A metal element typified by Ni has an adverse effect on device properties of a
TFT, and consequently, a step for removing the elements (hereinafter referred to
as a gettering step) has been carried out. However, gettering steps as described
above have the disadvantage of high cost due to an increase in the number of steps.
Accordingly, a manufacturing method of a crystalline semiconductor film, which
does not require a gettering step, has been in demand.
A TFT of the present invention is characterized by reducing the concentration
of
the metal element, typically Ni, in the crystalline semiconductor film to less
than 41016 atoms/cm3, more specifically, 51015
atoms/cm3 to 31016 atoms/cm3, preferably,
71015 atoms/cm3 to 31016 atoms/cm3.
And the present invention enables crystallization even by the metal element with
a low concentration and an omission of a gettering step.
