Patent Publication Number: US-7902609-B2

Title: Semiconductor devices including multiple stress films in interface area

Description:
REFERENCE TO PRIORITY APPLICATION 
     This application claims priority to U.S. application Ser. No. 11/851,500, filed Sep. 7, 2007, now U.S. Pat. No. 7,642,148 the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein. 
     FIELD OF THE INVENTION 
     The present invention relates to semiconductor devices and methods of producing the same and, more particularly, to semiconductor devices including stress films and methods of producing the same. 
     BACKGROUND 
     As the integration density and/or speed of metal oxide semiconductor field effect transistors (MOSFETs) has continued to increase, various processes have been studied to try increase the performance and/or reliability of the transistors. Particularly, many processes have been developed to try increase mobility of electrons or holes in order to produce high-performance transistors. 
     A process of applying physical stress to a channel area to change an energy band structure of the channel area may be performed to increase the mobility of the electrons or the holes. For example, NMOS transistors may have improved performance in the case of when tensile stress is applied to a channel, and PMOS transistors may have improved performance in the case of when compressive stress is applied to a channel. Accordingly, a dual stress film structure has been proposed where a tensile stress film is formed on the NMOS transistors and a compressive stress film is formed on the PMOS transistors, to allow improved performances of both the NMOS transistors and the PMOS transistors. 
     SUMMARY 
     Some embodiments of the present invention provide semiconductor devices including a semiconductor substrate that includes a first transistor area having a first gate electrode and first source/drain areas, a second transistor area having a second gate electrode and second source/drain areas, and an interface area provided at an interface of the first transistor area and the second transistor area and having a third gate electrode. A first stress film is on the first gate electrode and the first source/drain areas of the first transistor area and on at least a portion of the third gate electrode of the interface area. A second stress film is on the second gate electrode and the second source/drain areas of the second transistor area and on at least a portion of the third gate electrode of the interface area and not overlapping the first stress film on the third gate electrode of the interface area or overlapping at least a portion of the first stress film. The second stress film overlapping at least the portion of the first stress film is thinner than the second stress film in the second transistor area. 
     Other embodiments of the present invention provide methods of producing a semiconductor device that include forming a first stress film on a first gate electrode and first source/drain areas of a first transistor area of a semiconductor substrate and on at least a portion of a third gate electrode of an interface area between the first transistor area and a second transistor area and forming a second stress film on a second gate electrode and second source/drain areas of the second transistor area of the semiconductor substrate and overlapping at least a portion of the first stress film on the third gate electrode of the interface area. A first interlayer insulating film is formed on the first stress film and the second stress film. The first interlayer insulating film is planarized to expose the second stress film overlapping at least a portion of the first stress film on the third gate electrode. At least a portion of the exposed second stress film is removed, and a second interlayer insulating film is formed on the first interlayer insulating film. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
         FIG. 1A  is a cross-sectional view of a semiconductor device according to various embodiments of the present invention; 
         FIG. 1B  is a cross-sectional view of a semiconductor device according to other embodiments of the present invention; 
         FIG. 1C  is a cross-sectional view of a semiconductor device according to yet other embodiments of the present invention; 
         FIGS. 2 to 17  are cross-sectional views sequentially illustrating methods of producing semiconductor devices and devices so produced according to various embodiments of the present invention; and 
         FIG. 18  is a cross-sectional view illustrating methods of producing semiconductor devices and devices so produced according to other embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention is described more fully hereinafter with reference to the accompanying drawings, in which example embodiments of the present invention are shown. The present invention may, however, be embodied in many different forms and should not be construed as limited to the example embodiments set forth herein. Rather, these example embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. In the drawings, the sizes and relative sizes of layers and regions may be exaggerated for clarity. 
     It will be understood that when an element or layer is referred to as being “on,” “connected to” or “coupled to” another element or layer, it can be directly on, connected or coupled to the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to” or “directly coupled to” another element or layer, there are no intervening elements or layers present. Like reference numerals refer to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention. 
     Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper,” “top,” “bottom” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” “including,” “have” and/or “having” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Example embodiments of the present invention are described herein with reference to cross-section illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of the present invention. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, example embodiments of the present invention should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an implanted region illustrated as a rectangle will, typically, have rounded or curved features and/or a gradient of implant concentration at its edges rather than a binary change from implanted to non-implanted region. Likewise, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation takes place. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of the present invention. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     Some embodiments of the invention may arise from recognition that when a dual stress film is applied, an area where the tensile stress film and the compressive stress film partially overlap may be formed at the interface of the NMOS transistor and the PMOS transistor according to characteristics of devices and/or photolithography margins. The overlapping area of the stress film is generally thicker than the area where the single stress film is layered. Therefore, in the case of when contact holes are formed through the single stress film and the overlapping area using an etching process, the contact holes are first formed through the single stress film, and a lower structure of the contact holes which are formed beforehand may be attacked before the contact holes are formed through the overlapping area. Accordingly, contact characteristics and/or reliability of the semiconductor device may be reduced. Embodiments of the invention provide devices and methods that can reduce or eliminate this overlap of the first and second stress films. 
     Hereinafter, a description will be given of semiconductor devices according to embodiments of the present invention with reference to the accompanying drawings. 
