Abstract:
A plasma etching method includes the steps of exciting an etching gas introduced in a processing vessel into a plasma, the etching gas including 1,1,1,4,4,5,5,5-octafluoro-2-pentyne, and carrying out a plasma etching on a film on a target object accommodated in the processing vessel via opening patterns of a resist mask on the film. Therefore, it is possible to perform plasma etching having a high selectivity to resist and/or suppressing the etch stop.

Description:
[0001]     This application is a Continuation Application of PCT International Application No. PCT/JP03/02750 filed on Mar. 7, 2003, which designated the United States. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to a method of plasma etching in the fabrication process of a semiconductor device.  
       BACKGROUND OF THE INVENTION  
       [0003]     Conventionally, as an etching gas for plasma etching a SiO 2  film on a substrate to be processed via opening patterns of a photoresist mask, a gas species such as fluorocarbon gas, particularly, a high order species gas such as C 4 F 6  or C 4 F 8 , cyclo-C 5 F 8  (octafluorocyclopentyne) and the like as the major component has been used, so as to achieve a high selectivity of SiO 2  film (etching rate of SiO 2  film/etching rate of photoresist) over photoresist material and to improve the quality of microprocessing.  
         [0004]     However, for a gas species containing C 4 F 6 , C 4 F 8 , cyclo-C 5 F 8  and the like as the major component, it is not possible to improve the photoresist selectivity while trying to maintain better microprocessing results.  
         [0005]     Further, in case of using a gas species containing C 4 F 6 , C 4 F 8 , cyclo-C 5 F 8  and the like as the major component, if the amount of C 4 F 6 , C 4 F 8 , cyclo-C 5 F 8  is increased to achieve a higher etching rate, as etching proceeds, etching byproducts become deposited in etching holes, thereby lowering the etching rate. The etching rate would continuously slow down and arrive at so-call etch stop, where the etching process is finally terminated.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention has been developed with such background. It is therefore an object of the present invention to provide a plasma etching method having a high selectivity to photoresist and/or capable of suppressing an etch stop.  
         [0007]     In accordance with a preferred embodiment of the present invention, there is provided a plasma etching method, including the steps of: exciting an etching gas introduced in a processing vessel into a plasma, the etching gas including an aliphatic C 5 F 8  but not including CO; and carrying out a plasma etching on a film on a target object accommodated in the processing vessel via opening patterns of a resist mask disposed on the film, wherein the aliphatic C 5 F 8  is 1,1,1,4,4,5,5,5-octafluoro-2-pentyne.  
         [0008]     It is not preferable that CO is included in the etching gas containing the aliphatic C 5 F 8  as a major component, since the etch stop is likely to occur. Accordingly, in accordance with the present invention, a plasma of the etching gas including the aliphatic C 5 F 8  but not including CO is used, so that a plasma etching having a high selectivity to photoresist and/or capable of suppressing an etch stop is realized.  
         [0009]     Here, the etching gas may contain O 2 , or contain He, Ne, Ar, N 2 , or the like.  
         [0010]     In accordance with another preferred embodiment of the present invention, there is provided a plasma etching method, including the steps of: exciting an etching gas introduced in a processing vessel into a plasma, the etching gas including an aliphatic C 5 F 8 , O 2 , and an inert gas; and carrying out a plasma etching on a film on a target object accommodated in the processing vessel via opening patterns of a resist mask disposed on the film, wherein the aliphatic C 5 F 8  is 1,1,1,4,4,5,5,5-octafluoro-2-pentyne.  
         [0011]     As the aliphatic C 5 F 8 , the following may be acceptable: CF≡CC 3 F 7  (1,3,3,4,4,5,5,5-octafluoro-1-pentyne), CF 3 C≡CC 2 F 5  (1,1,1,4,4,5,5,5-octafluoro-2-pentyne), CF 2 ═C═CFC 2 F 5  (1,1,3,4,4,5,5,5-octafluoro-1,2-pentadiene), CF 2 ═CFCF═CFCF 3  (1,1,2,3,4,5,5,5-octafluoro-1,3-pentadiene), CF 2 ═CFCF 2 CF═CF 2  (1,1,2,3,3,4,5,5-octafluoro-1,4-pentadiene), CF 3 CF═C═CFCF 3  (1,1,1,2,4,5,5,5-octafluoro-2,3-pentadiene), or the like can be used. However, CF 3 C≡CC 2 F 5  is suitable for use, since it can be relatively easily produced.  
