Patent Publication Number: US-2002000199-A1

Title: Film forming apparatus and method for producing tungsten nitride film

Description:
FIELD OF THE INVENTION  
       [0001] This invention relates to the technical field of forming metal nitrides. More particularly, it provides a technique adequate for forming tungsten nitride films.  
       BACKGROUND OF THE INVENTION  
       [0002] In recent years, aluminum has been replaced by copper as the material mainly employed in metal interconnecting films for semiconductor devices. In the case of aluminum films, titanium nitride films are formed as barrier films at the interface between the aluminum films and silicon substrates. However, these titanium nitride films are poor in the ability to prevent the diffusion of copper. Thus, W x N films (tungsten nitride films) have attracted attention as barrier films against copper films.  
       [0003] It has been a practice to produce W x N films at a high temperature (i.e., 500° C. or above) under high pressure (i.e., film-forming pressure: several thousand Pa) . However, a large-scaled apparatus should be employed to sustain such a high pressure and, moreover, troublesome operations are needed for the maintenance thereof. In a pretreatment apparatus for forming W x N films and a film forming apparatus for forming copper film on the W x N films, substrates should be treated in vacuum. Thus, there arises an additional problem that these apparatuses are poor in the connection properties with a W x N film forming apparatus and thus the substrates cannot be treated continuously.  
       [0004] Accordingly, it has been required to develop a film forming apparatus by which W x N films can be produced in vacuum (under reduced pressure). In FIG. 5( a ), a substrate  120 , on which a W x N film and a copper film are to be formed, consists of a silicon substrate  150 , a silicon oxide film  152  formed on the silicon substrate  150  and a pore  160  formed in the silicon oxide film  152 .  
       [0005] When a W x N film is to be formed on the substrate  120  by using a CVD apparatus  102  of the prior art as shown in FIG. 6, a reactor  111  is first evacuated. Then the substrate  120  is carried thereinto and placed on a holder  114  provided in the bottom side of the reactor  111 .  
       [0006] A shower nozzle  112  is provided in the ceiling side of the reactor  111 . After heating the substrate  120  to a prescribed temperature with a heater contained in the holder  114 , two types of feedstock gases (for example, WF 6  gas and NH 3  gas) are jetted from the shower nozzle  112  toward the substrate  120  as shown by arrows  151 , thereby inducing the following chemical reaction:  
       4WF 6 +8NH 3 b →2 W 2 N+24HF+3N 2 .  
       [0007] Thus, a W x N film  153  is formed on the surface of the substrate  120  as shown in FIG. 5( b ), wherein X is referred tentatively as to 2.  
       [0008] When a prescribed thickness of the W x N film is achieved, the substrate  120  is taken out from the reactor  111 . Then a copper film  154  is formed on the W x N film  153  as shown in FIG. 5( c ) and followed by the transportation to the subsequent stage, i.e., the patterning of the copper film  154 , etc.  
       [0009] When the W x N film  153  and the copper film  154  are formed in vacuum as described above, the substrate  120  can be continuously treated without exposing to the atmosphere by connecting a apparatus for forming a tungsten film and a apparatus for forming a copper film to a multi-chamber type apparatus.  
       [0010] However, a CVD apparatus of the prior art as described above suffers from the problem of serious dusting. This is because the reaction between WF 6  and NH 3  proceeds even at room temperature and not W x N but WF 6 .4NH 3  etc. are formed at room temperature, different from the above reaction formula, and adhere to the inner wall of the reactor  111 .  
       [0011] When the wall of the reactor  111  is heated to a temperature close to the temperature of the substrate  120 , at least the formation of WF 6 .4NH 3  can be prevented. In this case, however, W x N is deposited on the inner wall of the reactor  111  on the contrary and causes dusting.  
       [0012] In addition, the above-described reactor  111  of the prior art suffers from another problem of a low growth speed of the W x N film. Thus, it has been required to clarify the cause of this phenomenon and to establish a countermeasure effective therefor.  
       SUMMARY OF THE INVENTION  
       [0013] The present invention, which has been made to overcome the above-described problems encountering in the prior art, aims at providing a technique for forming a tungsten nitride film without causing dusting, and a technique for forming a tungsten nitride film showing a high growth speed.  
