Abstract:
A manufacturing method of a semiconductor device disclosed herein, comprises: forming a buried insulating film in a semiconductor substrate; forming semiconductor elements isolated by the buried insulating film; cleaning a surface side of the semiconductor substrate with a cleaning solution; and covering a surface side of the buried insulating film with a protective film before the step of cleaning the surface side of the semiconductor substrate, wherein a protective film is resistant to the cleaning solution.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
         [0001]    This application claims benefit of priority under 35 U.S.C.§119 to Japanese Patent Application No. 2002-210666, filed on Jul. 19, 2002, the entire contents of which are incorporated by reference herein.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a manufacturing method of a semiconductor device and the semiconductor device, and particularly relates to a manufacturing method of a semiconductor device in which semiconductor elements having favorable characteristics are formed and the semiconductor device.  
           [0004]    2. Description of the Related Art  
           [0005]    In recent semiconductor devices, in order to achieve a reduction in the resistance of polysilicon wiring and a diffusion layer, a salicide metal layer is formed on the surface sides thereof. In forming the salicide metal layer, the formation of the uniform salicide metal layer on the polysilicon wiring and a wiring layer is demanded. A manufacturing process to form such a salicide metal layer is disclosed, for example, in Japanese Patent Laid-open No. 8-250716.  
           [0006]    The manufacturing process of a related semiconductor device, which is disclosed in Japanese Patent Laid-open No. 8-250716 and so on, will be explained based on FIG. 1 to FIG. 3. FIG. 1 is a diagram showing a section of the related semiconductor device before the salicide metal layer is formed, and FIG. 2 is a diagram showing a section of the related semiconductor device after the salicide metal layer is formed. FIG. 3 is a plan view of FIG. 2.  
           [0007]    As shown in FIG. 1, to form the uniform the salicide metal layer, cleaning with dilute HF is performed before the salicide metal layer is formed. Namely, oxide films and particles, which are naturally formed on the surfaces of P +  diffusion regions  10  and  10 , the surfaces of N +  diffusion regions  12  and  12 , and the surfaces of the gate electrodes  14  made of a polysilicon layer, are removed.  
           [0008]    Thereafter, as shown in FIG. 2, the salicide metal layer is formed on the surfaces of the P +  diffusion regions  10  and  10 , the surfaces of the N +  diffusion regions  12  and  12 , and the surfaces of the gate electrodes  14  made of the polysilicon layer.  
           [0009]    However, in the related manufacturing method, there is a problem that during cleaning treatment with dilute HF, a silicon oxide film (SiO 2 ) which forms a buried insulating film  20  for element isolation dissolves due to the dilute HF. In other words, there is a problem that SiO 2  and HF react with each other as shown in the following formula to thereby precipitate water mark.  
           SiO 2 +4HF→SiF 4 +2H 2 O 
           [0010]    Particularly as shown in FIG. 3, when this precipitated water mark  30  adheres to the surfaces of P +  diffusion regions  10  and  10 , the surfaces of N +  diffusion regions  12  and  12 , and the surfaces of the gate electrodes  14  made of the polysilicon layer, the water mark  30  functions like a mask material. Hence, as shown in FIG. 2, the salicide metal layer is not formed in portions corresponding to the water mark  30 , and as a result, the uniform saliside metal layer cannot be obtained. If the uniform salicide metal layer is not formed, the resistance of the P +  diffusion regions  10  and  10 , the N +  diffusion regions  12  and  12 , and the gate electrodes  14  made of the polysilicon layer increases, which deteriorates characteristics of MISFETs as semiconductor elements.  
           [0011]    Moreover, in the semiconductor device shown in FIG. 2, the height of the buried insulating film  20  and the height of the gate electrode  14  are different, thereby a step occurs between the buried insulating film  20  and the gate electrode  14 . Therefore, there is a problem that when an interlayer dielectric is formed thereon, the planarity of the interlayer dielectric is deteriorated.  
