Elucidation of the layer exchange mechanism in the formation of polycrystalline silicon by aluminum-induced crystallization

Abstract

Aluminum-induced crystallization of amorphous silicon is studied as a promising low-temperature alternative to solid-phase and laser crystallization. Its advantages for the formation of polycrystalline silicon on foreign substrates are the possible usage of simple techniques, such as thermal evaporation and dc magnetron sputtering deposition, and relatively short processing times in the range of 1 h. The overall process of the Al and Si layer exchange during annealing at temperatures below the eutectic temperature of 577 °C is investigated by various microscopy techniques. It is shown that the ratio of the Al and a-Si layer thicknesses is vitally important for the formation of continuous polycrystalline silicon films on glass substrates. The grain size of these films is dependent on the annealing temperature and evidence is given that grain sizes of 20 μm and more can be achieved. The poly-Si films are described as solid solutions containing 3×1019 cm−3 Al atoms as solute. Only a fraction of the solute is located at substitutional sites, and therefore, electrically active leading to the p-type character of the polycrystalline silicon films. Additional Al is trapped in the form of small clusters between the continuous Si layer and the substrate. The interaction of the Al and Si layers is discussed as a diffusion-controlled process where the depletion of Si solute in the Al matrix around growing Si grains is of major importance for the overall crystallization process and the size of the resulting Si grains.

On the Mechanisms Governing Aluminum-Mediated Solid-Phase Epitaxy of Silicon

“…This is in agreement with the results previously reported by Nast and co-authors 24,25 for a layer-exchange aluminum-induced crystallization mechanism on glass substrates. During the SPE process, the Al film is segregated above the SPE-Si and forms an amorphous-like film like the one shown in Fig.…”

Metal Induced Crystallization

“…The Si oxide layer is transformed by the Al into a mixture of Al oxide and an Al x Si phase. This newly formed Al x Si phase provides a diffusion channel for the Si and Al atoms (Nast & Wenham, 2000). The evaporated Al films are of polycrystalline nature, there are four different diffusion paths available for the diffusion of the Si atoms.…”

High Gauge Factor Piezoresistors Using Aluminium Induced Crystallisation of Silicon at Low Thermal Budget

“…It shows that the aluminium concentration remains unchanged in the intrinsic and the phosphorus doped cases. From previous study [1], the aluminium concentration in the intrinsic case is estimated to be 2.8 × 10 18 /cm 3 . However, the phosphorus concentration in the AIC polysilicon increases as more phosphorus doping is introduced into the precursor.…”

“…Upon annealing in dry N2 ambience at 450 °C for 2 h, a continuous polysilicon film is formed underneath the aluminium layer through the process of aluminium induced crystallization [1].…”

“…However, these processes require high temperature making them incompatible with post CMOS-MEMS integration. AIC polysilicon films formed at temperatures less than 550 °C is commonly used for solar cell applications [1]. But, their use for piezo-resistive applications has been limited due to the formation of polysilicon films with small gauge factor of less than 20 [2,3].…”