Abstract:
The present invention provides a method of manufacturing a lens, in which the method includes exposing a photoresist to light using a phase shift mask. Here, the phase shift mask includes layout portions respectively corresponding to pixels and lens, in which each of the layout portions has: a light-blocking portion which has a shape of a substantially circle or a substantially concentric zone; a light-transmitting portion which has a shape of a substantially circle or a substantially concentric zone; a phase shift portion which has a shape of a substantially circle or a substantially concentric zone; and a light-blocking frame. Furthermore, the light-transmitting portion, the light-blocking portion and the phase shift portion are arranged alternately so as to form concentric circles, and the light-blocking frame corresponds to a whole or a part of a perimeter of the lens.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to a manufacturing method of a light-collecting device to be formed as a lens in a solid-state image sensor and the like, the light-collecting device, and to a phase shift mask. 
     (2) Description of the Related Art 
     In general, an apparatus which converts an image into an electric signal (this apparatus is referred to as an imaging apparatus) is used for an appliance which electromagnetically records an image such as a digital video recorder, a digital still camera, and a camera-equipped cellular phone which has been rapidly growing in number. In recent years, a charge-coupled device sensor which is a type of a semiconductor device (this is commonly called as a CCD sensor and is referred to as a CCD sensor, hereinafter) and a MOS sensor are used as such imaging apparatuses. The introduction of such sensors has contributed to make the appliance smaller and lower-priced. Each of these imaging apparatuses is made up of fine-pixels respectively including one photodiode that are arranged on a plane. Accordingly, performance of an imaging apparatus is determined depending on the performances of these number of pixels. The particularly significant performances of the imaging apparatus are a capability of converting a fine input image into an electric signal with low noise (i.e. high S/N ratio) and a capability of outputting the input image as a high electric signal (i.e. with high amplification factor). As a method for realizing a high S/N ratio and high amplification factor, a method of improving the S/N ratio and amplification factor of an imaging device in a pixel is generally suggested. Here, the following method is also commonly adopted. 
       FIG. 1  is a diagram showing a cross-section of a pixel unit in a typical conventional imaging apparatus. The pixel unit includes a pixel  901  and a light-collecting device  903  which is a lens. The pixel  901  includes a photodiode  902 , a color filter  904  and the like. The incident light  905  entering the pixel  901  is collected by the light-collecting device  903  and separated into one of red, blue and green light by the color filter  904 , and inputted into the photodiode  902 . The intensity and density of the incident light  905  entering the photodiode  902  is increased by the light-collecting device  903 . Therefore, the high S/N ratio and the improvement in amplification factor can be realized. Here, a problem is that a focal point of the light-collecting device  903  is changed along with the change of the incident angle of the incident light  905 , so that the light cannot be collected on the photodiode  902 . This is obvious in the case where the pixel  901  is a peripheral pixel in the imaging apparatus. In order to overcome this problem, there is a conventional technology of arranging light-collecting devices  903  in pixels so as to be asymmetrical to each other (e.g. Japanese Laid-Open Patent Application No. 2001-196568). In addition, there is another conventional technology of shifting the position of the light-collecting device  903  to the photodiode  902  in a peripheral pixel of the imaging apparatus. However, these conventional technologies are effective when the incident angle of the incident light  905  is relatively small. However, they are less effective for a larger incident angle. 
     SUMMARY OF THE INVENTION 
     Here, in order to maintain pixel characteristics even in the case where light enters at a large incident angle, there is a suggested technique of forming a light-collecting device, which is different from the technique used for the light-collecting device shown in  FIG. 1 , with light-transmission films  1001  which are processed into circles having the same center or into zones as shown in  FIGS. 3A and 3B . 
     However, it is difficult to fine-process, as a light-collecting device, the circles or zones as fine as a wavelength of natural light for image-taking as the light-transmitting films  1001  shown in  FIGS. 3A and 3B . Or, there is a problem that this fine-structured light-collecting device cannot be manufactured. 
