Abstract:
Disclosed is a method of forming a titanium nitride film on a substrate through the reaction of titanium tetrachloride and ammonia while minimizing corrosion of the underlying layer. A first titanium nitride layer is formed on a substrate by reacting titanium tetrachloride and ammonia with each other in the supply-limited region while minimizing corrosion of the underlying layer. Thereafter, a second titanium nitride layer is formed on the first titanium nitride layer in the reaction-limited region while achieving good step coverage.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a method of forming a titanium nitride film on a substrate to be processed through the reaction of tetrachloride (TiCl 4 ) and ammonia (NH 3 ). 
       BACKGROUND ART 
       [0002]    JP2000-68232A discloses a method of forming a TiN film while changing TiCl 4 /NH 3  flow rate ratio. In this method, however, as the TiCl 4 /NH 3  flow rate ratio is not proper, the underlying layer is likely to be etched due to Cl or HCl produced from TiClx (x=1 to 4) during the film formation. In the event that the underlying layer is etched: if the underlying layer is a conductive layer, the TiN film is separated from the conductive layer, resulting in increase of the contact resistance; if the underlying layer is a dielectric layer, the dielectric capacity is decreased, resulting in deterioration of device property of the element. 
       DISCLOSURE OF THE INVENTION 
       [0003]    The object of the present invention is to provide a film-forming technique that solves the foregoing problem. 
         [0004]    The objective can be achieved by the inventions defined in the independent claims. The dependent claims define advantageous concrete embodiments of the present invention. 
         [0005]    In order to solve the foregoing problem, according to the first aspect of the present invention, there is provide a film-forming method of forming a titanium nitride film on a substrate to be processed through reaction of titanium tetrachloride and ammonia, the method including: a first step of reacting titanium tetrachloride and ammonia with each other in supply-limited region, thereby forming a first titanium nitride layer on the substrate; and a second step of reacting titanium tetrachloride and ammonia with each other in reaction-limited region, thereby forming a second titanium nitride layer on the first titanium nitride layer. 
         [0006]    As the first titanium nitride film (layer) is formed under titanium tetrachloride supply-limited condition in the first step, the titanium tetrachloride concentration in the first titanium nitride layer thus formed and the concentration of corrosive gases such as chlorine gas and hydrochloride gas generated due to the reaction is very low. Thus, even if the underlying layer is formed of a material vulnerable to etching by a corrosive-gas, etching of the underlying layer can be suppressed in the first step. The underlying layer has been covered with the first titanium nitride film in the second step that forms the second titanium nitride film (layer). Therefore, even if the second titanium nitride film is formed under reaction-limited condition in the second step, etching of the underlying layer can be suppressed. Thus, according to the present invention, a titanium nitride film with good step coverage can be formed, while suppressing the etching of the underlying layer. 
         [0007]    Preferably, partial pressure ratio of the titanium tetrachloride to the ammonia in the first step is higher than that in the second step. For example, the partial pressure ratio in the first step is not less than 0.13 but less than 0.2, and the partial pressure ratio in the second step is not less than 0.2 but less than 1.5. 
         [0008]    Preferably, temperature of the substrate in the first step is lower than that in the second step. Preferably, the temperature of the substrate in the first step is lower than 400° C., and the temperature of the substrate in the second step is not lower than 400° C. Due to this, a titanium nitride film having a low electric resistance and having a lower chloride concentration can be formed, while suppressing the etching of the underlying layer. 
         [0009]    The present invention further provides a film-forming method of forming a titanium nitride film on a substrate to be processed in a chamber through reaction of titanium tetrachloride and ammonia, the method including: a first step of supplying titanium tetrachloride and ammonia into the chamber with flow rate ratio of the titanium tetrachloride to the ammonia being a first flow rate ratio, while pressure in the chamber being maintained within a range of 3.94×10 −4  to 1.32×10 −2  atm, thereby forming a first titanium nitride layer on the substrate; a second step of supplying titanium tetrachloride and ammonia into the chamber with flow rate ratio of the titanium tetrachloride to the ammonia being a second flow rate ratio smaller than the first flow rate ratio, while pressure in the chamber being maintained within a range of 3.94×10 −4  to 1.32×10 −2  atm, thereby forming a second titanium nitride layer on the first titanium nitride layer. 
         [0010]    According the second aspect of the present invention, there is provided a semiconductor device including a titanium nitride film formed by the foregoing methods. 
         [0011]    According the third aspect of the present invention, there is provided a storage medium storing a software executable by a control computer of a film-forming apparatus, wherein upon execution of the software the control computer controls the film-forming apparatus so that the apparatus performs the foregoing film-forming methods of forming a titanium nitride film. 
