Patent Publication Number: US-6703997-B2

Title: Electrooptical apparatus, method of producing the same and electronic apparatus

Description:
This is a Continuation of application Ser. No. 09/240,888 filed Feb. 1, 1999 now U.S. Pat. No. 6,433,767. The entire disclosure of the prior application(s) is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to an electrooptical apparatus such as an active matrix liquid crystal apparatus driven by thin-film transistors (hereinafter also referred to as TFTs), and also to a method of producing such an electrooptical apparatus. More particularly, the present invention relates to an electrooptical apparatus such as a liquid crystal apparatus suitable for use in a liquid crystal projector, and including peripheral circuits such as a data line driving circuit and a scanning line driving circuit, wherein a light blocking film is disposed under each TFT. The present invention further relates to a method of producing such an electrooptical apparatus. 
     2. Description of Related Art 
     In conventional liquid crystal apparatus having built-in peripheral circuits, peripheral circuits such as a data line driving circuit, a scanning line driving circuit, and a sampling circuit are formed on a TFT array substrate, which is one of two substrates between which a liquid crystal is disposed. In general, these peripheral circuits are produced using the same production process as that for producing TFTs for switching an image signal applied to pixel electrodes provided in respective pixels (hereinafter such TFTs will also be referred to as pixel TFTs) so as to achieve a high production efficiency. 
     On the TFT array substrate, there are provided a great number of data lines and scanning lines in an image displaying area in contact with the liquid crystal, wherein these data lines and scanning lines cross each other at different layer levels. Input/output interconnections connected to peripheral circuits are disposed in a sealing area, outside the image displaying area and in contact with a sealing material for enclosing a liquid crystal, and in a peripheral area outside the sealing area. More specifically, leading interconnections which extend from the data lines, the scanning lines, and the capacitance lines, and which serve as the input/output interconnections for the peripheral circuits, are disposed in the sealing area and image signal lines, control signal lines, power supply lines, clock signal lines, and other signal lines, connected to external input terminals, and are disposed in the peripheral area. 
     In particular, in a liquid crystal apparatus having a sampling circuit as a peripheral circuit, when an image signal is supplied to an image signal line via an external input terminal, the image signal is sampled, from one data line to another, by sampling switches of the sampling circuit, in response to a sampling circuit driving signal output with predetermined timing from the data line driving circuit. 
     Because the image signal line is a signal line used to supply the image signal itself, which defines the voltage applied to the liquid crystal, it is extremely important that the image signal line has a low electric resistance and a small time constant to prevent degradation in the picture quality. To this end, the image signal line is generally formed of a thin metal film such as an aluminum film which has the lowest resistivity of all thin films used in the active matrix TFT liquid crystal apparatus, and which is also used to form data lines. 
     On the other hand, there are no currently available techniques which can be used to form the scanning lines of a thin metal film or a thin metal silicide film, because existing techniques would be subject to the problem that the scanning lines would peel off during a high-temperature process performed after the formation of the scanning lines. For the above reason, the scanning lines are generally formed of a thin polysilicon film. The interconnection formed of a thin polysilicon film has as high a resistance as 200 times that of an interconnection formed of a thin metal film, and thus has a correspondingly high time constant. For the above reason, if the image signal line was formed of a thin polysilicon film, degradation in the image quality would occur depending on the resistance and the time constant of the interconnection employed as the image signal line. In practice, to avoid the above problem, the image signal line is formed of a thin metal film, as described above. 
     In the above-described type liquid crystal apparatus including the peripheral circuit, if there is only one image signal line, it is possible to form the image signal line with an interconnection formed of a thin metal film at the same single layer level (produced in the same process) over the entire path from an external input terminal disposed at an end of a substrate to respective sampling switches of the sampling circuit. However, in the case where a plurality of image signal lines are required to transmit image signals expanded into a plurality of phases so as to handle high-frequency driving operation in the liquid crystal apparatus, or in the case where a plurality of image signal lines are required to handle respective colors of an RGB color image signal, at least one image signal line has to cross another image signal line somewhere in the path to sampling switches. That is, it is impossible to produce interconnections for all image signal lines using only a thin metal film at the same layer level. 
     Therefore, a relay interconnection is formed using a polysilicon film at a different layer level separated by an interlayer insulating film from the thin metal film. More specifically, one interconnection includes a first interconnection (main interconnection) made of a thin metal film and disposed at a crossing point. Another interconnection includes a second interconnection (relay interconnection) made of a thin polysilicon film extending at a different level and crossing below or above the first interconnection via an interlayer insulating film, wherein the second interconnection is electrically connected to a part of the interconnection made of a thin metal film via contact holes formed, at both sides of the crossing point, in the interlayer insulating film. 
     If only a part, which crosses another interconnection, is constructed in the form of a relay interconnection made of a thin polysilicon film, and the other parts are constructed in the form of main interconnections made of a thin metal film which are connected to each other via the relay interconnection as described above, then the relay interconnection made of the thin polysilicon film has a very small length, and thus the existence of the relay line made of the thin polysilicon film does not cause the image signal line to have so significant increases in the overall resistance and time constant that can cause a problem to occur during practical applications. 
     When a liquid crystal apparatus of the above-described type is used as a light valve in a liquid crystal projector or the like, a projection light ray is generally incident on an opposite substrate opposing, via a liquid crystal layer, a TFT array substrate. If the channel region made of an a-Si (amorphous silicon) film or a p-Si (polysilicon) film of TFTs is exposed to the projection light, a photocurrent is generated in the channel region by the photoelectric conversion effect, and the transistor characteristic of the TFTs are degraded. To avoid the above problem, a light blocking film, called a black matrix or a black mask, made of a metal material such as Cr (chromium), or a black resin is formed on the opposite substrate so that each TFT is covered with the light blocking film. This light blocking film defines opening areas (through which the projection light ray is allowed to pass) of the respective pixels. That is, the light blocking film serves not only to prevent the p-Si layer of TFTs from being exposed to light, but also to improve the contrast and prevent colors from mixing. 
     In the case of the liquid crystal apparatus for use as a light valve, in particular when a normal stagger type or coplanar type a-Si or p-Si TFT with the top gate structure (in which the gate electrode is disposed above the channel on the TFT array substrate) is employed, it is required to prevent the channels of TFTs from being exposed to a part of projection light reflected from a projection optical system of the liquid crystal projector and striking the TFT array substrate. Furthermore, it is also required to prevent the channels of TFTs from being exposed to a part of light reflected from the surface of the TFT array substrate which can occur when the projection light passes through the light valve. Still furthermore, when a plurality of liquid crystal apparatus are combined to handle a colored image, it is required to prevent the channel of TFTs from being struck by a leakage light component emerging from another liquid crystal apparatus and incident from the TFT array substrate side. In some known techniques, to avoid the above problem, as disclosed for example in Japanese Unexamined Patent Publication No. 9-127497, Japanese Patent Publication No. 3-52611, Japanese Unexamined Patent Publication No. 3-125123, and Japanese Unexamined Patent Publication No. 8-171101, an additional light blocking film made of transparent refractory metal or the like is provided on a TFT array substrate, at locations opposite to TFTs (that is, at locations under the TFTs). 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention. 
     To meet the general requirement for improved image quality, the driving frequency of liquid crystal apparatus of XGA, SXGA, or EWS type becomes increasingly higher. With the increase in the driving frequency, the number of expanded phases becomes large. More specifically, 24 phases are employed recently. 
     However, to handle such a large number of expanded phases, it is required that a correspondingly great number of image signal lines be disposed in parallel. As a result, the relay interconnections made of the thin polysilicon film become longer. Because the resistance of the interconnection increases in proportion to the length of the interconnection, the resistance of the relay interconnections becomes large. As a result, the image signal lines have a large resistance and a large time constant which result in degradation in the image quality. More specifically, an increase in the resistance or the time constant of image signal lines causes the image signal to have fluctuations via coupling capacitance or causes the image signal on the previous line (column) to be written onto the next line (column), and thus a ghost or crosstalk occurs. 
     To avoid the above problem, if the relay interconnections in the sealing area or periphery area are formed of a thin metal film which is not used in the pixel area, the efficiency of the production process based on the planar technology becomes low. As a result, the production cost becomes high and the fundamental advantages of the liquid crystal apparatus of the type including built-in peripheral circuits are lost. 
     In view of the above, it is an object of the present invention to provide an electrooptical apparatus, such as a liquid crystal apparatus of the type including a built-in peripheral circuit, in which the resistance of input/output interconnections in the peripheral circuit is reduced by effectively using thin films forming pixels, thereby making it possible to display a high-quality image. 
     Means for Solving the Problems. 
     According to a first aspect of the present invention, to solve the above problems, there is provided an electrooptical apparatus including an electrooptical material disposed between a pair of substrates wherein, on one of the substrates, there are provided: a plurality of pixel electrodes arranged in a matrix fashion; a plurality of thin-film transistors that drive the plurality of pixel electrodes, respectively; a plurality of data lines connected to the plurality of thin-film transistors, respectively, and a plurality of scanning lines connected to the plurality of thin-film transistors, the plurality of data lines and the plurality of scanning lines crossing each other at different layer levels, an electrically-conductive light blocking film disposed such that at least a channel region of each of the plurality of thin-film transistors is covered with the light blocking film when viewed from the side of the one of substrates; at least a peripheral circuit for supplying an image signal to the data lines; and peripheral interconnections that input and output predetermined types of signals including the image signal to and from the peripheral circuit; wherein the peripheral interconnections include: an interconnection made of a first conductive film, which is one of a plurality of thin-film layers constituting the thin-film transistors, the data lines, and the scanning lines; and an interconnection made of the light blocking film. 
     In the electrooptical apparatus according to the first aspect of the invention, there are provided peripheral circuits such as a sampling circuit and a data line driving circuit on one of substrates, so that the electrooptical apparatus acts as the type including built-in peripheral circuits. The electrically-conductive light blocking film is disposed such that at least the channel region of each of the plurality of thin-film transistors is covered with the light blocking film when viewed from the side of the one of substrates. Therefore, the channel region of each thin-film transistor is prevented by the light blocking film from being exposed to light, such as a reflected light ray coming from the side of the one of substrates, thereby preventing the thin-film transistors from being degraded in characteristics by the reflected light. In particular, in the present invention, the peripheral interconnections include an interconnection made of a first conductive film (for example the thin metal film forming the data lines) which is one of a plurality of thin-film layers constituting the thin-film transistors, the data lines, and the scanning lines, and also include an interconnection made of the light blocking film. 
     It is possible to obtain a lower resistance for the peripheral interconnections by employing the light blocking film with good electrical conductivity as the material for the peripheral interconnections, compared with the conventional peripheral interconnections made of one conductive thin film (hereinafter referred to as a second conductive film) selected from the plurality of thin films forming the thin film transistors, data lines, and scanning lines except the first conducive film, wherein the second conductive film is worse in conductivity than the first conductive film, and the light blocking film is better in conductivity than the second conductive film. For example, when a polysilicon film is used as the second conductive film, if the light blocking film is made of an electrically-conductive and refractory metal film including Ti (titanium), Cr (chromium), W (tungsten), Ta (tantalum), Mo (molybdenum), or Pd (lead), then the interconnection resistance of the peripheral interconnection is greatly reduced. In this technique, the light blocking film serves not only as a film for preventing the thin-film transistors from being exposed to light, but also as a peripheral interconnection, and thus the structure and the production process can be simplified. 
     Therefore, various signals, including an image signal, can be input and output to and from the peripheral circuits via the peripheral interconnections that have low resistance. Therefore, the driving frequency of the electrooptical apparatus can be increased or the number of expanded phases or the number of image signals which are input in parallel can be increased without causing voltage fluctuations, ghosts, or crosstalk due to capacitive coupling associated with the peripheral interconnections such as image signal lines, which are problems in the conventional technique, thereby ensuring that a high-quality image is displayed. 
     In one mode of the electrooptical apparatus according to the first aspect of the invention, the peripheral interconnections include a single-layer interconnection made of the first conductive film in the form of a single layer when viewed in the thickness direction of the one of substrates; and a two-layer interconnection constructed in the form of two layers when viewed in the thickness direction of the one of substrates, one of the two layers being made of a second conductive film, which is one of the plurality of thin-film layers constituting the data lines and the scanning lines, the other layer being made of the light blocking film. 
