Patent Publication Number: US-2011074049-A1

Title: Method of manufacturing semiconductor device, mask and semiconductor device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of manufacturing a semiconductor device by performing connective exposure. The present invention also relates to a mask employed in the method of manufacturing a semiconductor device and a semiconductor device manufactured by this method. 
     2. Description of the Background Art 
     Connective exposure is performed in order to manufacture a semiconductor device such as an image sensor having an element size (device size, chip size) larger than the exposable size of an exposer. According to this connective exposure, a large-pattern semiconductor device is manufactured by temporarily dividing a large pattern to be transferred into a plurality of exposable small patterns and exposing the plurality of divided small patterns in a connective manner. A semiconductor device having a plurality of layers can be manufactured by repeating steps of forming single layers by connective exposure. 
     As a technique of such connective exposure, U.S. Pat. No. 6,194,105, for example, describes a method of dividing a mask into a plurality of mask through a blind while forming opaque trace patterns on the respective masks. A necessary mask is selected from the plurality of divided masks and arranged on a prescribed position for performing exposure. Arrangement of the masks is so adjusted as to align the trace patterns formed on the masks with each other. A large-sized pattern is formed by repeating such movement of the masks and exposure. As to dicing regions, dicing lines are first formed on a wafer for forming patterns to be connected with each other along the dicing lines so that overlap quantities of the patterns can be easily controlled and the patterns can be arranged to have a constant width along the dicing lines by setting the overlap quantities, as described in U.S. Pat. No. 6,225,013. 
     Japanese Patent Laying-Open No. 02-005568 (1990) describes a wafer stepper type photolithographic manufacturing method forming an array of patterns on a wafer, moving the wafer for performing exposure and repeating such operations until the wafer is entirely covered with the array of patterns. According to this method, alignment marks are exposed on a substrate through photolithography, and alignment patterns are formed in correspondence to the alignment marks. Then, an array of other alignment patterns is formed by alignment through the alignment marks. The aforementioned gazette describes that a large image region can be formed through a conventional wafer stepper according to this method. According to this method utilizing offset printing through photolithography, however, adjacent patterns are not superposed with each other and hence misalignment in printing disadvantageously results in disconnection on junctions between the adjacent patterns. 
     SUMMARY OF THE INVENTION 
     Connective exposure is performed by repeating operations of forming a pattern on a substrate by exposure through a mask, thereafter exchanging the mask, moving a stage of an exposer, performing exposure and connecting a new pattern to the previously formed pattern. In such connective exposure, therefore, it is important to correctly connect adjacent patterns with each other with excellent reproducibility, and pattern connection accuracy depends on accuracy for setting the mask on the exposer, stage accuracy of the exposer etc. Under the present circumstances, the patterns are superposed with each other with margins so that circuits are not disconnected on the connected portions of the patterns upon occurrence of an error in connection, leading to a hindrance to refinement etc. of the circuits. 
     An object of the present invention is to provide a method of manufacturing a semiconductor device answerable to refinement of circuits by correctly connecting adjacent small patterns with each other with excellent reproducibility in connective exposure and a semiconductor device manufactured by this method. Another object of the present invention is to provide a mask useful in such manufacture. 
     The present invention provides a method of manufacturing a semiconductor device through connective exposure performed by dividing a pattern formed on a semiconductor substrate into a plurality of patterns and exposing the plurality of divided patterns in a connective manner, by forming marks for adjusting arrangement of the patterns to be connected with each other on the semiconductor substrate before exposing patterns of a semiconductor element and connectively exposing the patterns of the semiconductor element in coincidence with the marks for adjusting arrangement. 
     According to another aspect, the present invention also provides a mask employed in manufacture of a semiconductor device through connective exposure for forming marks for adjusting arrangement of patterns to be connected with each other on a substrate before exposing patterns of a semiconductor element, in which the marks for adjusting arrangement are formed on either an X-dicing region or a Y-dicing region of the substrate. According to still another aspect, the present invention further provides a mask employed for exposing patterns of a semiconductor element to be connected with each other, in which marks for adjusting arrangement of the patterns to be connected with each other are formed on either an X-dicing region or a Y-dicing region of a substrate. 
