Patent Publication Number: US-2005127036-A1

Title: Method of cleaning a reaction chamber

Description:
TECHNICAL FIELD  
      The present invention relates to manufacturing a semiconductor device, and more particularly, to a method of cleaning a phosphorus polymer in a reaction chamber using a cleaning gas in a plasma ion implantation apparatus.  
     DISCUSSION OF THE RELATED ART  
      In general, the processes used in manufacturing semiconductor devices are intricate and complex. Any mishandling during the processes directly affects product yield. Cleaning is one of the manufacturing processes. The cleaning process is typically divided into, directly cleaning wafers, and cleaning a reaction chamber. Wafer cleaning is performed during the manufacturing process, while the reaction chamber is cleaned periodically over a predetermined period.  
      The reaction chamber may be cleaned by stopping the manufacturing process, opening the reaction chamber, and performing a wet cleaning. U.S. Pat. Nos. 6,274,058, 5,254,176 and 5,647,953, disclose cleaning where reaction deposition materials or byproducts may be removed using a cleaning gas.  
      In a semiconductor device, a capacitor is composed of a lower electrode, a dielectric layer and an upper electrode. The lower electrode generally employs a storage polysilicon such as a doped silicon layer, a conductive metal layer, a metal oxide layer, a metal nitride layer or metal oxide nitride layer, and on the surface thereof, a hemisphere-type particle layer is formed to increase an effective surface area and overall capacitance of the capacitor. This hemisphere type particle layer may employ an HSG (Hemi-Spherical Grain) silicon layer.  
      In the hemisphere type storage polysilicon, an impurity ion such as phosphorus, is implanted to increase an impurity density in the lower electrode. When implanting phosphorus into the lower electrode a thermal PHA (Phosphorus anneal) and a plasma PHA are used. The thermal PHA employs a phosphine (PH 3 ) gas as a reactive gas that diffuses phosphorus ions inside the lower electrode. The plasma PHA applies plasma to a PH 3  gas to decompose the PH 3  gas, and directs the decomposed ions so that the phosphorus ions diffuse inside the lower electrode.  
      After the phosphorus is implanted into the lower electrode, an oxide layer is formed in the lower electrode and a nitride layer is formed on the oxide layer. Once the lower electrode is formed, a dielectric layer is formed, and on the dielectric layer an upper electrode is formed, thus forming a capacitor.  
      Here, the oxide layer of the lower electrode may be formed as a spontaneous oxide layer or formed continuously in the same reaction chamber immediately after the implantation of phosphorus. In particular, when forming the nitride layer it may be desirable to continue the process in situ (e.g., in the same reaction chamber) to maintain a vacuum state.  
      The reaction chamber, in which the implantation of phosphorus and the formation of the nitride layer are performed, is a plasma ion implantation chamber. The reaction chamber includes a source of PH 3  plasma for implanting phosphorus, and a source of anhydrous ammonia (NH 3 ) plasma for forming the nitride layer. The implantation of phosphorus and formation of the nitride layer is known as a Phosphorus Nitridation (PN) process.  
      When forming the capacitor, however, phosphorus that is not implanted in the wafer is deposited inside the reaction chamber. For example, the phosphorus implanted into the reaction chamber may be left in a tube, boat, boat cap or discharge pipe of the reaction chamber. As the number of PN processes increases, the amount of phosphorus in the reaction chamber increases. Thus, as the amount of phosphorus increases, portions thereof may become separated from parts of the reaction chamber and cause defects on wafers that undergo PN processes therein.  
      In order to remove phosphorus polymers inside the reaction chamber a wet cleaning is periodically performed. However, the wet cleaning is typically unsatisfactory and inefficient because phosphorus polymers remain in the chamber after cleaning, thus leading to the wet cleaning operations being performed periodically and often, which eventually lowers an operating ratio and productivity of an ion implantation apparatus.  
