Amorphous SiGe deposition by LPCVD from Si₂H₆ and GeH₄ precursors

Abstract
This paper presents results on the deposition of Si_1-xGe_x layers in a hot wall low pressure chemical vapor deposition system, using disilane and germane as source gases, and hydrogen as carrier gas. The effect of the composition of the gas (with disilane flow rates between 4 and 20 sccm, germane flow rates between 0 and 20 sccm and hydrogen flow rates between 0 and 120 sccm), the deposition temperature (between 450 and 600°C) and the total pressure (between 300 mTorr and 1 Torr) on the growth rate, composition and crystallinity of the film has been investigated. The growth rate depends linearly on the composition of the gas when a carrier gas is used, but the dependence changes to a more complicated U-shaped dependence for depositions with pure precursors atmosphere. The film composition depends mainly on the composition of the gas, but it is also affected by the precursors partial pressure. The H₂ carrier gas acts only as a dilution agent and does not affect the hydrogen desorption from the surface, which is the mechanism that limits the growth. Depositions at temperatures below 500°C produce an amorphous material but films grown at higher temperatures are polycrystalline.