Patent Publication Number: US-7910970-B2

Title: Programmable element and manufacturing method of semiconductor device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2007-162401, filed on Jun. 20, 2007, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a programmable element and a manufacturing method of a semiconductor device including the programmable element, particularly to a programmable element used in a programmable logic device such as a field programmable gate array (hereinafter, referred to as FPGA) and a manufacturing method of a semiconductor device including the programmable element. 
     2. Description of the Related Art 
     A programmable logic device such as an FPGA is a semiconductor device including multiple logic circuitries and programmable elements formed on interconnections between the multiple logic circuitries. The programmable logic device exerts a predetermined function with predetermined ones of the multiple logic circuitries connected to or disconnected from each other through an appropriate control of the programmable elements. 
     In a conventional programmable logic device, antifuses, erasable programmable read-only memories (EPROMs), electrically erasable programmable read-only memories (EEPROMs) or static random access memories (SRAMs) are employed as the programmable elements with which desired logic circuitries are made connected to or disconnected from one another. 
     However, a semiconductor device including antifuses as programmable elements (refer to Japanese Patent Application Publication No. 2003-115537 (FIG. 3)) has a problem that a program therein cannot be rewritten. Meanwhile, a semiconductor device including EPROMs or EEPROMs as programmable elements has a problem that withstand voltages of elements and the like in the semiconductor device need to be increased, since these programmable elements require a high program voltage, that is, a high voltage needs to be applied to these programmable elements when the semiconductor device is programmed. Moreover, a semiconductor device including SRAMs as programmable elements has a problem that a program written therein is erased once the semiconductor device is powered off. 
     Thus, it is currently difficult to provide such a program element with good program characteristics that: a program can be re-written; the program voltage is low; and the program is retained after powering-off. 
     SUMMARY 
     Aspects of the invention relate to an improved semiconductor device. 
     In one aspect of the present invention, a programmable element, may include a semiconductor substrate, source/drain layers formed apart from each other in the upper surface of the semiconductor substrate, a gate insulating film including a charge-trapping film containing Hf and formed on a portion between the source/drain layers of the semiconductor substrate, and a gate electrode formed on the gate insulating film with a program voltage applied to the gate electrode. 
     In another aspect of the invention, a manufacturing method of a semiconductor device including a programmable element, a logic circuit element, a programmable element formation region and a logic circuit element formation region divided by element isolations may include forming an insulating film containing Hf on the programmable element formation region and the logic circuit element formation region, depositing a gate-electrode material on the insulating film, selectively etching the gate-electrode material and the insulating film to leave a stacking structure of the gate insulating film and a gate electrode on each region of the programmable element formation region and the logic circuit element formation region, and forming source/drain layers in respective portions, adjacent to the stacking structures each consisting of the gate insulating film and the gate electrode, of the programmable element formation region and the logic circuit element formation region, by the implanting of impurity ions into the portions, and thereby forming the programmable element and a logic circuit element on the programmable element formation region and the logic circuit element formation region, respectively. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
       A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings. 
         FIG. 1  is a cross-sectional view showing a configuration of a programmable element according to an embodiment of the present invention. 
         FIG. 2  is a plan view showing a configuration of a semiconductor device including the programmable elements according to the embodiment of the present invention. 
         FIG. 3  is a graph showing amounts of threshold voltage change caused by a program voltage application on the basis of a simulation using the programmable element according to the embodiment of the present invention. 
         FIGS. 4A and 4B  are graphs based on a simulation using the programmable element according to the embodiment of the present invention.  FIG. 4A  shows an amount of threshold voltage change with the change of thickness of a gate insulating film, while  FIG. 4B  shows an amount of threshold voltage change with the change of thickness of an interlayer. 
         FIGS. 5A to 5G  are process cross-sectional views for illustrating a manufacturing method of the semiconductor device including the programmable elements according to the embodiment of the present invention. 
