Abstract:
A semiconductor IC includes grooves formed in a substrate to define a first dummy region and second dummy regions formed at a scribing area, and third dummy regions and a fourth dummy region formed at a product area. A width of the first dummy region is greater than widths of each of the second and third dummy regions and a width of the fourth dummy region is greater than widths of each of the third dummy regions. A conductor pattern is formed over the first dummy region for optical pattern recognition. The first dummy region is formed under the conductor pattern so the grooves are not formed under the conductor pattern. The second dummy regions are spaced from one another by a predetermined spacing at the scribing area, and the third dummy regions are spaced from one another by a predetermined spacing at the product area.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of application Ser. No. 12/757,364, filed Apr. 9, 2010, which, in turn, is a continuation of application Ser. No. 11/948,626, filed Nov. 30, 2007 (now U.S. Pat. No. 7,327,014), which in turn, is a continuation of application Ser. No. 11/602,178, filed Nov. 21, 2006 (now U.S. Pat. No. 7,327,014), which, in turn is a continuation of application Ser. No. 11/410,949, filed Apr. 26, 2006 (now U.S. Pat. No. 7,154,164), which is a Continuation of application Ser. No. 11/028,208 (now U.S. Pat. No. 7,112,870), filed Jan. 4, 2005, which, in turn is a Divisional of application Ser. No. 10/405,615 (now U.S. Pat. No. 7,009,233), filed Apr. 3, 2003, which is a Continuation of application Ser. No. 09/692,450, (now U.S. Pat. No. 6,603,162), filed Oct. 20, 2000, the entire disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a semiconductor integrated circuit device and to a process for manufacturing the same; and, in particular, the invention relates to a process which can effectively be applied to a semiconductor integrated circuit device comprising a step for flattening a surface using CMP (Chemical Mechanical Polishing). 
     In semiconductor integrated circuit devices, such as a DRAM (Dynamic Random Access Memory), demand has been increasing in recent years for finer detail and a higher degree of integration. Due to the demand for greater detail in semiconductor integrated circuit devices, laminated structures in multilayer interconnections are unavoidable, but if a multilayer structure is used, imperfections are formed on the surface of the upper layer reflecting the imperfections in the substrate. If photolithography is performed when imperfections are present on the surface, sufficient tolerance of focal depth cannot be obtained in the exposure step, and this leads to poor resolution. Therefore, the surface is flattened using CMP in order to improve the photolithography of components formed on the surface. 
     The CMP technique is used also to form isolation regions. In the LOCOS (Local Oxidation of Silicon) technique, which was frequently used in the past, it is difficult to achieve more than a certain amount of detail due to the presence of a bird&#39;s beak. Thus, a shallow groove is formed on Ia main surface of the semiconductor substrate; this groove is filled with a silicon oxide film; and the silicon oxide in the regions outside the groove are removed by CMP to form a shallow groove isolation. With a shallow groove isolation, the periphery of the isolation region is sharply defined, so the periphery can also be used effectively as an element part, so that it is easier to achieve finer detail. 
     However, when the CMP technique is used for polishing, it is impossible to completely remove surface imperfections. When there are imperfections on the polishing surface, a history of imperfections remains on the polishing surface to some extent. Further, if parts which are easily polished and parts which are difficult to polish are both present on the polishing surface, dishing (polishing depressions) tends to occur in the part which is easy to polish. Due to the nature of polishing in the CMP method, this history of imperfections or dishing is particularly significant when the imperfections or parts which are easy to polish have a large area. Specifically, in polishing by the CMP method, although small imperfections can be flattened relatively well, undulations (global undulations) remain over a large area when a large pattern (usually of the order of several μm or more) is repeated, for example, and so it is difficult to flatten the surface completely. 
     However, a method has been proposed where a dummy pattern is disposed in regions where there are large patterns or where there is a wide pattern interval. In this method, the pattern interval is decreased due to the dummy pattern, so that the aforesaid wide area (global) dishing or undulations are suppressed. For example, in Japanese Unexamined Patent Publication No. Hei 10-335333 (1998) (Koho) (U.S. Ser. No. 09/050,416, 31 Mar. 1998), a technique is disclosed wherein a dummy pattern is disposed in a region with a wide pattern interval to improve the flatness of the surface of an insulating film which fills the pattern. 
     SUMMARY OF THE INVENTION 
     By disposing a dummy pattern in a region where there is a large distance between patterns, so as to decrease the pattern interval, it is possible to deal with the problem of dishing (depressions) or undulations over a wide area. In dishing, the larger the area is the lower the position of the depression in the central part is; and, therefore, by disposing the dummy pattern so as to decrease the area over which dishing occurs, the depth of the depression can be relatively decreased. 
     Nevertheless, no matter how small the pattern interval is made, dishing cannot be completely eliminated. When the problem surface to be flattened is a single layer, the depression amount is largely improved compared with the dishing which occurs in large area parts, but when the layer to be flattened is a laminate of plural layers, dishing components (depressions) are superimposed due to the positioning of the pattern, and a large amount of dishing occurs in the upper layer. In such a case, there is a decreased tolerance in the focal depth when photolithography is performed on the upper layer in a photolithography step, the overetching amount in an etching step increases, and the yield decreases. 
