Abstract:
A method for cleaning a process chamber of a plasma treatment device includes introducing gas that has been activated with a remote plasma source into a process chamber, reactivating the activated gas in the process chamber, reacting the reactivated gas with a deposit inside the process chamber and exhausting the reacted gas.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a cleaning method and a cleaning device that removes unwanted Chemical Vapor Deposition (CVD) film accumulated in a process chamber of a plasma treatment device using plasma.  
         [0003]     2. Description of the Related Art  
         [0004]     Conventionally, a method for cleaning a CVD device that forms a CVD thin film on a semiconductor substrate is performed by the following manner, for example, in manufacturing of silicon oxide film using a plasma CVD method. A silicon substrate or the like on which a CVD film is deposited is put into a vacuum chamber in which a pair of electrodes whose surface is insulated are provided in parallel, and the temperature is kept constant. After vacuuming inside the chamber, a monosilane and a nitrogen monoxide are flowed. After achievement of a gas flow rate and the pressure at a fixed value, a radio frequency (RF) is applied to the electrodes. Silicon oxide film is grown by a vapor phase epitaxy while keeping the condition for a given time. Then, the RF application is stopped. After exhausting the gas inside the vacuum chamber by vacuuming, the silicon substrate is taken out.  
         [0005]     Then, the excess silicon oxide film adhering inside the chamber is cleaned by a plasma cleaning method as follows. After taking out the substrate from the chamber, a mixture gas of fluorine etching gas such like C2F6, CF4, NF3, or the like, and O2 or Ar is flowed. The RF is applied so as to perform the plasma cleaning by etching and removing the excess silicon oxide film formed inside the vacuum chamber.  
         [0006]     Here, a chamber cleaning of the CVD device will be explained. In cleaning the chamber for the thin film forming (hereinafter referred to as process chamber) of the CVD device, deposits such like silicon oxide film and silicon nitride film accumulated inside the chamber are reacted with the cleaning gas in the CVD process, being removed.  
         [0007]     The cleaning method, while several methods are applicable, is classified into two types. One is an in-situ plasma cleaning method in which plasma is generated inside the process chamber, and the other is a remote plasma cleaning method performed with gas converted to plasma outside the process chamber.  
         [0008]     For cleaning gases, CF4, C2F6, C3F8, C4F8, and NF3 are representatively exemplified. C2F6 is mainly used for the in-situ plasma method. NF3 is used for the remote plasma method.  
         [0009]     The cleaning gases used for the above-mentioned plasma cleaning methods are included in global warming gases. Thus, they need to be turned out to be harmless (detoxication) from an environmental point of view.  
         [0010]     In the in-situ method in which plasma is generated inside the process chamber, a destruction efficiency of the cleaning gas to plasma is nearly from 30 to 50%. The percentage of efficiency in using the gas that actually contributes to the cleaning is nearly from 15 to 30%. Therefore, more than half of the amounts of the cleaning gas used are exhausted unchanged. Since the cleaning gas is a global warming gas, it needs to be detoxified.  
         [0011]     One of the solutions for global warming gas reduction is the remote plasma using NF3. Since 90% and above of NF3 are decomposed by this method, the method can reduce the global warming gas in the exhausted gas. However, since NF3 gas converted to plasma outside the process chamber is introduced into the process chamber with a pipe, the gas collides with a pipe wall or the like before entering the process chamber, losing activation energy. As a result, the gas is so inactive that NF3 is decomposed into N2, F2, F * , and F * 2, or the like. Accordingly, the percentage of efficiency in use of NF3 for cleaning becomes extremely low, approximately 10%. Almost all of F3 are changed to F2 so as to be detoxified in factory scrubber facilities without utilization even though high destruction efficiency of NF3 itself. In sum, NF3 has the problem of low efficiency in use.  
         [0012]     Taking the aforesaid situation into account, the present invention is aimed to provide a cleaning method and a cleaning device that are capable of increasing efficiency in use of cleaning gases while maintaining benefits of the remote plasma method for global warming gas reduction.  
