Surface Roughening of Undoped and In situ B-doped SiGe Epitaxial Layers Deposited by Using Reduced Pressure Chemical Vapor Deposition

Si1−xGex(:B) epitaxial layers were deposited by using reduced pressure chemical vapor deposition with SiH4, GeH4, and B2H6 source gases, and the dependences of the surface roughness of undoped Si1−xGex on the GeH4 flow rate and of Si1−xGex:B on the B2H6 flow rate were investigated. The root-mean-square (RMS) roughness value of the undoped Si1−xGex at constant thickness increased gradually with increasing Ge composition, resulting from an increase in the amplitude of the wavy surface before defect formation. At higher Ge compositions, the residual strain in Si1−xGex significantly decreased through the formation of defects along with an abrupt increase in the RMS roughness. The variation of the surface roughness of Si1−xGex:B depended on the boron (B) concentration. At low B concentrations, the RMS roughness of Si1−xGex remained constant regardless of Ge composition, which is similar to that of undoped Si1−xGex. However, at high B concentrations, the RMS roughness of Si1−xGex:B increased greatly due to B islanding. In addition, at very high B concentrations (∼ 9.9 at%), the RMS roughness of Si1−xGex:B decreased due to non-epitaxial growth.