Method for manufacturing semiconductor device

Abstract

To provide a manufacturing method of a highly reliable TFT, by which a more refined pattern can be formed through a process using four or three masks, and a semiconductor device. A channel-etched bottom gate TFT structure is adopted in which a photoresist is selectively exposed to light by rear surface exposure utilizing a gate wiring to form a desirably patterned photoresist, and further, a halftone mask or a gray-tone mask is used as a multi-tone mask. Further, a step of lifting off using a halftone mask or a gray-tone mask and a step of reflowing a photoresist are used.

1 . A method for manufacturing a semiconductor device, comprising:
 forming a first conductive film over a substrate;   etching the first conductive film using a first photoresist to form a gate electrode;   forming a gate insulating film over the gate electrode;   forming a first semiconductor layer over the gate insulating film;   forming a second semiconductor layer including an impurity element imparting one conductivity type over the first semiconductor layer;   performing rear surface exposure to form a second photoresist;   etching the first semiconductor layer and the second semiconductor layer including the impurity element imparting one conductivity type using the second photoresist, thereby forming a first semiconductor island and a second semiconductor island including the impurity element imparting one conductivity type;   forming a second conductive film over the substrate;   forming a third photoresist using a multi-tone mask over the second conductive film;   etching the second conductive film using the third photoresist;   ashing the third photoresist;   etching the second conductive film using the ashed third photoresist to form a source electrode and a drain electrode; and   etching the first semiconductor island and the second semiconductor island including the impurity element imparting one conductivity type using the ashed third photoresist to form a channel region, a source region, and a drain region.   
   
   
       2 . The method for manufacturing a semiconductor device, according to  claim 1 , wherein the multi-tone mask is a halftone mask or a gray-tone mask. 
   
   
       3 . The method for manufacturing a semiconductor device, according to  claim 1 , wherein the rear surface exposure is performed through the first semiconductor layer and the second semiconductor layer including the impurity element imparting one conductivity type. 
   
   
       4 . The method for manufacturing a semiconductor device, according to  claim 1 , wherein the first semiconductor layer is an amorphous semiconductor layer. 
   
   
       5 . The method for manufacturing a semiconductor device, according to  claim 1 , wherein the first semiconductor layer is an i-type amorphous silicon layer. 
   
   
       6 . A method for manufacturing a semiconductor device, comprising:
 forming a first conductive film over a substrate;   etching the first conductive film using a first photoresist to form a gate electrode;   forming a gate insulating film over the gate electrode;   forming a first semiconductor layer over the gate insulating film;   forming a second semiconductor layer including an impurity element imparting one conductivity type over the first semiconductor layer;   performing rear surface exposure to form a second photoresist;   etching, using the second photoresist, the first semiconductor layer and the second semiconductor layer including the impurity element imparting one conductivity type, thereby forming a first semiconductor island and a second semiconductor island including the impurity element imparting one conductivity type;   forming a second conductive film over the substrate;   forming a third photoresist using a multi-tone mask over the second conductive film;   etching, using the third photoresist, the second conductive film, the second semiconductor island including the impurity element imparting one conductivity type, and the first semiconductor island to form a wiring;   ashing the third photoresist;   etching the second conductive film using the ashed third photoresist to form a source electrode and a drain electrode;   etching the second semiconductor island including the impurity element imparting one conductivity type and the first semiconductor island using the ashed third photoresist to form a channel region, a source region, and a drain region;   forming a protective film over the substrate;   forming a contact hole in the protective film using a fourth photoresist;   forming a third conductive film over the protective film; and   etching the third conductive film using a fifth photoresist to form a pixel electrode.   
   
   
       7 . The method for manufacturing a semiconductor device, according to  claim 6 , wherein the multi-tone mask is a halftone mask or a gray-tone mask. 
   
   
       8 . The method for manufacturing a semiconductor device, according to  claim 6 , wherein the rear surface exposure is performed through the first semiconductor layer and the second semiconductor layer including the impurity element imparting one conductivity type. 
   
   
       9 . The method for manufacturing a semiconductor device, according to  claim 6 , wherein the first semiconductor layer is an amorphous semiconductor layer. 
   
   
       10 . The method for manufacturing a semiconductor device, according to  claim 6 , wherein the first semiconductor layer is an i-type amorphous silicon layer. 
   
   
       11 . The method for manufacturing a semiconductor device, according to  claim 6 , wherein the pixel electrode is a transparent conductive film. 
   
