Patent Publication Number: US-2015076644-A1

Title: Method for manufacturing solid-state image sensor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for manufacturing a solid-state image sensor. 
     2. Description of the Related Art 
     A solid-state image sensor can employ a recess structure in which the upper surface of a portion including a wiring pattern and an interlayer insulation film provided on a substrate is higher in a region immediately above the peripheral portion of a pixel array than in a region immediately above the pixel array, and have steps (a height difference) on the upper surface. In the process of manufacturing the solid-state image sensor, this height difference may cause stripes and unevenness (so-called striations) in a film formed by spin coating. Hence, it is not preferable to locally form such height difference. 
     Japanese Patent Laid-Open No. 2008-270500 discloses a recess structure in which a stepwise height difference including a plurality of steps is provided so as not to locally form a height difference on an upper surface. According to Japanese Patent Laid-Open No. 2008-270500, when a wiring pattern and an interlayer insulation film are formed on a substrate, a plurality of wiring patterns are provided in advance on the above-described peripheral portion such that a distance from the boundary between a pixel array and its peripheral portion becomes larger in an upper layer than in a lower layer. That is, the plurality of wiring patterns are formed such that an opening increases in size from the lower layer to the upper layer. After that, etching is performed on an insulation member immediately above the pixel array, thereby forming the recess structure. When the etching is performed, each of the plurality of wiring patterns described above is used as an etching mask. As a result of removing the portion of the insulation member which is not covered by each wiring pattern, the recess structure having the stepwise height difference on the upper surface is formed. 
     However, according to this method, the upper surface of each wiring pattern suffers damage by etching. This may cause a loss in quality of the solid-state image sensor. 
     SUMMARY OF THE INVENTION 
     The present invention provides a technique advantageous in improving the quality of a solid-state image sensor with a recess structure. 
     One of the aspects of the present invention provides a method for manufacturing a solid-state image sensor, comprising preparing a substrate including a pixel region where a plurality of pixels are provided and a peripheral region located outside the pixel region, forming a structure including a wiring layer and an interlayer insulation film on the pixel region and the peripheral region of the substrate, forming a first wiring pattern only on the structure located in the peripheral region, forming a protective film covering the first wiring pattern and the structure, forming a second wiring pattern on a convex portion of the protective film, the convex portion formed by steps between an upper surface of the first wiring pattern and an upper surface of the structure, so that an end of the second wiring pattern is located away from the pixel region than an end of the first wiring pattern in a state in which the protective film covers the first wiring pattern, and forming an optical member on the structure of the pixel region. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view for explaining an example of the arrangement of a solid-state image sensor; 
         FIGS. 2A to 2I  are views for explaining an example of a method for manufacturing the solid-state image sensor; 
         FIGS. 3A to 3I  are views for explaining another example of a method for manufacturing a solid-state image sensor; 
         FIGS. 4A to 4J  are views for explaining still another example of a method for manufacturing a solid-state image sensor; 
         FIGS. 5A to 5J  are views for explaining still another example of a method for manufacturing a solid-state image sensor; and 
         FIGS. 6A to 6D  are views for explaining another example of the arrangement of a solid-state image sensor. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     First Embodiment 
     A method for manufacturing a solid-state image sensor I1 according to the first embodiment will be described with reference to  FIG. 1  and  FIGS. 2A to 2I .  FIG. 1  schematically illustrates an example of the sectional structure of the solid-state image sensor I1. The solid-state image sensor I1 can include a substrate SUB including a pixel region R1 and a peripheral region R2, a structure ST1 provided on the substrate SUB, a structure ST2 provided on the structure ST1, and an optical system OP made of optical members. 
     A pixel array in which a plurality of pixels are arrayed is formed in the pixel region R1. In the pixel region R1, photoelectric conversion portions  101 , and (the gates of) transistors  102  configured to read out charges generated and accumulated in the photoelectric conversion portions  101  as pixel signals are illustrated as the components of the respective pixels. The components of the respective pixels represent elements provided on the substrate SUB below. The peripheral region R2 is a region peripheral to the pixel region R1. For example, a driving unit configured to drive the respective pixels and a processor configured to process the pixel signals read out from the respective pixels can be arranged in the peripheral region R2. 
