Patent Publication Number: US-2015064925-A1

Title: Deposit removing method and gas processing apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Continuation of International Application No. PCT/JP2013/002509 filed on Apr. 12, 2013, which claims the benefits of Japanese Patent Application No. 2012-094439 filed on Apr. 18, 2012, and U.S. Provisional Application Ser. No. 61/637,385 filed on Apr. 24, 2012. The entire disclosure of the prior application is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The embodiments described herein pertain generally to a deposit removing method and a gas processing apparatus. 
     BACKGROUND 
     Conventionally, in the field of manufacturing semiconductor devices, a film forming process or an etching process is performed on a substrate such as a semiconductor wafer to form a desired pattern thereon. In such a manufacturing process of semiconductor devices, if a STI (Shallow Trench Isolation) process is performed, a deposit of silicon oxide (e.g., SiO 2  or SiOBr) may be deposited on a sidewall portion of the pattern. Conventionally, such a deposit is removed through a process using a HF single gas, for example. 
     If, however, a composition or a bonding state of the deposit is similar to that of silicon dioxide of a certain structure (e.g., a gate oxide film) in the pattern, there is a problem that selectivity therebetween may not be achieved. Further, water, which is a byproduct generated by a reaction (SiO 2 +4HF→SiF 4 +2H 2 O) between the deposit and the HF gas, may accelerate the reaction to cause a chain reaction. As a result, the silicon dioxide of the structure in the pattern as well as the deposit may also be etched. 
     Moreover, if an exposure time during which the substrate is left after the etching process becomes longer, the selectivity may be further deteriorated by being affected by moisture depending on a moisture absorption state of the deposit. As a technique for removing a native oxide film formed on a surface of a silicon substrate, there is known a method of using HF vapor and H 2 O or alcohol vapor (see, for example, Patent Document 1). However, this method is a technique for removing a native oxide film, and is not a technique for removing a deposit formed on a sidewall portion of a pattern. 
     Patent Document 1: Japanese Patent Laid-open Publication No. H07-263416 
     As stated above, conventionally, when removing the deposit deposited on the pattern, there has been a problem that silicon dioxide of the structure in the pattern may be damaged because of low selectivity between the deposit and the silicon dioxide of the structure in the pattern. Further, if the exposure time after the etching process becomes longer, the selectivity may be further deteriorated by being affected by moisture depending on the moisture absorption state of the deposit. 
     Further, a deposit removing rate at a central portion of the substrate and a deposit removing rate at a peripheral portion of the substrate may easily get differed. As a result, it is difficult to improve processing uniformity in the entire surface of the substrate. 
     SUMMARY 
     In view of the foregoing problems, example embodiments provide a deposit removing method and a gas processing apparatus capable of removing a deposit efficiently regardless of the length of the exposure time after an etching process, and, also, capable of removing the deposit uniformly while suppressing damage on silicon dioxide of a structure in a pattern. 
     In one example embodiment, a deposit removing method of removing a deposit deposited on a surface of a pattern formed on a substrate in an etching process includes performing an oxygen plasma process of exposing the substrate to oxygen plasma while heating the substrate; and performing a cycle process in which, after the performing of the oxygen plasma process, the substrate is exposed to an atmosphere of a mixture gas of a hydrogen fluoride gas and an alcohol gas within a processing chamber, and a first period during which a total pressure of the mixture gas or a partial pressure of the alcohol gas is set to be a first total pressure or a first partial pressure of the alcohol gas and a second period during which the total pressure of the mixture gas or the partial pressure of the alcohol gas is set to be a second total pressure lower than the first total pressure or a second partial pressure of the alcohol gas lower than the first partial pressure of the alcohol gas by evacuating the processing chamber are repeated multiple cycles. In the performing of the cycle process, the mixture gas is supplied to the substrate from a region facing the substrate, and a supply amount of the mixture gas per a unit area from a circular first region including a central portion of the substrate and having a diameter smaller than a diameter of the substrate is set to be larger than a supply amount of the mixture gas per a unit area from an annular second region at an outside of the first region. 
