Method for fabricating polysilicon liquid crystal display device

1. A method of fabricating a polysilicon liquid crystal display device, comprising:

forming a gate electrode on a substrate;

forming a first insulating layer on the gate electrode;

forming a first amorphous silicon layer on the first insulating layer;

forming a photoresist on the first amorphous silicon layer;

patterning the photoresist using a mask to form a photoresist pattern on a channel region of the first amorphous silicon layer, wherein the photoresist pattern has a width smaller than a width of the gate electrode;

forming a second amorphous silicon layer including high density impurity ions over the photoresist pattern and the first amorphous silicon layer, wherein the second amorphous silicon layer including high density impurity ions is formed by infusing the high density impurity ions into a chamber while the second amorphous silicon layer is deposited by PECVD;

removing the photoresist pattern and a portion of the second amorphous silicon layer on the photoresist pattern by a lift-off process to define a channel region on the first amorphous silicon layer;

performing dehydrogenation by heating the first and second amorphous silicon layers to remove hydrogen within the first and second amorphous silicon layers;

crystallizing the first and second amorphous silicon layers by a laser crystallization process;

forming a conductive layer on the crystallized first and second silicon layers;

forming a photoresist film on the conductive layer;

exposing the photoresist film by a slit mask to form a stepped photoresist pattern having a thinner thickness at an upper portion of the channel region than that at other regions;

removing the conductive layer, the crystallized first and second silicon layers, and the first insulating layer by an etching process using the stepped photoresist pattern as a mask to define an active layer;

ashing the stepped photoresist pattern to remove a portion of the stepped photoresist pattern on the channel region to expose a portion of the conductive layer;

removing an exposed portion of the conductive layer on the crystallized first silicon layer to form source and drain electrodes;

removing the ashed photoresist pattern t4ae remaining on the source and drain electrodes;

forming a second insulating layer on the substrate including the source and drain electrodes;

forming a contact hole exposing the drain electrode in the second insulating layer; and

forming a pixel electrode on the second insulating layer and electrically connected to the drain electrode through the contact hole.

2. The method of claim 1 , wherein the high density impurity ions includes Group III or Group V type ions.

3. The method of claim 1 , wherein in the performing dehydrogenation, the substrate having the first and second amorphous layers is put into a furnace and heated at about 400° C. so as to remove the hydrogen.

4. A method of fabricating a polysilicon liquid crystal display device, comprising:

forming a buffer layer on a substrate;

forming a gate electrode on the buffer layer;

forming a first insulating layer on the gate electrode;

forming a first amorphous silicon layer on the first insulating layer;

forming a photoresist on the first amorphous silicon layer;

patterning the photoresist using a mask to form a photoresist pattern on a channel region of the first amorphous silicon layer, wherein the photoresist pattern has a width smaller than a width of the gate electrode;

forming a second amorphous silicon layer including high density impurity ions over the photoresist pattern and the first amorphous silicon layer, wherein the second amorphous silicon layer including high density impurity ions is formed by infusing the high density impurity ions into a chamber while the second amorphous silicon layer is deposited by PECVD and wherein the high density impurity ions includes Group III or Group V type ions;

removing the photoresist pattern and a portion of the second amorphous silicon layer on the photoresist pattern by a lift-off process to define a channel region on the first amorphous silicon layer;

performing dehydrogenation by heating the first and second amorphous silicon layers to remove hydrogen within the first and second amorphous silicon layers, wherein in the performing dehydrogenation, the substrate having the first and second amorphous silicon layer is put into a furnace and heated at about 400 degrees C. so as to remove the hydrogen;

crystallizing the first and second amorphous silicon layers by a laser crystallization process;

forming a conductive layer on the crystallized first and second silicon layers;

forming a photoresist film on the conductive layer;

exposing the photoresist film by a slit mask to form a stepped photoresist pattern having a thinner thickness at an upper portion of the channel region than that at other regions;

removing the conductive layer, the crystallized first and second silicon layers, and the first insulating layer by an etching process using the stepped photoresist pattern as a mask to define an active layer;

ashing the stepped photoresist pattern to remove a portion of the stepped photoresist pattern on the channel region to expose a portion of the conductive layer;

removing the conductive layer on the crystallized first silicon layer to form source and drain electrodes;

removing the ashed photoresist pattern remaining on the source and drain electrodes;

forming a second insulating layer on the substrate including the source and drain electrodes;

forming a contact hole exposing the drain electrode in the second insulating layer; and

forming a pixel electrode on the second insulating layer and electrically connected to the drain electrode through the contact hole.