Patent Publication Number: US-2006003235-A1

Title: Semiconductor manufacturing method and an exposure mask

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a semiconductor manufacturing method and an exposure mask used in a lithography process for manufacturing semiconductor devices.  
      2. Description of the Related Art  
      The integration of semiconductor devices has constantly increased by four times every three years, because MOS type logic devices require higher functionality and memory devices require larger storing capacity. The improvement in the integration is provided by miniaturizing the design size of semiconductor devices. The miniaturization is very advantageous because it increases operating speed and reduces power consumption in semiconductor devices, and therefore it is desired more and more.  
      Under this situation, downsizing to 0.1 μm or less has been required as the minimum processing size of semiconductor devices, for example a wiring pitch, gate clearance, etc., and manufacturing processes of semiconductor devices are becoming more and more difficult.  
      Especially, lithography technology is confronted with much more difficulty. In lithography technology, a circuit pattern formed in a mask is transferred to a resist film of a semiconductor substrate using ultraviolet light generated by an exposure apparatus. The resist film is then developed to form the circuit pattern in the resist film. Etching is performed based on the circuit pattern, to form circuit elements such as gate electrodes and wirings. An ArF excimer laser having a wavelength of 0.193 μm is used as an ultraviolet light source.  
      Recently, the minimum processing size of semiconductor devices became smaller than the wavelength of light sources of exposure apparatuses. Even if image reduction projection is employed to increase the numerical aperture, resolution limit is exceeded. Therefore, there exists a problem that edge positions and shapes of the exposed pattern on the resist film are deformed, that is, the pattern formed in the mask cannot be accurately transferred onto the resist film.  
      If a mask pattern  101  as shown by the chain line in  FIG. 1  is used, end portions of actual wiring  102  formed on a resist film retreat or are put back, and corner portions thereof are rounded, as shown by the solid line in  FIG. 1 . This phenomenon is called “shortening”. This shortening phenomenon is becoming much more remarkable as designed wiring widths are reduced. If the amount of the shortening exceeds tolerances, bad connections or short circuits of wirings occur.  
      A variety of technologies (for example, in the patent references cited below) are proposed to inhibit the shortening phenomenon due to this optical proximity effect. For example, an Optical Proximity Correction (OPC) method has been proposed. In the OPC method, a mask pattern is broadened more than a designed wiring pattern at a place where shortening occurs. Alternatively, dummy patterns are arranged around a place where shortening occurs, in order to inhibit the shortening.  
      For example, as shown in  FIG. 2A , four correction patterns  104  called “hammer heads” or “Serif” are added at corners of wiring pattern  103 . Alternatively, as shown in  FIG. 2B , many correction patterns  106  are arranged around ends of wiring patterns  105  to inhibit the shortening. 
          Patent reference 1: Japanese Laid-Open Patent Application 10-198048     Patent reference 2: Japanese Laid-Open Patent Application 11-95406        

      In the method shown in  FIG. 2A , however, when plural wiring patterns  103  are arranged in parallel and close to each other, there is not enough room to admit required correction patterns  104 , resulting in the shortening not being inhibited enough. If the correction patterns  104  are extremely extended, they become connected to each other, which creates another problem.  
      In the method shown in  FIG. 2B , when the wiring patterns  105  are arranged close to each other, there is also not enough room to accept required correction patterns  106 , especially at the circle region B, resulting in the same problem as in  FIG. 2A .  
     SUMMARY OF THE INVENTION  
      Accordingly, the present invention is made in view of the above-mentioned problems, and aims at offering a semiconductor manufacturing method and an exposure mask that inhibit the shortening problem and bad connections and short circuits of wiring in lithography processes.  
      According to one aspect of the present invention, a semiconductor manufacturing method including a lithography process having an exposure step for projecting an image of a mask pattern of a mask onto a photo resist layer using exposure light is provided. In the method, the mask pattern comprises: a first pattern having a light transparency characteristic, corresponding to a circuit pattern; and a second pattern having an inverted light transparency characteristic, arranged within and spaced apart from the first pattern.  
