crystallizing a semiconductor layer with a laser selected from the group consisting of a continuous wave laser and a pulsed laser with a repetition rate of 10 MHz to 100 GHz;

forming a first insulating layer on the semiconductor layer after crystallizing the semiconductor layer by oxidation treatment with the use of oxygen radicals produced by plasma with an electron temperature of 3 eV or less and an electron density of 1×10¹¹ cm⁻³ or more;

forming a first conductive layer over the first insulating layer;

etching the first conductive layer by using a first mask pattern which is intentionally formed to have a portion with a nonuniform thickness and a second mask pattern which is formed to have a uniform thickness by using a photomask or a reticle including an auxiliary pattern having a function of reducing the light intensity;

forming a second insulating layer over the first conductive layer after etching the first conductive layer;

forming a second conductive layer over the second insulating layer;

etching the second conductive layer;

forming a third insulating layer over the second conductive layer after etching the second conductive layer; and

etching the first insulating layer, the second insulating layer and the third insulating layer to form a contact hole reaching the semiconductor layer.