     In this mode, the single-layer interconnection of the peripheral interconnection is made of the first conductive film into a single layer structure when viewed in the thickness direction of the one of substrates. The two-layer interconnection of the peripheral interconnection is made of the second conductive film and the light blocking film into a two layer structure when viewed in the thickness direction of the one of substrates. Therefore, when the first conductive film is made of a thin film layer having a low resistance such as a metal film, and the second conductive film is made of a thin film layer such as a polysilicon film having a higher resistance than the first conductive film, the overall resistance of the peripheral interconnection becomes lower by an amount corresponding to the reduction in the resistance of the two-layer interconnection achieved by the existence of the light blocking film compared with a combination of two types of conventional peripheral interconnections made of the first and second conductive films, respectively, into a single layer structure, which cross each other somewhere. For example, when the second conductive film is formed of a polysilicon film and the light blocking film is formed of a refractory metal film having a high conductivity including Ti, Cr, W, Ta, Mo, or Pd, the resistance of the two-layer interconnection, measured along the interconnection, is dominated by the sheet resistance of the light blocking film. Thus, it becomes possible to greatly reduce the resistance of the two-layer interconnection compared with the single-layer interconnection formed of only a single layer of polysilicon according to the conventional technique. Furthermore, in the present invention, the resistance of the single-layer interconnection can be reduced by employing the first conductive film such as Al (aluminum). Thus, the peripheral interconnection including a single-layer interconnection and a two-layer interconnection electrically connected in series to each other has a low enough resistance. 
     Furthermore, the peripheral interconnection has a redundant structure in which even if either a part formed of the thin polysilicon film or a part formed of the light blocking film of the two-layer interconnection is broken due a foreign particle or the like, the electrical conduction is still maintained via the remaining part. Since the two-layer interconnection that has the small resistance is formed using the first conductive film, which is also used to form pixels, and also using the light blocking film which is also used to protect the TFTs from light, the two-layer interconnection according to the present invention can be produced without causing a significant reduction in the production efficiency of the production process of the electrooptical apparatus with a planar structure. Thus, it is possible to achieve fundamental advantages of the electrooptical apparatus of the type including built-in peripheral circuits. 
     In the peripheral interconnection including the single-layer interconnection and the two-layer interconnection according to the present invention, the single-layer interconnection made of the same film as the first conductive film may also be formed into a two-layer or three-layer structure by adding a redundant interconnection. Such a multilayer interconnection still includes a single-layer interconnection according to the invention. Furthermore, an additional redundant interconnection may be added to the two-layer interconnection made of the same film as the second conductive film and the light blocking film so as to obtain an interconnection structure including three or more layers. Such a multilayer interconnection still includes a two-layer interconnection according to the invention. 
     In the mode of the electrooptical apparatus according to the first aspect of the invention in which the peripheral interconnection includes the two-layer interconnection, the second conductive film may have a resistance higher than that of the first conductive film. 
     In this structure, the first conductive film, such as aluminum, has the lowest resistance of all thin films used to form the thin-film transistors, and the second conductive film, such as the low-resistance polysilicon film, has the next lowest resistance of all thin films used to form the thin-film transistors. As a result, the overall resistance of the peripheral interconnection becomes lower by an amount of reduction in the resistance of the two-layer interconnection achieved by employing the light blocking film having a high conductivity compared with the case where peripheral interconnections are formed of first and second conductive films in a single-layer structure crossing each other at different layer levels, according to the conventional technique. 
     In a mode of the electrooptical apparatus according to the first aspect of the invention in which the peripheral interconnections include the two-layer interconnection, the electrooptical apparatus further includes a first interlayer insulating film disposed between the light blocking film and the thin-film transistors; and a second interlayer insulating film disposed between the first conductive film and the second conductive film; wherein the two-layer interconnection includes a relay interconnection which is electrically connected to a part of the single-layer interconnection and which crosses another part of the single-layer interconnection in a three-dimensional fashion via the first or second interlayer insulating films. 
     In this mode, the relay interconnection is electrically connected to a part of the single-layer interconnection and crosses another part of the single-layer interconnection in a three-dimensional fashion via the first or second interlayer insulating film (that is, the relay interconnection passes over or under another part of the single-layer interconnection). That is, because peripheral interconnections must cross each other somewhere, it is impossible to dispose all peripheral interconnections at the same layer level. This problem is solved by employing a relay interconnection. That is, the relay interconnection makes it possible to dispose peripheral interconnections into any desired pattern. 
     In the mode of the electrooptical apparatus according to the first aspect of the invention in which the two-layer interconnection includes the relay interconnection, the peripheral interconnections may include an image signal line for supplying the image signal from an external input terminal; and the peripheral circuit may include a sampling circuit for sampling the image signal, a data line driving circuit for driving the sampling circuit with predetermined timing thereby supplying the image signal on the image signal line to the plurality of data lines via the sampling circuit, and a scanning line driving circuit for driving the scanning lines. 
     This allows the image signal line, which has to cross another peripheral interconnection somewhere and which could not be disposed in a desired manner if it were disposed at the same layer level, to be disposed in any desired pattern via a relay interconnection. 
     In the mode of the electrooptical apparatus according to the first aspect of the invention in which the peripheral interconnections include the image signal line, the image signal may be expanded to N phases (where N is an integer equal to or greater than 2) and there may be provided N image signal lines, and the N image signal lines may include a relay interconnection at a location where some of the N image signal lines cross to each other. 
     In this structure, increases in the resistance and time constant of the relay interconnection are minimized even when long relay interconnections are required to handle a large number (N) of expanded phases, or to handle a large number of image signals which are input in parallel as is the case with RGB color image signals, in particular compared with the case where relay interconnections are formed of a single layer of a thin polysilicon film according to the conventional technique. 
     In the mode of the electrooptical apparatus according to the first aspect of the invention in which the peripheral interconnections include the image signal line, the electrooptical apparatus may further include a plurality of sampling circuit driving signal lines that supply a sampling circuit driving signal from the data line driving circuit to the sampling circuit, and at least a part of the sampling circuit driving signal lines which crosses any of the image signal lines may be made of the relay interconnection. 
     This technique makes it possible to form sampling circuit driving signal lines extending from the data line driving circuit to the sampling circuit using relay interconnections disposed at locations where they cross for example an image signal line. Furthermore, this technique allows the interconnection layout to be designed in a more flexible manner. Still furthermore, increases in the resistance and time constant of the sampling circuit driving signal lines can be reduced compared with the case where relay interconnections of the sampling circuit driving signal lines are formed of a single layer of a thin polysilicon film according to the conventional technique. 
     In the mode of the electrooptical apparatus according to the first aspect of the invention in which the peripheral interconnections include the two-layer interconnection, the second conductive film and the light blocking film both constituting the two-layer interconnection may be electrically connected to each other via a contact hole formed in the first interlayer insulating film. 
     This technique makes it possible to obtain a high-reliability two-layer interconnection whose layers are electrically connected to each other via a contact hole. The contact hole for this purpose may be formed relatively easily using the process for producing the pixel TFTs. 
     In the mode of the electrooptical apparatus according to the first aspect of the invention in which the peripheral interconnections include the two-layer interconnection, the first conductive film may be made of a thin metal film forming the data lines connected to the source or drain of the thin-film transistors, and the second conductive film may be made of a thin polysilicon film forming the scanning lines including gate electrodes of the thin-film transistors. 
     In this case, because the single-layer interconnection is formed of the thin metal film, such as aluminum, the single-layer interconnection has a low resistance. Although the part formed of the thin polysilicon film has a resistance 200 times greater than that of the thin metal film, that part has a parallel path formed of the light blocking film with electrical conductivity, and thus the overall resistance of the two-layer interconnection is much smaller than the resistance of the thin polysilicon film. If the electrically-conductive light blocking film is made of metal, including at least one of Ti, Cr, W, Ta, Mo, or Pd or a metal silicide, the overall resistance and time constant can be reduced to several tenths (for example, about ½ or ⅓) of those that would be obtained with a single-layer of thin polysilicon film. 
     In the mode of the electrooptical apparatus according to the first aspect of the invention in which the peripheral interconnections include the two-layer interconnection, the electrooptical apparatus may further include a sealing material for enclosing the electrooptical material between the pair of substrates, and at least three films including the first conducive film, the second conductive film, and the light blocking film may be disposed in a multilayer fashion in a sealing area, in contact with the sealing material, on the one of substrate, around the periphery of the electrooptical material, and furthermore, the leading interconnections of the data lines and scanning lines extending across the sealing area may be formed of at least one of the above-described three films. 
     In this structure, the electrooptical material is enclosed by the sealing material between the pair of substrates such that a so-called electrooptical cell is formed. Because at least three films including the first conducive film, the second conductive film, and the light blocking film are disposed in a multilayer fashion in the sealing area around the periphery of the electrooptical material, it is possible to minimize the variation in the gap, including the effects of various thin films, between the two substrates over the entire sealing area around the electrooptical material. Thus, it becomes possible to more precisely control the gap of the liquid crystal cell when the gap is controlled by the sealing material containing gap materials with a particular diameter. Furthermore, by using the leading interconnections of the data lines and scanning lines, which are formed of at least one of the three films and which extend across the sealing area, it is possible to supply signals into the image displaying area without encountering any problems. 
     In the mode of the electrooptical apparatus according to the first aspect of the invention in which the three-layer film is disposed in the sealing area, the leading interconnections may each include a two-layer or three-layer interconnection whose layers are made of at least two of the three films, respectively, wherein the layers are electrically connected to each other via a contact hole. This structure allows a reduction in the resistance of the leading interconnections. 
     Alternatively, the leading interconnections may each include a single-layer interconnection made of one of the three films, and the other two films of the three films may be dummy interconnections which do not serve as an interconnection in the sealing region. In this structure, the gap in the sealing area between the two substrates is determined by the thickness of the dummy interconnections, and thus it is possible to relatively easily minimize the variation in the gap. 
     In the mode of the electrooptical apparatus according to the first aspect of the invention in which the peripheral interconnections include the two-layer interconnection, the two-layer interconnection may have such a structure that the part made of the light shielding film is covered with the part made of the second conductive film when viewed from the side of the other one of the pair of substrates. 
     In this mode, because the part, made of the light blocking film, of the two-layer interconnection is covered with the part made of the second conductive film, the single-layer interconnection such as an image signal line crossing the part made of the light blocking film has a less capacitive coupling with the part made of the light blocking film, and thus the increase in the time constant associated with the single-layer interconnection causes by the capacitive coupling can be suppressed. In particular, when the second conductive layer is disposed between the first conductive film and the light blocking film, it is possible to suppress the increase in the capacitive coupling between the first conductive film and the light blocking film in the structure in which the light blocking film is employed in the two-layer interconnection. This makes it possible to effectively prevent degradation in the image signal at the single-layer interconnection of the image signal line. 
     In the mode of the electrooptical apparatus according to the first aspect of the invention in which the part made of the light blocking film is covered with the part made of the second conductive film, in the two-layer interconnection, the part made of the light blocking film may have an interconnection width smaller than the part made of the second conducive film. 
     This technique ensures that the increase in the capacitive coupling between the first conductive film and the light blocking film is suppressed. 
     According to a second aspect of the present invention, to solve the above problems, there is provided an electrooptical apparatus including an electrooptical material disposed between a pair of substrates wherein, on one of the substrates, there are provided: a plurality of scanning lines; a plurality of data lines; thin-film transistors connected to the plurality of scanning lines, respectively, and also to the plurality of data lines, respectively; pixel electrodes connected to the respective thin-film transistors; an electrically-conductive light blocking film disposed such that at least the channel region of each thin-film transistor is covered with the light blocking film when viewed from the side of the one of substrates; a plurality of image signal lines that supply an image signal; and a sampling circuit that samples the image signals supplied via the plurality of image signal lines and supplies the resultant signals to the plurality of data lines, respectively; wherein at least a part of each of relay interconnections connecting the image signal lines to the sampling circuit is made of the light blocking film. 