         [0012]    According the fourth aspect of the present invention, there is provided a film-forming system for forming a titanium nitride film on a substrate through reaction of titanium tetrachloride and ammonia, the system including: at least one film-forming apparatus including: a film-forming chamber; a substrate support member that supports a substrate in the film-forming chamber; a first supply line, provided thereon with a first gas flow controller, that supplies titanium tetrachloride into the film-forming chamber; a second supply line, provided thereon with a second gas flow controller, that supplies titanium ammonia into the film-forming chamber; and an exhaust device that evacuates an atmosphere in the film-forming chamber; and a control unit that controls said at least one of the film-forming apparatus so that the apparatus performs a first step of reacting titanium tetrachloride and ammonia with each other under supply-limited condition, thereby forming a first titanium nitride layer on the substrate, and a second step of reacting titanium tetrachloride and ammonia with each other under reaction-limited condition, thereby forming a second titanium nitride layer on the first titanium nitride layer. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0013]      FIG. 1  is a schematic diagram showing the structure of the film-forming system  100  of a multi-chamber type provided with a Ti film-forming apparatus and TiN film-forming apparatus that perform the film-forming method in one embodiment of the present invention; 
           [0014]      FIG. 2  is a cross-sectional view of the TiN film-forming apparatus  3 . 
           [0015]      FIG. 3  shows other embodiments of a wafer elevating mechanism. 
           [0016]      FIG. 4  is a flowchart illustrating the first embodiment of the TiN film-forming method; 
           [0017]      FIG. 5  is a graph showing the growth rate of a TiN film with respect to the titanium tetrachloride partial pressure ratio; 
           [0018]      FIG. 6  shows tables respectively showing the film-forming conditions of the first TiN film and the second TiN film; 
           [0019]      FIG. 7  is a flowchart illustrating the second embodiment of the TiN film-forming method; and 
           [0020]      FIG. 8  is a cross-sectional view showing a part of a semiconductor device including a first TiN film  24  and a second TiN film  25  formed according to the film-forming method in one embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    Preferred embodiments of the present invention will now be specifically described with reference to the accompanying drawings.  FIG. 1  is a schematic diagram showing the configuration a film-forming system  100  of a multi-chamber type, including Ti film-forming apparatus TiN film-forming apparatus for performing a film-forming method according to the present invention. The film-forming system  100  includes four film-forming apparatuses: Ti film-forming apparatuses  1  and  2  for forming a Ti film by plasma CVD; and TiN film-forming apparatuses  3  and  4  for forming a TiN film by thermal CVD. The film-forming apparatuses  1 ,  2 ,  3 , and  4  are respectively provided on four sides of a wafer transfer chamber  5  having a hexagonal cross section. Note that, although the film-forming system  100  in this embodiment includes the Ti film-forming apparatuses  1  and  2  and the TiN film-forming apparatuses  3  and  4 , a dielectric film-forming apparatus may be substituted for the Ti film-forming apparatus  1  in another embodiment. 
         [0022]    Load-lock chambers  6  and  7  are provided on the remaining two sides of the wafer transfer chamber  5 . A wafer carrying-in-and-out chamber  8  is provided on the sides of the load-lock chambers  6  and  7  opposite to the wafer transfer chamber  5 . Provided on the side of the wafer carrying-in-and-out chamber  8  opposite to the load-lock chambers  6  and  7  are three ports  9 ,  10 , and  11 , to which three FOUPs, or wafer containers, each being capable of accommodating wafers W (a wafer W is an example of a substrate to be processed) therein, can be attached, respectively, and through which ports wafers W are carried into and out of the film-forming system  100 . 
         [0023]    Each of the Ti film-forming apparatuses  1  and  2  has a Ti film-forming chamber  51 ; and each of the TiN film-forming apparatuses  3  and  4  has a TiN film-forming chamber  151 . The Ti film-forming chambers  51 , the TiN film-forming chambers  151 , and the load-lock chambers  6  and  7  are connected to respective sides of the wafer transfer chamber  5  through respective gate valves G, as shown in  FIG. 1 . The chambers  51 ,  151 ,  6  and  7  are communicated with the wafer transfer chamber  5  when their respective gate valves G are opened; while they are separated from the wafer transfer chamber  5  when these gate valves G are closed. Gate valves G are also arranged at the joint between the load-lock chambers  6 ,  7  and the wafer carrying-in-and-out chamber  8  through respective gate valves G. The load-lock chambers  6  and  7  are communicated with the wafer carrying-in-and-out chamber  8  when these gate valves are opened; they are separated from the wafer carrying-in-and-out chamber  8  when these gate valves are closed. 
         [0024]    The wafer transfer chamber  5  is provided therein with a wafer transfer device  12  to transfer a wafer W to be processed to and from the Ti film-forming apparatuses  1  and  2 , the TiN film-forming apparatuses  3  and  4  and the load-lock chambers  6  and  7 . The wafer transfer device  12  is disposed approximately at the center of the wafer transfer chamber  5 , and includes a rotatable-and-retractable part  13  which is provided on its tips with two blades  14   a  and  14   b  each for holding a wafer W. The blades  14   a  and  14   b  are attached to the rotatable-and-retractable part  13  such that they face in opposite directions. The blades  14   a  and  14   b  can be projected and retracted independently and simultaneously. The interior of the wafer transfer chamber  5  can be maintained at a predetermined degree of vacuum. 
         [0025]    A HEPA filter (not shown) is provided on the ceiling portion of the wafer carrying-in-and-out chamber  8 . Clean air passed through the HEPA filter supplied into the wafer carrying-in-and-out chamber  8  flows downward therein, which allows a wafer W to be transferred into and from the wafer carrying-in-and-out chamber  8  of a clean-air atmosphere of atmospheric pressure. A shutter (not shown) is provided on each of the three ports  9 ,  10 , and  11 , each for holding a FOUP, of the wafer carrying-in-and-out chamber  8 . When a FOUP F accommodating wafers W or an empty FOUP F is attached to one of the port, the shutter is opened so that the interior of the FOUP is communicated with the wafer carrying-in-and-out chamber  8  while preventing ambient-air entry. An alignment chamber  15 , in which a wafer W is aligned, is provided on a side of the wafer carrying-in-and-out chamber  8 . 