       FIG. 1A  is a cross-sectional view of a semiconductor device that is produced using methods according to various embodiments of the present invention. With reference to  FIG. 1A , a semiconductor device includes a plurality of transistors that are formed on a semiconductor substrate  100 . The semiconductor substrate  100  may be divided into at least three areas, for example, an NMOS transistor area (I), a PMOS transistor area (II), and an interface area (III). 
     The semiconductor substrate  100  is included in the NMOS transistor area (I), the PMOS transistor area (II), and the interface area (III). The semiconductor substrate  100  may comprise a single monolithic substrate including the different areas. The semiconductor substrate  100  may be made of, for example, Si, Ge, SiGe, GaP, GaAs, SiC, SiGeC, InAs and/or InP. Moreover, the semiconductor substrate  100  may be a laminated substrate where at least two layers including a semiconductor substance layer formed of the above-mentioned substances and an insulating layer are layered. Examples of the semiconductor substrate may include an SOI (Semiconductor On Insulator) substrate. An element isolation film  111  that defines an active area is formed in the semiconductor substrate  100 . Furthermore, a P-type well may be formed in the semiconductor substrate  100  of the NMOS transistor area (I) and a N-type well may be formed in the semiconductor substrate  100  of the PMOS transistor area (II), which are not shown for clarity. 
     The NMOS transistor which is formed in the NMOS transistor area (I) and the PMOS transistor which is formed in the PMOS transistor area (II) include gate electrodes  125   a  and  125   b  on the semiconductor substrate  100  so that gate insulating films  123  are interposed between the gate electrodes and the semiconductor substrate. Source/drain areas  121   a  and  121   b  are provided in the semiconductor substrate  100  so that the source/drain areas face each other while the gate electrodes  125   a  and  125   b  are provided between the source/drain areas. Channel areas are provided between the source/drain areas  121   a  and  121   b  facing each other and overlapping lower portions of the gate electrodes  125   a  and  125   b.    
     The gate electrodes  125   a  and  125   b  may be a single film formed of, for example, a polysilicon film, a metal film, or a metal silicide film, or a laminated film thereof. In the polysilicon film, for example, an N-type impurity is doped into the NMOS transistor area (I) and a P-type impurity is doped into the PMOS transistor area (II). However, the polysilicon film is not limited to the above-mentioned structure. The conductivity types of impurity doped into the areas of the polysilicon film may be reversed as compared to the above-mentioned structure, or the areas may have the same conductivity type. Examples of metal components constituting the metal film or the silicide film may include tungsten (W), cobalt (Co), nickel (Ni), titanium (Ti) and/or tantalum (Ta). However, hereinafter, only a description of the gate electrodes  125   a  and  125   b  that include the polysilicon film and the silicide films  127   a  and  127   b  formed on the polysilicon film will be given, for the sake of simplicity. 
     The gate insulating films  123  are interposed between the semiconductor substrate  100  and the gate electrodes  125   a  and  125   b . The gate insulating films  123  may be formed of, for example, a silicon oxide film. However, a film constituting the gate insulating film is not limited to the silicon oxide film, but another high dielectric insulating film and/or low dielectric insulating film may be used if necessary. Multilayer gate insulating films  123  also may be provided. 
     Spacers  129  are formed on walls (sidewalk) of the gate electrodes  125   a  and  125   b  and the gate insulating films  123 . The spacers are formed of, for example, a silicon nitride film. 
     The source/drain areas  121   a  and  121   b  may include an LDD (lightly doped drain) area that overlaps the spacers  129  and a high-concentration doping area that does not overlap the spacers  129 . In the NMOS transistor area (I), the N-type impurity is doped into the LDD area at a low concentration, and the N-type impurity is doped into the high-concentration doping area at a high concentration. In the PMOS transistor area (II), the P-type impurity is doped into the LDD area at a low concentration, and the P-type impurity is doped into the high-concentration doping area at a high concentration. In modified embodiments of the present invention which is not shown, a DDD (double diffused drain) area may be provided instead of the LDD area. 
     The source/drain areas  121   a  and  121   b  may include the silicide films  127   a  and  127   b  that are identical or similar to the silicide films formed on upper parts of the gate electrodes  125   a  and  125   b . In the specification, the silicide films  127   a  and  127   b  are divided for the convenience of description. That is, the silicide films  127   a  and  127   b  included in the source/drain areas  121   a  and  121   b  and the silicide films  127   a  and  127   b  included in the gate electrodes  125   a  and  125   b  are designated by the same reference numeral if they are provided in the same area. However, substances constituting the films may be different from each other or the same as each other. 
     Meanwhile, a gate electrode  125   c  and a spacer  129  that have substantially the same structure as those of the NMOS transistor area (I) and the PMOS transistor area (II) are provided in the interface area (III). Accordingly, an upper part of the gate electrode  125   c  of the interface area (III) may include a silicide film  127   c . The gate electrode  125   c  of the interface area (III) may be provided on the element isolation film  111 . In this case, as shown in  FIG. 1 , the gate insulating film  123  may be omitted. However, a gate insulating film may also be present. Meanwhile, in other embodiments, the gate electrode  125   c  of the interface area (III) may be formed on the active area. In this case, the gate electrode  125   c  may constitute a portion of the NMOS transistor or the PMOS transistor. 
