Juyong Chung

Epitaxial growth of 3C-SiC on Si(001) using hexamethyldisilane and comparison with growth on Si(111)

Abstract Growth of 3C-SiC on Si substrates has been carried out by atmospheric pressure chemical vapor deposition using hexamethyldisilane as the source and a H 2 /Ar gas mixture as the carrier gas. No separate carbonization step was used. Single crystalline 3C-SiC on Si(001) was grown using a two-step growth technique. For Si(001) substrates, the nucleation stage was optimum in the temperature range 1250–1300°C for a growth time of approximately 2 min. A high concentration of H 2 (12%) in the carrier gas favored epitaxial growth on these substrates. On the other hand, the optimum temperature range for the nucleation stage on Si(111) was 1150–1200°C and the optimum time for the nucleation stage was longer (∼5 min). Additionally, it was possible to achieve single crystallinity on Si(111) substrates with a lower H 2 content (8%) in the carrier gas. The second stage of growth (at higher temperature of ∼1380°C) was identical for both substrate orientations. The difference in the nucleation stage can be attributed to the lower surface free energy of the Si(111) substrate resulting in a smaller critical cluster size. Additionally, the presence of microtwins in the nucleated clusters enhances growth of the SiC(111) oriented nuclei on Si(001) substrates.

Modelling of HREM and nanodiffraction for dislocation kinks and core reconstruction

The ability to directly image individual dislocation kinks (Kolar H et al 1996 Phys. Rev. Lett. 77 4031) opens up many possibilities for the study of kink dynamics by in situ TEM. Unfortunately, this technique is limited by surface roughness. For ceramics, however, high temperature annealing has been found to produce inert and atomically smooth surfaces that even survive ambient pressures (Susnitzky D 1992 J. Am. Ceram. Soc. 75 2463). We have prepared such samples of 3C-SiC, in order to image kinks by the forbidden reflections method. Using multislice simulations for 30 and 90° partial dislocations in Si we show that not only the number of kinks along the dislocation core can be determined, but also their structure assuming an aberration corrected TEM. We also show how the recently proposed double period reconstruction along the 90° partial dislocation in Si can easily be verified experimentally using convergent beam electron diffraction.

Deposition and Characterization of In-Situ Boron Doped Polycrystalline Silicon Films for Microelectromechanical Systems Applications

In an effort to develop thick, p-type polycrystalline silicon (polysilicon) films for microelectromechanical systems (MEMS) applications, in-situ boron-doped polysilicon films were deposited by a single-step APCVD process at susceptor temperatures ranging from 700°C to 955°C. The process produces boron-doped films at a deposition rate of 73 nm/min at 955°C. Spreading resistance measurements show that the boron doping level is constant at 2 × 10 19 /cm 3 throughout the thickness of the films. Doped films deposited at the low temperatures exhibit compressive stress as high as 666 Mpa; however films deposited at 955°C exhibited stress as low as 130 MPa. TEM and XRD show that the microstructure strongly depends on the deposition conditions. Surface micromachined, singly clamped cantilevers and strain gauges were successfully fabricated and used to characterize the residual stress of 5.0 µm-thick doped films deposited at a susceptor temperature of 955°C.