     In the electrooptical apparatus according to the second aspect of the invention, because at least a part of each of relay interconnections connecting the image signal lines to the sampling circuit is made of the light blocking film, it is possible to obtain a lower resistance for the relay interconnections compared with the case where, of thin film layers forming the thin-film transistors, the data lines, and the scanning lines, the second conductive film having a lower conductivity than the first conductive film is selected as the material of the relay interconnections. If the light blocking film is formed of, for example, a refractory metal film having electrical conductivity, it is possible to greatly reduce the interconnection resistance of the relay interconnections. In this case, the light blocking film serves not only as a film that prevents the thin-film transistors from being exposed to light but also as a peripheral interconnection, and thus the construction and the production process can be simplified. 
     In this technique, because the image signals are input to the sampling circuit via the relay interconnections having low resistance, the driving frequency of the electrooptical apparatus can be increased, or the number of expanded phases, or the number of image signals which are input in parallel can be increased without causing voltage fluctuations, ghosts, or crosstalk due to capacitive coupling associated with the relay interconnections of, for example, image signal lines, which are problems in the conventional technique, thereby ensuring that a high-quality image is displayed. 
     In one mode of the electrooptical apparatus according to the second aspect of the invention, at least a part of sampling circuit driving signal lines that supply a sampling circuit driving signal to the sampling circuit is made of the light blocking film. 
     In this mode, because at least a part of sampling circuit driving signal lines is made of the light blocking film with electrical conductivity, it is possible to obtain a lower resistance for the sampling circuit driving signal lines compared with the case where, of thin film layers forming the thin-film transistors, the data lines, and the scanning lines, the second conductive film that has a lower conductivity than the first conductive film is selected as the material of the sampling circuit driving signal lines. Because the sampling circuit drive signals are input to the sampling circuit via sampling circuit driving signal lines having low resistance, it is possible to display a high-quality image. 
     To solve the problems described earlier, the invention provides a first method of producing an electrooptical apparatus including an electrooptical material disposed between a pair of substrates wherein, on one of the substrates, there are provided: a plurality of scanning lines; a plurality of data lines; thin-film transistors connected to the plurality of scanning lines, respectively, and also to the plurality of data lines, respectively; pixel electrodes connected to the respective thin-film transistors; an electrically-conductive light blocking film disposed such that at least the channel region of each thin-film transistor is covered with the light blocking film when viewed from the side of the one of substrates; a plurality of image signal lines that supply an image signal; and a sampling circuit that samples the image signals supplied via the plurality of image signal lines and supplies the resultant signals to the plurality of data lines, respectively; the method including the steps of: forming the light blocking film and first relay interconnections that connect the image signal lines to the sampling circuit using the same material; forming a first interlayer insulating film on the first relay interconnections and the light blocking film; forming the scanning lines on the first interlayer insulating film and also forming a second relay interconnection connected to the first relay interconnection via a contact hole formed in the first interlayer insulating film; forming a second interlayer insulating film on the scanning lines and the second relay interconnection; and forming the data lines connected to the thin-film transistors via contact holes formed in the second interlayer insulating film and also forming the image signal lines connected to the second relay interconnection. 
     In the first method of producing the electrooptical apparatus according to the invention, the light blocking film and the first relay interconnections that connect the image signal lines to the sampling circuit are formed using the same material. This allows simplification in the production process. Then the first interlayer insulating film is formed on the first relay interconnections and the light blocking film, and scanning lines are formed on this first interlayer insulating film. The second relay interconnection is then formed such that it is connected to the first relay interconnection via a contact hole formed in the first interlayer insulating film. The second interlayer insulating film is then formed on the scanning lines and the second relay interconnection. After that, the data lines connected to the thin-film transistors via contact holes formed in the second interlayer insulating film and also the image signal lines connected to the second relay interconnections are formed. Thus, in this technique, because the image signals are input to the sampling circuit via the relay interconnections that have low resistance, it is possible to produce an electrooptical apparatus capable of displaying a high-quality image, even if the driving frequency of the electrooptical apparatus is increased, or the number of expanded phases, or the number of image signals which are input in parallel is increased. 
     To solve the problems described earlier, the invention also provides a second method of producing an electrooptical apparatus including an electrooptical material disposed between a pair of substrates wherein, on one of the substrates, there are provided: a plurality of scanning lines; a plurality of data lines; thin-film transistors connected to the plurality of scanning lines, respectively, and also to the plurality of data lines, respectively; pixel electrodes connected to the respective thin-film transistors; an electrically-conductive light blocking film disposed such that at least the channel region of each thin-film transistor is covered with the light blocking film when viewed from the side of the one of substrates; a plurality of image signal lines that supply an image signal; and a sampling circuit that samples the image signals supplied via the plurality of image signal lines and supplies the resultant signals to the plurality of data lines, respectively; the method including the steps of: forming the light blocking film and first relay interconnections that connect the image signal lines to the sampling circuit using the same material; forming a first interlayer insulating film on the first relay interconnections and the light blocking film; successively forming a plurality of films into a multilayer structure on the first interlayer insulating film, the plurality of films including a semiconductor layer acting as a source and drain of each thin-film transistor, a gate insulating film, and a gate electrode; forming a second interlayer insulating film on the gate electrode; and forming the data lines connected to the thin-film transistors via contact holes formed in the second interlayer insulating film and also forming image signal lines connected to the first relay interconnections via contact holes formed in the first and second interlayer insulating films. 
     In the second method of producing the electrooptical apparatus according to the invention, the light blocking film and the first relay interconnections for connecting the image signal lines to the sampling circuit are formed using the same material. This allows simplification in the production process. After that, the first interlayer insulating film is formed on the first relay interconnections and the light blocking film. Furthermore, the semiconductor layer acting as a source and drain of each said thin-film transistor, the gate insulating film, and the gate electrode are successively formed into the multilayer structure on the first interlayer insulating film. The second interlayer insulating film is then formed on the gate electrode. Furthermore, the data lines connected to the thin-film transistors via contact holes formed in the second interlayer insulating film are formed. After that, the image signal lines connected to the first relay interconnection via contact holes formed in the first and second interlayer insulating films are formed. Thus, in this technique, because the image signals are input via the relay interconnections that have low resistance, it is possible to produce an electrooptical apparatus capable of displaying a high-quality image, even if the driving frequency of the electrooptical apparatus is increased, or the number of expanded phases, or the number of image signals which are input in parallel is increased. 
     These and other features and advantages of the present invention will become more apparent from the following detailed description referring to the following drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic of a liquid crystal apparatus, including equivalent circuits of interconnections of various elements provided in respective pixels arranged in a matrix fashion in an image display area and peripheral circuits, according to an embodiment of the invention. 
     FIG. 2 is a plan view illustrating a plurality of adjacent pixels including data lines, scanning lines, and pixel electrodes formed on a TFT array substrate of the liquid crystal apparatus according to the embodiment of the invention. 
     FIG. 3 is a cross-sectional view taken along plane A-A′ of FIG.  2 . 
     FIG. 4 is a fragmentary plan view of a TFT array substrate on which peripheral interconnections are formed. 
     FIG. 5 is an enlarged plan view illustrating in an enlarged fashion the relay interconnections and the leading interconnections shown in FIG.  4 . 
     FIG. 6 is a cross-sectional view taken along plane B-B′ of FIGS. 4 and 5. 
     FIG. 7 is a cross-sectional view taken along plane C-C′ of FIGS. 4 and 5. 
     FIG. 8 is a cross-sectional view illustrating an alternative structure in cross-section taken along plane B-B′ of FIGS. 4 and 5. 
     FIG. 9 is a cross-sectional view illustrating an alternative structure in cross-section taken along plane C-C′ of FIGS. 4 and 5. 
     FIG. 10 is a cross-sectional view illustrating various embodiments of relay interconnections of a sampling circuit driving signal line, taken along plane D-D′ of FIG.  5 . 
     FIG. 11 is a cross-sectional view illustrating processing steps of producing a liquid crystal apparatus according to an embodiment of the invention, wherein a cross-section corresponding to that shown in FIG. 6 is shown for various processing steps. 
     FIG. 12 is a cross-sectional view illustrating processing steps of producing a liquid crystal apparatus according to an embodiment of the invention, wherein the cross-section corresponding to that shown in FIG. 6 is shown for various processing steps. 
     FIG. 13 is a cross-sectional view illustrating processing steps of producing a liquid crystal apparatus according to an embodiment of the invention, wherein a cross-section corresponding to that shown in FIG. 3 is shown for various processing steps. 
     FIG. 14 is a cross-sectional view illustrating processing steps of producing a liquid crystal apparatus according to an embodiment of the invention, wherein the cross-section corresponding to that shown in FIG. 3 is shown for various processing steps. 
     FIG. 15 is a plan view as viewed from the side of an opposite substrate, showing various elements formed on the TFT array substrate of the liquid crystal apparatus according to the embodiment of the invention. 
     FIG. 16 is a cross-sectional view taken along plane H-H′ of FIG.  15 . 
     FIG. 17 is a block diagram illustrating a general structure of an electronic device according to an embodiment of the invention. 
     FIG. 18 is a cross-sectional view illustrating a liquid crystal projector which is an example of an electronic device. 
     FIG. 19 is a front view illustrating a personal computer which is another example of an electronic device. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Description of the Embodiments 
     Referring to the drawings, embodiments of the invention are described below. In the embodiments described below, a liquid crystal apparatus is taken as an example of an electrooptical apparatus according to the invention. 
     Construction and Operation of Liquid Crystal Apparatus 
     Referring to FIGS. 1 to  10 , the construction and the operation of a liquid crystal apparatus according to an embodiment of the invention are described below. 
     First, the circuit configuration of the liquid crystal apparatus is described with reference to the schematic shown in FIG.  1 . 
     FIG. 1 illustrates an equivalent circuit of interconnections and various other elements in a plurality of pixels formed in an array fashion in an image displaying area on an TFT array substrate of the liquid crystal apparatus, and also illustrates peripheral circuits disposed in a peripheral area outside the image displaying area. 
     In the present embodiment, as shown in FIG. 1, a plurality of pixels are arranged in a matrix fashion in the image displaying area of the liquid crystal apparatus, and a plurality of TFTs  30  that control the respective pixel electrodes  9   a  are arranged in a matrix fashion. The source of each TFT  30  is electrically connected to a data line  6   a  through which an image signal is supplied. Although image signals may be supplied to data lines  6   a  in a line-sequential fashion in the order S 1 , S 2 , . . . , Sn, the image signals S 1 , S 2 , . . . , Sn, in the present embodiment, are expanded into N phases (where N is an integer equal to or greater than 2) and image signals with the expanded phases are supplied via the N image signal lines  115  to N adjacent data lines  6   a  from one group to another, each including N data lines  6   a.    
     The gate of each TFT  30  is electrically connected to a scanning line  3   a . Scanning signals are applied to the scanning lines  3   a  with predetermined timing in a line-sequential fashion in the order G 1 , G 2 , . . . , Gm. Each pixel electrode  9   a  is electrically connected to the drain of a corresponding TFT  30 . By closing TFTs  30  serving as switching elements for a particular period of time, image signals S 1 , S 2 , . . . , Sn supplied via the data lines  6   a  are written with predetermined timing. The image signals at particular levels written via the pixel electrodes  9   a  into the liquid crystal serving as an electrooptical material are held for a fixed period of time between the pixel electrodes  9   a  and an opposite electrode (which will be described later) formed on an opposite substrate (which will be described later). The liquid crystal changes in the orientation or order of molecules depending on the applied voltage level. Light is modulated as a result of the change in the orientation of the liquid crystal, and thus an image with various intensity levels is displayed. In a normally white mode, an incident light ray is blocked by the liquid crystal to a degree determined by the applied voltage. On other hand, in a normally black mode, the incident light ray is allowed to pass through the liquid crystal to a degree determined by the applied voltage. The liquid crystal apparatus as a whole emits light forming an image with a contrast corresponding to the image signal. To prevent leakage of the image signal held, there is provided a storage capacitor  70  added in parallel to a liquid crystal capacitance formed between each pixel electrode  9   a  and the opposite electrode. For example, the voltage of the pixel electrode  9   a  is held by the storage capacitor  70  for a period of time which is 3 orders of magnitude longer than the period of time during which the source voltage is applied. This allows a further improvement in the holding characteristic, and it becomes possible to realize a liquid crystal apparatus having a high contrast ratio. The storage capacitor  70  may be formed by forming a capacitance line  3   b  with a capacitance component, or by forming capacitance with the scanning line  3   a  at the previous stage. 
