Patent Publication Number: US-2012040085-A1

Title: METHOD FOR FORMING Cu FILM AND STORAGE MEDIUM

Description:
This application is a Continuation Application of PCT International Application No. PCT/JP2010/051122 filed on Jan. 28, 2010, which designated the United States. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a method for forming a Cu film by chemical vapor deposition (CVD) on a substrate such as a semiconductor substrate or the like, and a storage medium. 
     BACKGROUND OF THE INVENTION 
     Recently, along with the trend toward high speed of semiconductor devices and miniaturization of wiring patterns, Cu having higher conductivity and electromigration resistance than Al attracts attention as a material for wiring, a Cu plating seed layer, and a contact plug. 
     As for a method for forming a Cu film, physical vapor deposition (PVD) such as sputtering has been widely used. However, it is disadvantageous in that a step coverage becomes poor due to miniaturization of semiconductor devices. 
     Therefore, as for a method for forming a Cu film, there is used CVD for forming a Cu film on a substrate by a thermal decomposition reaction of a source gas containing Cu or by a reduction reaction of the source gas by a reducing gas. A Cu film formed by CVD (CVD-Cu film) has a high step coverage and a good film formation property for a thin, long and deep pattern. Thus, the Cu film has high conformability to a fine pattern and is suitable for formation of wiring, a Cu plating seed layer and a contact plug. 
     In the case of using a method for forming a Cu film by CVD, there is suggested a technique for using as a film-forming material (precursor) a Cu complex such as copper hexafluoroacetylacetonate trimethylvinylsilane (Cu(hfac)TMVS) or the like and thermally decomposing the Cu complex (see, e.g., Japanese Patent Application Publication No. 2000-282242). 
     Meanwhile, there is suggested a technique which uses, as a barrier metal or an adhesion layer of Cu, an Ru film (CVD-Ru film) formed by CVD (see Japanese Patent Application Publication No. H10-229084). The CVD-Ru film has a high step coverage and high adhesivity to a Cu film. Hence, it is suitable for the barrier metal or the adhesion layer of Cu. 
     However, when a Cu film is formed by CVD, heat needs to be supplied during the film formation. Therefore, migration of Cu on the surface of the Cu film is facilitated and an agglutination reaction occurs, which makes it difficult to obtain a smooth Cu film. Although Cu(hfac)TMVS as a conventionally used film-forming source material has a good thermal decomposition characteristics at a low temperature and a good film formation property at a relatively low temperature, it is not sufficient. In the case of using Cu(hfac)TMVS, Cu is produced by a thermal decomposition reaction accompanying a disproportionate reaction, so that it is theoretically difficult to further decrease a temperature. 
     Further, when a monovalent β-diketone complex such as the aforementioned Cu(hfac)TMVS is used as a film-forming source material, a by-product such as Cu(hfac) 2  having a low vapor pressure is produced during the film formation and adsorbed on the surface of the formed film. Hence, the adsorption of the Cu source material is hindered, and the initial nucleus density of Cu is decreased. Accordingly, the smoothness of the Cu film is decreased. 
     Thus, the CVD-Cu film is not suitable for the case of requiring high smoothness or the case of requiring an extremely thin Cu film. 
     SUMMARY OF THE INVENTION 
     In view of the above, the present invention provides a method for forming a Cu film which is capable of forming a smooth high-quality Cu film. 
     The present invention also provides a storage medium for storing a program for performing this film forming method. 
     The present inventors have performed examinations in order to obtain a Cu film having high smoothness. As a result, they have found that when a monovalent β-diketone complex as a Cu complex is used as a film-forming source material, the film formation can be performed at a lower temperature by decreasing activation energy of a Cu production reaction by adding a predetermined reducing agent and, also, the decrease in the initial nucleus density of Cu due to the adsorption hindrance of Cu can be prevented. The present invention has been conceived by the above conclusion. 
     In accordance with a first aspect of the present invention, there is provided a method for forming a Cu film, including loading a substrate in a processing chamber; 
     introducing into the processing chamber a monovalent Cu β-diketone complex and a reducing agent for reducing the monovalent Cu β-diketone complex in a vapor state; and forming a Cu film by reducing the monovalent Cu β-diketone complex by the reducing agent and depositing Cu on the substrate by CVD. 