     In general, for manufacturing a fine structure, in recent years, light exposure is performed with light of a short wavelength such as light using KrF (wavelength of 0.248 μm) or light using ArF (wavelength of 0.193 μm). Furthermore, a phase shift mask is used as a photomask for light exposure so as to realize the fine processing. There are two types of phase shift mask: a halftone type; and an interleave (Levenson) type. It is known that the Levenson type is more effective for the fine processing. The Levenson type phase shift mask (simply referred to as a phase shift mask, hereinafter) is characterized in that light-transmitting portions and phase shift portions are alternately arranged on both sides of respective light-blocking portions. Also, the light-transmitting portions and the phase shift portions cannot be connected to each other due to the structure of the phase shift mask. Therefore, the light-blocking portions always have to be placed between the light-transmitting portions and the phase shift portions. Light which passes through a phase shift portion is shifted 180° in phase compared to light which passes through a light-transmitting portion. 
     With respect to the light-collecting device shown in  FIGS. 3A and 3B , in the imaging plane in which pixels are arranged in a matrix, the image-collecting devices of the peripheral pixels are actually placed so as to be shifted from the center of the imaging plane. Therefore, a shape of the light-collecting device as shown in  FIG. 2  is repeatedly seen in the peripheral pixels.  FIG. 2  is a schematic diagram showing a top view of adjacent four pixels. In the diagram,  1102  indicates a pixel boundary and  1103   a  to  1103   c  indicate apertures. In order to manufacture a light collecting device using photolithography technique, a photomask must be used. The photomask has a light-blocking element placed in a region corresponding to the light-transmitting film  1001  and the apertures  1103  which allow transmission of light (whereas opposite case is available depending on a manufacturing method, it is assumed that the photomask has the light-blocking material placed in a region corresponding to the light-transmitting film  1001 , hereinafter). Furthermore, in order to realize a fine structure, this manufacturing method of a light-collecting device requires a process of light-exposure using a phase shift mask. However, it is difficult to apply a phase shift mask to the aforementioned shape. This is because the aperture  1103   a  and the aperture  1103   b  adjacent to the light-transmitting film  1001  are connected to the aperture  1103   c  of an adjacent pixel at the pixel boundary  1102 , so that this shape cannot be realized with a phase shift mask in which a light-transmitting portion, a light-blocking portion and a phase shift portion need to be alternatively arranged. For example, if a light-transmitting portion corresponds to the aperture  1103   a , a phase shift portion needs to correspond to the aperture  1103   b . Here, if the aperture  1103   c  is the light-transmitting portion, the aperture  1103   b  and the aperture  1103   c  are connected at the pixel boundary  1102  so that the light-transmitting portion and the phase shift portion are connected to each other. Thus, there is a problem that a fine structure cannot be realized in a light-collecting device having a substantially concentric zone shape as shown in  FIGS. 3A and 3B . 
     An object of the present invention is to provide a phase shift mask which facilitates the realization of a fine structure of a light-collecting device as a lens having a substantially concentric zone shape, a method of manufacturing a light-collecting device using the phase shift mask, and the light-collecting device. 
     In order to achieve the aforementioned object, a method of manufacturing a lens of the present invention includes exposing a photoresist to light using a phase shift mask, wherein the phase shift mask includes layout portions respectively corresponding to pixels and lens. Here, each of the layout portions has: a light-blocking portion which has a shape of a substantially circle or a substantially concentric zone; a light-transmitting portion which has a shape of a substantially circle or a substantially concentric zone; a phase shift portion which has a shape of a substantially circle or a substantially concentric zone; and a light-blocking frame, wherein the light-transmitting portion, the light-blocking portion and the phase shift portion are arranged alternately so as to form concentric circles, and the light-blocking frame corresponds to a whole or a part of a perimeter of the lens. 
     According to this structure, in the process of manufacturing a lens having a near-concentric zone shape, the lens can be easily fine-processed by placing a light-blocking frame. This is because that the light-blocking frame is always placed between the light-transmitting portions and the phase shift portions so that the light-transmitting portions and phase shift portions are not connected to each other at pixel boundaries. 
