Abstract:
A substrate is prepared whose surface has a partial area exposing an insulating material containing fluorine and at least a partial area in the other area exposing a conductive material containing copper as a main composition. The surface of the substrate is exposed to hydrogen plasma to clean the surface. A first insulating film made of insulating material is formed on the cleaned surface. It is possible to form a lamination structure having a fluorine-doped interlayer insulating film hard to be peeled off.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
         [0001]    This application is based on Japanese Patent Application No. 2002-70298, filed on Mar. 14, 2002, the entire contents of which are incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    A) Field of the Invention  
           [0003]    The present invention relates to a lamination structure with copper wiring and its manufacture method, and more particularly to a method which is suitable for manufacturing semiconductor devices and includes a process of forming a copper wiring layer by a damascene method, and to a lamination structure having a conductive member such as copper embedded in a film made of an insulating material which contains fluorine.  
           [0004]    B) Description of the Related Art  
           [0005]    Demands for high performance and high speed of semiconductor devices require to shorten a delay time of an electric signal transmitting in a wiring layer. One approach to shortening a delay time is a lowered dielectric constant of an interlayer insulating film. If fluorine is doped in an interlayer insulating film, the dielectric constant can be lowered.  
           [0006]    However, if fluorine is doped in an interlayer insulating film, peeling off is likely to occur at the interface of the interlayer insulating film when the film is laminated. JP-A-HEI-11-8235 discloses techniques of preventing peeling off by doping nitrogen into an interlayer insulating film doped with fluorine.  
           [0007]    Even if nitrogen is doped in a fluorine-doped interlayer insulating film, local peeling off occurs in some cases.  
         SUMMARY OF THE INVENTION  
         [0008]    An object of this invention is to provide a lamination structure having a fluorine-doped interlayer insulating film in which lamination structure peeling off is difficult to occur, and its manufacture method.  
           [0009]    According to one aspect of the present invention, there is provided a method of manufacturing a lamination structure, comprising: (a) a step of exposing a surface of a substrate to hydrogen plasma to clean the surface, a partial area of the surface exposing an insulating material containing fluorine and at least a partial area in the other area of the surface exposing a conductive material containing copper as a main composition; and (b) a step of forming a first film made of an insulating material on the cleaned surface.  
           [0010]    By exposing the surface of a conductive member to hydrogen plasma, fluorine atoms in the surface layer can be efficiently removed. Removal of fluorine atoms promotes adhesion of the first film on the surface of the conductive member and the first film can be prevented from being peeled off.  
           [0011]    According to another aspect of the invention, there is provided a lamination structure comprising: a first insulating film made of fluorine-containing insulating material; a conductive member filled in a recess formed through the first insulating film, the conductive member containing copper as a main composition; and a second insulating film made of insulating material and disposed on surfaces of the first insulating film and the conductive member, wherein a fluorine density on an upper surface of the conductive member is 10 atom % or lower.  
           [0012]    By setting the fluorine density on the upper surface of the conductive member to 10 atom % or lower, adhesion of the second film on the conductive member can be promoted and the second film can be prevented from being peeled off. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a cross sectional view of a semiconductor device according to an embodiment of the invention and prior art.  
         [0014]    [0014]FIG. 2A is a graph showing Auger electron spectroscopy (AES) analysis results of a copper wiring layer, and FIG. 2B is a cross sectional view of the copper wiring layer and an insulating film.  
         [0015]    [0015]FIGS. 3A to  3 F are cross sectional views of a substrate illustrating a semiconductor device manufacturing method.  
         [0016]    [0016]FIG. 4 is a schematic diagram showing a plasma treatment system used by the embodiment method.  
         [0017]    [0017]FIG. 5A is a graph showing densities of atoms on the surface of a copper wiring layer before and after hydrogen plasma treatment, and FIG. 5B is a graph showing densities of atoms on the surface of a copper wiring layer before and after ammonia plasma treatment.  
         [0018]    [0018]FIGS. 6A and 6B are graphs showing the relation between a radio frequency power during hydrogen plasma treatment and a sheet resistance of a copper wiring layer after the hydrogen plasma treatment.  
         [0019]    [0019]FIG. 7A is a graph showing densities of impurity atoms on the surface of a copper wiring layer after hydrogen plasma treatment, and FIG. 7B is a graph showing depths of intruded impurity atoms from the surface of the copper wiring layer.  
         [0020]    [0020]FIG. 8 is a graph showing etching amounts of a fluorine-containing silicate glass (FSG) film and a SiO 2  film by hydrogen plasma.  
