Abstract:
To provide a method for manufacturing a TFT substrate in which a channel length can be stably formed while the number of masks is reduced, and a method for manufacturing a TFT substrate which can individually control impurity concentrations for channels of an n-type TFT and a p-type TFT without increasing the number of masks. A method for manufacturing a TFT substrate includes processing a gate of the n-type TFT, a gate of the p-type TFT, and an upper capacitor electrode by using a half-tone mask instead of some of normal masks to reduce the number of masks, and changing impurity concentrations of semiconductor films located in regions which become a channel of the n-type TFT, a source and a drain of the n-type TFT, a channel of the p-type TFT, a source and a drain of the p-type TFT, and an lower capacitor electrode, by using a pattern of the half-tone mask and a normal mask.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority from Japanese application JP 2007-272088 filed on Oct. 19, 2007, the content of which is hereby incorporated by reference into this application. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a method for manufacturing a thin film transistor (TFT) substrate which is used in a liquid crystal display apparatus or a display apparatus using an organic electroluminescence device. More particularly, the present invention relates to a method for manufacturing a CMOS TFT substrate on which an n-type thin film transistor (TFT) and a p-type thin film transistor are included. 
         [0004]    2. Description of the Related Art 
         [0005]    A thin film transistor (hereinafter, referred to as TFT in some cases) is used in a liquid crystal display apparatus or the like. In a case where drive circuits are formed on a substrate in addition to pixels, there is generally used a TFT including a polycrystalline Si film, which is capable of providing high mobility. Particularly, a so-called CMOS TFT substrate on which both of n-type TFTs and p-type TFTs are formed has an advantage of flexibility in circuit design, compared with a TFT substrate on which only n-type TFTs are formed. However, there has conventionally been a problem that the number of masks used in manufacturing is increased. 
         [0006]    In general, one more mask is required for formation of sources and drains of the p-type TFTs. In a case where threshold values are individually adjusted for the p-type TFTs and the n-type TFTs, another mask is required. As a method for reducing the number of masks, a contact process with pixel electrodes is eliminated. Further, a mask having semitransparent regions besides transparent regions and opaque regions, that is, a half-tone mask, is used to reduce the number of masks. 
         [0007]    Examples of a method for unifying processing of a semiconductor film and processing of a metal film by using the half-tone mask, and a method for eliminating contacts with pixel electrodes are disclosed, for example, in SID 07 DIGEST, p. 73 (2007). An example of a method for unifying masks which are used for doping at a time of forming a gate and a source and drain is disclosed, for example, in JP 2002-217429 A and JP 2007-72451 A. 
         [0008]    An example of a method for manufacturing a gate and doping for a semiconductor film of a CMOS TFT substrate according to a conventional technology, in which the half-tone mask is used, is shown in  FIG. 19 .  FIG. 19  is a view showing mask patterns used in the manufacturing method and the structure of the TFT substrate obtained by using the mask patterns. Impurity implantation into an n-type TFT, a p-type TFT, and a capacitor, and electrode formation are performed by using three masks including two masks MSK 1 , MSK 2  and a half-tone mask HMK. Note that  FIG. 20  is a table showing correspondence relations between the mask patterns and respective regions of members formed on the TFT substrate. Each end of a channel PCH of the p-type TFT is defined by a boundary between an opaque region BL of the half-tone mask HMK and a transparent region OP thereof. Further, each end of a channel NCH of the n-type TFT is defined by a boundary between the opaque region BL of the half-tone mask HMK and a semitransparent region HT thereof, and a boundary between the opaque region BL of the half-tone mask HMK and the transparent region OP thereof, respectively. 
         [0009]    Further,  FIGS. 21A to 21D  and  22 A to  22 D are process views showing an example of a method for manufacturing the TFT substrate shown in  FIG. 19 . In  FIG. 21A , polysilicon PSI films are patterned on a glass substrate GLS via an undercoat film UDC, and a gate insulating film GI and metal films M 1  and M 2  are laminated thereon. Then, a thick-film resist pattern RST which corresponds to the opaque region BL and a thin-film resist pattern TFR which corresponds to the semitransparent region HT are formed by using the half-tone mask HMK. The metal films M 2  and M 1  are simultaneously etched to obtain a shape shown in  FIG. 21C , and then the thin-film resist is removed by ashing. In this case, part of the thick-film resist is also removed and a dimension thereof is reduced. The metal film M 2  is etched by using the remaining resist as a mask. After that, n-type impurities are implanted at low concentration via the metal film M 1  and the gate insulating film GI, and gate overlapped drains GLD are formed, thereby obtaining the structure shown in  FIG. 21D . After the resist is removed, the n-type impurities are implanted over the entire surface at high concentration and at low acceleration, and a source and drain NSD of the n-type TFT is formed by using the metal films M 1  and M 2  as masks. In addition, a different mask is used to form the resist pattern RST, and the n-type impurities are implanted to form a lower capacitor electrode BD, while protecting the TFTs, thereby obtaining the structure shown in  FIG. 22B . After the resist is removed, as shown in  FIG. 22C , a different mask is used to form the resist pattern RST for covering the n-type TFT and the capacitor, and p-type impurities are implanted at higher concentration than that of the n-type impurities to form a source and drain PSD of the p-type TFT. Then, the resist is removed, thereby obtaining the structure shown in  FIG. 22D . With the three masks, the gates, the sources, and the drains of the n-type TFT and the p-type TFT, and the lower capacitor electrode are formed. 
         [0010]    However, in the case where the processing of the semiconductor film and the processing of the metal film are unified by using the half-tone mask, the above-mentioned method for manufacturing the TFT substrate involves a problem of increasing the manufacturing processes in which another insulating film is provided so as to prevent metal contamination in the channels made of the semiconductor films. 
         [0011]    Further, in the case of eliminating the contacts with the pixel electrodes, a layout of the pixel electrodes is limited and there arises a problem that an aperture ratio is reduced. A method for unifying only a gate formation and doping has an advantage in that the number of masks can be reduced without changing the layout around the pixel electrodes, which has influence on the aperture ratio. However, conventionally, the method has not sufficed to stably form a channel length which affects TFT characteristics. Specifically, the use of a pattern which defines the boundaries of the sources, the drains, and the channels by using the boundaries of the opaque region of the half-tone mask, and variation in amount of regression at a time of resist ashing have caused a problem of inconstant channel length. For example, in the above-mentioned structural example shown in  FIG. 19 , the second metal film M 2  for a gate PGT of the p-type TFT and the second metal film M 2  for a gate NGT of the n-type TFT are formed by a pattern obtained by ashing of the resist pattern corresponding to the opaque region of the half-tone mask in the manufacturing process shown in  FIG. 21D , and the second metal films M 2  are affected by the amount of regression due to ashing of the resist pattern RST. Accordingly, dimension accuracy is degraded. Because the second metal film for the gate PGT corresponds to the channel PCH of the p-type TFT as shown in  FIG. 22C , and the second metal film for the gate NGT corresponds to the channel NCH of the n-type TFT as shown in  FIG. 21D , the dimension accuracy of the channel length is degraded. 
         [0012]    Further, conventional methods have involved a problem that, in order to individually adjust the threshold values of the n-type TFT and the p-type TFT, another mask is required to adjust impurity concentrations for the channels even when the half-tone mask is used. 
       SUMMARY OF THE INVENTION 
       [0013]    The present invention has an object to provide a method for manufacturing a TFT substrate, in which a half-tone mask is used to reduce the number of masks and, at the same time, the above-mentioned defects are eliminated. 
         [0014]    In the present invention disclosed in the subject application, the outlines of representative aspects of the present invention are briefly described as follows. 
         [0015]    (1) A method for manufacturing a thin film transistor substrate including thin film transistors, according to the present invention, for example, 
         [0016]    each of the thin film transistors including:
       a semiconductor film portion formed on an insulating substrate;   a gate insulating film portion laminated on the semiconductor film portion;   a gate made of a metal film portion formed on the gate insulating film portion; and   a channel formed in a region covered by the gate, which is formed of the semiconductor film portion,       
 