         [0026]    A wafer transfer device  16  is arranged in the wafer carrying-in-and-out chamber  8  to transfer a wafer W to and from the FOUP F and the load-lock chambers  6  and  7 . The wafer transfer device  16  has an articulated arm structure and can be moved on a rail  18  in the direction in which the FOUPs F are arrayed. The wafer transfer device  16  transfers a wafer W while holding it on the hand  17  provided at the tip of the an articulated arm structure. 
         [0027]    A control unit  19  controls the operation of the entire system, such as the operations of the wafer transfer devices  12  and  16 , etc. 
         [0028]    In the foregoing film-forming system  100 , first, the wafer transfer device  16 , which is arranged in the wafer carrying-in-and-out chamber  8  providing a clean-air atmosphere of atmospheric pressure therein, removes a wafer W from one of the FOUPs and transfers it to the alignment chamber  15 , in which the wafer W is aligned. Thereafter, the wafer W is transferred to either the load-lock chamber  6  or  7 ; after the load-lock chamber is evacuated, the wafer transfer device  12  in the wafer transfer chamber  5  transfers the wafer W from the load-lock chamber to the Ti film-forming chamber  51  of the Ti film-forming apparatus  1  or  2 , in which the Ti film-forming process is performed. Thereafter, the wafer W having been subjected to the Ti film-forming process is subsequently loaded into the Ti film-forming chamber  151  of the TiN film-forming apparatus  3  or  4 , in which the TiN film-forming process is performed. That is, the Ti film-forming process and the TiN film-forming process are sequentially performed, in-situ. Thereafter, the wafer transfer device  12  transfers the wafer W having been subjected to the film-forming processes to the load-lock chamber  6  or  7 . Then, after the load-lock chamber is brought back to atmospheric pressure, the wafer transfer device  16  in the wafer carrying-in-and-out chamber  8  removes the wafer W from the load-lock chamber and returns it to one of the FOUPs F. The above operations are performed repeatedly to wafers W of one process lot, completing a set of film-forming processes. 
         [0029]      FIG. 2  is a cross-sectional view of the TiN film-forming apparatus  3 . The TiN film-forming apparatuses  3  and  4  have the same structure, and thus only the structure of the TiN film-forming apparatus  3  will be described hereinafter. The TiN film-forming apparatus  3  has the TiN film-forming chamber  151  as mentioned above. The TiN film-forming chamber  151  is a hermetically-sealed, cylindrical chamber, in which a susceptor  52  for supporting a wafer W horizontally is arranged with the susceptor  52  being supported by a cylindrical support member  53  arranged below the susceptor  52 . 
         [0030]    The susceptor is made of a ceramic material such as AlN, and provided at the periphery thereof with a guide ring  54 . A heater  55  is embedded in the susceptor  52 . The heater  55  heats the wafer W up to a predetermined temperature when it is supplied with electric power by the heater power supply  56 . An electrode  58  that functions as a lower electrode is embedded in the susceptor  52  above the heater  55 . 
         [0031]    A shower head  60  is attached to a ceiling wall  151   a  of the chamber  151  through an insulating member  59 . The shower head  60  includes an upper block  60   a , a middle block  60   b  and a lower block  60   c . A ring-shaped heater  96  is embedded in the peripheral portion of the lower block  40   c . The heater  96  receives power from a heater power supply  97 , whereby the heater  96  is capable of heating the shower head  60  up to a predetermined temperature. 
         [0032]    Discharge holes  67  and discharge holes  68  are alternately formed in the lower block  60   c  to discharge a gas therefrom. A first gas introduction port  61  and a second gas introduction port  62  are formed in the upper surface of the upper block  60   a . A number of gas passages  63  branch off from the first gas introduction port  61  in the upper block  60   a . Gas passages  65  are formed in the middle block  60   b . The gas passages  63  are connected to the gas passages  65  through communication passages  63   a . A number of gas passages  64  branch off from the second gas introduction port  62  in the upper block  60   a . Gas passages  66  are formed in the middle block  60   b . The gas passages  64  are connected to the gas passages  66 . The gas passages  66  are connected to communication passages  66   a  horizontally extending in the middle block  60   b , and the communication passages  66   a  are connected to the discharge holes  68  formed in the lower block  68 . 
         [0033]    The gas supply mechanism  110  includes: a ClF 3  gas supply source  111  for supplying ClF 3  gas as a cleaning gas; a TiCl 4  gas supply source  112  for supplying TiCl 4  gas as a Ti-containing gas; a first N 2  gas supply source  113  for supplying N 2  gas; an NH 3  gas supply source  114  for supplying NH 3  gas as a nitriding gas; and a second N 2  gas supply source  115  for supplying N 2  gas. A ClF 3  gas supply line  116  is connected to the ClF 3  gas supply source  111 ; a TiCl 4  gas supply line  117  is connected to the TiCl 4  gas supply source  112 ; a first N 2  gas supply line  118  is connected to the first N 2  gas supply source  113 ; an NH 3  gas supply line  119  is connected to the NH 3  gas supply source  114 . The gas supply mechanism  110  further includes an Ar gas supply source, not shown. A mass flow controller  122  and two valves  121  arranged on opposite sides of the mass flow controller  122  are provided in each gas supply line. A pre-flow line  124  is connected to the TiCl 4  gas supply line  117 . 