     Here, a width of the light-blocking frame may be as large as a minimum manufacturing dimension of the phase shift mask. 
     Here, a width of the light-blocking frame may be approximately 0.4 μm. 
     Here, the layout portions include a first layout portion corresponding to a first pixel, and four adjacent layout portions corresponding to four pixels which are respectively adjacent in all four directions to the first pixel. Phase shift portions may be positioned in regions of the adjacent layout portions, the regions corresponding to a region of the first layout portion in which a light-transmitting portion is positioned, and light-transmitting portions may be positioned in regions of the adjacent layout portions, the regions corresponding to a region of the first layout portion in which a phase shift portion is positioned. 
     With this structure, the frame placed on the lens corresponding to the light-blocking frame can be manufactured through more precise fine processing so that deterioration in characteristics due to distortion of the lens can be prevented. 
     Here, in the method of manufacturing a lens, the layout portions include a first layout portion corresponding to a first pixel, and a second layout portion corresponding to a pixel adjacent to the first pixel. A first section and a second section may be included in a light-blocking frame at which the first layout portion and the second layout portion are adjacent to each other; the first section may be smaller than the second section; the first section may be a section having phase shift portions on both sides of the light-blocking frame, and be a section having light-transmitting portions on both sides of the light-blocking frame; and the second section may be a section having a phase shift portion on one side of the light-blocking frame and a light-transmitting portion on the other side of the light-blocking frame. 
     With this structure, a lens can be fine-processed with lesser distortions. 
     Here, in the method of manufacturing a lens, the layout portions may include a first layout portion corresponding to a first pixel and a second layout portion corresponding to a second pixel adjacent to the first pixel. A light-blocking frame may be positioned in a specific section in a boundary between the first layout portion and the second layout portion, and the specific section may be a section having a phase shift portion on one side of the boundary and a light-transmitting portion on the other side of the boundary. 
     With this structure, by forming the light-blocking frame not on an entire perimeter of a layout portion that is one pixel but on a part of the perimeter, the deterioration in characteristics due to a frame placed on a corresponding lens can be controlled at minimum. 
     Here, the specific section may be smaller than other sections in the boundary of a perimeter of each layout portion. 
     Furthermore, the lens of the present invention includes light-collecting films which have a shape of substantially circles or substantially concentric zones, and a frame which surrounds a whole or a part of a perimeter of the lens. 
     According to this structure, a lens can be easily fine-processed by placing a frame. 
     Here, the frame may be made of a same material used for the light-transmitting film or be made of an absence of the light-transmitting film. 
     Here, a width of the frame may be obtained approximately by dividing a minimum manufacturing dimension of a phase shift mask by a light-exposure ratio. 
     Here, the width of the frame may be 0.1 μm or less. 
     Furthermore, a phase shift mask of the present invention is a phase shift mask used for manufacturing a lens. The phase shift mask includes layout portions respectively corresponding to pixels and lenses. Here, each of the layout portions has: a light-blocking portion which has a shape of a substantially circle or a substantially concentric zone; a light-transmitting portion which has a shape of a substantially circle or a substantially concentric zone; a phase shift portion which has a shape of a substantially circle or a substantially concentric zone; and a light-blocking frame, wherein the light-transmitting portion, the light-blocking portion and the phase shift portion are arranged alternately so as to form concentric circles, and the light-blocking frame corresponds to a whole or a part of a perimeter of the lens. 
     Here, a width of the light-blocking frame may be as large as a minimum manufacturing dimension of the phase shift mask. 
     Here, a width of the light-blocking frame may be approximately 0.4 μm. 
     As described in the above, according to the manufacturing method of the present invention, in a process of manufacturing a lens having a substantially concentric zone shape, a light-blocking frame is always positioned between the light-transmitting portion and the phase shift portion so that the light-transmitting portion and the phase shift portion do not connect to each other. Consequently, a fine processing can be facilitated. 
     Further, the frame placed on the lens corresponding to the light-blocking frame can be manufactured through more precise fine processing so that deterioration in characteristics due to distortion of the lens can be prevented. 