         [0021]    the thin film transistor substrate including:
       an n-type thin film transistor having regions of the semiconductor film portion, which are not covered by the gate and to which n-type impurities are doped, the regions becoming a source and a drain;   a p-type thin film transistor having regions of the semiconductor film portion, which are not covered by the gate and to which p-type impurities are doped, the regions becoming a source and a drain; and   a capacitor including:   a lower capacitor electrode formed in a region of another semiconductor film portion, to which the n-type impurities are doped, the another semiconductor film portion being formed on the same layer as the semiconductor film portion;   an upper capacitor electrode made of a metal film portion; and   another insulating film portion formed on the same layer as the gate insulating film portion to be interposed between the lower capacitor electrode and the upper capacitor electrode,       
 
         [0028]    the method including:
       processing the gate of the n-type thin film transistor, the gate of the p-type thin film transistor, and the upper capacitor electrode by using a first mask and a second mask; and   changing impurity concentrations of semiconductor film portions located in regions which become the channel of the n-type thin film transistor, the source and the drain of the n-type thin film transistor, the channel of the p-type thin film transistor, the source and the drain of the p-type thin film transistor, and the lower capacitor electrode, by using a pattern of the first mask and a pattern of the second mask,   the first mask being a half-tone mask having a transparent region, an opaque region, and a semitransparent region,   the second mask having a transparent region and an opaque region,       
 
         [0033]    in which boundaries between the channel of the n-type thin film transistor and the source and the drain of the n-type thin film transistor, and boundaries between the channel of the p-type thin film transistor and the source and the drain of the p-type thin film transistor are defined by boundaries other than a boundary between the opaque region and the semitransparent region of the half-tone mask or a boundary between the opaque region and the transparent region of the half-tone mask. 
         [0034]    According to the present invention, a pattern of the half-tone mask by which dimension accuracy is degraded is not used for the definition of the boundaries between the channels and the sources and drains, whereby channel lengths can be stably formed while the number of masks is reduced. 
         [0035]    (2) A method for manufacturing a thin film transistor substrate including thin film transistors, according to the present invention, for example, 
         [0036]    each of the thin film transistors including:
       a semiconductor film portion formed on an insulating substrate;   a gate insulating film portion laminated on the semiconductor film portion;   a gate made of a metal film portion formed on the gate insulating film portion; and   a channel formed in a region covered by the gate, which is formed of the semiconductor film portion,       
 
         [0041]    the thin film transistor substrate including:
       an n-type thin film transistor having regions of the semiconductor film portion, which are not covered by the gate and to which n-type impurities are doped, the regions becoming a source and a drain;   a p-type thin film transistor having regions of the semiconductor film portion, which are not covered by the gate and to which p-type impurities are doped, the regions becoming a source and a drain; and   a capacitor including:
           a lower capacitor electrode formed in a region of another semiconductor film portion, to which the n-type impurities are doped, the another semiconductor film portion being formed on the same layer as the semiconductor film portion;   an upper capacitor electrode made of a metal film portion; and   another insulating film portion formed on the same layer as the gate insulating film portion to be interposed between the lower capacitor electrode and the upper capacitor electrode,   
               
 
         [0048]    the method including:
       processing the gate of the n-type thin film transistor, the gate of the p-type thin film transistor, and the upper capacitor electrode by using a first mask and a second mask;   forming the channel of the n-type thin film transistor and the channel of the p-type thin film transistor in regions which are half-exposed with the first mask and unexposed with the second mask;   forming the source and the drain of the n-type thin film transistor in regions which are half-exposed with the first mask and exposed with the second mask;   forming the source and the drain of the p-type thin film transistor in regions which are exposed with the first mask and unexposed with the second mask; and   forming the lower capacitor electrode in a region which is unexposed with the first mask and exposed with the second mask,   the first mask being a half-tone mask having a transparent region, an opaque region, and a semitransparent region,   the second mask having a transparent region and an opaque region.       
 
         [0056]    (3) A method for manufacturing a thin film transistor substrate including thin film transistors, according to the present invention, for example, 
         [0057]    each of the thin film transistors including:
       a semiconductor film portion formed on an insulating substrate; and   a gate insulating film portion laminated on the semiconductor film portion,       
 
         [0060]    the thin film transistor substrate including:
       an n-type thin film transistor including:
           a first gate made of a metal film portion formed on the gate insulating film portion;   a channel formed in a region covered by the first gate, which is formed of the semiconductor film portion; and   a source and a drain formed in regions of the semiconductor film portion, which are not covered by the first gate and to which n-type impurities are doped;   
           a p-type thin film transistor including:
           a second gate made of a metal film portion formed on the gate insulating film portion;   a channel formed in a region covered by the second gate, which is formed of the semiconductor film portion; and   a source and a drain formed in regions of the semiconductor film portion, which are not covered by the second gate and to which p-type impurities are doped; and   
           a capacitor including:
           a lower capacitor electrode formed in a region of another semiconductor film portion, to which the n-type impurities are doped, the another semiconductor film portion being formed on the same layer as the semiconductor film portion;   an upper capacitor electrode made of a metal film portion; and   another insulating film portion formed on the same layer as the gate insulating film portion to be interposed between the lower capacitor electrode and the upper capacitor electrode,   
               
 
         [0073]    the method including:
       processing the first gate of the n-type thin film transistor, the second gate of the p-type thin film transistor, and the upper capacitor electrode by using a first mask and a second mask;   forming the channel of the n-type thin film transistor in a region which is half-exposed with the first mask and unexposed with the second mask;   forming the source and the drain of the n-type thin film transistor in regions which are half-exposed with the first mask and exposed with the second mask;   forming the channel of the p-type thin film transistor in a region which is exposed with the first mask and unexposed with the second mask;   forming the source and the drain of the p-type thin film transistor in regions which are exposed with the first mask and exposed with the second mask; and   forming the lower capacitor electrode in a region which is unexposed with the first mask and exposed with the second mask,   the first mask being a half-tone mask having a transparent region, an opaque region, and a semitransparent region,   the second mask having a transparent region and an opaque region.       
 