       SUMMARY OF THE INVENTION  
       [0013]     A method for cleaning a process chamber of a plasma treatment device according to a first aspect of the invention includes the following steps. First, gas activated in a remote plasma source is introduced into the process chamber. Then, the gas is reactivated in the process chamber. Subsequently, the gas is reacted with deposits inside the process chamber. Finally, the reacted gas is exhausted.  
         [0014]     The cleaning method of the first aspect of the invention can increase efficiency in use of gas by the following manner. The gas, for example, including fluorine (F) is converted to plasma with the remote plasma source. The gas that becomes inactive during the process from the remote plasma source to the process chamber of the plasma treatment device is converted to plasma again (reactivated) in the process chamber so as to enhance the reaction of cleaning gas with the deposits, thereby enabling efficiency in use of the gas to be increased.  
         [0015]     A cleaning method of a process chamber of a plasma treatment device of a second aspect of the invention includes a first activation step in which the gas supplied to the process chamber is activated with a first plasma source and a second activation step in which the gas that has been activated is reactivated with a second plasma source in the process chamber. A reaction step is provided in which the gas activated in the second activation step is reacted with a deposit inside the process chamber, and an exhausting step is provided in which a reacted product that has been produced in the reaction step is exhausted.  
         [0016]     The cleaning method of the second aspect of the invention can increase efficiency in use of gas by the following manner. The gas including fluorine (F) is converted to plasma (activated) with the remote plasma source. The gas that becomes inactive during the process to be introduced into the process chamber of the plasma treatment device is converted to plasma again (reactivated) in the process chamber so as to enhance the reaction of cleaning gas with the deposits, thereby enabling efficiency in use of the gas to be increased.  
         [0017]     In addition, it is preferable that the cleaning method further includes a detoxifying step in which the exhausted gas is turned out to be harmless.  
         [0018]     This makes it possible to turn out the exhausted gas to be harmless, thereby being exhausted.  
         [0019]     Also, it is preferable that the cleaning method further includes a third activation step. The third activation step is provided between the first activation step and the second activation step. In the third activation step, the activated gas is led out from the first plasma source with a plurality of pipes. Then, the gas is further activated with a plurality of third plasma sources each of which is provided to each of the plurality of pipes so as to proceed to the second activation step.  
         [0020]     The cleaning method can further increase efficiency in use of gas for cleaning by the following manner. The gas including fluorine (F) is converted to plasma with the remote plasma source. The gas that becomes inactive during the process from the remote plasma source to the CVD process chamber is converted to plasma (activated) again immediately before the process chamber. Then, the gas is converted to plasma (activated) again, thereby enabling efficiency in use of the gas for cleaning to be further increased.  
         [0021]     A cleaning device for a process chamber of a plasma treatment device of a third aspect of the invention includes a first plasma source activating the gas supplied to the process chamber, a second plasma source reactivating the activated gas in the process chamber, and an exhausting device exhausting a reacted product produced by the reaction of the gas reactivated by the second plasma source with a deposit inside the process chamber.  
         [0022]     The cleaning device can increase efficiency in use of gas for cleaning by the following manner. The gas including fluorine (F) is converted to plasma with the remote plasma source. The gas that becomes inactive during the process from the remote plasma source to the process chamber of the plasma treatment device is converted to plasma (activated) again in the process chamber, thereby enabling efficiency in use of the gas for cleaning to be increased.  
         [0023]     In addition, it is preferable that the cleaning device further includes a detoxification device to turn out the exhausted gas to be harmless.  
         [0024]     This makes it possible to turn out the exhausted gas to be harmless, thereby being exhausted.  
         [0025]     In addition, it is preferable that the cleaning device further includes a third plasma source. The third plasma source is provided between the first plasma source and the second plasma source. In the third plasma source, the activated gas is led out from the first plasma source with a plurality of pipes in each of which the gas is further activated so as to be supplied to the second plasma source.  