      According to another aspect of the present invention, a method for manufacturing a semiconductor device including a first region having close gate patterns and a second region having sparse gate patterns, including a lithography process having an exposure step for projecting an image of a mask pattern of a mask onto a photo resist layer of the semiconductor device using exposure light is provided. In the method, the mask pattern comprises: in a region corresponding to the first region, a first pattern being light shielding and corresponding to the gate electrode patterns, and a second pattern being light transparent and arranged within and spaced apart from the first pattern; and in a region corresponding to the second region, a third pattern being light shielding and corresponding to the gate electrode patterns; wherein a width of the first pattern is larger than a width of the third pattern.  
      According to another aspect of the present invention, a method for manufacturing a semiconductor device including a first region having close wiring patterns and a second region having sparse wiring patterns, including a lithography process having an exposure step for projecting an image of a mask pattern of a mask onto a photo resist layer of the semiconductor device using exposure light is provided. In the method, the mask pattern comprises: in a region corresponding to the first region, a first pattern being light transparent and corresponding to the wiring patterns, and a second pattern being light shielding and arranged within and separated from the first pattern; and in a region corresponding to the second region, a third pattern being light transparent and corresponding to the wiring patterns; wherein a width of the first pattern is larger than a width of the third pattern.  
      According to the present invention, the shortening phenomenon can be effectively inhibited.  
      Features and advantages of the present invention are set forth in the description that follows, and in part will become apparent from the description and the accompanying drawings, or may be learned by practice of the invention according to the teachings provided in the description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows a prior art mask pattern and its wiring pattern formed on a resist film.  
       FIG. 2A  shows prior art correction hammerhead patterns;  
       FIG. 2B  shows another set of prior art correction patterns;  
       FIGS. 3A-3C  illustrate the principle of the present invention;  
       FIG. 4  is a plan view of a mask pattern according to a first embodiment of the present invention;  
       FIG. 5A  shows a mask pattern and its formed wiring pattern according to a first example of the first embodiment;  
       FIG. 5B  shows a prior art comparison sample mask pattern and its formed wiring pattern;  
       FIG. 6  is a chart illustrating the relations between shortening and the width of an auxiliary pattern;  
       FIG. 7A  shows mask patterns and their simulated wiring patterns according to the embodiment;  
       FIG. 7B  shows mask patterns and their simulated wiring patterns according to the comparison sample;  
       FIGS. 8A-8D  show alternative mask patterns according to a first alternative example of the first embodiment;  
       FIG. 9  is a plan view of a second alternative example of the first embodiment;  
       FIG. 10  is a plan view of mask patterns having close and sparse patterns;  
       FIGS. 11A-11C  illustrate a lithography process according to a second embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      In the following, embodiments of the present invention are described with reference to the accompanying drawings.  
       FIGS. 3A-3C  illustrate the principle of the present invention.  FIG. 3A  is a top plan view of an exposure mask according to the present invention.  FIG. 3B  is a cross-sectional side view of the exposure mask.  FIG. 3C  illustrates illumination distribution on a resist layer surface.  
      Referring to  FIG. 3A , a mask pattern MP formed in an exposure mask comprises a first pattern MP 1  and a second pattern MP 2 . The first pattern MP 1  has first mask regions A 1  at ends thereof and a second mask region A 2  at the center thereof, as shown in  FIG. 3A . The second pattern MP 2  is placed within the first pattern MP 1 , and in the second mask region A 2 .  
      In this case, the first pattern MP 1  is transparent to light. The second pattern MP 2  and the region outside of the first pattern MP 1  have light shielding characteristics. Another mask pattern having an inverted transparent characteristic is also included in the present invention, but its explanation is omitted.  
      Referring to  FIGS. 3B and 3C , if no second pattern MP 2  is provided, illumination on a resist film (not shown) onto which an image of the mask pattern MP is projected, is represented by a chain line IL 1  in  FIG. 3C . Exposure light transmitted through the first region A 1  of the first pattern MP 1  illuminates a region R 1  corresponding to the region A 1 . Upon reaching R 1   a , the illumination decreases because of the proximity effect by the edge MP 1   a  of the first pattern MP 1 . Illumination on a region R 2  corresponding to the second mask region A 2  is higher than the region R 1 , because of less proximity effect. Supposing a threshold value for enough exposure is TH as shown in  FIG. 3C , shortening occurs in a region where the illumination is lower than TH. The shortening amount is represented by S 1 .  