     In another example embodiment, a gas processing apparatus removes a deposit deposited on a surface of a pattern formed on a substrate in an etching process by performing a cycle process in which the substrate is exposed to an atmosphere of a mixture gas of a hydrogen fluoride gas and an alcohol gas within a processing chamber, and a first period during which a total pressure of the mixture gas or a partial pressure of the alcohol gas is set to be a first total pressure or a first partial pressure of the alcohol gas and a second period during which the total pressure of the mixture gas or the partial pressure of the alcohol gas is set to be a second total pressure lower than the first total pressure or a second partial pressure of the alcohol gas lower than the first partial pressure of the alcohol gas by evacuating the processing chamber are repeated multiple cycles. Here, the mixture gas is supplied to the substrate from a region facing the substrate such that a supply amount of the mixture gas per a unit area from a circular first region including a central portion of the substrate and having a diameter smaller than a diameter of the substrate is larger than a supply amount of the mixture gas per a unit area from an annular second region at an outside of the first region. 
     In accordance with the example embodiments, it is possible to provide a deposit removing method and a gas processing apparatus capable of removing a deposit efficiently regardless of the length of exposure time after an etching process, and, also, capable of removing the deposit uniformly while suppressing silicon dioxide of a pattern structure from being damaged. 
     The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the detailed description that follows, embodiments are described as illustrations only since various changes and modifications will become apparent to those skilled in the art from the following detailed description. The use of the same reference numbers in different figures indicates similar or identical items. 
         FIG. 1  is a schematic cross sectional configuration view of a plasma processing apparatus in accordance with an example embodiment; 
         FIG. 2  is a schematic cross sectional configuration view of a gas processing apparatus in accordance with the example embodiment; 
         FIG. 3A  and  FIG. 3B  are diagrams illustrating configuration of major components of the gas processing apparatus of  FIG. 2 ; 
         FIG. 4  is a flowchart for describing a process sequence in the example embodiment; 
         FIG. 5  is a graph showing a pressure variation in the example embodiment; and 
         FIG. 6  is a graph showing a relationship between a pressure, a methanol gas flow rate and a temperature under which the deposit can be removed. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings, which form a part of the description. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. Furthermore, unless otherwise noted, the description of each successive drawing may reference features from one or more of the previous drawings to provide clearer context and a more substantive explanation of the current example embodiment. Still, the example embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein and illustrated in the drawings, may be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein. 
     In the following, example embodiments will be described in detail, and reference is made to the accompanying drawings, which form a part of the description. 
       FIG. 1  is a longitudinal cross sectional view schematically illustrating a configuration example of a plasma processing apparatus  100  to be used in an oxygen plasma process in a deposit removing method in accordance with an example embodiment. As depicted in  FIG. 1 , the plasma processing apparatus  100  includes a processing chamber  101  configured to be hermetically sealed. The processing chamber  101  includes therein a stage  102  configured to mount thereon a semiconductor wafer (substrate) W. The stage  102  includes a non-illustrated temperature control device and is configured to control a temperature of the semiconductor wafer W mounted on the stage  102  to be a certain level. 
     The processing chamber  101  is made of, but not limited to, quartz. A window  103  made of quartz is provided at a ceiling portion of the processing chamber  101 , and a RF coil  104  connected to a non-illustrated high frequency power supply is provided at the outside of the window  103 . A gas inlet line  105 , through which an oxygen-containing processing gas (e.g., an O 2  single gas) is introduced into the processing chamber  101 , is formed at a part of the window  103 . The processing gas introduced through the gas inlet line  105  is excited into plasma P by applying a high frequency power to the RF coil  104 . 
