amorphous germanium film with magnetron sputtering growth is highly hydrophilic and its surface roughness RMS meets the bonding conditions.With the increase of the thickness of a-Ge,the interface bubbles decrease continuously,and when the thickness reaches 20nm,it can obtain an approximate non-bubble bonding interface.The bonding strength is also related to the interface bubbles,and the bonding strength increases with the decrease of the bubbles.After annealed at 400? for 20h,the bonding strength of the sample with a 30nm thick a-Ge can reach the strength of the bulk Si.The by-product H2 that produced by the interfacial hydrophilic reaction can be removed through the a-Ge.The carrier transport of the Si-based PN junction annealed at 350 ? is consistent with the trap-assisted tunneling model and that annealed at 400 ? is related to the carrier recombination model.3.With the increase of sputtering power,the surface roughness of amorphous germanium films also showed a tendency to increase with the increase of sputtering power.The surface roughness of a-Ge film on the Ge substrate increases with the increase of the film thickness.When the thickness of the thin film<2 nm,the contact angle sharply reduced with the increase of thickness;when thickness>2 nm,contact angle stable at around 3 °.Compared with the traditional method for the bonding of Ge substrate and Si02,the method of introducing amorphous germanium transition layer was a significant improvement in bond strength and interface bubble.When the thickness of the a-Ge layer is 2nm,the interface bubble of the bonding sample is basically eliminated,and the bonding strength reaches the maximum(4.5MPa).