      On the other hand, when the second pattern MP 2  is provided within the first pattern MP 1 , the light transmitted through the second mask region A 2  is partially shielded by the second pattern MP 2 . The second pattern MP 2  is small enough so that no image of the second pattern MP 2  can be projected on the resist layer, and therefore the light transmitted outside of the second pattern MP 2  is diffracted and distributed over the whole region R 2  on the resist layer. Therefore, the illumination distribution IL 2  in the penumbra region R 2  is even, and is lower than the illumination distribution IL 1 .  
      On the other hand, since the second pattern MP 2  is not formed in the first mask region A 1 , the illumination on the region R 1  is substantially the same as in the illumination distribution IL 1 .  
      Under this condition, when the intensity of the light source is increased, resultant illumination IL 3  becomes larger proportionally. Then the shortening portion where the illumination distribution IL 3  is lower than TH becomes smaller. That is, the shortening amount S 2  is smaller than S 1 .  
      In this manner, the present invention can suppress the shortening effectively. Although  FIG. 3  utilizes illumination only for simplicity, the actual exposure amount is determined by (exposure X time). Therefore, instead of increasing the intensity of the light source, exposure time can be lengthened, or sensitivity can be increased.  
     First Embodiment  
      A mask pattern according to a first embodiment of the present invention is explained below.  
       FIG. 4  is a plan view of a mask pattern according to the first embodiment of the present invention. The mask pattern shown in  FIG. 4  is, for example, a mask pattern of an exposure mask used in forming a wiring layer on a semiconductor device.  
      Referring to  FIG. 4 , the mask pattern  10  comprises wiring patterns  11  and auxiliary patterns  12  formed within the wiring patterns  11 . Four rectangular patterns  11  are placed in parallel, and one rectangular pattern  11  is placed perpendicular to the four patterns. Ultraviolet light is shielded outside of the wiring patterns  11  and transmits through the wiring patterns  11 .  
      The auxiliary patterns  12  are formed within the wiring patterns  11 , and configured so as to shield ultraviolet light. Each of the wiring patterns  11  has first regions  11 - 1  at the longitudinal ends  11   a  thereof and a second region  11 - 2  between the first regions. The auxiliary patterns  12  are formed in the second regions  11 - 2 . The auxiliary patterns  12  are placed in parallel to the wiring patterns  11  and spaced apart from the sides of the wiring patterns  11 . As shown in  FIG. 4 , the first regions  11 - 1  lie between the ends of the wiring patterns  11  and the ends of the auxiliary patterns  12 .  
      The width W 1  of each of the auxiliary patterns  12  is determined so as not to form an image on a resist film (not shown) that is an image-formation plane onto which the mask pattern  10  is transferred by exposure. By defining the auxiliary patterns  12  in this manner, ultraviolet light transmitting through the wiring patterns  11  is diffused to regions on the image-formation plane corresponding to the auxiliary patterns  12 , and its intensity of illumination is lowered compared with a case where no auxiliary pattern  12  is provided.  
      On the other hand, there is no auxiliary pattern  12  in the first regions  11 - 1  at the ends of the wiring patterns  11 . Therefore, the intensity of illumination is not lowered at regions on the image-formation plane corresponding to the first regions, and is the same as in a case where no auxiliary pattern  12  is provided, because the intensity of illumination is determined by the proximity effect in outer regions of the wiring patterns  11 . Accordingly, by providing the auxiliary patterns  12 , the intensity of illumination is relatively increased at the regions on the image-formation plane corresponding to the first regions  11 - 1  compared to the regions on the image-formation plane corresponding to the second region  11 - 2  due to the above explained principle. The amount of exposure (referred to as “exposure amount on light receiving face” herein) becomes equal over a larger area, resulting in inhibiting the shortening at the ends  11   a  of the wiring patterns.  