     Gas diffusion plates  106  for plasma shielding and gas dispersion are provided under the window  103 . Through the gas diffusion plates  106 , radicals in the plasma are supplied to the semiconductor wafer W on the stage  102  in a dispersed state. When allowing the plasma to act on a substrate, it may be possible to set the substrate and the plasma to be in direct contact with each other, or to perform a remote plasma process, as in the present example embodiment, in which the substrate and the plasma are not brought into direct contact with each other, but radicals separated from the plasma generated in a space distanced apart from the substrate are made to act on the substrate. 
     Further, a gas exhaust pipe  107  is provided at a bottom portion of the processing chamber  101 . The gas exhaust pipe  107  is connected to a non-illustrated vacuum pump or the like and is configured to evacuate the chamber  101  to a preset pressure. 
       FIG. 2  is a longitudinal cross sectional view schematically illustrating a configuration example of a gas processing apparatus  200  to be used in a cycle process in the deposit removing method in accordance with the example embodiment. As depicted in  FIG. 2 , the gas processing apparatus  200  includes a processing chamber  201  configured to be hermetically sealed. The processing chamber  201  includes therein a stage  202  configured to mount thereon a semiconductor wafer (substrate) W. The stage  202  includes a non-illustrated temperature control device and is configured to control a temperature of the semiconductor wafer W mounted on the state  202  to be a preset level. 
     A gas inlet line  203 , through which a preset processing gas (a mixture gas of a HF gas and a methanol gas in the present example embodiment) is introduced into the processing chamber  201 , is formed at an upper portion of the processing chamber  201 . Further, a gas diffusion plate  206  having a multiple number of through holes  205  is provided under an opening  204 , at which the gas inlet line  203  is opened to an inside of the processing chamber  201 , to face the semiconductor wafer W mounted on the stage  202 . The processing gas is supplied onto a surface of the semiconductor wafer W from the through holes  205  of the gas diffusion plate  206 , i.e., from a region facing the semiconductor wafer W. 
     As shown in  FIG. 3A , for a semiconductor wafer W having a diameter of, e.g., 300 mm, the gas diffusion plate  206  has a circular first region  206   a  having a diameter of, e.g., 250 mm and an annular second region  206   b  at an outside of the first region  206   a . The through holes  205  are formed in the circular first region  206   a  at a regular pitch, whereas no through hole  205  is formed in the annular second region  206   b . With this configuration, among the regions facing the semiconductor wafer W, a flow rate of the processing gas supplied from the first region  206   a  per a unit area is set to be higher than a flow rate (zero (0) in the present example embodiment) of the processing gas supplied from the second region  206   b  per a unit area. 
     In  FIG. 3A , an imaginary line indicating a boundary between the first region  206   a  and the second region  206   b  is shown by a dashed dotted line. Further,  FIG. 3B  depicts a gas diffusion plate  216  having through holes  215  formed at a regular pitch in the entire surface thereof without separating a first region and a second region. The number of the through holes  205  in the gas diffusion plate  206  of  FIG. 3A  and the number of the through holes  215  in the gas diffusion plate  216  of  FIG. 3B  are same. The through holes  205  are formed at a pitch of, e.g., 28 mm, and the through holes  215  are formed at a pitch of, e.g., 40 mm. Further, a diameter d2 of a region of the gas diffusion plate  216  in which the through holes  215  are arranged is set be to be, e.g., 345 mm, larger than the diameter of the semiconductor wafer W. 
     Additionally, in  FIG. 3A  and  FIG. 3B , the diameter d1 of the first region  206   a  and the diameter d2 of the region in which the through holes  215  are arranged indicate minimum diameters of circles drawn to include all the through holes  205  and all the through holes  215  therein, respectively. Further, in  FIG. 3A  and  FIG. 3B , the number of the through holes  205 , the number of the through holes  215 , the pitches between the through holes  205  and the pitches between the through holes  215  are not actual values, and illustration of some of them are omitted. 