         [0082]    According to this structure, there is also provided an effect of individually controlling impurity concentrations for the channels of the n-type TFT and the p-type TFT without increasing the number of masks. 
         [0083]    (4) A method for manufacturing a thin film transistor substrate including thin film transistors, according to the present invention, for example, 
         [0084]    each of the thin film transistors including:
       a semiconductor film portion formed on an insulating substrate; and   a gate insulating film portion laminated on the semiconductor film portion,       
 
         [0087]    the thin film transistor substrate including:
       an n-type thin film transistor including:
           a first gate made of a metal film portion formed on the gate insulating film portion;   a channel formed in a region covered by the first gate, which is formed of the semiconductor film portion; and   a source and a drain formed in regions of the semiconductor film portion, which are not covered by the first gate and to which n-type impurities are doped;   
           a p-type thin film transistor including:
           a second gate made of a metal film portion formed on the gate insulating film portion;   a channel formed in a region covered by the second gate, which is formed of the semiconductor film portion; and   a source and a drain formed in regions of the semiconductor film portion, which are not covered by the second gate and to which p-type impurities are doped; and   
           a capacitor including:
           a lower capacitor electrode formed in a region of another semiconductor film portion, to which the n-type impurities are doped, the another semiconductor film portion being formed on the same layer as the semiconductor film portion;   an upper capacitor electrode made of a metal film portion; and   another insulating film portion formed on the same layer as the gate insulating film portion to be interposed between the lower capacitor electrode and the upper capacitor electrode,   
               
 
         [0100]    the method including:
       processing the first gate of the n-type thin film transistor, the second gate of the p-type thin film transistor, and the upper capacitor electrode by using a first mask and a second mask;   forming the channel of the n-type thin film transistor in a region which is unexposed with the first mask and unexposed with the second mask;   forming the source and the drain of the n-type thin film transistor in regions which are unexposed with the first mask and exposed with the second mask;   forming the channel of the p-type thin film transistor in a region which is half-exposed with the first mask and unexposed with the second mask;   forming the source and the drain of the p-type thin film transistor in regions which are half-exposed with the first mask and exposed with the second mask; and   forming the lower capacitor electrode in a region which is exposed with the first mask and unexposed with the second mask,   the first mask being a half-tone mask having a transparent region, an opaque region, and a semitransparent region,   the second mask having a transparent region and an opaque region.       
 
         [0109]    According to this structure, there is also provided an effect of individually controlling impurity concentrations for the channels of the n-type TFT and the p-type TFT without increasing the number of masks. 
         [0110]    (5) A method for manufacturing a thin film transistor substrate including thin film transistors, according to the present invention, for example, 
         [0111]    each of the thin film transistors including:
       a semiconductor film portion formed on an insulating substrate; and   a gate insulating film portion laminated on the semiconductor film portion,       
 
         [0114]    the thin film transistor substrate including:
       an n-type thin film transistor including:
           a first gate made of a metal film portion formed on the gate insulating film portion;   a channel formed in a region covered by the first gate, which is formed of the semiconductor film portion; and   a source and a drain formed in regions of the semiconductor film portion, which are not covered by the first gate and to which n-type impurities are doped;   
           a p-type thin film transistor including:
           a second gate made of a metal film portion formed on the gate insulating film portion;   a channel formed in a region covered by the second gate, which is formed of the semiconductor film portion; and   a source and a drain formed in regions of the semiconductor film portion, which are not covered by the second gate and to which p-type impurities are doped; and   
           a capacitor including:
           a lower capacitor electrode formed in a region of another semiconductor film portion, to which the n-type impurities are doped, the another semiconductor film portion being formed on the same layer as the semiconductor film portion;   an upper capacitor electrode made of a metal film portion; and   another insulating film portion formed on the same layer as the gate insulating film portion to be interposed between the lower capacitor electrode and the upper capacitor electrode,   
               
 
         [0127]    the method including:
       processing the first gate of the n-type thin film transistor, the second gate of the p-type thin film transistor, and the upper capacitor electrode by using a first mask and a second mask;   forming the channel of the n-type thin film transistor in a region which is half-exposed with the first mask and unexposed with the second mask;   forming the source and the drain of the n-type thin film transistor in regions which are half-exposed with the first mask and exposed with the second mask;   forming the channel of the p-type thin film transistor in a region which is unexposed with the first mask and unexposed with the second mask;   forming the source and the drain of the p-type thin film transistor in regions which are unexposed with the first mask and exposed with the second mask; and   forming the lower capacitor electrode in a region which is exposed with the first mask and unexposed with the second mask,   the first mask being a half-tone mask having a transparent region, an opaque region, and a semitransparent region,   the second mask having a transparent region and an opaque region.       
 