     The peripheral region R2 is located outside the pixel region R1 on the substrate SUB. The number of layers of a wiring pattern provided in the peripheral region R2 is larger than that in the pixel region R1. A boundary K between the pixel region R1 and the peripheral region R2 can be decided by, for example, the end of the wiring pattern which has more layers than in the pixel region R1. Also, the peripheral region R2 may include an optical black pixel region where, for example, wiring patterns for light-shielding (light-shielding patterns) are provided more than effective pixels that light can enter. 
     The structure ST1 includes wiring layers and interlayer insulation films. In the structure ST1, interlayer insulation films  103 ,  105 , and  107 , the first wiring layer which includes a wiring pattern  104  provided between the interlayer insulation films  103  and  105 , and the second wiring layer which includes a wiring pattern  106  provided between the interlayer insulation films  105  and  107  are illustrated. 
     The structure ST2 can be provided above the peripheral region R2, and include wiring patterns  108  and  110 , and an insulation member  109  (interlayer insulation film) provided between the wiring patterns  108  and  110 . In a planar view, the distance from the boundary K between the pixel region R1 and the peripheral region R2 to the end portion of the wiring pattern  110  is larger than the distance from the boundary K to the end portion of the wiring pattern  108 . On the above-described structures ST1 and ST2, a passivation film  111  can be provided to cover them. 
     The optical system OP (optical members) can be provided above the pixel region R1, and include a first planarization film  112 , a color filter  113 , a second planarization film  114 , and microlenses  115 . The planarization films  112  and  114  are films configured to form a flat upper surface so as to advantageously perform the formation process of members (such as the color filter  113  and the microlenses  115 ) to be formed later. The color filter  113  is provided corresponding to each pixel (of the photoelectric conversion portion  101 ) in accordance with, for example, Bayer arrangement. Each microlens  115  is provided corresponding to each pixel. 
     As described above, the solid-state image sensor I1 employs a so-called recess structure in which the upper surface of a portion including the wiring pattern (such as  104 ) and the interlayer insulation film (such as  103 ) provided on the substrate SUB is higher in a portion immediately above the peripheral region R2 than in a portion immediately above the pixel region R1. According to this structure, in the vicinity of the boundary K between the pixel region R1 and the peripheral region R2, a height difference on the upper surface of this structure is formed to be stepwise including the plurality of steps, but not formed locally. Therefore, according to this structure, for example, when a film is formed by spin coating in the formation process of the optical system OP or the like to be performed later, stripes and unevenness (so-called striations) that may occur in the film can be prevented. 
     The method for manufacturing the solid-state image sensor I1 will be described below with reference to  FIGS. 2A to 2I . The solid-state image sensor I1 can be manufactured using a known semiconductor process. 
     First, as exemplified in  FIG. 2A , the substrate SUB is prepared, and the structure ST1 is formed on the substrate SUB. As the substrate SUB, a semiconductor substrate such as a silicon substrate may be prepared by forming the respective elements (for example, the photoelectric conversion portions  101  and the transistors  102 ) on the substrate, or a substrate on which various kinds of elements are already formed may be prepared. In  FIG. 2A , a structure which includes the wiring layers made of two layers, namely the wiring patterns  104  and  106  is illustrated as the structure ST1. However, the structure ST1 is not limited to this as long as it can be the base of the structure ST2 to be formed later. Then, a photoresist pattern  116   a  which has an opening in a region including the pixel region R1 is formed on the structure ST1. 