       [0014] To achieve these objects, the present invention relates to a film forming apparatus providedwith an evacuatable reactor, an adhesion preventive container placed in said reactor, a holder whereby a object on which the film is to be formed is located in said adhesion preventive container, a first gas inlet equipment which faces to said holder and constructed so that it can jet a gas into said adhesion preventive container, and a second gas inlet equipment which is constructed so that it can jet a gas between said first gas inlet equipment and said holder.  
       [0015] The present invention relates to the film forming apparatus, which is constructed so that, in said adhesion preventive container, at least the part around said material on which the film is to be formed is maintained at a temperature of 150 to 300° C.  
       [0016] The present invention relates to the film forming apparatus wherein said first gas inlet equipment has a shower nozzle provided with a number of gas jet orifices formed on the almost same plane.  
       [0017] The invention relates to the film forming apparatus wherein said second gas inlet equipment has a nozzle made of a hollow pipe shaped into a ring and a number of gas jet orifices are formed in said hollow pipe.  
       [0018] The present invention relates to a method for producing a tungsten film which comprises jetting a first feedstock gas having a nitrogen atom in its chemical structure and a second feedstock gas having a tungsten atom in its chemical structure into a reactor and reacting said first feedstock gas with said second feedstock gas so as to form a tungsten nitride film on the surface of a material on which the film is to be formed, wherein the distance between the position from which said first feedstock gas is jetted and the surface of said material on which the film is to be formed is different from the distance between the position from which said second feedstock gas is jetted and the surface of said material on which the film is to be formed.  
       [0019] The present invention relates to the method for producing a tungsten film which comprises providing an adhesion preventive container in said reactor and placing said object on which a film is to be formed in the adhesion preventive container; heating, in said adhesion preventive container, at least the part around said material on which the film is to be formed to a temperature of 150 to 250° C.; and jetting said first feedstock gas and second feedstock gas into said adhesion preventive container.  
       [0020] The present invention relates to the method for producing a tungsten film, wherein one of said first feedstock gas and second feedstock gas is jetted downward in the vertical direction toward the surface of said object on which a film is to be formed.  
       [0021] The present invention relates to the method for producing a tungsten film, wherein, between said first feedstock gas and second feedstock gas, the one gas jetted from the lower position is jetted sideways toward center of said object on which a film is to be formed.  
       [0022] Many other features, advantages and additional objects of the present invention will become manifest to those versed in the art upon making reference to the detailed description which follows and the accompanying sheet of drawings. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0023]FIG. 1 is a drawing which shows an example of the film forming apparatus according to the present invention.  
     [0024]FIG. 2 is a drawing which illustrates the adhesion preventive container of the film forming apparatus.  
     [0025]FIG. 3( a ) is a perspective view of the nozzle shaped into a ring; FIG. 3( b ) is an enlarged partial view thereof; and FIG.  3 ( c ) is a perspective view of a nozzle in another shape.  
     [0026]FIG. 4( a ) is a plan view of an example of the shower nozzle of the present invention; and FIG. 4( b ) is aplan view of a shower nozzle of the prior art.  
     [0027]FIG. 5( a )-( c ) are drawings which show the steps of forming a tungsten nitride film and a copper film.  
     [0028]FIG. 6 is a drawing which shows a apparatus for forming a tungsten nitride film of the prior art. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0029] The film forming apparatus according to the present invention, which has the constitution as described above, has an adhesion preventive container placed in the reactor. In this adhesion preventive container, a holder is provided so that a object on which a film is to be formed (i.e., the substrate) can be hold in the adhesion preventive container.  
     [0030] This film forming apparatus is provided with a first gas inlet equipment and a second gas inlet equipment through which feedstock gases are respectively jetted into the adhesion preventive container. The second gas inlet equipment is located at such a position that it can jet the gas between the jetting position of the first gas inlet equipment and the holder.  
     [0031] By locating the gas jetting positions of the first and second gas inlet equipment at different heights on the surface of the object on which a film is to be formed and jetting the feedstock gases into the adhesion preventive container, the first and second feedstock gases respectively jetted from the gas inlet equipment can attain the surface of the object on which a film is to be formed located on the holder without mixing with each other even under a pressure within the viscous flow region (i.e., 1.0 to 100 Pa).  