         SUMMARY OF THE INVENTION  
         [0012]    In order to accomplish the aforementioned and other objects, according to one aspect of the present invention, a manufacturing method of a semiconductor device, comprises:  
           [0013]    forming a buried insulating film in a semiconductor substrate;  
           [0014]    forming semiconductor elements isolated by the buried insulating film;  
           [0015]    cleaning a surface side of the semiconductor substrate with a cleaning solution; and  
           [0016]    covering a surface side of the buried insulating film with a protective film before the step of cleaning the surface side of the semiconductor substrate, wherein a protective film is resistant to the cleaning solution.  
           [0017]    According to another aspect of the present invention, a semiconductor device, comprises:  
           [0018]    a buried insulating film which is formed in a semiconductor substrate;  
           [0019]    semiconductor elements which are formed on the semiconductor substrate and which are isolated by the buried insulting film; and  
           [0020]    a protective film which covers all of a surface side of the buried insulating film but which does not cover at least a region in which a salicide metal layer of the semiconductor element is formed, wherein the protective film is resistant to a hydrofluoric acid based solution.  
           [0021]    According to another aspect of the present invention, a semiconductor device, comprises:  
           [0022]    a buried insulating film which is formed in a semiconductor substrate;  
           [0023]    MISFETs which are formed on the semiconductor substrate and which are isolated by the buried insulating film;  
           [0024]    a protective film which covers all of a surface side of the buried insulating film and which is resistant to a hydrofluoric acid based solution; and  
           [0025]    a salicide metal layer which is formed on source/drain diffusion regions of the MISFET and which is formed in a self-alignment manner relative to the protective film. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]    [0026]FIG. 1 is a sectional view explaining a manufacturing process of a related semiconductor device (cleaning treatment);  
         [0027]    [0027]FIG. 2 is a sectional view explaining the manufacturing process of the related semiconductor device (salicide metal layer forming processing);  
         [0028]    [0028]FIG. 3 is a plan view of the semiconductor device in FIG. 2;  
         [0029]    [0029]FIG. 4 is a sectional view explaining part of a manufacturing process of a semiconductor device according to a first embodiment;  
         [0030]    [0030]FIG. 5 is a sectional view explaining part of the manufacturing process of the semiconductor device according to the first embodiment;  
         [0031]    [0031]FIG. 6 is a sectional view explaining part of the manufacturing process of the semiconductor device according to the first embodiment;  
         [0032]    [0032]FIG. 7 is a sectional view explaining part of the manufacturing process of the semiconductor device according to the first embodiment;  
         [0033]    [0033]FIG. 8 is a sectional view explaining part of the manufacturing process of the semiconductor device according to the first embodiment;  
         [0034]    [0034]FIG. 9 is a sectional view explaining part of the manufacturing process of the semiconductor device according to the first embodiment;  
         [0035]    [0035]FIG. 10 is a sectional view explaining part of a manufacturing process of a semiconductor device according to a second embodiment;  
         [0036]    [0036]FIG. 11 is a sectional view explaining part of the manufacturing process of the semiconductor device according to the second embodiment;  
         [0037]    [0037]FIG. 12 is a sectional view explaining part of the manufacturing process of the semiconductor device according to the second embodiment;  
         [0038]    [0038]FIG. 13 is a sectional view for explaining an example of a case where a wiring layer is formed in the semiconductor device according to the second embodiment; and  
         [0039]    [0039]FIG. 14 is a circuit diagram for explaining an example of a case where an SRAM cell includes MISFETs shown in FIG. 13. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
     First Embodiment  
       [0040]    In the first embodiment, by covering at least the surface of a buried insulating film with a protective film resistant to dilute HF before cleaning a semiconductor device with dilute HF, dissolution of the buried insulating film at the time of cleaning with dilute HF is avoided. Further details will be given below.  