         [0012]     In case where CF 3 C≡CC 2 F 5  is employed and the etching gas contains O 2 , it is preferred that a flow rate ratio of the CF 3 C≡CC 2 F 5  to the O 2  is in the range from about 0.79 to about 1.12. If the ratio is less than about 0.79, a selectivity to resist becomes small and an etch stop is likely to occur. In fact, when the ratio was about 0.68 and less corresponding to a value less than about 0.79, a selectivity to resist became small. On the other hand, when the ratio was about 1.32 corresponding to a value greater than about 1.12, the etch stop was likely to occur. Even though the test is not performed in case where the ratio is about 1.32 or greater, it is considered that the etch stop is likely to occur, as the ratio is high. An inner pressure of a processing vessel is preferably greater than or equal to about 2.67 Pa (about 20 mTorr), and more preferably, about 2.67 to about 4 Pa (about 20 to about 30 mTorr).  
         [0013]     In accordance with still another preferred embodiment of the present invention, there is provided a plasma etching method, including the steps of: exciting an etching gas introduced in a processing vessel into a plasma, the etching gas including 1,1,1,4,4,5,5,5-octafluoro-2-pentyne; and carrying out a plasma etching on a film on a target object accommodated in the processing vessel via opening patterns of a resist mask disposed on the film.  
         [0014]     The etching gas may contain O 2 . In this case, it is preferred that a flow rate ratio of the 1,1,1,4,4,5,5,5-octafluoro-2-pentyne to the O 2  is in the range from about 0.79 to about 1.12. Further, it is preferred that the CF 3 C≡CC 2 F 5  partial pressure is in the range from about 0.0746 to about 0.105 Pa (about 0.56 to about 0.79 mTorr). If the CF 3 C≡CC 2 F 5  partial pressure is less than about 0.0746 Pa, a selectivity to resist becomes small, and if it is greater than about 0.105 Pa, an etch stop is likely to occur. In fact, when the CF 3 C≡CC 2 F 5  partial pressure was about 0.0626 Pa (about 0.47 mTorr) or about 0.0653 Pa (about 0.49 mTorr) corresponding to a value smaller than about 0.0746 Pa, the selectivity to resist became small. On the other hand, when the CF 3 C≡CC 2 F 5  partial pressure was about 0.119 Pa (about 0.88 mTorr) corresponding to a value greater than about 0.105 Pa, the etch stop was likely to occur. Even though the test is not performed in case where the partial pressure is greater than about 0.119 Pa, it is considered that the etch stop is likely to occur, as the partial pressure is high.  
         [0015]     While the etching gas may contain O 2 , preferably, it does not contain CO, substantially. The reason is that the etch stop is likely to occur due to CO.  
         [0016]     In the aforementioned preferred embodiments of the present invention, as a film to be etched, there may be used an oxide film (oxygen compound) such as SiO 2 , TEOS, BPSG, PSG, SOG, thermal oxide film, HTO, FSG, organic silicon oxide film, CORAL (Novellus system), or the like; a low-k organic insulating film; or the like. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments, given in conjunction with the accompanying drawings, in which:  
         [0018]      FIG. 1  shows a schematic cross sectional view of a plasma etching apparatus in accordance with the present invention; and  
         [0019]      FIG. 2  is a schematic cross-sectional view of the portion of a target object, which is subject to etching. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]     Hereinafter, a preferred embodiment of the present invention will be described with reference to the accompanying drawings.  
         [0021]      FIG. 1  shows a schematic cross sectional view of a plasma etching apparatus in accordance with the present invention. A processing vessel  2 , which is frame grounded, is formed of metal, e.g., aluminum whose surface is oxidized. In the bottom portion inside the processing vessel  2 , a susceptor  5  serving as a lower electrode of a parallel plate electrode is installed having an insulator  3  interposed between the susceptor and the bottom portion of the vessel. A high pass filter (HPF)  6  is connected to the susceptor  5 . An electrostatic chuck  11  is installed on the susceptor  5 , and a target object W, e.g., a semiconductor wafer or the like, is mounted on the electrostatic chuck. The electrostatic chuck  11  is formed of an insulator having an electrode  12  embedded therein, and electrostatically adsorbs the target object W by applying a DC voltage from a DC power supply  13  connected to the electrode  12 . Further, a focus ring  15  is disposed such that it surrounds the target object W. The focus ring  15  is made of Si, SiO 2 , or the like, and is there to improve etching uniformity.  