         [0034]    The TiCl 4  gas supply line  117  extending from the TiCl 4  gas supply source  112  is connected to the first gas introduction port  61  of the shower head  60 . The ClF 3  gas supply line  116  extending from the ClF 3  gas supply source  111  and the first N 2  gas supply line  118  extending from the first N 2  gas supply source  113  are connected to the TiCl 4  gas supply line  117 . The NH 3  gas supply line  119  extending from the NH 3  gas supply source  114  is connected to the second gas introduction port  62 . The second N 2  gas supply line  120  extending from the first N 2  gas supply source  115  is connected to the NH 3  gas supply line  119 . Therefore, during film-forming process, TiCl 4  gas supplied from the TiCl 4  gas supply source  112  is supplied through the TiCl 4  gas supply line  117  into the shower head  60  through the first gas introduction port  61  together with N 2  gas supplied from the first N 2  gas supply source  113 , and passes through the gas passages  63  and  65  to be discharged into the TiN film-forming chamber  151  through the discharge ports  67 ; while NH 3  gas as a nitriding gas supplied from the NH 3  gas supply source  114  is supplied through the NH 3  gas supply line  119  into the shower head  60  through the second gas introduction port  62  together with N 2  gas supplied from the second N 2  gas supply source  114 , and passes through the gas passages  64  and  66  to be discharged into the TiN film-forming chamber  151  through the discharge ports  68 . That is, the shower head  60  is of a post-mix type which supplies TiCl 4  gas and NH 3  gas separately into the TiN film-forming chamber  151 , and hence these gases are mixed and react with each other after they are discharged. The valves  121  and the mass flow controllers  122  are controlled by a controller  123 . 
         [0035]    A circular hole  85  is formed in the center portion of a bottom wall  151   b  the TiN film-forming chamber  151 ; and an exhaust chamber  86  is attached to the bottom wall  151   b  such that the exhaust chamber  86  protrudes downward and covers the hole  85 . An exhaust pipe  87  is connected to the side of the exhaust chamber  86 . An exhaust device  88  is connected to the exhaust pipe  87 . Thus, the interior of the TiN film-forming chamber  151  can be uniformly evacuated to a predetermined vacuum via the exhaust chamber  86  by operating the exhaust device  88 . 
         [0036]    Three wafer support pins  89  (only two of which are shown) for supporting and for elevating and lowering the wafer W penetrate through the susceptor  52 . The wafer support pins  89  are fixed to a support member  90 , and are raised and lowered by a drive mechanism  91  (e.g., a motor) through the support member  90  and a support rod  93  supporting the support member  90 . The support pins  89 , support member  90  and/or a support rod  93  may be formed of a ceramic material such as Al 2 O 3 , or quartz. 
         [0037]    In a case where the surface of a film formed on the susceptor  52  is likely to take (electric) charge such as a case where plasma is used for the film formation or a case where a reaction gas that likely to charge such as chlorine-containing gas is used, it is preferable that at least the surface of each wafer support pin  89  is formed of an electrically-conductive material. Preferably, the electrically-conductive material is one having a high corrosion resistance against cleaning gases, such as nickel (Ni) or HASTELLOY (trademark). The electrically-conductive material may be a ceramic material having electrical conductivity. If at least the surface of each wafer support pin  89  is formed of an electrically-conductive material, the wafer support pin  89  is preferably configured to be connected to ground when the wafer support pin  89  is in contact with the wafer W. 
         [0038]    A carrying-in-and-out port  92  and a gate valve G for opening and closing the carrying-in-and-out port  92  are provided in a side wall of the TiN film-forming chamber  51 . Note that, in this embodiment, a radio-frequency power source is connected to an upper part of the TiN film-forming chamber  51 , and thus the TiN film-forming chamber  51  is a chamber of a plasma CVD apparatus. Except for this point, the TiN film-forming chamber  51  has the same structure as the TiN film-forming chamber  151 . 
         [0039]      FIG. 3  shows other embodiments of a wafer elevating mechanism. In this embodiment, the wafer elevating mechanism comprises wafer support pins  89 , a support member  90 , a support rod  93  and a charge-removing pin  94 . The wafer support pins  89  and a support member  90  are formed of a ceramic material such as Al 2 O 3  or aluminum nitride (AlN), or a quartz material. At least the surface of each of the support rod  93  and the charge-removing pin  94  may be formed of an electrically-conductive material such as Ni or a Ni alloy, e.g., HASTELLOY. The charge-removing pin  94  is arranged so that a part thereof can contact to the susceptor  52 , and is configured to be connected to ground at least when the charge-removing pin  94  is in contact with the susceptor  52 . It is preferable that the charge-removing pin  94  is arranged such that it contacts to a surface of the susceptor  52  opposite to the surface of the susceptor  52  on which the wafer W is placed. It is also preferable that at least the surface of each of the wafer support pins  89  and the support member  90  is formed of an electrically-conductive material, and is electrically connected to the charge-removing pins  94 . 
