LOW-TEMPERATURE SILICON-WAFER BONDING

This paper is focused on a modified process for silicon direct bonding. Thin intermediate sodium silicate layers are used to decrease the process temperatures. Oxidized silicon wafers are used for the characterization of the process. After a hydrophilic pretreatment, a diluted solution of sodium silicate in water is spun onto one of the two surfaces and the two wafers are brought into contact. The attraction force of the hydrophilic surfaces results in very close contact and the two wafers are fixed together. After a final temperature treatment in the range 200-300-degrees-C, a surface energy of about 3 J/m2 can be measured. In comparison, this value is obtained in conventional silicon direct bonding at temperatures above 1000-degrees-C. The influence of chemical and temperature treatments on the surface energies is described in detail.