         [0136]    According to this structure, there is also provided an effect of individually controlling impurity concentrations for the channels of the n-type TFT and the p-type TFT without increasing the number of masks. 
         [0137]    Note that the present invention is not limited to the above-mentioned structures, and various modifications can be made without departing from the technical idea of the present invention. 
         [0138]    According to the method for manufacturing the TFT substrate according to the present invention, a pattern of the half-tone mask by which dimension accuracy is degraded is not used for the definition of the boundaries between the channels and the sources and drains, whereby channel lengths can be stably formed while the number of masks is reduced. 
         [0139]    Further, according to the method for manufacturing the TFT substrate according to the present invention, impurity concentrations for the channels of the n-type TFT and the p-type TFT can be individually controlled without increasing the number of masks. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0140]    In the accompanying drawings: 
           [0141]      FIG. 1  is a view showing mask patterns used in a method for manufacturing a TFT substrate (in a first embodiment) according to the present invention, and showing the structure of the TFT substrate obtained by using the mask patterns; 
           [0142]      FIG. 2  is a table showing correspondence relations between the mask patterns and respective regions of members formed on the TFT substrate shown in  FIG. 1 ; 
           [0143]      FIGS. 3A to 3D  are process sectional views showing, together with  FIGS. 4A to 4D , the method for manufacturing the TFT substrate according to the first embodiment of the present invention; 
           [0144]      FIGS. 4A to 4D  are process sectional views showing, together with  FIGS. 3A to 3D , the method for manufacturing the TFT substrate according to the first embodiment of the present invention; 
           [0145]      FIGS. 5A to 5F  are process plan views showing the method for manufacturing the TFT substrate according to the first embodiment of the present invention; 
           [0146]      FIG. 6  is a view showing mask patterns used in a method for manufacturing a TFT substrate (in a second embodiment) according to the present invention, and showing the structure of the TFT substrate obtained by using the mask patterns; 
           [0147]      FIG. 7  is a table showing correspondence relations between the mask patterns and respective regions of members formed on the TFT substrate shown in  FIG. 6 ; 
           [0148]      FIGS. 8A to 8E  are process sectional views showing, together with  FIGS. 9A to 9D , the method for manufacturing the TFT substrate according to the second embodiment of the present invention; 
           [0149]      FIGS. 9A to 9D  are process sectional views showing, together with  FIGS. 8A to 8E , the method for manufacturing the TFT substrate according to the second embodiment of the present invention; 
           [0150]      FIGS. 10A to 10G  are process plan views showing the method for manufacturing the TFT substrate according to the second embodiment of the present invention; 
           [0151]      FIG. 11  is a view showing mask patterns used in a method for manufacturing a TFT substrate (in a third embodiment) according to the present invention, and showing the structure of the TFT substrate obtained by using the mask patterns; 
           [0152]      FIG. 12  is a table showing correspondence relations between the mask patterns and respective regions of members formed on the TFT substrate shown in  FIG. 11 ; 
           [0153]      FIGS. 13A to 13D  are process sectional views showing, together with  FIGS. 14A to 14D , the method for manufacturing the TFT substrate according to the third embodiment of the present invention; 
           [0154]      FIGS. 14A to 14D  are process sectional views showing, together with  FIGS. 13A to 13D , the method for manufacturing the TFT substrate according to the third embodiment of the present invention; 
           [0155]      FIG. 15  is a view showing mask patterns used in a method for manufacturing a TFT substrate (in a fourth embodiment) according to the present invention, and showing the structure of the TFT substrate obtained by using the mask patterns; 
           [0156]      FIG. 16  is a table showing correspondence relations between the mask patterns and respective regions of members formed on the TFT substrate shown in  FIG. 15 ; 
           [0157]      FIGS. 17A to 17D  are process sectional views showing, together with  FIGS. 18A to 18E , the method for manufacturing the TFT substrate according to the fourth embodiment of the present invention; 
           [0158]      FIGS. 18A to 18E  are process sectional views showing, together with  FIGS. 17A to 17D , the method for manufacturing the TFT substrate according to the fourth embodiment of the present invention; 
           [0159]      FIG. 19  is a view showing mask patterns used in a conventional method for manufacturing a TFT substrate, and showing the structure of the TFT substrate obtained by using the mask patterns; 
           [0160]      FIG. 20  is a table showing correspondence relations between the mask patterns and respective regions of members formed on the TFT substrate shown in  FIG. 19 ; 
           [0161]      FIGS. 21A to 21D  are process sectional views showing, together with  FIGS. 22A to 22D , an example of the conventional method for manufacturing the TFT substrate; 
           [0162]      FIGS. 22A to 22D  are process sectional views showing, together with  FIGS. 21A to 21D , the example of the conventional method for manufacturing the TFT substrate; 
           [0163]      FIG. 23  is a plan view showing an embodiment of a TFT substrate manufactured according to the present invention; 
           [0164]      FIG. 24  is a sectional view showing the embodiment of a pixel portion of the TFT substrate shown in  FIG. 23 ; and 
           [0165]      FIG. 25  is a plan view showing the embodiment of the pixel portion of the TFT substrate shown in  FIG. 23 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0166]    Hereinafter, a method for manufacturing a TFT substrate according to the present invention is described with reference to the drawings. 
       First Embodiment  
       [0167]      FIG. 1  is a view showing mask patterns used in a method for manufacturing a TFT substrate according to a first embodiment of the present invention, and showing the structure of the TFT substrate obtained by using the mask patterns. 
         [0168]    In  FIG. 1 , there are used a total of two masks, that is, a normal mask MSK having a transparent region and an opaque region (indicated as BL in  FIG. 1 ), and a half-tone mask HMK having a transparent region, a semitransparent region (indicated as HT in  FIG. 1 ), and an opaque region (indicated as BL in  FIG. 1 ). With the two masks, a source and drain PSD and a channel PCH of a p-type TFT, a source and drain NSD and a channel NCH of an n-type TFT, an upper capacitor electrode UD, and a lower capacitor electrode BD are separately formed. 
         [0169]      FIG. 2  is a table showing correspondence relations between the mask patterns and respective regions of the members formed on the TFT substrate. In other words,  FIG. 2  shows that the channel NCH of the n-type TFT and the channel PCH of the p-type TFT are formed in regions which are shielded from light through the opaque regions BL of the normal mask MSK to be unexposed, and are half-exposed through the semitransparent region HT of the half-tone mask HMK.  FIG. 2  also shows that the source and drain NSD of the n-type TFT is formed in a region which is exposed through the transparent region of the normal mask MSK, and is half-exposed through the semitransparent region HT of the half-tone mask HMK. Note that, in this embodiment, a lead-out electrode LD, which is connected to the lower capacitor electrode and made of a semiconductor film not covered by the upper capacitor electrode, is formed through the same regions of the normal mask MSK and the half-tone mask HMK. 