     In regions, such as scribe regions, in which elements which become products are not normally formed, a target is formed for an exposure device (such as a stepper or the like) which is used in photolithography. A dummy pattern cannot be disposed on the periphery of this target as it is necessary to recognize the pattern. The area of the target is normally of the order of several μm or more. Therefore, if a dummy pattern is not disposed in this large (large area) pattern region, dishing occurs as described above. In the prior art, as this large area pattern was formed in a scribe region and not in a product region, this was not considered to be a problem. However, the dishing in the scribe region also affects the product region, and since the tolerance of focal depth in the exposure step is becoming more critical due to the trend towards higher detail, the decreased flatness of the product region (in particular the periphery) is a matter of concern. 
     It is therefore an object of this invention to suppress dishing on a surface to be flattened comprising a laminate of plural layers. 
     It is another object of this invention to improve surface flattening in a pattern region having a large area for optical position detection such as a target. 
     It is still another object of this invention to improve a surface to be flattened comprising plural layers, or the flattening of a pattern of large area such as a target, thereby improving the patterning margin in a photolithography step and etching step. 
     The aforesaid and other objects of this invention and novel features thereof will become apparent from the following description and appended drawings. 
     Of the inventive features disclosed in the present application, the most typical can simply be summarized as follows. 
     A semiconductor integrated circuit device according to this invention comprises a semiconductor substrate having a semiconductor element formed on a main surface, a first pattern comprising a dummy pattern formed on the main surface or on one of the layers on the main surface, and a second pattern formed on an upper layer of the first pattern and comprising a pattern which serves as a target for optical pattern recognition, the pattern which serves as a target for optical pattern recognition being enclosed within the flat shape of the dummy pattern. According to this semiconductor integrated circuit device, the dummy pattern is disposed underneath the pattern used for optical pattern recognition, so that a decrease of the overall flatness in this pattern region is suppressed. 
     The first pattern may contain another dummy pattern having a smaller area than the dummy pattern. The dummy pattern and another dummy pattern may also be formed in a scribe region. Further, other dummy patterns may be formed in a product region and a scribe region. 
     The dummy pattern is formed with an area equal to or greater, than a pattern prohibition region on the periphery of the pattern used for optical pattern recognition. Therefore, a decrease in the recognition rate of optical pattern recognition of this pattern is prevented. 
     The first pattern has patterning dimensions of the same order as the design rule of the semiconductor elements and contains another dummy pattern having a smaller area than the dummy pattern, but the other dummy pattern is not disposed in the pattern prohibition region. In this way, by disposing a small area dummy pattern, except in the vicinity of the pattern used for optical pattern recognition, the flatness of these regions is improved, and by prohibiting provision of the small area dummy pattern in the vicinity of this pattern, a decrease in the recognition rate of the pattern used for optical pattern recognition is prevented. 
     The dummy pattern is formed in the scribe region of the semiconductor wafer, and the other dummy pattern is formed in the product region and scribe region of the semiconductor wafer. Hence, the flatness of the scribe region, as well as that of the product region, is improved, and the flatness in the vicinity of the boundary of the product region and scribe region is improved. This contributes to improvement of the product yield. 
     The semiconductor integrated circuit device according to this invention comprises a semiconductor substrate having a semiconductor element formed on its main surface, a first pattern formed on the main surface or on one of the layers on the main surface, and a second pattern formed on an upper layer of the first pattern. The first pattern comprises a first dummy pattern, the second pattern comprises a second dummy pattern having a pattern pitch and pattern width of identical design dimensions to those of the first dummy pattern, and the second dummy pattern is formed over a space of the first dummy pattern in its flat position. One of the side edges of the second dummy pattern is formed so as to overlap with the first dummy pattern in its flat surface position, or the first dummy pattern and second dummy pattern are offset by a distance of ½ pitch in its flat surface position. In such a semiconductor integrated circuit device, dishing does occur in the pattern interval between first small area dummy patterns, but the second small area dummy pattern is formed in the upper layer of the part where this dishing occurs, so that overlapping with the dishing formed between the second small area patterns is prevented. As a result, overlapping of dishing between upper and lower layers is suppressed, and flatness is improved. 
     In this semiconductor integrated circuit device, the first pattern may further comprise another dummy pattern having a larger area than that of the first dummy pattern, the second pattern may further comprise a pattern used for optical pattern recognition, and the pattern used for optical pattern recognition may be enclosed within the flat shape of the other dummy pattern. The other dummy pattern is formed with an area equal to or greater than the area of the pattern prohibition region on the periphery of the pattern used for optical pattern recognition, and the first dummy pattern is not disposed in the pattern prohibition region. The other dummy pattern may also be formed in the scribe region of the semiconductor wafer, and the first and second dummy patterns may also be formed in the product region and scribe region of the semiconductor wafer. 
     In all of the aforesaid semiconductor integrated circuit devices, the first pattern may be an active region pattern formed on the main surface, and the second pattern may be a pattern formed in the same layer as that of the gate electrode forming the semiconductor elements. 
     The method of manufacturing the semiconductor integrated circuit device of this invention comprises (a) a step of forming a first pattern comprising a dummy pattern on the main surface or on any component surface on the main surface of a semiconductor substrate, (b) a step of depositing an insulating film on the main surface on which the first pattern is formed or on a component patterned on the first pattern, and flattening the surface by polishing the insulating film, and (c) a step of forming a second pattern comprising a pattern used for optical pattern recognition on the upper layer of the flattened surface. The pattern used for optical pattern recognition is enclosed within the flat shape of the dummy pattern. 