     A first stress film  131  and/or a second stress film  135  are provided on the above-mentioned gate electrodes  125   a ,  125   b , and  125   c  of the NMOS transistor area (I), the PMOS transistor area (II), and the interface area (III). 
     In detail, the first stress film  131  having tensile stress is provided in the NMOS transistor area (I), and the second stress film  135  having compressive stress is provided in the PMOS transistor area (II). The first stress film  131  and the second stress film  135  may be formed of, for example, SiN, SiON, SiBN, SiC, SiC:H, SiCOH, SiCN and/or SiO 2 , and each may have a thickness in the range of about 1 to about 1,000 Å. In some embodiments, the first stress film  131  and the second stress film  135  may be substantially the same as each other in terms of thickness. 
     The stress of the first stress film  131  and the second stress film  135  may be controlled depending on a composition ratio of substances constituting the films and/or formation conditions of the substances. For example, the first stress film  131  may have tensile stress of about 0.01 to about 5 GPa, and the second stress film  135  may have compressive stress of about −0.01 to about −5 GPa. 
     The first stress film  131  and the second stress film  135  apply stress to the channel area so as to increase mobility of carriers. That is, the first stress film  131  is on, and in some embodiments covers, the gate electrode  125   a  and the source/drain areas  121   a  of the NMOS transistor to apply tensile stress to the channel area, thereby increasing mobility of the electron carriers. The second stress film  135  is on, and in some embodiments covers, the gate electrode  125   b  and the source/drain areas  121   b  of the PMOS transistor to apply compressive stress to the channel area, thereby increasing mobility of the hole carriers. 
     Meanwhile, the first stress film  131  and the second stress film  135  meet each other in the interface area (III). The area where the first stress film  131  and the second stress film  135  partially overlap while the contact hole  147   c  formed on the gate electrode  125   c  is provided between the first stress film and the second stress film may be included in the interface area according to the process margin. However, the thickness (Dc) of the second stress film  135  in the area where the first stress film  131  and the second stress film  135  partially overlap may be smaller than the thickness of (Db) in the second transistor area. 
     Since the second stress film  135  is relatively thin in the area where the first stress film  131  and the second stress film  135  partially overlap, the level of the second stress film  135  in the area where the first stress film  131  and the second stress film  135  partially overlap may be substantially similar to the level of the first stress film  131  on the gate electrode  125   a  of the first transistor area (I) or the level of the second stress film  135  on the gate electrode  125   b  of the second transistor area (II). In connection with this, the term “level” means the height or distance from the semiconductor substrate  100 . 
       FIG. 1A  illustrates that the first stress film  131  is provided under the second stress film  135  in the overlapping area. Hereinafter, a description will be given on the assumption that the first stress film  131  is provided under the second stress film  135  in the overlapping area. However, the order of layering may be changed. 
     A first interlayer insulating film  140  is provided on the first stress film  131  and on the second stress film  135 . That is, the first interlayer insulating film  140  may be provided so that the interlayer insulating film is not divided into the NMOS transistor area (I), the PMOS transistor area (II), and the interface area (III). 
     The first interlayer insulating film  140  and a second interlayer insulating film  142  are provided on the first stress film  131  and the second stress film  135 . The upper side of the first interlayer insulating film  140 , that is, the interface between the first interlayer insulating film  140  and the second interlayer insulating film  142 , can be flat, and has a level that is about the same as that of the highest upper side (furthest from the substrate) of the upper sides of the first stress film  131  and the second stress film  135  provided on the upper sides of the gate electrodes  125   a ,  125   b , and  125   c.    
     The first and the second interlayer insulating films  140  and  142  may be formed of, for example, TEOS (tetra ethyl ortho silicate), O 3 -TEOS, USG (undoped silicate glass), PSG (phosphosilicate glass), BSG (borosilicate glass), BPSG (borophosphosilicate glass), FSG (fluoride silicate glass), SOG (spin on glass) and/or TOSZ (tonen silazene). The first interlayer insulating film  140  and the second interlayer insulating film  142  may be formed of the same material. 
     Contact holes  147   a ,  147   b , and  147   c  are provided in the interlayer insulating films  140  and  142 , the first stress film  131 , and the second stress film  135  to expose the gate electrodes  125   a ,  125   b , and  125   c  and/or the source/drain areas  121   a  and  121   b . In detail, the contact hole  147   a  may be formed through the interlayer insulating film  140  and the first stress film  131  in the NMOS transistor area (I). The second contact hole  147   b  may be formed through the interlayer insulating film  140  and the second stress film  135  in the PMOS transistor area (II). The third contact hole  147   c  may be formed through the interlayer insulating film  140 , the second stress film  135 , and the first stress film  131  in the interface area (III). The thickness (Dc) of the second stress film  135  through which the third contact hole  147   c  is formed may be smaller than the thickness (Db) of the second stress film  135  of the second transistor area (II) through which the second contact hole  147   b  is formed. 
