1. Technical Field
Several aspects of the present invention relate to a method for manufacturing a semiconductor thin film and a semiconductor device using the semiconductor thin film.
2. Related Art
In displays of forming images using a thin film transistor (hereinafter referred to as a “TFT”) as the switching element, such as liquid crystal displays, achieving higher performance of TFT is demanded.
Higher performance can be achieved by what has been referred to as a polysilicon TFT, which uses polycrystalline silicon for the active layer.
For the purpose of reducing cost of displays, a method of recrystallizing (modifying) an amorphous silicon layer deposited on a low-cost glass substrate at temperatures equal to or less than the strain point of the glass substrate is generally used.
JP-A-9-293687, a first example of related art, discloses a laser annealing method where an amorphous silicon layer is melt and re-crystallized by laser annealing as a technique of recrystallizing an amorphous silicon layer at low temperature.
JP-A-9-156916, a second example of related art, discloses a method where a metal element is added onto an amorphous silicon layer to decrease the temperature required for re-crystallization by a chemical vapor deposition (CVD) apparatus using electrodes made of a material containing a metal element to facilitate crystallization of silicon.
However, the above-mentioned two methods involve the following problems.
In the former, cost reduction is difficult because laser oscillators are expensive.
In the latter, achieving higher performance of TFT is difficult, not only because the device is expensive but also because a metal element remaining in the recrystallized silicon film decreases mobility in a silicon film.