     [0032] When the first feedstock gas having a nitrogen atom in its chemical structure and the second feedstock gas having a tungsten atom in its chemical structure are supplied respectively from the first gas inlet equipment and the second gas inlet equipment, therefore, these gases react with each other not in the space but on the surface of the object on which a film is to be formed and thus a tungsten nitride film can be efficiently formed.  
     [0033] A tungsten film having a good film thickness distribution can be formed on the surface of the object on which a film is to be formed by providing the first gas inlet equipment with a shower nozzle and thus jetting downward the feedstock gas toward the object on which a film is to be formed. FIG. 4( a )  71  shows the surface of the shower nozzle. On this shower nozzle which has a number of jet orifices  72 , the same feedstock gas is jetted.  
     [0034] In the shower nozzle  171  of the prior art shown in FIG. 4( b ), two types of gas jet orifices  173  and  174  are formed. From one type  173  of these orifices, a feedstock gas containing nitrogen atom is jetted, while another feedstock gas containing tungsten atom is jetted from the remainders  174 . In this case, these gases are mixed together and react with each other before attaining the surface of the object on which a film is to be formed, which supposedly results in the low film formation (deposition) rate achieved by the prior art.  
     [0035] In the present invention, a nozzle shaped into a ring is further provided in the second gas inlet equipment. This nozzle has a number of gas jet orifices from which a gas is jetted toward the center of the ring, optionally somewhat shifting toward the object on which a film is to be formed. Thus, the feedstock gas supplied from the second gas inlet equipment can uniformly attain the surface of the object on which a film is to be formed.  
     [0036] In this case, the feedstock gas supplied from the first gas inlet equipment attains the surface of the object on which a film is to be formed via the center of the ring of the nozzle. Therefore, the gases supplied respectively from the first and second gas inlet equipment can attain the surface of the object on which a film is to be formed, without being mixed together and thus the reaction can efficiently proceed on the surface of the object on which a film is to be formed.  
     [0037] When a feedstock gas containing nitrogen in its chemical structure (for example, NH 3  gas) and another feedstock gas containing tungsten in its chemical structure (for example, WF 6  gas) are separately introduced into the adhesion preventive container in particular under a pressure of from 1.0 to 100 Pa, WF 6 .4NH 3  is formed at a temperature less than 150° C. while a W x N (i.e., a tungsten nitride film) is formed at a temperature exceeding 300° C.  
     [0038] In the present invention, the adhesion preventive container is maintained at a temperature of from 150 to 250 ° C. (preferably around 200° C.). As a result, neither WF 6 .4NH 3  nor W x N is formed on the surface of the adhesion preventive container, thereby causing no dusting.  
     [0039] These and other objects of the invention will become more apparent in the detailed description and examples which follow.  
     [0040] Now, the present invention will be described by reference to the attached drawings.  
     [0041] In FIG. 1, sign  2  shows an example of the film forming apparatus according to the present invention which has a reactor  11 . A cavity adhesion preventive container  8  is placed in this reactor  11 .  
     [0042] As FIG. 2 shows, this adhesion preventive container  8  is provided with a bottom plate  31 , a rectifier plate  32  and a top plate  33 , each in a circular shape, and a cylindrical wall plate  30 .  
     [0043] Circular holes  36  to  38  are formed at the center of the bottom plate  31 , the rectifier plate  32  and the top plate  33  respectively.  
     [0044] The bottom plate  30  is located at the bottom of the wall plate  30 , while the rectifier plate  32  is located above the bottom plate  31  and surrounded by the wall plate  30 . The top plate  33  is located at the opening of the wall plate  30  above the rectifier plate  32 .  
     [0045] The bottom plate  31 , the rectifier plate  32  and the top plate  33  are arranged in parallel at definite intervals and each fixed to the wall plate  30 .  
     [0046] The holes  36  to  38  formed respectively on the bottomplate  31 , the rectifier plate  32  and the top plate  33  are each arranged in such a manner that the center thereof is located on the center axis of the wall plate  30 .  