         [0041]    First, as shown in FIG. 4, a buried insulating film  102  is formed in a semiconductor substrate  100 , for example, made of silicon. In this embodiment, the buried insulating film  102  is formed by a silicon oxide film (SiO 2 ). Additionally, in this embodiment, the buried insulating film  102  is formed by an STI manufacturing process. Subsequently, an N-type well  110  is formed by implanting impurity ions such as arsenic into the surface side of the semiconductor substrate  100 , and a P-type well  112  is formed by implanting impurity ions such as boron into the surface side of the semiconductor substrate  100 .  
         [0042]    Thereafter, as shown in FIG. 5, an insulating film such as a silicon oxide film and a polysilicon layer are formed on the surface of the semiconductor substrate  100 , and these insulating film and polysilicon layer are etched in a predetermined pattern by RIE (Reactive Ion Etching), so that gate insulating films  114  and  116  and gate electrodes  120  and  122  are formed. Then, by covering a region corresponding to the P-type well  112  and a predetermined region of the N-type well  110  with a resist or the like and implanting the impurity ions such as boron, P +  diffusion regions  130  and  130  are formed. One of these p +  diffusion regions  130  and  130  becomes a source diffusion region and the other thereof becomes a drain diffusion region. Subsequently, contrary to the above, by covering a region corresponding to the N-type well  110  and a predetermined region of the P-type well  112  with the resist or the like and implanting the impurity ions such as arsenic, N +  diffusion regions  132  and  132  are formed. One of these N +  diffusion regions  132  and  132  becomes a source diffusion region and the other thereof becomes a drain diffusion region. Hence, a P-type MISFET and an N-type MISFET each with an LDD structure (Lightly Doped Drain Structure) are formed.  
         [0043]    Next, as shown in FIG. 6, an insulating film  140  is formed on the surface of the semiconductor substrate  100 . In this embodiment, the insulating film  140  is formed of a silicon nitride film (SiN). Then, a resist  142  is formed and patterned on the insulating film  140  so as to cover an upper portion of the buried insulating film  102 .  
         [0044]    Thereafter, as shown in FIG. 7, by etching the insulating film  140  by RIE, sidewalls  150  and  152  are formed on the side of the gate electrodes  120  and  122 , and a protective film  154  which covers all the surface side of the buried insulating film  102  is formed on the buried insulating film  102 . Namely, by etching back the insulating film  140 , the sidewalls  150  and  142  are formed in a self-alignment manner. Moreover, the protective film  154  is formed by leaving a portion of the insulating film  140 , which is covered with the resist  142 , by etching. This protective film  154  is formed so as to cover all the surface side of the buried insulating film  102  and so as not to cover at least a region in which an undermentioned salicide metal layer is formed. Subsequently, a natural oxide film and particles on the surface of the semiconductor substrate  100  are removed by cleaning with dilute HF. Since the buried insulating film  102  is covered with the protective film  154  at the time of this cleaning with dilute HF, the dissolution of SiO 2  can be prevented, which can prevent the generation of water mark.  
         [0045]    Thereafter, as shown in FIG. 8, salicide metal layers  160 ,  162 ,  170 , and  172  are formed on the surface sides of the polysilicon layers of the gate electrodes  120  and  122  and the surface sides of the diffusion regions  130  and  132 . In this embodiment, the salicide metal layers  160 ,  162 ,  170 , and  172  are formed as follows. Namely, a high melting point metal film is formed on the surface side of the semiconductor substrate  100 . This high melting point metal film is made of, for example, Ti, Mo, W, Ni, or the like. Since, as described above, the water mark is not generated when this high melting point metal film is formed, it is possible to form the uniform high melting point metal film. Then, by subjecting it to thermal processing, the salicide metal layers  160  and  170  are formed on the surface sides of the gate electrodes  120  and  122  in a self-alignment manner, and the salicide metal layers  162  and  172  are formed on the surface sides of the diffusion regions  130  and  132  in a self-alignment manner relative to the protective film  154 .  