     The present invention further provides a semiconductor device having a semiconductor element larger in size than an exposable region of an exposer, in which a mark formed on a substrate for adjusting arrangement of an exposed pattern is arranged on either an X-dicing region or a Y-dicing region. 
     According to the present invention, patterns can be correctly connected with each other in connective exposure, and circuits can be refined by reducing the quantities of superposition of the patterns. Further, correct connective exposure can be performed with excellent reproducibility in manufacture of an image sensor, an infrared sensor, a large-sized liquid crystal display or the like having a size larger than that of an exposable region of an exposer. The present invention is not restricted to such devices, but is also applicable to a memory, a mass storage device and a logic device. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of a semiconductor device having a size larger than that of an exposable region of an exposer; 
         FIGS. 2A to 2D  are process drawings showing a method of manufacturing a MOS device according to the present invention; 
         FIG. 3  is a flow chart as to formation of arrangement adjusting marks and element isolation regions in the method of manufacturing a MOS device according to the present invention; 
         FIG. 4  is a plan view of a mask employed for forming arrangement adjusting marks in Example 1 of the present invention; 
         FIG. 5  is a plan view showing arrangement of masks employed for forming the arrangement adjusting marks in Example 1 of the present invention; 
         FIG. 6  is a plan view of a mask employed for forming an element pattern in Example 1 of the present invention;. 
         FIG. 7  is an alignment tree in Example 2 of the present invention; 
         FIGS. 8A and 8B  are plan views showing a mask and a semiconductor wafer employed and manufactured in Example 3 of the present invention respectively; 
         FIGS. 9A and 9B  are plan views showing a mask and a semiconductor wafer employed and manufactured in Example 4 of the present invention respectively; and 
         FIG. 10  is a plan view of a MOS device manufactured according to the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a plan view of a semiconductor device  1  manufactured by connecting three masks with each other. This semiconductor device  1  comprises an element region  2  provided on the center, circuit regions  3  provided on both ends and a dicing region  4  provided on the outer edge. When the size of semiconductor device  1  is large than that of an exposable region of an exposer, a pattern formed on a semiconductor substrate is divided into a plurality of patterns  5   a,    5   b  and  5   c  in coincidence with the size of the exposable region so that the plurality of divided patterns  5   a,    5   b  and  5   c  are exposed in a connective manner for manufacturing semiconductor device  1  of a large size. The present invention provides a method of manufacturing a semiconductor device through connective exposure by forming marks (alignment marks and/or superposition inspection marks, for example, hereinafter referred to as “arrangement adjusting marks”) for adjusting arrangement of patterns to be connected with each other on a substrate before exposing patterns of a semiconductor element and connectively exposing the patterns of the semiconductor element in coincidence with the marks for adjusting arrangement. The marks for adjusting arrangement are previously formed on the substrate before connectively exposing the patterns of the semiconductor element for performing connective exposure in coincidence with these marks, so that patterns of the semiconductor element subsequent to a first layer can be aligned with each other with reference to the marks for adjusting arrangement, for example. Therefore, the patterns can be so correctly connected with each other that circuits can be refined by reducing the quantities of superposition of the patterns. Further, superposed states of the marks for adjusting arrangement are so measured that the exposer can be previously adjusted on the basis of the measured values. 
     As a specific mode of the present invention, such a mode that the semiconductor substrate has a first region and a second region adjacent to each other so that marks for adjusting arrangement of the semiconductor element patterns to be connected with each other are formed on the first region and the second region through a first mask, a semiconductor element pattern is thereafter formed by exposing the first region in coincidence with the arrangement adjusting marks through a second mask, another semiconductor element pattern is formed by exposing the second region in coincidence with the arrangement adjusting marks through a third mark and a first connective element pattern is formed by connecting the element pattern of the first region and the element pattern of the second region with each other is preferable, for example. 
