| Summary: | 碩士 === 逢甲大學 === 材料科學所 === 91 === The electrophoretic deposition (EPD) technique has been used as a simple but effective way to produce thin ceramic layers onto the electrically conductive substrates. This study is aimed to employ EPD method in engineering aspects of microelectronic and microelectromechanical systems regarding to fabrication of dielectric passivation layers for metallic films and IC top interconnections by EPD of nanosized SiO2 and Al-B-Si-O glass powders. The effects of stability of EPD suspension and rapid thermal annealing (RTA) conditions on both EPD performance and properties of deposited layer were taken into account. The optimized EPD yield and suspension stability can be obtained by choosing adequate types of solvent, mixing ratio of various solvents, and particle size distribution of glass powders.
Nanosized silica powder of 0.5 g added in 150 ml acetone solvent was formed as EPD suspension, of which pH value can be modified by adding minor amount of HNO3 or NH4OH. The result showed that EPD suspension at pH = 1.76 resulted in a perfect dispersion of glass powder and good EPD yield as well. In contrast, when EPD suspension was controlled to be basic (pH = 6 ~ 9), poor powder dispersion would appear due to the pronounced agglomeration. Though the EPD yield was higher with EPD suspension at basic condition, the deposited glass layers were prone to have cracking during drying step or after.
Furthermore, another EPD suspension was prepared by adding nanosized Al-B-Si-O glass powder in 100 ml mixed solvents of IPA/acetone, ethyl acetate/EtOH, and Acac/EtOH in their various volume ratios. The optimized volume ratio to achieve better layer morphology and good EPD yield was found to be 20/80 for IPA/acetone, 80/20 for ethyl acetate/EtOH or 20/80 for Acac/EtOH. Attrition milling turned out to be an effective route to reduce the powder size of Al-B-Si-O glass powder. The results showed that Al-B-Si-O glass powder after attrition milling for 12 hr led to considerably good EPD yield and denser powder packing in the EPD layers.
When SiO2 EPD layers were treated with various RTA conditions, the microstructure of sintered glass thin layers was still associated with individual particulates, which indicates the pure silica powder has softening point higher than RTA temperature of 950oC. On other hand, the Al-B-Si-O glass layers through RTA at 750oC/20 min had substantial changes in microstructures of glass passivation layers by reaching the full densification due to its lower softening point.
To use the EPD method for making the dielectric passivation layers for metal bond wires to serve as IC top interconnections, the deposition of glass powder was much favorable to be around both ends of a conductive wire when the applied electrical field was less than 50 V/cm. In such a particular case, the above-mentioned drawback is conjunction with the non-uniform electrical field throughout the dimension of the fine metallic bond wires used as working electrodes for EPD process, that is, the concentrated electrical lines gathered at the ends of conductive wires. The distribution of electrical lines can be effectively altered by using counter-electrodes in different geometry; therefore, the smooth, uniform deposition of glass layers can be expected via EPD process. The results of this study would have a number of contributions regarding to the potential applications in advanced microelectronic packaging.
|
|---|
