STM-Movies
"In vivo" scanning tunneling microscopy studies during semiconductor growth
Today scanning tunneling microscopy (STM) is used routinely to image surfaces with a resolution down to the atomic level. The capability of this method has been recently expanded to follow semiconductor growth processes live. Scanning of the surface with the STM tip is done at high temperature during growth (MBSTM). Continuous imaging of the growing surface results in movies showing details of the growth process on the atomic level. The ability of the microscope to access the evolution of specific features during growth is demonstrated for the technological important systems Silicon on Silicon growth and Germanium growth on Silicon.
Movie of Ge/Si(001) heteroepitaxy (1300x1300Å, T=575K):
Perspective view of the growth of 3D "hut" islands as function of coverage. The following "flight" through the nanoworld of Ge islands on Si(001) shows that the complete growth morphology is measured at any stage during growth. Details can be found in: Physical Review Letters 82 (1999) 2745.
Movie of Si(001) homoepitaxy (3000x3000Å, T=725K):
Fast growth of the rough step edges and slow growth of the straight step edges occurs. Nucleation of islands and coalescence with the upper terrace is observed. Details may be found in: Physical Review Letters 78 (1997) 2164.
Movie of "rotating" steps during Si(001) homoepitaxy (3000x3000Å, T=825K):
The movie shows Si growth on Si(001) in the step-flow regime. Initially the mean step orientation (vertical) is ~30° off the [110] dimer row direction. During the step-flow growth the steps seem to "rotate" to a direction parallel to the dimer rows.
Movie of Ge/Si(001) heteroepitaxy (1600x1600Å, T=575K):
Layer-by-layer growth of the wetting layer. The formation of trenches relieves part of the strain, which is caused by the 4% larger lattice constant of Germanium relative to the Si substrate. The distance between the trenches decreases with increasing coverage. The images are slightly differentiated to enhance the visibility of the trenches.
Movie of Si(111) homoepitaxy (500x500Å, T=775K):
Growth occurs along rows of the width of the (7x7) reconstruction unit cell. The growth stops after the completion of a row for some time. This leads to the kinetic stabilization of magic island sizes. Details can be found in: Physical Review Letters 81(1998) 858.
Movie of coalescence of two islands in Si(111) homoepitaxy (1400x1100Å, T=700K):
Growth and coalescence of two Si islands on Si(111). Lateral growth of the islands occurs along rows of the width of the (7x7) unit cell. Upon coalescence growth with higher speed along new facets is observed. Details can be found in: Physical Review Letters 77 (1996) 3861 and Physical Review B 54 (1996) 7709.
Movie of Ge/Si(111) heteroepitaxy (3000x3000Å, T=773K):
Initial layer-growth of the Stranski-Krastanov wetting layer is observed. Details can be found in: Review of Scientific Instruments 67 (1996) 2568.
Movie of Ge/Si(111) heteroepitaxy (5000x5000Å, T=623K):
Subsequent island-growth of Stranski-Krastanov islands. The atomic distances in a Germanium crystal are larger than in Silicon. The resulting mechanical stress leads to the formation of three dimensional Germanium islands. The "growth movie" shows the evolution of the three dimensional islands at the same location as function of coverage. The form of the Germanium islands is a flat toped tetrahedron. At low coverage the size-fluctuations of the islands are quite large, whereas at higher coverage the size of the islands becomes quite uniform. Typical dimensions of the islands are 700 base length and 80 height. Further analysis shows that an anomaly in the aspect ratio of the islands (height divided by base length) as function of coverage indicates a transition from strained coherent islands (high aspect ratio) to relaxed islands with dislocations (lower aspect ratio) at higher coverage. Details can be found in: Applied Physics Letters 63 (1993) 3055.