         [0026]     The cleaning device can further increase efficiency in use of gas for cleaning by the following manner. The gas including fluorine (F) is converted to plasma with the remote plasma source. The gas that becomes inactive during the process from the remote plasma source to the process chamber of the plasma treatment device is converted to plasma (activated) again immediately before the process chamber. Then, the gas is converted to plasma (activated) again in the process chamber, thereby enabling efficiency in use of the gas for cleaning to be further increased. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]      FIG. 1  is a diagram explaining a cleaning method of a first embodiment of the present invention.  
         [0028]      FIG. 2  is a diagram explaining the principle of the cleaning method of the first embodiment of the present invention.  
         [0029]      FIG. 3  is a diagram explaining a cleaning method of a second embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]     Embodiments of the present invention applied for a CVD device will be explained with reference to the drawings.  
         [0031]     A method for cleaning a process chamber of a CVD device according to the embodiments of the invention includes the following steps. First, gas activated in a remote plasma source is introduced into the process chamber. Then, the gas is reactivated in the process chamber. Subsequently, the gas is reacted with deposits inside the process chamber. Finally, the reacted gas is exhausted.  
         [0000]     (First Embodiment)  
         [0032]      FIG. 1  is a diagram explaining a cleaning method of a first embodiment of the invention. In the embodiment, the method for cleaning the process chamber of the CVD device will be explained. As for the CVD device, a cleaning device for the plasma CVD device is exemplified.  
         [0033]     As shown in  FIG. 1 , a cleaning device  10  includes a plasma CVD device  11  and a remote plasma generator  30 . The plasma CVD device  11  includes a process chamber  12  kept in vacuum condition (reduce pressure condition), which can be kept at a constant vacuum condition (reduced condition) by exhausting gas from inside the chamber to the outside through an exhaust gas path  13  provided at a bottom wall  12   c  of the process chamber  12 , a high vacuum pump  14 , a lower vacuum pump  15 , and a detoxification device  16 . The detoxification device  16  is the device to turn out the exhausted gas to be harmless and to exhaust it to the outside in an exhausting process before CVD film deposition or after cleaning.  
         [0034]     Inside the process chamber  12 , a lower electrode  17  is provided. The lower electrode  17  serves as a placement stage on which a substrate P is placed. The substrate P is, for example, a silicon wafer on which silicon thin film is deposited (including by vapor deposition). The lower electrode  17  is provided, passing through the bottom wall 12   c  of the process chamber  12 . Sealing elements (not shown) such as a seal ring or the like are provided between the lower electrode  17  and the bottom wall  12   c  to maintain a degree of vacuum inside the process chamber  12 .  
         [0035]     An upper electrode  18  is provided at the upper side of the process chamber  12 . A proximal end  19  of the upper electrode  18  passes through an upper wall  12   a  of the process chamber  12  to connect a radio frequency power supply  20  provided outside the process chamber  12 . A radio frequency apply device  21  such as a radio frequency coil (not shown) is provided to the upper electrode  18 . A matching circuit  22  is provided between the radio frequency apply device  21  and the radio frequency power supply  20 . The matching circuit  22  can transmit the radio frequency generated with the radio frequency power supply  20  to the radio frequency apply device  21  such as the radio frequency coil without loss.  
         [0036]     In addition, a raw gas supply path  23  is provided at the wall of the process chamber  12 , for example, at the upper wall  12   a . This makes it possible to introduce raw gas to the inside of the process chamber  12  kept at a reduced pressure state from a raw gas supply source (not shown). The raw gas supply path  23  may pass through the upper electrode  18  such that the raw gas flows into the process chamber  12  through the upper electrode  18 . The process chamber  12 , the radio frequency power supply  20 , the radio frequency apply device  21 , the lower electrode  17 , and the upper electrode  18  are included in a second plasma source of the plasma cleaning as well as in the CVD plasma source.  
