Abstract:
An etching method includes a modification process of supplying a mixture gas to a surface of a silicon oxide film, modifying the silicon oxide film to generate a reaction product, and a heating process of heating and removing the reaction product. The modification process includes a first modification process of supplying the mixture gas containing a gas including a halogen element and an alkaline gas to the surface of the silicon oxide film, and a second modification process of stopping supplying the alkaline gas and supplying the mixture gas containing the gas including the halogen element to the surface of the silicon oxide film.

Description:
TECHNICAL FIELD 
     The present disclosure relates to an etching method and a recording medium. 
     BACKGROUND 
     In a semiconductor device manufacturing process, a method has been known, which dry-etches a silicon oxide film existing in a surface of a semiconductor wafer (hereinafter referred to as “wafer”) without using plasma. Such a dry-etching method includes: a modification process in which a reaction product is generated by supplying a mixture gas including a hydrogen fluoride gas (HF) and an ammonia gas (NH 3 ) into a chamber in which the wafer is received while controlling an interior of the chamber to have a low pressure close to a vacuum state and adjusting a temperature of the wafer to a predetermined temperature, thereby modifying the silicon oxide film; and a heating process in which the reaction product is heated so as to be vaporized (sublimated). The dry-etching method etches the silicon oxide film by modifying the surface of the silicon oxide film to the reaction product and removing the reaction product by heating (see Patent Documents 1 and 2). 
     The etching process described above is applied to, for example, a process for etching a sacrificial oxide film of a wafer W having a structure shown in  FIG. 1 . As shown in  FIG. 1 , in the wafer W, a HDP-SiO 2  film  101 , which is an interlayer insulating film, is formed on a surface of a Si layer  100 . In a surface of the HDP-SiO 2  film  101 , a resist film  102  is formed. Moreover, in the HDP-SiO 2  film  101 , a groove H (e.g., a contact hole) is formed, and a sacrificial oxide film  103  is formed in a lower portion of the groove H. Further, a SiN film  104 , which is an insulator, is formed in a side wall portion of the groove H. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     Patent Document 1: Japanese Patent Application Publication No. 2007-180418 
     Patent Document 2: Japanese Patent Application Publication No. 2009-94307 
     However, if etching of the sacrificial oxide film  103  in the lower portion of the groove of the wafer W is performed, in the conventional dry-etching method including the etching method described in Patent Documents 1 and 2, a reaction between the sacrificial oxide film  103  and the mixture gas in the modification process becomes slow along with a processing time, and a modification amount of the sacrificial oxide film  103  with respect to the processing time goes to a saturation state. 
     This phenomenon is caused by a reaction product (ammonium fluorosilicate) generated by a reaction between the ammonia gas in the mixture gas and the sacrificial oxide film  103 . The reaction product  105  is formed to become thicker in proportion to a modification processing time of the sacrificial oxide film  103  in the modification process. When the mixture gas passes through the reaction product formed to be thick in that manner, a passing speed of the mixture gas is lowered, so that it becomes difficult for the mixture gas to reach the sacrificial oxide film  103  in the lower portion of the groove. For these reason, it becomes difficult to modify the sacrificial oxide film  103  in the lower portion of the groove , so that, while the reaction product  105  is sublimated in the subsequent heating process, the unmodified sacrificial oxide film  103  remains. 
     Moreover, as shown in  FIG. 2 , in the conventional etching method, the sacrificial oxide film  103  tends to be more modified in a peripheral portion of the lower portion of the groove than a central portion of the lower portion of the groove. For these reason, if the modification process is ended at a timing when, for example, the sacrificial oxide film  103  in the central portion of the lower portion of the groove is completely removed, the sacrificial oxide film  103  remains in the peripheral portion of the lower portion of the groove. 
     If the sacrificial oxide film  103  cannot be removed sufficiently in the etching process, a film thickness of a gate oxide film to be formed in a subsequent process is reduced by a thickness of the remaining sacrificial oxide film  103 . As a result, an effective channel length is shortened, so that performance as a semiconductor deteriorates. In order to avoid such a situation, the sacrificial oxide film  103  in the lower portion of the groove needs to be removed uniformly and sufficiently in the etching process of the sacrificial oxide film  103 . In other words, the sacrificial oxide film  103  in the lower portion of the groove needs to be modified uniformly and sufficiently in the modification process of the etching process. 
     As described above, although the modification reaction between the sacrificial oxide film  103  and the mixture gas becomes slow as the modification processing time passes, all of the sacrificial oxide film  103  in the peripheral portion of the lower portion of the groove can be modified by increasing the modification processing time. However, if the modification processing time is increased, the modification reaction occurs even in a top surface portion of the HDP-SiO 2  film  101 , so that a desired film thickness cannot be obtained. 
