Methods for process time reduction and structural improvement of SiGe films obtained by Solid Phase Crystallization

Abstract

Two methods, ion implantation and crystallization at two different temperatures, have been investigated to reduce the process time and to improve the structural properties of polycrystalline SiGe films obtained by solid phase crystallization for thin film transistors applications. The starting material was amorphous SiGe films deposited by low pressure chemical vapour deposition on oxidized silicon substrates. The crystallization kinetics and microstructure were analyzed in both cases using transmission electron microscopy and X-ray diffractometry. The first method consisted of the ion implantation with C or F and the subsequent crystallization at 600 °C. The implanted samples show greater grain sizes, smaller grain size dispersion and stronger (111) preferred orientation than the unimplanted ones. The second method consisted of the crystallization by sequential annealing at two different temperatures. The samples were processed by rapid thermal annealing at 625 °C for several minutes to form a certain density of crystalline nuclei. The subsequent crystallization at 525 °C takes place mainly from the previously induced nuclei. The process time is reduced by 50 %. The grain size in the samples processed in this way is at least equal than in the samples crystallized without the RTA treatment. This crystallization method does not affect the preferred orientation of the grains.