     [0047] The adhesion preventive container  8  having the above-described constitution is placed as such on the bottom of the reactor  11 .  
     [0048] The reactor  11  is provided with a holder  14  on the bottom thereof and the adhesion preventive container  8  is placed so that the holder  14  is located in the hole  36  of the bottom plate  31  and the hole  37  of the rectifier plate  32 . The surface of the holder  14  is located between the rectifier plate  31  and the top plate  33 .  
     [0049] A first gas source  45  and a second gas source  46 , each consisting of a gas cylinder, a mass flow controller, valves, pipes, etc., are provided outside the reactor  11 .  
     [0050] In FIG. 1, 61 1  to  61   4  are mass flow controller, and  62   1  to  62   1  are valves.  
     [0051] The first gas source  45  is connected to a shower nozzle  12  as a first gas inlet equipment. A first gas inlet system consists of this first gas source  45  and the shower nozzle  12  which is a first gas inlet equipment.  
     [0052] The shower nozzle  12  has a cavity structure and a number of orifices are formed on the bottom  18  thereof. Thus, a gas is supplied from the first gas source  45  into the cavity part of shower nozzle  12  is jetted from the orifices on the bottom.  
     [0053] The shower nozzle  12  is located above the hole  38  of the top plate  33  and attached to the top part of the reactor  11  so that the bottom  18  of the shower nozzle  12  faces to the surface of the holder  14 .  
     [0054] The hole  38  of the top plate  33  is larger than the bottom  18  of the shower nozzle  12 . The bottom  18  of the shower nozzle  12  is located almost at the same height as the top plate  33  but the bottom  18  is located lower than the hole  38  of the top plate  33 .  
     [0055] Due to this construction, the gas jetted form the shower nozzle  12  is introduced directly into the adhesion preventive container  8  and blown to the surface of the holder  14 .  
     [0056] The second gas source  46  is connected to a gas jet member  4  as a second gas inlet equipment. A second gas inlet system  42  consists of the second gas source  46  and the gas jet member  4  which is a second gas inlet equipment.  
     [0057] This gas jet member  4 , which is roughly shaped into a ring, is arranged between the holder  14  and the shower nozzle  12  in the adhesion preventive container  8  in parallel to the surface of the holder  14 . Namely, the gas jet member  4  is located between the rectifier plate  32  and the top plate  33  and in parallel to the rectifier plate  32  and the top plate  33 .  
     [0058]FIG. 3( a ) is a perspective view of the gas jet member  4 .  
     [0059] This gas jet member  4  consists of a ring nozzle  21 , a support  22  supporting this nozzle  21 , and a pipe  23  with which the support  22  is connected to the gas inlet system  42  which is located outside of the reactor  11 .  
     [0060] The nozzle  21 , the support  22  and the pipe  23  are each made up of a hollow pipe. When a gas is introduced from the second gas source  46  into the gas jet member  4 , the gas passes through the pipe  23  and the support  22  and attains the nozzle  21 .  
     [0061] The gas nozzle  21  shaped into a ring is provided a number of holes  25  on the inner face. FIG. 3( b ) is an enlarged view of the holes  25 . These holes  25  are arranged on somewhat lower part of the surface of the ring gas nozzle  21  at almost constant intervals so that the gas flown into the nozzle  21  is regularly discharged from these holes  25  somewhat downward toward the center.  
     [0062] Next, a method for forming a tungsten film by using the above-described film forming apparatus  2  will be illustrated.  
     [0063] In this case, the first gas source  45  is provided with a gas cylinder containing the first feedstock gas comprising a nitrogen atom in its chemical structure (NH s  in this case), while the second gas source  46  is provided with another gas cylinder containing the second feedstock gas comprising a tungsten atom in its chemical structure (WF 6  in this case), thus allowing the introduction of these gases respectively from the first and second gas inlet systems  41  and  42  into the reactor  11 .  
     [0064] First, the reactor  11  is evacuated into vacuum atmosphere with the evacuation system  48  connected to the reactor  11 . The substrate holder  17  is comprised operable to lift up and down. Then the substrate  20  is carried into the reactor  11  while lifting up the substrate holder  17  and placed on the holder  14 . This substrate  20  is arranged in parallel to the bottom  18  of the shower nozzle  12 . Next, the substrate holder  17  is taken down and the substrate  20  is adhered to the holder  14  followed by heating by switching on the heater  15 .  