     In this manufacturing method, a step may further be provided for detecting the pattern used for optical pattern recognition to perform alignment of the semiconductor substrate. 
     Alternatively, the method of manufacturing the semiconductor integrated circuit device of this invention further comprises (a) a step of forming a first pattern comprising a dummy pattern on the main surface or on any component surface on the main surface of the semiconductor substrate, (b) a step of forming a second pattern comprising a pattern used for optical pattern recognition on the upper layer of the first pattern, and (c) a step of detecting the pattern used for optical pattern recognition to perform alignment of the semiconductor substrate. The pattern used for optical pattern recognition is enclosed within the flat shape of the dummy pattern. 
     In either of the manufacturing methods described above, the dummy pattern may be formed with an area equal to or greater than the pattern prohibition region on the periphery of the pattern used for optical pattern recognition. 
     The first pattern further comprises a first dummy pattern, and the second pattern further comprises a second dummy pattern having a pattern pitch and pattern width identical to the design dimensions of the first dummy pattern, the second dummy pattern being formed over a space of the first dummy pattern in its flat surface position. 
     One of the side edges of the second dummy pattern is formed so as to overlap with the first dummy pattern, or the first dummy pattern and second dummy pattern are offset at a distance of ½ pitch in its flat surface position. 
     The dummy patterns may be formed in the scribe region of the semiconductor wafer, and the first and second dummy patterns may be formed in the product region and scribe region of the semiconductor wafer. 
     The component to which the first pattern is transferred is the semiconductor substrate, and the component to which the second pattern is transferred is the gate electrode. 
     The aforesaid semiconductor integrated circuit device can be manufactured by these semiconductor integrated circuit device manufacturing methods. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view showing a silicon wafer used for manufacturing a semiconductor integrated circuit device according to one embodiment of this invention. 
         FIG. 2  is a plan view showing an enlargement of a chip part of a wafer according to this embodiment. 
         FIG. 3  is a plan view showing an end region of the chip comprising a scribe line. 
         FIG. 4  is a plan view showing an enlargement of a product region of the chip. 
         FIG. 5(   a ) and  FIG. 5(   b ) are sectional views showing an example of a method of manufacturing the semiconductor integrated circuit device according to the embodiment as a sequence of processes. 
         FIG. 6(   a ) and  FIG. 6(   b ) are sectional views showing an example of a method of manufacturing the semiconductor integrated circuit device according to the embodiment as a sequence of processes. 
         FIG. 7(   a ) and  FIG. 7(   b ) are sectional views showing an example of a method of manufacturing the semiconductor integrated circuit device according to the embodiment as a sequence of processes. 
         FIG. 8(   a ) and  FIG. 8(   b ) are sectional views showing an example of a method of manufacturing the semiconductor integrated circuit device according to the embodiment as a sequence of processes. 
         FIG. 9(   a ) and  FIG. 9(   b ) are sectional views showing an example of a method of manufacturing the semiconductor integrated circuit device according to the embodiment as a sequence of processes. 
         FIG. 10(   a ) and  FIG. 10(   b ) are sectional views showing an example of a method of manufacturing the semiconductor integrated circuit device according to the embodiment as a sequence of processes. 
         FIG. 11(   a ) and  FIG. 11(   b ) are sectional views showing an example of a method of manufacturing the semiconductor integrated circuit device according to the embodiment as a sequence of processes. 
         FIG. 12(   a ) and  FIG. 12(   b ) are sectional views showing an example of a method of manufacturing the semiconductor integrated circuit device according to the embodiment as a sequence of processes. 
         FIG. 13(   a ) and  FIG. 13(   b ) are sectional views showing an example of a method of manufacturing the semiconductor integrated circuit device according to the embodiment as a sequence of processes. 
         FIG. 14(   a ) and  FIG. 14(   b ) are sectional views showing an example of a method of manufacturing the semiconductor integrated circuit device according to the embodiment as a sequence of processes. 
         FIG. 15(   a ) and  FIG. 15(   b ) are sectional views showing an example of a method of manufacturing the semiconductor integrated circuit device according to the embodiment as a sequence of processes. 
         FIG. 16(   a ) and  FIG. 16(   b ) are sectional views showing an example of a method of manufacturing the semiconductor integrated circuit device according to the embodiment as a sequence of processes. 
         FIG. 17  is a plan view showing an example of a method of manufacturing the semiconductor integrated circuit device according to the embodiment as part of a sequence of processes. 
         FIG. 18  is an enlarged plan view of  FIG. 17 . 
         FIG. 19(   a ) and  FIG. 19(   b ) are sectional views showing an example of a method of manufacturing the semiconductor integrated circuit device according to the embodiment as a sequence of processes. 
         FIG. 20(   a ) and  FIG. 20(   b ) are sectional views showing an example of a method of manufacturing the semiconductor integrated circuit device according to the embodiment as a sequence of processes. 
         FIG. 21(   a ) and  FIG. 21(   b ) are sectional views showing an example of a method of manufacturing the semiconductor integrated circuit device according to the embodiment as a sequence of processes. 
         FIG. 22(   a ) and  FIG. 22(   b ) are sectional views showing an example of a method of manufacturing the semiconductor integrated circuit device according to the embodiment as a sequence of processes. 
         FIG. 23(   a ) and  FIG. 23(   b ) are sectional views showing an example of a method of manufacturing the semiconductor integrated circuit device according to the embodiment as a sequence of processes. 