         [0046]    Subsequently, as shown in FIG. 9, a silicon oxide film is formed on all the surface of the semiconductor substrate  100 . Since the protective film  154  is formed on this occasion, a step between the gate electrodes  120  and  122  and the buried insulating film  102  is reduced, leading an improvement in the planarity of the silicon oxide film. Then, by planarizing the silicon oxide film by CMP (Chemical Mechanical Polishing), an interlayer dielectric  180  is formed.  
         [0047]    As described above, according to the semiconductor device of this embodiment, the buried insulating film  102  is covered with the protective film  154  before cleaning with dilute HF, whereby the precipitation of water mark from the buried insulating film  102  during cleaning treatment can be avoided. Hence, the uniform salicide metal layers  160 ,  162 ,  170 , and  172  can be formed, and the characteristics of MISFETs can be maintained favorably.  
         [0048]    Moreover, by covering the buried insulating film  102  with the protective film  154 , the step between the buried insulating film  102  and the gate electrodes  120  and  122  can be reduced, resulting in improved planarity when the interlayer dielectric is formed thereon.  
         [0049]    Furthermore, a material of the protective film  154  is the insulating film  140  and therefore the material of the protective film  154  is the same as that of the sidewalls  150  and  152 , whereby the protective film  154  can be obtained without adding a new film forming process.  
       Second Embodiment  
       [0050]    In the second embodiment, the parasitic capacitance of the MISFET is increased by greatly extending the protective film  154  in the aforementioned first embodiment to the sides of the diffusion regions  130  and  132 . Further details will be given below.  
         [0051]    A manufacturing method of a semiconductor device according to this embodiment is the same as that in the aforementioned first embodiment in FIG. 4 and FIG. 5. However, a change is made to the size of the resist  142  in the aforementioned first embodiment. Namely, as shown in FIG. 10, a resist  242  is formed on the insulating film  140 , and the resist  242  is not only formed on the buried insulating film  102  but also formed so as to extend onto the P +  diffusion region  130  and the N +  diffusion region  132 , so that it is formed larger.  
         [0052]    Then, as shown in FIG. 11, by etching the insulating film  140  by RIE, the sidewalls  150  and  152  are formed on sidewall portions of the gate electrodes  120  and  122 , and a protective film  254 , which covers the buried insulating film  102  and a portion of each of the diffusion regions  130  and  132 , is formed on the buried insulating film  102 . Namely, by etching back the insulating film  140 , the sidewalls  150  and  152  are formed in a self-alignment manner. Moreover, the protective film  254  is formed by leaving a portion of the insulating film  140 , which is covered with the resist  242 , by etching. This protective film  254  is formed so as to cover all the surface side of the buried insulating film  102  and a portion of each of the diffusion regions  130  and  132  and so as not to cover at least a region in which the undermentioned salicide metal layer is formed. Subsequently, a natural oxide film on the surface side of the semiconductor substrate  100  and particles are removed by cleaning with dilute HF. Also in this embodiment, since the buried insulating film  102  is covered with the protective film  254  at the time of this cleaning with dilute HF, the dissolution of SiO 2  can be prevented, which can prevent the generation of water mark.  
         [0053]    The manufacturing process thereafter is the same as that in the aforementioned first embodiment. Namely, as shown in FIG. 12, the salicide metal layers  160 ,  162 ,  170 , and  172  are formed on the surface sides of the polysilicon layers of the gate electrodes  120  and  122  and the surface sides of the diffusion regions  130  and  132  in a self-alignment manner. Subsequently, a silicon oxide film is formed on all the surface of the semiconductor substrate  100 . Since the protective film  254  is formed on this occasion, a step between the gate electrodes  120  and  122  and the buried insulating film  102  is reduced, leading an improvement in the planarity of the silicon oxide film. Then, by planarizing the silicon oxide film by CMP (Chemical Mechanical Polishing), the interlayer dielectric  180  is formed.  