     Note that in the structure ST1, the interlayer insulation film may be made of an insulating material, and can be formed by, for example, a High Density Plasma CVD method. The interlayer insulation film can include, for example, an NSG (Non-doped Silicate Glass) film, a PSG (Phosphorus SG) film, and a BPSG (Boron Phosphorus SG) film. Metal materials such as Al, Cu, AlCu, TiN, and Ti are used for the wiring patterns of the respective wiring layers. Each wiring pattern may be formed by a single layer or a multilayer. In the description below, the same applies to the respective processes for forming the structure ST2. 
     As exemplified in  FIG. 2B , the interlayer insulation film  107  in the structure ST1 is etched using the photoresist pattern  116   a . This removes a part of the interlayer insulation film  107  above the pixel region R1. Note that the part can be removed to leave the interlayer insulation film  107  having a film thickness of, for example, 0.25 μm. Then, the photoresist pattern  116   a  is removed. 
     As exemplified in  FIG. 2C , a metal member  108   a  is formed by depositing the metal material on the interlayer insulation film  107  in the structure ST1, and a photoresist pattern  116   b  is additionally formed. 
     As exemplified in  FIG. 2D , the metal material  108   a  is then etched using the photoresist pattern  116   b . This forms the wiring pattern  108  above the peripheral region R2. Then, the photoresist pattern  116   b  is removed. 
     As exemplified in  FIG. 2E , the insulation member  109  is formed to cover the wiring pattern  108  and the structure ST1, and a photoresist pattern  116   c  is additionally formed. The distance from the boundary K to the end portion of the photoresist pattern  116   c  is larger than the distance from the boundary K to the end portion of the photoresist pattern  116   b.    
     As exemplified in  FIG. 2F , a part of the insulation member  109  is then removed using the photoresist pattern  116   c . Note that the part can be removed to leave the insulation member  109  having a film thickness of, for example, 0.25 μm. The insulation member  109  functions as a protective film to protect the wiring pattern  108  in the subsequent formation process of the wiring pattern  110 . Then, the photoresist pattern  116   c  is removed. The protective film has a convex portion formed by covering the steps between the upper surface of the wiring pattern  108  and that of the structure ST1. The side surface of the convex portion is located closer to the pixel region than the end of the first wiring pattern. That is, the distance from the boundary K to the side surface of the convex portion is smaller than the distance from the boundary K to the end of the first wiring pattern. 
     As exemplified in  FIG. 2G , a metal member  110   a  is formed by depositing the metal material on the insulation member  109 , and a photoresist pattern  116   d  is additionally formed. The distance from the boundary K to the end portion of the photoresist pattern  116   d  is larger than the distances from the boundary K to the end portions of the photoresist patterns  116   b  and  116   c , respectively. 
     As exemplified in  FIG. 2H , the metal member  110   a  is then etched using the photoresist pattern  116   d . This forms the wiring pattern  110  on the convex portion formed by the steps between the upper surface of the wiring pattern  108  of the insulation member  109  and the upper surface of the structure ST1. The distance between the boundary K to the end portion of the wiring pattern  110  is larger than the distance between the boundary K to the end portion of the wiring pattern  108 . Then, the photoresist pattern  116   d  is removed. 
     As described above, the structure ST2 can be formed. According to the above-described manufacturing method, since the wiring pattern  108  is covered by the insulation member  109 , damage to the wiring pattern  108  in the respective steps is prevented. When the uppermost interlayer insulation film  107  in the structure ST1 is etched, the wiring pattern  108  is not used as an etching mask. As a result, the upper surface of the interlayer insulation film  107  is flat in the vicinity of the end of the wiring pattern  108 . The vicinity of the end need at least include a region which extends from the end to the side of the pixel region R1, and may include the vicinity of the end outside the pixel region R1 in addition to the vicinity of the end inside the pixel region R1. Furthermore, since the wiring pattern  108  is not used as the etching mask, damage to the wiring pattern  108  can be reduced. 
     Note that in the structure ST2, the arrangement which includes the wiring layers made of two layers, namely the wiring patterns  108  and  110  is illustrated. However, the present invention is not limited to this arrangement, and also applies to a case where the arrangement includes three or more wiring layers. 