         FIG. 24  is a plan view showing an example of a method of manufacturing the semiconductor integrated circuit device according to the embodiment as part of a sequence of processes. 
         FIG. 25  is an enlarged plan view showing another example of the semiconductor integrated circuit device according to the embodiment. 
         FIG. 26  is an enlarged plan view showing another example of the semiconductor integrated circuit device according to the embodiment. 
         FIG. 27  is an enlarged plan view showing yet another example of the semiconductor integrated circuit device according to the embodiment. 
         FIG. 28  is an enlarged plan view showing yet another example of the semiconductor integrated circuit device according to the embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     One embodiment of this invention will now be described in detail with reference to the drawings. In all of the drawings which illustrate this embodiment, the same symbols are used for members having identical functions, and their description will not be repeated. 
       FIG. 1  is a plan view showing a silicon wafer used for manufacturing a semiconductor integrated circuit device according to one embodiment of the invention. A notch In is made in a single crystal silicon wafer  1   w  and serves as a crystal plane index mark of the wafer  1   w . A chip  1   c  is formed on the wafer  1   w . The chip  1   c  is formed in the effective processing area of the wafer  1   w , and a chip region  1   g  outside the effective processing area is not used. 
       FIG. 2  is a plan view showing an enlargement of the chip  1   c  of the wafer  1   w . The chip  1   c  is scribed and divided by a scribe line SL. In the steps described hereafter, each step is performed in the state of the wafer  1   w , the chip  1   c  being divided in the final step. 
     In this form of the invention, the typical DRAM chip  1   c  is shown as an example. It may also be another product, for example a logic product, such as a CPU, a memory element, such as an SRAM (Static Random Access Memory), or a memory which can be erased in one step and be electrically rewritten (so-called EEPROM: Electrical Erasable Read Only Memory), or a system LSI where a logic circuit and memory element coexist on the same chip. A memory cell array MA, direct peripheral circuit PCd and indirect peripheral circuit Pci are formed in the chip  1   c . DRAM memory cells are formed in the memory cell array MA. The direct peripheral circuit PCd is formed on the periphery of the memory cells MA. The indirect peripheral circuit Pci is formed in the center region of the chip  1   c.    
       FIG. 3  is a plan view showing an edge region of the chip  1   c  comprising the region of the scribe line SL.  FIG. 3  shows the state where an isolation region is formed on a semiconductor substrate  1  (wafer  1   w , chip  1   c ). The regions other than a scribe region SR are product regions PR. 
     A target pattern T 1 , large area dummy pattern DL and small area pattern Ds are formed simultaneously when the isolation region is formed in the scribe region SR. A TEG (Test Equipment Group) element is also formed in the scribe region SR, but it is not shown in the drawings. The target pattern T 1  is a pattern formed simultaneously in a step when an isolation region pattern is formed, and it is used for alignment in an exposure step when a gate electrode pattern, to be described later, is formed. Specifically, it is used as a target for position detection when mask alignment of a target electrode pattern is performed. In an exposure device, a mask is aligned with respect to the wafer by, for example, performing optical pattern recognition of the target, and a photoresist film is then exposed. 
     The large area dummy pattern DL and small area dummy pattern Ds are patterns which are simultaneously formed in the step when the isolation region pattern is formed. A target pattern T 2  is formed simultaneously with the target electrode pattern on the large area dummy pattern DL. The target pattern T 2  is used for alignment in the exposure step when the upper layer pattern, for example, an interconnection pattern or connecting hole pattern, is formed. Due to the provision of the large area pattern DL, dishing in the target pattern region is prevented, the recognition rate of the target pattern is improved, and fine patterning can advantageously be performed. In the prior art, a dummy pattern was not provided on the periphery of the prior art target pattern, so that the surface flatness of the target pattern periphery was impaired; however, by providing the large area dummy pattern DL underneath the target pattern, the flatness is improved and the recognition rate of the target pattern is improved. The large area dummy pattern DL is formed to be larger than the target pattern so as to enclose the target pattern. In other words, the large area dummy pattern DL is present underneath the target pattern region used for optical pattern recognition, so that dishing is prevented and the recognition rate of the target pattern is improved. On the periphery of the target pattern, there is a region where any kind of pattern is prohibited, thereby to prevent interference with target pattern recognition. The large area dummy pattern DL has an area equal to or greater than this pattern prohibition region. Therefore, the large area dummy pattern DL is not recognized as a pattern by the exposure device, and the recognition rate of the target patterns T 1 , T 2  is not decreased. 
     The small area dummy pattern Ds is formed in the scribe region SR and the product region PR. In other words, it is formed over the whole surface of the wafer W. Thus, the small area dummy pattern Ds is disposed in a region in which there is a wide interval between patterns functioning as elements. Since there is a wide interval between patterns functioning as elements, if the small area dummy pattern Ds were not disposed in this wide pattern interval, dishing would occur in the pattern interval. Since this dishing becomes larger in depth as the pattern interval becomes wider, the flatness is largely impaired. By disposing this small area dummy pattern Ds in this wide inter-pattern space, the flatness is improved. As the pattern size and inter-pattern space are formed with dimensions of approximately the same order as those of the pattern forming the elements, the pattern interval is narrow, and a small amount of dishing according to the narrow pattern interval occurs. In this situation, the depression amount can be much improved and the flatness can be improved compared with the case when the dummy pattern is not provided. The pattern size of the small area dummy pattern Ds is of the same order as the element design rule, and a suitable value is selected with regard to the ease of photolithography and the effect on suppression of dishing. When the element design rule is of the order of, for example, 0.2 μm, the pattern size of the small area dummy pattern Ds may also be set to the order of 0.2 μm. However, if a KrF excimer laser is used as the exposure light source, a technique must be used to improve the resolution, such as use of a Levenson mask. If priority is given to the ease of forming the mask, the pattern size of the small area dummy pattern Ds may be set to be of the order of 1 μm, and the inter-pattern space may be set to be of the order of 0.4 μm. It will of course be understood that other figures can be selected from the requirements of the photolithography step. However, if the pattern size and inter-pattern space are too large, dishing in the inter-pattern space becomes more marked, which is undesirable. 
