The Effect of Surface Finish on the Dislocation Density in Sublimation grown SiC Layers
- PDF / 1,221,846 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 16 Downloads / 177 Views
The Effect of Surface Finish on the Dislocation Density in Sublimation grown SiC Layers E. K. Sanchez, J. Liu, W.M. Vetter1, M. Dudley1, R. Bertke2, W.C. Mitchel2 and M. Skowronski Department of Materials Science & Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213, USA. 1 Department of Materials Science & Engineering, State University of New York, Stony Brook, NY 11794, USA. 2 Air Force Research Laboratory, Materials and Manufacturing Directorate, AFRL/MLP, Wright Patterson AFB, OH 45433
ABSTRACT The effect of the seed surface finish on the dislocation density of sublimation grown silicon carbide was investigated. Growth on seeds that were polished down to 1 µm diamond paste resulted in the nucleation of threading screw dislocations in a density of 106 cm-2 and threading edge dislocations in densities of 107 cm-2. Following the mechanical polish of the seeds with a hydrogen etch or chemo-mechanical polish prior to growth resulted in the screw dislocation density decreasing by four orders of magnitude and the threading edge dislocation density dropping two orders of magnitude. Using the dislocations density and the hydrogen etch rate, the depth of damage in mechanically damaged seeds was determined to be between 400 and 1000 Å. INDRODUCTION Silicon carbide’s (SiC) unique properties make it a potential material for high power, high frequency and high temperature devices. These devices require large diameter, low defect density wafers. Intense development of single crystal SiC growth has recently resulted in industrial wafers that are four inches in diameter [1]. However, these wafers still have numerous defects including threading screw dislocations with densities on the order of 103-104 cm-2 and threading edge dislocations on the order of 104-106 cm-2 [2,3]. Threading screw dislocations have been shown to be detrimental to the performance of SiC devices while the effect of threading edges has yet to be determined [4]. Several mechanisms have been proposed for threading dislocation nucleation and multiplication. Ha et al. argued that threading edge dislocations in SiC can form by plastic deformation [5]. Dudley et al. have proposed that threading screw dislocations may form during lateral overgrowth of surface inclusions [6]. Another possible formation mechanism is the nucleation of material on seed crystals with mechanical surface damage. Surface finish has been shown to affect the quality of epitaxial layers by leading to step bunching [7] and surface growth pits [8]. This paper will attempt to quantify the mechanical damage to the surface of SiC crystals used to seed the growth and its effect on the formation of threading dislocations during physical vapor transport (PVT). SiC has a high mechanical hardness and is resistant to most chemical etchants, making it difficult to polish. The standard polishing technique is a mechanical polish using diamond paste H1.3.1
with decreasing grit sizes. Although this polish can produce a near perfect specular surface it has been shown that subs
Data Loading...