         [0021]    [0021]FIGS. 9A is a graph showing etching amounts of an FSG film and an SiO 2  film by high density hydrogen plasma, and FIG. 9B is a graph showing sheet resistances of copper wiring layers after a cleaning process when high density hydrogen plasma and ammonia plasma are used.  
         [0022]    [0022]FIG. 10 is a schematic diagram showing a remote plasma treatment system. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0023]    Prior to describing an embodiment of the invention, a peeling off phenomenon will be described which occurs in a semiconductor device having a copper wiring layer embedded by a damascene method in an interlayer insulating film which contains fluorine. This peeling off phenomenon was newly found by the present inventor.  
         [0024]    [0024]FIG. 1 is a cross sectional view of a semiconductor device having a copper wiring layer formed by a damascene method. A semiconductor device according to an embodiment of the invention has the cross sectional structure same as that shown in FIG. 1.  
         [0025]    An active region is defined by a field oxide film  2  formed in the surface layer of a silicon substrate  1 . A MOSFET  3  is formed in this active region. MOSFET  3  is constituted of a source region  3 S, a drain region  3 D, a gate electrode  3 G, and a gate oxide film  31 .  
         [0026]    Covering MOSFET  3 , an interlayer insulating film  10  of SiO 2  and a stopper film  11  of SiN are formed on the substrate. A contact hole  12  is formed through the interlayer insulating film  10  at the position corresponding to the drain region  3 D. A barrier layer  13  of TiN covers the side wall and bottom of the contact hole  12 . A plug  14  of tungsten (W) is buried in the contact hole  12 .  
         [0027]    On the stopper film  11 , a first layer insulating film  20  made of fluorine-containing silicate glass and having a thickness of 400 nm is formed. A wiring groove  21  is formed through the first layer insulating film  20 , reaching the stopper film  11 . The wiring groove  21  crosses the area where the plug  14  is disposed. A barrier layer  22  made of TaN and having a thickness of 50 nm covers the side wall and bottom of the wiring groove  21 . A first wiring layer  23  of copper is embedded in the wiring groove  21 .  
         [0028]    A barrier layer  30  of silicon nitride (SiN) is formed on the first layer insulating film  20  and first wiring layer  23 . A second layer insulating film  32  made of fluorine-containing silicate glass is formed on the barrier layer  30 . The barrier layer  30  prevents copper atoms in the wiring layer  23  from being diffused.  
         [0029]    A via hole  33  reaching the first wiring layer  23  is formed through the second insulating film  32 , and a wiring groove  34  reaching an intermediate depth of the second layer insulating film  32  and partially crossing the via hole  33  is formed. A barrier layer  35  made of TaN and having a thickness of 50 nm covers the inner surfaces of the wiring groove  34  and via hole  33 . A second wiring layer  36  of copper is embedded in the wiring groove  34  and via hole  33 . The second wiring layer  36  is electrically connected to the first wiring layer  23  via the via hole  33 .  
         [0030]    A barrier layer  40  of silicon nitride is formed on the second layer insulating film  36  and second wiring layer  34 . A third layer insulating film  41  of fluorine-containing silicate glass is formed on the barrier layer  40 .  
         [0031]    The present inventor has found that peeling off is likely to occur at the interface between the first wiring layer  23  and overriding barrier layer  30  and at an interface between the second wiring layer  36  and overriding barrier layer  40 . This peeling off condition was able to be detected through observation of the copper wiring layers with a metallurgical microscope.  
         [0032]    Next, studies are made for the reason why peeling off occurs at the interface between the copper wiring layer and barrier layer. The surface of a copper wiring layer was analyzed through Auger electron spectroscopy (AES).  
         [0033]    [0033]FIG. 2A shows the AES analysis results. The abscissa represents electron energy in the unit of “eV” and the ordinate represents an intensity of a detection signal. A solid line a in FIG. 2A shows the analysis results of the surface of a copper wiring layer embedded in an insulating film made of fluorine-containing silicate glass (FSG). For comparison purposes, the analysis results of the surface of a copper wiring layer embedded in an insulating film made of undoped silicon oxide are shown as indicated by a solid line b. A peak corresponding to fluorine (F) does not appear on the solid line b, whereas a large peak corresponding to fluorine appears on the solid line a  
         [0034]    It can be considered from these analysis results that peeling off results from fluorine on the surface of the copper wiring layer. As shown in FIG. 2B, it can be considered that fluorine atoms in an insulating film  52  of FSG are supplied to and left on the surface of a copper wiring layer  51  while a copper wiring layer deposited on the insulating film  52  is removed by chemical mechanical polishing (CMP). In the embodiment to be described below, peeling off can be prevented by removing fluorine atoms resident on the surface of a copper wiring layer.  