     The width of the scribe region SR is approximately 100 μm. 
     In  FIG. 3 , active regions which form elements are formed apart from the aforesaid small area dummy pattern Ds in the product region PR. According to this embodiment, an active region LI forming a channel region of a MISFET (Metal Insulator Semiconductor Field Effect Transistor), an active region L 2  for well feed and an active region L 3  for guard band feed are shown as examples. It will be understood that other active regions may also be formed. The aforesaid small area dummy pattern Ds is formed between the patterns of the active regions L 1 , L 2 , L 3 . The large area dummy pattern DL may also be formed in the product region PR. 
       FIG. 4  is a plan view showing an enlargement of a region comprising the active regions L 1 , L 2  of the product region PR. Plural small area dummy patterns Ds are disposed between the patterns of the active regions L 1 , L 2 , as described above. As stated above, the pattern size d 1  of the small area dummy pattern Ds is approximately 1 μm, and the pattern interval S 1  is approximately 0.4 μm. 
     The small Area dummy pattern Ds is formed by automatically generating patterns of the aforesaid size in a lattice (grid) with the pattern pitch (1.4 μm in the case of this embodiment). At each lattice point, the small area dummy pattern Ds is not generated in parts where the active regions L 1 , L 2  are present. Specifically, in a mask design device, a graphic computation is performed which expands patterns such as the active regions L 1 , L 2 . This expanded pattern region is a pattern prohibition region R 1  of the small area dummy pattern Ds. Next, of the aforesaid lattice points, the lattice within the pattern prohibition region R 1  is excluded from the graphic computation, and the small area dummy pat@ern Ds is generated at the remaining lattice points. This generated small area dummy pattern Ds is added to the active regions R 1 , R 2  to give mask generation data. The pattern prohibition region R 1  for the small area dummy pattern Ds is formed also on the periphery of the large area dummy pattern DL. As a result, the pattern to be expanded also contains the large area dummy pattern DL. In this way, a mask pattern wherein dummy patterns are disposed is easily generated automatically. This can also be done manually or automatically by disposing a layer (pattern layer) corresponding to the pattern prohibition region R 1 , and then specifying positions where it is not desired to dispose other small area dummy patterns Ds. 
     Next, the method of manufacturing the semiconductor integrated circuit device of this invention will be described, including the steps for forming the aforesaid active regions and a dummy region (isolation region) DR. 
       FIG. 5  to  FIG. 23  (excluding  FIG. 17 ,  FIG. 18 ) are sectional views showing the sequence of steps in one example of the method of manufacturing the semiconductor integrated circuit device of this invention. In these sectional views, figures with numbers to which (a) is appended represent a section as seen on a line A-A in  FIG. 3  and  FIG. 4 , and figures with numbers to which (b) is appended represent a section through a line B-B in  FIG. 3 . In the (a) figures, the dummy region DR where a dummy pattern is formed, circuit region CR and voltage supply region SR where a voltage supply pattern is formed, are respectively shown. In the (b) figures, a target region TR, small area dummy pattern prohibition region IR and dummy region DR are respectively shown. 
     As shown in  FIGS. 5(   a ) and  5 ( b ), the semiconductor substrate  1  (wafer  1   w ) is provided, and a thin silicon oxide (SiO) film  2  and silicon nitride (SiN) film  3  are formed thereon. The semiconductor substrate  1  is a single crystal silicon wafer wherein, for example, p type impurities are introduced, and it has a resistivity of the order of several ohmcm. The silicon oxide film  2  is a sacrifice film for alleviating the stress between the silicon nitride film  3  and semiconductor substrate  1 , and it is formed, for example, by thermal oxidation. The silicon nitride film  3  is used as a mask for forming a groove, as will be described later. The film thickness of the silicon nitride film  3  is several hundred nm, and it is formed for example by CVD (Chemical Vapor Deposition). 
     Next, as shown in  FIGS. 6(   a ) and  6 ( b ), a photoresist film  4  is formed on the silicon nitride film  3 . The photoresist film  4  is formed to cover the regions where the active regions L 1 , L 2 , L 3 , the large area dummy pattern DL and the small area dummy pattern Ds, which were described in  FIG. 3  and  FIG. 4 , are respectively formed. As stated above, regarding the size of the small area dummy pattern Ds, the fine patterning which would be required with a Levenson mask is not necessary, so that in the region where the small area dummy pattern Ds is formed, there is no impairment of machinability due to the decrease of focal point tolerance that is inherent in super-high resolution techniques, such as the Levenson method. This simplifies the mask design. 
     Next, as shown in  FIGS. 7(   a ) and  7 ( b ), dry etching is performed in the presence of the photoresist film  4 , and the silicon nitride film  3  and silicon oxide film  2  are etched to remove them. 