     Furthermore, according to the lens of the present invention, a fine processing can be facilitated in accordance with a shape of the lens. 
     In addition, with the phase shift mask of the present invention, the lens can be easily fine-processed and deterioration in characteristics due to distortion of the lens can be prevented. 
     As further information about technical background to this application, the disclosure of Japanese Patent Application No. 2005-178586 filed on Jun. 17, 2005 including specification, drawings and claims is incorporated herein by reference in its entirety. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects, advantages and features of the invention wilt become apparent from the following description thereof taken in conjunction with the accompanying drawings that illustrate a specific embodiment of the invention. In the drawings: 
         FIG. 1  is a diagram showing a cross-section of a pixel unit in an imaging device using a conventional technology; 
         FIG. 2  is a schematic diagram showing a top view of four adjacent pixels; 
         FIG. 3A  is a cross-section diagram of a light-collecting device according to a first embodiment of the present invention; 
         FIG. 3B  is a top view according to the first embodiment of the present invention; 
         FIG. 4A  is a diagram showing a structure of a phase shift mask used for manufacturing a light-collecting device; 
         FIG. 4B  to  FIG. 4E  are diagrams, each showing a process of manufacturing an imaging device; 
         FIG. 5  is a phase shift mask according to a second embodiment of the present invention; 
         FIG. 6A  is a diagram showing a shape of a photoresist in a manufacturing method according to the first embodiment; 
         FIG. 6B  is a diagram showing a shape of a photoresist in a manufacturing method according to the second embodiment; 
         FIG. 7A  and  FIG. 7B  are diagrams, each showing a structure of a phase shift mask according to a third embodiment of the present invention; 
         FIG. 8A  and  FIG. 8B  are diagrams, each showing a shape of a photoresist in a manufacturing method of a light-collecting device according to the second and third embodiments; 
         FIG. 9A  and  FIG. 9B  are diagrams, each showing a structure of a phase shift mask according to a fourth embodiment; 
         FIG. 10  is a diagram showing a structure of a phase shift mask according to a fifth embodiment; and 
         FIG. 11  is a diagram showing a shape of a photoresist in a manufacturing method of a light-collecting device according to the fifth embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention shall be described with reference to the drawings, hereinafter. In the drawings, same reference numbers indicate same constituent elements. 
     First Embodiment 
       FIG. 3A  is a diagram showing a cross-section of a pixel unit having a light-collecting device (a lens) according to the first embodiment.  FIG. 3B  shows a top view of the pixel unit. This pixel unit includes light-transmitting films  1001 , a substrate  1002 , a color filter  1003 , a photodiode  1004 , Aluminum wiring  1006 , a planarized film  1007 , and a frame  1008 . The light-transmitting films  1001  have been processed into a substantially circle shape or a substantially concentric zone shape. A radial difference between adjacent zones (the perimeter of the light-transmitting film  1001  in  FIG. 3B ) is assumed to be a constant value. The width of a zone is as long as a wavelength of natural light. The width of a zone is typically as long as 0.1 μm. The refractive index of the incident light  1005  which passes through the respective light-transmitting films  1001  and a medium (typically, air) is a mean value between a value of the refractive index of the light-transmitting film  1001  and a value of the refractive index of the medium (typically, air), in a region as large as a wavelength on the surface of the light-transmitting film  1001 . Since the width of a zone is very small, the refractive index of the incident light  1005  depends on the width of the zone, and becomes an intermediate value between the refractive index of the light-transmitting film  1001  and the refractive index of the medium. Specifically, the incident light  1005  enters the light transmitting films  1001  in which refractive indexes are concentrically distributed. Due to this refractive index distribution, the incident light  1005  which has passed through the respective light-transmitting films  1001 , and the medium (typically, air) and the substrate  1002  is collected by a diffraction effect and reaches the photodiode  1004 . A position where the incident light  1005  is collected can be controlled by changing a shape of the light-transmitting films  1001 . Accordingly, incident light can be collected by the photodiode  1004  without causing performance deterioration by designing the shape of the light-transmitting films  1001  in consideration with an incident angle of the incident light  1005 . The light-collecting efficiency thus can be increased even in the case where light enters at a large incident angle. The frame  1008  is made of the light-transmitting films so as to surround entire periphery of the pixel unit. The frame  1008  in  FIG. 3B  may surround only a part of the periphery instead of surrounding the entire periphery. Here, the width of the frame is 0.1 μm or less. It should be noted that the frame  1008  in  FIG. 3B  is made of a light-transmitting film. However, the frame  1008  may be formed with the absence of the light-transmitting film (i.e. air) instead. With the formation of this frame  1008 , a fine-processing can be realized using the phase shift mask. 