     Moreover, as an alternative, a method is available, in which the reaction product  105  is sublimated once in a step in which a production amount of the reaction product  105  is increased, and then the modification of the sacrificial oxide film  103  is performed by supplying the mixture gas again. However, since heating of the wafer W is needed to sublimate the reaction product  105 , heating in the chamber or a heating process in which the wafer W is transferred to a separate heating chamber should be included in the modification process, thereby spending time for removal of the sacrificial oxide film  103 . Further, in some cases, it is necessary to repeatedly perform the modification process and the heating process several times so as to sufficiently modify the sacrificial oxide film  103 . Thus, the etching process has reduced productivity. 
     The present disclosure is made in consideration of the above situation. The object of the present disclosure is to provide an etching method which can uniformly and sufficiently etch a silicon oxide film formed in a wafer. 
     SUMMARY 
     In order to solve the problem, according to the present disclosure, there is provided an etching process including: a modification process of supplying a mixture gas to a surface of a silicon oxide film to cause a chemical reaction between the silicon oxide film and the mixture gas, and modifying the silicon oxide film to generate a reaction product; and a heating process of heating and removing the reaction product, wherein the modification process includes: a first modification process of supplying the mixture gas containing a gas including a halogen element and an alkaline gas to the surface of the silicon oxide film; and a second modification process of stopping supplying the alkaline gas and supplying the mixture gas containing the gas including the halogen element to the surface of the silicon oxide film. 
     Moreover, according to the present disclosure, there is provided a recording medium storing a program which can be executed by a controller computer of a processing system, wherein the program is executed by the controller computer to cause the etching method to be performed in the processing system. 
     Effect of Some Embodiments of the Present Disclosure 
     According to the present disclosure, a sacrificial oxide film formed on a wafer can be modified uniformly and sufficiently by performing a second modification step after a first modification step. As a result, the sacrificial oxide film can be removed uniformly and sufficiently without a remaining sacrificial oxide film by sublimating a reaction product in a subsequent heating process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic vertical sectional view illustrating a structure of a surface of a wafer (a face on which a device is formed) before performing an etching of a sacrificial oxide film. 
         FIG. 2  is a schematic vertical sectional view illustrating a condition of a surface of a wafer when a conventional etching method is used. 
         FIG. 3  is a schematic plan view of a processing system. 
         FIG. 4  is an explanation drawing illustrating a configuration of a PHT processing apparatus. 
         FIG. 5  is an explanation drawing illustrating a configuration of a COR processing apparatus. 
         FIG. 6  is a schematic vertical sectional view illustrating a condition of a surface of a wafer when an etching method according to an embodiment of the present disclosure is used. 
         FIG. 7  is a schematic plan view of a processing system according to another embodiment of the present disclosure. 
         FIGS. 8A to 8C  are schematic vertical sectional views illustrating a structure of a surface of a wafer according to another embodiment. 
         FIG. 9  is a diagram illustrating a relationship between a COR processing time and an etching amount of an oxide film related to an example. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, a suitable embodiment of the present disclosure will be described. First, a condition of a wafer which is a substrate processed by an etching method related to the present embodiment. As shown in  FIG. 1 , a wafer W is, for example, a silicon wafer formed in a substantially disc-shaped thin plate, and has, for example, a HDP-SiO 2  film (silicon oxide film)  101  formed on a surface of a silicon (Si) layer  100 . The HDP-SiO 2  film  101  is a CVD-based silicon oxide film (plasma CVD oxide film) formed by using a bias high-density plasma CVD method (HDP-CVD method), and is used as an interlayer insulating film. 
     In a gap in the HDP-SiO 2  film  101 , a contact hole H is formed. In a side wall portion of the contact hole H, for example, a SiN film  104 , which is an insulator, is formed. A lower portion of the SiN film  104  is formed extending to such a position as to contact a top surface of the wafer W. Further, in a lower portion of the contact hole H, a sacrificial oxide film  103 , which is an example of a silicon oxide film, is formed. 
     Next, a processing system which performs an etching process to the sacrificial oxide film  103  formed in the lower portion of the contact hole H with respect to the wafer W will be described. The processing system  1  shown in  FIG. 3  includes a loading/unloading part  2  which loads/unloads the wafer W with respect to a processing system  1 , two load lock chambers  3  which is installed adjacent to the loading/unloading part  2 , post heat treatment (PHT) processing apparatuses  4  which are respectively installed adjacent to each of the load lock chambers  3  and performs a PHT process as a heating process, chemical oxide removal (COR) processing apparatuses  5  which are respectively installed adjacent to each of the PHT processing apparatuses  4  and performs a COR process as a modification process, and a controller computer  8  which sends control commands to respective parts of the processing system  1 . The PHT processing apparatuses  4  and the COR processing apparatuses  5  connected to each of the load lock chambers  3 , respectively, are arranged and installed in this order from the load lock chambers  3  side. 
     The loading/unloading part  2  includes a transfer chamber  12 . A first wafer transfer mechanism  11  transferring the wafer W, having, e.g., a substantially disk shape, is installed in the transfer chamber  12 . The first wafer transfer mechanism  11  includes two transfer arms  11   a  and  11   b  which substantially horizontally hold the wafer W. In one side of the transfer chamber  12 , a mounting table  13  (e.g., three) on which carriers  13   a  are mounted is provided. Each of the carriers  13   a  is capable of accommodating a plurality of sheets of wafers W arranged therein. Further, an orienter  14  which performs position alignment by optically obtaining eccentric amounts through the rotation of the wafer W is installed. 