         FIGS. 6A to 6C  are process cross-sectional views for illustrating the manufacturing method of the semiconductor device including the programmable elements according to the embodiment of the present invention. 
         FIG. 7  is a cross-sectional view showing a configuration of a programmable element according to a modified embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Various connections between elements are hereinafter described. It is noted that these connections are illustrated in general and, unless specified otherwise, may be direct or indirect and that this specification is not intended to be limiting in this respect. 
     Embodiments of the present invention will be explained with reference to the drawings as next described, wherein like reference numerals designate identical or corresponding parts throughout the several views. 
     First Embodiment 
     Hereinafter, with reference to drawings, description will be given of a semiconductor device according to an embodiment of the present invention, and the manufacturing method thereof. 
     Firstly, with reference to  FIG. 1 , description will be given of a configuration of a programmable element according to this embodiment.  FIG. 1  is a cross-sectional view showing the configuration of the programmable element according to the embodiment of the present invention. 
     As shown in  FIG. 1 , the programmable element according to this embodiment is an n-MOSFET in which a well region  102  and source/drain layers  103  are formed in the upper surface of a programmable element formation region  100   a  defined by element isolations  101  in the upper surface of the semiconductor substrate  100  formed of a single-crystal silicon or the like. In order to form the well region  102 , p-type impurity ions, such as boron or indium ions, for example, are implanted in the upper surface of the programmable element formation region  100   a . Meanwhile, in the source/drain layers  103 , n-type impurity ions, such as phosphorus or arsenic ions, are implanted, for example. The source/drain layers  103  are spaced apart from each other. 
     On a channel region between the source/drain layers  103  formed in the upper surface of the programmable element formation region  100   a  of the semiconductor substrate  100 , an interlayer  104  which is a thin silicone oxide film or the like is formed. In addition, a gate insulating film  105  is formed on the interlayer  104 . In this embodiment, the gate insulating film  105  is an insulating layer containing Hf (HfSiON film) to function as a charge-trapping film. 
     On the gate insulating film  105  (charge-trapping film), formed is a gate electrode  106  made of a material such as a polysilicon doped with impurity ions, or a metal, for example. The metal used here may be nickel, tungsten or the like. On the gate electrode  106 , a lead line for supplying a program voltage is formed, and an interconnection (not shown) and the like, are formed on the gate electrode  106  with a contact plug interposed therebetween, for example. In addition, on the semiconductor substrate  100 , gate-sidewall insulating films  107  are formed in contact with the both side surfaces of the gate electrode  106  and the gate insulating film  105 . Here, each gate-sidewall insulating film  107  is a silicone oxide film, a silicon nitride film or the like. 
     Next, with reference to  FIG. 2 , description will be given of a configuration of an FPGA that is a semiconductor device including the programmable elements according to this embodiment.  FIG. 2  is a plan view of the semiconductor device including the programmable elements according to this embodiment. 
     In the semiconductor device according to this embodiment, logic circuitries  108  are disposed in a grid pattern on the semiconductor substrate  100 . Each logic circuitry  108  consists of multiple logic circuit elements and the like, and interconnections  109  made of a metal such as copper are connected to input/output parts of the logic circuitries  108 . The interconnections  109  are formed extending along regions between the logic circuitries  108 , which are disposed in a grid pattern. 
     On each intersection of the interconnections  109  extending along the regions between the logic circuitries  108 , a programmable element  110  is formed. The interconnections  109  are connected to the source/drain layers  103  of the programmable elements  110  with contact plugs (not shown) interposed therebetween. Each of the interconnections  109  connected to the source/drain layers  103  establishes an electrical connection through the corresponding programmable element  110 , when this programmable element  110  is switched on. On the other hand, each interconnection  109  establishes no electrical connection when the corresponding programmable element  110  is switched off. Thus, in the semiconductor device according to this embodiment, predetermined two or more logic circuitries  108  are electrically connected to one another through the interconnections  109 , when one or more programmable elements  110  disposed on the interconnections  109  between the logic circuitries  108  are switched on. On the other hand, the predetermined logic circuitries  108  are electrically disconnected from one another, when these programmable elements  110  are switched off. 