     When using the gas diffusion plates  206  and  216 , if a flow rate of the processing gas is, e.g., 2800 sccm, a back pressure of the gas diffusion plates  206  and  216  may be, e.g., 13.3 KPa (100 Torr). Meanwhile, an internal pressure of the processing chamber  201  in which the semiconductor wafer W is placed may be, e.g., 665 Pa (5 Torr). Since there is a great difference between the back pressure of the gas diffusion plates  206  and  216  and the internal pressure of the processing chamber  201 , the processing gas may be discharged at a substantially uniform flow rate from the through holes  205  and  215  regardless of whether the through holes  205  and  215  are arranged at the central portion or the peripheral portion in the surface of the gas diffusion plates  206  and  216 . 
     Referring back to  FIG. 2 , a gas exhaust pipe  207  is provided at a bottom portion of the processing chamber  201 . The gas exhaust pipe  207  is connected to a non-illustrated vacuum pump or the like, and is configured to evacuate the processing chamber  201  to a preset pressure. 
     In the present example embodiment, by using the plasma processing apparatus  100  and the gas processing apparatus  200  having the above-described configurations, a deposit removing process is performed as follows. 
     As depicted in a flowchart of  FIG. 4 , an etching process is performed in a pre-treatment (block  301 ), and a reaction product generated by the etching process is deposited on a sidewall portion of a pattern formed on a semiconductor wafer. By way of example, if a STI (Shallow Trench Isolation) process is performed, a deposit of silicon oxide (e.g., SiO 2  or SiOBr) is deposited on the sidewall portion of the pattern. Accordingly, the deposit deposited on the sidewall portion of the pattern is removed through the deposit removing process in accordance with the present example embodiment. 
     The aforementioned etching process (block  301 ) is performed by two processes as specified below. 
     (Process 1) 
     Pressure: 6.65 Pa (50 mTorr) 
     High frequency powers (high frequency)/(low frequency): 400 W/1500 W 
     Etching gas: HBr/NF 3 /O 2 =400 sccm/75 sccm/5 sccm 
     Stage temperature: 110° C. 
     Time: 5 seconds 
     (Process 2) 
     Pressure: 6.65 Pa (50 mTorr) 
     High frequency powers (high frequency)/(low frequency): 400 W/1400 W 
     Etching gas: HBr/NF 3 /O 2 =350 sccm/32 sccm/19 sccm 
     Stage temperature: 110° C. 
     Time: 20 seconds 
     After the etching process, an oxygen plasma process in the deposit removing process is performed (block  302 ). The oxygen plasma process may be performed in the plasma processing apparatus  100  shown in  FIG. 1  or the like. The deposit removing process may be performed immediately after the completion of the etching process or after a certain time (e.g., several hours to several days) has been elapsed. 
     The oxygen plasma process in the plasma processing apparatus  100  may be performed as follows, for example. That is, in the oxygen plasma process, a semiconductor wafer W is mounted on the stage  102  which is set to have a preset temperature previously. Then, by being attracted to and held by a non-illustrated electrostatic chuck or the like, the semiconductor wafer W is heated to a preset temperature. In this state, a processing gas containing an oxygen gas is introduced through the gas inlet line  105 , and the processing chamber is evacuated through the gas exhaust pipe  107 , so that an inside of the processing chamber  101  is turned into the processing gas atmosphere of a preset pressure. Then, as a high frequency power is applied to the RF coil  104 , inductively coupled plasma of the oxygen gas is generated. Ions in this plasma are shielded by the gas diffusion plates  106 , and oxygen radicals without having electric charges are supplied to the semiconductor wafer W on the stage  102  in a dispersed state. As a result, the oxygen plasma process with the oxygen radicals is performed. 
     This oxygen plasma process is performed to obtain constant moisture absorption states of the pattern and the deposit (i.e., to dehydrate the pattern and the deposit) regardless of the length of the exposure time after the etching process. Accordingly, influence from the different moisture absorption states between the pattern and the deposit can be avoided in a subsequent cycle process. Thus, it is possible to remove the silicon oxide (e.g., SiO 2  or SiOBr), which is the deposit deposited on the sidewall portion of the pattern. Further, it is possible to suppress a SiO 2  layer of a gate oxide film or the like, which is a pattern structure, from being damaged due to the excessive reaction. 