     Contact plugs  171 ,  173 , and  175  are in, and in some embodiments may fill, the contact holes  147   a ,  147   b , and  147   c . The contact plugs  171 ,  173 , and  175  are electrically connected to the gate electrodes  125   a ,  125   b , and  125   c  or the source/drain areas  121   a  and  121   b . The contact plugs  171 ,  173 , and  175  may be made of a metal substance such as W, Cu and/or Al, and/or a conductive substance such as conductive polysilicon. 
       FIG. 1B  is a cross-sectional view of a semiconductor device according to other embodiments of the present invention. In the present embodiments, a description may be omitted or briefly given of the same structure as the embodiment of  FIG. 1A , and a difference in the embodiments will be mainly described. 
     With reference to  FIG. 1B , a semiconductor device according to the present embodiments is different from that of the embodiments of  FIG. 1A  in that an etch stop film  133  is further provided on the first stress film  131 . The etch stop film  133  may be formed of a silicon oxide film, and/or an LTO (low temperature oxide) film. 
     The interface area (III) may include the area where the first stress film  131  and the second stress film  135  partially overlap, and the etch stop film  133  may be interposed between the first stress film and the second stress film in this interface area. Meanwhile, the overlapping area where the etch stop film  133  is provided on the first stress film  131  is shown in  FIG. 1B , and the structure having the overlapping area will be described. However, the etch stop film  133  may be provided on the second stress film  135 . In this case, the order of layering of the first stress film  131  and the second stress film  135  may be changed. Additionally, modifications of the present embodiments may include the etch stop film  133  formed on both the first stress film  131  and the second stress film  135 . 
     In the case of when the etch stop film  133  is formed on the first stress film  131 , the first interlayer insulating film  140  is formed on the etch stop film  133  and the second stress film  135 . The second interlayer insulating film  142  may be formed on the first interlayer insulating film  140 . 
     In the case of when the etch stop film  133  is formed, the first contact hole  147   a  may be formed through the first and the second interlayer insulating films  140  and  142 , the etch stop film  133 , and the first stress film  131 . The third contact hole  147   c  may be formed through the first and the second interlayer insulating films  140  and  142 , the second stress film  135 , the etch stop film  133 , and the first stress film  131 . However, the thickness (Dc) of the second stress film  135  through which the third contact hole  147   c  is formed is smaller than the thickness (Db) in the second transistor area. 
       FIG. 1C  is a cross-sectional view of a semiconductor device according to other embodiments of the present invention. In the present embodiments, a description may be omitted or briefly given of the same structure as the embodiment of  FIG. 1A , and a difference in embodiments will be mainly described. 
     With reference to  FIG. 1C , a semiconductor device according to the present embodiments is different from those of the embodiments of  FIGS. 1A and 1B  in that the second stress film  135  does not overlap the third gate electrode  125   c . Rather, the second stress film  135  abuts against the first stress film  131  in the interface area (III). In the case of when the second stress film  135  does not overlap the third gate electrode  125   c  and the etch stop film  133  is formed on the third gate electrode  125   c , the etch stop film  133  is exposed to the second interlayer insulating film  142 . In the case of when the etch stop film  133  is not formed, the first stress film  131  is exposed. This is not shown for clarity. 
     As shown in  FIG. 1C , since the second stress film  135  does not overlap the third gate electrode  125   c , the level of the etch stop film  133  on the third gate electrode  125   c  may be substantially similar to the level of the first stress film  131  on the gate electrode  125   a  of the first transistor area (I) or the level of the second stress film  135  on the gate electrode  125   b  of the second transistor area (II). 
     The first contact hole  147   a  may be formed through the first and the second interlayer insulating films  140  and  142 , the etch stop film  133 , and the first stress film  131  in the NMOS transistor area (I), and the second contact hole  147   b  may be formed through the first and the second interlayer insulating films  140  and  142 , and the second stress film  135  in the PMOS transistor area (II). The third contact hole  147   c  may be formed through the first and the second interlayer insulating films  140  and  142 , the etch stop film  133 , and the first stress film  131 . This may be different from the case of when the third contact hole  147   c  is formed through the second stress film  135  in  FIG. 1A . 
     Hereinafter, a description will be given of methods of producing the above-mentioned semiconductor devices. 
       FIGS. 2 to 17  are cross-sectional views of intermediate structures at steps of methods of producing semiconductor devices, and devices so produced, according to the embodiments of the present invention shown in  FIG. 1A . 
     With reference to  FIG. 2 , the semiconductor substrate  100  is divided into the NMOS transistor area (I), the PMOS transistor area (II), and the interface area (III), and the element isolation films  111  are formed in the areas to define active areas. The element isolation films  111  may be formed of, for example, a silicon oxide film, and the formation may be performed using a LOCOS (local oxidation of silicon) process and/or an STI (shallow trench isolation) process. Since various types of methods of forming the element isolation films  111  are known to those skilled in the art, a detailed description thereof will be omitted. 
     Meanwhile, the cross-sectional view of  FIG. 2  shows the formation of only the element isolation film  111  in the interface area (III). However, only the active area may be formed in the interface area (III), or both the element isolation film  111  and the active area may be formed in the interface area (III). 