     Accordingly, by selectively programming on/off conditions of the programmable elements  110  formed on the interconnections  109  between predetermined logic circuitries  108  in the semiconductor device according to this embodiment, it is possible to make the predetermined logic circuitries  108  connected or disconnected to/from one another, and thereby to cause the semiconductor device to provide a predetermined function. 
     Next, description will be given of a method for programming the programmable elements according to this embodiment. 
     In the programmable element according to this embodiment, a threshold voltage of the channel region is changed to program an on/off condition of the programmable element. Specifically, when a program voltage is applied to the gate electrode  106  of each predetermined element, that is, when bias is applied between the gate electrode  106  and the semiconductor substrate  100  of each predetermined element, some charges in the channel region of the programmable element are trapped in the gate insulating film  105 , and, as a result, the threshold voltage of the channel region is changed. As described above, the present invention makes it possible to control the on/off condition of predetermined programmable elements in a semiconductor device during its operation, by increasing only the threshold voltage of the predetermined programmable elements. Accordingly, the predetermined logic circuitries in the semiconductor device can be connected or disconnected to/from one another as appropriate, and thus the semiconductor device can be caused to provide a predetermined function. 
     Note that the gate insulating film  105  serving as a charge-trapping film in the programmable element according to this embodiment is configured to have more than a certain atomic concentration of Hf contained therein. The atomic concentration should be 30 percent or more of the total atomic concentration of Hf and Si such that more charges can be trapped in the gate insulating film  105 , and that thereby the threshold voltage of the channel region can be greatly changed. 
     Here, with reference to  FIG. 3 , description will be given of characteristics of the n-type programmable element according to this embodiment.  FIG. 3  shows amounts of threshold voltage change before and after application of a program voltage on the basis of a simulation using the programmable element according to this embodiment. In  FIGS. 3 and 4 , Vth denotes a threshold voltage, VBL denotes a program voltage, Vg denotes a gate voltage, and Id denotes a drain current. 
     As shown in  FIG. 3 , when a program voltage of 1.5 V is applied to the gate electrode  106  of the n-type programmable element according to this embodiment, the threshold voltage of the n-type programmable element increases by approximately 0.5 V, compared to a voltage in a case of no program voltage applied. As described above, if the threshold voltage of some of the programmable elements formed on the interconnections  109  between the logic circuitries are increased, these programmable elements can be switched off. 
     As a conventional semiconductor device, there is a programmable logic device, such as an FPGA, including EPROMs or EEPROMs as programmable elements. Programmable elements of such semiconductor devices require a program voltage with a large absolute value, such as a high voltage approximately 10 V or more. Accordingly, such a semiconductor device has a problem that other various logic circuit elements and the like disposed together with such programmable elements on the semiconductor substrate must be designed and processed such that the they can withstand a high voltage. 
     By contrast, the n-type programmable element of a semiconductor device according to this embodiment requires an extremely low program voltage with an absolute value of approximately 3 V or less to be applied thereto, in order to be programmed. This eliminates the need for the special designing and processing for causing the logic circuit elements and the like to have enhanced withstand voltages. 
     Moreover, the n-type programmable element according to this embodiment allows a program that has been written therein to be easily rewritten. More specifically, when the zero voltage is applied to the gate electrode  106  of each n-type programmable element in which a charge is trapped in the gate insulating film  105 , the charge having been trapped in the gate insulating film  105  escapes to the channel region. This lowers the threshold voltage in the channel region, and, as a result, the program having been written in the n-type programmable element can be erased. Furthermore, when the program voltage is applied to the gate electrode  106  of each predetermined n-type programmable element again, the threshold voltage in the channel region can be increased again, and, as a result, the program can be rewritten in the n-type programmable element. 
