Microstructural evolution of polycrystalline Si films during Ni-silicide-mediated lateral crystallization of amorphous Si films has been studied. The growth direction of the crystallized needle-like grains was not parallel to the crystallization direction of the film. The grains were aligned nearly parallel to each other and consequently, a macroscopic quasi grain was formed. The dominant growth directions of the needle-like grains with respect to the crystallization direction were Ϯ(35 Ϯ 5)°and Ϯ(55 Ϯ 5)°, which were well matched for the growth of ͕110͖-oriented, needle-like grains along the ͗111͘ directions with 70°branching and 110°b ranching, respectively. The length of the transition region in front of the silicide-mediated lateral crystallization was about 5 m; thin-film transistors should not be located here because of poor microstructure.
A viscous Ni solution was coated over amorphous Si thin film for evenly spread of Ni metal source. The Ni solution was prepared by dissolving NiCl 2 into 1N HCl and mixing with propylene glycol. NiCl 2 and Ni were deposited on the amorphous film after oven dry and they enabled to obtain a uniform crystallization. The crystallization using the viscous Ni solution was a Ni-silicide mediated process, the same process used with Ni metal layer. The crystallization temperature was lowered to 480 °C by the synergy effect of silicide-mediated crystallization and microwave-induced crystallization. Lateral crystallization was also enhanced such that the velocity of lateral crystallization by microwave annealing became faster than by furnace annealing.
A polycrystalline Si film with uniform and large grains can be grown by crystallizing with
Al∕Ni
chloride vapor transport. At the initial stage of crystallization, the poly-Si grains had round-shaped cores with needles at the growth front. It showed that the needles were grown by the Ni-induced lateral crystallization process and the sidewall of the needles was enlarged by the Al-induced crystallization process. The needles were emerged coherently to an extent by the sidewall growth. As a result, a poly-Si film with grains larger than
15μmdiam
and fewer intragrain defects was obtained. The Ni concentration was constant through out the film thickness with a value of
1×1019cm−3
. The Al concentration at the surface was
1019cm−3
and was reduced below
1016cm−3
at 25 -nm depth. The thin film transistor utilizing the film showed an electron mobility of
47cm2∕Vs
at a drain voltage of
Vnormald=0.1
. But the threshold voltage was
5.2V
that is considered as relatively high due to Al doping.
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