Surface roughening of undoped and in situ B-doped SiGe epitaxial layers deposited by using reduced pressure chemical vapor deposition

Si_1−xGe_x(: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 Si_1−xGe_x on the GeH₄ flow rate and of Si_1−xGe_x:B on the B₂H₆ flow rate were investigated. The root-mean-square (RMS) roughness value of the undoped Si_1−xGe_x 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 Si_1−xGe_x significantly decreased through the formation of defects along with an abrupt increase in the RMS roughness. The variation of the surface roughness of Si_1−xGe_x:B depended on the boron (B) concentration. At low B concentrations, the RMS roughness of Si_1−xGe_x remained constant regardless of Ge composition, which is similar to that of undoped Si_1−xGe_x. However, at high B concentrations, the RMS roughness of Si_1−xGe_x:B increased greatly due to B islanding. In addition, at very high B concentrations (~ 9.9 at%), the RMS roughness of Si_1−xGe_x:B decreased due to non-epitaxial growth.