     Moreover, the n-type programmable element according to this embodiment can store and retain the program therein even after the semiconductor device thereof is powered off. This is because, in this n-type programmable element, the charge once trapped in the gate insulating film  105  serving as a charge-trapping film is less likely to escape to the channel region unless the zero voltage is applied to the gate electrode  106 . 
     Incidentally, in a conventional semiconductor device such as an FPGA including antifuses as programmable elements, an electrical connection is established in the semiconductor device when the corresponding fuse is physically destructed. Accordingly, such a semiconductor device has a problem that a program once written in the semiconductor device cannot be rewritten. Meanwhile, in a conventional semiconductor device such as an FPGA including SRAMs as programmable elements, a memory content therein is erased once the semiconductor device is powered off. Accordingly, such a semiconductor device has a problem that the program must be rewritten in the semiconductor device every time the semiconductor device is powered on. 
     By contrast, the programmable element according to this embodiment has advantages: that a program can be rewritten freely by the controlling of the voltage applied to the gate electrode  106 , as described above; and that a program can be stored and retained even after the semiconductor device is powered off, since the gate insulating film  105  serving as a charge-trapping film can retain the charge trapped therein. 
     As described above, the programmable element according to this embodiment and the semiconductor device including this programmable element each requires a lower program voltage, allows a program therein to be rewritten, and can store and retain the program therein even after the semiconductor device is powered off. Accordingly, they are successfully improved in program characteristics over conventional programmable elements and semiconductor devices including the conventional programmable elements. 
     The characteristics of the n-type programmable element according to this embodiment, especially the characteristics of the threshold voltage change during the program voltage application, depend on either a thickness T HfSiON  of the gate insulating film  105  as a charge-trapping film containing Hf, or a thickness TIL of the interlayer  104 , shown in  FIG. 1 . Hereinbelow, description will be given of simulation results showing threshold voltage change dVth with the change of the thickness T HfSiON  of the gate insulating film  105  or the thickness TIL of the interlayer  104  in the programmable element. 
       FIG. 4A  shows the threshold voltage change dVth with the change of the thickness T HfSiON  of the gate insulating film  105  while a program voltage of 1.5 V is applied to the programmable element. Note that the programmable element is designed such that the interlayer  104  has a thickness TIL of 0.6 nm. 
     As is clear from  FIG. 4A , the threshold voltage of the programmable element is greatly changed when the thickness T HfSiON  of the gate insulating film  105  is approximately 4 nm or more, since an effectively increased amount of charge is trapped in the film. 
     On the other hand,  FIG. 4B  shows the threshold voltage change dVth with the change of the thickness TIL of the interlayer  104  while a program voltage of 1.5 V is applied to the programmable element. Note that the programmable element is designed such that the gate insulating film  105  has a thickness T HfSiON of 5 nm. 
     As is clear from  FIG. 4B , the threshold voltage of the programmable element is greatly changed when the thickness TIL of the interlayer  104  is approximately 1 nm or less, since an effectively increased amount of charge is trapped in the gate insulating film  105 . 
     As is clear from these simulation results, when the programmable element according to this embodiment is designed such that the thickness T HfSiON  of the gate insulating film  105  serving as a charge-trapping film is approximately 4 nm or more, and that the thickness TIL of the interlayer  104  is approximately 1 nm or less, the effectively increased amount of charge is trapped in the gate insulating film  105 , and thus the threshold voltage of the programmable element can be greatly changed. Accordingly, the programmable element can be programmed more easily. 
     Next, with reference to  FIGS. 5A to 6C , description will be given of a manufacturing method of the semiconductor device including the aforementioned programmable elements.  FIGS. 5A to 6C  are process cross-sectional views for illustrating a manufacturing method of the semiconductor device including the programmable elements. In each of  FIGS. 5A to 6C , the main parts of the programmable element formation region  100   a  and a logic circuit element formation region  100   b  are extracted and shown on the right and left, respectively, viewed from the observer. 