       FIG. 4  is a diagram showing a structure of the phase shift mask used for manufacturing a light-collecting device shown in  FIG. 3A . This phase shift mask includes light-blocking portions  101 , phase shift portions  102 , light-transmitting portions  103 , and light-blocking frames  104  that are formed as shown in  FIG. 4A . The light-blocking portions  101 , the phase shift portions  102  and the light-transmitting portions  103  are shaped into concentric circles having a same center or zones. 
     In the phase shift mask, there is a restriction that a light-transmitting portion and a phase shift portion should not be adjacent to each other so that a light-blocking portion has to be placed between them. In the phase shift mask shown in  FIG. 4A , the light-blocking frames  104  are placed so as to surround the pixel layout  108 . The width of the light-blocking frame  104  may be a minimum manufacturing dimension of the phase shift mask, which is, for example, about 0.4 μm. Thus, by placing the light-transmitting portions  103  and the phase shift portions  102  in the pixel layout  108  so as not to be adjacent to each other, the light-blocking frame  104  prevents the light-transmitting portion  103  and the phase shift portion  102  from being adjacent to each other at the boundary with adjacent pixels. The above restriction is thus satisfied. 
     Hereinafter, the method of manufacturing a light-collecting device according to the first embodiment of the present invention shall be described in order of manufacturing processes.  FIGS. 4B to 4E  are diagrams showing processes of manufacturing an imaging device using a phase shift mask shown in  FIG. 4A . 
     As shown in  FIG. 4B , first, a substrate  107  and the light-transmitting film  106  are uniformly formed on the top surface of the pixel  108 . A photoresist  105  is applied on top of the light-transmitting film  106 . The photoresist  105  is then exposed to light using the phase shift mask shown in  FIG. 4A  and developed.  FIG. 4C  shows the result of the development. In the phase shift mask shown in  FIG. 4A , the light-transmitting portion  103  is placed in an adjacent region on one side of the light-blocking portion  101 , and the phase shift portion  102  is placed in an adjacent region on the other side of the light-blocking portion  101 . Consequently, even in the case where the width of the light-blocking portion  101  is very small, light transmitted by the light-transmitting portion  103  and light transmitted by the phase shift portion  102  cancel each other out under the light-blocking portion  101 , and the photoresist  105  is exposed to light with the shape of the light-blocking portion  101 . Thus, a fine-processing can be easily realized. 
     After the photoresist  105  is exposed to light and developed as shown in  FIG. 4C , the light-transmitting film  101  is etched using the photoresist  105  as an etching mask, and is processed into the shape of a phase shift mask as shown in  FIG. 4A  ( FIG. 4D ). Finally, the photoresist  105  is removed ( FIG. 4E ). 
     It should be noted that the structure of the imaging apparatus shown in  FIGS. 4B to 4E  is explained as an example, the structure may exclude the substrate  107  and include the light-transmitting film positioned directly on the pixel  108  (in this case, the pixel  108  is considered as a substrate). Furthermore, in the case where the top surface of the pixel  108  or the substrate  107  is flat, the pixel  108  and the substrate  107  may be structured differently from the structure shown in  FIG. 4 . 