     Additionally, before and/or after the element isolation films  111  are formed, the NMOS transistor area (I) of the semiconductor substrate  100  may include the p-type impurity doped at a low concentration, and the PMOS transistor area (II) of the semiconductor substrate  100  may include the n-type impurity doped at a low concentration, which are not shown. For example, in the case of when a P-type substrate is used as the semiconductor substrate  100 , the n-type impurity may be doped into the PMOS transistor area (II) to form an n-well. In the case of when the P-type substrate is used as the base substrate, the p-type impurity may be doped into the NMOS transistor area (I) to form a p-well, but this is not done in other embodiments. 
     With reference to  FIG. 3 , an insulating substance and a conductive substance are applied to a front surface of the semiconductor substrate  100 . 
     The insulating substance layer may be, for example, a silicon oxide film. The application may be performed by a thermal oxidation process, chemical vapor deposition (CVD), low pressure chemical vapor deposition (LPCVD) and/or plasma enhanced chemical vapor deposition (PECVD). 
     The conductive substance may be, for example, polysilicon and/or metal into which n-type or p-type impurity is doped. The application may be performed by low pressure CVD (LPCVD), atomic layer deposition (ALD), physical vapor deposition (PVD) and/or metal organic CVD (MOCVD). Hereinafter, the case of when polysilicon is used as the conductive substance will be described. 
     The conductive substance layer and the insulating substance layer are patterned to form the gate electrodes  125   a ,  125   b , and  125   c , and the gate insulating film  123 . 
     Subsequently, the source/drain areas are formed in the active areas of the semiconductor substrate  100 , and the silicide films are formed on the upper sides of the gate electrodes  125   a ,  125   b , and  125   c  and the source/drain areas.  FIGS. 4 to 7  illustrate the formation of the source/drain areas and the silicide films. With reference to  FIG. 4 , the low concentration n-type impurity (see reference numeral  120   a ) is doped into the active area of the NMOS transistor area (I), and the low concentration p-type impurity (see reference numeral  120   b ) is doped into the active area of the PMOS transistor area (II). For example, when the low concentration n-type impurity is doped, a photoresist film covers the PMOS transistor area (II) to dope the n-type impurity into only the NMOS transistor area (I). When the low concentration p-type impurity is doped, the photoresist film covers the NMOS transistor area (II) to dope the p-type impurity into only the PMOS transistor area (I). 
     With reference to  FIG. 5 , the spacers  129  are formed on walls of the gate electrodes  125   a ,  125   b , and  125   c , and the gate insulating films  123 . The spacers  129  may be formed of, for example, a silicon nitride film. The silicon nitride film may be layered on a front side of the semiconductor substrate  100  and an etch back process may be performed to form the spacers  129 . In the drawing, the spacers  129  are arranged so that the upper side of the gate electrode is exposed and the upper sides of the spacers  129  are on the same horizontal plane as the upper sides of the gate electrodes  125   a ,  125   b , and  125   c . Hereinafter, the above-mentioned structure will be described. However, the spacer  129  may be recessed so that the upper side of the spacer is lower than the upper sides of the gate electrodes  125   a ,  125   b , and  125   c  which may facilitate forming the silicide film. Alternatively, the spacer  129  may be formed so as to at least partially cover the upper sides of the gate electrodes  125   a ,  125   b , and  125   c.    
     With reference to  FIG. 6 , the high concentration n-type impurity is doped into the active area of the NMOS transistor area (I), and the high concentration p-type impurity is doped into the active area of the PMOS transistor area (II). In detail, when the high concentration n-type impurity is doped, the photoresist film covers the PMOS transistor area (II) and the gate electrodes  125   a ,  125   b , and  125   c  and the spacer  129  are doped using a doping mask, thereby doping the high concentration n-type impurity into only the exposed active area of the NMOS transistor area (I). Additionally, when the high concentration p-type impurity is doped, the photoresist film covers the NMOS transistor area (I) and the gate electrodes  125   a ,  125   b , and  125   c  and the spacer  129  are doped using the doping mask, thereby doping the high concentration p-type impurity into only the PMOS transistor area (II). As a result, the source/drain areas  121   a  and  121   b  including the high concentration doping area and the low concentration doping area are produced. 
     With reference to  FIG. 7 , the upper sides of the gate electrodes  125   a ,  125   b , and  125   c  and the exposed upper sides of the source/drain areas  121   a  and  121   b  are subjected to silicidation. A metal film for silicidation, for example, metal such as tungsten (W), cobalt (Co), nickel (Ni), titanium (Ti), and/or tantalum (Ta), may be applied to the front side of the semiconductor substrate  100  and then subjected to heat treatment to perform the silicidation. For example, in the case of when the gate electrodes  125   a ,  125   b , and  125   c  are formed of polysilicon, the upper sides of the source/drain areas  121   a  and  121   b  and the upper sides of the gate electrodes  125   a ,  125   b , and  125   c  may be silicidated by the heat treatment of the semiconductor substrate  100 . Subsequently, the metal film for silicidation that is not silicidated on the semiconductor substrate  100  may be removed to form the self-aligned silicide films  127   a ,  127   b , and  127   c  on the upper sides of the gate electrodes  125   a ,  125   b , and  125   c  and the exposed upper sides of the source/drain areas  121   a  and  121   b.    
