Safer alternative liquid germanium precursors for relaxed graded SiGe layers and strained silicon by MOVPE

Commercial strategy to graded SiGe buffer layers and “strained silicon” involves passing germane (GeH4) gas or germanium tetrachloride (GeCl4) vapors as the preferred germanium sources, along with a silicon source over a heated substrate. Today, one of the major limitations impacting the commercialization of SiGe technology is the lack of a commercially viable and safer process that eliminates hazards associated with GeH4 and the excessively higher thermal budget associated with GeCl4. The key to growing successful SiGe structures is thus a strategic deposition process that employs safer alternative germanium sources, and allows a wide growth temperature window without degrading the film properties and jeopardizing the environment, health and safety (EHS) aspects of overall operation. In this paper, we report on the development of safer alternative liquid germanium precursors along with the first successful use of a new organo germanium precursor, iso-butyl germane (IBGe) for the growth of high purity Ge and SiGe films. We also detail our strategy to identify the most appropriate candidates from a large number of organo germanium compounds along with initial results on SiGe films and high-quality epitaxial Ge films deposited using IBGe.