     In the loading/unloading part  2 , with an operation of the wafer transfer mechanism  11 , the wafer W is rotated and moved straight in a substantially horizontal plane, and is vertically moved while being held by the transfer arms  11   a  and  11   b,  thereby being transferred to a desired position. Further, the transfer arms  11   a  and  11   b  move to/from the carriers  13   a  mounted on the mounting table  13 , the orienter  14 , and the load lock chambers  3  respectively, for loading/unloading. 
     The load lock chambers  3  are respectively connected to the transfer chamber  12  through gate valves  16  each installed between load lock chamber  3  and the transfer chamber  12 . In each of the load lock chambers  3 , a second wafer transfer mechanism  17  which transfers the wafer W is installed. The wafer transfer mechanism  17  includes a transfer arm  17   a  which substantially horizontally holds the wafer W. Further, the load lock chambers  3  are capable of being vacuumized. 
     In the load lock chambers  3 , with an operation of the wafer transfer mechanism  17 , the wafer W is rotated and moved straight in a substantially horizontal plane, and is vertically moved while being held by the transfer arm  17   a,  thereby being transferred. Moreover, when the transfer arm  17   a  moves to/from the PHT processing apparatus  4  longitudinally connected to each of the load lock chambers  3 , the wafer W is loaded/unloaded with respect to the PHT processing apparatus  4 . Further, when the transfer arm  17   a  moves to/from the COR processing apparatus  5  through each of the PHT processing apparatuses  4 , the wafer W is loaded/unloaded with respect to the COR processing apparatus  5 . 
     The PHT processing apparatus  4  includes a processing chamber (processing space)  21  which has an air-tight structure and receives a wafer W. Moreover, while not shown, a loading/unloading gate is formed to load/unload the wafer W with respect to an interior of the processing chamber  21 . A gate valve  22  which opens/closes the loading/unloading gate is installed. The processing chamber  21  is connected to the load lock chamber  3  with gate valves  22  interposed between the processing chamber  21  and the load lock chamber  3 . 
     As shown in  FIG. 4 , in the processing chamber  21  of the PHT processing apparatus  4 , a mounting table  23  on which the wafer W is substantially horizontally mounted is installed. Moreover, a supply mechanism  26  and an exhaust mechanism  28  are installed. The supply mechanism  26  includes a supply path  25  through which an inert gas such as nitrogen gas N 2  or the like is heated and supplied to the processing chamber  21 . The exhaust mechanism  28  includes an exhaust path  27  for exhausting the processing chamber  21 . The supply path  25  is connected to a nitrogen gas supply source  30 . Further, in the supply path  25 , a flow rate adjusting valve  31 , which is capable of performing an open/close operation of the supply path  25  and controlling a supply flow rate of the nitrogen gas, is installed. In the exhaust path  27 , an open/close valve  32  and an exhaust pump  33  for performing forced exhaust are installed. 
     Moreover, operations of respective parts such as the gate valve  22 , the flow rate adjusting valve  31 , the open/close valve  32 , the exhaust pump  33  and so forth in the PHT processing apparatus  4  are controlled by control commands of the controller computer  8 , respectively. In other words, the controller computer  8  controls the supply of the nitrogen gas by the supply mechanism  26 , the exhaust by the exhaust mechanism  28  and so forth. 
     As shown in the  FIG. 5 , the COR processing apparatus  5  includes a chamber  40  which has an air-tight structure. An interior of the chamber  40  is defined as a processing chamber (processing space)  41  in which the wafer W is received. A mounting table  42  on which the wafer W is substantially horizontally mounted is installed inside of the chamber  40 . Moreover, in the COR processing apparatus  5 , a supply mechanism  43  supplying a gas to the processing chamber  41  and an exhaust mechanism  44  exhausting an interior of the processing chamber  41  are installed. 
     In a side wall portion of the chamber  40 , a loading/unloading gate  53  for loading/unloading the wafer W into/out of the interior of the processing chamber  41  is installed, and a gate valve  54  for opening/closing the loading/unloading gate  53  is formed. The processing chamber  41  is connected to the processing chamber  21  of the PHT processing apparatus  4  with the gate valve  54  interposed between the processing chamber  41  and the processing chamber  21 . A ceiling portion of the chamber  40  includes a shower head  52  having a plurality of discharge holes discharging a processing gas. 
     The mounting table  42  has a substantially circular shape when viewed from a plan view, and is fixed to a lower portion of the chamber  40 . Within the mounting table  42 , a temperature controller  55  which controls a temperature of the mounting table is installed. The temperature controller  55  includes a pipe line through which, for example, temperature control liquid (e.g., water and so forth) is circulated, whereby a temperature of a top surface of the mounting table  42  is controlled by heat exchange with the liquid flowing inside of the pipe line. A temperature of the wafer W is controlled by heat exchange between the mounting table  42  and the wafer W on the mounting table  42 . Moreover, the temperature controller  55  is not limited to this type, but may be, for example, an electric heater heating the mounting table  42  and the wafer W by using resistance heat, or the like. 
