Ion Beam Synthesis of Silicon Germanium Alloy Layers
Abstract
A systematic study of the processing procedures required for minimizing structural defects generated during the ion beam synthesis (IBS) of SiGe alloy layers has been performed. The synthesis of 200 nm thick SiGe alloy layers by implantation of Ge ions with an incident energy of 120 keV into <100> oriented Si wafers yielded various Ge peak concentrations after the following doses, 2 times 10^{16}cm^ {-2} 3 times 10 ^{16}cm^ {-2} and 5 times 10^{16}cm^ {-2}. Following implantation, SPE annealing in a nitrogen ambient at 800^circ C for 1 hour resulted in only slight redistribution of the implanted Ge. Two kinds of extended defects were observed in alloy layers synthesized at doses over 3 times 10^{16}cm ^{-2} at room temperature: end-of-range (EOR) dislocation loops and strain-induced stacking faults. The density of EOR dislocation loops was much lower in those alloys produced by liquid nitrogen temperature (LNT) implantation than by room temperature (RT) implantation. Decreasing the implantation dose to obtain 5 at% peak Ge concentration prevents strain relaxation, while those SPE layers with more than 7 at% Ge peak show high densities of misfit-induced stacking faults. Sequential implantation of C following high dose (5 times 10^{16}/cm ^2) Ge implantation (12 at% Ge peak concentration in the layer) brought about a remarkable decrease in density of misfit-induced defects (stacking faults). When the nominal peak concentration of implanted C was greater than 0.55 at%, stacking fault generation in the epitaxial layer was considerably suppressed. This effect is attributed to strain compensation by C atoms in the SiGe lattice. A SiGe alloy layer with 0.9 at% C peak concentration under a 12 at% Ge peak exhibited the best microstructure. The experimental results, combined with a simple model calculation, indicate that the optimum Ge/C ratio for strain compensation is between 11 and 22. The interface between the amorphous and regrown phases (a/c interface) showed a dramatic morphology change during its migration to the surface. The initial <100> planar interface decomposes into a < 111> faceted interface, changing the growth kinetics. These phenomena are associated with strain relaxation by stacking fault formation on (111) planes in the a/c interface.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1994
- Bibcode:
- 1994PhDT........11I
- Keywords:
-
- SILICON-GERMANIUM;
- Engineering: Materials Science; Physics: Condensed Matter; Physics: Radiation