     In accordance with a second aspect of the present invention, there is provided a computer readable storage medium storing a program for controlling a film forming apparatus. The program, when executed, controls the film forming apparatus to perform a method for forming a Cu film which includes: loading a substrate in a processing chamber; introducing into the processing chamber a monovalent Cu β-diketone complex and a reducing agent for reducing the monovalent Cu β-diketone complex in a vapor state; and forming a Cu film by reducing the monovalent Cu β-diketone complex by the reducing agent and depositing Cu on the substrate by CVD. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a substantial cross section of an exemplary configuration of a film forming apparatus for performing a method for forming a Cu film in accordance with an embodiment of the present invention. 
         FIG. 2  is a cross sectional view showing an exemplary structure of a semiconductor wafer as a substrate to which the method for forming a Cu film in accordance with the embodiment of the present invention is applied. 
         FIG. 3  is a timing diagram showing an example of a film forming sequence. 
         FIG. 4  is a timing diagram showing another example of the film forming sequence. 
         FIG. 5  is a timing diagram showing still another example of the film forming sequence. 
         FIG. 6  is a cross sectional view showing a state in which a CVD-Cu film is formed as a wiring material on the semiconductor wafer having the structure shown in  FIG. 2 . 
         FIG. 7  is a cross sectional view showing a state in which a CVD-Cu film is formed as a Cu plating seed layer on the semiconductor wafer having the structure shown in  FIG. 2 . 
         FIG. 8  is a cross sectional view showing a state in which CMP is performed on the semiconductor wafer having the structure shown in  FIG. 6 . 
         FIG. 9  is a cross sectional view showing a state in which Cu plating is performed on the semiconductor wafer having the structure shown in  FIG. 7 . 
         FIG. 10  is a cross sectional view showing a state in which CMP is performed on the semiconductor wafer having the structure shown in  FIG. 9 . 
         FIG. 11  is a cross sectional view showing another exemplary structure of the semiconductor wafer serving as the substrate to which the method for forming a Cu film in accordance with the embodiment of the present invention is applied. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, the embodiments of the present invention will be described with reference to the accompanying drawings which form a part hereof. 
     &lt;Configuration of Film Forming Apparatus for Performing Film Forming Method of the Present Invention&gt; 
       FIG. 1  is a substantial cross sectional view showing an exemplary configuration of a film forming apparatus for performing a method for forming a Cu film in accordance with an embodiment of the present invention. 
     A film forming apparatus  100  includes a substantially cylindrical airtight chamber  1  as a processing chamber, and a susceptor  2  provided in the chamber  1 . The susceptor  2  for horizontally supporting a semiconductor wafer W as a substrate to be processed is supported by a cylindrical supporting member  3  provided at the center of the bottom portion of the chamber  1 . The susceptor  2  is made of ceramic such as AlN or the like. 
     Further, a heater  5  is buried in the susceptor  2 , and a heater power supply  6  is connected to the heater  5 . Meanwhile, a thermocouple  7  is provided near the top surface of the susceptor  2 , and a signal from the thermocouple  7  is transmitted to a heater controller  8 . The heater controller is configured to transmit an instruction to the heater power supply  6  in accordance with the signal from the thermocouple  7  and control the wafer W to a predetermined temperature by controlling the heating of the heater  5 . 
     A circular opening  1   b  is formed at a ceiling wall  1   a  of the chamber  1 , and a shower head  10  is fitted in the circular opening  1   b  to protrude into the chamber  1 . The shower head  10  discharges a film forming gas supplied from a gas supply mechanism  30  to be described later into the chamber  1 . The shower head  10  has, at an upper portion thereof, a first inlet line  11  for introducing, as a film forming source material, a monovalent Cu ⊕-diketone complex, e.g., copper hexafluoroacetylacetonate trimethylvinylsilane (Cu(hfac)TMVS), and a second inlet line  12  for introducing a reducing agent into the chamber  1 . The first second inlet lines  11  and  12  are separately provided in the shower head  10 , and the film-forming gas and the reducing agent are mixed after being injected. 