     The supply mechanism  43  includes the aforementioned shower head  52 , a hydrogen fluoride gas supply path  61  for supplying a hydrogen fluoride gas (HF) to the processing chamber  41 , an ammonia gas supply path  62  for supplying an ammonia gas (NH 3 ) to the processing chamber  41 , an argon gas supply path  63  for supplying an argon gas (Ar) as an inert gas to the processing chamber  41 , and a nitrogen gas supply path  64  for supplying nitrogen gas (N 2 ) as an inert gas to the processing chamber  41 . The hydrogen fluoride gas supply path  61 , the ammonia gas supply path  62 , the argon gas supply path  63 , and the nitrogen gas supply path  64  are connected to the shower head  52 , and thus the hydrogen fluoride gas, ammonia gas, argon gas, nitrogen gas are spread and discharged through the shower head  52  into the processing chamber  41 . 
     The hydrogen fluoride gas supply path  61  is connected to a hydrogen fluoride gas supply source  71 . Further, in the hydrogen fluoride gas supply path  61 , a flow rate adjusting valve  72 , which is capable of performing an open/close operation of the hydrogen fluoride gas supply path  61  and controlling a supply flow rate of the hydrogen fluoride gas, is installed. The ammonia gas supply path  62  is connected to an ammonia gas supply source  73 . Further, in the ammonia gas supply path  62 , a flow rate adjusting valve  74 , which is capable of performing an open/close operation of the ammonia gas supply path  62  and controlling a supply flow rate of the ammonia gas, is installed. The argon gas supply path  63  is connected to an argon gas supply source  75 . Further, in the argon gas supply path  63 , a flow rate adjusting valve  76 , which is capable of performing an open/close operation of the argon gas supply path  63  and controlling a supply flow rate of the argon gas, is installed. The nitrogen gas supply path  64  is connected to a nitrogen gas supply source  77 . Further, in the nitrogen gas supply path  64 , a flow rate adjusting valve  78 , which is capable of performing an open/close operation of the nitrogen gas supply path  64  and controlling a supply flow rate of the nitrogen gas, is installed. 
     The exhaust mechanism  44  includes an exhaust path  85  in which an open/close valve  82  and an exhaust pump  83  for performing forced exhaust are installed. An end opening part of the exhaust path  85  is opened at a lower portion of the chamber  40 . 
     Moreover, operations of respective parts such as the gate valve  54 , the temperature controller  55 , the flow rate adjusting valves  72 ,  74 ,  76  and  78 , the open/close valve  82 , the exhaust pump  83  and so forth in the COR processing apparatus  5  are controlled by control commands of the controller computer  8 , respectively. In other words, the controller computer  8  controls the supply of the hydrogen fluoride gas, the ammonia gas, the argon gas and the nitrogen gas by the supply mechanism  43 , the exhaust by the exhaust mechanism  44 , the temperature control by the temperature controller  55  and so forth. 
     Each of functional components of the processing system  1  is connected to the controller computer  8  which automatically controls an overall operation of the processing system  1  through respective signal lines. Here, the functional components refer to every component which are operated to fulfill predetermined process conditions, for example, the wafer transfer mechanism  11 , the wafer transfer mechanism  17 , the gate valve  22  of the PHT processing apparatus  4 , the flow rate adjusting valve  31 , the exhaust pump  33 , the gate valve  54  of the COR processing apparatus  5 , the temperature controller  55 , the flow rate adjusting valves  72 ,  74 ,  76  and  78 , the open/close valve  82 , the exhaust pump  83  and so forth which are described above. The controller computer  8  is typically a general-purpose computer which is capable of realizing a certain function using executable software. 
     As shown in  FIG. 3 , the controller computer  8  includes a calculation part  8   a  having a central processing unit (CPU), an input/output part  8   b  connected to the calculation part  8   a,  and a recording medium  8   c  inserted into the input/output part  8   b  and storing a control software. In the recording medium  8   c,  a control software (program), which is executed by the controller computer  8  and causes a predetermined substrate processing method (to be described later) to be performed in the processing system  1 , is recorded. By executing the control software, the controller computer  8  controls the respective functional components of the processing system  1  to realize the various process conditions (e.g., a pressure of the processing chamber  41 , etc.) defined by a predetermined process recipe. In other words, as described in detail later, a control command for realizing an etching method in which the COR process in the COR processing apparatus  5  and the PHT process in the PHT processing apparatus  4  are performed in this order, is provided. 
