Initiatively embedding silver colloids in glass used in silver paste to improve metallization ohmic contact on silicon wafers

Abstract

One of the decisive factors in realizing ohmic contact of silver (Ag) paste metallization on silicon (Si) wafers is the presence of Ag colloids in the glass phase at the Ag/Si interface. The Ag colloids are formed during the reaction between glass frit and Ag powder in the sintering process of Ag paste; thus, it is difficult to control the quantity of Ag colloids formed. In this study, we attempted to prepare a glass embedded with a large number of Ag colloids first to further improve the quality of ohmic contact of Ag paste metallization. In the PbO–TeO2–SiO2 glass system, a route was found for increasing the solubility of Ag in the glass melt by precipitating the Ce1.88Pb2.12O6.53 crystal, which enabled a molar amount of recrystallized Ag colloids reach a high level of about 1/10 of oxides in the glass. As a result, the resistivity of the Ag/Si contact can be decreased substantially. The formation mechanism of Ag colloids in glass is revealed by various characterization and analysis methods, such as X-ray diffraction, electron energy loss spectroscopy, X-ray photoelectron spectroscopy, UV–visible and so on. Furthermore, it was also found that too high content of Ag in the glass melt would destroy the pyramid texture surface structure of Si wafers, which is not conducive to obtain high-quality Ag/Si ohmic contact. For this concern, optimal content of Ag colloids formed in glass is discussed.