     The inner space of the shower head  10  is separated into an upper space  13  and a lower space  14 . The first inlet line  11  is connected to the upper space  13 , and a first gas injection line  15  extends from the upper space  13  to the bottom surface of the shower head  10 . The second inlet line  12  is connected to the lower space  14 , and a second gas injection line  16  extends from the lower space  14  to the bottom surface of the shower head  10 . In other words, the shower head  10  is configured to separately inject a Cu complex gas as a film-forming source material and a reducing agent through the injection lines  15  and  16 , respectively. 
     A gas exhaust chamber  21  is provided at a bottom wall of the chamber  1  so as to protrude downward. A gas exhaust line  22  is connected to a side surface of a gas exhaust chamber  21 , and a gas exhaust unit  23  including a vacuum pump, a pressure control valve or the like is connected to the gas exhaust line  22 . By driving the gas exhaust unit  23 , the interior of the chamber  1  can be set to a predetermined depressurized state. 
     Formed on the sidewall of the chamber  1  are a loading/unloading port  25  for loading and unloading the wafer W with respect to a wafer transfer chamber (not shown) and a gate valve G for opening and closing the loading/unloading port  25 . Moreover, a heater  26  is provided on a wall of the chamber  1 , and can control the temperature of the inner wall of the chamber  1  during the film formation. 
     The gas supply mechanism  30  has a film-forming source material tank  31  for storing, as a film-forming source material, a monovalent Cu β-diketone complex in a liquid state, e.g., Cu(hfac)TMVS. As for the monovalent Cu β-diketone, it is possible to use Cu(hfac)MHY, Cu(hfac)ATMS, Cu(hfac)DMDVS, Cu(hfac)TMOVS, Cu(hfac)COD or the like. In the case of using a monovalent Cu β-diketone complex in a solid state at a room temperature, it can be stored in the film-forming source material tank  31  while being dissolved in a solvent. 
     pressurized feed gas line  32  for supplying a pressurized feed gas such as He gas or the like is inserted from above into the film forming source material tank  31 , and a valve  33  is installed in the pressurized feed gas line  32 . Further, a source material discharge line  34  is inserted from above into the film forming source material tank  31 , and a vaporizer (VU)  37  is connected to the other end of the source material discharge line  34 . A valve  35  and a liquid mass flow controller  36  are installed in the source material discharge line  34 . 
     By introducing a pressurized feed gas into the film-forming source material tank  31  via the pressurized feed gas line  32 , a Cu complex, e.g., Cu(hfac)TMVS, in the film-forming source material tank  31  is supplied in a liquid state to the vaporizer  37 . At this time, the liquid supply amount is controlled by the liquid mass flow controller  36 . A carrier gas line  38  for supplying Ar or H 2  gas as a carrier gas is connected to the vaporizer  37 . A mass flow controller  39  and two valves  40  positioned at both sides of the mass flow controller  39  are provided in the carrier gas line  38 . 
     Moreover, a film forming-material gas supply line  41  for supplying a Cu complex in a vapor state toward the shower head  10  is connected to the vaporizer  37 . A valve  42  is installed in the film-forming source material gas supply line  41 , and the other end of the film-forming source material gas supply line  41  is connected to the first inlet line  11  of the shower head  10 . Furthermore, the Cu complex vaporized by the vaporizer  37  is discharged to the film-forming source material gas supply line  41  while being carried by the carrier gas, and then is supplied into the shower head  10  from the first inlet line  11 . 
     A heater  43  for preventing condensation of the film-forming source material gas is provided at a region including the vaporizer  37 , the film-forming source material gas supply line  41 , and the valve  40  disposed at the downstream side of the carrier gas supply line. The heater  43  powered by a heater power supply (not shown), and the temperature of the heater  43  is controlled by a controller (not shown). 
     A reducing agent supply line  44  for supplying a reducing agent in a vapor state is connected to the second inlet line  12  of the shower head  10 . The reducing agent supply line  44  is connected to a reducing agent supply source  46 . Besides, a valve  45  is installed near the second inlet line  12  of the reducing agent supply line  44 . Moreover, a mass flow controller  47  and two valves  48  disposed at both sides of the mass flow controller  47  are installed in the reducing agent supply line  44 . In addition, a reducing agent for reducing the monovalent Cu β-diketone complex is supplied from the reducing agent supply source  46  into the chamber  1  through the reducing agent supply line  44 . 