     Firstly, as shown in  FIG. 5A , in the upper surface of a silicon substrate to serve as the semiconductor substrate  100 , the element isolations  101 , such as shallow trench isolations (STIs), are formed. Thereby, the programmable element formation regions  100   a  and the logic circuit element formation regions  100   b  which are individually defined by the element isolations  101  are formed in the upper surface of semiconductor substrate  100 . 
     Specifically, a silicone oxide film and a silicon nitride film are firstly formed on the semiconductor substrate  100 . Thereafter, the portions, to be formed into the programmable element formation regions  100   a  and the logic circuit element formation regions  10   b , of the upper surface of the semiconductor substrate  100  are masked with a resist film, and then the silicone oxide film, the silicon nitride film and even the semiconductor substrate  100  are selectively etched off by reactive ion etching (RIE) with this mask. Thereby, trenches are formed in the upper surface of the semiconductor substrate  100 . 
     Then, after the resist film is incinerated, silicone oxide films are formed, by use of a CVD method, on the inner surfaces of the trenches formed in the upper surface of the semiconductor substrate  100 , as well as on the portions, on which the films including the silicon nitride film are formed, of the semiconductor substrate  100 . Thereafter, the silicone oxide films and the silicon nitride film outside the trenches are ground off by chemical mechanical polishing (CMP), so that the semiconductor substrate  100  outside the trenches is exposed. Thereby, the element isolations  101  are formed in the upper surface of the semiconductor substrate  100 , and, consequently, the programmable element formation regions  10   a  and the logic circuit element formation regions  100   b  are individually defined by the element isolations  101 . 
     Subsequently, a sacrificial oxide film with a thickness of approximately 10 nm, such as a silicone oxide film, is formed on the semiconductor substrate  100  by the CVD method or a thermal oxidation method. Thereafter, p-type impurity ions, such as boron or indium ions, are implanted into the programmable element formation regions  100   a  and the logic circuit element formation regions  100   b , and these regions  100   a  and  100   b  are heat-treated. Thereby, the well regions  102  with adjusted threshold voltages are formed. Then, the sacrificial oxide film is peeled off with dilute hydrofluoric acid. 
     Next, as shown in  FIG. 5B , an HfSiON film with a thickness of approximately 3 nm to serve as the gate insulating film  105  is formed on the entire upper surface of the semiconductor substrate  100  by use of a metal organic chemical vapor deposition (MOCVD) method and a plasma nitridation method. 
     Then, as shown in  FIG. 5C , portions, on the programmable element formation regions  100   a , of the HfSiON film are masked with resist films by a photolithography method. Thereafter, only the other portions, on the logic circuit element formation regions  100   b , of the HfSiON film are removed by wet etching. 
     Then, as shown in  FIG. 5D , after the resist films on the programmable element formation regions  100   a  are peeled off, another HfSiON film with a thickness of approximately 2.5 nm to serve as the gate insulating film  105  is formed on each of the logic circuit element formation regions  100   b  and the remaining portions of the HfSiON film in the programmable element formation regions  100   a , by an MOCVD method and a plasma nitridation method. 
     Here, the HfSiON films formed on the programmable element formation regions  100   a  are to be formed into the gate insulating films  105  to serve as charge-trapping films in the programmable elements. Accordingly, the atomic concentration of Hf contained in each of these HfSiON films is set to a predetermined value or more, for example, 30 percent of the total atomic concentration of Hf and Si contained in the HfSiON film so that the threshold voltage of the programmable element thereof can be effectively changed when a program voltage is applied thereto. 
     Thereafter, the semiconductor device is annealed in an atmosphere containing a trace of oxygen (oxidized at reduced oxygen partial pressure) while the HfSiON films are annealed at the same time. Through this reduced pressure oxidation, the interlayer  104  (not shown), which is a film such as a silicone oxide film, is formed on each of the interfaces between the HfSiON films and the silicon substrate in the programmable element formation regions  100   a . Note that, in this process, the oxygen partial pressure and the temperature are set such that the thickness of the interlayer  104  can be approximately 1 nm or less. This setting allows the thin HfSiON films formed on the respective logic circuit element formation regions  100   b  of the semiconductor substrate  100  to be oxidized so that the thickness of the interlayer  104  in each of the regions  100   b  can be 1 nm or less, and good interface characteristics can be obtained. 