         [0040]    In the embodiment shown ( a ) to ( c ) of  FIG. 3 , the charge-removing pin  94  can retract into the support rod  93 . The charge-removing pin  94  is constructed so that a part thereof can protrude from the support member  90  in the raising-and-lowering direction of the wafer support pins  89 . The charge-removing pin  94  is preferably arranged such that, when the charge-removing pin  94  is not in contact with the susceptor  52 , the gap between the charge-removing pin  94  and the susceptor  52  is smaller than the gap between each wafer support pin  89  and the wafer W. That is, the charge-removing pin  94  is preferably arranged such that, when moving the wafer support pins  89  to approach the wafer W, the charge-removing pin  94  comes into contact with the susceptor  52  before the wafer support pins  89  comes into contact with the wafer W. 
         [0041]    The charge-removing pin  94  is arranged such that, when the charge-removing pin  94  is subjected to a force that moves the charge-removing pin  94  into the support rod  93 , the charge-removing pin  94  moves into the support rod  93 , but when the force is released, the charge-removing pin  94  protrudes from the support rod  93 . In an illustrative embodiment, the charge-removing pin  94  is held in the support rod  93  via an elastic member. 
         [0042]    Next, the operation of the wafer elevating mechanism will be described. At the time of the completion of the TiN film on the wafer W, the wafer support pins  89  and the charge-removing pin  94  are spaced at respective distances from the wafer W and the susceptor  52 , respectively ( FIG. 3(   a )). That is, the wafer support pins  89  and the charge-removing pin  94  are not in contact with wafer W and the susceptor  52 , respectively. 
         [0043]    As the driving mechanism  91  moves the wafer support pins  89  so that they approach the wafer W, the charge removing pin  94  firstly comes into contact with the susceptor  52  ( FIG. 3(   b )). A TiN film is formed on the surface of the susceptor  52  when a TiN film is formed on the wafer W. An electric charge accumulated in the susceptor  52  and the wafer W is removed through the charge-removing pin  94  which is connected to ground. As the driving mechanism  91  further moves the wafer support pins  89  in the same direction, the wafer support pins  89  come into contact with the wafer W, and subsequently lift the wafer W off the susceptor  52  ( FIG. 3(   c )). 
         [0044]    In the embodiment shown in  FIG. 3(   d ), the charge-removing pin  94  is formed of an elastic material. The charge-removing pin  94  may be formed of an electrically-conductive material having elasticity. The charge-removing pin  94  may also be formed in a shape having spring property such as a shape of a coil spring as illustrated. The illustrated charge-removing pin  94  has spring property with respect to the raising-and-lowering direction of the wafer support pins  89 , and is arranged on the support member  90 . 
         [0045]    Also in the embodiment shown in  FIG. 3  ( d ), the charge-removing pin  94  is preferably arranged such that, when the charge-removing pin  94  is not in contact with the susceptor  52 , the gap between the charge-removing pin  94  and the susceptor  52  is smaller than the gap between each wafer support pin  89  and the wafer W. The wafer elevating mechanism shown in  FIG. 3(   d ) operates in the same manner as that of the wafer elevating mechanism shown in ( a ) to ( c ) of  FIG. 3 . 
         [0046]    According to the embodiments shown in  FIG. 3 , the electric charge accumulated in the susceptor  52  can be discharged therefrom by contacting the charge-removing pin  94 , connected to ground, to the susceptor  52 . Thus, the difference of the electric potential between the wafer W and the susceptor  52 , or between the TiN film on the susceptor  52  and the wafer W can be reduced to a very low level. Accordingly, electrostatic discharge failure of the elements formed on the wafer W can be prevented. 
         [0047]    Referring again to  FIG. 2 , the control unit  19 , which controls the whole operations of the film-forming system  100 , is embodied as a control computer which includes a central processing unit (CPU)  19   a ; a circuit  19   b  that supports the CPU  19   a ; a storage medium  19   c  storing control software. The control unit  19  controls all the functional elements (e.g., the heater power supply  56 , the exhausting device  88 , driving mechanism  91 , the heater power supply  91 , the valves  121 , the mass-flow controllers  122 ) of the TiN film-forming apparatus  3  through signal lines  19   d  (only some of them are illustrated) in order to achieve various process conditions (e.g., process gas flow rate, process pressure, process temperature) defined by a process recipe. 
         [0048]    The storage medium  19   c  may be one fixedly mounted to the control computer, or one detachably loaded to a reader mounted to the control computer and readable by the reader. In the most typical embodiment, the storage medium  19   c  is a hard disk drive in which the control software including a process recipe is installed by a service person of the manufacturer of the film-forming system  100 . In another embodiment, the storage medium  19   c  is a removable disk such as a CD-ROM or a DVD-ROM. Such a removable disk is read by an optical reader mounted to the control computer. The storage medium  19   c  may be a ROM type or a RAM type. The storage medium  19   c  may be a cassette ROM. It should be noted that any storage medium known in the computer art can be used as the storage medium  19   a . In a factory equipped with plural film-forming systems  100 , the control software may be installed in a managing computer that manages the control computers (control units  19 ) of the film-forming systems  100  in an integrated fashion. In this case, each of the film-forming system is controlled by the managing computer through a communication line to perform a predetermined process. 