         [0035]    A semiconductor device manufacturing method according to the embodiment will be described with reference to FIGS. 3A to  3 F. FIGS. 3A to  3 F show the first layer insulating film  20  and upper layers of the semiconductor device shown in FIG. 1.  
         [0036]    Processes up to the state shown in FIG. 3A will be described. On an underlying substrate  15  having the stopper layer  11  and lower layers shown in FIG. 1, a first layer insulating film  20  is formed which is made of FSG and has a thickness of 400 nm. The first layer insulating film  20  is formed by chemical vapor deposition (CVD).  
         [0037]    A wiring groove  21  is formed through the first layer insulating film  20 . A TaN layer and a copper layer are sequentially formed on the inner surface of the wiring groove  21  and the surface of the first layer insulating film  20 . The TaN layer is formed by sputtering. The copper layer is formed by depositing a thin copper seed layer by sputtering and then by performing copper plating.  
         [0038]    Unnecessary TaN layer and copper layer deposited on the first later insulating film  20  are removed by CMP. The barrier layer  22  of TaN and the copper wiring layer  23  are left in the wiring groove  21 . The surface of the copper wiring layer  23  is exposed to hydrogen plasma to clean the surface. This hydrogen plasma process will be later detailed.  
         [0039]    A barrier layer  30  of silicon nitride is formed on the first layer insulating film  20  and copper wiring layer  23  by CVD. A second layer insulating film  32  of FSG is formed on the barrier layer  30 . The second layer insulating film  32  is formed by a method similar to the method of forming the first layer insulating film  20 .  
         [0040]    A silicon nitride film  37  is formed on the surface of the second layer insulating film  32 . An opening  37   a  corresponding to the wiring groove  34  shown in FIG. 1 is formed through the silicon nitride film  37 . Next, a resist film  38  is formed covering the silicon nitride film  37  and opening  37   a.  An opening  38   a  corresponding to the via hole  33  shown in FIG. 1 is formed through the resist film  38 .  
         [0041]    As shown in FIG. 3B, by using the resist film  38  as a mask, the second layer insulating film  32  is etched to the intermediate depth to form a via hole  33 . The resist film  38  is thereafter removed. The second layer insulating film  32  can be etched by reactive ion etching (RIE).  
         [0042]    As shown in FIG. 3C, by using the silicon nitride film  37  as a mask, the second layer insulating film  32  is etched to form a wiring groove  34  reaching the intermediate depth of the second layer insulating film  32 . In this case, the second layer insulating film  32  exposed on the bottom of the via hole  33  is also etched so that the via hole  33  passes through the second layer insulating film  30  and reaches the barrier layer  30 .  
         [0043]    As shown in FIG. 3D, the silicon nitride film  37  left on the second layer insulating film  32  and the barrier layer  30  exposed on the bottom of the via hole  33  are etched and removed. The copper wiring layer  23  is therefore exposed on the bottom of the via hole  33 .  
         [0044]    As shown in FIG. 3E, a TaN film  35   a  of 50 nm in thickness is formed covering the inner surfaces of the via hole  33  and wiring groove  36  and the upper surface of the second layer insulating film  32 . A copper layer  36   a  is formed being filled in the via hole  33  and wiring groove  34 . CMP is performed until the  20  surface of the second wiring layer  32  is exposed, to thereby leave the barrier layer  35  and copper wiring layer  36  in the via hole  33  and wiring groove  34 . The surface of the copper wiring layer  36  is exposed to hydrogen plasma to clean the surface.  
         [0045]    As shown in FIG. 3F, a barrier layer  40  made of silicon nitride and having a thickness of 50 nm is formed on the second layer insulating film  32  and copper wiring layer  36 , and a third layer insulating film  41  of FSG is formed on the barrier layer  40 .  
         [0046]    [0046]FIG. 4 is a schematic diagram showing a hydrogen plasma treatment system to be used for cleaning the surfaces of the copper wiring layers  23  and  36 .  
         [0047]    A susceptor  51  is mounted in a chamber  50  capable of being evacuated. A substrate  52  with a copper wiring layer to be cleaned is placed on the susceptor  51 . A shower head  53  is disposed above the susceptor  51 . The susceptor  51  and shower head  53  constitute a pair of electrodes of a diode parallel plate type. The susceptor  51  is grounded and a radio frequency power source  54  applies a radio frequency voltage of 13.56 MHz to the shower head  53 .  