     The recording medium  8   c  may be fixedly installed in the controller computer  8 , or detachably installed to a reading device (not shown) installed in the controller computer  8  so as to be read by the reading device. As a most typical embodiment, the recording medium  8   c  is a hard-disc drive in which a control software is installed by a service man of a manufacturer of the processing system  1 . In another embodiment, the recording medium  8   c  is a removable disc such as a CD-ROM or a DVD-ROM in which the control software is recorded. Such a removable disc is read by an optical reading device (not shown) installed in the controller computer  8 . Moreover, the recording medium  8   c  may be one type of a random access memory (RAM) or a read only memory (ROM). Further, the recording medium  8   c  may be a cassette type ROM. That is, any medium known in the field of computer technology may be used as the recording medium  8   c.  In addition, in a factory where a plurality of processing systems  1  is arranged, the control software may be stored in a management computer for collectively controlling the controller computer  8  of the respective processing systems  1 . In this case, each of the processing systems  1  is operated by the management computer through a communication line so as to execute a predetermined process. 
     Next, a processing method of the wafer W performed in the processing system  1  having a configuration described above, will be described. First, as shown in  FIG. 1 , the wafer W in which the contact hole H is formed in the HDP-SiO 2  film  101  is received in the carrier  13   a  and is transferred to the processing system  1 . 
     In the processing system  1 , as shown in  FIG. 3 , the carrier  13   a  accommodating a plurality of the wafers W is mounted on the mounting table  13 . One sheet of the wafer W is taken out from the carrier  13   a  by the wafer transfer mechanism  11 , and then loaded into the load lock chamber  3 . After the wafer W is loaded in the load lock chamber  3 , the load lock chamber  3  is sealed and depressurized. Thereafter, the gate valves  22  and  54  are opened, and the load lock chamber  3 , the processing chamber  21  of the PHT processing apparatus  4  and the processing chamber  41  of the COR processing apparatus  5  communicate with one another, wherein the processing chambers  21  and  41  are in a state depressurized below atmospheric pressure. The wafer W is taken out from the load lock chamber  3  by the wafer transfer mechanism  17 , and moves in a straight line so as to pass into the loading/unloading gate (not shown) of the processing chamber  21 , the processing chamber  21 , and the loading/unloading gate  53  in this order, thereby being loaded into the processing chamber  41 . 
     In the processing chamber  41 , the wafer W is transferred to the mounting table  42  from the transfer arm  17   a  of the wafer transfer mechanism  17  in a state that the device formation surface of the wafer W faces upward. After the wafer W is loaded, the transfer arm  17   a  is retracted from the processing chamber  41 , and the loading/unloading gate  53  is closed, so that the processing chamber  41  is sealed. Subsequently, the COR process starts. 
     After the processing chamber  41  is sealed, the ammonia gas, the argon gas and the nitrogen gas are supplied to the processing chamber  41  from the ammonia gas supply path  62 , the argon gas supply path  63 , and the nitrogen gas supply path  64 , respectively. Moreover, a pressure within the processing chamber  41  is controlled to be in a low pressure state lower than atmospheric pressure. Further, a temperature of the wafer W on the mounting table  42  is controlled to a predetermined target value (e.g., about 35 degrees C.) by the temperature controller  55 . 
     Thereafter, the hydrogen fluoride gas is supplied from the hydrogen fluoride gas supply path  61  to the processing chamber  41 . Herein, by supplying the hydrogen fluoride gas to the processing chamber  41  in which the ammonia gas has been previously supplied, an atmosphere of the processing chamber  41  becomes a processing atmosphere of a mixture gas including the hydrogen fluoride gas and the ammonia gas. In this way, by supplying the mixture gas onto the surface of the wafer W in the processing chamber  41 , a first COR process (a first modification step) is performed on the wafer W. 
     Due to the processing atmosphere of the low pressure state within the processing chamber  41 , the sacrificial oxide film  103  existing in the lower portion of the contact hole H of the wafer W chemically reacts with hydrogen fluoride gas molecules and ammonia gas molecules of the mixture gas, thereby being modified to the reaction product  105  (see,  FIG. 2 ). As the reaction product  105 , ammonium fluorosilicate, water or the like is generated. Further, this chemical reaction progresses isotropically, so that it occurs from the lower portion of the contact hole H to the top surface of the Si layer  100 . 
     During the first COR process, a pressure of the mixture gas (the processing atmosphere) is preferably maintained at a pressure ranging from equal to or higher than 20 mTorr, which is a pressure lower than atmospheric pressure, to equal to or lower than 600 mTorr (e.g., about 2.7 to about 80.0 Pa) by adjusting the supply flow rates of the respective processing gases, the supply flow rate of the inert gas, the exhaust flow rate and so forth. Moreover, a partial pressure of the hydrogen fluoride gas within the mixture gas is preferably adjusted to fall within a range from equal to or higher than 5 mTorr to equal to or lower than 200 mTorr (e.g., about 0.7 to about 26.7 Pa). Further, a temperature of the mixture gas (the processing atmosphere) is preferably adjusted to fall within a range from equal to or higher than 20 degrees C. to equal to or lower than 120 degrees C. More preferably, it is adjusted to fall within a range from equal to or higher than 35 degrees C. to equal to or lower than 45 degrees C. In addition, the flow rate of the mixture gas is preferably set to about three times of the flow rate of the hydrogen fluoride gas. A flow rate of the hydrogen fluoride gas is preferably adjusted to fall within a range from equal to or higher than 100 sccm to equal to or lower than 500 sccm. Moreover, in principle, a processing time of the first COR process is changed depending on a thickness of the sacrificial oxide film  103 . However, considering performing a second COR process described later, it is not preferable for the processing time to be lengthened in a viewpoint of productivity. For these reasons, the processing time of the first COR process is preferably set to be equal to or lower than 60 sec. 