         [0170]    Further,  FIG. 2  shows that the source and drain PSD of the p-type TFT is formed in a region which is shielded from light through the opaque region BL of the normal mask MSK to be unexposed, and is exposed through the transparent region of the half-tone mask HMK. 
         [0171]    In this structure, the channel PCH of the p-type TFT is defined by the pattern of the semitransparent region HT of the half-tone mask HMK, and does not include the boundaries with the opaque region BL of the half-tone mask HMK. Further, the channel NCH of the n-type TFT is defined by the pattern of the opaque region BL of the normal mask MSK, and similarly to the channel PCH, the channel NCH does not include the boundaries with the opaque region BL of the half-tone mask HMK. Accordingly, there is no influence of resist pattern which is reduced in size at a time of ashing as described below, and an effect of suppressing the accuracy reduction of the channels. 
         [0172]    Note that the TFT of this embodiment is a so-called lightly-doped drain (LDD) TFT, in which an n-type region LDD with a low concentration, which is not covered by a gate, is connected to each channel end of the n-type TFT, respectively. This is because the LDD TFT is excellent in breakdown voltage and has an advantage of causing less leak current. 
         [0173]      FIGS. 3A to 3D ,  4 A to  4 D, and  5 A to  5 F are process views showing an embodiment of the method for manufacturing the TFT substrate shown in  FIG. 1 .  FIGS. 3A to 3D  and  4 A to  4 D are sectional views, and  FIGS. 5A to 5F  are plan views. 
         [0174]    First, polycrystalline Si films PSI are formed on a glass substrate GLS via an undercoat film UDC. For the undercoat film UDC, for example, there is used a laminated film of a silicon nitride film and a silicon oxide film which are deposited by plasma chemical vapor deposition (CVD). Each of the polycrystalline Si films PSI can be formed by a known method of forming an amorphous Si film made from silane by plasma CVD, and then crystallizing by laser. After the polycrystalline Si films PSI are processed by photolithography using another mask, a gate insulating film GI formed of a silicon oxide film is deposited by plasma CVD using tetra-ethyl-ortho-silicate (TEOS). The gate insulating film GI is set to have a thickness equal to or larger than 30 nm to equal to or smaller than 150 nm, and preferably about 100 nm. In addition, a first metal film M 1  and a second metal film M 2  are deposited by sputtering to obtain the structure shown in  FIG. 3A  and  FIG. 5A . A Ti film or a TiN film is used as the first metal film M 1 , and a Mo film or a MoW alloy film is used as the second metal film M 2 . The first metal film M 1  and the second metal film M 2  should be made of combination of two metals, which can be individually etched. The thickness of the first metal film M 1  is set to about 20 nm to 50 nm, and preferably about 30 nm. The thickness of the second metal film M 2  is set to equal to or larger than 100 nm to equal to or smaller than 300 nm, and preferably about 200 nm. Note that, after or before the formation of the gate insulating film GI, impurities can be implanted into the polycrystalline Si films PSI so as to adjust a threshold value as necessary. 
         [0175]    After a resist is applied, the resist is exposed and developed by using the normal mask MSK, thereby forming a resist pattern RST shown in  FIG. 3B . The second metal film M 2  is etched by using the resist pattern RST as a mask. For etching, wet etching in which a mixed solution of phosphoric acid and nitric acid is used can be performed. In this case, a technique called side etching is used for processing of the second metal film M 2  so that the second metal film M 2  is formed into a shape recessed from the resist pattern by about 1 μm. With the resist pattern RST being further used as a mask, n-type impurities are implanted into the polycrystalline Si films PSI which become the source and drain NSD of the n-type TFT and the lower capacitor electrode BD via the first metal film M 1  and the gate insulating film GI, thereby obtaining the structure shown in  FIGS. 3C and 5B . As the n-type impurities, phosphorus ions are accelerated to about 70 keV, and implanted at a dose of about 1×10 15 /cm 2 . After the resist is removed, phosphorus which becomes the n-type impurities is accelerated to about 80 keV and implanted at low concentration of a dose of about 1×10 13 /cm 2 . Then, the low concentration n-type region LDD is formed in the vicinity of each gate end of the n-type TFT, thereby obtaining the structure shown in  FIGS. 3D and 5C . Subsequently, the half-tone mask HMK is used to form resist patterns having different thickness. Note that each of the resists used in this embodiment is a positive resist by which an exposed portion is removed. The resist in the semitransparent region HT of the half-tone mask HMK is half-exposed to partially leave the resist, thereby forming a thin-film resist pattern TFR. At the same time, a resist pattern RST having a normal thickness is formed in an unexposed region corresponding to the opaque region BL, thereby obtaining the structure shown in  FIG. 4A . Next, the resist pattern TFR and the resist pattern RST are used as masks to etch the second metal film M 2 . Then, p-type impurities are implanted into a region which is exposed with the half-tone mask HMK and on which a resist pattern is not formed, and the source and drain PSD of the p-type TFT is formed, thereby obtaining the structure shown in  FIGS. 4B and 5D . Boron (B) is used as the p-type impurities and implanted at an accelerating voltage of about 30 keV and at a dose of about 1×10 15 /cm 2 . In this embodiment, since the n-type impurities are not implanted into the source and drain PSD of the p-type TFT, the dose of the p-type impurities and the dose of the n-type impurities are independently determined, resulting in an advantage of reducing implantation dose. After the resist is subjected to ashing and the thin-film resist pattern is removed, the first metal film M 1  is etched as shown in  FIGS. 4C and 5E , whereby a gate PGT of the p-type TFT, a gate NGT of the n-type TFT, and an upper capacitor electrode UD are formed. For ashing, plasma ashing which uses a gas containing oxygen is employed, and an ashing time is adjusted so that only the thin-film resist is opened. Dry etching is performed as etching for the first metal film M 1 , and the second metal film M 2  and the thick-film resist RST which is left after ashing are used as masks. After the processing, the resist is removed to obtain the structure shown in  FIGS. 4D and 5F , thereby forming the n-type TFT, the p-type TFT, and the capacitor. 
         [0176]    According to the above-mentioned embodiment, the processing of the gates, the sources, and the drains of the n-type TFT and the p-type TFT, and the capacitor electrodes, which is conventionally performed by using three masks, can be performed by using only the two masks. Further, there is not used, for the channels of the TFTs, a pattern obtained from the opaque region of the half-tone mask in which a resist pattern shrinks at a time of ashing. Therefore, accuracy reduction of the channel lengths is suppressed, and the TFT having uniform characteristics can be manufactured. 
         [0177]      FIGS. 23 to 25  show an example of a TFT substrate for a liquid crystal display apparatus, which is manufactured by the method for manufacturing the TFT substrate according to the present invention. 
         [0178]    As shown in  FIG. 23 , a plurality of pixels PXL for displaying an image are formed in matrix on the glass substrate GLS, and a gate line GLN and a drain line DLN for individually driving each of the pixels are formed. A scanning circuit VDR for driving the pixels and a signal line driving circuit HDR for distributing video signals are formed by using the TFTs in the same manner. The n-type and p-type TFTs are used for the scanning circuit VDR and the signal line driving circuit HDR. Further, for example, the n-type TFT and the capacitor are formed for each of the pixels. 
         [0179]      FIG. 24  is a sectional view of a pixel portion, and  FIG. 25  is a plan view of the pixels.  FIG. 24  shows a cross section of a portion obtained by taking along the line XXIV-XXIV shown in  FIG. 25 . 