     Subsequently, the first stress film  131  is formed in the NMOS transistor area (I), and the second stress film  135  is formed in the PMOS transistor area (II). In connection with this, the first stress film  131  and the second stress film  135  are set to partially overlap each other in the interface area (III) in consideration of the process margin. More specific processes are shown in  FIGS. 8 to 11 . 
     With reference to  FIG. 8 , a layer for a first stress film  131   a  is formed on the front side of the resulting structure of  FIG. 7 . The layer for a first stress film  131   a  may be, for example, a tensile stress film. The layer for a first stress film  131   a  may be formed of, for example, SiN, SiON, SiBN, SiC, SiC:H, SiCOH, SiCN and/or SiO 2 . The layer for a first stress film  131   a  may have a thickness in the range of about 1 to about 1,000 Å, and may be formed by CVD (chemical vapor deposition), thermal CVD, PECVD (plasma enhanced CVD) and/or high density plasma CVD. For example, the layer for a first stress film  131   a  made of SiN may be formed by a silicon source gas such as SiH 4  and a nitrogen source gas such as NH 3  and/or N 2  at a temperature of about 300 to about 600° C. and a pressure of about 1 to about 10 torr. 
     Tensile stress of the layer for a first stress film  131   a  may be controlled using a deposition condition or a composition ratio of substances constituting the film. For example, the stress may be controlled to the range of about 0.01 to about 5 GPa. 
     Subsequently, a first photoresist pattern  201  is formed on the layer for a first stress film  131   a . The first photoresist pattern  201  may cover the entire surface of the NMOS transistor area (I) while the PMOS transistor area (II) is exposed. Additionally, the first photoresist pattern  201  may be formed to cover a portion of the gate electrode  125   c  of the interface area (III), and in some embodiments the entire gate electrode, so as to provide the process margin, that is, to completely cover the entire NMOS transistor area (I). 
     With reference to  FIG. 9 , the layer for a first stress film  131   a  is etched using the first photoresist pattern  201  as an etching mask. The etching may be performed using a dry etching process and/or a wet etching process. As shown in  FIG. 9 , the first stress film (see reference numeral  131 ) is formed in the NMOS transistor area (I) and the layer for a first stress film  131   a  is removed from the PMOS transistor area (II) resulting from the etching. The first stress film (see reference numeral  131 ) is formed in the interface area (III) so that the first stress film overlaps a portion of the gate electrode  125   c . Subsequently, an ashing process or a strip process is performed to remove the first photoresist pattern  201 . 
     With reference to  FIG. 10 , a layer for a second stress film  135   a  is formed on the front (exposed) side of the resulting structure of  FIG. 9 . The layer for a second stress film  135   a  may be, for example, a compressive stress film. The layer for a second stress film  135   a  may be formed of SiN, SiON, SiBN, SiC, SiC:H, SiCOH, SiCN and/or SiO 2 , like the first stress film  131   a . The process that is used to form the layer for a second stress film  135   a  may be the same as the layer for a first stress film  131   a . However, the deposition condition of the layer for a second stress film  135   a  and/or a composition ratio of substances constituting the film may be controlled so that the layer for a second stress film  135   a  has different stress from that of the first stress film. For example, the stress of the layer for a second stress film  135   a  may be about −0.01 to about −5 GPa. 
     The layer for a second stress film  135   a  may have a thickness in the range of about 1 to about 1,000 Å. In some embodiments, the thickness of the layer for a second stress film  135   a  may be substantially the same as the thickness of the first stress film  131 . 
     Subsequently, a second photoresist pattern  202  is formed on the layer for a second stress film  135   a . The second photoresist pattern  202  can cover the entire surface of the PMOS transistor area (II) while the NMOS transistor area (II) is exposed. Additionally, the second photoresist pattern  202  may be formed to cover a portion of the gate electrode  125   c  of the interface area (III), and in some embodiments the entire gate electrode, so as to provide the process margin, that is, to completely cover the entire PMOS transistor area (II). 
     With reference to  FIG. 11 , the layer for a second stress film  135   a  is etched using the second photoresist pattern  202  as an etching mask. The etching of the layer for a second stress film  135   a  may be performed using a dry etching process and/or a wet etching process. As shown in  FIG. 11 , the second stress film (see reference numeral  135 ) is formed in the PMOS transistor area (II) and the layer for a second stress film  135   a  is removed from the NMOS transistor area (I) resulting from the etching. The second stress film (see reference numeral  135 ) is formed in the interface area (III) so that the second stress film overlaps a portion of the gate electrode  121   c . Accordingly, the interface area (III) may include an overlapping area (OA) where the first stress film  131  and the second stress film  135  are layered on the gate electrode  121   c  so as to overlap each other. 
     With reference to  FIG. 12 , the first interlayer insulating film  140  is formed on the resulting structure of  FIG. 11 . The first interlayer insulating film  140  may be formed of, for example, TEOS (tetra ethyl ortho silicate), O 3 -TEOS, SiO 2 , SiON and/or SiOC. For example, the formation may be performed using processes such as CVD and/or spin coating. 