         [0022]     Further, an upper electrode  21  is installed above the susceptor  5  so that the two electrodes face each other. The upper electrode  21  is fixed at the upper part of the processing vessel  2  via an insulator  22 , and is formed of a showerhead-shaped electrode plate  24  and a supporter  25  for holding the electrode plate  24  in place.  
         [0023]     In the central part of the supporter  25 , a gas inlet port  26  is installed. To the gas inlet port  26 , the following components are connected in the given order: a gas supply line  27 , a valve  28 , a mass flow controller  29 , and an etching gas supply source  30 . From the etching gas supply source  30 , an etching gas including aliphatic C 5 F 8  but without CO is supplied. Further, it is also acceptable that the etching gas contains O 2 . As an aliphatic C 5 F 8  species, as discussed above, the following are acceptable: CF≡CC 3 F 7 , CF 3 C≡CC 2 F 5 , CF 2 ═C═CFC 2 F 5 , CF 2 ═CFCF═CFCF 3 , CF 2 ═CFCF 2 CF═CF 2 , CF 3 CF═C═CFCF 3 , or the like can be used. However, CF 3 C≡CC 2 F 5  is preferable.  
         [0024]     In case of using an etching gas containing CF 3 C≡CC 2 F 5  and O 2 , it is preferred that a volumetric ratio of the CF 3 C—CC 2 F 5  to the O 2  [CF 3 C≡CC 2 F 5  flow rate)/[O 2  flow rate] is in the range from about 0.79 to about 1.12. Further, it is acceptable that the etching gas contains Ar.  
         [0025]     In case of using the CF 3 C≡CC 2 F 5  as the aliphatic C 5 F 8  species, although it is not necessary to exclude CO from the etching gas, still, it is preferable not to include CO. Further, in case of using the CF 3 C≡CC 2 F 5 , it is preferable that the partial pressure of the species is in the range from about 0.0746 to about 0.105 Pa.  
         [0026]     In addition, to the bottom part of the processing vessel  2 , a gas exhaust line  31  is connected, and a gas exhaust unit  35  is connected to the gas exhaust line  31 . Further, a gate valve  32  is disposed in the sidewall of the processing vessel  2 , so that the target object W can be transported to a neighboring load-lock chamber (not shown).  
         [0027]     To the upper electrode  21 , a low pass filter (LPF)  42  and a first high frequency power source  41  via a matching unit  41  are connected, respectively. A second high frequency power source  50  is connected to the susceptor  5 , which is the lower electrode, via a matching unit  51 .  
         [0028]     Hereinafter, a process for plasma etching of a SiO 2  film  61  on the target object W shown in  FIG. 2  through opening patterns of a resist mask  62 , by using the aforementioned plasma etching apparatus  1 , will be discussed.  
         [0029]     The gate valve  32  is opened to load the target object W into processing vessel  2  and then the object W is mounted on the electrostatic chuck  11 . Subsequently, the gate valve  32  is closed, and the inside of the processing vessel  2  is depressurized by the gas exhaust unit  35 . Thereafter, the valve  28  is opened to supply the etching gas, e.g., CF 3 C≡CC 2 F 5 , O 2 , and Ar, from the etching gas supply source  30 , so that the pressure in the processing vessel  2  reaches a predetermined level, preferably greater than or equal to about 2.67 Pa, and more preferably, about 2.67 to about 4 Pa.  
         [0030]     In such a condition, high frequency power is supplied to the upper electrode  21  and the susceptor  5 , serving as the lower electrode, and thereafter, the etching gas is excited to generate a plasma to etch the SiO 2  film  61  on the target object W. Also, before or after supplying high frequency power to the upper and lower electrodes, a DC voltage is applied to the electrode  12  inside the electrostatic chuck  11  from the DC power supply  13  to electrostatically adsorb the target object W on the electrostatic chuck  11 .  
         [0031]     In the course of etching, a predetermined emission intensity is detected by using an endpoint detector (not shown), and based on the result, the etching is stopped.  
         [0032]     In the present embodiment, the SiO 2  film  61  is etched through opening patterns of the resist mask  62 , by using the plasma generated from an etching gas containing an aliphatic species such as C 5 F 8 , preferably, CF 3 C≡CC 2 F 5 . Accordingly, it becomes possible to perform a plasma etching having a high selectivity to photoresist and/or suppressing an etch stop.  
         [0033]     Further, the configuration of the etching apparatus is not limited to that of  FIG. 1 .  
         [0034]     Hereinafter, the preferred embodiment of the present invention will be discussed in detail.  
