The synergetic effect produced by coimplantation of H and He in Si is currently used to initiate thin layer transfer. More recently, Reboh et al. have shown the possibility of obtaining freestanding thick films of Si by micron-scale depth implantation of H and He. In our study, implantation parameters for layer transfer of 1.5µm thick films have been investigated.

For this work, the damage induced by H and He implantation in Si at moderate energy (168keV, 345keV respectively) as a function of fluence and annealing temperature were studied through complementary techniques (XRD, XTEM, SEM). In particular, combining both X-ray diffraction experiments and simulation has led us to obtain accurate strain profiles. H and He coimplantation has been shown to result in a complex picture with mechanisms related to implanted ions and gas-vacancy complexes. For low fluence, the strain profile is related to the H-distribution. With increasing fluence, a widening of the strain profile is observed. This evolution is supposed to result from an increasing contribution of the He-distribution. Upon annealing at 350^oC, TEM observations show a narrow layer of long nanocracks for low fluence and a heterogeneous distribution of nanocracks and bubbles for higher fluences. The correlation of strain in the as-implanted samples and the cavity distribution upon annealing suggests that the gas-vacancy complexes are the physical origin of strain. After annealing at 700^oC, an optimal exfoliation occurs within a specific interval of fluences. These implantation conditions were used to transfer Si films of ≈ 1.5 µm onto glass substrates demonstrating an alternative route for the integration of semiconducting materials in micron-scale thicknesses, with potential application for solar cells.

Shay Reboh, PGCIMAT, UFRGS, Brazil
Fernando Schaurich, UFRGS - Porto Alegre, Brazil
Jean François Barbot, Pprime Institut - CNRS-Université de Poitiers-ENSMA, France
Alain Declémy, Pprime Institut - CNRS-Université de Poitiers-ENSMA, France
Nikolay Cherkashin, CEMES-CNRS, France
Paulo F.P. Fichtner, UFRGS-Porto Alegre, Brazil
Marie-France Beaufort*, Pprime Institut - CNRS-Université de Poitiers-ENSMA, France

*presenting author