     SUMMARY OF THE INVENTION  
      A method of cleaning a reaction chamber is provided, in which a nitrogen triflouride (NF 3 ) cleaning gas is supplied into the reaction chamber over a predetermined period when executing a Phosphorus Nitridation (PN) process, thus removing a phosphorus polymer in the reaction chamber due to a chemical reaction between the phosphorus polymer and the cleaning gas.  
      An aspect of the present invention provides a method of cleaning a reaction chamber, which includes taking wafers out of the reaction chamber after completing a plasma ion implantation process; implanting an NF 3  gas into the reaction chamber; and vaporizing and discharging a phosphorus polymer from the reaction chamber using the NF 3  gas.  
      Another aspect of the present invention provides a method of cleaning a reaction chamber, which includes taking wafers out of the reaction chamber after completing a plasma ion implantation process; implanting the NF 3  gas into the reaction chamber; applying radio frequency (RF) power to the reaction chamber to form an NF 3  plasma; and vaporizing and discharging a phosphorus polymer from the reaction chamber using the NF 3  plasma. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Exemplary embodiments of the invention are described with reference to the accompanying drawings, of which:  
       FIG. 1  is a flowchart illustrating a cleaning process according to a first exemplary embodiment of the invention;  
       FIG. 2  is a flowchart illustrating a cleaning process according to a second exemplary embodiment of the invention; and  
       FIG. 3  is a graph indicating a removal rate of phosphorus according to an exemplary embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      According to the present invention, a phosphorus polymer generated as a byproduct during a Phosphorus Nitridation (PN) process in a plasma ion implantation apparatus can be removed by an in-situ dry cleaning using a nitrogen triflouride (NF 3 ) gas as a cleaning gas or NF 3  plasma for cleaning.  
      As will be described below with reference to table 1, the NF 3  gas is very effective for accomplishing a smooth reaction with a solid phosphorus polymer. For example, table 1 indicates a thermodynamic computation result (H) for the reaction of the NF 3  gas and solid phosphorus. In addition, the table indicates a result (G) for an enthalpy energy for a given temperature and a Gibbs free energy of a reversible reaction. The reaction between the NF 3  gas and phosphorus is represented as a negative value in the Gibbs free energy of the reversible reaction indicating that the reaction between two materials is generated spontaneously.  
                       TABLE 1                       Temperature (K)   H (KJ)   G (KJ)                                            298.1   −299   −468.2       300   −298.8   −469.2       400   −282.8   −528.4       500   −265   −592       600   −246.1   −659       700   −226.1   −729.3       800   −204.8   −802.6       855.3   −192.4   −844.3                  
 
      Table 2 (shown below) illustrates a thermodynamic computation result for main generation materials and a change of a mol number thereof for a reaction temperature between the NF 3  gas and a solid phosphorus.  
                                       TABLE 2                          Main                                             Generation   Reaction Temperature                                         Material   100° C.   200° C.   300° C.   400° C.   500° C.   600° C.               PF 3     0.666   0.666   0.666   0.666   0.666   0.666       N 2     0.333   0.333   0.333   0.333   0.333   0.333       PF 5     0.106e−04   0.113e−06   0.157e−06   0.385e−06   0.106e−05   0.24e−05       PN   0.253e−15   0.39e−09   0.3e−07   0.241e−06   0.675e−06   0.143e−05       PF 2     0.13e−18   0.399e−13   0.286e−10   0.209e−08   0.421e−07   0.419e−06                  
 
      As shown in table 2, the main generation materials in the reaction between the NF 3  gas and phosphorus are N 2  and PF 3  (both in a gas state). The reaction is indicated by the following formula [2NF 3 +2P →N 2 +2PF 3 ].  
      At this time, there is almost no change in the mol number of the main generation materials based on the reaction temperature, thus there is no correlation between the temperature of the reaction chamber and the reaction between the NF 3  gas and phosphorus. Thus, the NF 3  gas is suitable for the removal of phosphorus at low temperatures.  
      A method of cleaning a phosphorus polymer deposited within a reaction chamber in a plasma ion implantation apparatus according to the present invention is shown in  FIG. 1 .  