     The film forming apparatus  100  includes a control unit  50  which is configured to control the respective components, e.g., the heater power supply  6 , the gas exhaust unit  23 , the mass flow controllers  36  and  39 , the valves  33 ,  35 ,  40 ,  42  and  45  and the like, and control the temperature of the susceptor  2  by using the heater controller  8 . The control unit  50  includes a process controller  51  having a micro processor (computer), a user interface  52 , and a storage unit  53 . The respective components of the film forming apparatus  100  are electrically connected to and controlled by the process controller  51 . 
     The user interface  52  is connected to the process controller  51 , and includes a keyboard through which an operator performs a command input to manage the respective units of the film forming apparatus  100 , a display for visually displaying the operational states of the respective components of the film forming apparatus  100 , and the like. 
     The storage unit  53  is also connected to the process controller  51 , and stores therein control programs to be used in realizing various processes performed by the film forming apparatus  100  under the control of the process controller  51 , control programs, i.e., processing recipes, to be used in operating the respective components of the film forming apparatus  100  to carry out a predetermined process under processing conditions, various database and the like. 
     The processing recipes are stored in a storage medium provided in the storage unit  53 . The storage medium may be a fixed medium such as a hard disk or the like, or a portable device such as a CD-ROM, a DVD, a flash memory or the like. Alternatively, the recipes may be suitably transmitted from other devices via, e.g., a dedicated transmission line. 
     If necessary, a predetermined processing recipe is read out from the storage unit  53  by the instruction via the user interface  52  and is executed by the process controller  51 . Accordingly, a desired process is performed in the film forming apparatus  100  under the control of the process controller  51 . 
     &lt;Method for Forming Cu Film in Accordance with the Embodiment of the Present Invention&gt; 
     Hereinafter, a method for forming a Cu film in accordance with the present embodiment by using a film forming apparatus configured as described above will be described. 
     Here, a case in which Cu(hfac) TMVS as a monovalent Cu β-diketone is used as a film-forming source material will be described as an example. 
     Further, a Cu film (CVD-Cu film) is formed by CVD on an Ru film (CVD-Ru film) formed by CVD. For example, as shown in  FIG. 2 , a CVD-Cu film is formed on a wafer W which is obtained by forming a lower Cu wiring layer  101  on a lower wiring insulating layer  103  with a CVD-Ru film  102  interposed therebetween, forming a cap insulating film  104 , an interlayer insulating layer  105  and a hard mask layer  106  thereon in that order, forming an upper wiring insulating layer  107  thereon, forming a via hole  108  that penetrates through the hard mask layer  106 , the interlayer insulating film  105  and the cap insulating film  104  to reach the lower Cu wiring layer  101 , forming a trench  109  as a wiring groove in the upper wiring insulating layer  107 , and forming a CVD-Ru film  110  as a barrier layer (diffusion prevention layer) on the inner wall of the via hole  108  and the trench  109  and the top surface of the upper wiring insulating layer  107 . 
     Preferably, the CVD-Ru film is formed by using Ru 3 (CO) 12  as a film-forming source material. Accordingly, a CVD-Ru film of high purity can be obtained, and a pure and robust interface of Cu and Ru can be formed. The CVD-Ru film can be formed by using an apparatus having the same configuration as that shown in  FIG. 1  except that vapor generated by heating Ru 3 (CO) 12  in a solid state at a room temperature is supplied. 
     In forming a Cu film, the gate valve G opens, and the wafer W having the above structure is loaded into the chamber  1  by a transfer device (not shown) and then mounted on the susceptor  2 . Next, the interior of the chamber  1  is exhausted by the gas exhaust unit  23 , and a pressure in the chamber  1  is set to about 1.33 to 266.6 Pa (about 10 mTorr to 2 Torr). The susceptor  2  is heated by the heater  5 , and a carrier gas is supplied at a flow rate of about 100 to 1500 mL/min(sccm) via the carrier gas line  38 , the vaporizer  37 , the film-forming source material gas supply line  41 , and the shower head  10  to obtain stable processing conditions. 