     With reference to  FIG. 13 , the planarization process may be performed so that the second stress film  135  of the third gate electrode  125   c  in the interface area (III) is planarized. The planarization may be, for example, a CMP (chemical mechanical polishing) process and/or an etch back process. In the case of when the CMP process is performed, slurry where polishing selectivity of the second stress film  135  to the first interlayer insulating film  140  is high may be used. In the case of when the etch back process is performed, the etchant where etching selectivity of the second stress film  135  to the first interlayer insulating film  140  is high may be used. The CMP process and/or the etch back process may be excessively performed so as to expose the second stress film  135 . 
     The CMP process and/or the etch back process may be performed using the second stress film  135  of the interface area (III) as a process stopper. However, the process stopper is not limited to the above-mentioned example. The CMP process or the etch back process may be stopped using the time control and/or an end point detector (EPD). 
     With reference to  FIG. 14 , the exposed second stress film  135  is at least partially removed from the interface area (III). The removal of the exposed second stress film  135  may be performed using dry etching and/or wet etching. In connection with this, the etching gas or the etchant where the etching selectivity to the second stress film  135  is higher than the etching selectivities to the first interlayer insulating film  140  may be used to selectively remove only the exposed second stress film  135 . The etching selectivity may be, for example, about 20:1 or more. 
     As shown in  FIG. 14 , the second stress film  135  that is exposed by the dry etching process or the wet etching process is partially removed. The degree of removal of the second stress film  135  may depend on the degree of etching. The degree of etching may be controlled using the time control and/or the end point detector. 
     In the case of when the second stress film  135  is partially etched, the thickness (Dc) of the second stress film  135  in the interface area (III) may be smaller than the thickness (Db) of the second stress film  135  in the second transistor area. As a result, the level of the area where the first stress film  131  and the second stress film  135  partially overlap, that is, the second stress film  135  on the third gate electrode  125   c , may be substantially similar to the level of the first stress film  131  provided on the gate electrode  125   a  of the first transistor area (I), or the level of the second stress film  135  provided on the gate electrode  125   b  of the second transistor area (II). The lateral etching may be performed during the etching of the second stress film  135 . 
     As shown in  FIG. 15 , the second interlayer insulating film  142  is formed on the first interlayer insulating film  140 . Subsequently, the planarization is performed using the CMP etc. Like the first interlayer insulating film  140 , the second interlayer insulating film  142  may be formed of, for example, TEOS (tetra ethyl ortho silicate), O 3 -TEOS, SiO 2 , SiON and/or SiOC. For example, the formation may be performed using a process such as CVD and/or spin coating. The second interlayer insulating film  142  may be formed of the same substance as the first interlayer insulating film  140 . 
     The upper (exposed) side of the first interlayer insulating film  140  that is provided by forming the second interlayer insulating film  142 , that is, the interface between the first interlayer insulating film  140  and the second interlayer insulating film  142  can be substantially flat, and may have about the same level as the highest upper side of the upper sides of the first stress film  131  and the second stress film  135  provided on the upper sides of the gate electrodes  125   a ,  125   b , and  125   c.    
     With reference to  FIGS. 16 and 17 , the interlayer insulating films  140  and  142  are patterned to form contact holes  147   a ,  147   b , and  147   c  in the NMOS transistor area (I), the PMOS transistor area (II), and the interface area (III). The patterning of the first and the second interlayer insulating films  140  and  142  may be performed using, for example, a photolithography process by means of a photoresist pattern. The etching may be performed using the dry etching process and/or the wet etching process. In some embodiments, the dry etching process may be used. 
     The contact holes  147   a ,  147   b , and  147   c  are formed to correspond to the gate electrodes  125   a ,  125   b , and  125   c  and/or the source/drain areas  121   a  and  121   b . The first contact hole  147   a  may be formed through the first and the second interlayer insulating films  140  and  142  and the first stress film  131 , and the third contact hole  147   c  may be formed through the first and the second interlayer insulating films  140  and  142 . Since the third contact hole  147   c  is formed through the overlapping area (OA) where the first stress film  131  and the second stress film  135  overlap, the third contact hole may be formed through the thinner second stress film  135  in comparison with the second transistor area (II). 
     In order to form contacts of a device having dual stress films, the contact holes  147   a ,  147   b , and  147   c  that are formed through the stress films  131  and  135  should expose the silicide films  127   a ,  127   b , and  127   c . In some methods of producing semiconductor devices according to some embodiments of the present invention, the level of the second stress film  135  provided on the third gate electrode  125   c  in the interface area (III) may be substantially similar to the level of the first stress film  131  provided on the gate electrode  125   a  in the first transistor area (I) or the level of the second stress film  135  provided on the gate electrode  125   b  in the second transistor area (II). In other words, the thicknesses of the stress films to be removed during the formation of all the contact holes may be substantially the same as each other. 