     Next, as shown in  FIG. 5E , a conductive material film to be formed into the gate electrodes  106  is formed on the HfSiON films. For example, conductive impurity ions such as phosphorus are added to silane on its thermal decomposition in nitrogen by a thermal CVD method, and thereby a doped polysilicon film is formed on the HfSiON films. Alternatively, as a film to be formed into the gate electrodes  106 , a metal film made of nickel, tungsten or the like may be formed by sputtering or the like. 
     Then, as shown in  FIG. 5F , the gate electrodes  106  and the gate insulating films  105  are selectively etched by a photolithography method and RIE, and thereby a stacking structure consisting of the gate insulating film  105  and the gate electrode  106  is caused to remain on each of the programmable element formation regions  100   a  and the logic circuit element formation regions  100   b.    
     Next, as shown in  FIG. 5G , n-type impurity ions such as arsenic ions are implanted into portions, adjacent to the sides of the stacking structures each consisting of the gate insulating film  105  and the gate electrode  106 , of the programmable element formation regions  100   a  and the logic circuit element formation regions  100   b . Here, the ion implantation is performed such that the n-type impurity ions concentration of the portions can be approximately 1×1015 cm-3. Thereafter, the portions are annealed at 900° C./5 s by rapid thermal annealing (RTA), and thereby, shallow source/drain layers  103  to serve as extension layers are formed in these respective portions. 
     Subsequently, films such as silicon nitride films, silicone oxide films or the like are formed on the semiconductor substrate  100  and the gate electrodes  106 , respectively. Thereafter, the films are etched back and thus the gate-sidewall insulating films  107  are formed on the sides of the stacking structures each consisting of the gate insulating film  105  and the gate electrode  106 . 
     Thereafter, n-type impurity ions such as phosphorus ions are implanted into portions, adjacent to the sides of the gate-sidewall insulating films  107 , of the programmable element formation regions  100   a  and the logic circuit element formation regions  10   b . Here, the ion implantation is performed such that the n-type impurity ions concentration of the portions can be approximately 5×1015 cm-3. Thereafter, the portions are activated by spike annealing, and thereby, the deep source/drain layers  103  are formed in these respective portions. 
     In this way, the n-type programmable elements  110  are formed on the respective programmable element formation regions  100   a , while logic circuit elements  111 , which are n-MOSFETs, are formed on the respective logic circuit element formation region  100   b.    
     Next, as shown in  FIG. 6A , a binary compound film (not shown) consisting of nickel silicide or cobalt silicide is formed on each of the upper surfaces of the gate electrodes  106  and the surfaces of the source/drain layers  103 , with ordinary salicide processes. Specifically, for example, a film consisting of a refractory metal such as nickel (Ni), cobalt (Co), titanium (Ti), iridium (Ir) or platinum (Pt) is formed on each of the gate electrodes  106  and the source/drain layers  103 . Thereafter, the semiconductor device is heat-treated to cause the refractory metal to react with the gate electrodes  106  and the source/drain layers  103 , and, as a result, the aforementioned binary compound film is formed. 
     Thereafter, an interlayer insulating layer  112  made of a film such as a silicone oxide film is formed on the semiconductor substrate  100  by a CVD method or the like. 
     Then, as shown in  FIG. 6B , a resist film or the like is formed on the interlayer insulating layer  112  on the semiconductor substrate  100 , and openings are formed in the resist film by a photolithography method. Thereafter, portions, respectively corresponding to the bottoms of the openings, of the interlayer insulating layer  112  are etched off by RIE, and thus contact holes are formed such that the gate electrode  106  and the source/drain layers  103  of each of the programmable elements  110  on the programmable element formation regions  100   a  and the logic circuit elements  111  on the logic circuit element formation regions  100   b  can be exposed. 