     Moreover, a temperature of the wafer W, i.e., a temperature of a portion where a chemical reaction occurs in the sacrificial oxide film  103  (a temperature of a portion where the sacrificial oxide film  103  makes contact with the mixture gas), may be maintained at a constant temperature, e.g., about equal to or higher than 35 degrees C. In this way, the chemical reaction is accelerated and a generation rate of the reaction product  105  is increased, whereby a layer of the reaction product  105  can be formed rapidly. Further, a sublimation point of the ammonium fluorosilicate within the reaction product  105  is about 100 degrees C. If the temperature of the wafer W is equal to or higher than 100 degrees C., there is a possibility that producing the reaction product  105  is not favorably performed. For that reason, the temperature of the wafer W is preferably set to be equal to or lower than 100 degrees C. 
     By performing the first COR process for a predetermined time in this way, the sacrificial oxide film  103  is modified and the reaction product  105  is generated. However, as the processing time advances, the thickness of the reaction product  105  is getting thicker, so that a rate at which the mixture gas passes through the reaction product  105  is decreased. Therefore, the amount of the mixture gas contacting the sacrificial oxide film  103  is decreased and a modification amount of the sacrificial oxide film  103  is decreased. In particular, a peripheral portion of the lower portion of the contact hole H stays in a state where it has more unmodified sacrificial oxide film  103  than the central portion thereof. 
     Therefore, in the present embodiment, after performing the first COR process, the second COR process (a second modification step) is further performed to the wafer W. In other words, after performing the first COR process for the predetermined time, the supply of the ammonia gas into the processing chamber  41  is stopped, the modification process of the sacrificial oxide film  103  is performed by constituting the mixture gas supplied into the processing chamber  41  with the hydrogen fluoride gas, the argon gas, and the nitrogen gas. In this way, the mixture gas easily passes through the reaction product  105  (ammonium fluorosilicate) generated during the first COR process and easily makes contact with the unmodified sacrificial oxide film  103 . At this time, the hydrogen fluoride gas within the mixture gas passing through the reaction product  105  reacts with ammonia component within the reaction product  105 , thereby becoming a reaction gas modifying the sacrificial oxide film  103 . With the contact between the reaction gas and the sacrificial oxide film  103 , the sacrificial oxide film  103 , which could not be modified during the first COR process, is uniformly and sufficiently modified as shown in  FIG. 6 . 
     The reason why the ammonia gas is stopped during the second COR process is that, if the ammonia gas is supplied, a new reaction product  105  is deposited on the surface of the reaction product (ammonium fluorosilicate), so that a passing rate of the mixture gas becomes slower. Meanwhile, if the ammonia gas is stopped, the new reaction product  105  is not generated on the surface of the reaction product  105 , so that the mixture gas including the hydrogen fluoride gas easily passes through the reaction product. 
     Moreover, during the second COR process, a pressure of the mixture gas (the processing atmosphere) is preferably set to be higher than the pressure of the first COR process by adjusting the supply flow rates of the respective processing gases, the supply flow rate of the inert gas, the exhaust flow rate and so forth. Specifically, it is preferable that a pressure difference between the mixture gas (the processing atmosphere) of the second COR process and the mixture gas (the processing gas) of the first COR process is set to fall within a range from equal to or higher than 100 mTorr to equal to or lower than 200 mTorr (about 13.3 to about 26.7 Pa). By setting the pressure of the processing atmosphere of the second COR process to a pressure higher than the pressure of the processing atmosphere of the first COR process in this way, the rate at which the mixture gas passes through the reaction product  105  is increased, so that the sacrificial oxide film  103  is uniformly and sufficiently modified. It is preferable that other processing conditions are the same as the first COR process. 
     However, in the COR process, since the HDP-SiO 2  film  101  can chemically react with the mixture gas, there is concern that the HDP-SiO 2  film  101  is modified. In order to suppress the modification of the HDP-SiO 2  film  101 , a partial pressure of the ammonia gas within the mixture gas should be lower than a partial pressure of the hydrogen fluoride gas. In other words, the supply flow rate of the ammonia gas should be lower than the supply flow rate of the hydrogen fluoride gas. By doing so, the chemical reaction can be prevented in the HDP-SiO 2  film  101  while the chemical reaction actively occurs in the sacrificial oxide film  103 . In other words, only of the sacrificial oxide film  103  can be selectively and efficiently modified while suppressing the modification of the HDP-SiO 2  film  101  and so forth. Therefore, a damage of the HDP-SiO 2  film  101  can be prevented. By adjusting the partial pressure of the ammonia gas within the mixture gas in this way, it is possible to make differences in the reaction speed of the chemical reaction, the production amount of the reaction product  105  and so forth, between the sacrificial oxide film  103  and the HDP-SiO 2  film  101 , which are all silicon oxide film but are different in density, composition, film forming method and so forth. Furthermore, an etching amount after performing the PHT process described later can be made different from each other. In addition, it is thought that the chemical reaction when the partial pressure of the ammonia gas is lower than the partial pressure of the hydrogen fluoride gas is not a reaction rate control meaning that the generation rate of the reaction product  105  is determined by the chemical reaction of the sacrificial oxide film  103  and the mixture gas, but a supply rate control meaning that the generation rate of the reaction product  105  is determined by the supply flow rate of the hydrogen fluoride gas. 