     In this oxygen plasma process, an oxygen-containing gas such as, but not limited to, an oxygen single gas or a mixture gas of an oxygen gas and a nitrogen gas may be used as the processing gas. A heating temperature of the semiconductor wafer W (i.e., stage temperature) may be set to be in the range from, e.g., 200° C. to 300° C. Further, the pressure may be set to be in the range from, e.g., 66.5 Pa (0.5 Torr) to 266 Pa (2 Torr). 
     After the oxygen plasma process as stated above, the cycle process in the deposit removing process is performed (blocks  303  to  305 ). This cycle process may be performed in the gas processing apparatus  200  depicted in  FIG. 2 . 
     The cycle process in the gas processing apparatus  200  is performed as follows. That is, in the cycle process, the semiconductor wafer W is mounted on the stage  202  which is set to have a preset temperature previously, so that the semiconductor wafer W is maintained at a preset temperature. In this state, a certain processing gas (in this example embodiment, a HF gas+a methanol gas) is introduced through the gas inlet line  203 , and the processing chamber is evacuated through the gas exhaust pipe  207 , so that the inside of the processing chamber  201  is turned into the processing gas atmosphere of the preset pressure. 
     As shown in the flowchart of  FIG. 4 , in the cycle process, a first period during which a partial pressure of the methanol gas is set to be a first partial pressure (block  303 ) and a second period during which the partial pressure of the methanol gas is set to be a second partial pressure lower than the first partial pressure by evacuating the inside of the processing chamber (block  304 ) are repeated multiple cycles (block  305 ). In order to vary the partial pressure of the methanol gas, the following methods may be utilized, for example. 
     First, a method of varying a gas supply may be used. For example, during the first period, a mixture gas of a preset flow rate is supplied, and then, during the second period, the supply of the mixture gas is stopped and a nitrogen gas of a certain flow rate is supplied. Alternatively, a method of varying a pressure may be used. For example, during the first period, while supplying the mixture gas of a preset flow rate, the inside of the processing chamber is maintained at a preset pressure by an automatic pressure controller (APC). Then, during the second period, by lowering a set pressure of the APC or by fully opening the APC, the entire processing chamber is evacuated by a vacuum pump, so that the pressure within the processing chamber is lowered. In the present example embodiment, as shown in  FIG. 5 , the first period and the second period are set by using the method of the latter. 
     At this time, it may be desirable to set the temperature of the semiconductor wafer W to a low temperature equal to or less than, e.g., several tens of degrees (e.g., 30° C. or less). Further, desirably, the pressure in the first period may be set to be in the range from, e.g., 665 Pa (5 Torr) to 1330 Pa (10 Torr), and a mixture gas of a HF gas and an alcohol gas (a CH 3 OH gas in the present example embodiment) may be used as the processing gas. 
     In the first period of the cycle process, a pressure of the mixture gas or a partial pressure of the alcohol gas is set such that a deposit can be removed by the action of the mixture gas. Further, in the second period, the pressure of the mixture gas or the partial pressure of the alcohol gas is decreased so that the deposit is not removed but substances (H 2 O, etc.) generated by a reaction between the deposit and the mixture gas during the first period is exhausted out of the processing chamber  201 . The first period and the second period may be set to range from, e.g., 5 seconds to 20 seconds, respectively, and are repeated multiple cycles. 
     After repeating this cycle process preset number of times, the deposit removing process is ended (block  306 ). 
     In the above-described deposit removing process in accordance with the example embodiment, the constant moisture absorption states of the pattern and the deposit are obtained through the oxygen plasma process regardless of the length of the exposure time after the etching process. 