     Second Embodiment 
     The following problem is found in the method of manufacturing the light-collecting device according to the aforementioned first embodiment.  FIG. 6A  is a diagram showing a shape of the photoresist  105 , which is calculated by simulation, in the process shown in  FIG. 4C  according to the first embodiment of the present invention. In the diagram, white regions indicate where the photoresist  105  is to be remained and black regions indicate where the photoresist  105  is to be removed by development, seen from the top. In  FIG. 6A , it is found that a portion corresponding to the peripheral light-blocking frames  104  of the pixel layout  108  cannot be formed precisely. In other words, whereas the light-blocking frames  104  are formed on the corners of the pixel layout  108 , they are not formed in regions other than the corners. Therefore, it is assumed that the shape of the light-collecting device is distorted and the characteristics are deteriorated. Accordingly, in the second embodiment of the present invention, the following manufacturing method is adopted in order to precisely forming the light-blocking frames  104 . 
       FIG. 5  shows a diagram showing a structure of the phase shift mask according to the second embodiment. This phase shift mask includes, for each pixel, a light-blocking portion  201 , a light-transmitting portion  202 , a phase shift portion  203 , and a light-blocking frame  204 . The phase shift mask includes two patterns of a fist pixel layout  205  and a second pixel layout  206 . The first pixel layout  205  and the second pixel layout  206  are adjacent to each other. The phase shift mask shown in  FIG. 5  is characterized in that the light-transmitting portions  202  and the phase shift portions  203  placed in the first pixel layout  205  are arranged in reverse in the second pixel layout  206 . 
     The method of manufacturing a light-collecting device according to the second embodiment of the present invention is same as the manufacturing method according to the first embodiment of the present invention shown in  FIGS. 4B to 4E , except using the phase shift mask shown in  FIG. 5 . In the phase shift mask shown in  FIG. 5 , the light-transmitting portion  202  is placed in a region on one side of the light-blocking frame  204  and the phase shift portion  203  is placed in a region on the other side of the light-blocking frame  204 . Therefore, at the time of light exposition, light transmitted by the light-transmitting portion  202  and light transmitted by the phase shift portion  203  cancel each other out under the light-blocking frame  204 , so that the light-blocking frames  204  are also precisely developed and formed. 
       FIG. 6B  shows a simulation result of a shape of the photoresist in the case of the method of manufacturing the light-collecting device according to the second embodiment. Compared with the case of the first embodiment of the present invention shown in  FIG. 6A , it can be seen that regions corresponding to light-blocking frames  204  are also precisely developed. 
     Third Embodiment 
     The following problem is found in the method of manufacturing the light-collecting device according to the aforementioned second embodiment.  FIG. 7A  is a diagram showing a structure of a phase shift mask used for a method of manufacturing a light-collecting device according to the third embodiment of the present invention. The difference between the phase shift mask in  FIG. 7A  and the phase shift mask in  FIG. 5  is that  FIG. 5  shows a shape of light-collecting devices placed near the center of the imaging plane in which pixels are arranged in a matrix while  FIG. 7A  shows a shape of light-collecting devices placed in the periphery of the imaging plane. In other words, each of the light-collecting devices shown in  FIG. 7A  is placed being shifted toward the center of the imaging plane. This phase shift mask includes light-blocking portions  401 , light-transmitting portions  402 , phase shift portions  403  and light-blocking frames  404 . The phase shift portions  403  are placed on both sides of the light-blocking frames  404 .  FIG. 8A  shows a simulation result of a shape of the photoresist after being exposed to light using the phase shift mask shown in  FIG. 7A . In  FIG. 8A ,  501  shows regions corresponding to portions of the light-blocking frames  404 . Here, it can be seen that there is a problem that the light-blocking frames  404  are distorted from the original shape designed by the phase shift mask. In other words, the second embodiment also has a problem to be solved that is the remaining distortion of the shape. 