     Further, such a mode that the method has the steps of forming still another semiconductor element pattern by exposing the first region through a fourth mask after forming the first connective element pattern, forming a further semiconductor element pattern by exposing the second region through a fifth mask and forming a second connective element pattern by connecting the element patterns of the first region and the element patterns of the second region with each other while adjusting arrangement of the fourth mask through the element pattern formed through the second mask in the first region and adjusting arrangement of the fifth mask through the element pattern formed through the third mask in the second region is preferable in a point that positional accuracy of the first connective element pattern and the second connective element pattern is improved. 
     A mode of forming the marks for adjusting arrangement by exposure through a single mask is preferable. In conventional connective exposure, the pattern of a first layer is formed through a plurality of masks and hence array precision of the pattern and marks is deteriorated through set accuracy of the plurality of masks and slide accuracy of a stage. According to the present invention, on the other hand, the marks for adjusting arrangement are so formed through the single mask that array precision is not deteriorated through set accuracy of the unexchanged mask. 
     A mode of forming the marks for adjusting arrangement by locally exposing a region of a mask to be formed with the marks for adjusting arrangement is preferable. The marks can be formed with stage accuracy of an exposer by repeating operations of locally exposing the portion of the marks for adjusting arrangement, thereafter moving a stage of the exposer and similarly locally exposing an adjacent region. Further, distortion can be reduced for further improving exposure accuracy by exposing a mark forming region of the mask. 
     According to this method, a mode of arranging arrangement adjusting marks  86  in an array grid  88  for arranging product chips in a semiconductor wafer  87  can be employed as shown in  FIG. 8B , for example. Alternatively, a mode of arranging arrangement adjusting marks  96  on regions out of an array grid  98  in a semiconductor wafer  97  can be employed, as shown in  FIG. 9B . According to this mode, the marks can be arrayed through the same mask with slide accuracy of a stage, so that adjacent patterns can be superposed with each other within the range of alignment accuracy and distortion in subsequent steps. Further, high exposure accuracy can be attained by performing exposure while centering the arrangement adjusting marks, while a dicing region can be narrowed, the throughput can be improved and productivity for element chips can be improved particularly according to the latter mode arranging the arrangement adjusting marks on the regions out of the array grid. 
     A mode of adjusting the positional relation between adjacent marks is preferable in the step of forming the marks for adjusting arrangement. Positional accuracy of marks for adjusting arrangement in a subsequent processing lot can be improved by forming superposition inspection marks for measuring positional relation between adjacent marks on the marks for adjusting arrangement, measuring the positional accuracy through the inspection marks, feeding back measured data to the exposer and adjusting the exposer. Further, superposition accuracy of element patterns of second and subsequent layers can be improved by adjusting arrangement with reference to highly accurate marks. As to superposition of element patterns, therefore, a design allowance can be more reduced as compared with the prior art, for allowing refinement of circuits. 
     A mode of forming the marks for adjusting arrangement on the semiconductor substrate, performing connective exposure of the pattern of the semiconductor element in coincidence with the marks for adjusting arrangement and thereafter further performing connective exposure in coincidence with the connected pattern is possible. This mode is preferable in a case where positional accuracy of a formed pattern and another pattern further formed on this position is regarded as important. A general manufacturing method and a general design method in a case of performing no connective exposure in a superposition inspection apparatus or an APC (advanced process control) system for correcting a superposition error can be applied. According to the inventive manufacturing method, positional accuracy of the marks for adjusting arrangement formed on the substrate is so high that sufficient positional accuracy can be obtained through simple arrangement on a previously formed pattern. 
     A mode of forming the marks for adjusting arrangement on either an X-dicing region or a Y-dicing region of the semiconductor substrate is preferable. In general, alignment marks in X- and Y-directions are formed on X- and Y-dicing regions respectively, in order to adjust positions in the X- and Y-directions. If the alignment marks in the X- and Y-directions are similarly formed on the X- and Y-dicing regions respectively also in connective exposure, however, the marks for adjusting arrangement are disadvantageously formed on a pattern region of the semiconductor element connected in a subsequent step. Therefore, the marks for adjusting arrangement are preferably formed on either the X-dicing region or the Y-dicing region of the substrate. In each of the mask employed for forming the marks for adjusting arrangement and a mask employed for forming the semiconductor element patterns to be connected with each other, therefore, the marks for adjusting arrangement are preferably formed on either the X-dicing region or the Y-dicing region of the substrate. A semiconductor device having a semiconductor element larger in size than an exposable region of an exposer and marks for adjusting arrangement formed on either an X-dicing region or a Y-dicing region of a substrate can be manufactured through such masks. 