     When the processing conditions are stabilized, Cu(hfac)TMVS in a liquid state is vaporized at about 50 to 70° C. by the vaporizer  37  and then is introduced into the chamber  10 , while the carrier gas is supplied. Further, a reducing agent in a vapor state is introduced from the reducing agent supply source  46  into the chamber  1 . Thereafter, the Cu film formation onto the wafer W is started. 
     As for the reducing agent, one capable of reducing a monovalent Cu β-diketone complex as a film-forming source material is used. Preferably, it is possible to use NH 3 , a reductive Si compound, carboxylic acid. As for the reductive Si compound, it is preferable to use a diethylsilane-based compound, e.g., diethylsilane, diethyldichlorosilane or the like. As for the carboxylic acid, it is possible to use a formic acid (HCOOH), an acetic acid (CH 3 COOH), a propionic acid (CH 3 CH 2 COOH), a butyric acid (CH 3 (CH 2 ) 2 COOH), a valeric acid (CH 3 (CH 2 ) 3 COOH) or the like. Preferably, HCOOH can be used. 
     When a Cu film is formed, Cu(hfac)TMVS is supplied in a liquid state at a flow rate of about 100 to 500 mg/min. Although the flow rate of the reducing agent is varied depending on types of reducing agents, is about 0.1 to 100 mL/min(sccm). 
     Cu(hfac)TMVS as a film-forming source material is decomposed on the wafer W as a target substrate heated by the heater  5  of the susceptor  2  by the disproportionate reaction described in the following Eq. (1). As a result, Cu is produced. 
       2Cu(hfac)TMVS→Cu+Cu(hfac) 2 +2TMVS   Eq. (1)
 
     Among the monovalent Cu β-diketone complexes, Cu(hfac)TMVS has a lowest thermal decomposition temperature. However, in order to proceed the reaction of the above Eq. (1), Cu(hfac)TMVS needs to be heated at a relatively high temperature of about 150 to 200° C. Therefore, migration of Cu on the surface of the Cu film is facilitated during film formation and an agglutination reaction occurs, which makes it difficult to obtain a smooth Cu film. 
     Moreover, Cu(hfac)TMVS as a monovalent Cu β-diketone complex produces, as a by-product, Cu(hfac) 2  having a low vapor pressure during the film formation. The by-product thus produced is adsorbed on the surface of the formed film. Thus, the adsorption of Cu(hfac)TMVS is hindered, and the initial nucleus density of Cu is decreased. Accordingly, the smoothness of the Cu film is deteriorated. 
     In the present embodiment, Cu is produced by reducing Cu(hfac)TMVS as a monovalent Cu β-diketone complex by a reducing agent, and the thus-produced Cu is deposited on the wafer W. 
     The activation energy of the reduction reaction by the reducing agent is lower than that of the reaction of the above Eq. (1), so that the reduction reaction proceeds at a temperature lower than that of the thermal decomposition reaction of the above Eq. (1). Hence, the film formation temperature can be decreased to about 130° C. 
     The reducing agent is easily adsorbed on the base compared to Cu(hfac) 2  as a by-product. When Cu(hfac)TMVS is supplied to the site where the reducing agent is adsorbed, the reduction occurs, which results in production and adsorption of Cu. Accordingly, the initial nucleus density of Cu can be increased. 
     Due to the effect of decreasing the film formation temperature and the effect of increasing the initial nucleus density of Cu, a smooth high-quality Cu film can be obtained. 
     As shown in  FIG. 3 , the film forming sequence includes the simultaneously supply of Cu(hfac)TMVS and the reducing agent. In the example of  FIG. 3 , the flow rate of the reducing agent is the same from the start of the film formation to the end thereof. However, as shown in  FIG. 4 , the reducing agent may be supplied at a first flow rate during the initial stage of the film formation and then may be supplied at a second flow rate lower than the first flow rate or may not be supplied (flow rate of zero). Although this reduces the effect of decreasing the film formation temperature, the absorption of the reducing agent into the film can be prevented, and the quality of the Cu film can be further increased. 
     In the film forming sequence, there may be used so-called ALD (Atomic Layer Deposition) in which Cu(hfac)TMVS and the reducing agent are supplied alternately with a purge process interposed therebetween as shown in  FIG. 5 . The purge process can be performed by supplying a carrier gas. The film formation temperature can be further decreased by ALD. 