         [0054]    As described above, also according to the semiconductor device according to this embodiment, by covering the buried insulating film  102  with the protective film  254 , the precipitation of water mark from the buried insulating film  102  during cleaning treatment can be avoided, and hence the uniform salicide metal layers  160 ,  162 ,  170 , and  172  can be formed. Consequently, the characteristics of the MISFETs can be maintained favorably.  
         [0055]    Moreover, by covering the buried insulating film  102  with the protective film  254 , the step between the buried insulating film  102  and the gate electrodes  120  and  122  is reduced, resulting in improved planarity when the interlayer dielectric is formed thereon.  
         [0056]    Furthermore, a material for the protective film  254  is the same insulating film  140  used for the sidewalls  150  and  152 , whereby the protective film  254  can be obtained without adding a new film forming process.  
         [0057]    Additionally, the protective film  254  is formed in such a manner as to cover as far as a portion of each of the diffusion regions  130  and  132 , whereby the diffusion regions  130  and  132  function as capacitors, and the parasitic capacitance of the MISFET can be increased. For example, it is assumed that a wiring layer  300  which electrically connects the diffusion region  130  and the diffusion region  132  is formed across the protective film  254  as shown in FIG. 13. In this case, the protective film  254  is sandwiched as a capacitor dielectric between the wiring layer  300  and the diffusion region  130 , and the protective film  254  is also sandwiched as a capacitor dielectric between the wiring layer  300  and the diffusion region  132 , so as to constitute capacitors. Therefore, the parasitic capacitances of two MISFETs can be increased, leading to an improvement in the drive capabilities of the MISFETs.  
         [0058]    Hence, for example, by using the MISFETs according to this embodiment for an SRAM cell such as shown in FIG. 14, the data line drive capability of the SRAM cell can be improved. Namely, when a P-type MISFET in FIG. 13 is taken as QP and an N-type MISFET therein is taken as QN, in the SRAM cell in FIG. 14, one complementary MIS inverter is composed of a MISFET QP 1  and a MISFET QN 1 , and the other complementary MIS inverter is composed of a MISFET QP 2  and a MISFET QN 2 . A MISFET QN 3  and a MISFET QN 4  are selection transistors which are connected to bit lines BL as data read lines. Gates of these MISFET QN 3  and MISFET QN 4  are connected to a word line WL.  
         [0059]    When the complementary MIS inverters structured as shown in FIG. 13 are used in such an SRAM cell, capacitors C 1  and C 2  are added to data output nodes N 1  and N 2  of the complementary MIS inverters, respectively. Hence, the drive capabilities of the data output nodes N 1  and N 2  for the bit lines BL can be raised.  
         [0060]    It should be mentioned that the present invention is not limited to the aforementioned embodiments, and various changes may be made therein. For example, although in the aforementioned embodiments, in FIG. 7 and FIG. 11, a hydrogen fluoride (HF) solution is used as a solution used when the surface side of the semiconductor substrate  100  is cleaned, other hydrofluoric acid based solutions such as ammonium fluoride (NH 4 F) may be used. In this case, a protective film resistant to the hydrofluoric acid based solution is required to be used as the protective films  154  and  254 . However, hydrogen fluoride (HF) has a higher etching rate for oxide, and hence the hydrogen fluoride (HF) solution is the most suitable as a cleaning solution out of hydrofluoric acid based solutions.  
         [0061]    Moreover, in FIG. 7 and FIG. 11, the solution used when the surface side of the semiconductor substrate  100  is cleaned is not limited to a hydrofluoric acid based solution, and any other cleaning solution having an equal cleaning effect can be used. In this embodiment, a protective film resistant to this used cleaning solution is required to be used as the protective films  154  and  254 .  
         [0062]    Furthermore, although the MISFETs are given as an example of semiconductor elements isolated by the buried insulating film  102  in the aforementioned embodiments, other semiconductor elements may be formed and isolated by the buried insulating film  102 .