         [0037]     In addition, a remote plasma generator  30  in which fluorine cleaning gas is converted to plasma is provided at a side of the process chamber  12 . The cleaning gas converted to plasma with the remote plasma generator  30  can be introduced into the chamber  12  from, for example, a sidewall  12   b  of the process chamber  12  through a pipe  31  included in a gas path.  
         [0038]     The remote plasma generator  30  is used as a first plasma source when the plasma cleaning is performed inside the chamber after taking out the substrate P on which the film has been deposited, while the remote plasma generator  30  is not used for CVD film forming. The above-mentioned plasma source including the process chamber  12 , the radio frequency power supply  20 , the radio frequency apply device  21 , the lower electrode  17 , and the upper electrode  18  functions not only as the plasma source at CVD film forming but also as the second plasma source at the plasma cleaning. The second plasma source plays a role to reactivate the gas that has been activated (converted to plasma) with the remote plasma source in the chamber  12  at the plasma cleaning.  
         [0039]     The plasma CVD device  11  of the cleaning device  10 , which is constructed as above-mentioned, according to the invention operates as follows.  
         [0040]     The substrate P, which is, for example, a silicon wafer on which a silicon thin film is deposited, is placed on the placement stage of the lower electrode  17  in the process chamber  12 .  
         [0041]     The inside of the process chamber  12  is kept at a constant vacuum condition (reduced pressure condition), for example, from 10 to 2000 Pa by exhausting gas from inside the chamber to the outside through the exhaust gas path  13  provided at the bottom wall  12   c  of the process chamber  12 , the pump  14 , the pump  15 , or the like. Then, raw gas is introduced into the process chamber  12  from the raw gas supply source (not shown) through the raw gas supply path  23 .  
         [0042]     In this case, the raw gases supplied from the raw gas supply source (not shown) are exemplified as follows. Monosilane (SiH4), N2O, N2, O2, Ar, or the like, are supplied for forming silicon oxide (SiO2). Monosilane (SiH4), NH3, N2, O2, and Ar are supplied for forming silicon nitride (Si3N4 or the like). However, the raw gas is not limited to these gases. Depending on the thin film to be formed, for example, disilane (Si2H6), tetraethoxysilane (TEOS; Si(OC2H5)4), or the like, can be used for raw gas. O2,O3, or the like, can be used for carrier gas.  
         [0043]     The radio frequency apply device  21  such as the radio frequency coil or the like generates a radio frequency electric field at the upper electrode  18  using the radio frequency generated with the power supply  20 . The electric field triggers excitation of a raw gas to be at a highly active plasma state (hereinafter referred to as activated reactive gas). The activated reactive gas acts to form a silicon thin film on the surface of the substrate P such as a silicon wafer placed on the lower electrode  17 .  
         [0044]     In such a plasma CVD device  10 , thin film materials such like SiO2, Si3N4, or the like, adhere on the inside wall, the surface of the electrodes, or the like of the process chamber  12 , other than the semiconductor substrate P to be deposited, due to the discharge inside the process chamber  12  in a film forming process. If the deposits grow to a certain thickness, they are peeled off and scattered by their own weight or stress, or the like. This causes fine particles mixing and contamination in the substrate P, which is, for example, a semiconductor substrate, as foreign materials in the film forming process. As a result, a high quality film cannot be manufactured. Also, this causes a wire break or an electrical short in a semiconductor circuit, thereby adversely affecting a yield drop.  