      To clean the reaction chamber, a plasma ion implantation process should be first completed or temporarily stopped (step  110 ). In other words, a predetermined number of PN processes should be arranged and the plasma ion implantation process should be stopped at a predetermined period.  
      The process stop indicates that wafers have stopped being loaded after removing wafers that have undergone a PN process from the reaction chamber. This procedure is performed in preparation of an in-situ cleaning, and once performed, an NF 3  gas is implanted into the reaction chamber (step  120 ).  
      When the NF 3  gas is implanted into the reaction chamber, the NF 3  gas reacts with a phosphorus polymer that was already deposited on several portions within the reaction chamber (step  130 ), and the phosphorus polymer is vaporized. Then, the vaporized phosphorus polymer is discharged through an exhaust line of the reaction chamber.  
      A flow amount of the NF 3  gas implanted into the reaction chamber to remove the phosphorus polymer is about 100 cc˜1000 cc. In addition, the temperature of the reaction chamber during the cleaning process does not influence the reaction between the NF 3  gas and phosphorus polymer and is about 100° C.˜700° C. Thus, the original PN process temperature may remain intact. An internal pressure of the reaction chamber may be about 10 torr˜20 torr so that the vaporized phosphorus polymer is discharged through an exhaust line of the reaction chamber. Further, it is desirable that the NF 3  gas and phosphorus polymer have a sufficient amount of time to react when in the reaction chamber.  
      According to the second exemplary embodiment of the invention as shown in  FIG. 2 , the plasma ion implantation process is temporarily stopped (step  210 ) and then the NF 3  gas is implanted into the reaction chamber (step  220 ).  
      In other words, a predetermined number of PN processes is arranged, and at a predetermined period a PN process is temporarily stopped. After which, a wafer that has already undergone the PN process is taken out of the reaction chamber, and the NF 3  gas is implanted into the reaction chamber prior to loading additional wafers.  
      As shown in  FIG. 2 , after the NF 3  gas is implanted, a radio frequency (RF) power is applied to the reaction chamber to generate an NF 3  plasma (step  230 ). The NF 3  plasma generated in the reaction chamber then vaporizes a phosphorus polymer and the vaporized phosphorus polymer is discharged through the exhaust line of the reaction chamber (step  240 ).  
      According to the second exemplary embodiment, a flow amount of the NF 3  gas implanted into the reaction chamber to remove the phosphorus polymer is about 100 cc˜1000 cc. The temperature of the reaction chamber during the cleaning process does not influence the reaction between the NF 3  gas and phosphorus polymer and is about 100° C.˜700° C. Thus, the original PN process temperature remains intact. An internal pressure of the reaction chamber may be about 10 torr˜20 torr so that the vaporized phosphorus polymer is easily discharged through the exhaust line of the reaction chamber.  
      The RF power applied to the reaction chamber is about 100 W˜500 W. Similar to that of the first exemplary embodiment, it is desirable that the NF 3  plasma and the phosphorus polymer have a sufficient amount of time to react in the reaction chamber. In the second exemplary embodiment of the invention, the NF 3  plasma can remove phosphorus polymers more effectively than NF 3  gas even at low reaction chamber temperatures.  
      As shown in  FIG. 3 , about 95% of all phosphorus polymers in a reaction chamber can be removed when the reaction chamber is cleaned for about 3 hours at 300° C. using NF 3  plasma. Thus, phosphorus polymer removal employing NF 3  plasma is more effective than using NF 3  gas.  
      The exemplary embodiments of the invention provide an in-situ cleaning by executing a dry cleaning instead of a wet cleaning. Thus, cleaning efficiency of the reaction chamber in an ion implantation apparatus is improved and the number of times a PN process must be stopped for cleaning is reduced. In addition, as the in-situ cleaning is performed under the same conditions as the PN process, the time for re-executing the PN process is reduced, and thus the efficiency of the PN process increases.  
      While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims.