Patent Publication Number: US-6222600-B1

Title: Reflective liquid crystal display apparatus with low manufacturing cost

Description:
This is a divisional of application Ser. No. 08/906,256 filed Aug. 5, 1997, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a reflective liquid crystal display (LCD) apparatus. 
     2. Description of the Related Art 
     LCD apparatuses are divided into light penetration type LCD apparatuses requiring backlights and reflective LCD apparatuses reflecting environmental light. 
     In the reflective LCD apparatuses, in order to obtain high display quality, the efficiency of reflecting and scattering environmental light is important. Also, since available environmental light is limited, the loss of light has to be reduced. Particularly, in a colored LCD apparatus using color filters, the loss of light is large. 
     In a prior art reflective LCD apparatus (see Naohito Kimura, “Colored Reflection type LCD”, Semiconductor World, pp. 108-112, Feb. 1995), inverted staggered thin film transistors (TFTs) where gate electrodes are beneath amorphous silicon layers are formed on a glass substrate. Further, a photosensitive acrylic resin layer having an uneven surface is formed on the TFTs. Also, pixel electrodes made of aluminum are formed on the photosensitive acrylic resin layer and each of the pixel electrodes is connected to one of the source electrodes. A counter glass substrate is prepared, and a transparent common electrode is formed on the glass substrate. 
     After orientation processes including orientation layer coating processes and rubbing processes are performed upon the two substrates, the two substrates are adhered to each other with a predetermined spacing therebetween, and a liquid crystal layer is then inserted into this spacing. This will be explained later in detail. 
     In the prior art reflective LCD apparatus, since the photosensitive acrylic resin layer has an uneven surface, the pixel electrodes also have uneven surfaces, so that the pixel electrodes serve as optical reflecting means as well as optical scattering means. Therefore, the scattering characteristics of reflected light can be improved to make the brightness of reflected light uniform over a broad visual angle. In addition, since the pixel electrodes are formed over the TFTs, effective use can be made of reflected light, thus increasing the numerical aperture. Further, if guest-host (G-H) liquid crystal which does not require polarization plates is used, a brighter display can be obtained. 
     In order to manufacture the prior art reflective LCD apparatus, however, a large number of photolithography and etching processes are required due to the complex configuration of the pixel electrodes, thus increasing the manufacturing cost. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to reduce the manufacturing cost of a reflective LCD apparatus. 
     According to the present invention, in a reflective liquid crystal apparatus, a drain electrode and a source electrode are formed on a insulating substrate and are formed by an aluminum alloy layer. The source electrode serves as a light reflecting pixel electrode. Also, a non-doped semiconductor layer is formed on a part of the drain electrode and a part of the source electrode, and impurity-doped semiconductor layers are formed between the drain and source electrodes and the non-doped semiconductor layer. Further, a gate electrode is formed via a gate insulating layer on the non-doped semiconductor layer. In addition, a counter common electrode is formed on a transparent insulating substrate, and a liquid crystal layer is interposed between the insulating substrate and the transparent insulating substrate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more clearly understood from the description as set forth below, as compared with the prior art, with reference to the accompanying drawings, wherein: 
     FIG. 1 is a cross-sectional view illustrating a prior art reflective LCD apparatus; 
     FIGS. 2A through 2G are cross-sectional views illustrating a first embodiment of the reflective LCD apparatus according to the present invention; 
     FIGS. 3A through 3G are cross-sectional views illustrating a second embodiment of the reflective LCD apparatus according to the present invention; 
     FIGS. 4A through 4G are cross-sectional views illustrating a third embodiment of the reflective LCD apparatus according to the present invention; 
     FIGS. 5A through 5G are cross-sectional views illustrating a fourth embodiment of the reflective LCD apparatus according to the present invention; 
     FIGS. 6A through 6G are cross-sectional views illustrating a fifth embodiment of the reflective LCD apparatus according to the present invention; 
     FIGS. 7A,  7 B,  7 C,  7 D and  7 E are cross-sectional views illustrating modifications of the apparatuses of FIGS. 2G,  3 G,  4 G,  5 G and  6 G, respectively; 
     FIGS. 8A,  8 B,  8 C,  8 D and  8 E are cross-sectional views illustrating modifications of the apparatuses of FIGS. 2G,  3 G,  4 G,  5 G and  6 G, respectively; 
     FIGS. 9A,  9 B,  9 C,  9 D and  9 E are cross-sectional views illustrating modifications of the apparatuses of FIGS. 2G,  3 G,  4 G,  5 G and  6 G, respectively; 
     FIGS. 10A,  10 B,  10 C,  10 D and  10 E are cross-sectional views illustrating modifications of the apparatuses of FIGS. 2G,  3 G,  4 G,  5 G and  6 G, respectively; 
     FIGS. 11A through 11G are cross-sectional views illustrating a sixth embodiment of the reflective LCD apparatus according to the present invention; 
     FIGS. 12A through 12G are cross-sectional views illustrating a seventh embodiment of the reflective LCD apparatus according to the present invention; 
     FIGS. 13A through 13G are cross-sectional views illustrating an eighth embodiment of the reflective LCD apparatus according to the present invention; 
     FIGS. 14A through 14G are cross-sectional views illustrating a ninth embodiment of the reflective LCD apparatus according to the present invention; 
     FIGS. 15A through 15G are cross-sectional views illustrating a tenth embodiment of the reflective LCD apparatus according to the present invention; 
     FIGS. 16A through 16G are cross-sectional views illustrating an eleventh embodiment of the reflective LCD apparatus according to the present invention; 
     FIGS. 17A through 17G are cross-sectional views illustrating a twelfth embodiment of the reflective LCD apparatus according to the present invention; 
     FIGS. 18A through 18G are cross-sectional views illustrating a thirteenth embodiment of the reflective LCD apparatus according to the present invention; and 
     FIGS. 19A through 19G are cross-sectional views illustrating a fourteenth embodiment of the reflective LCD apparatus according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Before the description of the preferred embodiments, a prior art reflective LCD apparatus will be explained next with reference to FIG. 1 (see Naohito Kimura, “Colored Reflection type LCD”, Semiconductor World, pp. 108-112, Feb. 1995). 
     In FIG. 1, a conductive layer  102  made of Cr or the like is formed on a glass substrate  101 , and is patterned to form gate electrodes. Then, a gate insulating layer  103  made of silicon nitride is formed on the gate electrodes  103 . Also, an amorphous silicon layer  104  is formed as a semiconductor layer on the gate insulating layer  103 , and a passivation layer  105  is formed on the amorphous silicon layer  104 . Further, a conductive layer is formed thereon and is patterned to form drain electrodes  106 D and source electrodes  106 S. Also, N+-type regions  107  are formed between the amorphous silicon layer  104  and the drain electrodes  106 D (the source electrodes  106 S). Thus, inverted staggered TETs where the gate electrodes  102  are beneath the amorphous silicon layer  104  are formed. 
     Further, a photosensitive acrylic resin layer  108  having an uneven surface is formed on the TFTs. Also, pixel electrodes  109  made of aluminum are formed on the photosensitive acrylic resin layer  108  and each of the pixel electrodes  109  is connected to one of the source electrodes  106 S. 
     In addition, a counter glass substrate  110  is prepared, and a transparent common electrode  111  is formed on the glass substrate  110 . 
     After orientation processes including orientation layer coating processes and rubbing processes are performed upon the two substrates  101  and  110 , the two substrates  101  and  110  are adhered to each other with a predetermined spacing therebetween and then, a liquid crystal layer  112  is inserted into this spacing. 
     In FIG. 1, since the photosensitive acrylic resin layer  108  has an uneven surface, the pixel electrodes  109  also have uneven surfaces, so that the pixel electrodes  109  serve as optical reflecting means as well as optical scattering means. Therefore, the scattering characteristics of reflected light can be improved to make the brightness of reflected light uniform over a broad visual angle. In addition, since the pixel electrodes  109  are formed over the TETs, effective use can be made of reflected light, thus increasing the numerical aperture. Further, if guest-host (G-H) liquid crystal which does not require polarization plates is used, a brighter display can be obtained. 
     In order to manufacture the reflective LCD apparatus of FIG. 1, however, a large number of photolithography and etching processes, i.e., five processes in this case, are required due to the complex configuration of the pixel electrodes  109 , thus increasing the manufacturing cost. 
     A first embodiment of the method for manufacturing a reflective LCD apparatus according to the present invention will be explained next with reference to FIGS. 2A through 2G. 
     First, referring to FIG. 2A, an about 100 nm thick Al—Nd—Si alloy layer  2  is deposited by a sputtering process on a glass substrate  1 . Then, a photoresist pattern  3  corresponding to a drain electrode and a source (pixel) electrode is formed by a photolithography process. 
     Next, referring to FIG. 2B, the aluminum alloy layer  2  is etched by a wet etching process using a phosphoric acid/nitric acid solution with a mask of the photoresist pattern  3 . As a result, a drain electrode  2 (D) and a pixel electrode  2 (E) are formed by the aluminum layer  2 . In this case, the side edges of the drain electrode  2 (D) and the pixel electrode  2 (E) are tapered. Note that, if a dry etching process using Cl 2  gas is performed upon the aluminum alloy layer  2 , the side edges of the drain electrode  2 (D) and the pixel electrode  2 (E) are not tapered. 
     Next, referring to FIG. 2C, the photoresist pattern  3  is removed. 
     Next, referring to FIG. 2D, a thin natural oxide layer (not shown) formed on the drain electrode  2 (D), and the pixel electrode  2 (E), and then, the natural oxide layer is etched by a sputtering process using inert gas or by a chemical etching process using halogen gas. Immediately after that, a phosphor rich amorphous silicon layer, i.e., an about  5  nm thick N+-type amorphous silicon layer  4  is deposited by a PCVD process using pH 3  (phosphin) gas added by a very small amount of SiH 4  (monosilane) gas only on the drain electrode  2 (D) and the pixel electrode  2 (E). Note that the N+-type amorphous silicon layer  4  can be formed by a PH 3  plasma-doping process. 
     Subsequently, an about 50 nm thick I-type (non-doped) amorphous silicon layer  5  is deposited by a PCVD process using SiH 4  gas and H 2  gas on the entire surface. In addition, an about 300 nm thick silicon nitride layer  6  serving as a gate insulating layer is deposited by a PCVD process using SiH 4  gas, NH 3  gas and N 2  gas. Note that all the above-mentioned PCVD processes are carried out in the same PCVD apparatus. 
     Then, an about 100 nm thick Al—Nd—Si alloy layer  7  is deposited by a sputtering process on the silicon nitride layer  6 . Then, a photoresist pattern  3 A corresponding to a gate electrode is formed on the aluminum alloy layer  7 . 
     Next, referring to FIG. 2E, the aluminum alloy layer  7  is etched by a wet etching process using phosphoric acid/nitric acid solution with a mask of the photoresist pattern  3 A to form a gate electrode  7 (G). Note that the aluminum alloy layer  7  can be etched by a dry etching process using Cl 2  gas. Then, the silicon nitride layer  6 , the I-type amorphous silicon layer  5 , and the N+-type amorphous silicon layer  4  are sequentially etched by a dry etching process using CF 4  gas and O 2  gas with a mask of the photoresist pattern  3 A. Thus, an island is formed. Also, since the aluminum alloy layer  2  is not etched by the above-mentioned dry etching process using fluorine gas, the drain electrode  2 (D) and the pixel electrode  2 (E) outside of the island are exposed. 
     Next, referring to FIG. 2F, the photoresist pattern  3 A is removed. Thus, the island for a staggered TFT where the gate electrode  7 (G) is below the amorphous silicon layer  5  is formed. 
     Finally, referring to FIG. 2G, a counter glass substrate  8  having an uneven (rough) surface is prepared. For example, the surface of the glass substrate  8  is made uneven by using a sand blast method. Then, a transparent common electrode  9  is formed on the glass substrate  8 . Then, after orientation processes including orientation layer coating processes and rubbing processes are performed upon the two substrates  1  and  8 , the two glass substrates  1  and  8  are attached to each other with a predetermined spacing therebetween defined by plastic spacers (not shown). Then, the sides of the two glass substrates  1  and  8  are adhered to each other by epoxy adhesives, and then, a guest-host liquid crystal layer  11  is inserted into this spacing. Then, the device is sealed by an ultraviolet-setting resin. 