         [0049]    Next, the method of forming a TiN film according to the present invention will be described. The description will be made for an example in which the TiN film-forming apparatus  3  forms a TiN film on a wafer W after the Ti film-forming apparatus  1  or  2  forms a Ti film on the wafer W. Preferably, the below-described method is automatically performed based on a process schedule and a process recipe stored in the storage medium  19   c  in the control computer (control unit)  19 . 
         [0050]      FIG. 4  is a flowchart illustrating the first embodiment of the TiN film-forming method. After a Ti film is formed on a wafer W in the Ti film-forming apparatus  1  or  2 , the wafer transfer device  12  carries the wafer W from the Ti film-forming apparatus  1  or  2  into the wafer transfer chamber  5 . The exhausting device  88  evaluates the interior of the TiN film-forming chamber  151  so that pressure in the TiN film-forming chamber  151  be at a predetermined value. Then, the gate valve G is opened, and the wafer transfer device  12  carries the wafer from the wafer transfer chamber  5  into the TiN film-forming chamber  151  through the carrying-in-and-out port  92  (STEP  500 ). 
         [0051]    Then, N 2  gas and NH 3  gas is supplied into the TiN film-forming chamber  151 , while the wafer W is preheated by the heater  5 . After the temperature of the heated wafer W has been substantially stabilized at a predetermined value and pre-flowing of TiCl 4  gas through the pre-flow line  124  has been performed, TiCl 4  gas, NH 3  gas are N 2  gas supplied into the TiN film-forming chamber  151  through the TiCl 4  gas supply line  177 , the valves  121 , and N 2  gas supply lines  118  and  120 , respectively. The flow rate of the TiCl 4  gas and the NH 3  gas are determined such that the reaction between the TiCl 4  gas and the NH 3  gas on the wafer W occurs under the supply-limited condition (i.e., the condition under which the deposition rate is limited by the supply rates of the gases). In other words, the partial pressure ratio of the TiCl 4  gas to the NH 3  gas is set so that the TiCl 4  gas and the NH 3  gas react with each other in the supply-limited region. Thus, a first TiN film is formed on the Ti film formed on the wafer W through the reaction between the TiCl 4  gas and the NH 3  gas on the wafer W heated up to the predetermined temperature (STEP  510 ). 
         [0052]    In this embodiment, the flow rate ratio NH 3 /TiCl 4  (i.e., the flow rate ratio of the NH 3  gas to the TiCl 4  gas) is set to be 60 or below such that the reaction rate of the TiCl 4  gas and the NH 3  gas on the wafer W is limited by the supply of the gases. The flow rate ratio NH 3 /TiCl 4  is preferably in a range of 2.5 to 15, more preferably, 5 to 7.5. In this case, the flow rate of the TiCl 4  gas is preferably in a range of 6 to 18 sccm, while the flow rate of the NH 3  gas is in a range of 45 to 90 sccm. The internal pressure of the TiN film-forming chamber  151  is in a range of 0.3 to 10 Torr (3.94×10 −4  to 1.32×10 −2  atm), preferably in a range of 1 to 8 Torr (1.32×10 −3  to 1.06×10 −2  atm). The temperature of the wafer W is in a range of 350 to 700° C. 
         [0053]    After forming the first TiN film, the first TiN film may be annealed with NH 3  gas, which is an example of a nitrogen-atom-containing gas, being supplied into the TiN film-forming chamber  151 . For example, the flow rate of the NH 3  gas supplied into the TiN forming chamber  151  is in a range of 45 to 90 sccm. The internal pressure of the TiN film-forming chamber  151  is in a range of 0.3 to 10 Torr (3.94×10 −4  to 1.32×10 −2  atm), preferably in a range of 1 to 8 Torr (1.32×10 −3  to 1.06×10 −2  atm). The temperature of the wafer W is in a range of 350 to 700° C., more preferably, in a range of 500 to 600° C. Thereby, the chlorine concentration in the first TiN film can be further reduced, and thus a TiN film having a low resistivity and an excellent barrier property can be obtained. 
         [0054]    In this embodiment, the TiN film is annealed by using NH 3  gas as a nitrogen-containing gas. In another embodiment, nitrogen gas or monomethyl hydrazine gas may be used as a nitrogen-atom-containing gas. Alternatively, the TiN film may be annealed by using a hydrogen-atom-containing gas such as hydrogen gas. In this embodiment, the forming and the annealing of the TiN film is performed in the same chamber, the chamber  151 . In another embodiment, the after forming the TiN film, the wafer may be transferred to another chamber to perform the annealing therein. 
         [0055]    Next, the flow rates of the NH 3  gas to the TiCl 4  gas supplied into the TiN film-forming chamber  151  are changed such that the reaction between the TiCl 4  gas and the NH 3  gas on the wafer W occurs under the reaction-limited condition (i.e., the condition under which the deposition rate is limited by the reaction rate of the gases). In other words, the partial pressure ratio of the TiCl 4  gas to the NH 3  gas is set such that the TiCl 4  gas and the of the NH 3  gas react with each other in the reaction-limited region. In detail, the flow rates of the NH 3  gas to the TiCl 4  gas are set such that the partial pressure ratio in this step is higher than that in the step of forming the first TiN film (STEP  500 ). Thus, a second TiN film is formed on the first TiN film formed on the wafer W through the reaction between the TiCl 4  gas and the NH 3  gas on the wafer W heated up to the predetermined temperature (STEP  520 ). Preferably, the second TiN film is thicker than the first TiN film. Thereby, the chlorine concentration in the first TiN film can be further reduced, and thus a TiN film having a low resistivity and an excellent barrier property can be obtained. 