     Finally, as exemplified in  FIG. 2I , the solid-state image sensor I1 is obtained by forming the passivation film  111  and the optical system OP as described above. The passivation film  111  and the respective members which make up the optical system OP can be deposited by spin coating. However, according to the above-described manufacturing method, the height difference on the upper surface is formed to be stepwise including the plurality of steps, but not formed locally. Therefore, the respective films can uniformly be formed. 
     As described above, the aforementioned recess structure is formed. The height difference on the upper surface of the structure in the vicinity of the boundary K is formed to be stepwise including the plurality of steps. According to the above-described manufacturing method, the individual sizes of the plurality of steps are small as compared to a case where a local step (for example, one large step) is formed. Furthermore, according to the above-described manufacturing method, additional steps can also be formed in the insulation member  109  between the wiring patterns  108  and  110 . This is therefore advantageous in preventing a striation that may occur when forming a film by spin coating later. According to the above-described manufacturing method, since the wiring pattern  108  is covered by the insulation member  109  which functions as the protective film, damage to the wiring pattern  108  can be prevented. Accordingly, this embodiment is advantageous in improving the quality of a solid-state image sensor with a recess structure. 
     Second Embodiment 
     The second embodiment will be described with reference to  FIGS. 3A to 3I . In the above-described first embodiment, the insulation member  109  which serves as the interlayer insulation film is formed as the protective film of the wiring pattern  108  in the formation process of the structure ST2. However, the present invention is not limited to this mode. The protective film and the interlayer insulation film may individually be formed as in this embodiment. 
     First, as exemplified in  FIG. 3A , a substrate SUB is prepared, and a structure ST1 2  is formed on the substrate SUB. In this embodiment, the structure ST1 2  includes an etching stopper STP formed by using the same material as a protective film PRT (to be described later) under an uppermost interlayer insulation film  107  (between a wiring layer including a wiring pattern  106  and the interlayer insulation film  107 ). For example, silicon oxynitride (SiON) or silicon nitride (SiN) can be used for the etching stopper STP. Then, a photoresist pattern  116   a  which has an opening in a region including a pixel region R1 is formed on the structure ST1 2 . 
     As exemplified in  FIG. 3B , the interlayer insulation film  107  is then etched using the photoresist pattern  116   a . This removes the upper portion of the interlayer insulation film  107  in the pixel region R1. Since the structure ST1 2  includes the etching stopper STP in this embodiment, the portion can be removed to expose the upper surface of the etching stopper STP. Then, the photoresist pattern  116   a  is removed. 
     As exemplified in  FIG. 3C , a metal member  108   a  is formed by depositing a metal material on the interlayer insulation film  107  in the structure ST1 2 , and a photoresist pattern  116   b  is additionally formed. 
     As exemplified in  FIG. 3D , the metal material  108   a  is then etched using the photoresist pattern  116   b . This forms a wiring pattern  108  above a peripheral region R2. Then, the photoresist pattern  116   b  is removed. 
     As exemplified in  FIG. 3E , the protective film PRT is formed to cover the wiring pattern  108  and the structure ST1 2 , an insulation member  109  is formed to cover the protective film PRT, and a photoresist pattern  116   c  is additionally formed. For example, silicon oxynitride (SiON) or silicon nitride (SiN) can be used for the protective film PRT. The protective film PRT functions as a protective film to protect the wiring pattern  108  in the subsequent formation process of a wiring pattern  110 . 
     As exemplified in  FIG. 3F , a part of the insulation member  109  is then removed using the photoresist pattern  116   c , and an insulating pattern  109 ′ is formed. Then, the photoresist pattern  116   c  is removed. 
     As exemplified in  FIG. 3G , a metal member  110   a  is formed by depositing the metal material on the insulating pattern  109 ′ and the protective film PRT, and a photoresist pattern  116   d  is additionally formed. 