     Thereafter, by a method such as plating or sputtering, the contact holes are filled with a metal such as copper or aluminum, and simultaneously a film consisting of the metal is formed on the interlayer insulating layer  112 . The metal film outside the contact holes is ground off by CMP, and thus the contact plugs  113  to be respectively connected to the gate electrodes  106  and the source/drain layers  103  are formed. Note that barrier films, such as TiN films, may be formed on the inner walls of the contact holes before the contact plugs  113  are formed, to prevent the metal for the contact plugs  113  from overflowing onto the interlayer insulating layer  112 . 
     Next, as shown in  FIG. 6C , an upper interlayer insulating layer  112  made of a film such as a silicone oxide film is further formed on the interlayer insulating layer  112 . Then, a resist film is formed on the upper interlayer insulating layer  112 , and an interconnection pattern is formed in the resist film by a photolithography method. Thereafter, the upper interlayer insulating layer  112  are selectively etched off by RIE by use of, as a mask, the interconnection pattern formed in the resist film, and thus interconnection trenches are formed on the contact plugs  113 . 
     Thereafter, the interconnection trenches are filled with a metal such as copper or aluminum, and simultaneously a film consisting of the metal is formed on the upper interlayer insulating layer  112 . Then, the metal film outside the interconnection trenches is ground off by CMP, and thus the interconnections  109  are formed. Some of the interconnections  109  are electrically connected to the gate electrodes  106  of the programmable elements  110  and the logic circuit elements  111  through the contact plugs  113 , respectively, and used for applying a program voltage or a gate voltage to the corresponding element. Meanwhile, others of the interconnections  109  are electrically connected to the source/drain layers  103  of the programmable elements  110  and the logic circuit elements  111  through the contact plugs  113 , respectively. In this process, the predetermined programmable elements  110  and logic circuit elements  111  are electrically connected to one another via the interconnections  109 . Note that barrier films, such as TiN films, may be formed on the inner walls of the interconnection trenches in advance to prevent the metal for the interconnections  109  from overflowing onto the upper interlayer insulating layer  112 . By the method as described above, the semiconductor device including the programmable elements  110 , that is, a logic device programmable as required can be manufactured. 
     In each conventional semiconductor device in which EPROMs, EEPROMs or antifuses are employed as programmable elements, each programmable element has a different configuration from that of a MOSFET so that the logic circuit elements and the programmable elements need to be manufactured by different manufacturing methods. By contrast, according to the manufacturing method of the semiconductor device including the programmable elements according to this embodiment, each programmable element  110  has the same configuration as that of a MOSFET so that the logic circuit elements  111  and the programmable elements  100  can be manufactured by a single manufacturing process. Thus, the manufacturing method according to this embodiment can simplify the manufacturing process of semiconductor devices as compared to the conventional manufacturing methods. 
     Modified Embodiment 
     Next, with reference to  FIG. 7 , description will be given of a modified example of the programmable element according to the aforementioned embodiment.  FIG. 7  is a cross-sectional view showing a configuration of the programmable element according to the modified embodiment of the present invention. The configuration of the gate insulating film  105  of the programmable element is the only difference between the programmable element according to this modified embodiment and the one according to the aforementioned embodiment. Accordingly, the same constituents as those of the programmable element of the aforementioned embodiment are denoted by the same reference numerals, and the description thereof will be omitted. 
     Unlike the aforementioned embodiment, in the programmable element according to this modified embodiment, a gate insulating film  105  consisting of two layers made of different materials is formed on the channel region between the source/drain layers  103  formed apart from each other in the upper surface of the semiconductor substrate  100 . In this modified embodiment, an upper gate insulating film  105   a  and a lower gate insulating film  105   b  constituting the gate insulating film  105  are respectively formed of an HfSiO film and an HfSiON film. 