         [0180]    As shown in  FIG. 24 , an NTFT which is the n-type TFT according to the present invention and a capacitor CST are formed on the glass substrate GLS. After the process shown in  FIG. 4D , an interlayer insulating film ILI is deposited and a contact hole CNT is formed by photolithography technology. Further, wiring DLN is formed to be connected to the drain NSD of the NTFT. An inorganic protective film PAS made of a SiN film is formed, and then an organic protective film OPC made of a photosensitive organic film is formed to thereby form a through hole TH in the inorganic protective film PAS. Finally, a transparent electrode made of indium-tin-oxide (ITO) is formed by sputtering to be processed into a pixel electrode ITO, thereby obtaining the TFT substrate having the structure shown in  FIG. 24 . The method according to the present invention is not different from conventional manufacturing methods for the deposition process of the interlayer insulating film ILI and the subsequent processes, and the shape of the pixel electrode is made the same as in the conventional methods. Accordingly, reduction of the aperture ratio involving the reduced number of masks is suppressed. 
       Second Embodiment  
       [0181]      FIG. 6  is a view showing mask patterns used in a method for manufacturing a TFT substrate according to a second embodiment of the present invention, and showing the structure of the TFT substrate obtained by using the mask patterns.  FIG. 7  is a table showing correspondence relations between the mask patterns and respective regions of members formed on the TFT substrate. 
         [0182]    In  FIG. 6 , a channel PCH of a p-type TFT is formed in a region which is unexposed through an opaque region BL of a normal mask MSK and is exposed through a transparent region of a half-tone mask HMK. 
         [0183]    A channel NCH of an n-type TFT is formed in a region which is unexposed through the opaque region BL of the normal mask MSK and is half-exposed through a semitransparent region HT of the half-tone mask HMK. 
         [0184]    A source and drain PSD of the p-type TFT is formed in a region which is exposed through a transparent region of the normal mask MSK and is exposed through the transparent region of the half-tone mask HMK. 
         [0185]    A source and drain NSD of the n-type TFT is formed in a region which is exposed through the transparent region of the normal mask MSK and is half-exposed through the semitransparent region HT of the half-tone mask HMK. Note that a lead-out electrode LD is formed through the same regions of the normal mask MSK and the half-tone mask HMK. 
         [0186]    A lower capacitor electrode BD is formed in a region which is exposed through the transparent region of the normal mask MSK and is unexposed through an opaque region BL of the half-tone mask HMK. Note that, in this embodiment, wiring WR is formed in a region which is unexposed with both the normal mask MSK and the half-tone mask HMK. 
         [0187]    In this embodiment, both the channel PCH of the p-type TFT and the channel NCH of the n-type TFT are obtained through the opaque region BL of the normal mask MSK, and do not include the boundaries between the opaque region and the semitransparent region or between the opaque region and the transparent region of the half-tone mask HMK in which the pattern is affected by regression of the resist at a time of ashing. Accordingly, lowering of dimension accuracy of the channel lengths is suppressed. 
         [0188]      FIGS. 8A to 8E ,  9 A to  9 D, and  10 A to  10 G show an example of a method for manufacturing the TFT substrate having the structure shown in  FIG. 6 .  FIGS. 8A to 8E  and  9 A to  9 D are sectional views, and  FIGS. 10A to 10G  are plan views. Similarly to the first embodiment of the present invention, semiconductor films PSI made of polycrystalline Si films are formed in a plurality of regions of a glass substrate GLS via an undercoat film UDC. Thereon, a gate insulating film GI, a first metal film M 1 , and a second metal film M 2  are laminated in the stated order, thereby obtaining the structure shown in  FIGS. 8A and 10A . Note that, after or before the gate insulating film GI is formed, impurities are implanted into the semiconductor films PSI so as to adjust a threshold value for the n-type TFT. 
         [0189]    A resist pattern RST is formed by using the normal mask MSK to obtain the structure shown in  FIG. 8B . The second metal film M 2  and the first metal film M 1  are processed by using the resist pattern RST as a mask. In this case, the second metal film M 2  and the first metal film M 1  are processed into a shape recessed from the resist pattern RST. N-type impurities are implanted with the use of the resist pattern RST as a mask, and the source and drain NSD of the n-type TFT and the lower capacitor electrode BD are formed, thereby obtaining the structure shown in  FIGS. 8C and 10B . In this stage, the n-type impurities are also implanted into the source and drain PSD of the p-type TFT. After the removal of the resist, the n-type impurities are implanted at low concentration, and a low concentration impurity regions LDD are formed in regions in which the second metal film M 2  and the first metal film M 1  are recessed from the resist pattern RST, thereby obtaining the structure shown in  FIGS. 8D and 10C . Further, a third metal film M 3  is formed by sputtering, and a resist pattern RST′ having a different thickness is formed by using the half-tone mask HMK, thereby obtaining the structure shown in  FIG. 8E . Through the third metal film M 3  and the gate insulating film GI, p-type impurities are implanted by using the second metal film M 2  and the resist pattern RST′ as masks, and the source and drain PSD of the p-type TFT is formed, thereby obtaining the structure shown in  FIGS. 9A and 10D . A dose of the p-type impurities is larger than a dose corresponding to the concentration of the n-type impurities implanted when the source and drain NSD of the n-type TFT is formed in  FIG. 8C , and is adjusted so that the source and drain PSD becomes p-type. For example, a dose of the n-type impurities is set to 1×10 15 /cm 2 , and a dose of the p-type impurities is set to 2×10 15 /cm 2 . The third metal film M 3  is set to, for example, a thickness of 30 nm of Mo so that the p-type impurities can permeate. Further, the third metal film M 3  and the second metal film M 2  are etched to form a gate PGT of the p-type TFT, the gate PGT being formed only of the first metal film M 1 . After that, the n-type impurity implantation for adjusting a threshold value of the p-type TFT is performed on the channel PCH at low concentration via the first metal film M 1  and the gate insulating film GI, thereby obtaining the structure shown in  FIGS. 9B and 10E . The dose is set to much smaller than the dose at the time of forming the LDD, for example, set to 2×10 12 /cm 2 . The resist is subjected to ashing to remove a thin-film resist portion. Further, the third metal film M 3  and the second metal film M 2  are removed to form a gate NGT of the n-type TFT, which is formed only of the first metal film M 1 , and at the same time, an upper capacitor electrode UD formed of the third metal film M 3  is formed, thereby obtaining the structure shown in  FIGS. 9C and 10F . The resist is removed and the structure shown in  FIGS. 9D and 10G , in which the p-type TFT, the n-type TFT, and the capacitor are formed, is obtained. At the same time, wiring WR which is formed by lamination of the first metal film M 1 , the second metal film M 2 , and the third metal film M 3  can be formed in this embodiment, whereby the wiring WR can be employed as low resistance wiring. Note that the TFT substrate thus obtained can be used as a TFT substrate for a liquid crystal display by forming similar wiring and pixel electrodes as shown in  FIG. 24  after the process shown in  FIG. 9D . 
         [0190]    In this embodiment, there is provided an advantage in that the threshold values of the p-type TFT and the n-type TFT can be individually adjusted by implanting the impurities having the different concentrations into the p-type channel and the n-type channel, without increasing the number of masks compared with the first embodiment of the present invention. 