     Example 1 
     According to Example 1, a MOS (metal oxide semiconductor) device was manufactured through connective exposure.  FIG. 10  is a plan view showing the manufactured MOS device  10 .  FIG. 10  omits illustration of an interlayer dielectric film and wires, in order to clearly illustrate the structure of MOS device  10 . This MOS device  10  has a connected portion A-A, and is constituted of photodiodes  10   a,  gate electrodes  15 , impurity regions  16  such as source and drain regions, element isolation regions  14 , contacts  18  etc.  FIG. 2D  is a sectional view taken along the line IID-IID in  FIG. 10 . As shown in  FIG. 2D , a MOS device  20  comprises element isolation regions  24  on a substrate  21 , and has gate electrodes  25  and impurity regions  26 . An interlayer dielectric film  27  is formed on substrate  21 , and contacts  28  are formed between substrate  21  and wires  29  formed on interlayer dielectric film  27 . 
       FIGS. 2A to 2D  show a method of manufacturing MOS device  20 . Referring to each of  FIGS. 2A to 2D , symbol A-A denotes a connected portion, and reference numerals ( 2 - 1 ) and ( 2 - 2 ) show a step of manufacturing marks for adjusting arrangement and a step of manufacturing a semiconductor element region respectively. First, a resist film  22  was formed on p-type semiconductor substrate  21  and patterned by exposure and development through a mask, in order to form arrangement adjusting marks  23  ( FIG. 2A ). Then, arrangement adjusting marks  23  were formed by etching ( FIG. 2B ), an SiO 2  film was formed by oxidation, and an Si 3 N 4  film was formed on the SiO 2  film by LPCVD. Then, another resist film was formed and element isolation regions were connectively exposed, developed and patterned while adjusting arrangement of masks through arrangement adjusting marks  23 . Thereafter the Si 3 N 4  film was selectively removed by etching, and element isolation regions  24  of SiO 2  were formed through field oxidation by heat treatment at a temperature of 1000° C. for 150 minutes ( FIG. 2C ). Then, the Si 3 N 4  film was separated, and MOS device  20  was manufactured by depositing polysilicon, forming gate electrodes  25 , thereafter forming impurity regions  26  and further forming interlayer dielectric film  27 , contacts  28  and wires  29  ( FIG. 2D ). 
       FIG. 3  is a flow chart as to formation of the arrangement adjusting marks and the element isolation regions. The arrangement adjusting marks were formed on the substrate before exposing patterns of the isolation regions in a semiconductor element, as shown in  FIG. 3 . First, resist was applied onto the substrate (step  1 ) (steps  2  to  12  are hereinafter referred to as S 2  to S 12 ), exposed (S 2 ) and thereafter developed (S 3 ). Then, pattern superposition accuracy was measured (S 4 ), and the substrate was etched when the accuracy was within a prescribed standard (S 5 ). The measured value was fed back for adjusting the exposer for correctly superposing portions to be connected with each other in a subsequent processing lot (S 4 ). If the measured value of the superposition accuracy is out of the prescribed standard, the resist is removed and another resist is applied for feeding back the aforementioned measured value and performing exposure. 
     The exposure (S 2 ) was performed through a single mask  40  shown in  FIG. 4 , and connective exposure was performed by moving a stage of the exposer and arranging the substrate. According to Example 1, the arrangement adjusting marks were formed through this single pattern mask  40 . Therefore, mask  40  was not exchanged and it was possible to suppress accuracy deterioration resulting from set accuracy of mask  40 . Mask  40  comprised a pattern region  49  for forming a pattern of a semiconductor element and X-dicing regions  45  and  46  with superposition inspection patterns  41  to  44 , an X-directional alignment pattern  47  and a Y-directional alignment pattern  48  provided on X-dicing regions  45  and  46 . The arrangement adjusting marks were formed only on X-dicing regions  45  and  46  through this mask  40 . Therefore, no marks for adjusting arrangement were formed on a pattern region for a semiconductor element connected in a subsequent step. 