     In FIG. 1, the liquid crystal apparatus includes peripheral circuits such as a data line driving circuit  101  that drives the data lines  6   a , a scanning line driving circuit  104  that drives the scanning lines  3   a , and a sampling circuit  103  that samples the image signal, which are disposed in an peripheral area outside the image displaying area on the TFT array substrate, wherein the data lines  6   a  and scanning lines  3   a  are formed in the image displaying area as described above. In the peripheral area outside the image displaying area, there are provided N image signal lines  115 , which are examples of peripheral interconnections, that supply image signals S 1 , S 2 , . . . , Sn with expanded N phases input via the external input terminals. 
     N-phase image signals S 1 , S 2 , . . . , Sn are supplied to the image signal lines  115  from a control circuit (not shown) via external input terminals. The number (N) of expanded phases may be set to a rather small value such as 3 or 6 when the sampling ability of the sampling circuit  103  is relatively high. If the sampling ability is relatively low, the number of phases is preferably set to 12 or 24. 
     In particular, in the present embodiment, because the resistance of the relay interconnections (which extend from image signal lines  115  and which pass under other image signal lines  115  located nearer to the image displaying area), whose length become longer depending on the number (N) of expanded phases or the number (N) of image signal lines  115 , is reduced by employing the two-layer interconnection structure, it is possible to increase the number (N) of expanded phases (the number of image signal lines  115 ) without causing a significant increase in the resistance or the time constant of the interconnections for transmitting the image signals. Thus, it is possible to increase the driving frequency of the liquid crystal apparatus without causing degradation in the image quality. Because the color image signal contains information of three colors (red, blue, yellow), if the number (N) of expanded phases is set to an integral multiple of 3, it becomes possible to simplify the controlling process and circuits required to display a video signal according to the NTSC or PAL standard. 
     When the image signal is not expanded into phases, if there are provided a plurality of image signal lines, for example, to handle RGB color image signals, the structure including low-resistance relay interconnections according to the present embodiment, which will be described below, is still useful. 
     In the present embodiment, the resistance of the sampling circuit driving signal lines  114  extending from the data line driving circuit  101  to the sampling circuit  103  is also reduced by employing the two-layer interconnection structure, as will be described in detail later. 
     In response to the gate voltage in the form of a series of pulses transmitted to the scanning lines  3   a  from the scanning line driving circuit  104 , the data line driving circuit  101  supplies sampling circuit driving signals via the sampling circuit driving signal lines  114  to the control terminals of the respective sampling switches  103   a  in the sampling circuit  103 . In response to the sampling circuit driving signals, the sampling circuit  103  samples the image signals on the image signal lines  115 , and supplies the resulting signals to the data lines  6   a.    
     To achieve a high production efficiency, it is preferable that the respective sampling switches  103   a  in the sampling circuit  103  be produced into the form of n-channel type, p-channel type, or complementary type TFTs, which can be produced in the same production process for the TFTs  30  used in pixels. 
     Referring now to FIGS. 2 and 3, the construction of pixels in the image displaying area of the liquid crystal apparatus is described below. FIG. 2 is a plan view illustrating a plurality of adjacent pixels formed on the TFT array substrate, wherein data lines, scanning lines, pixel electrodes, and a light blocking film are shown in the figure. FIG. 3 is a cross-sectional view taken along plane A-A′ of FIG.  2 . In FIG. 3, the layers and other elements are shown such that they have a large enough size in the figure in order to provide a visible representation, and thus they are not drawn to scale. 
     On the TFT array substrate of the liquid crystal apparatus, as shown in FIG. 2, a plurality of transparent pixel electrodes  9   a  (contours thereof are denoted by broken lines  9   a ′) are formed in a matrix fashion and data lines  6   a , scanning lines  3   a , and capacitance lines  3   b  are formed in such a manner that the data lines  6   a  extend along the vertical boundaries of the pixel electrodes  9   a  and the scanning lines  3   a , and the capacitance lines  3   b  extend along the horizontal boundaries. The data lines  6   a  are electrically connected via contact holes  5  to corresponding source regions, which will be described later, of a semiconductor layer  1   a  made of a polysilicon film or the like. The pixel electrodes  9   a  are electrically connected via contact holes  8  to corresponding drain regions, which will be described later, of the semiconductor layer  1   a . The data line  6   a  is disposed at a location corresponding to the channel region, which will be described layer, of the semiconductor layer  1   a . First light blocking films  11   a  are formed in areas, hatched with lines slanted to right in FIG. 2, in the respective pixels. That is, the first light blocking films  11   a  are formed at locations so that TFTs including channel regions of the semiconductor layer  1   a  are covered with the corresponding first light blocking films  11   a  when viewed from the side of the TFT array substrate. For the purpose of preventing the pixel TFTs from having leakage due to a photocurrent, the first light blocking films  11   a  are required to cover only the channel regions of the semiconductor layer  1   a . However, in the present embodiment, the first light blocking films  11   a  are provided in the form of stripes extending along the scanning lines  3   a  so that the first light blocking films  11   a  also serve as interconnections for maintaining the first light blocking films  11   a  themselves at a constant voltage, and so that the first light blocking films  11   a  also serve to define opening areas (through which light is allowed to pass) in the pixels. 
     As shown in FIG. 3, the liquid crystal apparatus includes a TFT array substrate  10  serving as an example of a transparent substrate which is one of two substrates, and also includes an opposite substrate  20  serving as an example of the other transparent substrate disposed at a location opposing the TFT array substrate  10 . The TFT array substrate  10  is made of, for example, a quartz substrate, and the opposite substrate  20  is made of, for example, a glass substrate or a quartz substrate. Pixel electrodes  9   a  are formed on the TFT array substrate  10 , and an orientation film  16  subjected to an orientation process, such as a rubbing process, is further formed thereon. The pixel electrodes  9   a  are made of transparent conducting thin films, such as ITO (indium tin oxide) films. The orientation film  16  is made of an organic thin film, such as a polyimide thin film. 
     An opposite electrode (common electrode)  21  is formed over an entire surface of the opposite substrate  20 . Under the opposite electrode  21 , there is provided an orientation film  22  subjected to an orientation process, such as a rubbing process. The opposite electrode  21  is made of a transparent conducting thin film, such as an ITO film. The orientation film  22  is made of an organic thin film, such as a polyimide thin film. 
     Furthermore, as shown in FIG. 3, pixel switching TFTs  30  that switch the pixel electrodes  9   a  are disposed on the TFT array substrate  10 , at locations adjacent to the respective pixel electrodes. 
     On the opposite substrate  20 , as shown in FIG. 3, there is also provided a second light blocking film  23  in an area other than the opening areas of the respective pixels. The second light blocking film  23  prevents the incident light coming from the side of the opposite substrate  20  from striking the channel region  1   a′  or the LDD (lightly doped drain) regions  1   b  and  1   c  of the semiconductor layer  1   a  of the TFTs  30  serving as pixel switching elements. The second light blocking film  23  also serves to improve the contrast and prevent the colors of coloring materials from mixing. 
     A liquid crystal is placed into a space surrounded by a sealing material  52  (refer to FIGS. 4 and 5 and also FIGS.  15  and  16 ), which will be described layer, and formed between the TFT array substrate  10  and the opposite substrate  20 , which are disposed so that the pixel electrodes  9   a  and the opposite electrode  21  face each other, thereby forming a liquid crystal layer  50 . When no electric field is applied from the pixel electrode  9   a  to the liquid crystal layer  50 , the liquid crystal layer  50  is oriented in a particular direction determined by the orientation films  16  and  22  (refer to FIG.  3 ). The liquid crystal layer  50  is made of one type of nematic liquid crystal, or a mixture of two or more types of nematic liquid crystals. The sealing material  52  is an adhesive such as a photo-curing resin or a thermal curing resin by which the two substrates  10  and  20  are bonded to each other along their peripheries. The sealing material  52  contains a spacer made of glass fibers or glass beads, whereby the two substrates are spaced from each other by a predetermined distance. 
     As shown in FIG. 3, first light blocking films  11   a  are formed between the TFT array substrate  10  and the respective pixel switching TFTs  30 , at locations corresponding to the respective pixel switching TFTs  30 . Preferably, the first light blocking films  11   a  are made of element metal, an alloy, or a metal silicide, including at least one opaque and refractory metal selected from the group consisting of Ti, Cr, W, Ta, Mo, and Pd. If such a material is employed, the first light blocking films  11   a  are not broken or melted by a high temperature treatment in the process of forming the pixel switching TFTs  30  performed after the process of forming the first light blocking films  11   a  on the TFT array substrate  10 . The presence of the first light blocking films  11   a  prevents a light ray reflected by the TFT array substrate  10  from being incident on the channel regions  1   a′  or LDD regions  1   b  and  1   c  of the pixel switching TFTs  30 , thereby preventing the pixel switching TFTs  30  from having degradation due to a photocurrent. 
     Furthermore, the first interlayer insulating film  12  is disposed between the first light blocking films  11   a  and the plurality of pixel switching TFTs  30 . The first interlayer insulating film  12  serves to electrically isolate the semiconductor layer  1   a  of the respective pixel switching TFTs  30  from the first light blocking films  11   a . The first interlayer insulating film  12  is formed over the entire surface of the TFT array substrate  10 , so that the first interlayer insulating film  12  also serves as an underlying film of the pixel switching TFTs  30 . That is, the first interlayer insulating film  12  serves to prevent the surface of the TFT array substrate  10  from being damaged during the lapping process, and also prevents the pixel switching TFTs  30  from being degraded in characteristics by contamination remaining after the cleaning process. 
     The first interlayer insulating film  12  is made of, for example, high resistivity glass, such as NSG (non-doped silicate glass), PSG (phosphosilicate glass), BAG (boronsilicate glass), or BPSG (boron phosphosilicate glass), or a silicon oxide or film or a silicon nitride film. The first interlayer insulating film  12  also prevents the first light blocking film  11   a  from contaminating the pixel switching TFTs  30  and other elements. 
     In the present embodiment, the storage capacitors  70  are formed as follows. That is, the gate insulating films  2 , between the scanning line (gate electrode)  3   a  and the semiconductor layer  1   a , are extended from the locations under the scanning line (gate electrode)  3   a , so that the extended portions are used as the dielectric films of the respective storage capacitors  70 , the semiconductor layers  1   a  are extended and used as the first storage capacitor electrodes If, and parts of the capacitance lines  3   b  at corresponding locations are used as the second storage capacitor electrodes. More specifically, the heavily doped drain region  1   e  of each semiconductor layer  1   a  is extended into an area under the corresponding data line  6   a  and the scanning line  3   a , and also extended into an area under the capacitance line  3   b  extending along the data line  6   a  and the scanning line  3   a , so that the extended portion of the semiconductor layer acts as the first storage capacitor electrode  1   f  which opposes the data line  6   a , the scanning line  3   a , and the capacitance line  3   b  via the insulating film  2 . In this technique, the dielectric film  2  serving as the dielectric of the storage capacitor  70  is realized using the gate insulating film  2 , itself formed on the polysilicon film by means of high-temperature oxidation, and thus it is possible to achieve a thin insulating film with a high breakdown voltage. Therefore, it is possible to achieve a storage capacitor  70  having a high capacitance using a rather small area. 
