Low Stress In Situ Boron Doped Poly SiGe Layers for MEMS Modular Integration with CMOS

Abstract

In-situ boron doped LPCVD polycrystalline silicon-germanium (poly Si30Ge70) layers are deposited from silane (SiH4) and germane (GeH4) with fixed GeH4 to SiH4 partial pressure ratio at 430 oC and 0.2 mbar. The layers exhibit resistivities less than 1 mΩ-cm with a uniform boron distribution over the film thickness. The effect of the diborane (B2H6) partial pressure on the properties of the SiGe alloy is investigated. The layers deposited at low partial pressures of B2H6 exhibit very low stress with a trend from tensile to compressive with increasing B2H6 partial pressure, accompanied by a phase transition from polycrystalline to amorphous, allowing to tune for minimal stress.