     As similar to the programmable element according to the aforementioned embodiment, in the programmable element according to this modified embodiment as well, when a relatively low program voltage of approximately 3 V or less is applied thereto, the voltage causes the charge in the channel region to be trapped in the gate insulating film  105 . This increases the threshold voltage of the channel region, and thus the on/off condition of the programmable element can be controlled. Accordingly, the semiconductor device including this programmable element requires a lower program voltage, allows a program therein to be rewritten, and can store and retain the program therein even after the semiconductor device is powered off. Accordingly, they are successfully improved in program characteristics over conventional programmable elements and semiconductor devices including the conventional programmable elements. 
     Note that, in the programmable element according to this modified embodiment, not both the lower and upper gate insulating films  105   b  and  105   a  need to contain Hf, but a configuration may be employed in which only either one of the gate insulating films contains Hf. In this case, the one of the gate insulating films that contains Hf functions as a charge-trapping film while the programmable element is programmed through adjustment of the gate voltage 
     In addition, in the programmable element of this modified embodiment, the atomic concentration of Hf contained in the entire gate insulating film  105  to serve as a charge-trapping film should preferably be set to a predetermined value or more, for example, 30 percent of the total atomic concentration of Hf and Si contained in the entire gate insulating film  105  to serve as a charge-trapping film so that the threshold voltage of the channel region thereof can be effectively changed. Moreover, the thickness TIL of the interlayer  104  formed between the semiconductor substrate  100  and the lower gate insulating film  105   b  should preferably be 1 nm or less, and the thickness T HfSiON  of the one of the upper and lower gate insulating films that contains Hf should preferably be 4 nm or more. 
     A manufacturing method of a semiconductor device including the programmable elements according to this modified embodiment is almost the same as that of the semiconductor device including the programmable elements according to the aforementioned embodiment, but is partially different. Specifically, the steps of forming the gate insulating film are different from those in the aforementioned embodiment shown in  FIGS. 5B to 5D . 
     More specifically, in the aforementioned embodiment, the two HfSiON films are stacked to serve as the gate insulating film  105  of the programmable element on each programmable element formation region  100   a  of the semiconductor substrate  100  by a CVD method or the like, as shown in  FIGS. 5B to 5D . By contrast, in this modified embodiment, after an HfSiON film is stacked on each programmable element formation region  100   a  by a CVD method or the like, an insulating film different from an HfSiON film, such as an HfSiO film, is stacked on the HfSiON film by the CVD method or the like. Thereby, a multilayer consisting of an HfSiON film and an insulating film different from an HfSiON film is formed on each programmable element formation region  100   a.    
     As similar to the aforementioned embodiment, according to the manufacturing method of the semiconductor device including the programmable elements according to this modified embodiment as well, the logic circuit elements  111  and the programmable elements  100  can be manufactured by a single manufacturing process. Thus, the manufacturing method according to this modified embodiment can also simplify the manufacturing process of semiconductor devices as compared to the conventional manufacturing methods. 
     Moreover, in this modified embodiment, as the gate insulating films  105  of the logic circuit elements  111 , for gate insulating films  105  containing no Hf, for example, silicone oxide films can be employed. Accordingly, the logic circuit elements  111  can be designed to have any desired function. 
     Note that the present invention is not restricted by the aforementioned embodiment and modified embodiment, but can be implemented as various modified forms without departing from the gist of the present invention. For example, although each of the programmable elements according to the aforementioned embodiment and modified embodiment has an n-MOSFET structure, each programmable element may have a p-MOSFET structure. 
     The p-type programmable elements can be programmed as follows. Specifically, a program voltage is applied to each of desired ones of the p-type programmable elements, and thus a threshold voltage of the channel region thereof is reduced. Accordingly, these desired P-type programmable elements are set to be switched on and thereby desired ones of the logic circuitries are connected to one another, if no drain voltage is applied to the P-type programmable elements. 
     Embodiments of the invention have been described with reference to the examples. However, the invention is not limited thereto. 
     Other embodiments of the present invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and example embodiments be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following.