       FIG. 5  is a plan view showing arrangement of masks employed for forming the arrangement adjusting marks. According to Example 1, single masks were employed and connective exposure was performed by moving the stage of the exposer to superpose adjacent masks with each other, as shown in  FIG. 5 . Adjacent patterns were so arranged that a superposition inspection pattern  51   a  for a pattern  50   a  coincided with a superposition inspection pattern  51   b  for a leftwardly adjacent pattern  50   b,  for example, as shown in  FIG. 5 . Superposition inspection pattern  51   a  was rendered larger than superposition inspection pattern  51   b.  Superposition accuracy was measured by measuring misalignment of inner superposition inspection pattern  51   b  with respect to outer superposition inspection pattern  51   a.  Similarly, another superposition inspection pattern  52   a  for pattern  50   a  was arranged to coincide with another superposition inspection pattern  52   b  for leftwardly adjacent pattern  50   b,  for similarly measuring misalignment. In addition, still another superposition inspection pattern  53   a  for pattern  50   a  was arranged to coincide with a superposition inspection pattern  53   c  for a pattern  50   c  adjacent on the other side while a superposition inspection pattern  54   a  was arranged to coincide with a superposition inspection pattern  54   c,  for similarly measuring misalignment. Misalignment of the remaining patterns was also measured. According to Example 1, the results of measurement were fed back to the exposer and adjusted after the measurement of superposition accuracy, whereby positional accuracy of the arrangement adjusting marks was improved also as to subsequent lots so that arrangement accuracy of element patterns arranged with reference to the arrangement adjusting marks was continuously improved and maintained also between different lots. 
     The element isolation regions were formed after forming the arrangement adjusting marks. First, as shown in  FIG. 3 , an oxide film and a nitride film were formed on the substrate (S 6 ), thereafter resist was applied (S 7 ), and the patterns of the element isolation regions were exposed as the patterns of the semiconductor element (S 8 ). After the exposure, development was performed (S 9 ), superposition was inspected (S 10 ), the nitride film was etched (S 11 ) and field oxidation was performed (S 12 ) for forming the element isolation regions, as shown in  FIG. 3 . The semiconductor element patterns were exposed (S 8 ) by moving the stage in coincidence with a first alignment mark formed on the substrate as the arrangement adjusting mark, exposing the mark through a mask  1  (S 8 - 1 ), moving the stage in coincidence with a next alignment mark and exposing the mark through a mask  2  (S 8 - 2 ) and repeating such operations up to a mask m thereby performing connective exposure (S 8 - 3 ). Superposition was inspected (S 10 ) between an inspection pattern formed through mask  1  and an inspection pattern on the substrate (S 10 - 1 ) and inspected between an inspection pattern formed through mask  2  and the inspection pattern on the substrate (S 10 - 2 ), while such operations were repeated up to the mask m. 
     The patterns of the semiconductor element were exposed (S 8 ) through a pattern mask  60  shown in  FIG. 6 , and the substrate was arranged by adjusting the position of the stage of the exposer for performing connective exposure. Mask  60  comprised a semiconductor element pattern region  69  and X-dicing regions  65  and  66  with superposition inspection patterns  61  to  64 , an X-directional alignment pattern  67  and a Y-directional alignment pattern  68  provided on X-dicing regions  65  and  66 . Arrangement adjusting marks were formed only on the X-dicing regions  65  and  66  through this mask  60 . Therefore, no arrangement adjusting marks were formed on a circuit region of a pattern connected in a subsequent step. In a semiconductor device as obtained, the size of the semiconductor element was larger than that of an exposable region of the exposer, and the arrangement adjusting marks were arranged only on the X-dicing regions. 