      The appropriate width W 1  of the auxiliary patterns  12  is determined depending on projecting resolution of the exposure device. A reduced width W 1  projected onto the image-forming plane is preferably in the range of 2%-20% of the wavelength of the light source. If the reduced width is larger than 20%, the auxiliary patterns  12  may form images. If the reduced width is smaller than 2%, the equality of the illumination is degraded. For example, if an excimer laser having a wavelength of 193 μm is used as a light source, a reduced width W 1  of the auxiliary pattern  12  projected onto the image-forming plane is preferably in the range of 4 nm-40 nm, and more preferably in the range of 15 nm-40 nm.  
      The length of any portion of the mask pattern  10  means a reduced length projected onto the image-forming plane unless otherwise defined. If an exposure device has a reduction ratio of 4:1 for projecting, the length of any portion of the mask pattern is reduced to ¼ on the image-forming plane. In this specification, width direction lengths mean lengths in the shorter side direction of rectangles.  
      A distance L 1  between the ends  12   a  of the auxiliary patterns  12  and the ends  11   a  of the wiring patterns  11  is appropriately selected depending on the wavelength of light source to be used for exposure, the configuration, and layout of the wiring patterns  11 . For example, if an ArF excimer laser (wavelength: 193 nm) is used as a light source, and widths of the wiring patterns are 90 nm, then the distance L 1  is preferably in the range of 50 nm-200 nm.  
      It is preferable that the auxiliary patterns  12  be placed substantially at the center of the widths of the wiring patterns  11 , so as to prevent the images of wiring patterns  11  projected on the image-forming plane from decreasing in width.  
      The mask pattern  10  having the auxiliary patterns  12  within the wiring patterns  11  according to this embodiment can effectively inhibit the shortening problem, even if the wiring patterns  11  are arranged so closely that no hammer head can be provided. The mask patterns  10  according to this embodiment can still be utilized under conditions where the spaces between the wiring patterns  11  become shorter and the wavelength of exposure devices becomes shorter.  
      In the mask pattern  10  of the exposure mask according to this embodiment, the inside of the wiring patterns  11  is light transparent and the region outside of the wiring patterns  11  and the auxiliary patterns have shielding characteristics. However, a mask pattern having inverted light transparency can be used. That is, the inside of the wiring patterns  11  can have shielding characteristics and the region outside of the wiring patterns  11  and the auxiliary patterns  12  can be light transparent. In this case, the light transmitting through the auxiliary patterns  12  diffuses and illumination is increased at the middle portion rather than at the ends of the image-formed wiring patterns  11 , resulting in equal illumination distribution over the wiring patterns  11 . Therefore, by lowering the amount of light source power (brightness) multiplied by exposure time (referred to as “exposure amount of light source” herein), the shortening problem can be inhibited. Such mask patterns can be utilized in forming gate layers as gate electrodes of MOS transistors, for example, and are explained in more detail in a second embodiment below.  
     FIRST EXAMPLE  
      A wiring pattern was formed on a resist film applied on a silicon substrate using an exposure mask according to the first embodiment of the present invention.  
       FIG. 5A  shows a mask pattern having an auxiliary pattern and a wiring pattern formed in accordance with the first embodiment.  FIG. 5   b  shows a prior art mask pattern having hammer heads and a wiring pattern formed for comparison.  
      Referring to  FIG. 5A , a mask pattern according to the first embodiment comprises a wiring pattern  11  and an auxiliary pattern  12  placed inside of the wiring pattern  11 . A reduced longitudinal length L 2  of the wiring pattern  11  projected onto a resist film is 750 nm. A reduced width of the wiring pattern  11  projected onto a resist film is 90 nm. A reduced longitudinal length of the auxiliary pattern  12  is 650 nm. A reduced width W 3  of the auxiliary pattern  12  is in the range of 4 nm-15 nm. A distance L 1  between the ends  11   a  of the wiring pattern  11  and the ends  12   a  of the auxiliary pattern  12  is defined as to be 50 nm. For comparison purposes, a mask having no auxiliary pattern (the width W 3  is 0) was also formed.  