       Third Embodiment  
       [0191]      FIG. 11  is a view showing mask patterns used in a method for manufacturing a TFT substrate according to a third embodiment of the present invention, and showing the structure of the TFT substrate obtained by using the mask patterns.  FIG. 12  is a table showing correspondence relations between the mask patterns and respective regions of members formed on the TFT substrate. 
         [0192]    In  FIG. 11 , a channel PCH of a p-type TFT is formed in a region which is unexposed through an opaque region BL of a normal mask MSK and is half-exposed through a semitransparent region HT of a half-tone mask HMK. Further, a channel NCH of an n-type TFT is formed in a region which is unexposed through the opaque region BL of the normal mask MSK and is unexposed through an opaque region BL of the half-tone mask HMK. A source and drain PSD of the p-type TFT is formed in a region which is exposed through a transparent region of the normal mask MSK and is half-exposed through the semitransparent region HT of the half-tone mask HMK. A source and drain NSD of the n-type TFT is formed in a region which is exposed through the transparent region of the normal mask MSK and is unexposed through the opaque region BL of the half-tone mask HMK. Further, a lower capacitor electrode BD is formed in a region which is unexposed through the opaque region BL of the normal mask MSK and is exposed through a transparent region of the half-tone mask HMK. Note that a lead-out electrode LD, which is connected to the lower capacitor electrode BD and made of a semiconductor film not covered by an upper capacitor electrode UD, is formed in a region which is exposed through both the transparent region of the normal mask MSK and the transparent region of the half-tone mask HMK. 
         [0193]    In this embodiment as well, the channel PCH of the p-type TFT and the channel NCH of the n-type TFT are defined by the opaque region of the normal mask MSK, and do not include the boundaries between the opaque region and the transparent region or between the opaque region and the semitransparent region of the half-tone mask HMK. Accordingly, an effect of stabilizing a channel dimension is produced without being affected by a resist deformation at a time of ashing. 
         [0194]      FIGS. 13A to 13D  and  14 A to  14 D are views showing the method for manufacturing the TFT substrate shown in  FIG. 11 . 
         [0195]    First,  FIG. 13A  shows a state in which semiconductor films PSI made of polycrystalline Si films are formed on a glass substrate GLS via an undercoat film UDC, and thereon, a gate insulating film GI and a first metal film M 1  are laminated. Note that, as necessary, p-type impurities are implanted into the polycrystalline Si films PSI at low concentration so as to adjust a threshold value of the n-type TFT before the formation of the first metal film M 1 . Subsequently, with the use of the half-tone mask HMK, a thin-film resist pattern TFR is formed in the region which is half-exposed through the semitransparent region HT of the half-tone mask HMK, and a thick-film resist pattern RST is formed in the region which is unexposed through the opaque region BL thereof, respectively, thereby obtaining the structure shown in  FIG. 13B . The first metal film M 1  is etched using the resists as masks, and the n-type impurities are implanted using the resists and the first metal film M 1  as masks, to thereby perform first n-type impurity implantation on the lower capacitor electrode BD. The first metal film M 1  is formed of a refractory metal having a thickness of about 200 nm so as to be a mask in the impurity implantation. Further, after ashing is performed to remove the thin-film resist, the first metal film M 1  is etched again, and, for adjusting the threshold value of the p-type TFT, n-type impurities are implanted at low concentration into the region which becomes the channel PCH of the p-type TFT, thereby obtaining the structure shown in  FIG. 13D . After the thick-film resist is removed and a second metal film M 2  is laminated by sputtering, a resist pattern RST is formed with the use of the normal mask MSK, thereby obtaining the structure shown in  FIG. 14A . With the use of the resist pattern RST and the first metal film M 1  as masks, p-type impurities are implanted via the second metal film M 2  and the gate insulating film GI, and the source and drain PSD of the p-type TFT is formed, thereby obtaining the structure shown in  FIG. 14B . In this case, the p-type impurities are also implanted into a region which becomes the lead-out electrode LD. Note that a thin metal film having a thickness of about 50 nm is used for the second metal film M 2  so as to have permeability with respect to the implanted p-type impurities. 
         [0196]    Further, with the use of the resist as a mask, the second metal film M 2  and the first metal film M 1  are etched. The second metal film M 2  and the first metal film M 1  are simultaneously etched, and the second metal film M 2  is processed into a shape recessed from the resist. For example, the first metal film M 1  and the second metal film M 2  can be formed of a MoW alloy, and processed with an etchant containing phosphoric acid and nitric acid. With the use of the resist as a mask, second n-type impurity implantation is performed to form the source and drain NSD of the n-type TFT, thereby obtaining the structure shown in  FIG. 14C . In this case, the n-type impurities are also implanted into the region which becomes the lead-out electrode LD and into the region which becomes the source and drain PSD of the p-type TFT. In order to set the source and drain PSD of the p-type TFT to be p-type, a dose for the second n-type impurity implantation is set to be smaller than a dose for the p-type impurity implantation. Further, in order to set the lead-out electrode LD to be n-type similarly to the lower capacitor electrode BD, the sum of a dose for the first n-type impurity implantation and the dose for the second n-type impurity implantation is set to be larger than the dose for the p-type impurity implantation. For example, when the dose for the first n-type impurity implantation is set to 1×10 15 /cm 2 , the dose for the second n-type impurity implantation is set to 5×10 14 /cm 2 , and the dose for the p-type impurity implantation is set to 1×10 15 /cm , the source and drain NSD of the n-type TFT is doped with the n-type impurities of 5×10 4 /cm 2  to become n-type, the source and drain PSD of the p-type TFT is doped with the n-type impurities of 5×10 4 /cm 2  and with the p-type impurities of 1×10 15 /cm 2  to become p-type, and the lead-out electrode LD is doped with the n-type impurities of 1.5×10 15 /cm 2  through the first and second n-type impurity implantations and with the p-type impurities of 1×10 15 /cm 2  to become n-type, respectively. 
         [0197]    Further, after the resist is removed, the n-type impurities are implanted over the entire surface at low acceleration and at low concentration while the first metal film M 1  and the second metal film M 2  are used as masks, and a low concentration impurity region LDD is formed near each channel end of the n-type TFT, thereby obtaining the structure shown in  FIG. 14D . At this time, an accelerating voltage for the n-type impurity implantation is adjusted so as to be shielded by the second metal film M 2  as well. For example, in a case where phosphorus ions are implanted into the gate insulating film having a thickness of 100 nm and into the second metal film formed of the MoW alloy having a thickness of 50 nm, an accelerating voltage is set to about 50 keV. 