         [0045]     Consequently, in the cleaning device  10  of the plasma CVD device  11 , fluorine cleaning gas, for example, NF3 is converted to plasma with the remote plasma generator  30  so as to be introduced into the process chamber  12  kept at a reduced pressure through the pipe  31 . In the remote plasma generator  30 , a radio frequency electric field is formed so as to act with the cleaning gas to be activated reactive gas. For example, NF3 is decomposed into N2, F2, F * , F * 2, or the like. They are reacted with the deposits such like SiO2, Si3N4, or the like, which are stuck and deposited on the inside wall and the surface of the electrodes of the process chamber  12 , so as to convert the deposits to gas such as volatile SiF4. Thus, the deposits can be exhausted to the outside of the process chamber  12  as exhausted gas through the exhaust gas path  13 , the pump  14 , the pump  15 , and the detoxification device  16 .  
         [0046]     In this cleaning method, the cleaning gas is decomposed to the activated reactive gas with the remote plasma generator  30  that is the remote plasma source. Then the reactive gas is introduced into the process chamber  12 . The activated cleaning gas touches on and collides with the inside wall of the pipe  31  whose length is approximately 50 cm, losing active energy. As a result, the efficiency in which the deposits in the chamber  12  are converted to gas with a reaction is dropped. In order to prevent this, in the cleaning device  10  of the invention, the gas activated in the remote plasma generator  30  is further activated (namely, reactivated) by performing the in-situ plasma in process chamber  12  simultaneously with the introduction of the gas into the process chamber  12 . The re-activation of the cleaning gas is performed by the following way. The activated reactive gas generated by the remote plasma is introduced into the process chamber  12 . The radio frequency (RF) is supplied to the radio frequency apply device  21  so as to be applied to the upper electrode  18 .  
         [0047]     In sum, the present invention is characterized in the following manner. The gas including fluorine (F) is converted to plasma with the remote plasma source. The gas that becomes inactive during the process from the remote plasma source to the CVD process chamber is converted to plasma (activated) again in the process chamber, thereby increasing efficiency in use of gas for cleaning.  
         [0048]     In this case, as for the fluorine gases converted to plasma with the remote plasma generator  30 , CF4, C2F6, C3F8, C4F8, or the like, are exemplified other than NF3.  
         [0049]     Another gas can be mixed and used for the cleaning gas without adversely affecting the effect of the invention. O2, Ar, or the like, are exemplified as another gas. A blending amount of another gas is not limited to any amount. The blending amount of another gas is determined depending on the amount, the thickness of the deposits stuck on the inside wall, or the like of the process chamber  12  of the CVD device  11 , the types of gas including fluorine, composition of the deposits, or the like.  
         [0050]      FIG. 2  is a diagram explaining the principles of the cleaning method of the first embodiment of the invention.  
         [0051]     The cleaning gas including fluorine (F) such like NF3, or the like, is introduced to the remote plasma generator  30  that is the first plasma source so as to be converted to plasma. For example, NF3 is decomposed into N2, F2, F * , F * 2, or the like. The activated gas and F2 are introduced into the process chamber  12  including the second plasma source. The second plasma source generates plasma again in the process chamber  12  to generate F2 plasma. The F2 plasma enhances the reaction with the excess deposits accumulated on the inside wall, or the like of the process chamber  12 . If the in-situ plasma is not generated by the second plasma in the process chamber  12 , almost all of the F2 among the gases decomposed with the first plasma source are exhausted unchanged without use. However, the cleaning method of the invention can utilize F2 efficiently, thereby enabling efficiency in use of gas to be increased.  
         [0000]     (Second Embodiment)  
         [0052]      FIG. 3  is a diagram illustrating a cleaning device to explain a cleaning method of a second embodiment of the invention. In  FIG. 2 , the same code is given to the part that is same as that in  FIG. 1  for explanation.  