     As a result, etching ending points may be controlled to be similar when the contact holes are formed in the NMOS transistor area (I), the PMOS transistor area (II), and the interface area (III). When the contact holes  147   a ,  147   b , and  147   c  are simultaneously formed in all the areas, even if the etching ending point is set to correspond to the second stress film  135  on the third gate electrode  125   c  of the interface area (III), the upper side of the third silicide film  127   c  included in the third gate electrode  125   c  may be stably exposed. Additionally, since the contact hole  147   c  that is formed through the above-mentioned process is formed through the overlapping area (OA) where the first stress film  131  and the second stress film  135  overlap to desirably transfer electric signal, reliability and/or other characteristics of the semiconductor device may be improved. Moreover, it is possible to reduce or prevent the overetching from occurring in the NMOS transistor area (I) and the PMOS transistor area (II) having the single stress film. Additionally, it is possible to reduce or prevent the exposure of the source/drain areas  121   a  and  121   b  and the gate electrodes  125   a  and  125   b  through the contact holes  147   a ,  147   b , and  147   c  resulting from the removal of the silicide films  127   a  and  127   b  due to the overetching. 
     A next step will be described with reference to  FIG. 1A . Subsequently, the contact plugs  171 ,  173 , and  175  are formed in the contact holes  147   a ,  147   b , and  147   c . The contact plugs  171 ,  173 , and  175  are made of a metal substance such as W, Cu and/or Al, and/or a conductive substance such as conductive polysilicon. The contact plugs  171 ,  173 , and  175  may be formed by means of the above-mentioned substance(s) using low pressure CVD (LPCVD), atomic layer deposition (ALD), physical vapor deposition (PVD), metal organic CVD (MOCVD), electrolytic plating and/or electroless plating. If desired, the planarization process such as CMP (chemical mechanical polishing) and/or etchback may be performed until the surface of the interlayer insulating film  140  is exposed, thereby producing the semiconductor device shown in  FIG. 1A . 
     Hereinafter, a description will be given of the production of semiconductor devices according to embodiments of the present invention shown in  FIG. 1B  with reference to  FIG. 18 . In the present embodiments, a description of the intermediate structures that are the same as those of the embodiment of  FIGS. 2 to 17  or are easily analogized from those of the embodiment of  FIGS. 2 to 17  will be omitted, and a difference in embodiments will be mainly described. 
     Methods of producing semiconductor devices according to the present embodiments can be substantially the same as that of the description with reference to  FIGS. 2 to 8 . That is, methods of the present embodiments can be substantially the same as the methods of producing the semiconductor device shown in  FIG. 1A , with the exception of the processes after the formation of the layer for a first stress film  131   a  on the front side of the semiconductor substrate  100  after the source/drain areas  121   a  and  121   b  and the silicide films  127   a ,  127   b , and  127   c  are formed on the semiconductor substrate  100 . 
     The methods of the embodiments of the present invention include forming the layer for an etch stop film  133   a  on the upper side of the layer for a first stress film  131   a  after forming the layer for first stress film  131   a . The layer for an etch stop film  133   a  may be formed of a silicon oxide film such as an LTO film. Subsequently, as shown in  FIG. 18 , a third photoresist pattern  211  is formed on the layer for an etch stop film  133   a  provided on the layer for a first stress film  131   a . The third photoresist pattern  211  can be substantially the same as the first photoresist pattern  201  of  FIG. 8  except that the third photoresist pattern  211  is formed on the layer for an etch stop film  133   a.    
     Subsequent processes can be substantially the same as the processes of  FIGS. 9 to 17  except that the etch stop film  133  is formed on the upper side of the first stress film  131 . However, in the present embodiments, since the etch stop film  133  is formed on the first stress film  131 , in the case of when the first stress film  131  and the second stress film  135  have the same thickness, the total thickness of the first stress film  131  and the etch stop film  133  of the NMOS transistor area (I) may be larger than the thickness of the second stress film  135 . The thickness of the first stress film  131  where the etch stop film  133  is provided may be smaller than the thickness of the second stress film  135 . 
     Hereinafter, a description will be given of the production of semiconductor devices according to embodiments of the present invention shown in  FIG. 1C . In the present embodiments, a description of the intermediate structures that are the same as those of the embodiment of  FIGS. 2 to 17  or are easily analogized from those of the embodiment of  FIGS. 2 to 17  will be omitted, and a difference in embodiments will be mainly described. 
     With reference to  FIG. 14 , the exposed second stress film  135  is removed in the interface area (III). In connection with this, the dry etching and/or the wet etching may be used as described above. However, the degree of removal of the second stress film  135  may depend on the degree of etching. Accordingly, the semiconductor device shown in  FIG. 1A  is different from the semiconductor device shown in.  FIG. 1C  in that the second stress film  135  is wholly etched on the third gate electrode  125   c . Therefore, the second stress film  135  may not overlap the third gate electrode  125   c . The third contact hole  147   c  may be formed through the first and the second interlayer insulating films  140  and  142 , and the etch stop film  133 , but not through the second stress film  135 . 
     Additionally, in modifications of the present embodiments, the etch stop film  133  may be formed on both the first stress film  131  and the second stress film  135 , or the etch stop film  133  may not be formed on either film of the first stress film  131  and the second stress film  135 . 
     In semiconductor devices and methods of producing semiconductor devices according to some embodiments of the present invention, a second stress film is partially or wholly removed from an overlapping region where a first stress film and the second stress film overlap during the formation of contact holes. Thereby, the attack to a lower structure such as an upper side of a gate electrode and upper sides of source/drain areas due to the formation of the contact holes may be reduced, and contact characteristics and reliability of the semiconductor device may be improved. 
     In the drawings and specification, there have been disclosed embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.