         [0056]    In this embodiment, the flow rate ratio NH 3 /TiCl 4  (i.e., the flow rate ratio of the NH 3  gas to the TiCl 4  gas) is set to be 16 or below such that the reaction rate of the TiCl 4  gas and the NH 3  gas on the wafer W is limited of the reaction of the gases. The flow rate ratio NH 3 /TiCl 4  is preferably in a range of 0.3 to 10, more preferably, 0.7 to 5. In this case, the flow rate of the TiCl 4  gas is preferably in a range of 9 to 130 sccm, while the flow rate of the NH 3  gas is in a range of 45 to 90 sccm. The internal pressure of the TiN film-forming chamber  151  is in a range of 0.3 to 10 Torr (3.94×10 −4  to 1.32×10 −2  atm), preferably in a range of 1 to 8 Torr (1.32×10 −3  to 1.06×10 −2  atm), more preferably in a range of 1 to 5 Torr (1.32×10 −3  to 6.6×10 −3  atm). The temperature of the wafer W is in a range of 350 to 700° C. 
         [0057]    After forming the second TiN film, the supply of the TiCl 4  gas and the NH 3  gas, and the N 2  gas as a purge gas is supplied into the TiN film-forming chamber  151  at a predetermined flow rate in order to purge the TiN film-forming chamber  151  and to remove the gases remaining in the TiN film-forming chamber  151 . After the TiN film-forming chamber  151  is purged, the second TiN film may be annealed by supplying N 2  gas and NH 3  gas into the TiN film-forming chamber  151 . In this case, the second TiN film is preferably annealed under the same conditions as those for the annealing of the first TiN film. 
         [0058]      FIG. 5  shows the growth rate of the TiN film with respect to the TiCl 4  partial pressure ratio. As shown in  FIG. 5 , as the partial pressure ratio of the TiCl 4  gas to the NH 3  gas is increased while keeping the flow rate of the NH 3  gas supplied into the TiN film-forming chamber  151  constant, the TiN film growth rate increases at a substantially-constant increasing rate if the TiCl 4  partial pressure ratio is in a low level (Range I in  FIG. 5 ). That is, the TiN film growth rate increases in proportion to the TiCl 4  partial pressure ratio. In this embodiment, the first TiN film is formed by supplying the TiCl 4  gas and the NH 3  gas into the TiN film-forming chamber  151  at respective flow rates which results in the partial pressure ratio of TiCl 4  gas to the NH 3  gas being within the Range I. 
         [0059]    If the TiCl 4  partial pressure is increased beyond the Range I, the TiN film growth rate decreases at a substantially-constant increasing rate in proportion to the TiCl 4  partial pressure ratio. If the TiCl 4  partial pressure ratio is further increased, the TiN film growth rate (deposition rate) is substantially constant regardless of the TiCl 4  partial pressure ratio (Range II in  FIG. 5 ). In this embodiment, the second TiN film is formed by supplying the TiCl 4  gas and the NH 3  gas into the TiN film-forming chamber  151  at respective flow rates which results in the partial pressure ratio of TiCl 4  gas to the NH 3  gas being within the Range II. 
         [0060]      FIG. 6  includes tables illustrating examples of preferable film-forming conditions.  FIG. 6(   a ) shows film-forming conditions for the first TiN film; and  FIG. 6  ( b ) shows film-forming conditions for the second TiN film. 
         [0061]    As shown in  FIG. 6(   a ), the first TiN film is preferably formed by supplying the TiCl 4  gas and the NH 3  gas into the TiN film-forming chamber  151  while the partial pressure ratio of TiCl 4  gas to the NH 3  gas is maintained within a range of 0.13 to 0.20. In this case, the control unit  190  preferably controls the total pressure in the TiN film-forming chamber  151  at about 5 Torr (6.58×10 −3  atm). 
         [0062]    As shown in  FIG. 6(   b ), the first TiN film is preferably formed by supplying the TiCl 4  gas and the NH 3  gas into the TiN film-forming chamber  151  while the partial pressure ratio of the TiCl 4  gas to the NH 3  gas is maintained at a range of 0.20 to 1.50. Also in this case, the control unit  190  preferably controls the total pressure in the TiN film-forming chamber  151  at about 5 Torr (6.58×10 −3  atm). 
         [0063]      FIG. 7  is a flowchart illustrating the second embodiment of the TiN film-forming method. In this embodiment, the temperature of the wafer when forming the first TiN film is lower than that when forming the second TiN film. In addition, the film-forming method in this embodiment forms the first TiN film in a TiN forming apparatus (chamber), and thereafter forms the second TiN film in another TiN forming apparatus. The TiN film-forming method in this embodiment will be described with reference to the flowchart. 