     In FIG. 3, each pixel switching TFT  30  has an LDD (lightly doped drain) structure that includes a scanning line  3   a  (gate electrode), a channel region  1   a′  in the semiconductor layer  1   a  where a channel is formed by an electric field from the scanning line  3   a , a gate insulating film  2  isolating the semiconductor layer  1   a  from the scanning line  3   a , data line  6   a  (source electrode), a lightly doped source region (an LDD region on the source side)  1   b  in the semiconductor layer  1   a , a lightly doped drain region (an LDD region on the drain side)  1   c  in the semiconductor layer  1   a , a heavily doped source region  1   d  in the semiconductor layer  1   a , and a heavily doped drain region  1   e  in the semiconductor layer  1   a . The heavily doped drain region  1   e  is connected to a corresponding one of the plurality of pixel electrodes  9   a . The source regions  1   b  and  1   d  and the drain regions  1   c  and  1   e  are formed, as will be described in further detail later, by doping an n-type or p-type dopant into the semiconductor layer  1   a  to a proper concentration, wherein the type of the dopant is selected depending on whether an n-type or p-type channel is formed. The n-channel TFT has the advantage that it can operate at a high speed, and thus n-channel TFTs are usually employed as the pixel switching TFTs  30 . In the present embodiment, the data line  6   a  is preferably made of an opaque thin film, such as a thin aluminum film or similar metal film, or otherwise an alloy film, such as a metal silicide film. The second interlayer insulating film  4  is formed over the scanning line  3   a , the gate insulating film  2 , and the first interlayer insulating film  12 , wherein contact holes  5  reaching the respective heavily doped source regions  1   d  and contact holes  8  reaching the respective heavily doped drain regions are formed in the second interlayer insulating film  4 . The data lines  6   a  are electrically connected to the corresponding heavily doped source regions  1   d  via the respective source contact holes  5 . Furthermore, the third interlayer insulating film  7  is formed over the data lines  6   a  and the second interlayer insulating film  4 , wherein contact holes  8  for the heavily doped drain regions  1   e  are formed in the third interlayer insulating film  7 . The pixel electrodes  9   a  are electrically connected to the corresponding heavily doped regions  1   e  via the contact holes  8  for the heavily doped drain regions  1   e . The pixel electrodes  9   a  described above are formed on the upper surface of the third interlayer insulating film  7  formed in the above-described manner. 
     As described above, each pixel switching TFT  30  is preferably formed into the LDD structure. However, the pixel switching TFTs  30  may also formed into an offset structure in which no impurity ions are implanted into the lightly doped source region  1   b  and the lightly doped drain region  1   c . Alternatively, the pixel switching TFTs  30  may be formed into a self-aligned structure which may be obtained by implanting high-concentration impurity ions using the gate electrode  3   a  as a mask, thereby forming heavily doped source and drain regions in a self-aligned manner. 
     Although in the present embodiment, each pixel switching TFT  30  has a single-gate structure in which only a single gate electrode (scanning line  3   a ) is disposed between the source region  1   d  and the drain region  1   e , two or more gate electrodes may be disposed between the source and drain regions. In this case, the same signal is applied to those two or more gates electrodes. In the case where the dual gate (double gate) structure or the triple gate structure is employed, the resultant TFT has a less leakage current at junctions between the channel and the source and drain regions, and thus the current in the off-state can be reduced. If at least one gate electrode of these is formed to have the LDD or offset structure, the current in the off-state is further reduced, and thus it is possible to realize high-performance and high-reliability switching elements. 
     In general, if the semiconductor layer  1   a  made of the polysilicon layer including the channel region  1   a′ , the lightly doped source region  1   b , and the lightly doped drain region  1   c  is illuminated with light, a photocurrent is generated due to the photoelectric conversion effect of the polysilicon film. Such a photocurrent results in degradation in the transistor characteristics of the TFT  30 . In the present embodiment, because the data line  6   a  is formed of an opaque thin metal film such as Al so that the scanning line  3   a  is covered with the data line  6   a , at least the channel region  1   a′  and the LDD regions  1   b  and  1   c  of the semiconductor layer  1   a  are effectively prevented from being exposed to incident light. Furthermore, as described above, the first light blocking film  11   a  is disposed under each pixel switching TFT  30  so that at least the channel region  1   a′  and the LDD regions  1   b  and  1   c  of the semiconductor layer  1   a  are effectively prevented from being exposed to reflected light. 
     Furthermore, in the present embodiment, the light blocking film  11   a  is electrically connected to a constant voltage source so that the first light blocking film  11   a  is maintained at a constant voltage. Therefore, the voltage variation of the first light blocking film  11   a  does not exert an adverse effect on the pixel switching TFTs  30  disposed at locations corresponding to the first light blocking film  11   a . As for the constant voltage source for the above purpose, various voltage sources are available. They include a negative power supply that supplies a voltage to peripheral circuits (such as a scanning line driving circuit, data line driving circuit, sampling circuit) to drive the liquid crystal apparatus, a constant voltage source such as a positive power supply, a ground voltage source, and a constant voltage source that supplies a voltage to the opposite electrode  21 . In this specific embodiment, the first light blocking film  11   a  is connected to the negative power supply of the scanning line driving circuit. By employing a power supply in the peripheral circuits, it becomes possible to maintain the first light blocking film  11   a  at a constant voltage without having to provide an additional dedicated voltage interconnection or an external input terminal. If the first interlayer insulating film  12  has a large enough thickness, the first light blocking film may be produced into the form of a plurality of islands corresponding to the respective pixels and they may be electrically floated. 
     Referring now to FIGS. 4 to  7 , input/output interconnections and peripheral interconnections in the peripheral circuits of the liquid crystal apparatus are described below. 
     FIG. 4 is a fragmentary plan view of a TFT array substrate on which peripheral interconnections are formed. FIG. 5 is an enlarged plan view illustrating in an enlarged fashion the relay interconnections and the leading interconnections shown in FIG.  4 . FIG. 6 is a cross-sectional view taken along plane B-B′ of FIGS. 4 and 5. FIG. 7 is a cross-sectional view taken along plane C-C′ of FIGS. 4 and 5. 
     In FIG. 4, scanning line driving signal lines  105   a  extend to the scanning line driving circuit  104  from the external connection terminals  102  provided in the peripheral area of the TFT array substrate  10 . A plurality of image signal lines  115  are disposed along the scanning lines in an area between the data line driving circuit  101  and the sealing area where the sealing material  52  is disposed. 
     As shown in FIGS. 4 and 5, the sampling circuit  103  is disposed in the area inside the sealing area and under the third light blocking film  53  (denoted by the hatching lines slanted to right in the figures) which is disposed on the opposite substrate  20 , so as to serve as a partition for defining the boundary between the image displaying area and the outer area. In a part of the sealing area where extensions of the data lines  6   a  extend, there are provided leading interconnections  301  including leading interconnections  301   a  of the sampling circuit driving signal lines  114  extending from the data line driving circuit  101 , and also including leading interconnections  301   b  of the image signal lines  115 . On the other hand, in a part of the sealing area where extensions of the scanning lines  3   a  extend, there are provided leading interconnections  402  of the scanning lines extending from the scanning line driving circuit  104 . The leading interconnections  402  include an opposite electrode (common electrode) voltage line  112  disposed at an end of the leading interconnections  402 . The opposite electrode (common electrode) voltage line  112  is connected to the opposite common electrode  21  (refer to FIG. 3) formed on the opposite substrate  20  via the layer-to-layer conducting terminal  106   a  and the layer-to-layer conducting element  106 . Alternatively, the opposite electrode (common electrode) voltage line  112  maybe disposed at a location adjacent to a test terminal  111  through which a predetermined test signal is input to the data line driving circuit  101  and adjacent to the data line driving circuit  101 . 
     As shown in a cross-sectional view in FIG. 6 taken along plane B-B′ of FIG. 5, image signal lines  115 , which are examples of peripheral interconnections, are formed into a single layer structure using a single metal film (first conductive film) such as an Al film, which is produced in the same process for producing the data lines  6   a . The relay interconnections  116 , which are another example of peripheral interconnection, and which extend from the image signal lines  115  to the leading interconnections  301   b , are formed in the two-layer structure when viewed in the thickness direction of the TFT array substrate, wherein one layer is realized with the second conductive film  116   a , which is made of the same film as the polysilicon film used to form the scanning line  3   a , and which is electrically connected via the contact hole  305  to the corresponding image signal line  115 , and the other layer is realized with the third conductive film  116   b , which is made of the same film as the first light blocking film, and which is electrically connected via the contact hole  305  to the corresponding relay interconnection  115 . In order to further reduce the resistance of the leading interconnections  301   b , the leading interconnections  301   b  may be coupled with the first conductive film  116   b  and the third conductive film  116   a.    
     In this structure, the resistance of the relay interconnections  116  is reduced by the existence of the first light blocking film with electrical conductivity compared with the conventional relay interconnection formed of a single layer of polysilicon. More specifically, because the first light blocking film is formed of a refractory metal film with electrical conductivity including Ti, Cr, W, Ta, Mo, or Pd, the overall resistance of the relay interconnections, measured along the interconnections, is dominated by the sheet resistance of the first light blocking film. In the case of the polysilicon film, when the thickness is, for example 3000 A, the sheet resistance is about 25 Ω/□. If such a polysilicon film is used in a small liquid crystal apparatus with a width across corner of 1.3 or 0.9 inches, the interconnection has a resistance of 100 KΩ to 200 KΩ, and thus the interconnection has a time constant of about a few ten μsec. If the sheet resistance is reduced using the first light blocking film, it is possible to reduce the time constant of the interconnection to a few μsec. As a result, voltage fluctuations, crosstalk, ghosts on the image signal lines  115  and the relay interconnections  116  are reduced by the capacitive coupling between the image signal lines  115  and the relay interconnections  116  passing under the image signal lines  115 . When the liquid crystal apparatus is constructed into the type of XGA, SXGA, or EWS which requires a high driving frequency, the number (N) of expanded phases or the number (N) of image signal lines can be increased without causing a significant increase in the voltage fluctuation, crosstalk, and ghosts, because the overall time constant of the image signal lines  115  including the relay interconnections  116  is small enough. 
     Furthermore, as shown in FIG. 6, the relay interconnections  116  have a redundant structure in which, even if either the second conductive film  116   a  or the third conductive film  116   b  is broken due a foreign particle or for another reason, the electrical conduction is still maintained via the other film. Furthermore, even if the second conductive film  116   a  and the third conductive film  116   b  are short-circuited with each other via a path formed through the first interlayer insulating film  12 , such a path does not result in a fatal failure. Thus, according to the present embodiment, it is possible to realize a high-reliability liquid crystal apparatus capable of displaying a high-quality image, which can be produced with high production yield. Since the relay interconnections  116  are formed using the first conductive film, which is also used to form pixel TFTs, the relay interconnections according to the present invention can be produced without causing a significant reduction in the production efficiency of the production process, which will be described later. 
     The sampling circuit driving signal lines  114  shown in FIGS. 4 and 5 have a two-layer structure, similar to that of the relay interconnections  116  shown in FIG. 6, which extend under the image signal lines  115  in a direction crossing the image signal lines  115 . By employing such a structure, it is possible to suppress the increases in the resistance and the time constant of the sampling circuit driving signal lines  114  compared with those formed of a single layer of polysilicon according to the conventional technique, and thus the sampling circuit driving signal lines  114  with such a structure can be used in a high-frequency driving operation. 
     Furthermore, as shown in FIGS. 6 and 7, the leading interconnections  301   b  of the data lines  6   a  under the sealing area are formed into a three-layer structure in which the second conductive film  116   a ′ and the third conductive film  116   b ′ serve as redundant interconnections. This structure allows the interconnection to have an extremely low resistance. Furthermore, as shown in FIG. 5, three layers are electrically connected to one another via contact holes  305  at a plurality of locations under the sealing area thereby achieving high-degree redundancy. Thus the leading interconnections  301   b  have extremely high reliability. Alternatively, an extension of either one of the second conductive film  116   a  or the third conductive film  116   b  may be employed as a redundant interconnection so as to obtain a two-layer interconnection structure, which can provide similar effects and advantages. The leading interconnections  301   a  of the sampling circuit driving signal lines  114  may also be formed into a similar two- or three-layer interconnection structure. 
     On the other hand, as shown in FIG. 4, the leading interconnections  402  of the scanning lines extend along the scanning lines and adjacent leading interconnections are spaced from each other. The leading interconnections  402  are made of the same polysilicon film as that used to form the scanning lines  3   a . Dummy interconnections made of the same Al film as that of the data lines  6   a  are provided above the respective leading interconnections  402 . Although the resistance of the leading interconnections  402  of the scanning lines  3   a  is not important in many cases, the leading interconnections  402  of the scanning lines  3   a  may also be formed into a two-layer or three-layer interconnection structure similar to that of the leading interconnections  301  of the data lines  6   a.    