     Example 2 
     According to Example 2, a MOS device was manufactured similarly to Example 1 except that gate electrodes were formed by further performing connective exposure in coincidence with the patterns of element isolation regions formed by connective exposure after the connective exposure of the element isolation regions.  FIG. 7  is an alignment tree of Example 2. As shown in  FIG. 7 , marks for adjusting arrangement of respective patterns of the element isolation regions were formed on a substrate, for forming element isolation regions  1  to  3  by performing connective exposure in coincidence with the marks for adjusting arrangement. Then, gate electrodes  1  to  3  were formed by connective exposure through alignment with the patterns of element isolation regions  1  to  3 , for manufacturing the MOS device. 
     In the manufactured MOS device, positional accuracy of gate electrodes  1  to  3  with respect to element isolation regions  1  to  3  was so high that a high-characteristic MOS device was obtained since superposition accuracy between patterns of element isolation regions and patterns of gate electrodes is regarded as important in a MOS device. Further, positional accuracy of the arrangement adjusting marks formed on the substrate was so high that sufficient positional accuracy was attained by simply adjusting arrangement with respect to previously formed patterns without adjusting the arrangement between right and left patterns. Therefore, it was possible to reduce the processing time for superposition inspection. Further, a general manufacturing method and a general design method in a case of performing no connective exposure in a superposition inspection apparatus or an APC (advanced process control) system for correcting a superposition error, applied to the gate electrodes in Example 2, can also be applied to wire patterns or hole patterns of a higher layer as shown in  FIG. 7 . In particular, it was possible to accurately connect wires  29  on the connected portion as shown in  FIG. 2D . 
     Example 3 
     When forming arrangement adjusting marks on a substrate according to Example 3, a region  85  of arrangement adjusting marks including a superposition inspection mark  82 , an X-directional alignment mark  83  and a Y-directional alignment mark  84  was locally exposed in a mask  81  as shown in  FIG. 8A . In this exposure, mask  81  was set on an exposer to center region  85 . After the exposure, a wafer stage of the exposer was moved so that exposure and movement of the stage were repeated for thereafter performing development and etching. Consequently, as shown in  FIG. 8B , a semiconductor wafer  87  having arrangement adjusting marks  86  arranged in an array grid  88  for arraying product chips was obtained for manufacturing the MOS device similarly to Example 1. 
     According to Example 3, the same mask was employed for forming the arrangement adjusting marks by sliding the wafer stage, whereby it was possible to perform patterning within the range of slide accuracy with no error resulting from mask arrangement as compared with a mode of employing a plurality of masks and arranging the masks every exposure. Consequently, it was possible to superpose adjacent patterns within the range of alignment accuracy and distortion in subsequent steps. According to the mode of Example 3, it was possible to set and expose the mask to center the region for forming the arrangement adjusting marks, whereby distortion was reduced as compared with a case where regions for forming arrangement adjusting marks were provided around an exposed region and it was possible to further improve exposure accuracy. 
     Example 4 
     When forming marks for adjusting arrangement on a substrate according to Example 4, a region  95  for forming arrangement adjusting marks including an X-directional alignment mark  93  and a Y-directional alignment mark  94  in a mask  91  was locally exposed as shown in  FIG. 9A . In this exposure, mask  91  was set on an exposer to center region  95  on an exposure region. After the exposure, a wafer stage of the exposer was moved so that exposure and movement of the stage were repeated for thereafter performing development and etching. Consequently, as shown in  FIG. 9B , a semiconductor wafer  97  having arrangement adjusting marks  96  arranged on regions out of an array grid  98  for arraying product chips was obtained for manufacturing the MOS device similarly to Example 1. 
     According to Example 4, the same mask was employed for forming the arrangement adjusting marks by sliding the wafer stage, whereby it was possible to perform patterning within the range of slide accuracy similarly to Example 3. Consequently, it was possible to superpose adjacent patterns with each other within the range of alignment accuracy, distortion and array accuracy in subsequent steps. Further, it was possible to set and expose the mask to center the region for forming the arrangement adjusting marks on the exposure region, whereby distortion was reduced as compared with a case where arrangement adjusting marks were provided around an exposed region and it was possible to further improve exposure accuracy. In addition, arrangement adjusting marks  96  were arranged on the regions out of array grid  98  for arraying the product chips, whereby it was possible to reduce the size of dicing regions, improve the throughput and increase manufacturing efficiency for the semiconductor device. 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.