Fabrication method of thin film transistor

1. Field of Invention

The invention relates to a thin-film transistor (TFT) fabrication method and, in particular, to a fabrication method of TFT using four-mask process.

2. Related Art

FIGS. 1A to 1F show the cross-sectional views of a conventional TFT fabrication method. As shown in FIG. 1A , a first metal is deposited on an insulating substrate 100 by sputtering (not shown). The first metal layer is etched to form a gate 101 on the substrate 100 . The substrate 100 is alkaline-free glass. The first metal layer can be an Al, Cr or Mo layer. The etching process is a wet etching process.

As shown in FIG. 1B , the plasma enhanced chemical vapor deposition (PECVD) method is employed to deposit a gate insulation layer 102 , a semiconductor layer 103 , and an ohmic contact layer 104 on the substrate 100 to cover the gate 101 in sequence. A Photolithographic and etching process is used to pattern the semiconductor layer 103 and the ohmic contact layer 104 , and then a patterned ohmic contact layer 104 and a patterned semiconductor layer 103 are formed. The etching method is a dry etching process. The semiconductor layer 103 is an amorphous silicon layer. The ohmic contact layer 104 is an n-doped amorphous silicon layer. The gate insulation layer 102 is a silicon nitride layer.

As shown in FIGS. 1C and 1D , a second metal layer 105 is deposited on the ohmic contact layer 104 by sputtering to cover the gate insulation layer 102 . A photolithographic and etching process is employed to etch the second metal layer 105 , and then the second metal layer 105 is patterned to form a source 105 a and a drain 105 b . A back channel etching (BCE) process is used to etch the ohmic contact layer 104 and the semiconductor layer 103 to form a channel region 106 . The second metal layer 105 may be an Al, Cr, or Mo layer.

As shown in FIG. 1E , the PECVD method is used to deposit a passivation layer 107 over the substrate 100 , covering the patterned second metal layer 105 and the gate insulation layer 102 . A photolithographic and etching process is employed to etch the passivation layer 107 to form a patterned passivation layer 107 . A contact hole 108 is formed above the drain 105 b . The passivation layer 107 is a silicon nitride layer.

As shown in FIG. 1F , a pixel electrode layer 109 is deposited on the substrate 100 by sputtering. A photolithographic and etching process is employed to pattern the pixel electrode layer 109 . The pixel electrode layer 109 is made of indium tin oxide (ITO).

An objective of the invention is to provide a fabrication method of TFT, which uses fewer processes to save time and costs and increases the yield and thus the production efficiency.

The disclosed TFT fabrication method includes the steps of: forming a gate on a substrate; forming a gate insulation layer, a semiconductor layer, and a metal layer on the substrate in sequence, which cover the gate; patterning the metal layer and the semiconductor layer to form a patterned metal layer and a patterned semiconductor layer covering the gate; forming a patterned first passivation layer on the substrate and exposing the patterned metal layer; forming a pixel electrode layer on the substrate to cover the patterned first passivation layer and the patterned metal layer; forming a patterned photoresist layer on the substrate and exposing the pixel electrode layer above the gate; etching the pixel electrode layer and the patterned metal layer above the gate to form a patterned pixel electrode layer, a source, and a drain to form a channel region on the patterned semiconductor layer; forming a second passivation layer on the substrate; and removing the patterned photoresist layer to lift off the second passivation layer, thereby exposing the patterned pixel electrode layer.

According to another embodiment of the invention, the disclosed method includes the steps of: forming a gate on a substrate; forming a gate insulation layer, a semiconductor layer, an ohmic contact layer, and a metal layer on the substrate in sequence, which cover the gate; patterning the metal layer, the ohmic contact layer, and the semiconductor layer to form a patterned metal layer, a patterned ohmic contact layer, and a patterned semiconductor layer covering the gate; forming a patterned first passivation layer on the substrate and exposing the patterned metal layer; forming a pixel electrode layer on the substrate to cover the patterned first passivation layer and the patterned metal layer; forming a patterned photoresist layer on the substrate and exposing the pixel electrode layer above the gate; etching the pixel electrode layer, the patterned ohmic contact layer and the patterned metal layer above the gate to form a patterned pixel electrode layer, a source and a drain and to form a channel region on the patterned semiconductor layer; forming a second passivation layer on the substrate; and removing the patterned photoresist layer to lift off the second passivation layer, thereby exposing the patterned pixel electrode layer.