     In a process using a HF single gas, if the oxygen plasma process is performed, H 2 O serving as a reaction accelerator is removed by performing the oxygen plasma process. Accordingly, a processing result may be stabilized, whereas it may be difficult to remove the deposit while obtaining selectivity against a SiO 2  film in the pattern structure. For this reason, in the cycle process in accordance with the present example embodiment, the mixture gas of the HF gas and the alcohol gas (methanol gas in the present example embodiment) is used as the processing gas. In this case, however, the amount of the H 2 O generated by the reaction may become excessive within the processing chamber, so that a pattern structure such as a gate oxide film may be damaged or a deposit may be generated again as a result of a reverse reaction. To suppress this problem, through the cycle process, by repeating the first period during which the deposit is removed and the second period during which the deposit is not removed but the reaction product is exhausted, an excessive increase of the amount of the H 2 O within the processing chamber can be suppressed. 
     Accordingly, it is possible to remove the silicon oxide (e.g., SiO 2  or SiOBr), which is the deposit deposited on the sidewall portion of the pattern. Further, it is possible to suppress a SiO 2  layer of the pattern structure such as the gate oxide film from being damaged as a result of the excessive reaction caused by a catalytic action by H 2 O. 
     Further, in the present example embodiment, as for the semiconductor wafer W having a diameter of 300 mm, the gas diffusion plate  206  of the gas processing apparatus  200  has the through holes  205  formed at the uniform pitch in the circular first region  206   a  having a diameter of 250 mm, whereas no through hole  205  is formed in the annular second region  206   b  at the outside of the first region  206   a , as shown in  FIG. 3A . With this configuration, among the regions facing the semiconductor wafer W, a flow rate of the processing gas supplied from the first region  206   a  per a unit area is set to be higher than a flow rate of the processing gas supplied from the second region  206   b  per a unit area. Accordingly, it is possible to perform the deposit removal process more uniformly in the entire surface of the semiconductor wafer W. 
     That is, as depicted in  FIG. 3B , for example, in case of using the gas diffusion plate  216  having the through holes  215  formed at the uniform pitch in the entire surface without separating the first region and the second region substantially, a deposit removing rate at a central portion of the semiconductor wafer W may become increased, and a deposit removing rate at a peripheral portion of the semiconductor wafer W becomes decreased. That is, a processing rate in the entire surface of the semiconductor wafer W may become non-uniform. This phenomenon occurs when a pattern is formed on the semiconductor wafer W. When etching a so-called beta film without having a pattern formed on a semiconductor wafer W, an etching rate at a peripheral portion of the semiconductor wafer W may become higher than an etching rate at a central portion thereof. 
     As stated above, the reason why the reverse phenomena take place in the respective cases where the pattern is formed on the semiconductor wafer W and the pattern is not formed on the semiconductor wafer W is deemed to be as follows. That is, a gas velocity above the central portion of the semiconductor wafer W is lower than a gas velocity above an edge portion thereof, and H 2 O, which is generated as a result of the reaction, may not be efficiently exhausted from an inside of the pattern but may stay within the pattern. As a result, the reaction may progress through a catalytic reaction by the H 2 O. Accordingly, by setting a supply amount of the processing gas to the central portion of the semiconductor wafer W per a unit area to be larger than a supply amount of the processing gas to the edge portion per a unit area, i.e., by increasing the gas velocity above the central portion of the semiconductor wafer W, exhaust of the H 2 O from the inside of the pattern at the central portion of the semiconductor wafer W may be accelerated, so that the processing uniformity in the entire surface of the semiconductor wafer W may be improved. 