         [0053]     In  FIG. 3 , the cleaning device  10 A includes the plasma CVD device  11 , the remote plasma generator  30 , and a plurality of plasma sources, each of which is correspondingly provided to each of a plurality of pipes that connect the plasma CVD device  11  and the remote plasma generator  30 . Specifically, activated gas is led out from the remote plasma generator  30 , which is the first plasma source, through a plurality of pipes. In this case, four pipes, namely, pipes  32 ,  33 ,  34 , and  35  are shown in  FIG. 2 . The plurality of plasma sources are provided to the pipes correspondingly to be a third plasma source. In this case, four plasma sources, namely, plasma sources  36 ,  37 ,  38 , and  39  are shown in  FIG. 2 . Each of the plurality of plasma sources is provided to each of the plurality of pipes so as to be close to the process chamber  12 . Thus, the activated gas from the remote plasma generator  30  is further activated with the third plasma source (plasma sources  36 ,  37 ,  38 , and  39 ) and then supplied to the second plasma source included in the process chamber  12 .  
         [0054]     In  FIG. 3 , cleaning is performed by the following manner.  
         [0055]     The cleaning gas supplied to the process chamber, for example, NF3 is activated with the remote plasma generator  30  that is the first plasma source. The activated and decomposed gas, for example, N2, F2, F * , F * 2 are led out with the pipes  32 ,  33 ,  34 , and  35 . The gas is further activated with the plasma sources  36 ,  37 ,  38 , and  39 , each of which is provided to each pipe to be the third plasma source. Then, the gas is introduced into the process chamber  12 . Subsequently, the gas is activated again by the second plasma source included in the process chamber  12  using the in-situ plasma method. The gas activated by the second plasma source is reacted with the deposits inside the process chamber  12 . The reacted product is exhausted with the pump  14  and  15 . In addition, the exhausted gas is turned out to be harmless with the detoxification device  16 , exhausted to the outside.  
         [0056]     The embodiment shown in  FIG. 3  enables the deposits inside the chamber to be more efficiently reacted and more effectively converted to gas for exhausting as compared with the embodiment shown in  FIG. 1  by the following way. The remote plasma generator  30  that is the first plasma source and the second plasma source included in the process chamber  12  are connected with the pipes  32 ,  33 ,  34 , and  35 . The third plasma sources  36 ,  37 ,  38 , and  39  is correspondingly provided to the pipes  32 ,  33 ,  34 , and  35 , which connects the first plasma source and the second plasma source. Thus, the cleaning gas activated with the remote plasma generator  30  is further activated with the plasma sources  36 ,  37 ,  38 , and  39 , which is provided to close the process chamber  12 . Then, the gas is activated again with the second plasma source included in the process chamber  12 . In this way, the activated gas that is efficiently decomposed with the remote plasma source can be equally introduced into the chamber  12  with the pipes  32 ,  33 ,  34 , and  35 . Also, the decomposed gas can be introduced into the chamber  12  without an inactive state. Further, the gas is activated again by the in-situ plasma in the process chamber  12 .  
         [0057]     In the above-mentioned embodiments, a radio frequency (RF) electric field is used to generate plasma in the plasma source. Instead of this plasma source, an Electron-Cyclotron-Resonance (ECR) may be used as the plasma source so as to generate high density, hyperactive plasma under high vacuum. Using this plasma, the CVD method and plasma cleaning may be performed.  
         [0058]     In the above-mentioned embodiments, the second plasma source including the radio frequency power supply  20  used for film forming by plasma CVD is used for plasma cleaning in order to clean and remove the unwanted deposits accumulated inside the process chamber of the plasma CVD device. However, a radio frequency power supply for cleaning, for example, which has a frequency or an output different from the radio frequency for plasma CVD film forming, may be separately provided.  
         [0059]     In addition, if the radio frequency power supply and the radio frequency apply device that are different from those for plasma CVD film forming are used, the CVD device is not limited to the CVD device using the plasma CVD method. The deposits inside the chamber of the CVD device using a normal pressure CVD method, a reduced pressure CVD method, a photo excitation CVD method, a thermal decomposition CVD method, or the like, can be efficiently removed in addition to the CVD device using the plasma CVD method.  
         [0060]     The present invention is not limited to the above-mentioned embodiments. There may be many modifications, changes, and alterations without departing from the scope or spirit of the present invention.