     In the sealing area, as described above, there are great number of interconnections with the multilayer structure along the periphery around the liquid crystal layer  50 , wherein the multilayer structure includes various layers disposed one on another in the thickness direction of the TFT array substrate  10 , such as the first light blocking film, the polysilicon film, the Al film, the first interlayer insulating film  12 , the second interlayer insulating film  4 , and the third interlayer insulating film  7 . In this structure, the height of the surface of the third interlayer insulating film  7  on the upper and lower sides of the image displaying area in the sealing area is coincident with the height of the surface of the third interlayer insulating film  7  on the left and right sides of the image displaying area. This allows a reduction in the variation in the gap, including the effects of various thin films, between the two substrates over the entire sealing area. Thus, it becomes possible to more precisely control the gap of the liquid crystal cell when the gap is controlled by the sealing material containing gap materials with a particular diameter. In particular, in this structure, even if some leading interconnection  301  or  402  is broken by the stress in the gap materials in the sealing area, even if the conducting film of Al and the polysilicon film are short-circuited with each other via a path formed through the second interlayer insulating film  4 , such a breakage or a short-circuiting path does not result in a fatal interconnection failure. 
     In the case where the precise gap control is important (when the resistance of the leading interconnections  301  is sufficiently low for the operation at a required driving frequency), the second conductive film  116   a ′ and the third conductive film  116   b ′ are not electrically connected to the leading interconnections  301   b  as opposed to FIG. 6, but the second conductive film  116   a ′ and the third conductive film  116   b ′ may be used as dummy interconnections dedicated to the purpose for achieving uniform thickness. 
     In the present embodiment, as shown in FIG. 5, the leading interconnections  301  are disposed in the form of stripes in a plane in the sealing area and gaps S are formed between adjacent interconnections so that light is allowed to pass through these gaps. Therefore, when a photo-curing resin is employed as the sealing material  52  in the production process of the liquid crystal apparatus, which will be described later, if the TFT array substrate  10  is exposed to light, the sealing material  52  is well illuminated with light via the light transmission gaps formed in the multilayer structure. Thus, the photo-curing resin serving as the sealing material  52  is well photo-cured with light coming through both substrates. When the photo-curing process is employed, unlike the thermal curing process, the liquid crystal apparatus is not subjected to a high temperature. This prevents various elements of the liquid crystal apparatus from being degraded by heat and from having defects due to thermal strain. Furthermore, because light illumination time is short enough, the orientation films  16  and  22  (refer to FIG. 3) are not damaged. As a result, a large tilt angle of the liquid crystal is maintained and degradation in the image quality due to orientation defects (disclination) of the liquid crystal does not occur. 
     In FIGS. 4 and 5, dummy pixels, having the same structure as that of the pixels formed in the image displaying area, are formed under the third light blocking film  53  serving as a peripheral partition film. Although pixels used to display an image are not required under the third light blocking film  53  serving to hide orientation failures of the liquid crystal, dummy pixels are disposed in an area with a particular width outside the image displaying area so that the characteristics of the pixels near the edge of the image displaying area are stabilized. 
     Furthermore, in the present embodiment, the relay interconnections  116  are preferably formed into such a structure that the second conductive film  116   a  made of the light blocking film is covered with the third conductive film  116   b  made of the polysilicon film when viewed from the opposite substrate side. More specifically, for example in FIG. 7, the interconnection width W1 of the second conductive film  116   a ′ is preferably set to a value equal to or greater than the interconnection width W2 of the third conductive film  116   b ′, that is, W1≧W2, in the area under the image signal lines  115  shown in FIG.  6  and in the sealing area shown in FIG.  7 . In this structure, the increase in the capacitive coupling between the third conductive film  116   b  and the image signal lines  115  in FIG. 6 is suppressed, and thus the increase in the time constant associated with the image signal lines  115  and the relay interconnections  116  caused by the capacitive coupling is suppressed. In particular, at crossing points, the second conductive film  116   a  is disposed between the third conductive film  116   b  and the image signal line  115 , and the third conductive film  116   b  is spaced from the image signal line  115  by a relatively large distance, and thus the increase in the capacitive coupling is minimized. 
     Although the relay interconnections shown in FIGS. 6 and 7 have a two-layer interconnection structure that includes the second conductive film  116   a  or  116   a ′ and the third conductive film  116   b  or  116   b ′, the second conductive film  116   a  or  116   a ′ may be removed from the two-layer interconnection structure shown in FIGS. 6 and 7, so that the relay interconnections have a single-layer interconnection structure that includes the third conductive film  116   a  made of the light blocking film, as shown in FIGS. 8 and 9. Although this structure does not have the advantages of the redundant structure, the structure has another advantage that the capacitance between the image signal line  115  and the third conductive film  116   c  under the image signal line  115  shown in FIG.  6  and the capacitance between the first conductive film  116   c ′ and the leading interconnection  301   a  or  301   b  under the sealing area shown in FIG. 7 become smaller by an amount caused by the existence of the interlayer insulating film  12  compared with the case where the relay interconnections are formed of the polysilicon film existing between the first and second interlayer insulating films  12  and  4 . 
     On the other hand, in FIGS. 4 and 5, because the image signal lines  115  are made of the Al film formed on the second interlayer insulating film  4 , the Al film cannot be employed to form the sampling circuit driving signal lines  114  extending from the data line driving circuit  101  to the leading interconnections  301  ( 301   a ) and crossing the image signal lines  115 , as in the case of the relay interconnection  116  shown in FIGS. 6 and 8. Therefore, the sampling circuit driving signal lines need a three-dimensionally crossing relay interconnection which passes under or above the image signal lines  115 . It is desirable that the relay interconnections have as small a time constant as possible. This can be achieved in various ways as described below. 
     In FIG. 10 step ( 1 ), the relay interconnection  116   d  is made of the same polysilicon film as that used to form the scanning lines  3   a , and is passed under the second interlayer insulating film  4 , such that it crosses the image signal lines  115 . The relay interconnection  116   d  is electrically connected to the sampling circuit driving signal line  114  located at the side of the data line driving circuit  101  and to the leading interconnection  301  (refer to FIG. 5) at the side of the sealing area, via contact holes formed, at both sides of the image signal lines  115  in the figure, in the second interlayer insulating film  4 . 
     In FIG. 10 step ( 2 ), the relay interconnection  116   e  is made of the same refractory metal film such as W (tungsten) or metal alloy film as that used to form the light blocking film  11   a , and is passed under the second interlayer insulating film  4  such that it crosses the image signal lines  115 . The relay interconnection  116   e  is electrically connected to the sampling circuit driving signal line  114  located at the side of the data line driving circuit  101  and to the leading interconnection  301  at the side of the sealing area, via contact holes formed, at both sides of the image signal lines  115  in the figure, in the first interlayer insulating film  12  and the second interlayer insulating film  4 . In this structure, the relay interconnection is made of refractory metal with a low resistance, and thus the interconnection has a low enough resistance that causes no delay in propagation of the image signal. 
     In FIG. 10 step ( 3 ), the relay interconnection includes a relay interconnection  116   g  made of the same polysilicon film as that used to form the scanning lines  3   a  and also includes a relay interconnection  116   f  made of the same refractory metal film such as W or metal alloy film as that used to form the light blocking film  11   a , wherein they are passed under the second interlayer insulating film  4  and under the first interlayer insulating film  12 , respectively, such that they cross the image signal lines  115 . The relay interconnection is electrically connected to the sampling circuit driving signal line  114  located at the side of the data line driving circuit  101  and to the leading interconnection  301  at the side of the sealing area, via contact holes formed, at both sides of the image signal lines  115  in the figure, in the first interlayer insulating film  12  and the second interlayer insulating film  4 . In this structure, two layers of relay interconnections  116   f  and  116   g  are formed above and below the image signal lines  115  via the first interlayer insulating film  12  and the second interlayer insulating film  4 , and thus a more redundant structure is realized. Furthermore, because the relay interconnection  116   f  is made of a refractory metal film or metal alloy film with a low resistance, the overall interconnection resistance becomes lower, and thus no delay occurs in propagation of the image signal. Although in the present embodiment, the relay interconnections  116   f  and  116   g  are electrically connected to each other in a direct fashion, the relay interconnection  116   f  and the sampling circuit driving signal line  114  or the leading interconnection  301  at the side of the sealing area may be electrically connected to each other. 
     In FIG. 10 step ( 4 ), the relay interconnection includes, in addition to relay interconnections  116   i  and  116   j  formed in substantially the same manner as the relay interconnections having redundancy shown in FIG. ( 3 ), an additional relay interconnection  116   h  formed on the third interlayer insulating film  7  using the same film as the refractory metal film or metal alloy film employed as the light blocking film with electrical conductivity which defines at least a part of pixel opening area. This additional relay interconnection  116   h  extends so that it crosses the image signals  115 . A fourth interlayer insulating film  117  is formed on the relay interconnection  116   h . The relay interconnection  116   h  is electrically connected to the sampling circuit driving signal line  114  located at the side of the data line driving circuit  101  and to the leading interconnection  301  at the side of the sealing area, via contact holes formed, at both sides of the image signal lines  115  in the figure, in the third interlayer insulating film  7 . In this structure, three layers of relay interconnections  116   h ,  116   i , and  116   j  are formed above and below the image signal lines  115  via the first interlayer insulating film  12 , the second interlayer insulating film  4 , and the third interlayer insulating film  7 , and thus a still more redundant structure is achieved. Furthermore, because the relay interconnections  116   h  and  116   j  are made of a refractory metal film or metal alloy film with a low resistance, the overall interconnection resistance becomes still lower, and thus no delay occurs in propagation of the image signal. 
     As shown in FIGS. 2 and 4, the first light blocking film  11   a  is extended such that it overlaps the scanning lines  3   a  in the image displaying area surrounded by the third light blocking film  53 . Outside the image displaying area, the first light blocking film  11   a  passes as the light blocking interconnections under the third light blocking film  53 , and is then connected via a contact hole to a negative power supply (constant voltage line) of the scanning line driving circuit. 
     In the present embodiment, as described above, the relay interconnections of the image signal lines and of the sampling circuit driving signal lines are formed into the two-layer or single-layer structure having a reduced resistance using the light blocking film. However, the application of the relay interconnection according to the invention is not limited to such an image signal line and sampling circuit driving signal line. For example, in peripheral circuits, such as a data line driving circuit, scanning line driving circuit, and sampling circuit, it is also possible that an arbitrary relay interconnection, in the peripheral circuits, formed of a polysilicon film at a crossing point where two Al interconnections cross each other may be converted into a two-layer structure having a low resistance using the light blocking film. Alternatively, the relay interconnection made of a polysilicon film may be replaced with a single-layer interconnection having a low resistance made of the light blocking film. In particular, the reduction in the resistance of the relay interconnections used in the data line driving circuit or the scanning line driving circuit results in a reduction in the delay of shift registers used in these circuits, and thus it becomes possible to increase the driving speed. The reduction in the resistance of the relay interconnections in the sampling circuit or the precharging circuit makes it possible to prevent the sampling circuit driving signal and the precharging circuit driving signal from becoming less sharp. This makes it possible to write an image signal in a desirable fashion so as to achieve an improvement in the image quality. The relay interconnections may also be formed into a structure that includes three or more layers of conductive films. 
     Process of Producing Liquid Crystal Apparatus. 
     Referring now to FIGS. 11 to  14 , a process of producing the liquid crystal apparatus with the above-described structure according to an embodiment of the invention is described below. FIGS. 11 and 12 are cross-sectional views taken, as in FIG. 6, along plane B-B′ of FIG. 4, and illustrating various layers on the TFT array substrate for the respective processing steps. FIGS. 13 and 14 are cross-sectional views taken, as in FIG. 3, along plane A-A′ of FIG. 2, and illustrating various layers on the TFT array substrate for the respective processing steps. The structure shown in the B-B′ cross section and the structure shown in the C-C′ cross section are both produced at the same time during the same process. Therefore, the processing steps are described below in parallel for both structures. 
     In step ( 1 ) shown in FIGS. 11 and 13, a quarts substrate, a hard glass substrate, or a substrate of another proper material for use as a TFT array substrate  10  is prepared. Preferably, the TFT array substrate  10  is annealed at a high temperature of about 900° C. to 1300° C. in an ambient of inert gas such as N 2  (nitrogen) so that the TFT array substrate  10  will have less strain in a high-temperature process which will be performed later. To this end, the TFT array substrate  10  is subjected to a heat treatment at a proper temperature equal to or higher than the highest temperature that the TFT array substrate  10  will encounter in the following production process. 
     After the heat treatment, a film of metal, such as Ti, Cr, W, Ta, Mo, or Pd, or a metal alloy, such as a metal silicide, is deposited on the TFT array substrate  10  over an entire surface thereof by means of sputtering, thereby forming a light blocking film  11  with a thickness of 1000 to 5000 A, and more preferably with a thickness of about 2000 A. 
     After that, in step ( 2 ) shown in FIG. 13, a resist mask having a pattern corresponding to the pattern of a first light blocking film  11   a  (refer to FIG.  2 ), that shields pixel TFTs from light, is formed on the light blocking film  11  by means of a photolithography process. The light blocking film  11  is then etched via the resist mask, thereby forming the first light blocking film  11   a.    
     At the same time, as shown in step ( 2 ) in FIG. 11, a resist mask having a pattern corresponding to the pattern of a relay interconnection  116  is formed on the light blocking film  11  by means of the photolithography process, and the light blocking film  11  is etched via the resist mask thereby forming third conductive films  116   a  and  116   b′.    
     Subsequently, as shown in step ( 3 ) in FIGS. 11 and 13, a silicate glass film, such as NSG, PSG, BSG or BPSG, a silicon nitride film, or a silicon oxide film, is formed on the first light blocking films  11   a  and  11   b  by means of, for example an atmospheric-pressure or low-pressure CVD technique using TEOS (tetraethyl orthosilicate) gas, TEB (tetraethyl borate) gas, or TMOP (tetramethyl oxyphosrate) gas, thereby forming a first interlayer insulating film  12 . The thickness of the first interlayer insulating film  12  is selected to a value, for example within the range from about 5000 to 2000 A. 
     In the next step ( 4 ), as shown in FIGS. 11 and 13, an amorphous silicon film is formed on the first interlayer insulating film  12  at a relatively low temperature of about 450 to 500° C., and more preferably at about 500° C. by means of a low-pressure CVD technique (for example at a pressure of about 20 to 40 Pa) using mono-silane gas or a disilane gas at a flow rate of about 400 to 600 cc/min. After that, annealing is performed in an ambient of nitrogen at about 600 to 700° C. for about 1 to 10 hours, and more preferably for 4 to 6 hours so that a polysilicon film  1 , with a thickness of about 500 to 2000 A, and more preferably about 1000 A, is formed by means of a solid phase growth process. 
     In the case where n-channel TFTs are employed as the pixel switching TFTs  30  shown in FIG. 3, a V-group element such as Sb (antimony), As (arsenic), or P (phosphorus) may be slightly doped into the channel region of each TFT  30  by means of ion implantation or the like. On the other case, when p-channel TFTs are employed as the pixel switching TFTs  30 , a III-group element such as B (boron), Ga (gallium), or In (indium) may be slightly doped by means of ion implantation or the like. The polysilicon film  1  may also be formed indirectly by means of a low-pressure CVD process or the like without forming an amorphous silicon film as an intermediate film. Still alternatively, after depositing a polysilicon film by means of a low-pressure CVD process or the like, silicon ions may be implanted so as to convert the film into an amorphous state, and then the film may be recrystallized by means of annealing, thereby forming the polysilicon film  1 . 
     In the next step ( 5 ) as shown in FIGS. 11 and 13, a semiconductor layer  1   a  with a pattern such as that shown in FIG. 2 is formed by means of a photolithography process and an etching process. In this process, a first storage capacitor electrode If extending from the semiconductor layer  1   a  of the pixel switching TFT  30  is also formed in an area where a capacitance line  3   b  is to be formed along a scanning line  3   a.    
     In the next step ( 6 ) shown in FIG. 13, the semiconductor layer  1   a  of the pixel switching TFT  30  and the first storage capacitor electrode If are thermally oxidized at a temperature of about 900 to 1300° C., and more preferably at about 1000° C., thereby forming a thermal silicon oxide film with a relatively small thickness such as about 300 A. Furthermore, a high-temperature silicon oxide (HTO) film or a silicon nitride film with a relatively small thickness, such as about 500 A, is deposited by means of, for example, a low-pressure CVD process, thereby forming a multilayer insulating film used as the gate insulating film  2  of the pixel switching TFT  30  and also as the insulating film  2  of the capacitor. As a result of the above process, the thickness of the semiconductor layer  1   a  becomes about 300 to 1500 A, and more preferably about 350 to 500 A, and the thickness of the gate insulating film becomes about 200 to 1500 A, and more preferably about 300 to 1000 A. By performing the high-temperature oxidation process for a short time as described above, it is possible to prevent the substrate from being warped by heat, in particular when the substrate has a large size, such as 8 inches. Alternatively, the gate insulating film  1  and the insulating film for the capacitor may also be formed into a single layer structure by performing only the process of thermally oxidizing the polysilicon layer  1 . 
     In the step ( 6 ), although not necessarily required, for example P ions may be doped into a particular part of the semiconductor layer, which will become the first storage capacitor electrode If, to a dose of about 3×10 12 /cm 2  so as to obtain lower resistance. 
     In the next step ( 7 ) in FIG. 1, contact holes  305   a  extending to the first light blocking film  11   b  are formed in the first interlayer insulating film  12  by means of dry etching, such as reactive etching or reactive ion beam etching or wet etching. Isotropic etching, such as reactive etching or reactive ion beam etching, has the advantage that contact holes  305   a  can be formed such that they have substantially the same shape as the mask shape. If dry etching is mixed with wet etching, it becomes possible to form contact holes  305   a  such that they have a tapered structure, which prevents the interconnections from being broken. 
     In the next step ( 8 ) in FIG. 11 or FIG. 13, a polysilicon layer  3  is deposited by means of a low-pressure CVD process, and phosphorus (P) is doped into the polysilicon layer  3  by means of thermal diffusion thereby converting the polysilicon film  3  into an electrically conductive layer. Alternatively, P ions may be doped into the polysilicon film  3  when the polysilicon film  3  is deposited. 
     Then in step ( 9 ) in FIG. 13, the polysilicon film  3  is etched by means of a photolithography process and an etching process using a resist mask, thereby forming a scanning line  3   a  having a pattern such as that shown in FIG.  2  and also a capacitance line  3   b.    
     At the same time in process ( 9 ) in FIG. 11, second conductive films  116   a  and  116   a ′ serving as relay interconnections  116   a  having a pattern, such as that shown in FIGS. 4 and 5, are formed. 
     In the next step ( 10 ) in FIGS. 11 and 13, when the pixel switching TFTs  30  shown in FIG. 3 are constructed into n-channel TFTs with the LDD structure, a lightly doped source region  1   b  and a lightly doped drain region  1   c  are first formed in the semiconductor layer  1   a  by doping a V-group element, such as P serving as a dopant  17  to a low concentration (for example P ions are doped to a dose of 1 to 3×10 13 /cm 2 ) using the scanning line  3   a  as a diffusion mask. As a result of this process, the part of the semiconductor layer  1   a  under the scanning line  3   a  becomes a channel region  1   a ′. The doping of the dopant  17  causes the capacitance line  3   b , the scanning line  3   a , and the polysilicon film  3   c  (that is, the relay interconnection  116   a ) to have a low resistance. 
     Then in step ( 11 ) in FIGS. 11 and 13, a resist mask layer  18  having a pattern wider than the scanning line  3   a  is formed over the scanning line  3   a , and a V-group element such as P serving as a dopant  17 ′ is doped to a high concentration (for example, P ions are doped to a dose of 1 to 3×10 15 /cm 2 ) thereby forming a heavily doped source regions  1   d  and a heavily doped drain region  1   e  of the pixel switching TFT  30 . On the other hand, in the case where the switching TFT  30  is formed into a p-channel type, a III-group element, such as B, is employed in the doping process to form the lightly doped source region  1   b  and the lightly doped drain region  1   c , and also the heavily doped source region  1   d  and the heavily doped drain region  1   e  in the semiconductor layer  1   a . The pixel switching TFT  30  may also be formed into an offset structure which will be obtained if lightly doping is not performed in the above-described process. The pixel switching TFT  30  may also be formed into a self-aligned type TFT by implanting P ions or B ions using the scanning line  3   a  as an implantation mask. As a result of doping of the dopant  17 ′, the second conductive films  116   a  and  116   a ′ serving as the capacitance line  3   b , the scanning line  3   a , and the relay interconnection  116  become further lower in resistance. 
     In parallel to the above-described processing steps, peripheral circuits including the data line driving circuit  101  and the scanning line driving circuit  104  are formed in the form of complementary configuration consisting of n-channel TFTs and p-channel TFTs in a peripheral area on the TFT array substrate  10 . In the present embodiment, as described above, because the polysilicon TFT is employed as the pixel switching TFT  30 , the peripheral circuits including the data line driving circuit  101  and the scanning line driving circuit  104  are produced at the same time during the process for producing the pixel switching TFT  30 . 
     In the next step ( 12 ) in FIGS. 12 and 14, a silicate glass film such as NSG, PSG, BSG, or BPSG, a silicon nitride film, or a silicon oxide film serving as a second interlayer insulating film  4  is formed using an atmospheric-pressure or low-pressure CVD process with TEOS gas or the like in such a manner that the scanning lines  3   a  of the pixel switching TFTs  30  and also the capacitance lines  3   b , the scanning lines  3   a , and the second conductive films  116   a  and  116   a ′ are covered with the second interlayer insulating film  4 . Preferably, the thickness of the second interlayer insulating film  4  is within the rage from about 5000 to 15000 A. 
     Then in step ( 13 ) in FIGS. 12 and 14, annealing for activating the heavily doped source region  1   d  and the heavily doped drain region  1   e  is performed at 1000° C. for 20 min. After that, a contact hole  5  for the data line  6   a  is formed by means of dry etching, such as reactive etching or reactive ion beam etching or wet etching. A contact hole  305   b  for electrically connecting the relay interconnection  116   a  to the leading interconnection  301   b  and a contact hole for connecting the scanning line  3   a  and the capacitance line  3   b  to an interconnection (not shown in the figures) are also formed in the second interlayer insulating film  4  during the process of forming the contact hole  5 . 
     In the next step ( 14 ) in FIGS. 12 and 14, a metal film  6  is formed on the second interlayer insulating film  4  by depositing opaque low-resistance metal, such as Al or a metal silicide, to a thickness of about 1000 to 5000 A, and more preferably about 3000 A. Then in step ( 15 ), the metal film  6  is subjected to a photolithography process and an etching process so as to form a data line  6   a , an image signal line  115 , and a leading interconnection  301   b.    
     In the next step ( 16 ) in FIGS. 12 and 14, a silicate glass film, such as NSG, PSG, BSG, or BPSG, a silicon nitride film, or a silicon oxide film serving as a third interlayer insulating film  7 , is formed using an atmospheric-pressure or low-pressure CVD process with TEOS gas or the like in such a manner that the data lines  6   a  are covered with the third interlayer insulating film  7 . Preferably, the thickness of the third interlayer insulating film  7  is within the range from about 5000 to 15000 A. 
     In the next step ( 17 ) in FIG. 14, a contact hole  8  used to electrically connecting the pixel electrode  9   a  to the heavily doped drain region  1   e  of the pixel switching TFT  30  is formed using a dry etching process such as reactive etching or reactive ion beam etching. 
     Then in step ( 18 ) in FIGS. 12 and 14, a transparent and electrically conductive thin film  9 , such as an ITO film, is formed on the third interlayer insulating film  7  to a thickness of about 500 to 2000 A using, for example, a sputtering process. Furthermore, in step ( 19 ) in FIGS. 12 and 14, a pixel electrode  9   a  is formed using a photolithography process and an etching process. When the present liquid crystal apparatus is used in the reflection type liquid crystal device, the pixel electrode  9   a  may be formed of an opaque material having a high reflectivity, such as Al. 