     Further, in the example shown in  FIG. 3A , no through hole  205  is formed in the second region  206   b  at the outside of the first region  206   a . However, it may be possible to adopt a configuration in which the through holes  205  are formed in the second region  206   b  at an arrangement density (the number of the through holes per a unit area) lower than that of the first region  206   a . Further, without changing the arrangement density of the through holes  205 , it may be also possible to adopt a configuration in which the supply amounts of the processing gas in the first region  206   a  and the second region  206   b  are independently changed. As a result, the supply amount of the processing gas from the first region  206   a  per a unit area may be set to be larger than the supply amount of the processing gas from the second region  206   b  per a unit area. Further, the diameter d1 of the first region  206   a  needs to be set to be smaller than the diameter of the semiconductor wafer W. Desirably, the diameter d1 may be set to range from 70% to 90% of the diameter of the semiconductor wafer W inclusive, and, more desirably, 75% to 85% inclusive. Additionally, in the configuration where the through holes  205  are formed in the second region  206   b , the outer diameter of the second region  206   b  may be set to be larger than the diameter of the semiconductor wafer W. 
     As an experimental example 1, a deposit removing process is performed on a semiconductor wafer W left for 1 month after forming a pattern thereon by the etching. First, the oxygen plasma process is performed under the following processing conditions. 
     Pressure: 133 Pa (1 Torr) 
     High frequency power: 1000 W 
     Etching gas: O 2 =1980 sccm 
     Stage temperature: 250° C. 
     Time: 120 seconds 
     Subsequently, the cycle process is performed under the processing conditions as follows. 
     Pressure: (931 Pa (7 Torr) for 10 seconds   173 Pa (1.3 Torr) for 10 seconds)×6 cycles 
     HF/CH 3 OH=2800 sccm/44 sccm 
     Stage temperature: 10° C. 
     As for the setting of the pressure in the aforementioned cycle process, as stated above, a state in which the set pressure of the APC is set to be 931 Pa (7 Torr) is maintained for 10 seconds during the first period, and, a state in which the APC is fully opened while supplying the processing gas is maintained for 10 seconds during the second period. An actual pressure variation in the processing chamber  201  is as shown in a graph of  FIG. 5 . That is, even if the set pressure of the APC is set to be 931 Pa (7 Torr) from the state in which the APC is fully opened, it takes 4 seconds to 5 seconds until the pressure actually reaches 931 Pa (7 Torr). Meanwhile, if the APC is fully opened from the state in which the set pressure of the APC is 931 Pa (7 Torr), the pressure may maintain at a constant level of 173 Pa (1.3 Torr) in a relatively short period of time. 
     Here, under the above-mentioned conditions for the stage temperature and the flow rate of the processing gas, the pressure at which the deposit can be removed (the deposit is peeled off) is 665 Pa (5 Torr). Accordingly, the time corresponding to the ½ cycle in the cycle process may be set to range from, e.g., 5 seconds to 20 seconds, desirably. Further, the first period and the second period are not necessarily the same but may be different from each other. 
     The semiconductor wafer after the above-described deposit removing process is observed while enlarged by a SEM. As a result, the deposit deposited on the sidewall portion of the pattern is found to be removed, and no damage on the SiO 2  layer of the pattern structure such as the gate oxide film is observed. 
     Meanwhile, as a comparative example 1, the same gas process as the experimental example 1 is performed by using a HF single gas after the oxygen plasma process in the first example embodiment, and the deposit is hardly removed. 
     Now, a result of investigating processing conditions under which the deposit can be removed will be explained. First, a relationship between an amount of the methanol gas added to the processing gas and a peeling force for the deposit is investigated. As compared to a sample in which the deposit is not removed since the methanol gas is not added, it is observed that the deposit is removed in case of adding the methanol gas of, e.g., 100 sccm. Further, if the addition amount of the methanol gas is increased to, e.g., 200 sccm, the peeling force is enhanced. In this experiment, however, since the gas process is continually performed without performing the cycle process, the gate oxide film which is the pattern structure is etched and damaged. 
     Additionally, in order to investigate a relationship between the pressure of the processing gas and the peeling force for the deposit, the deposit of the sample is removed by setting the pressure to, e.g., 665 Pa (5 Torr), 1330 Pa (10 Torr) and 1995 Pa (15 Torr), respectively. As a result, it is observed that the peeling force for the deposit is increased with the rise of the pressure. In this experiment, however, since the gas process is continually performed without performing the cycle process, the gate oxide film which is the pattern structure is etched and damaged. 