     When a layer of the reaction product  105  is sufficiently formed and the second COR process is ended, the processing chamber  41  is depressurized by performing forced exhaust. As a result, the hydrogen fluoride gas or the ammonia gas is forcibly discharged from the processing chamber  41 . When the forced exhaust of the processing chamber  41  is ended, the loading/unloading gate  53  is opened, the wafer W is unloaded from the processing chamber  41  by the wafer transfer mechanism  17  and then is loaded to the processing chamber  21  of the PHT processing apparatus  4 . In this way, the COR process is finished. 
     In the PHT processing apparatus  4 , the wafer W is mounted within the processing chamber  21  in a state that the device formation surface of the wafer W faces upward. When the wafer W is loaded, the transfer arm  17   a  is retracted from the processing chamber  21 , the processing chamber  21  is sealed, and then PHT process is started. In the PHT process, while the processing chamber  21  is exhausted, a heating gas having a high temperature is supplied into the processing chamber  21 , so that a temperature of the processing chamber  21  is increased. In this way, the reaction product  105  generated by the COR process is heated, vaporized, and discharged outside the wafer W from a lower side of the contact hole H through an inside of the contact hole. By performing the PHT process after the COR process in this way, the reaction product  105  is removed, so that the sacrificial oxide film  103  can be isotropically dry-etched. 
     After the PHT process ends, the supply of the heating gas is stopped and then the loading/unloading gate of the PHT processing apparatus  4  is opened. After that, the wafer W is unloaded from the processing chamber  21  by the wafer transfer mechanism  17 , and then is returned to the load lock chamber  3 . The PHT process in the PHT processing apparatus  4  is finished in this manner. 
     After the wafer W is returned to the load lock chamber  3  and the load lock chamber  3  is sealed, the load lock chamber  3  and the transfer chamber  12  are communicated with each other. Then, by the wafer transfer mechanism  11 , the wafer W is unloaded from the load lock chamber  3 , and is returned to the carrier  13   a  on the mounting table  13 . In this way, a series of etching process in the processing system  1  is finished. 
     According to the embodiment, by performing the COR process (the second modification step) in which the ammonia gas is stopped after the conventional COR process (the first modification step), the sacrificial oxide film  103  formed in the lower portion of the contact hole H can be uniformly and sufficiently modified. As a result, the generated reaction product  105  is sublimated during the PHT process (the heating process) and thus removing the sacrificial oxide film  103  is possible without permitting the same to remain. In other words, the sacrificial oxide film can be uniformly and sufficiently removed without repeatedly performing the modification process and the heating process several times. 
     While the preferred embodiments of the present disclosure have been described, the present disclosure is not limited to these examples. It is clear that a person skilled in the art can reach various modifications without departing from the scope of the technical ideas described in claims, and such modifications would fall within a technical scope of the present disclosure. 
     The types of gases supplied into the processing chamber  41  except the hydrogen fluoride gas and the ammonia gas are not limited to the combination described in the above embodiments. For example, the inert gas supplied into the processing chamber  41  may be argon gas only. Moreover, such an inert gas may be another inert gas, for example, any one of helium (He) gas and xenon (Xe) gas, or a mixture of two or more gases among the argon gas, the nitrogen gas, the helium gas and the xenon gas. 
     A structure of the processing system  1  is not limited to those mentioned in the above embodiments. For example, instead of the COR processing apparatus and the PHT processing apparatus, a processing system including a film forming apparatus may be used. For example, like a processing system  90  shown in  FIG. 7 , a configuration may be possible, in which a common transfer chamber  92  including a wafer transfer mechanism  91  is connected to the transfer chamber  12  through load lock chambers  93 , and a COR processing apparatus  95 , a PHT processing apparatus  96 , and film forming apparatuses  97  such as CVD apparatus and so forth are arranged around the common transfer chamber  92 . In the processing system  90 , the wafer W is loaded/unloaded with respect to each of the load lock chambers  93 , the COR processing apparatus  95 , the PHT processing apparatus  96  and the film forming apparatus  97  by the wafer transfer mechanism  91 . An interior of the common transfer chamber  92  can be vacuumized. In other words, by keeping the interior of the common transfer chamber  92  in a vacuum-state, the wafer W unloaded from the PHT processing apparatus  96  can be loaded into the film forming apparatus  97  without making contact with oxygen within air. 