     After the photoresist film  4  is removed, as shown in  FIGS. 8(   a ) and  8 ( b ), dry etching (anisotropic etching) is performed in the presence of the silicon nitride film  3 , and the semiconductor substrate  1  is etched to form a groove S. The depth of the groove  5  is several hundred nm. The pattern of the groove  5  formed in this step is the reverse of the pattern of the active regions L 1 , etc., shown in the aforesaid  FIG. 3  and  FIG. 4 . 
     In this step, the patterned silicon nitride film  3  is used as a hard mask. By using the thin silicon nitride film  3  as a hard mask, the etching properties are improved, and fine patterning can easily be performed. Instead of using the silicon nitride film  3  as a hard mask, the semiconductor substrate  1  can be etched in the presence of the photoresist film  4  to form the groove  5 . In this case, the steps are simplified. 
     Next, as shown in  FIGS. 9(   a ) and  9 ( b ), a silicon oxide film  6  is formed over the whole surface of the semiconductor substrate  1 , including the interior of the groove  5 . The silicon oxide film  6  can be formed by CVD using, for example, TEOS (tetraethoxysilane) gas and ozone (O 3 ) as raw material gases. The film thickness of the silicon oxide film  6  is a film thickness sufficient to fill the groove  5 . 
     Next, as shown in  FIGS. 10(   a ) and  10 ( b ), the silicon oxide film is polished using CMP. The polishing is performed until the surface of the silicon nitride film  3  is exposed. In this way, the isolation region  7  is formed leaving the silicon oxide film  6  only in the region of the groove  5 . 
     In this process, in the dummy region DR, the small area dummy pattern Ds is formed, so dishing occurs only slightly between the patterns of the small area dummy pattern Ds, and the flatness can be remarkably improved compared with the case where the dummy pattern is not present. Further, as the large area dummy pattern DL is formed also in the target region TR, global dishing is prevented, and the flatness in this region is improved. In the case of this embodiment, the target region TR is formed in the scribe region SR, and deterioration of the flatness in the target region TR may occasionally cause a decrease in the flatness in the product region PR, which is adjacent to the target region TR. However, according to this embodiment, the large area pattern DL is formed in the target region TR, so there is no such effect on the product region PR. 
     Next, as shown in  FIGS. 11(   a ) and  11 ( b ), the silicon nitride film  3  and silicon oxide film  2  are removed to expose the active regions L 1 , L 2 , L 3 , large area dummy pattern DL and small area dummy pattern Ds. The aforesaid  FIG. 3  and  FIG. 4  show the stage when this step is completed. To remove the silicon nitride film  3 , wet etching with hot phosphoric acid is used, for example. Subsequently, the surfaces of the silicon oxide film  2  and isolation region  7  are etched to a suitable degree by hydrofluoric acid (HF), and the substantially flat surface shown in  FIGS. 11(   a ) and  11 ( b ) is obtained. 
     Next, as shown in  FIGS. 12(   a ) and  12 ( b ), a photoresist film, not shown, is formed; p type or n type impurities are ion implanted; and a deep well  8 , n type well  9  and p type well  10  are formed. The deep well  8  functions to electrically isolate the p type well  10  from the semiconductor substrate  1 . 
     Next, as shown in  FIGS. 13(   a ) and  13 ( b ), a silicon oxide film  11 , polycrystalline silicon film  12  and tungsten silicide (WSi) film  13 , which function as a gate electrode, and a silicon nitride film  14 , which functions as a gap insulating film, are deposited. The silicon nitride film  11  is formed, for example, by thermal oxidation or by thermal CVD, and has a film thickness of several nm. The polycrystalline silicon film  12  is formed, for example, by CVD, and n type or p type impurities are introduced into it. The film thickness is several hundred nm. The tungsten silicide film  13  is formed by CVD or by sputtering, and likewise, the film thickness is several hundred nm. The tungsten silicide film  13  decreases the sheet resistance of the gate electrode (gate interconnection) and contributes to improving the response speed of the element. The silicon nitride film  14  is formed, for example, by CVD, and has a film thickness of several hundred nm. 
     Here, the tungsten silicide film  13  was shown as an example, but other metal silicide films, such as a titanium silicide (TiSi) film or a cobalt silicide (CoSi) film may be used. Also, a laminate comprising the tungsten silicide film  13  and polycrystalline silicon film  12  was shown as an example, but laminates of the polycrystalline silicon film, a barrier film and a metal film, such as tungsten (W), may be used. In this case, the resistivity of the gate electrode (gate interconnection) can be further reduced. A metal nitride film, such as tungsten nitride (WN), titanium nitride (TiN) or tantalum nitride (TaN), may be used for the barrier film. In addition to tungsten, tantalum (Ta) or titanium (Ti) can also be used for the metal film. 
     Next, as shown in  FIGS. 14(   a ) and  14 ( b ), a photoresist film  15  is formed on the silicon nitride film  14 , and dry etching (anisotropic etching) is performed to pattern the silicon nitride film  14 , as shown in  FIGS. 15(   a ) and  15 ( b ). In this way, a gap insulating film  16  is formed. The patterning of this gap insulating film  16  will be described later. In the exposure step for forming the photoresist film  15 , the target T 1  is used for position detection in mask alignment. 