     Further, in order to investigate a relationship between the temperature and the peeling force for the deposit, the deposit of the sample is removed by setting the temperature to 10° C., 30° C. and 50° C., respectively. As a result, it is found out that the peeling force for the deposit is increased as the temperature decreases. In this experiment, however, since the gas process is continually performed without performing the cycle process, the gate oxide film which is the pattern structure is etched and damaged. 
     From the above results, it is possible to determine a boundary line, for each of the processing temperatures, between a region in which the deposit removal progresses and a region in which the deposit removal does not progress, as depicted in a graph of  FIG. 6  in which a vertical axis represents a pressure and a horizontal axis indicate a flow rate of a methanol gas. If a processing condition (either one of or both of a total pressure and the flow rate of the methanol gas) is changed to pass the boundary line, it is possible to set the first period during which the deposit is removed and the second period during which the deposit is not removed in the cycle process. 
     Now, a result of investigating uniformity in the entire surface of the wafer of the deposit removing process will be discussed. As an experimental example 2, the above-described deposit removing process is performed on a semiconductor wafer W, in which a line and space pattern is formed and a deposit is deposited in spaces between the lines, by using the gas processing apparatus  200  equipped having the gas diffusion plate  206  shown in  FIG. 3A . Then, depths of the spaces between the lines are measured. The depths of the spaces are measured at a central portion and an intermediate portion of the semiconductor wafer W, and at positions of 30 mm and 4 mm away from an edge of the semiconductor wafer W, respectively. As a result, the depths are measured as follows: 
     central portion=107.2 nm 
     intermediate portion=75.4 nm 
     position of 30 mm away from the edge=74.1 nm 
     position of 4 mm away from the edge=75.4 nm 
     Accordingly, a depth difference between the central portion of the semiconductor wafer W and the position of 4 mm from the edge of the semiconductor wafer W is 31.8 nm. 
     Meanwhile, as a comparative example 2, the above-described deposit removing process is performed on a semiconductor wafer W, in which a line and space pattern is formed and a deposit is deposited in spaces between the lines, by using the gas processing apparatus  200  having the gas diffusion plate  216  shown in  FIG. 3B . Then, depths of the spaces between the lines are measured. In this comparative example 2, the deposit removing process is performed under the same conditions as those of the experimental example 2, excepting that the gas diffusion plate  216  is used. The depths of the spaces are measured at a central portion and an intermediate portion of the semiconductor wafer W, and at positions of 30 mm and 4 mm away from an edge of the semiconductor wafer W, respectively. As a result, the depths are measured as follows: 
     central portion=111.1 nm 
     intermediate portion=71.4 nm 
     position of 30 mm away from the edge=67.5 nm 
     position of 4 mm away from the edge=66.2 nm 
     Accordingly, a depth difference between the central portion of the semiconductor wafer W and the position of 4 mm from the edge of the semiconductor wafer W is 44.9 nm. 
     As can be clearly seen from the above results, in the experimental example 2, uniformity of the deposit removing process in the entire surface of the semiconductor wafer W is found to be improved, as compared to the case of the comparative example 2. 
     From the foregoing, it will be appreciated that various embodiments of the present disclosure have been described herein for purposes of illustration and are not intended to be limiting, and that various modifications may be made. By way of example, the above example embodiment and experimental examples have been described for the case of using the methanol gas as the alcohol gas, other types of alcohol gases, such as an ethanol gas or an isopropyl alcohol gas, may be utilized. 
     The example embodiment may be applicable to the field of manufacture of semiconductor devices, and, thus, has industrial applicability. 
     From the foregoing, it will be appreciated that various embodiments of the present disclosure have been described herein for purposes of illustration, and that various modifications may be made without departing from the scope and spirit of the present disclosure. Accordingly, the various embodiments disclosed herein are not intended to be limiting, with the true scope and spirit being indicated by the following claims.