     After the Cu film is formed in the above-described manner, the purge process is performed. In the purge process, the interior of the chamber  1  is purged by supplying a carrier gas as a purge gas into the chamber  1  while stopping the supply of Cu(hfac)TMVS and setting the vacuum pump of the gas exhaust unit  23  to a pull-end state. In this case, it is preferable to intermittently supply the carrier gas in order to rapidly purge the interior of the chamber  1 . 
     Upon completion of the purge process, the gate valve G opens, and the wafer W is unloaded via the loading/unloading port  25  by a transfer device (not shown). Accordingly, a series of processes for a single wafer W is completed. 
     The CVD-Cu film thus formed can be used as a wiring material or a Cu plating seed layer. When the CVD-Cu film is used as a wiring material, the CVD-Cu film  111  is formed until the via hole  108  and the trench  109  are covered as shown in  FIG. 5 . Thus, a wiring and a plug are formed of the CVD-Ru film  111 . When the CVD-Cu film is used as a Cu plating seed layer, the CVD-Cu film  111  is thinly formed thinly on the surface of the CVD-Ru film  110  and the exposed surface of the Cu wiring layer  101  as shown in  FIG. 7 . 
     When the wiring and the plug are formed of the CVD-Cu film  111  as shown in  FIG. 6 , excessive Cu is removed by performing CMP (chemical mechanical polishing) such that the wiring insulating film  107  and the CVD-Cu film  111  are positioned on the same plane as shown in  FIG. 8 . When the CVD-Cu film  111  is thinly formed as a Cu plating seed layer as shown in  FIG. 7 , the wiring and the plug are formed of a Cu plating layer  112  as shown in  FIG. 9 . Then, excessive Cu is removed by performing CMP such that the wiring insulating film  107  and the Cu plating layer  112  are positioned on the same plane as shown in  FIG. 10 . 
     In the above example, a single layer of the CVD-Ru film  110  is used as a barrier layer (diffusion prevention layer). However, as shown in  FIG. 11 , a laminated structure of the CVD-Ru film  110  as an upper layer and a high-melting point material film  113  as a lower layer may be used. In this case, one of Ta, TaN, Ti, W, TiN, WN, manganese oxide and the like can be used for the lower layer. 
     In accordance with the present embodiment, a Cu film is formed on the wafer W as a target substrate by CVD by introducing a monovalent Cu P-diketone complex and a reducing agent for reducing the monovalent Cu β-diketone complex in a vapor state into the chamber  1  as a processing chamber. Therefore, the film formation can be performed at a low temperature while decreasing the activation energy of the film formation reaction. Moreover, the reducing agent is adsorbed on the base in the initial stage of the film formation, so that the initial nucleus density of Cu can be increased. Accordingly, a Cu film having high smoothness can be obtained. 
     &lt;Another Embodiment of the Present Invention&gt; 
     The present invention can be variously modified without being limited to the above embodiment. For example, although the case in which Cu(hfac)TMVS is used as a Cu complex having a vapor pressure higher than that of a by-product produced by thermal decomposition has been described in the above embodiment, it is not limited thereto. As described above, another monovalent Cu β-diketone complex such as Cu(hfac)MHY, Cu(hfac)ATMS, Cu(hfac)DMDVS, Cu(hfac)TMOVS, Cu(hfac)COD or the like can be used. Besides, the reducing agent is not limited to the above-described one. Further, although the case in which a CVD-Ru film is used as a base film has been described, it is not limited thereto. 
     In the above embodiment, a Cu complex in a liquid state is force-fed to a vaporizer and then is vaporized therein. However, it may be vaporized in a different manner, e.g., bubbling or the like, other than the above-described manner. 
     Further, the film forming apparatus is not limited to that of the above embodiment, and there can be used various apparatuses such as one including a mechanism for forming a plasma to facilitate decomposition of a film-forming source material gas and the like. 
     The structure of the target substrate is not limited to those shown in  FIGS. 2 and 10 . Although the case in which a semiconductor wafer is used as a substrate to be processed has been described, another substrate such as a flat panel display (FPD) substrate or the like may also be used without being limited thereto. 
     While the invention has been shown and described with respect to the embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.