     In the first embodiment as illustrated in FIGS. 2A through 2G, only two photolithography and etching processes are carried out, thus reducing the manufacturing cost. 
     Also, in FIGS. 2A through 2G, since Si, which is the same component as in the N+-type amorphous silicon layer  4  and the amorphous silicon layer  6 , is included in the aluminum alloy layers  2  and  7 , the diffusion of aluminum atom and silicon atoms can be suppressed, thus avoiding the deterioration of the characteristics of the TFT. In addition, since Nd is included in the aluminum alloy layers  2  and  7 , the high temperature resistance and anti-electromigration characteristics of the aluminum alloy layers  2  and  7  can be improved. Further, incident light is-scattered at the counter glass substrate  8 , and penetrates the liquid crystal layer  11 . Then, the light is reflected by the pixel electrode  2 (E), and is further scattered at the counter glass substrate  8 . In this case, the transmittance of the light through the liquid crystal layer  11  is controlled by the liquid crystal layer  11 . Further, since the liquid crystal layer  11  uses guest-host liquid crystal where a color pigment (guest) is mixed into twisted-neumatic (TN) liquid crystal (host) and the absortion of light by the guest is controlled by the viscosity of the host, the polarization plates are unnecessary and a bright display can be obtained. 
     A second embodiment of the method for manufacturing a reflective LCD apparatus according to the present invention will be explained next with reference to FIGS. 3A through 3G. 
     First, referring to FIG. 3A, an about 20 nm thick Mo layer  12  is deposited by a sputtering process on a glass substrate  1 . Then, an about 80 nm thick Al—Nd—Si alloy layer  2  is deposited by a sputtering process on the Mo layer  12 . Then, a photoresist pattern  3  corresponding to a drain electrode and a source (pixel) electrode is formed by a photolithography process. 
     Next, referring to FIG. 3B, the aluminum alloy layer  2  and the Mo layer  12  are etched by a wet etching process using phosphoric acid/nitric acid solution with a mask of the photoresist pattern  3 . As a result, a drain electrode D and a pixel electrode E are formed by the aluminum layer  2  and the Mo layer  2 . In this case, the side edges of the drain electrode D and the pixel electrode E are tapered. Note that, if a dry etching process using Cl 2  gas is performed upon the aluminum alloy layer  2  and the Mo layer  12 , the side edges of the drain electrode D and the pixel electrode E are not tapered. 
     Next, referring to FIG. 3C, the photoresist pattern  3  is removed. 
     Next, referring to FIG. 3D, a phosphor rich amorphous silicon layer, i.e., an about 5 nm thick N+-type amorphous silicon layer  4  is deposited by a PCVD process using PH 3  gas added by a very small amount of SiH 4  gas only on the drain electrode D and the pixel electrode E. Note that the N+-type amorphous silicon layer  4  can be-formed by a PH 3  plasma-doping process. 
     Subsequently, an about 50 nm thick I-type (non-doped) amorphous silicon layer  5  is deposited by a PCVD process using SiH 4  gas and H 2  gas on the entire surface. In addition, an about 300 nm thick silicon nitride layer  6  serving as a gate insulating layer is deposited by a PCVD process using SiH 4  gas, NH 3  gas and N 2  gas. Note that all the above-mentioned PCVD processes are carried out in the same PCVD apparatus. 
     Then, an about 100 nm thick Al—Nd—Si alloy layer  7  is deposited by a sputtering process on the silicon nitride layer  6 . Then, a photoresist pattern  3 A corresponding to a gate electrode is formed on the aluminum alloy layer  7 . 
     Next, referring to FIG. 3E, the aluminum alloy layer  7  is etched by a wet etching process using phosphoric acid/nitric acid solution with a mask of the photoresist pattern  3 A to form a gate electrode  7 (G). Note that the aluminum alloy layer  7  can be etched by a dry etching process using Cl 2  gas. Then, the silicon nitride layer  6 , the I-type amorphous silicon layer  5 , and the N+-type amorphous silicon layer  4  are sequentially etched by a dry etching process using CF 4  gas and O 2  gas with a mask of the photoresist pattern  8 . Thus, an island is formed. Also, since the aluminum alloy layer  2  is not etched by the above-mentioned dry etching process using fluorine gas, the drain electrode D and the pixel electrode E outside of the island are exposed. 
     Next, referring to FIG. 3F, the photoresist pattern  3 A is removed. Thus, the island for a staggered TFT where the gate electrode  7 (G) is below the amorphous silicon layer  5  is formed. 
     Finally, referring to FIG. 3G, a counter glass substrate  8  having an uneven surface is prepared. For example, the surface of the glass substrate  8  is made uneven by using a sand blast method. Then, a transparent common electrode  9  is formed on the glass substrate  8 . Then, after orientation processes including orientation layer coating processes and rubbing processes are performed upon the two substrates  1  and  8 , the two glass substrates  1  and  8  are attached to each other with a predetermined spacing therebetween defined by plastic spacers (not shown). Then, the sides of the two glass substrates  1  and  8  are adhered to each other by epoxy adhesives, and then, a guest-host liquid crystal layer  11  is inserted into this spacing, and the device is sealed by an ultraviolet-setting resin. 
     Also, in the first embodiment, the aluminum alloy layer  2  has a bad ohmic contact characteristic to the N+-type amorphous silicon layer  4 , while in the second embodiment, the Mo layer  12  has good ohmic contact characteristics to the aluminum alloy layer  2  and the N+-type amorphous silicon layer  4 . Therefore, the aluminum alloy layer  2  can be electrically connected effectively via the Mo layer  12  to the N+-type amorphous silicon layer  4 . 
     In the second embodiment as illustrated in FIGS. 3A through 3G, although a step for forming the Mo layer  12  as an ohmic contact material for th N+-type amorphous silicon layer  4  is added to the first embodiment, only two photolithography and etching processes are carried out. In addition, the Mo layer  12  and the aluminum alloy layer  2  are sequentially formed in the same sputtering apparatus. Therefore, the manufacturing cost can be reduced. 
     Also, in FIGS. 3A through 3G, in the same way as in FIGS. 2A through 2G, the diffusion of aluminum atoms and silicon atoms can be suppressed, thus avoiding the deterioration of the characteristics of the TFT. In addition, the high temperature resistance and anti-electromigration characteristics of the aluminum alloy layers  2  and  7  can be improved. Further, polarization plates are unnecessary and a bright display can be obtained. 
     A third embodiment of the method for manufacturing a reflective LCD apparatus according to the present invention will be explained next with reference to FIGS. 4A through 4G. 
     First, referring to FIG. 4A, an about 80 nm thick Al—ND—Si alloy layer  2  is deposited by a sputtering process on a glass substrate  1 . Then, an about 20 nm thick Mo layer  12  is deposited by a sputtering process on the aluminum alloy layer  2 . Then, a photoresist pattern  3  corresponding to a drain electrode and a source (pixel) electrode is formed by a photolithography process. 
     Next, referring to FIG. 4B, the Mo layer  12  and the aluminum alloy layer  2  are etched by a wet etching process using a phosphoric acid/nitric acid solution with a mask of the photoresist pattern  3 . As a result, a drain electrode D and a pixel electrode E are formed by the Mo layer  12  and the aluminum alloy layer  2 . In this case, the side edges of the drain electrode D and the pixel electrode E are tapered. Note that, if a dry etching process using Cl 2  gas is performed upon the Mo layer  12  and the aluminum alloy layer  2 , the side edges of the drain electrode D and the pixel electrode E are not tapered. 
     Next, referring to FIG. 4C, the photoresist pattern  3  is removed. 
     Next, referring to FIG. 4D, a phosphor rich amorphous silicon layer, i.e., an about 5 nm thick N+-type amorphous silicon layer  4  is deposited by a PCVD process using PH 3  gas added by a very small amount of SiH 4  gas only on the drain electrode D and the pixel electrode E. Note that the N+-type amorphous silicon layer  4  can be formed by a PH 3  plasma-doping process. 
     Subsequently, an about 50 nm thick I-type (non-doped) amorphous silicon layer  5  is deposited by a PCVD process using SiH 4  gas and H 2  gas on the entire surface. In addition, an about 300 nm thick silicon nitride layer  6  serving as a gate insulating layer is deposited by a PCVD process using SiH 4  gas, NH 3  gas and N 2  gas. Note that all the above-mentioned PCVD processes are carried out in the same PCVD apparatus. 
     Then, an about 100 nm thick Al—Nd—Si alloy layer  7  is deposited by a sputtering process on the silicon nitride layer  6 . Then, a photoresist pattern  3 A corresponding to a gate electrode is formed on the aluminum alloy layer  7 . 
     Next, referring to FIG. 4E, the aluminum alloy layer  7  is etched by a wet etching process using a phosphoric acid/nitric acid solution with a mask of the photoresist pattern  3 A to form a gate electrode  7 (G). Note that the aluminum alloy layer  7  can be etched by a dry etching process using Cl 2  gas. Then, the silicon nitride layer  6 , the I-type amorphous silicon layer  5 , the N+-type amorphous silicon layer  4  and the Mo layer  12  are sequentially etched by a dry etching process using CF 4  gas and O 2  gas with a mask of the photoresist pattern  3 A. Thus, an island is formed. Also, since the Mo layer  12  is etched but the aluminum alloy layer  2  is not etched by the above-mentioned dry etching process using fluorine gas, the drain electrode D and the pixel electrode E outside of the island are exposed. 
     Next, referring to FIG. 4F, the photoresist pattern  3 A is removed. Thus, the island for a staggered TFT where the gate electrode  7 (G) is below the amorphous silicon layer  5  is formed. 
     Finally, referring to FIG. 4G, a counter glass substrate  8  having an uneven surface is prepared. For example, the surface of the glass substrate  8  is made uneven by using a sand blast method. Then, a transparent common electrode  9  is formed on the glass substrate  8 . Then, after orientation processes including orientation layer coating processes and rubbing processes are performed upon the two substrates  1  and  8 , the two glass substrates  1  and  8  are attached to each other with a predetermined spacing therebetween defined by plastic spacers (not shown). Then, the sides of the two glass substrates  1  and  8  are adhered to each other by epoxy adhesives, and then, a guest-host liquid crystal layer  11  is inserted into this spacing, and the device is sealed by an ultraviolet-setting resin. 
     Even in the third embodiment as illustrated in FIGS. 4A through 4G, although a step for forming the Mo layer  12  as an ohmic contact material for th N+-type amorphous silicon layer  4  is added to the first embodiment, only two photolithography and etching processes are carried out. In addition, the aluminum alloy layer  2  and the Mo layer  12  are sequentially formed in the same sputtering apparatus. Therefore, the manufacturing cost can be reduced. 
     Also, in the third embodiment, the Mo layer  12  has good ohmic contact characteristics to the aluminum alloy layer  2  and the N+-type amorphous silicon layer  4 . Therefore, the aluminum alloy layer  2  can be electrically connected effectively via the Mo layer  12  to the N+-type amorphous silicon layer  4 . 
     Note that, since the Mo layer  12  on the aluminum alloy layer  2  outside of the island is etched, the aluminum alloy layer  2  completely serves as reflecting means. 
     Also, in FIGS. 4A through 4G, in the same way as in FIGS. 2A through 2G, the diffusion of aluminum atoms and silicon atoms can be suppressed, thus avoiding the deterioration of the characteristics of the TFT. In addition, the high temperature resistance and anti-electromigration characteristics of the aluminum alloy layers  2  and  7  can be improved. Further, polarization plates are unnecessary and a bright display can be obtained. 
     A fourth embodiment of the method for manufacturing a reflective LCD apparatus according to the present invention will be explained next with reference to FIGS. 5A through 5G. In FIGS. 5A through 5G, an indium tin oxide (ITO) layer is used instead of the Mo layer  12  of FIGS. 3A through 3G. 
     First, referring to FIG. 5A, an about 20 nm thick ITO layer  13  is deposited by a sputtering process on a glass substrate  1 . Then, an about 80 nm thick Al—Nd—Si alloy layer  2  is deposited by a sputtering process on the ITO layer  13 . Then, a photoresist pattern  3  corresponding to a drain electrode and a source (pixel) electrode is formed by a photolithography process. 
     Next, referring to FIG. 5B, the aluminum alloy layer  2  and the ITO layer  13  are etched by a dry etching process using Cl 2  gas, CF 4  gas and H 2  gas with a mask of the photoresist pattern  3 . As a result, a drain electrode D and a pixel electrode E are formed by the aluminum alloy layer  2  and the ITO layer  13 . In this case, the side edges of the drain electrode D and the pixel electrode E are not tapered. 
     Next, referring to FIG. 5C, the photoresist pattern  3  is removed. 
     Next, referring to FIG. 5D, a phosphor rich amorphous silicon layer, i.e., an about 5 nm thick N+-type amorphous silicon layer  4  is deposited by a PCVD process using PH 3  gas added by a very small amount of SiH 4  gas only the drain electrode D and the pixel electrode E. Note that the N+-type amorphous silicon layer  4  can be formed by a PH 3  plasma-doping process. 
     Subsequently, an about 50 nm thick I-type (non-doped) amorphous silicon layer  5  is deposited by a PCVD process using SiH 4  gas and H 2  gas on the entire surface. In addition, an about 300 nm thick silicon nitride layer  6  serving as a gate insulating layer is deposited by a PCVD process using SiH 4  gas, NH 3  gas and N 2  gas. Note that all the above-mentioned PCVD processes are carried out in the same PCVD apparatus. 
     Then, an about 100 nm thick Al—Nd—Si alloy layer  7  is deposited by a sputtering process on the silicon nitride layer  6 . Then, a photoresist pattern  3 A corresponding to a gate electrode is formed on the aluminum alloy layer  7 . 
     Next, referring to FIG. 5E, the aluminum alloy layer  7  is etched by a wet etching process using a phosphoric acid/nitric acid solution with a mask of the photoresist pattern  3 A to form a gate electrode  7 (G). Note that the aluminum alloy layer  7  can be etched by a dry etching process using Cl 2  gas. Then, the silicon nitride layer  6 , the I-type amorphous silicon layer  5 , and the N+-type amorphous silicon layer  4  are sequentially etched by a dry etching process using CF 4  gas and O 2  gas with a mask of the photoresist pattern  3 A. Thus, an island is formed. Also, since the aluminum alloy layer  2  is not etched by the above-mentioned dry etching process using fluorine gas, the drain electrode D and the pixel electrode E outside of the island are exposed. 
     Next, referring to FIG. 5F, the photoresist pattern  3 A is removed. Thus, the island for a staggered TFT  20  where the gate electrode  7 (G) is below the amorphous silicon layer  5  is formed. 
     Finally, referring to FIG. 5G, a counter glass substrate  8  having an uneven surface is prepared. For example, the surface of the glass substrate  8  is made uneven by using a sand blast method. Then, a transparent common electrode  9  is formed on the glass substrate  8 . Then, after orientation processes including orientation layer coating processes and rubbing processes are performed upon the two substrates  1  and  8 , the two glass substrates  1  and  8  are attached to each other with a predetermined spacing therebetween defined by plastic spacers (not shown). Then, the sides of the two glass substrates  1  and  8  are adhered to each other by epoxy adhesives, and then, a guest-host liquid crystal layer  11  is inserted into this spacing, and the device is sealed by an ultraviolet-setting resin. 
     In the fourth embodiment as illustrated in FIGS.  5 A through  5 G, although a step for forming the ITO layer  13  as an ohmic contact material for the N+-type amorphous silicon layer  4  is added to the first embodiment, only two photolithography and etching processes are carried out. In addition, the ITO layer  13  and the aluminum alloy layer  2  are sequentially formed in the same sputtering apparatus. Therefore, the manufacturing cost can be reduced. 
     Also, in the fourth embodiment, the ITO layer  13  has good ohmic contact characteristics to the N+-type amorphous silicon layer  4 . Therefore, the aluminum alloy layer  2  can be electrically connected effectively via the ITO layer  13  to the N+-type amorphous silicon layer  4 . 
     Also, in FIGS. 5A through 5G, in the same way as in FIGS. 2A through 2G, the diffusion of aluminum atoms and silicon atoms can be suppressed, thus avoiding the deterioration of the characteristics of the TET. In addition, the high temperature resistance and anti-electromigration characteristics of the aluminum alloy layers  2  and  7  can be improved. Further, polarization plates are unnecessary and a bright display can be obtained. 
     A fifth embodiment of the method for manufacturing a reflective LCD apparatus according to the present invention will be explained next with reference to FIGS. 6A through 6G. In FIGS. 6A through 6G, an ITO layer is used instead of the Mo layer  12  of FIGS. 4A through 4G. 
     First, referring to FIG. 6A, an about 80 nm thick Al—Nd—Si alloy layer  2  is deposited by a sputtering process on a glass substrate  1 . Then, an about 20 nm thick ITO layer  13  is deposited by a sputtering process on the aluminum alloy layer  2 . Then, a photoresist pattern  3  corresponding to a drain electrode and a source (pixel) electrode is formed by a photolithography process. 
     Next, referring to FIG. 6B, the ITO layer  13  and the aluminum alloy layer  2  are etched by a dry etching process using Cl 2  gas, CF 4  gas and H 2  gas with a mask of the photoresist pattern  3 . As a result, a drain electrode D and a pixel electrode E are formed by the ITO layer  13  and the aluminum alloy layer  2 . In this case, the side edges of the drain electrode D and the pixel electrode E are not tapered. 
     Next, referring to FIG. 6C, the photoresist pattern  3  is removed. 
     Next, referring to FIG. 6D, a phosphor rich amorphous silicon layer, i.e., an about 5 nm thick N+-type amorphous silicon layer  4  is deposited by a PCVD process using PH 3  gas added by a very small amount of SiH 4  gas only the drain electrode D and the pixel electrode E. Note that the N 4 -type amorphous silicon layer  4  can be formed by a PH 3  plasma-doping process. 
     Subsequently, an about 50 nm thick I-type (non-doped) amorphous silicon layer  5  is deposited by a PCVD process using SiH 4  gas and H 2  gas on the entire surface. In addition, an about 300 nm thick silicon nitride layer  6  serving as a gate insulating layer is deposited by a PCVD process using SiH 4  gas, NH 3  gas and N 2  gas. Note that all the-above-mentioned PCVD processes are carried out in the same PCVD apparatus. 
