Research On Theory And Technology Of Low Temperature Wafer Bonding

Wafer bonding is an emerging micromanufacture technology. By this technology, the wafers with devices or not can be integrated into an entirety. Therefore it has been employed widely in materials manufacture, 3D microstrcture integration and IC MEMS devices fabrication and package. But the high temperature process often involved in the wafer bonding technology, which will cause the unstable and unreliable performance of the devices on wafers. And the impurity doped in wafers will be diffused again under the overhigh temperature. Thus the low temperature wafer bonding which performed under the temperature lower than 400℃or even 300℃attracts more and more attention over the world and will be the basic micromachining technology of wafer level package. So it is necessary to study the low temperature bonding mechanism and to find the reasonable process.This dissertation concentrated on the mechanism, process, and bonding quality measurement of low temperature wafer bonding and presented relative results.By analyzing of bonding experiments, the mechanism of low temperature Si-Si direct bonding was studied. Based on the analysis of roles of short distance forces in bonding processing and the threshold of wafer surface morphology for bonding was presented, the bonding model was definedThe low temperature hydrophobic and hydrophilic wafer bonding experiments were designed and performed. The results of experiments were analyzed carefully and by this means, the effect of different kinds of prescriptions and processes were discovered. It is obvious that the hydrophilic surface activated wafer bonding is much more suitable for low temperature Si-Si direct bonding than hydrophobic bonding and the RCA is the most proper activated solution for hydrophilic bonding.A new bonding technique to alleviate the high temperature adverse effect in silicon–glass bonding process is presented which combines the advantages of surface activated direct bonding and local laser bonding techniques. The hydrophilic surface activated solutions were used to make the bonding surfaces hydrophilic and the silicon-glass prebonding is accomplished at room temperature. The laser with a wavelength of 1064nm was used and its spot diameter was 500μm and the power is 70w. Without any external pressure, the prebonded pairs were bonded locally. The results of experiments shows that this bonding technique which employs surface activated prebonding to substitute pressure to maintain the intimate contact of bonding chips has overcome the disadvantages such as difficult focusing and easily breaking of bonding chips and glass cover in normal local laser bonding processing. This technique also improves the efficiency of surface activated direct bonding by shortening the annealing time.The hydrophilic surface activated bonding technology was used in pattern wafers bonding. The resuls of bonding experients indicted that this technology for bare wafers bonding is also fit for low temperature pattern wafers bonding.A low temperature Si-Si wafer bonding was realized by the aid of glass intermediate, the coefficient of thermal expansion of which is close to that of silicon. Thus the disadvantages caused by thermal stress were avoided. As shown in SEM figures, the cross section of bonding interface was smooth and the diffusion could be found around the interface. And the results of tension test indicated that the bonding strength is high enough.The typical manifestations of quality of wafer bonding were discussed, the relative test method was analyzed and the application environment was expounded. And for the sake of void detection, an infrared transmission inspection system was designed and built. The system can locate the void on the bonding interface and calculate the bonding rate nondestructively. And the inspection can be performed in static and dynamic mode. Thus, the system provides an effective and rapid measurement way for wafer bonding.