The invention will become more fully understood from the detailed description given hereinbelow illustration only, and thus are not limitative of the present invention, and wherein:

FIGS. 1A to 1F show cross-sectional views of a conventional TFT fabrication method; and

FIGS. 2A to 2J show cross-sectional views of the disclosed TFT fabrication method.

The cross-sectional views of the fabrication process disclosed herein are shown in FIGS. 2A to 2F . As shown in FIG. 2A , a physical vapor deposition (PVD) method such as sputtering is employed to deposit a first metal layer (not shown) on an insulating substrate 200 . A photolithographic and etching process is used to etch the first metal layer, forming a gate 201 on the substrate 200 . The substrate 200 is alkaline-free glass. The first metal layer can be an AL, Cr, Mo, Al—Nd, or stacked Mo/Al—Nd layer. The etching process is a wet etching or dry etching process.

As shown in FIG. 2B , the plasma enhanced chemical vapor deposition (PECVD) method is used to deposit a gate insulation layer 210 , a semiconductor layer 202 , an ohmic contact layer 209 on the substrate 200 in sequence, which cover the gate 201 . A second metal layer 203 is then deposited on the ohmic contact later 209 using a physical vapor deposition (PVD) method such as sputtering. The semiconductor layer 202 can be an amorphous silicon layer. The ohmic contact layer 209 can be an n-doped amorphous silicon layer. The gate insulation layer 210 can be either a silicon nitride or a silicon dioxide layer. The second metal layer 203 uses a material selected from the group consisting of Al, Cr, Mo, Al—Nd, and stacked Mo/Al—Nd/Mo layers.

As shown in FIG. 2C , a photolithographic and etching process is used to pattern the second metal layer 203 , the ohmic contact layer 209 , and the semiconductor layer 202 to form a patterned second metal layer 203 a , a patterned ohmic contact layer 209 a , and a patterned semiconductor layer 202 a . The etching method is wet etching.

As shown in FIG. 2D , the PECVD method is employed to deposit a first passivation layer (now shown) on the substrate 200 to cover the patterned second metal layer 203 a , the patterned ohmic contact layer 209 a , and the patterned semiconductor layer 202 a . A photolithographic and etching process is further used to etch the first passivation layer, exposing the patterned second metal layer 203 a and forming the patterned first passivation layer 204 . The first passivation layer uses such materials as silicon nitride or silicon dioxide.

As shown in FIG. 2E , a physical vapor deposition (PVD) method such as sputtering is used to deposit a pixel electrode layer 205 on the substrate 200 to cover the patterned first passivation layer 204 and the patterned second metal layer 203 a . The pixel electrode layer 205 can be made of transparent indium tin oxide (ITO).

With simultaneous reference to FIGS. 2F , 2 G, and 2 H, a photolithographic process is further performed. First, a patterned photoresist layer is formed on the substrate, exposing part of the pixel electrode layer above the gate 201 . A dry etching method is used to remove the exposed pixel electrode layer 205 and part of the patterned second metal layer 203 a under it, forming a source 211 , a drain 212 , and a patterned pixel electrode layer 205 a . A back channel etching (BCE) process is used to etch the exposed, patterned ohmic contact layer 209 a and part of the semiconductor layer 202 a , forming a channel region 207 .

As shown in FIG. 2I , the PECVD method is used to form a second passivation layer 208 on the substrate 200 at a lower temperature about 90° C. to cover the patterned photoresist layer 206 and the channel region 207 but exposing the side 213 of the patterned photoresist layer. The temperature for forming the second passivation layer 208 does not result in the thermal cracking of the patterned photoresist layer 206 . The second passivation layer 208 is made of a material such as silicon nitride or silicon oxide.

As shown in FIG. 2J , a wet photoresist removal method is used to remove the patterned photoresist layer 206 . It is achieved by adding an organic solvent in this process to dissolve the side of the patterned photoresist layer 206 . The second passivation layer 208 above the patterned photoresist layer 206 is thus lifted off, thereby exposing the patterned pixel electrode layer 205 above the source 211 and the drain 212 while leaving the patterned second passivation layer 208 a covering the channel region 207 . This completes the fabrication of the TFT.

In comparison with the conventional manufacturing method of TFT that requires five-mask process, the disclosed TFT fabrication method only requires four-mask process. This can reduce the time and cost of the fabrication, while increasing the yield and production efficiency.

Certain variations would be apparent to those skilled in the art, which variations are considered within the spirit and scope of the claimed invention.