         [0198]    In this embodiment as well, both the channel PCH of the p-type TFT and the channel NCH of the n-type TFT are defined by the opaque region of the normal mask, and do not include the boundaries between the opaque region and the semitransparent region or between the opaque region and the transparent region of the half-tone mask. Accordingly, pattern accuracy is not affected and not lowered by regression of the resist due to ashing. Further, also in this embodiment, there is produced an advantage in that the threshold values of the p-type TFT and the n-type TFT can be individually adjusted with the same number of masks as in the first embodiment of the present invention. In addition, similarly to the first and second embodiments of the present invention, there is produced an effect of achieving a TFT substrate for a liquid crystal display by adding a wiring process. 
       Fourth Embodiment  
       [0199]      FIG. 15  is a view showing mask patterns used in a method for manufacturing a TFT substrate according to a fourth embodiment of the present invention, and showing the structure of the TFT substrate obtained by using the mask patterns.  FIG. 16  is a table showing correspondence relations between the mask patterns and respective regions of members formed on the TFT substrate. 
         [0200]    In  FIG. 15 , a channel PCH of a p-type TFT is formed in a region which is unexposed through an opaque region BL of a normal mask MSK and is unexposed through an opaque region BL of a half-tone mask HMK. A channel NCH of an n-type TFT is formed in a region which is unexposed through the opaque region BL of the normal mask MSK and is half-exposed through a semitransparent region HT of the half-tone mask HMK. A source and drain PSD of the p-type TFT is formed in a region which is exposed through a transparent region of the normal mask MSK and is unexposed through the opaque region BL of the half-tone mask HMK. A source and drain NSD of the n-type TFT is formed in a region which is exposed through the transparent region of the normal mask MSK and is half-exposed through the semitransparent region HT of the half-tone mask HMK. A lower capacitor electrode BD is formed in a region which is unexposed through the opaque region BL of the normal mask MSK and is exposed through the transparent region of the half-tone mask HMK. 
         [0201]    Note that, in this embodiment, a lead-out electrode LD is formed in a region which is exposed through the transparent region of the normal mask MSK and is exposed through the transparent region of the half-tone mask HMK. This embodiment is an example for forming a so-called gate-overlapped-drain (GOLD) TFT. In the GOLD TFT, a region GLD, which is covered by a gate NGT and to which n-type impurities are implanted at low concentration, is formed near each channel end of the n-type TFT. 
         [0202]    In this embodiment as well, both the channels of the p-type TFT and the n-type TFT are defined by the opaque regions of the normal mask MSK, and are not derived from the boundaries between the opaque region and the transparent region or between the opaque region and the semitransparent region of the half-tone mask, which involves accuracy reduction at a time of ashing. Therefore, there is produced an effect of forming the channels at high accuracy. 
         [0203]      FIGS. 17A to 17D  and  18 A to  18 E are views showing the method for manufacturing the TFT substrate shown in  FIG. 15 . 
         [0204]    Similarly to the first embodiment of the present invention, first, the structure shown in  FIG. 17A  is formed. In this case as well, as necessary, n-type impurities are implanted at low concentration into polycrystalline Si films so as to adjust a threshold value of the p-type TFT before a first metal film M 1  and a second metal film M 2  are formed. Next, a resist pattern RST is formed by using the normal mask MSK to thereby obtain the structure shown in  FIG. 17B . After the second metal film M 2  and the first metal film M 1  are sequentially etched, p-type impurities are implanted to form the source and drain PSD of the p-type TFT, thereby obtaining the shape shown in  FIG. 17C . At this time, the p-type impurities are also implanted into regions which become the source and drain NSD of the n-type TFT and the lead-out electrode LD. Further, the second metal film M 2  is formed into a shape recessed from the resist pattern, and the first metal film M 1  is formed into a substantially the same shape as the shape of the resist pattern. Such a shape described above can be formed as follows: for example, a MoW alloy is used for the second metal film M 2  and Ta is used for the first metal film M 1 , the first metal film M 1  and the second metal film M 2  are processed by dry etching, and then the second metal film M 2  is recessed by using an etchant which etches only the second metal film M 2 . After the resist is removed, a thick-film resist pattern RST and a thin-film resist pattern TFR are formed by using the half-tone mask HMK, thereby obtaining the structure shown in  FIG. 18A . With the use of the resists as masks, the second metal film M 2  formed in a capacitor portion is etched to form an upper capacitor electrode UD which is made only of the first metal film M 1 . Further, first n-type impurity implantation is performed via the second metal film M 2  and a gate insulating film GI to implant the n-type impurities into the lower capacitor electrode BD and the lead-out electrode LD, thereby obtaining the structure shown in  FIG. 18B . After the thin-film resist is removed by ashing, n-type impurities are implanted at low concentration by using the second metal film M 2  and the resist pattern as masks to form a low concentration region GLD. In addition, second n-type impurity implantation is performed with the use of the first metal film M 1 , the second metal film M 2 , and the resist as masks, at lower acceleration than that for the first n-type impurity implantation. Then, the source and drain NSD of the n-type TFT is formed, thereby obtaining the structure shown in  FIG. 18C . A dose for the first n-type impurity implantation is made larger than a dose for the p-type impurity implantation so that the lower capacitor electrode BD becomes n-type. A dose for the second n-type impurity implantation is made larger than the dose for the p-type impurity implantation so that the source and drain NSD of the n-type TFT becomes n-type. Further, the second metal film M 2  is etched to form a gate NGT of the n-type TFT, which is formed only of the first metal film M 1 . P-type impurities are implanted at low concentration into the channel NCH via the first metal film M 1  so as to adjust a threshold value of the n-type TFT, thereby obtaining the structure shown in  FIG. 18D . The dose of the p-type impurities in this case is set to smaller than the dose of the n-type impurities used for the formation of the low concentration n-type regions GLD. For example, the dose for the n-type impurity implantation at low concentration is set to 3×10 3 /cm 2 , and the dose for the p-type impurity implantation for adjusting the threshold value is set to 3×10 2 /cm 2 . Further, the resist is removed, and the p-type TFT, the n-type TFT, and the capacitor are formed on the same substrate as shown in  FIG. 18E . 
         [0205]    Also in this embodiment, there is attained an advantage in that the threshold values for the n-type TFT and the p-type TFT can be individually adjusted. Besides, wiring and pixel electrodes may be formed to thereby form a TFT substrate for a liquid crystal display in the same way as in the first embodiment of the present invention. 
         [0206]    Note that the examples of the TFT substrate for liquid crystal display apparatuses have been described in the above-mentioned embodiments, but the present invention is applicable not only to liquid crystal display apparatuses, but also to other known apparatuses using the TFT substrate, such as a display apparatus using an organic electroluminescence device or a semiconductor device with a built-in sensor using the TFT substrate. 
         [0207]    Each of the above-mentioned embodiments may be used alone or in combination, because the effect of each of the above-mentioned embodiments can be exerted independently or synergistically. 
         [0208]    While there have been described what are at present considered to be certain embodiments of the invention, it will be understood that various modifications may be made thereto, and it is intended that the appended claims cover all such modifications as fall within the true spirit and scope of the invention.