     Next, the photoresist film  15  is removed by ashing or the like, and the tungsten silicide film  13 , polycrystalline silicon film  12  and silicon oxide film  11  are etched (anisotropically etched) in the presence of the gap insulating film  16  to form a gate electrode  17 , as shown in  FIGS. 16(   a ) and  16 ( b ). 
     At this time, a second small area dummy pattern Ds 2  and target T 2  are formed simultaneously with the gate electrode  17 . 
       FIG. 17  is a plan view showing the situation at this stage, corresponding to  FIG. 3 .  FIG. 18  is an enlarged plan view corresponding to  FIG. 4 . 
     As shown in  FIG. 17 , the target T 2  is formed in addition to the small area dummy pattern Ds 2  in the scribe region SR. The target T 2  is used for exposure, for example in a step to form interconnections or connection holes. The target T 2  is formed on the large area dummy pattern DL so as to be enclosed by it. The pattern prohibition region R 2  is also formed on the periphery of the target T 2  to prevent a decrease in the recognition rate when the target T 2  is used later, and the large area dummy pattern DL is formed to be larger than the pattern prohibition region R 2 . Hence, no pattern other than the target T 2  is formed inside the pattern prohibition region R 2 , so that the target T 2  can be accurately recognized. Further, since the target T 2  is formed on the large area dummy pattern DL, the target T 2  is not formed on a depressed substrate, but is formed on a flattened substrate. Therefore, in a subsequent exposure step using the target T 2 , the target T 2  can be accurately recognized, and the mask alignment precision is improved. Further, since the large area dummy pattern DL is formed underneath the target T 2 , the flatness of this region is improved, the flatness of its periphery, in particular the product region PR adjacent to the target T 2 , is improved, which results in an improvement of the photolithography margin, and etching is easily performed. 
     The small area dummy pattern Ds 2  is also formed in the scribe region SR. This improves the flatness of this region. However, it is not disposed in the small area dummy pattern prohibition region R 1 . The small area dummy pattern Ds 2  will be described later. 
     The gate electrode  17  is formed in the product region PR. Plural small area dummy patterns Ds 2  are disposed between the patterns of the gate electrode  17 . As in the case of  FIG. 3 , they are not disposed in the small area dummy pattern prohibition region R 2 . The pattern prohibition region R 1  is formed in the same way as described above. 
     The small area dummy pattern Ds 2  is formed on the inter-pattern spaces of the small area dummy pattern Ds of the lower layer, as shown in  FIG. 18 . Specifically, the pitch of the small area dummy pattern Ds 2  and that of the small area dummy pattern Ds in the layer underneath are offset by ½. In other words, the small area dummy pattern Ds 2  is offset by Px in the x direction and by Py in the y direction with respect to the small area dummy pattern Ds. Px, Py are, for example, both 0.7 μm. In this way, by forming the small area dummy pattern Ds 2  with an offset of ½ pitch, the effect of dishing in the layer underneath is eliminated and the flatness is improved. In other words, the dishing of the layer underneath occurs in a space part of the small area dummy pattern Ds, and since the small area dummy pattern Ds 2  is formed on top of it, the dishing is not superimposed. Dishing due to the small area dummy pattern Ds 2  occurs in its space part, but as the small area dummy pattern Ds is formed in the layer underneath it, dishing does not occur here. In other words, by providing the small area dummy patterns Ds, Ds 2  as in this embodiment, dishing does not occur in the layer above the region where dishing occurs in the lower layer, and the part where dishing occurs in the upper layer is formed over the region where dishing does not occur in the lower layer. Hence, the total amount of dishing due to the two layers is reduced, and the overall flatness can be increased. 
     The situation wherein the small area dummy pattern Ds 2  of the upper layer is not formed in the pattern prohibition region R 1  is identical to the case of the small area dummy pattern Ds. Further, the small area dummy pattern Ds 2  is generated in an identical way to the small area dummy pattern Ds, except that the lattice positions are shifted by ½ pitch. 
     Herein, a case was described where the small area dummy patterns Ds, Ds 2  were shifted by ½ pitch, but the shift amount may be any value provided that the side edge of Ds 2  is formed to overlap with Ds 1 . In other words, Ds 2  must be formed in a part above the space part of Ds 1 . 
     Next, impurities are ion-implanted to form an impurity semiconductor region  19 , as shown in  FIGS. 19(   a ) and  19 ( b ). Low concentrations of impurities are introduced into the impurity semiconductor region  19 . The conductivity of the impurity introduced is chosen according to the channel type of the MISFET that is being formed. Thus, p type impurities are implanted in an n type well region to form a p channel MISFET; and, n type impurities are introduced in a p well region to form an n channel MISFET. 
     Next, as shown in  FIGS. 20(   a ) and  20 ( b ), a silicon nitride film, for example, is formed over the whole surface of the semiconductor substrate  1 , and this is subjected to anisotropic etching to form a side wall spacer  20 . Subsequently, ion implantation is performed to form an impurity semiconductor region  21 . The impurity ions introduced into the impurity semiconductor region  21  are chosen to give a suitable conductivity depending on the region, as in the case described above. High concentrations of impurities are introduced into the impurity semiconductor region  21 , and a source/drain having an LDD (Lightly Doped Drain) structure is formed together with the impurity semiconductor region  19 . 