     Then, an about 100 nm thick Al—Nd—Si alloy layer  7  is deposited by a sputtering process on the silicon nitride layer  6 . Then, a photoresist pattern  3 A corresponding to a gate electrode is formed on the aluminum alloy layer  7 . 
     Next, referring to FIG. 6E, the aluminum alloy layer  7  is etched by a wet etching process using a phosphoric acid/nitric acid solution with a mask of the photoresist pattern  3 A to form a gate electrode  7 (G). Note that the aluminum alloy layer  7  can be etched by a dry etching process using Cl 2  gas. Then, the silicon nitride layer  6 , the I-type amorphous silicon layer  5 , and the N+-type amorphous silicon layer  4  are sequentially etched by a dry etching process using CF 4  gas and O 2  gas with a mask of the photoresist pattern  3 A. Thus, an island is formed. Also, since the ITO layer  13  is not etched by the above-mentioned dry etching process using fluorine gas, the drain electrode D and the pixel electrode E outside of the island are exposed. Note that, since the ITO layer  13  is transparent, even if the ITO layer  13  remains in the drain electrode D and the pixel electrode E, the aluminum alloy layer  2  can completely serve as reflecting means. 
     Next, referring to FIG. 6F, the photoresist pattern  3 A is removed. Thus, the island for a staggered TFT where the gate electrode  7 (G) is below the amorphous silicon layer  5  is formed. 
     Finally, referring to FIG. 6G, a counter glass substrate  8  having an uneven surface is prepared. For example, the surface of the glass substrate  8  is made uneven by using a sand blast method. Then, a transparent common electrode  9  is formed on the glass substrate  8 . Then, after orientation processes including orientation layer coating processes and rubbing processes are performed upon the two substrates  1  and  8 , the two glass substrates  1  and  8  are attached to each other with a predetermined spacing therebetween defined by plastic spacers (not shown). Then, the sides of the two glass substrates  1  and  8  are adhered to each other by epoxy adhesives, and then, a guest-host liquid crystal layer  11  is inserted into this spacing, and the device is sealed by an ultraviolet-setting resin. 
     In the fifth embodiment as illustrated in FIGS. 6A through 6G, although a step for forming the ITO layer  13  as an ohmic contact material for the N+-type amorphous silicon layer  4  is added to the first embodiment, only two photolithography and etching processes are carried out. In addition, the ITO layer  13  and the aluminum alloy layer  2  are sequentially formed in the same sputtering apparatus. Therefore, the manufacturing cost can be reduced. 
     Also, in the fifth embodiment, the ITO layer  13  has a good ohmic contact characteristics to the N+-type amorphous silicon layer  4 . Therefore, the aluminum alloy layer  2  can be electrically connected effectively via the ITO layer  13  to the N+-type amorphous silicon layer  4 . 
     Also, in FIGS. 6A though  6 G, in the same way as in FIGS. 2A through 2G, the diffusion of aluminum atoms and silicon atoms can be suppressed, thus avoiding the deterioration of the characteristics of the TET. In addition, the high temperature resistance and anti-electromigration characteristics of the aluminum alloy layers  2  and  7  can be improved. Further, polarization plates are unnecessary and a bright display can be obtained. 
     In FIGS. 7A through 7E, which are modifications of the apparatuses of FIGS. 2G,  3 G,  4 G,  5 G and  6 G, respectively, an opposite surface of the counter glass substrate  8  on which the transparent common electrode  9  is formed is made uneven. Even in this case, the same light scattering effect can be expected. 
     In FIGS. 8A through 8E, which are also modifications of the apparatuses of FIGS. 2G,  3 G,  4 G,  5 G and  6 G, respectively, both surfaces of the counter glass substrate  8  are made uneven. Even in this case, the same light scattering effect can be expected. 
     In FIGS. 9A through 9E, which are further modifications of the apparatuses of FIGS. 2G,  3 G,  4 G,  5 G and  6 G, respectively, a transparent insulating layer  14  made of photosensitive acrylic resin or polyimide resin having an uneven surface is formed on the TETs instead of providing an uneven surface on the counter glass substrate  8 . Note that a large difference in refractive index between the transparent insulating layer  14  and the liquid crystal layer  11  enhances the light scattering effect. Even in this case, the same light scattering effect can be expected. 
     In FIGS. 10A through 10E, which are still further modifications of the apparatuses of FIGS. 2G,  3 G,  4 G,  5 G and  6 G, respectively, a transparent insulating layer  15  is formed on the TETs instead of providing an uneven surface on the counter glass substrate  8 . In this case, the transparent insulating layer  15  is formed by spin-coating polyimide resin including light scattering particles (beeds)  15   a . Even in this case, the same light scattering effect can be expected. 
     A sixth embodiment of the method for manufacturing a reflective LCD apparatus according to the present invention will be explained next with reference to FIGS. 11A through 11G. Note that the sixth embodiment is a modification of the first embodiment as illustrated in FIGS. 2A through 2G. 
     First, referring to FIG. 11A, an about 200 nm thick Al—Si alloy layer  2 ′ is deposited by a sputtering process at a substrate temperature higher than 150° C. on a glass substrate  1 . As a result, the surface of the aluminum alloy layer  2 ′ is made uneven and turbid as aluminum crystal grains grow. In this case, the higher the substrate temperature, the larger the aluminum grain size. Also, the thicker the aluminum alloy layer  2 ′, the larger the aluminum crystal grain size. However, if the aluminum alloy layer  2 ′ is too thick, the coverage characteristics of PCVD layers which will be formed thereon become deteriorated. Thus, the aluminum alloy layer  2 ′ can serve as light scattering means as well as light reflecting means. Then, a photoresist pattern  3  corresponding to a drain electrode and a source (pixel) electrode is formed by a photolithography process. 
     Next, referring to FIGS. 11B through 11F, the same operations as in the steps as illustrated in FIGS. 2B through 2F are carried out. 
     Finally, referring to FIG. 11G, a counter glass substrate  8  is prepared. In this case, the surfaces of the counter glass substrate  8  are both flat. Then, a transparent common electrode  9  is formed on the glass substrate  8 . Then, after orientation processes including orientation layer coating processes and rubbing processes are performed upon the two substrates  1  and  8 , the two glass substrates  1  and  8  are attached to each other with a predetermined spacing therebetween defined by plastic spacers (not shown). Then, the sides of the two glass substrates  1  and  8  are adhered to each other by epoxy adhesives, and then, a guest-host liquid crystal layer  11  is inserted into this spacing, and the device is sealed by an ultraviolet-setting resin. 
     In the sixth embodiment the formation of a light scattering means on the counter glass substrate  8  is unnecessary, which reduces the manufacturing cost. 
     A seventh embodiment of the method for manufacturing a reflective LCD apparatus according to the present invention will be explained next with reference to FIGS. 12A through 12G. Note that the seventh embodiment is another modification of the first embodiment as illustrated in FIGS. 2A through 2G. 
     Referring to FIGS. 12A through 12E, the same operations as in the steps illustrated in FIGS. 2A through 2E are carried out. 
     Also, at a step as illustrated in FIG. 12E, the aluminum alloy layer  2  is etched by a dry etching process using Cl 2  gas and H 2  gas, to make the surface of the aluminum alloy layer  2  uneven. Note that this dry etching process can be sequentially carried out with the dry etching process for etching the silicon nitride layer  6 , the amorphous silicon layer  5  and the N+-type amorphous silicon layer  4 . 
     Finally, referring to FIG. 12G, the same operation as in a step illustrated in FIG. 11G is carried out. 
     Even in the seventh embodiment, the formation of a light scattering means on the counter glass substrate  8  is unnecessary, which reduces the manufacturing cost. 
     An eighth embodiment of the method for manufacturing a reflective LCD apparatus according to the present invention will be explained next with reference to FIGS. 13A through 13G. Note that the eighth embodiment is a modification of the second embodiment as illustrated in FIGS. 3A through 3G. 
     First, referring to FIG. 13A, an about 200 nm thick Mo layer  12  is deposited by a sputtering process on a glass substrate  1 . Then, an about 80 nm thick Al—Si alloy layer  2 ′ is deposited by a sputtering process at a substrate temperature higher than 150° C. on the Mo layer  12 . As a result, the surface of the aluminum alloy layer  2 ′ is made uneven and turbid as aluminum crystal grains grow. Thus, the aluminum alloy layer  2 ′ can serve as light scattering means as well as light reflecting means. Then, a photoresist pattern  3  corresponding to a drain electrode and a source (pixel) electrode is formed by a photolithography process. 
     Next, referring to FIGS. 13B through 13F, the same operations as in the steps illustrated in FIGS. 3B through 3F are carried out. 
     Finally, referring to FIG. 13G, a counter glass substrate  8  is prepared. In this case, the surfaces of the counter glass substrate  8  are both flat. Then, a transparent common electrode  9  is formed on the glass substrate  8 . Then, after orientation processes including orientation layer coating processes and rubbing processes are performed upon the two substrates  1  and  8 , the two glass substrates  1  and  8  are attached to each other with a predetermined spacing therebetween defined by plastic spacers (not shown). Then, the sides of the two glass substrates  1  and  8  are adhered to each other by epoxy adhesives, and then, a guest-host liquid crystal layer  11  is inserted into this spacing. Then, the device is sealed by an ultraviolet-setting resin. 
     In the eighth embodiment the formation of a light scattering means on the counter glass substrate  8  is unnecessary, which reduces the manufacturing cost. 
     A ninth embodiment of the method for manufacturing a reflective LCD apparatus according to the present invention will be explained next with reference to FIGS. 14A through 14G. Note that the ninth embodiment is another modification of the second embodiment as illustrated in FIGS. 3A through 3G. 
     Referring to FIGS. 14A through 14E, the same operations at the steps as illustrated in FIGS. 3A through 3E. 
     Also, at a step as illustrated in FIG. 14E, the aluminum alloy layer  2  is etched by a dry etching process using Cl 2  gas and H 2  gas, to make the surface of the aluminum alloy layer  2  uneven. Note that this dry etching process can be sequentially carried out with the dry etching process for etching the silicon nitride layer  6 , the amorphous silicon layer  5  and the N+-type amorphous silicon layer  4 . 
     Finally, referring to FIG. 14G, the same operation as in a step illustrated in FIG. 13G is carried out. 
     Even in the ninth embodiment, the formation of a light scattering means on the counter glass substrate  8  is unnecessary, which reduces the manufacturing cost. 
     A tenth embodiment of the method for manufacturing a reflective LCD apparatus according to the present invention will be explained next with reference to FIGS. 15A through 15G. Note that the tenth embodiment is a modification of the third embodiment as illustrated in FIGS. 4A through 4G. 
     First, referring to FIG. 15A, an about 80 nm thick Al—Si alloy layer  2 ′ is deposited by a sputtering process at a substrate temperature higher than 150° C. on a glass substrate  1 . Then, an about 20 nm thick Mo layer  12  on the aluminum alloy layer  2 ′. As a result, the surface of the aluminum alloy layer  2 ′ is made uneven and turbid as aluminum crystal grains grow. Thus, since the MO layer  12  will be removed at a later stage, the aluminum alloy layer  2 ′ can serve as light scattering means as well as light reflecting means. Then, a photoresist pattern  3  corresponding to a drain electrode and a source (pixel) electrode is formed by a photolithography process. 
     Next, referring to FIGS. 15B through 15F, the same operations as in the steps illustrated in FIGS. 3B through 3F are carried out. 
     Finally, referring to FIG. 15G, a counter glass substrate  8  is prepared. In this case, the surfaces of the counter glass substrate  8  are both flat. Then, a transparent common electrode  9  is formed on the glass substrate  8 . Then, after orientation processes including orientation layer coating processes and rubbing processes are performed upon the two substrates  1  and  8 , the two glass substrates  1  and  8  are attached to each other with a predetermined spacing therebetween defined by plastic spacers (not shown). Then, the sides of the two glass substrates  1  and  8  are adhered to each other by epoxy adhesives, and then, a guest-host liquid crystal layer  11  is inserted into this spacing, and the device is sealed by an ultraviolet-setting resin. 
     Also, in the tenth embodiment the formation of a light scattering means on the counter glass substrate  8  is unnecessary, which reduces the manufacturing cost. 
     An eleventh embodiment of the method for manufacturing a reflective LCD apparatus according to the present invention will be explained next with reference to FIGS. 16A through 16G. Note that the eleventh embodiment is another modification of the third embodiment as illustrated in FIGS. 4A through 4G. 
     Referring to FIGS. 16A through 16E, the same operations as in the steps illustrated in FIGS. 4A through 4E are carried out. 
     Also, at a step as illustrated in FIG. 16E, the aluminum alloy layer  2  is etched by a dry etching process sing Cl 2  gas and H 2  gas, to make the surface of the aluminum alloy layer  2  uneven. Note that this dry etching process can be sequentially carried out with the dry etching process for etching the silicon nitride layer  6 , the amorphous silicon layer  5  and the N+-type amorphous silicon layer  4 . 
     Finally, referring to FIG. 16G, the same operation as in a step illustrated in FIG. 15G is carried out. 
     Even in the eleventh embodiment, the formation of a light scattering means on the counter glass substrate  8  is unnecessary, which reduces the manufacturing cost. 
     A twelfth embodiment of the method for manufacturing a reflective LCD apparatus according to the present invention will be explained next with reference to FIGS. 17A through 17G. Note that the twelfth embodiment is a modification of the fourth embodiment as illustrated in FIGS. 5A through 5G. 
     First, referring to FIG. 17A, an about 20 nm thick ITO layer  13  is deposited by a sputtering process on a glass substrate  1 . Then, an about 80 nm thick Al—Si alloy layer  2 ′ is deposited by a sputtering process at a substrate temperature higher than 150° C. on the ITO layer  13 . As a result, the surface of the aluminum alloy layer  2 ′ is made uneven and turbid as aluminum crystal grains grow. Thus, the aluminum alloy layer  2 ′ can serve as light scattering means as will be light reflecting means. Then, a photoresist pattern  3  corresponding to a drain electrode and a source (pixel) electrode is formed by a photolithography process. 
     Next, referring to FIGS. 17B through 17F, the same operations as in the steps illustrated in FIGS. 5B through 5F are carried out. 
     Finally, referring to FIG. 17G, a counter glass substrate  8  is prepared. In this case, the surfaces of the counter glass substrate  8  are both flat. Then, a transparent common electrode  9  is formed on the glass substrate  8 . Then, after orientation processes including orientation layer coating processes and rubbing processes are performed upon the two substrates  1  and  8 , the two glass substrates  1  and  8  are attached to each other with a predetermined spacing therebetween defined by plastic spacers (not shown). Then, the sides of the two glass substrates  1  and  8  are adhered to each other by epoxy adhesives, and then, a guest-host liquid crystal layer  11  is inserted into this spacing. Then, the device is sealed by an ultraviolet-setting resin. 
     Even in the twelfth embodiment the formation of a light scattering means on the counter glass substrate  8  is unnecessary, which reduces the manufacturing cost. 
     A thirteenth embodiment of the method for manufacturing a reflective LCD apparatus according to the present invention will be explained next with reference to FIGS. 18A through 18G. Note that the thirteenth embodiment is another modification of the fourth embodiment as illustrated in FIGS. 5A through 5G. 
     Referring to FIGS. 18A through 18E, the same operations as in the steps illustrated in FIGS. 5A through 5E are carried out. 
     Also, at the step as illustrated in FIG. 18E, the aluminum alloy layer  2  is etched by a dry etching process using Cl 2  gas and H 2  gas, to make the surface of the aluminum alloy layer  2  uneven. Note that this dry etching process can be sequentially carried out with the dry etching process for etching the silicon nitride layer  6 , the amorphous silicon layer  5  and the N+-type amorphous silicon layer  4 . 
     Finally, referring to FIG. 18G, the same operation as in the step illustrated in FIG. 13G is carried out. 
     Even in the thirteenth embodiment, the formation of a light scattering means on the counter glass substrate  8  is unnecessary, which reduces the manufacturing cost. 
     A fourteenth embodiment of the method for manufacturing a reflective LCD apparatus according to the present invention will be explained next with reference to FIGS. 19A through 19G. Note that the fourteenth embodiment is a modification of the fifth embodiment as illustrated in FIGS. 6A through 6G. 
     First, referring to FIG. 19A, an about 80 nm thick Al—Si alloy layer  2 ′ is deposited by a sputtering process at a substrate temperature higher than 150° C. on a glass substrate  1 . Then, an about 20 nm thick ITO layer  13  is formed on the aluminum alloy layer  2 ′. As a result, the surface of the aluminum alloy layer  2 ′ is made uneven and turbid as aluminum crystal grains grow. Thus, the aluminum alloy layer  2 ′ can serve as light scattering means as well as light reflecting means. Then, a photoresist pattern  3  corresponding to a drain electrode and a source (pixel) electrode is formed by a photolithography process. 
     Next, referring to FIGS. 19B through 19F, the same operations as in the steps illustrated in FIGS. 6B through 6F are carried out. 
     Finally, referring to FIG. 19G, a counter glass substrate  8  is prepared. In this case, the surfaces of the counter glass substrate  8  are both flat. Then, a transparent common electrode  9  is formed on the glass substrate  8 . Then, after orientation processes including orientation layer coating processes and rubbing processes are performed upon the two substrates  1  and  8 , the two glass substrates  1  and  8  are attached to each other with a predetermined spacing therebetween defined by plastic spacers (not shown). Then, the sides of the two glass substrates  1  and  8  are adhered to each other by epoxy adhesives, and then, a guest-host liquid crystal layer  11  is inserted into this spacing. Then, the device is sealed by an ultraviolet-setting resin. 
     Also, in the fourteenth embodiment the formation of a light scattering means on the counter glass substrate  8  is unnecessary, which reduces the manufacturing cost. 
     As explained hereinabove, according to the present invention, since a drain electrode and a pixel electrode made of aluminum alloy can be simultaneously formed, the number of photolithography and etching processes can be reduced, which reduces the manufacturing cost. Note that the number of photolithography and etching processes is 2 in the above-described embodiments. 
     In addition, since a TFT adopts a staggered type, the light shield for the TET can be enhanced, which reduces a light OFF current. 
     In addition, since the drain electrode and the pixel electrode as well as a gate electrode are made of low conductive aluminum alloy, a signal delay can be suppressed even in a large scale LCD apparatus, which suppresses the deterioration of the display quality.