Reactive Force Field Molecular Dynamics Study of the Effects of Gaseous Species on the Composition and Crystallinity of Silicon-Germanium Thin Films

N Uene and T Mabuchi and M Zaitsu and S Yasuhara and T Tokumasu, CRYSTAL GROWTH & DESIGN, 23, 4990-5000 (2023).

DOI: 10.1021/acs.cgd.3c00240

The left reaction chamber indicatessilicon-germanium(SiGe) film growth by plasma-enhanced chemical vapor deposition (PECVD)methods. By using ReaxFF MD, we simulated the SiGe film growth incombinations of SiH3, SiH2, GeH3,and GeH2 radicals to evaluate the effects of gaseous specieson the film composition and crystallinity as well as to understandthe growth mechanisms. We simulated the growth of a silicon- germanium(SiGe) filmusing reactive force field molecular dynamics (ReaxFF MD) in combinationsof SiH3, SiH2, GeH3, and GeH2 radicals to evaluate the effects of gaseous species on thin-filmcomposition and crystallinity and to understand the growth mechanisms.The film compositions could be estimated in these combinations becauseof the linear increase in the Ge content of the films. The averagecrystallinity grown by SiH3 was higher than that by SiH2 radicals. The crystallinity of the film grown by SiH3 radicals tends to be drastically decreased by GeH2 radicals. The growth mechanisms for XH3 and XH2 (X = Si orGe) radicals were compared. XH3 radicals abstracted surfaceH atoms, and then more XH3 radicals chemisorbedonto the formed dangling bonds, resulting in film growth through atwo-step reaction known as the Eley-Rideal-type (ER-type) mechanism.The ER-type mechanism grows the film with a low hydrogen content andhigh crystallinity. In contrast, XH2 radicalsdisplayed not only the ER-type mechanism but also a one-step reaction,the H-capturing mechanism, which incorporates surface H atoms intothe gaseous species. The H-capturing mechanism results in film growthwith high hydrogen content and low crystallinity. The growth mechanismsare influenced by high/low H-coverage. The surface H atoms thermallymove around the bonded atoms and give their kinetic energy to thediffusing gaseous species. Excess surface H atoms promote desorption.Our results from the ReaxFF MD suggested experimental settings andconditions that would enable the growth of high-quality films. Ourresults also suggested that SiH3 and GeH3 radicalsshould be mainly generated in the gas phase for high-quality SiGefilm growth.

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