         [0048]    Hydrogen gas is supplied from the shower head  53  toward the susceptor  51 . Hydrogen plasma is generated between the susceptor  51  and shower head  53  by capacitive coupling, and the surface of the substrate  52  is exposed to hydrogen plasma.  
         [0049]    [0049]FIG. 5A is a graph showing atom densities on the surface of a copper wiring layer before and after a hydrogen plasma treatment. The atom densities were obtained by AES analysis. White bars indicate the atom densities before the plasma treatment, and hatched bars indicate the atom densities after the plasma treatment. The treatment time was set to 30 seconds.  
         [0050]    It can be seen from this graph that fluorine atoms of about 20 atom % are contained on the surface of the copper wiring layer before the hydrogen plasma treatment and that after the hydrogen plasma treatment, the fluorine atom density lowers to about 2 atom %. The fluorine plasma treatment can remove most of fluorine atoms resident on the surface of a copper wiring layer. In the semiconductor device subjected to the hydrogen plasma treatment, peeling off did not occur at the interface between the copper wiring layer and barrier layer.  
         [0051]    For comparison purposes, atom densities on the surface of a copper wiring layer before and after an ammonia plasma treatment are shown in FIG. 5B. Although the fluorine atom density is lowered little by the ammonia plasma treatment, it is not so remarkable as the hydrogen plasma treatment. In samples subjected to the ammonia plasma treatment, peeling off was observed at the interfaces between copper wiring layers and barrier layers. Although techniques of removing copper oxide formed on the surface of a copper wiring layer by an ammonia plasma treatment are disclosed in JP-A-HEI-12-232522 and JP-A-2000-200832, sufficient fluorine removal effects were not obtained by the ammonia plasma treatment.  
         [0052]    It is preferable to set the fluorine density on the surface of a copper wiring layer to 10 atom % or lower in order to prevent peeling off at the interface between the copper wiring layer and barrier layer.  
         [0053]    [0053]FIGS. 6A and 6B show the relation between a sheet resistance of a copper wiring layer subjected to the hydrogen plasma treatment and a radio frequency power used for the hydrogen plasma treatment. FIGS. 6A and 6B show the sheet resistances of copper wiring layers having a width of 0.54 μm and 1 μm, respectively. The abscissa represents an applied radio frequency power in the unit of “W” and the ordinate represents a sheet resistance in the unit of “mΩ/□”. For comparison purposes, sheet resistances of copper wiring layers subjected to the ammonia plasma treatment are shown by broken lines.  
         [0054]    It can be seen from these graphs that as the radio frequency power is raised, the sheet resistance becomes high. An increase in the sheet resistance may be ascribed to that the hydrogen plasma treatment etches the insulating film of FSG and emits silicon atoms which form a copper silicide film in the surface layer of the copper wiring layer.  
         [0055]    [0055]FIG. 7A shows the relation between an atom density on the surface of a copper wiring layer subjected to the hydrogen plasma treatment and a radio frequency power applied during the hydrogen plasma treatment. The abscissa represents a radio frequency power in the unit of  37  W” and the ordinate represents an atom density in the unit of “atom %”. In FIG. 7A, a black triangle indicates a silicon atom density, and a black circle indicates a fluorine atom density. It can be seen from this graph that as the radio frequency power is raised, the silicon atom density increases. The fluorine atom density is almost 0%.  
         [0056]    [0056]FIG. 7B shows the relation between an intrusion depth of impurity atoms into a copper wiring layer after the hydrogen plasma treatment and an applied radio frequency power. The abscissa represents a radio frequency power in the unit of “W” and the ordinate represents an intrusion depth of impurity atoms in the unit of “nm”. In FIG. 7B, a black triangle indicates an intrusion depth of a silicon atom, and a black circle indicates an intrusion depth of a fluorine atom. It can be seen from this graph that as the radio frequency power is raised, the intrusion depth of silicon atoms becomes deeper. This means that a thicker copper silicide film is formed.  
         [0057]    It can be seen from FIGS. 7A and 7B that as the applied radio frequency power during the hydrogen plasma treatment is raised, a thicker copper silicide film is formed in the surface layer of the copper wiring layer. As a thick copper silicide film is formed, the sheet resistance of a copper wiring layer becomes high.  