     In the above embodiments, the silicon wafer W that is a semiconductor wafer is provided as the substrate having the silicon oxide film. However, the substrate is not limited to this and different types, for example, glass for an LCD substrate, a CD substrate, a printed substrate, a ceramic substrate and so forth may be used as the substrate. 
     Moreover, a structure of the substrate processed in the processing system  1  is not limited those described in the above embodiments. Further, the etching performed in the processing system  1  is not limited to the etching performed on the lower portion of the contact hole H as shown in the embodiments, and the present disclosure may be applied to etching methods for various parts. 
     In the processing system  1 , the silicon oxide film, which is an object on which the etching is performed, is not limited to the sacrificial oxide film. The silicon oxide film may be other types of silicon oxide films, e.g., a HDP-SiO 2  film and so forth. Even in this case, the etching amount and so forth can be controlled by adjusting a temperature of the silicon oxide film in the COR process and a partial pressure of the hydrogen fluoride gas within the mixture gas according to the types of the silicon oxide film. 
     Moreover, regarding the CVD-based oxide film formed on the substrate, the types of CVD-method used to form the CVD-based oxide film are not specifically limited. For example, a thermal-CVD method, a normal pressure CVD-method, a low pressure CVD-method, a plasma CVD method and so forth may be used. 
     While modifying the sacrificial oxide film  103  in the lower portion of the contact hole H has been described in the above embodiments, the COR process according to the present disclosure can be applied to, for example, an etch-back process of the oxide film  103  as shown in the  FIGS. 8A to 8C .  FIG. 8A  is a diagram illustrating a state of a silicon wafer W of, for example, a manufacturing process of a recess transistor. As shown in  FIG. 8A , a groove H is formed in the wafer W, and a film  106  (e.g., SiN film) for protecting the wafer W when performing etch-back is formed in a surface of a convex portion of the wafer W. 
     In etching-back the oxide film  103  up to the middle of the groove H in the wafer W described above, according to the conventional COR process, the oxide film  103  is more difficult to be modified in a peripheral portion of the groove H on a surface of the oxide film  103  than in a central portion of the groove H, as shown in  FIG. 8B . In this case, it was impossible to only modify the oxide film  103  in the peripheral portion of the groove H in the conventional processing method, so that a transfer to the subsequent process was performed in a state that a surface shape of the oxide film  103  is in disorder. However, by performing the second COR process according to the present disclosure, the central portion and the peripheral portion in the surface of the oxide film are uniformly modified, so that the surface shape can be flat as shown in  FIG. 8C . 
     EXAMPLE 
     The etching process (the first COR process, the second COR process, and the PHT process) according to the present disclosure was performed on the wafer W (the wafer corresponds to the structure shown in  FIG. 1 ) having a sacrificial oxide film of about 13 nm formed in the lower portion of the contact hole. Moreover, in the present example, the first COR process was performed for 60 sec, and then the second COR process was performed for 60 sec. Further, the first COR process is performed under a processing atmosphere having a pressure of 50 mTorr and a temperature of 35 degrees C., and the second COR process is performed under a processing atmosphere having a pressure of a 150 mTorr and a temperature of 35 degrees C. 
     A relationship between a COR processing time and an etching amount of the oxide film when the etching process is performed in the processing condition described above is shown in  FIG. 9 . Further, in  FIG. 9 , a relationship between a COR processing time and an etching amount of the oxide film when only the first COR process (the conventional COR process) is performed is also shown. In addition, the modification of the oxide film does not progress in a totally-uniform-state, and thus the “etching amount” used herein refers to an average etching amount. The average etching amount refers to an average of differences between the film thickness measured in a plurality of points in the grooves on the wafer before the etching and the film thickness measured after the etching. 
     According to the result of  FIG. 9 , in the etching process which only performs the first COR process (the conventional COR process), a state where, although the processing time is lengthened, the etching amount is not increased, i.e., a state where the modification reaction of the oxide film is saturated in the COR process was confirmed. On the other hand, if the second COR process is performed after performing the first COR process for 60 sec, it is possible to confirm that the etching amount of the oxide film in the saturation state is increasing again. 
     In this example, in the case where the first COR process was performed for 60 sec, the etching amount of the oxide film was 5.23 nm. On the other hand, in the case where the second COR process was performed for 60 sec after the first COR process, the etching amount of the oxide film was 12.13 nm. In other words, it was confirmed, from the result of the present example, that performing the second COR process after the first COR process can remove the oxide film more than a case where only the first COR process is performed. Further, while the etching amount is decreased by increasing the processing time of the second COR process, it is assumed that this was because most of the oxide film to be removed has been already etched. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure is applicable to an etching process and a recording medium. 
     EXPLANATION OF REFERENCE NUMERALS 
     W: wafer, H: groove,  1 : processing system,  4 : PHT processing system,  5 : COR processing system,  8 : controller computer,  40 : chamber,  41 : processing chamber,  61 : hydrogen fluoride gas supply path,  62 : ammonia gas supply path,  85 : exhaust path,  100 : Si layer,  101 : HDP-SiO 2  film,  102 : resist film,  103 : oxide film,  104 : SiN film (side wall portion),  105 : reaction product,  106 : SiN film