     Subsequently, a polyimide-based solution serving as a material of an orientation film is coated on the pixel electrode  9   a  and rubbed in a particular direction at a pre-tilt angle, thereby forming an orientation film  16 . 
     The opposite substrate  20  shown in FIG. 3 is produced as follows. First, a glass substrate or the like is prepared. A second light blocking film  23  and a third light blocking film  53  (refer to FIGS. 4 and 5) are formed by first sputtering chromium and then performing a photolithography process and an etching process. Materials which can be used to form the second light blocking film  23  and the third light blocking film  53  include metals such as Cr, Ni, and Al and a resist black that includes a photoresist containing dispersed carbon or Ti. 
     After that, a transparent and electrically conductive thin film, such as an ITO film, is deposited over the entire surface of the opposite substrate  20  to a thickness of about 500 to 2000 A using, for example, a sputtering process, thereby forming an opposite common electrode  21 . Furthermore, a solution for a polyimide-based orientation film is coated over the entire surface of the opposite common electrode  21 . The resultant film is then subjected to a rubbing process in a particular direction at a predetermined pretilt angle, thereby forming an orientation film  22 . 
     Finally, the TFT array substrate  10  and the opposite substrate  20 , on which various layers have been formed as described above, are boned to each other via a sealing material, such that the orientation films  16  and  22  face each other. A liquid crystal containing two or more kinds of nematic liquid crystals is placed into the space between the two substrates by means of, for example, sucking, thereby forming a liquid crystal layer  50  with a predetermined thickness. 
     General Structure of Liquid Crystal Apparatus. 
     Referring first to FIGS. 15 and 16, the general structure of the liquid crystal apparatus is described below for various embodiments. FIG. 15 is a plan view as viewed from the side of an opposite substrate  20 , wherein various elements formed on the TFT array substrate are shown. FIG. 16 is a cross-sectional view taken along plane H-H′ of FIG. 16, wherein the opposite substrate is also shown. 
     As shown in FIG. 15, a sealing material  52  is disposed on a TFT array substrate  10  along the periphery thereof. A third light blocking film  53 , serving as a peripheral partition made of the same material as that of the second light blocking film  23  or a different material, is disposed in an inner area along the sealing material  52 . In an area outside the sealing material  52 , a data line driving circuit  101  and external connection terminals  102  are disposed along one side of the TFT array substrate  10 . Scanning line driving circuits  104  are disposed along two sides adjacent to the above-described side. In the case where a delay in the propagation of the scanning signal supplied to the scanning lines  3   a  is allowed, the scanning line driving circuit  104  may be disposed only on one side. The data line driving circuit  101  may be divided into two parts and they may be disposed at two sides of the image displaying area. For example, one data line driving circuit disposed along one side of the image display area may supply an image signal to odd-numbered data lines, and the other data line driving circuit disposed along the opposite side of the image displaying area may supply an image signal to even-numbered data lines. When the data lines  6   a  are driven in the comb fashion as described above, it is allowed to expand the area where the data line driving circuit  101  is formed, and thus it becomes possible to employ a complicated circuit. A plurality of interconnections  105  extend along the remaining side on the TFT array substrate  10  so that the two scanning line driving circuits disposed at two sides of the image displaying area are connected to each other via the interconnections  105 . An upper-to-lower conducting element  106  is disposed at least at one corner of the opposite substrate  20  so that the TFT array substrate  10  and the opposite substrate  20  are electrically connected via the conducting element  106 . As shown in FIG. 16, the opposite substrate  20  having an outer shape and size similar to those of the sealing material  52  shown in FIG. 15 is bonded to the TFT array substrate  10  via the sealing material  52 . 
     On the TFT array substrate  10  of the liquid crystal apparatus according to any embodiments described above with reference FIGS. 1 to  16 , there may be further provided a precharging circuit for writing a precharging signal with a particular voltage on the respective data lines  6   a  at a proper time before the image signal is written, thereby facilitating the process of writing the image signal on the data lines  6   a . Furthermore, there may be provided a test circuit for testing the quality or detecting a defect in the liquid crystal apparatus during the production process or before shipment. A part of peripheral circuits, such as a data line driving circuit  101  and scanning line driving circuit  104 , may be formed in a driving LSI mounted on a TAB (tape automated bonding substrate) and electrically and mechanically connected to the TFT array substrate  10  via an anisotropic conducting film. A polarizing film, a phase difference film, and/or a polarizing plate are properly disposed on the side of the opposite substrate  20  which is exposed to the projection light ray and also on the side of the TFT array substrate  10  from which the projection light ray emerges, depending on the operation mode such as an TN (twisted nematic) mode, an TN (twisted nematic) mode, a D-STN (double STN) mode, or normally white mode/normally black mode. 
     When the above-described liquid crystal apparatus is used in a color liquid crystal projector, three similar liquid crystal apparatus are used as RGB light valves, respectively, wherein light rays with different colors created by passing a light ray through RGB color separation dichroic mirrors are passed through the respective liquid crystal apparatus. Therefore, in the embodiment of the invention, no color filter is disposed on the opposite substrate  20 . However, an RGB color filter with a protective film may also be formed on the opposite substrate  20 , in proper areas corresponding to the pixel electrodes  9   a  where the second light blocking film  23  is not formed. This allows the liquid crystal apparatus according to the present embodiment to be employed in a color liquid crystal apparatus of a type other than the liquid crystal projector, such as a direct-view-type or reflection-type color liquid crystal television set. Furthermore, micro lenses may be formed on the opposite substrate  20 , at locations corresponding to the respective pixels so that the incident light is focused in a more efficient fashion, thereby achieving a brighter liquid crystal apparatus. Still furthermore, an interference film that includes a large number of layers with different refractive index may be deposited on the opposite substrate  20 , thereby forming a dichroic filter for producing an RGB color utilizing interference of light. By adding the dichroic filter to the opposite substrate, a still brighter color liquid crystal apparatus can be achieved. 
     Although in the above-described embodiments, light is incident on the liquid crystal apparatus from the opposite substrate side as in the conventional liquid crystal apparatus, light may be incident on the apparatus from the side of the TFT array substrate  10  and may emerge from the side of the opposite substrate  20  without causing a problem, because the first light blocking film  11   a  is provided. That is, when the liquid crystal apparatus is mounted on a liquid crystal projector, the channel region  1   a ′ and the LDD regions  1   b  and  1   c  of the semiconductor layer  1   a  are protected from illumination of light, and thus it is possible to display a high-quality image. In the conventional technique, to prevent light from being reflected at the back surface of the TFT array substrate  10 , it is required to place an additional polarizing plate coated with an anti-reflection film at an outer location or it is required to bond an anti-reflection film to the TFT array substrate  10 . In contrast, in the embodiments of the invention, the first light blocking film  11   a  is formed between the surface of the TFT array substrate  10  and the semiconductor layer  1   a  at least at locations corresponding to the channel region  1   a ′ and the LDD regions  1   b  and  1   c . This makes it unnecessary to use an anti-reflection film or a polarizing plate with an anti-reflection film, or it becomes unnecessary to perform an anti-reflection process on the TFT array substrate  10  itself. Thus, according to the embodiments, it is possible to reduce the material cost. Furthermore, because the polarizing plate is not required, no reduction in the production yield due to dust or defects occurs during the process of bonding a polarizing plate. Still furthermore, the excellent light blocking property makes it possible to employ a bright light source or a polarizing beam splitter for achieving an improved light usage efficiency without causing degradation in the image quality, such as light crosstalk. 
     In the embodiments, the switching elements of the respective pixels are each formed into the structure of a normal stagger type or coplanar type polysilicon TFT. Alternatively, other types of TFTs, such as a reverse stagger type TFT or an amorphous silicon TFT, may also be employed. 
     Electronic Apparatus. 
     Examples of electronic apparatus including the electrooptical apparatus are described below with reference to FIGS. 17-19. 
     FIG. 17 illustrates the general structure of an electronic apparatus including a liquid crystal apparatus  100  as an example of an electrooptical apparatus. 
     As shown in FIG. 17, the electronic apparatus includes an image information output source  1000 , an image information processing circuit  1002 , a driving circuit  1004 , a liquid crystal apparatus  100 , a clock generator  1008 , and a power supply  1010 . The image information output source  1000  includes a memory, such as a ROM (read only memory), a RAM (random access memory), or an optical disk and a tuning circuit that tunes an image signal and outputs the resultant image signal. In response to the clock signal supplied from the clock generator  1008 , the image information output source  1000  outputs image information, such as an image signal, to the image information processing circuit  1002 . The image information processing circuit  1002  includes various processing circuits such as an inverting amplifier, a serial-parallel converter, a rotation circuit, a gamma correction circuit, and a clamping circuit, which are all known in the art. The image information processing circuit  1002  successively generates a digital signal from the image information input in response to the clock signal, and outputs the resultant digital signal together with a clock signal CLK to the driving circuit  1004 . The driving circuit  1004  drives the liquid crystal apparatus  100 . The power supply  1010  supplies electric power to the various circuits described above. The driving circuit  1004  may be mounted on the TFT array substrate of the liquid crystal panel  100 . In addition, the image information processing circuit  1002  may also be mounted on the TFT array substrate. 
     Specific examples of electronic devices are described below with reference to FIGS. 18-19. 
     FIG. 18 illustrates a liquid crystal projector  1100 , which is an example of an electronic device. This liquid crystal projector  1100  includes three liquid crystal display modules, each including a liquid crystal apparatus  100  provided with a driving circuit  1004  of the above-described type formed on a TFT array substrate, wherein those three liquid crystal display modules are used as light valves  100 R,  100 G, and  100 B for R, G, and B colors, respectively. In this liquid crystal projector  1100 , a projection light ray is emitted from a white light source, such as a metal halide lamp serving as a lamp unit  110 . The light ray is divided by three mirrors  1106  and two dichroic mirrors  1108  into three light components R, G, B with three primary colors RGB. The three light components are then passed through the light valves  100 R,  100 G, and  100 B, respectively. In the above process, in order to prevent the blue light ray B from having a transmission loss caused by a long optical path, the blue light ray B is transmitted via the relay lens system  1121  including an incident lens  1122 , a relay lens  1123 , and an emerging lens  1124 . The light rays with three primary colors are separately modulated by the three light valves  100 R,  100 G, and  100 B, respectively, and mixed into a single ray through a dichroic prism  1112 . The resultant light ray is projected onto a screen  1120  via the projection lens  1114 , and thus a color image is formed thereon. 
     FIG. 19 illustrates another example of an electronic device, that is, a laptop personal computer (PC)  1200  capable of handing multi-media. The laptop personal computer  1200  includes a liquid crystal apparatus  100  of the above-described type disposed on the inner side of a top cover case. The main body  1204  of the laptop personal computer  1200  includes a CPU, a memory, a modem, and a keyboard  1202 . 
     In addition to the electronic devices described above with reference to FIGS. 18-19, there are other examples of the electronic device shown in FIG.  17 . They include a liquid crystal television set, a video tape recorder with a view-finder or a monitor display, a car navigation system, a pocket-sized electronic notebook, an electronic calculator, a word processor, an engineering workstation (EWS), a portable telephone, a video telephone, a POS terminal, and an apparatus with a touch panel. 
     According to the present embodiment, as described above, it is possible to realize various types of electronic apparatus provided within a liquid crystal apparatus capable of displaying a high-quality image, which can be produced in a highly efficient manner. 
     Advantages 
     In the electrooptical apparatus according to the present invention, since image signals and other signals are supplied via peripheral interconnections, including a relay interconnection made of a light blocking film and having a low resistance, the capacitance lines does not have a significantly large voltage fluctuation, crosstalk, and ghost due to the capacitive coupling between the capacitance lines and other lines, such as image signal lines and relay interconnections, even when the driving frequency of the electrooptical apparatus is increased. This allows the electrooptical apparatus to display a high-quality image. Another advantage of the electrooptical apparatus, in addition to the above advantage, is the redundant structure, whereby if a capacitance line is broken in the middle of the line due to dust or the like, a signal is still supplied via a light blocking film instead of the broken capacitance line. This makes it possible to easily achieve a high-reliability electrooptical apparatus.