      An exposure device used an ArF excimer laser (wavelength: 193 nm) as a light source and a reducing projection system having a reduction rate of ¼ (mask pattern size:image-formed pattern size=4:1). A 250 nm thickness positive type chemically amplified resist film was applied on a silicon substrate, exposed and developed to form an aperture of wiring pattern  16  in the resist film.  
      The exposure amount of the light source was selected so as to minimize the amount of shortening, which is explained below. For example, the exposure amount of the light source in a case where the width W 3  of the auxiliary pattern is 15 nm, was increased by 25% compared to the no auxiliary pattern case.  
      As shown on the right side of  FIG. 5A , an amount of shortening SH 1  is defined as to be a distance between the ends of the mask pattern and the ends of the formed wiring pattern  16 . That is, the amount of shortening SH 1 =(reduced length L 2  of the mask pattern projected onto an image-forming plane−length L 3  of wiring pattern  16  formed on the resist film)/2.  
      Comparing Sample  
      As shown in  FIG. 5B , a mask pattern  110  not in accordance with the present invention comprises a wiring pattern  111  having the same size as the first example and four auxiliary patterns (hammer heads)  112  formed at four corners of the wiring pattern  111 . A longitudinal length L 2  of the wiring pattern  111  is the same as the first example. Longitudinal lengths of the auxiliary patterns  112  are 50 nm, widths W 4  are 0 nm-15 nm. The conditions of the exposure device and resist film, etc., are the same as in the first example.  
       FIG. 6  illustrates relations between shortening amount and auxiliary pattern width in both the first example and the comparison sample. In  FIG. 6 , diamonds represent the shortenings in the first example and squares represent the shortenings in the comparison sample.  
      Referring to  FIG. 6 , it is understand that the wider the auxiliary pattern width is, the less the shortening amount is in both the first example and the comparison sample. The first example gives a substantially equal shortening amount compared to the comparison sample.  
      In the comparison sample, when plural wiring patterns are arranged in parallel, the wider the auxiliary pattern W 4  is, the shorter the space between adjacent wiring patterns becomes. In the first example, when plural wiring patterns are arranged in parallel, even if the auxiliary pattern W 3  becomes wider, the space between adjacent wiring patterns is constant. Therefore, the first embodiment is advantageous because it can prevent short circuits effectively, especially when the wiring pitch becomes shorter.  
      Simulation was performed for both the first example and the comparison sample under the condition that plural wiring patterns are closely arranged.  
       FIGS. 7A and 7B  illustrates simulation results for the first example and the comparison sample. In both  FIGS. 7A and 7B , mask patterns are shown on the left side and image patterns obtained by simulation are shown on the right side. The mask patterns and imaged patterns are adequately scaled in the drawings. Light source and image projection systems for simulation are selected the same as in the first example.  
      As shown at the left side of  FIG. 7A , a mask pattern according to the first example has nine wiring patterns arranged in parallel. These wiring patterns have a longitudinal length of 750 nm, and a width of 90 nm. Auxiliary patterns have a longitudinal length of 650 nm, and a width 20 nm. The distance between the ends of the wiring pattern and the ends of the auxiliary pattern is 50 nm. Wiring pattern pitch P 1  is selected as 170 nm.  
      On the other hand, as shown at the left side of  FIG. 7B , a mask pattern according to the comparison sample has nine wiring patterns arranged in parallel. These wiring patterns have a longitudinal length of 750 nm, and a width of 90 nm. Auxiliary patterns have a longitudinal length of 50 nm, and a width 30 nm.  
      As shown on the right side of  FIG. 7B  illustrating simulation results for the comparison sample mask pattern, the shortening amount of imaged patterns is 40 nm. The shortening is suppressed, but adjacent wiring patterns are connected at some portions, making short circuits.  
      On the other hand, as shown on the right side of  FIG. 7A  illustrating simulation result for the first example mask pattern, the shortening amount of imaged patterns is still 40 nm. However, there is no connecting portion between adjacent wiring patterns, and no short circuit.  