     As exemplified in  FIG. 3H , the metal member  110   a  is then etched using the photoresist pattern  116   d . This forms the wiring pattern  110  on the insulating pattern  109 ′. The distance between a boundary K to the end portion of the wiring pattern  110  is larger than the distance between the boundary K to the end portion of the wiring pattern  108 . Then, the photoresist pattern  116   d  is removed. 
     As described above, the structure ST2 2  can be formed. According to the above-described manufacturing method, since the wiring pattern  108  is covered by the protective film PRT, damage to the wiring pattern  108  in the respective steps is prevented. When the uppermost interlayer insulation film  107  in a structure ST1 is etched, the wiring pattern  108  is not used as an etching mask. As a result, the upper surface of the uppermost interlayer insulation film  107  in the structure ST1 is flat in the vicinity of the end of the wiring pattern  108  (at least in the region which extends from the end to the side of the pixel region R1). 
     Finally, as exemplified in  FIG. 3I , a solid-state image sensor I2 is obtained by forming a passivation film  111  and an optical system OP as described above. 
     As described above, according to this embodiment as well, a stepwise recess structure in which there are a plurality of steps on an upper surface is formed as in the first embodiment. 
     According to the above-described manufacturing method, since the wiring pattern  108  is covered by the protective film PRT, damage to the wiring pattern  108  can be prevented. Accordingly, this embodiment is advantageous in improving the quality of a solid-state image sensor with a recess structure. 
     Third Embodiment 
     The third embodiment will be described with reference to  FIGS. 4A to 4J . In the above-described second embodiment, the mode in which the etching stopper STP and the protective film PRT remain above the pixel region R1 has been exemplified. However, the present invention is not limited to this mode. After the etching stopper STP and the protective film PRT undergo a predetermined process, they may be removed as needed.  FIGS. 4A to 4G  are the same as  FIGS. 3A to 3I , and a description thereof will be omitted. 
     As exemplified in  FIG. 4H , a photoresist pattern  116   e  is additionally formed after forming a wiring pattern  110  on an insulating pattern  109 ′. The photoresist pattern  116   e  has an opening at least above a pixel region R1. 
     As exemplified in  FIG. 4I , an etching stopper STP and a protective film PRT are then removed by etching using the photoresist pattern  116   e . Note that this etching can be performed by setting a selectivity condition so that the etching rates of the etching stopper STP and the protective film PRT are higher than that of an interlayer insulation film. 
     Finally, as exemplified in  FIG. 4J , a solid-state image sensor I3 is obtained by forming a passivation film  111  and an optical system OP as described above. 
     As described above, according to the this embodiment as well, a stepwise recess structure in which there are a plurality of steps on an upper surface is formed as in the first and the second embodiments. According to the above-described manufacturing method, the upper portion of the etching stopper STP and the protective film PRT in the pixel region R1 is removed before forming the optical system OP. Consequently, the distance between the optical system OP and a substrate SUB can be made smaller than those in the above-described respective embodiments. Furthermore, scattering of light that may occur in these respective layers can be prevented. Therefore, according to this embodiment, it is possible to improve the light sensitivity of the solid-state image sensor I3, in addition to obtaining the same effects as in the first and the second embodiments. 
     Note that in the third embodiment, the mode in which both of the etching stopper STP and the protective film PRT are removed using the same material for the etching stopper STP and the protective film PRT has been exemplified. However, the present invention is not limited to this mode. For example, different materials may be used for the etching stopper STP and the protective film PRT, and the protective film PRT may be removed while leaving the etching stopper STP in the step of  FIG. 4I . 
     Fourth Embodiment 
     The fourth embodiment will be described with reference to  FIGS. 5A to 5J . In the above-described third embodiment, the mode in which the etching stopper STP and the protective film PRT are removed by etching using the photoresist pattern  116   e  has been exemplified. However, the present invention is not limited to this mode. The etching stopper STP and the protective film PRT can be removed by another method.  FIGS. 5A to 5G  are the same as  FIGS. 3A to 3I  and  FIGS. 4A to 4J , and a description thereof will be omitted. 
