Wafer back metallization for semiconductor packaging

Thin films metallization has found numerous uses in the semiconductor industry since the very beginning. One of these applications, wafer back metallization, has evolved to meet the increasingly demanding requirements of high power, greater speed, higher reliability, and improved circuit performance. Optimization of the electrical, mechanical, and thermal properties of a semiconductor package is necessary to meet the individual device design goals. Among the candidate metallurgical schemes, gold is still the material of choice in many applications although a number of multilayer metallization processes are being used or developed to meet special application requirements. Material requirements are described in this paper and material selection for wafer back metallization and its impacts on the performance of microelectronic devices are discussed. The significance of Au-Si contact is also discussed and a new observation on the low temperature behavior of gold—p-type silicon is reported.