Epitaxy of Si/Si1−xGex heterostructures with very small roughness using a production-compatible ultrahigh vacuum-chemical vapor deposition reactor

Abstract

Growth and characterization of ultrahigh vacuum/chemical vapor deposition SiGe epitaxial layers on bulk singlecrystal SiGe and Si substratesTwo different roughening mechanisms are studied using a production-ready epitaxial deposition system to grow various epilayers, including the base layer of bipolar transistors. Surface roughness is measured using atomic force microscopy and transmission electron microscopy is used for cross-sectional analysis. Very smooth surfaces are routinely obtained, with a root mean square roughness of 0.15 nm. However, two possible mechanisms are shown to increase surface roughness under certain conditions. Above a certain critical thickness, for growth temperatures higher than 525°C and Ge compositions above 25%, strain redistribution results in surface ripples with a typical wavelength of the order of 100 nm. In addition, we find that substrate contamination ͑C,O͒ can produce wide depressions, several hundreds of nm wide and on average 10 nm deep in Si epilayers. The addition of a small concentration of Ge ͑below 15%͒ seems to produce more planar growth compared to the same thickness ͑50 nm͒ of Si only. The origin of the different surface morphologies observed is discussed.

Stress-driven instability in growing multilayer films

“…Also, the nonzero substrate roughness ζ can affect the detailed film morphology, as found in experiments. 33,34 The second layer surface perturbation can then be calculated for rough film-substrate interface, with the result: The original k-layer structure that we study, with growing and undulating surface (located at z = h k (x, y, t)) and with nonplanar and frozen interfaces (located at z = hi(x, y)) between buried layers i = k − 1, k − 2, ..., 1, and 0 (substrate). The elastic displacement field of each layer is indicated as uα,i| k with α = x, y, z.…”