         [0058]    [0058]FIG. 8 shows the relation between an etching amount of an FSG film and a SiO 2  film by hydrogen plasma and a treatment time. The abscissa represents a hydrogen plasma treatment time in the unit of “sec” and the ordinate represents an etching amount in the unit of “nm”. In FIG. 8, a black triangle indicates an etching amount of the FSG film and a black circuit indicates an etching amount of the SiO 2  film. It can be seen that an etching rate of FSG is faster than that of SiO 2 .  
         [0059]    The ammonia plasma treatment hardly etches both the SiO 2  film and FSG film. It can be seen therefore that hydrogen plasma has stronger chemical reaction than ammonia plasma. It can be considered that this stronger chemical reaction can remove fluorine atoms on the surface of a copper wiring layer. However, since the hydrogen plasma etches the FSG film, emitted silicon atoms silicify the surface layer of the copper wiring layer so that the sheet resistance increases.  
         [0060]    It can be seen from FIGS. 6A and 6B that the applied radio frequency power is preferably set to 150 W or smaller in order to make the sheet resistance of a copper wiring layer subjected to the hydrogen plasma treatment approximately equal to that of a copper wiring layer subjected to the ammonia plasma treatment. By normalizing the applied power by an electrode area of the hydrogen plasma treatment system used in the embodiment, it is preferable to set the applied power per an electrode unit area to 0.2 W/cm 2 .  
         [0061]    In this embodiment, although the hydrogen plasma treatment is performed by using a plasma treatment system of a diode parallel plate type, other plasma treatment systems may also be used such as an inductive coupling type plasma treatment system and a remote plasma treatment system.  
         [0062]    [0062]FIG. 9A shows the etching amounts of an FSG film and an SiO 2  film by a high density hydrogen plasma treatment using an inductive coupled type plasma treatment system. The abscissa represents a treatment time in the unit of “sec” and the ordinate represents an etching amount in the unit of “nm”. In  
         [0063]    [0063]FIG. 9A, a black rhomboid indicates an etching amount of a thermal oxidation SiO 2  film, and a white square indicates an etching amount of an FSG film. It can be seen that a difference between both the etching amounts is small. It can be considered from this that in the process using high density hydrogen plasma generated by inductive coupling, reaction results from the effects different from those of the process using hydrogen plasma generated by capacitive coupling.  
         [0064]    [0064]FIG. 9B shows the sheet resistances of copper wiring layers subjected to the hydrogen plasma treatment and the ammonia plasma treatment using an inductive coupling type plasma treatment system. The abscissa represents a wiring layer or line width in the unit of “μm” and the ordinate represents a sheet resistance in the unit of “mΩ/□”. The sheet resistance after the hydrogen plasma treatment is higher than that after the ammonia plasma treatment, with a small difference therebetween. An increase in the sheet resistance of a copper wiring layer can be suppressed by using high density hydrogen plasma generated by inductive coupling.  
         [0065]    [0065]FIG. 10 is a schematic diagram of a remote plasma treatment system. A reaction unit  60  and a plasma generating unit  61  are coupled by a transport tube  62 . Hydrogen gas is supplied to the plasma generating unit  61  and micro waves are guided to the plasma generating unit  61  via a waveguide  63  to thereby generate hydrogen plasma. The generated hydrogen plasma is transported to the reaction unit  60  via the transport tube  62 .  
         [0066]    Hydrogen plasma transported to the reaction unit  60  is diffused while passing through a diffusion plate  64 , and poured upon a substrate  65 . By using a remote plasma treatment system, chemical reaction becomes more dominant than physical reaction. It is therefore possible to enhance the fluorine removal effects of chemical reaction.  
         [0067]    In the above-described embodiment, copper is used as the wiring material. Similar effects can be expected for other conductive materials which contain copper as the main composition. In the above-described embodiment, although FSG is used as the material of an insulation film in which a copper wiring layer is embedded, similar effect can be expected for other insulating materials which contain fluorine. Such materials include amorphous carbon fluoride, inorganic spin-on-glass (SOG) which contains fluorine, organic SOG which contains fluorine and the like. In the above-described embodiment, silicon nitride is used as the material of the barrier layer in contact with the copper wiring layer. Other materials may also be used such as silicon carbide, phosphosilicate glass, and silicon oxide which contains carbon.  
         [0068]    The present invention has been described in connection with the preferred embodiments. The invention is not limited only to the above embodiments. It is apparent that various modifications, improvements, combinations, and the like can be made by those skilled in the art.