   
       12 . A method for manufacturing a semiconductor device, comprising:
 forming a first conductive film over a substrate;   etching the first conductive film using a first photoresist to form a gate electrode;   forming a gate insulating film over the gate electrode;   forming a first semiconductor layer over the gate insulating film;   forming a second semiconductor layer including an impurity element imparting one conductivity type over the first semiconductor layer;   performing first rear surface exposure to form a second photoresist;   etching, using the second photoresist, the first semiconductor layer and the second semiconductor layer including the impurity element imparting one conductivity type, thereby forming a first semiconductor island and a second semiconductor island including the impurity element imparting one conductivity type;   forming a second conductive film over the substrate;   forming a third photoresist using a first multi-tone mask over the second conductive film;   etching, using the third photoresist, the second conductive film, the second semiconductor island including the impurity element imparting one conductivity type, and the first semiconductor island;   ashing the third photoresist;   etching the second conductive film using the ashed third photoresist to form a source electrode and a drain electrode;   etching the second semiconductor island including the impurity element imparting one conductivity type and the first semiconductor island using the ashed third photoresist to form a channel region, a source region, and a drain region;   forming a fourth photoresist using a second multi-tone mask;   ashing the fourth photoresist;   forming a third conductive film over the second conductive film and the fourth photoresist;   removing the fourth photoresist and part of the third conductive film formed thereon to form a pixel electrode;   forming a protective film over the substrate;   performing second rear surface exposure to form a fifth photoresist over the protective film;   performing a reflow process on the fifth photoresist; and   etching the protective film using the fifth photoresist subjected to the reflow process.   
   
   
       13 . The method for manufacturing a semiconductor device, according to  claim 12 , wherein each of the first and second multi-tone masks is a halftone mask or a gray-tone mask. 
   
   
       14 . The method for manufacturing a semiconductor device, according to  claim 12 , wherein the first rear surface exposure is performed through the first semiconductor layer and the second semiconductor layer including the impurity element imparting one conductivity type. 
   
   
       15 . The method for manufacturing a semiconductor device, according to  claim 12 , wherein the first semiconductor layer is an amorphous semiconductor layer. 
   
   
       16 . The method for manufacturing a semiconductor device, according to  claim 12 , wherein the first semiconductor layer is an i-type amorphous silicon layer. 
   
   
       17 . The method for manufacturing a semiconductor device, according to  claim 12 , wherein the pixel electrode is a transparent conductive film. 
   
   
       18 . A method for manufacturing a semiconductor device, comprising:
 forming a first conductive film over a substrate;   etching the first conductive film using a first photoresist to form a gate electrode and a wiring;   forming a gate insulating film over the gate electrode and a first wiring;   forming a first semiconductor layer over the gate insulating film;   forming a second semiconductor layer including an impurity element imparting one conductivity type over the first semiconductor layer;   performing first rear surface exposure to form a second photoresist;   etching, using the second photoresist, the first semiconductor layer and the second semiconductor layer including the impurity element imparting one conductivity type, thereby forming a first semiconductor island and a second semiconductor island including the impurity element imparting one conductivity type over the gate electrode and forming a third semiconductor island and a fourth semiconductor island including the impurity element imparting one conductivity type over the first wiring;   forming a second conductive film over the substrate;   forming a third photoresist using a first multi-tone mask over the second conductive film;   etching, using the third photoresist, a part of the second conductive film and the fourth semiconductor island including the impurity element imparting one conductivity type and the third semiconductor island over the first wiring;   ashing the third photoresist;   etching the second conductive film using the ashed third photoresist to form a source electrode and a drain electrode;   etching the second semiconductor island including the impurity element imparting one conductivity type and the first semiconductor island using the ashed third photoresist to form a channel region, a source region, and a drain region;   forming a fourth photoresist using a second multi-tone mask over the substrate;   etching part of the gate insulating film, which is not covered with the fourth photoresist, using the fourth photoresist to form a contact hole over the first wiring;   ashing the fourth photoresist;   forming a third conductive film over the second conductive film and the fourth photoresist;   removing the fourth photoresist and parts of the third conductive film formed on the fourth photoresist to form a pixel electrode and a second wiring;   forming a protective film over the substrate;   performing second rear surface exposure to form a fifth photoresist over the protective film;   performing a reflow process on the fifth photoresist; and   etching the protective film using the fifth photoresist subjected to the reflow process.   
   
   
       19 . The method for manufacturing a semiconductor device, according to  claim 18 , wherein each of the first and second multi-tone masks is a halftone mask or a gray-tone mask. 
   
   
       20 . The method for manufacturing a semiconductor device, according to  claim 18 , wherein the first rear surface exposure is performed through the first semiconductor layer and the second semiconductor layer including the impurity element imparting one conductivity type. 
   
   
       21 . The method for manufacturing a semiconductor device, according to  claim 18 , wherein the first semiconductor layer is an amorphous semiconductor layer. 
   
   
       22 . The method for manufacturing a semiconductor device, according to  claim 18 , wherein the first semiconductor layer is an i-type amorphous silicon layer. 
   
   
       23 . The method for manufacturing a semiconductor device, according to  claim 18 , wherein the pixel electrode is a transparent conductive film.