      Accordingly, the mask pattern according to the first example can suppress the shortening problem while avoiding wiring pattern short circuits even when the wiring pattern pitch is decreased.  
      Next, mask patterns according to a first alternative example of the first embodiment are explained below.  
       FIGS. 8A through 8D  are plan views of mask patterns according to the first alternative examples of the first embodiment.  
      With reference to  FIGS. 8A and 8B , mask patterns  30  and  35  according the first alternative example, have plural auxiliary sub-patterns  31   a - 31   c ,  36   a - 36   c  arranged serially and separately from each other inside of wiring patterns  11 . The auxiliary patterns are  31  and  36 .  
      As shown in  FIG. 8A , all the sub-patterns  31   a - 31   c  may have the same width. As shown in  FIG. 8B , the sub-patterns  36   a - 36   c  may have different widths. For example, a width of the middle sub-pattern  36   b  may be wider than the other sub-patterns  36   a ,  36   c . In this way, illumination around the middle of the imaged plane wiring pattern is further reduced, and therefore illumination becomes further equalized over the whole wiring pattern, suppressing the shortening problem. The number of the sub-patterns is not limited to three; two, four or another number can be utilized.  
      As shown in  FIG. 8C , a mask pattern  40  may have two auxiliary sub-patterns  41   a ,  41   b , which are arranged in parallel inside of a wiring pattern  11 . The number of the sub-patterns is not limited to two; it may be three or another number.  
      As shown in  FIG. 8D , a mask pattern  45  may have an auxiliary pattern  46  having a bulged middle portion, which results in the same advantage as in the  FIG. 8B  pattern.  
      The auxiliary patterns shown in  FIGS. 8A-8D  can be combined. The auxiliary patterns shown in  FIG. 8A  or  8 B can be arranged as shown in  FIG. 8C .  
       FIG. 9  is a plan view of a mask pattern according to a second alternative example of the first embodiment of the present invention.  
      With reference to  FIG. 9 , a mask pattern  50  comprises wiring patterns  51 , and auxiliary patterns  52  formed within the wiring patterns  51 . The mask patterns  51  are the same as the first example except that a width W 5  is broader than a designed width W 6  of a designed wiring pattern  53  (shown by a one dot chain line).  
      Since that the width W 5  is broader than the designed width W 6  of the designed wiring pattern  53 , illumination is further equalized at first regions  51 - 1  at the ends of the wiring pattern  51  and at a second region  51 - 2 . Therefore, shortening is suppressed and illumination is increased at an image-forming plane of the wiring pattern  51 , and the exposure amount of the light source can be decreased. The designed wiring patterns  53  are determined by considering wiring resistances and capacities between wirings in each wiring layer but without considering shortening.  
      It is preferred that a ratio W 5 /W 6  of the width W 5  and the width W 6  be 1.02-1.20. It is preferred that a difference between the width W 5  and the width W 6  be substantially equal to a width of the auxiliary pattern  52 .  
       FIG. 10  is a top plan view of a mask pattern having a close or dense layout region and a sparse layout region.  FIG. 10  utilizes the above mentioned second alternative example.  
      With reference to  FIG. 10 , the mask pattern  60  comprises a first mask portion  61  having densely arranged wiring patterns, and a second mask portion  62  having sparsely arranged wiring patterns. The mask pattern of the first mask portion  61  is formed by using the second alternative example mask pattern and has wiring patterns  51  having auxiliary patterns  52 . The actual wiring patterns  51  are wider than designed wiring patterns  53 . On the other hand, the mask patterns of the second mask portion  62  have no auxiliary patterns, and the actual wiring patterns have the same width as designed wiring patterns.  
      Since the wiring patterns  51  of the first mask portion  61  have the above mentioned second alternative example wiring patterns, illumination is increased at the image-forming plane of the wiring patterns  51 , and is substantially the same as the illumination of the wiring patterns  63  at its image-forming plane. Therefore, it is possible to have substantially the same exposure amount of a light source for the first and second mask portions  61 ,  62 , resulting in easy controlling of the exposure amount of the light source.  