     Next, as shown in  FIGS. 21(   a ) and  21 ( b ), a silicon oxide film  22  enclosing the gate electrode pattern is formed, and as shown in  FIGS. 22(   a ) and  22 ( b ), the silicon oxide film  22  is polished by CMP to flatten its surface. During this flattening, since the small area dummy pattern Ds 2  is formed in the same layer as the gate electrode pattern, the flatness is improved. In particular, since the small area dummy pattern Ds 2  is offset by ½ pitch with respect to the small area dummy pattern Ds of the lower layer, the dishing of the two layers in the spaces between the patterns is not superimposed. As a result, a decrease of the flatness due to superimposition of dishing is suppressed. Also, in the region of the target T 2 , since the large area dummy pattern DL is formed in the layer underneath, global dishing does not occur, and the flatness is improved also in the scribe region SR. Hence, there is no adverse effect on the product region PR, and the yield is improved. Moreover, the small area dummy pattern Ds 2  is also disposed in the scribe region SR, so that the flatness is improved in the same way as in the product region PR. 
     Herein, a case was described wherein the target T 2  was formed in the scribe region SR, but the target T 2  may also be formed in the product region PR. Further, the target pattern was given as an example of a pattern required for pattern recognition, but it will be understood that the invention may also be applied to any pattern which can be used for optical pattern recognition. For example, it may be a testing pattern used for quality control in mask alignment, a test pattern for monitoring the film thickness, or a position detecting pattern used for laser repair. 
     Next, as shown in  FIGS. 23(   a ) and  23 ( b ), a connecting hole  23  is formed in the silicon oxide film  22 , and a connecting plug  24  is formed in the connection hole  23 . An interconnection  25  is also formed on the silicon oxide film  22 . 
     The connecting hole  23  is formed by anisotropic etching using a photoresist film, not shown, as a mask. When this photoresist film is formed, i.e., for the exposure of this step, the aforesaid target T 2  may be used for position detection in mask alignment. In addition to polycrystalline silicon, laminates of titanium nitride films and tungsten films may, for example, be used for the connecting plug. To form the connecting plug, a connecting hole is opened, an electrically conducting material is formed to fill it, and the electrically conducting film in regions other than the connecting hole is removed by CMP. 
     The interconnection  25  is formed by anisotropic etching using a photoresist film, not shown, in the same way. When this photoresist film is formed, i.e. for the exposure of this step, the aforesaid target T 2  may be used for position detection in mask alignment. Metal materials, such as tungsten and laminates of, for example, titanium nitride and tungsten, may be used for the interconnection  25 . The interconnection  25  is formed by forming a film of the metal material, and patterning it. 
     A multilayer interconnection structure can be formed by forming interconnections in the upper layers, such as the second and third layers, and since this is identical to the case of the aforesaid interconnection  25 , its description will be omitted. 
       FIG. 24  is a plan view showing the situation when the wafer process is complete, and the scribe region SR is at the scribe stage. The wafer  1   w  is divided by the scribe line SL to form the chip  1   c . The width of the scribe line SL is a dimension obtained by adding play to the blade width (e.g., 35 μm) As a result, in the chip  1   c , a region of the order of several tens of μm remains as the distance from the edge of the product region PR to the edge of the chip  1   c . Part of the aforesaid targets T 1 , T 2 , and the large area dummy pattern DL, remain in this residual region. In  FIG. 24 , a target T 3  is shown. This is a target pattern formed simultaneously when the interconnection  25  of the first layer is patterned. The target T 3  is used to form an interconnection or through hole in the upper layer. 
     This invention as conceived by the inventors has been described in detail based on one embodiment of the invention, however it will be understood that the invention is not limited to this embodiment, various modifications being possible within the scope and spirit of the appended claims. 
     For example, in the embodiment, an example was given where the offset of the small area dummy patterns Ds, Ds 2  was provided in both the x direction and y direction, but the offset may be provided in only one direction. 
     Further, the case was shown where the small area dummy patterns Ds, Ds 2  were rectangular, but they may also be of another shape, such as oblong. For example, they may be lattice-shaped dummy patterns, as shown in  FIG. 25  and  FIG. 26 . Specifically, a lattice-shaped pattern  26  can be formed simultaneously with the active region L 1 , as shown in  FIG. 25 , or a lattice-shaped pattern  27  can be simultaneously formed with the gate electrode  17  with a ½ pitch shift relative to the pattern  26 , as shown in  FIG. 26 . Alternatively, instead of the small area target patterns Ds, Ds 2 , line-shaped dummy patterns can be formed, as shown in  FIG. 27  and  FIG. 28 . Specifically, a line-shaped dummy pattern  28  can be formed simultaneously with the active region L 1 , as shown in  FIG. 27 , or a line-shaped pattern  29  can be simultaneously formed with the gate electrode  17  with a ½ pitch shift relative to the pattern  28 , as shown in  FIG. 28 . These dummy patterns  26 ,  27 ,  28 ,  29  are not formed in the pattern prohibition region R 1 , which is identical to the case of the embodiment. Further, the sizes of the patterns  26 ,  27 ,  28 ,  29  are also identical to those of the embodiment. 
     Among the inventive features disclosed in this application, the effects obtained by representative aspects of the invention may simply be described as follows. 
     (1) Dishing in plural laminated flattened surfaces is suppressed. 
     (2) Surface flattening in pattern regions of a large area for optical position detection, e.g., of targets, is improved. 
     (3) The flatness of plural laminated surfaces, or the flatness of large area patterns, such as targets, is improved, and the machining margin in a photolithography step and etching step is improved.