PECVD GROWTH OF Six:Ge1-x FILMS FOR HIGH SPEED DEVICES AND MEMS

PECVD growth of Six:Ge1-x films for high speed devices and MEMS SiGe thin films were deposited by plasma enhanced chemical vapor deposition (PECVD; MV Systems, Colorado) for use in high speed devices, Micro-Electrical Mechanical Systems (MEMS) and measurement of electromagnetic radiation (bolomtery). SiGe films grown by PECVD typically have lower stress, lower deposition temperatures and high growth rate (200 Å/min) compared with other deposition techniques. Increasing the germane concentration in the vapor phase allows the deposition temperature to be decreased, which decreases the thermal conductivity of the samples and improves their properties for bolometry. Films with lower germanium concentration are smoother. The samples were deposited at temperatures from 500 C to 580 C and doped using either diborane (B2H6) or phosphine (PH3). As-deposited films had predominantly (111) texture and some (110) texture as determined by X-ray diffraction. Annealing produced crystalline material with no evidence of cracking as determined by resistivity measurements. Annealing produces a variation of crystallite orientation with predominantly (111) texture. As-grown, boron doped samples have resistivities varying from 1.3 mO-cm to 44 mO-cm depending upon germanium concentration (100% to 20%). As-grown phosphorous doped samples (Ts = 580 C) with Ge concentration at 30% had higher resistivity of ~ 5.1 O-cm. As-grown films had stresses as low as 18 MPa tensile. Stress in annealed samples varied with annealing temperature and time. An increase in annealing temperature increased stress in the films. For samples with low germanium concentration; Fourier transform infrared spectroscopy (FTIR) was used to identify the chemical bonding in the sample. Energy Dispersive X-Ray analysis (EDX) provided alloy compositions, which were verified by X-ray diffraction calculations. Photothermal Deflection Spectroscopy (PDS) was used to determine optical band gaps. SiGe is good for high speed devices and MEMS applications because of low as-grown stress and low resistivity in the samples.