The growth and transformation of Pd 2Si on (111), (110) and (100) Si

Abstract

Thin Pd films on (111), (110), (100) and amorphous Si substrates form [001] fiber textured Pd 2Si in the temperature range 100°–700°C. The degree of texture is a function of substrate orientation, increasing in the order amorphous Si, (100) Si, (110) Si and (111) Si. Only on the (111) Si substrate is the Pd 2Si film epitaxially oriented. Temperature-dependent growth on this orientation can be characterized by [001] textured growth, epitaxial azimuth orientation at the Si interface and progressive layer by layer formation of the mosaic crystal to the thin film surface. During Pd deposition, rapid non-diffusion-controlled growth of epitaxial Pd 2Si on (111) Si occurs at substrate temperatures of 100° and 200°C. An unidentified palladium silicide of low crystallographic symmetry forms during Pd deposition onto a 50°C substrate. The diffusion-controlled growth of Pd 2Si on (111) Si follows a t 0.5 dependence. The velocity constant is k = 7 × 10 −2 exp − 29200±800 RT cm 2/ sec Palladium deposited on 100°C (111) Ge substrates reacts during deposition to form epitaxially oriented Pd 2Ge. However, growth of this phase at higher temperatures results in a randomly oriented film. The transformation of Pd 2Ge to PdGe is kinetically controlled. After a 15 min anneal at 560°±10°C in N 2 only PdGe is detectable on (111) Ge. The high temperature stability of thin film Pd 2Si is controlled by time- temperature kinetics. For a given annealing cycle, the nucleation and growth rates of the PdSi phase are inversely related to the crystalline perfection of Pd 2Si. Decreasing transformation rates follow the order (100), (110), (111) Si. formation of thin film Pd 2Si occurs by the formation of PdSi and subsequent growth of Si within the PdSi phase. After a 30 min N 2 anneal, initial transformation occurs at 735°C on (100) Si, 760°C on (110) Si and 840°C on (111) Si. Extended high temperature annealing produces a two-phase structure of highly twinned and misoriented Si and small PdSi grains that penetrate as much as 3 μm into the Si.