     [0065] When another inner heater provided within the adhesion preventive container  8  is also switched on, the adhesion preventive container  8  is heated with the inner heater as well as the heat radiated from the holder  14 . In this step, the electricity supplied to the inner heater is controlled so as to maintain the temperature of the adhesion preventive container  8  to 200° C.  
     [0066] When temperature of the substrate  20  is elevated and attains to 300° C. or higher, the gas sources  45  and  46  are manipulated so that the first feedstock gas (NH 3 ) is jetted from the shower nozzle  12  toward the substrate  20  and, at the same time, the second feedstock gas (WF 6 ) is jetted from the nozzle  21  of the gas jet member  4 . Thus, the first and second feedstock gases (i.e., the NH 3  and WF 6  gases) are blown onto the substrate  20 .  
     [0067] In this case, two different feedstock gases (i.e., the NH 3  and WF 6  gases) are separately jetted respectively from the shower nozzle  12  and the gas jet member  4 , as described above. By controlling the supply rates of the gases by manipulating the first gas source  41  and second gas source  42 , the pressure in the adhesion preventive container  8  can be maintained within the viscous flow region (i.e., 1.0 to 100 Pa) and the first feedstock gas and the second feedstock gas can separately attain the surface of the substrate  20  without being mixed together. As a result, the reaction of forming thin W x N proceeds on the surface of the substrate  20  and thus a thin W x N film is obtained.  
     [0068] When the thin W x N film having a prescribed film thickness is formed, the substrate  20  is taken out from the reactor  11  and transported into a copper film forming apparatus. At the same time, another untreated substrate is carried into the reactor  11  and subjected to the formation of a thin W x N film. Thus, thin W x N films can be continuously formed.  
     [0069] In the above-described film forming apparatus  2 , the adhesion preventive container  8  is filled up with the first feedstock gas and the second feedstock gas different from each other (i.e., the NH 3  and WF 6  gases), which protects the inner wall of the reactor  11  from the deposition of WF 6 .4NH 3  or W x N thereon. Thus, no dust evolves from the reactor  11  and a defect-free W x N film can be produced.  
     [0070] Since the temperature of the adhesion preventive container  8  is controlled within a range of from 200 to 300° C., neither WF 6 .4NH 3 , which is liable to be formed at lower temperatures, nor W x N, which is liable to be formed at higher temperatures, is formed. Thus, W x N can be formed in dust-free environment. Because of being removable, moreover, the adhesion preventive container  8  can be easily cleaned.  
     [0071] As described above, by using the thin film forming apparatus  2  according to the present invention, different feedstock gases are not mixed together but can separately attain a substrate and the reaction efficiently proceeds on the substrate surface. Thus, a thin film made of the reaction product (for example, a W x N film) can grow quickly without causing dusting and a W x N film with excellent qualities can be formed.  
     [0072] Although a number of holes  25  are formed in the inner side of the gas jet member  4  in the above case, other constitutions may be employed therefor so long as the feedstock gas can uniformly jetted from two ormore positions toward the substrate  20 . For example, it is alsopossible that a tip  24  of the support  22  is bent toward the central axis of the substrate located below and the feedstock gas is jetted from the hole  26  formed on the tip  24 , as FIG. 3( c ) shows.  
     [0073] Although W x N is formed in vacuum (under reduced pressure) of 1.0 to 100 Pa in the above example, it can be formed under higher pressure, i.e., atmospheric pressure or more.  
     [0074] By using the present invention, different feedstock gases are not mixed together but can separately attain the surface of a object on which a film is to be formed. Thus, the film-formation speed can be elevated and a uniform film thickness can be obtained.  
     [0075] Also, no reaction occurs on the surface of the adhesion preventive container and thus no dusting arises. In addition, the feedstock gases are not consumed on the surface of the adhesion preventive container. Therefore, the reaction can efficiently proceed on the surface of the object on which a film is to be formed and no dust adheres to the surface of the adhesion preventive container.