      The first alternative example mask pattern, the second alternative example mask pattern and  FIG. 10  mask pattern may have inverted light transparency, as above mentioned.  
     Second Embodiment  
      A method for fabricating semiconductor devices according to a second embodiment of the present invention is now explained. A lithograph process in the semiconductor device fabrication method according to this embodiment uses an exposure mask having mask patterns according to the above mentioned first embodiment.  
       FIGS. 11A-11C  illustrate the lithograph steps for fabricating semiconductor devices in accordance with the second embodiment of the present invention, in which a gate layer is formed as a gate electrode on a silicon substrate.  
      In the step shown by  FIG. 11A , a gate oxide film  71  and a poly-silicon film  72  are formed on the silicon substrate  70 . And on a surface of these films, a positive type resist film  73  is formed and then pre-baked to remove solvent from the resist film  73 .  
      In a step shown by  FIG. 11A , an exposure mask  74  having an exposure mask pattern  74   b  is used for the exposing process. The mask pattern  74   b  is, for example, the mask pattern  10  shown in  FIG. 10 . The inside of the wiring pattern  11  is light shielding and the auxiliary pattern  12  is transparent. As shown in  FIG. 11A , gate layer patterns are formed by shielding mask films  76 . The mask films  76  are provided with apertures  76 - 1  as auxiliary patterns.  
      In the exposure process, ultraviolet light is irradiated from a light source  77  of an exposure device to the exposure mask  74  to make images of the mask patterns  74   b  at a surface of the resist film  73 , resulting in latent images  73   a . Ultraviolet light transmitting through the apertures  76 - 1  of the mask  76  is diffused, and illumination at the gate layer pattern region  73   b  (dark portion) becomes uniform.  
      In this example where the auxiliary pattern is transparent, the exposure amount of light source is preferably defined to be smaller than in a case where no auxiliary pattern is provided, and preferably defined so as to make the exposure amount on the light receiving face as small as possible but more than a minimum threshold value for exposing the resist layer at desired regions. By weakly and equally illuminating the gate layer regions  73   b  and highly illuminating the exposed portions  73   a  and photo-etching only the portions  73   a , shortening of the gate layers can be suppressed.  
      On the other hand, in a case where the auxiliary patterns  12  are light shielding and are inside of the wiring patterns  11 , the exposure amount of the light source is preferably defined to be larger than in a case where no auxiliary pattern is provided. By increasing the illumination on the image-formed wiring pattern regions equally, shortening of the gate layers can be suppressed.  
      Next, in a step shown by  FIG. 11B , the resist film  73  is developed and the exposed portions  73   a  that are the latent images are removed from the resist film  73  to form gate layer patterns  73   b . Then by utilizing the gate layer patterns  73   b  as a mask, the poly-silicon film  72  and the gate oxide film  71  are anisotropically etched by the RIE (Reactive Ion Etching) method, for example, to form gate layers  75  each comprising a poly-silicon layer  72   a  and a gate oxide layer  71   a.    
      The exposure mask  74  shown in  FIG. 11A  comprises a transparent substrate  74   a  and a shielding mask film  76 . The transparent substrate  74   a  is made of Soda lime or Alumina silicate, etc. The shielding mask film  76  is made of an emulsion or inorganic material such as chrome, chrome oxide, silicon, silicon-germanium, etc. The mask pattern  74   b  is formed by the above mentioned lithography process or a similar process. A laser beam or electron beam can be used for directly writing on the resist film.  
      The projecting system of the exposure device of  FIG. 11A  may be a reducing projecting system, an enlarging projecting system or a contacting exposing system. The light source for the exposure system is not limited to ultraviolet light and may be an X-ray or an electron beam. The mask pattern  74   b  of the exposure mask  74  may be a mask pattern according to the first alternative example or the second alternative example of the first embodiment.  
      Further, the present invention is not limited to these embodiments, but various variations and modifications may be made without departing from the scope of the present invention. Prior art POC methods such as hammer head can be combined with the present invention.  
      The present application is based on  
      Japanese Priority Application No. 2004-196963 filed on Jul. 2, 2004 with the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.