     After forming a wiring pattern  110  on an insulating pattern  109 ′ as exemplified in  FIG. 5H , the exposed portions of an etching stopper STP and a protective film PRT are removed by etching as exemplified in  FIG. 5I . This etching can be performed by setting a selectivity condition so that the etching rates of the etching stopper STP and the protective film PRT are higher than that of an interlayer insulation film. 
     Finally, as exemplified in  FIG. 5J , a solid-state image sensor I4 is obtained by forming a passivation film  111  and an optical system OP as described above. 
     As described above, according to the this embodiment as well, a stepwise recess structure in which there are a plurality of steps on an upper surface is formed as in the first to the third embodiments. According to the above-described manufacturing method, the upper portion of the etching stopper STP and the protective film PRT in a pixel region R1 is removed before forming the optical system OP. Consequently, the distance between the optical system OP and a substrate SUB can be made smaller than those in the above-described respective embodiments. Therefore, according to this embodiment, it is possible to obtain the same effects as in the third embodiment. 
     Fifth Embodiment 
     The fifth embodiment will be described with reference to  FIG. 6A . In the fifth embodiment, an insulation member  109  is provided under a wiring pattern  110 . In a planar view, the distance from the boundary K to the end portion of the wiring pattern  110  is larger than the distance from a boundary K to the end portion of the insulation member  109 . Microlenses  115  are provided between two end portions of the insulation member  109  in  FIG. 6A . In this arrangement as well, it is possible to form a stepwise recess structure in which there are a plurality of steps on an upper surface as in the first to the fourth embodiments. 
     Sixth Embodiment 
     The sixth embodiment will be described with reference to  FIG. 6B . Unlike the structure in the fifth embodiment, a protective film  1101  is additionally provided under a wiring pattern  110  in the sixth embodiment. In a planar view, the distance from a boundary K to the end portion of the protective film  1101  is larger than the distance from the boundary K to the end portion of an insulation member  109 , and smaller than the distance from the boundary K to the end portion of the wiring pattern  110 . In this arrangement as well, it is possible to form a stepwise recess structure in which there are a plurality of steps on an upper surface as in the first to the fifth embodiments. 
     Seventh Embodiment 
     The seventh embodiment will be described with reference to  FIG. 6C . Unlike the structure in the sixth embodiment, the parts of insulation members  109  and  107  are removed, and the end portions of the insulation members  109  and  107  are located in the same plane in the seventh embodiment. In this arrangement as well, it is possible to form a stepwise recess structure in which there are a plurality of steps on an upper surface as in the first to the sixth embodiments. 
     Eighth Embodiment 
     The eighth embodiment will be described with reference to  FIG. 6D . Unlike the structure in the seventh embodiment, the part of an insulation member  109  is further removed, and the insulation member  109  has two end portions whose distances from a boundary K are different in the eighth embodiment. In this arrangement as well, it is possible to form a stepwise recess structure in which there are a plurality of steps on an upper surface as in the first to the seventh embodiments. 
     The plurality of embodiments have been described above. However, the present invention is not limited to these. Changes and modifications can appropriately be made in accordance with objects, states, application purposes, functions, and other specifications, and the present invention can also be implemented by other embodiments. 
     (Imaging System) 
     In the above embodiments, the present invention has been described by exemplifying a solid-state image sensor included in an imaging system represented by a camera or the like. The concept of the imaging system includes not only apparatuses primarily aiming at shooting but also apparatuses (for example, personal computer and portable terminal) secondarily having a shooting function. The imaging system can include the solid-state image sensor according to the present invention exemplified in the above embodiments, and a processor that processes a signal output from the solid-state image sensor. The processor can include, for example, an A/D converter, and a processor that processes digital data output from the A/D converter. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2013-193486, filed Sep. 18, 2013, which is hereby incorporated by reference herein in its entirety.