       FIG. 7B  shows a structure of another phase shift mask used for the method of manufacturing the light-collecting device according to the third embodiment. In  FIG. 7A , phase shift portions  403  are placed on both sides of portions of the light-blocking frames  404 . Therefore, light is leaked under the light-blocking frames at the time of light exposition, which causes a problem of distorting the shape of the photoresist  501 . This is because the arrangement of the light-transmitting portions and the phase shift portions are simply reversed among adjacent pixel layouts placed on the right, left, top and bottom. In  FIG. 7B , the arrangements of the phase shift portions  403  and the light-transmitting portions  402  in pixel layouts are determined so that portions (i.c.  404 ) where the phase shift portions  403  are placed on both sides of the light-blocking frames are minimized. The arrangements of the phase shift portions  403  and light-transmitting portions  402  in pixel layouts are also similarly determined so that portions where the light-transmitting portions  402  are placed on both sides of the light-blocking frames are minimized. A portion  404 ′ of the light-blocking frame in  FIG. 7B  has the light-transmitting portion  402  on one side and the phase shift portion  403  on the other side. Therefore, as shown in  FIG. 5B , the distortions are lessened in the shape of the photoresist generated by the phase shift mask of  FIG. 7B  so that the aforementioned problem is overcome. Other manufacturing processes are same as those in the first and second embodiments according to the present invention. 
     Fourth Embodiment 
     In the aforementioned first to third embodiments, a phase shift mask in which light-blocking frames are arranged all around the pixel layouts is used. However, the light-blocking frames are not always necessary in the case where the light-transmitting portions are adjacent to each other at the pixel boundaries, or in the case where the phase shift portions are adjacent to each other at the pixel boundaries. The light-blocking frames are only necessary for the region in which the light-transmitting portions and the phase shift portions are adjacent to each other at the pixel boundaries. The phase shift masks shown in  FIGS. 9A and 9B  are used for the method of manufacturing the light-collecting device according to the fourth embodiment of the present invention, and the light-blocking frames are placed only on the regions in which the light-transmitting portions and the phase shift portions are adjacent to each other at the pixel boundaries. Other manufacturing processes are same as those in the first and third embodiments. 
       FIG. 9A  shows a phase shift mask used for manufacturing pixels positioned in the center of the imaging device. This phase shift mask includes light-blocking portions  601 , light-transmitting portions  602 , and phase shift portions  603 . Since perimeters of pixel layouts are all made of phase shift portions, the light-blocking frames are not present in  FIG. 9A . 
       FIG. 9B  shows a phase shift mask used for manufacturing pixels positioned in the periphery of the imaging device. The light-blocking frames  604  are placed only in the regions in which the phase shift portions  603  and the light-transmitting portions  602  are adjacent to each other at the pixel boundaries. 
     Fifth Embodiment 
     In the aforementioned fourth embodiment, as shown in  FIGS. 9A and 9B , the light-blocking frames are placed only in the regions in which the light-transmitting portions and the phase shift portions are adjacent to each other at the pixel layout boundaries. The light-blocking frames are unnecessary for the structure of a light-collecting device itself. The decrease in an area of the light-blocking frame results in an increase in the area of the light-collecting device. Therefore, the characteristics of the light-collecting device are improved. Furthermore, the unevenness of the optical characteristics due to the light-blocking frames can be reduced. 
       FIG. 10  is a diagram showing a structure of a phase shift mask which is used for the purpose of improving characteristics of the light-collecting device by minimizing the area of the light-blocking frames. This phase shift mask includes light-blocking portions  701 , light-transmitting portions  702 , and phase shift portions  703 . Firstly, in each pixel, the light-transmitting portions  702  and the phase shift portions  703  are arranged so that the light-transmitting portions  702  and the phase shift portions  703  are adjacent to each other at each pixel layout boundary with a minimum area. Next, the light-blocking frames are placed only in the regions in which the light-transmitting portions  702  and the phase shift portions  703  are adjacent to each other at each pixel layout boundary. Following this procedure, an area of the light-blocking frames can be minimized and the characteristics of the light-collecting device can be maximized. The phase shift mask shown in  FIG. 10  has a structure which does not require the light-blocking frames.  FIG. 11  is a diagram which shows a shape of the photoresist obtained by simulation. In the light-collecting device, frames are buried in the light-transmitting film (or a region in which the light-transmitting film does not exist). 
     Other manufacturing processes are same as those described in the first and fourth embodiments according to the present invention. Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be construed as being included therein.