         [0064]    First, the wafer transfer device  12  carries the wafer W from the wafer transfer chamber  5  through the carrying-in-and-out port  92  into the TiN film-forming chamber  151  of the TiN film-forming apparatus  3  (STEP  500 ). Then, N 2  gas and NH 3  gas is supplied into the TiN film-forming chamber  151 , while the wafer W is preheated by the heater  55  (STEP  502 ). The wafer is preferably heated up to a temperature in a range of 200 to 400° C., more preferably in a range of 300 to 400° C. After the temperature of the heated wafer W has been substantially stabilized at a predetermined value, the first TiN film is formed on the wafer W through the reaction between the TiCl 4  gas and the NH 3  gas in the supply-limited region in the same manner as that in the first embodiment (STEP  510 ). 
         [0065]    After forming the first TiN film on the wafer W, the wafer transfer device  12  removes the wafer W from the TiN film-forming apparatus  3 , and carries it into the TiN film-forming chamber  151  of the TiN film-forming apparatus  4  (STEP  512 ). Then, N 2  gas and NH 3  gas is supplied into the TiN film-forming chamber  151 , while the wafer W is preheated by the heater  55  (STEP  502 ). The wafer W is heated up to a temperature higher than the temperature of the wafer W when the first TiN film is formed, i.e., the temperature at which the wafer W is heated in the TiN film-forming apparatus  3 . The wafer is preferably heated up to a temperature in a range of 400 to 700° C., more preferably in a range of 450 to 600° C. After the temperature of the heated wafer W has been substantially stabilized at a predetermined value, the second TiN film is formed on the wafer W through the reaction between the TiCl 4  gas and the NH 3  gas in the reaction-limited region in the same manner as that in the first embodiment (STEP  520 ). 
         [0066]    Although the first TiN film and the second TiN film are formed in different TiN film-forming apparatuses in this embodiment, the first TiN film and the second TiN film may be formed in the same TiN film-forming apparatus while changing the temperature of the wafer W. In this case, the wafer W (or susceptor  52 ) is preferably heated by a lamp heater which enables rapid heating and/or cooling of the wafer W. 
         [0067]    Although the TiN films are formed in the first TiN film-forming step and the second TiN film-forming step in the supply-limited region and the reaction-limited region, respectively, by controlling the flow rates of the TiCl 4  gas and the NH 3  gas in the foregoing embodiments, the TiN films may be formed in the supply-limited region and the reaction-limited region, respectively, by controlling another process parameter such as the pressure in the chamber or the temperature of the wafer W in another embodiment. 
         [0068]      FIG. 8  shows parts of semiconductor devices having the first TiN film  24  and the second TiN film  25  formed by the film-forming method in the foregoing embodiments. 
         [0069]      FIG. 8(   a ) is a cross-sectional view of a part of a semiconductor device having a contact hole  22 . The illustrated semiconductor device comprises a underlying layer  20 , an interlayer insulating film  21 , the contact hole  22 , Ti film  23 , the first TiN film  24  and the second TiN film. The contact hole  22  is formed in the interlayer insulating film  22  to reach the underlying layer  21 . The Ti film  23  serving as a contact layer to the underlying layer is formed on the inner surface of the contact hole  22  and on the upper surface of the interlayer insulating film  22 . The first TIN film  24  and the second TiN film  25  serving as barrier layers are formed on the Ti film  23  according to the film-forming method in the foregoing embodiments. A film of a metal such as Al or W will be formed on the second TiN film  25  to form a wiring layer of the semiconductor device and to fill up the contact hole  22  with the metal. The underlying layer  22  may be formed of a metal, a semiconductor such as polycrystalline silicon, or a silicide such as cobalt silicide (CoSi) or nickel silicide (NiSi), for example. 
         [0070]      FIG. 8(   b ) is a cross-sectional view showing a part of a semiconductor device having a field effect transistor. The illustrated semiconductor device comprises an underlying layer  20 , a gate dielectric film  26 , the first TiN film  24  and the second TiN film  25 . The underlying layer  20  is a semiconductor layer in which a source, a drain and a channel are formed. The gate dielectric film  26  is formed on the channel. The first TiN film  24  and the second TiN film  25  are formed on the gate dielectric film  26  according to the film-forming method in the foregoing embodiments. It is preferable that the gate dielectric film  26  is formed of a high-k material such as hafnium oxide (HfO 2 ). 
         [0071]      FIG. 8(   c ) is a cross-sectional view showing a part of a semiconductor device having a capacitor. The illustrated semiconductor device comprises: an interlayer insulating film  21 ; and a lower electrode  27 , a capacitor dielectric film  28 , the first TiN film  24  and the second TiN film  25  which constitute a capacitor. The lower electrode  27  is formed of an electrically-conductive material such as polycrystalline silicon, and is formed on the interlayer insulating film  21 . The capacitor dielectric film is formed on the surfaces of the lower electrode  27  and the interlayer insulating film  26 . The first TiN film  24  and the second TiN film  25  are formed on the dielectric film  28  according to the film-forming method in the foregoing embodiments. 
         [0072]    The foregoing embodiments and applications explained in the foregoing description may be appropriately combined, varied or modified for various purposes. The present invention is not limited to the foregoing embodiments. It is apparent from the recitation of the claims that such combination, variation and modification can be within the technical scope of the present invention.