This work is supported by NREL under subcontract #XXL-5-44205-09 and NSF under grant # DMR-0307594

1. PECVD Growth Of Six:Ge1-x Films For High Speed Devices and MEMS Srinivasan Kannana with P.C. Taylora and D.D.Allredb a University of Utah b Brigham Young University Abstract Stress Measurements in Six:Ge1-x We report on thin films of SiGe deposited by plasma enhanced chemical vapor deposition (PECVD) for use in high speed devices, Micro-Electrical Mechanical Systems (MEMS) and bolometric infrared detectors. SiGe films grown by PECVD typically have lower stress, lower deposition temperatures and higher growth rates (200 Å/min) compared with other deposition techniques. The samples were deposited at temperatures from 500oC to 580 oC and doped using either diborane (B2H6) or phosphine (PH3). For lower germanium concentrations, the tensile stresses in as-grown films are as low as 18 MPa tensile. Tensile stress is preferred in as-grown films since they do not buckle. The films have more tensile stress with increasing Ge concentrations. Crystallite Texture in Six:Ge1-x ● Pressure: 440 mtorr; temperature:594 ºC; power:20watts;thickness:2.5μm ∙ Pressure: 430 mtorr; temperature: 590 ºC; power :19.5 watts; thickness:3.75 μm ▼ Pressure :460 mtorr; temperature : 587ºC; power:19 watts; thickness : 2.6 μm □ Pressure : 460 mtorr, temperature: 605 º C; power : 16 watts,thickness:3.75 μm. For as-grown samples at 20% Ge concentration, we have predominantly (111) and (110) crystal planes. The <hkl> values are shifted because the crystals grow with higher Ge concentrations. The shifted values correspond to germanium concentrations of approximately 90%. The crystallites have a high Ge concentration due to initial growth with pure germane in the reactor. Films were annealed in an atmosphere of N2 for varying time periods. For lower annealing temperatures (≤ 550 ºC), the films have lower stress but higher resistvity. As the annealing temperature increases, the stress also increases for fixed germanium concentrations. For annealing times up to 17 hours, the films do not crack after the hydrogen diffuses out. For annealing times greater than about 20 hours, the films crack due to a large tensile stresses. ● Anneal time was 30 minutes for 20% Ge concentration For annealed samples we see two peaks, one from the as-grown crystal and a second peak due to annealing of the samples. The peak that appears on annealing has the alloy concentration of 20% Ge verified by XRD analysis. The crystallites in the annealed samples grow preferentially in the (110) direction for thicker films. Films thinner than 2 μm preferentially grow in the (111) direction. Resistivity Measurements As the Ge concentration decreases, the resistvity of the films increases, and the deposition temperatures have to be increased in order to grow poly-crystalline films.The lower resistvity is attributed to an increase in the hole mobility and dopant activation as the Ge concentration increases. Annealing boron-doped samples yields resistvity as low as 1.3 mΩ-cm. Summary We have developed thin films of SixGe1-x with Ge concentrations of about 20% with low as-grown tensile stresses of about 18 MPa and resistvities as low as 1 mΩ-cm. X-ray diffraction of the as-grown samples indicates crystallites with high Ge content in the alloy. Crystallites with (111) and (110) planes are predominantly found. Annealing the samples leads to formation of dual peaks with different Ge concentrations but similar crystallite directions. Stress in the films increases with Ge concentration and annealing temperature. This work is supported by NREL under subcontract #XXL-5-44205-09 and NSF under grant # DMR-0307594