       EMBODIMENT 1  
       [0035]     Frequency of the high frequency power source, which applies power to the upper electrode: 60 MHz  
         [0036]     High frequency power applied to the upper electrode: 1800 W  
         [0037]     Frequency of the high frequency power source, which applies power to the lower electrode: 2 MHz  
         [0038]     High frequency power applied to the lower electrode: 1800 W  
         [0039]     Temperature of the susceptor: −10° C.  
         [0040]     Pressure inside the processing vessel: 2.67 Pa (20 mTorr)  
         [0041]     Flow rates of etching gas components:  
         [0042]     CF 3 C≡CC 2 F 5 : 0.013 to 0.034 L/min (13 to 34 sccm);  
         [0043]     O 2 : 0.019 to 0.038 L/min (19 to 38 sccm); and  
         [0044]     Ar: 0.5 L/min (500 sccm)  
         [0045]     Under these etching process conditions, as shown in  FIG. 2 , the SiO 2  film on the target object W was etched via the opening patterns of the photoresist mask. The results are shown below in TABLE 1.  
         [0046]     Further, in TABLE 1, the ‘etching penetration’ refers to whether or not a SiO 2  film having an opening size (or diameter) of 0.1 μm and a thickness of 2.0 μm could be etched. Namely, in case where the film could be penetrated by etching, ‘etching penetration’ is marked with ‘O’ whereas in case an etch stop occurs, it is marked with ‘X’ (same in TABLE 2).  
                                                                                                   TABLE 1                                               [CF 3 C≡CC 2 F 5     Selectivity                       Flow rate]/   to resist               CF 3 C≡CC 2 F 5     O 2     [O 2  flow   (−)   Etching                flow rate   flow rate   rate]   Flat   Shoulder   penetration       No.   (×10 −3  L/min)   (×10 −3  L/min)   (−)   part   part   ◯                    1   13   19   0.68   4.0   3.4   ◯       2   15   19   0.79   5.9   3.8   ◯       3   17   19   0.89   8.4   5.2   ◯       4   27   30   0.90   9.9   4.7   ◯       5   29   30   0.97   14.6   6.1   ◯       6   27   27   1.00   17.5   5.9   ◯       7   19   19   1.00   11.5   5.0   ◯       8   21   19   1.11   18.8   6.2   ◯       9   38   34   1.12   10.4   4.9   ◯       10   25   19   1.32   &gt;8.0   —   X                  
 
         [0047]     Based on TABLE 1, it can be confirmed that in an area where the flow rate ratio of the CF 3 C≡CC 2 F 5  to the O 2  is in the range from about 0.79 to about 1.12, the selectivity to resist is high and the etch stop is unlikely to occur. Further, in case where the flow rate ratio of the CF 3 C═CC 2 F 5  to the O 2  is about 1.32, the etch stop is likely to occur, however, given that the selectivity to resist is high, for etching a film having a small aspect ratio, i.e., [thickness of film subject to etching)/[size (or diameter) of area subject to etching], it is possible to use the ratio. In addition, in case where the flow ratio of the CF 3 C≡CC 2 F 5  to the O 2  is about 0.68, even though the selectivity to resist is not high, given that the etch stop is unlikely to occur, a thick resist film with a high aspect ratio can be etched.  
       EMBODIMENT 2  
       [0048]     Frequency of the high frequency power source, which applies power to the upper electrode: 60 MHz  
         [0049]     High frequency power applied to the upper electrode: 1800, 2170 W  
         [0050]     Frequency of the high frequency power source, which applies power to the lower electrode: 2 MHz  
         [0051]     High frequency power applied to the lower electrode: 1800, 1550 W  
         [0052]     Temperature of the susceptor: 20, −10° C.  
         [0053]     Pressure inside the processing vessel: 2 to 4 Pa (15 to 30 mTorr)  
         [0054]     Flow rates of etching gas components:  
         [0055]     CF 3 C≡CC 2 F 5 : 0.013 to 0.025 L/min (13 to 25 sccm);  
         [0056]     O 2 : 0.019 L/min (19 sccm); and  
         [0057]     Ar: 0.38 to 0.8 L/min (380 to 800 sccm)  
         [0058]     Under these etching process conditions, the same sample as that of embodiment 1 was etched. The result is shown below in TABLE 2.  
         [0059]     Further, ‘pressure’ in TABLE 2 refers to the ambient pressure around the target object W in the processing vessel, and ‘CF 3 C≡CC 2 F 5  partial pressure’ refers to the product of ‘pressure’ and ‘[CF 3 C≡CC 2 F 5  flow rate]/[total flow rate of etching gas]’.  
                                                                             TABLE 2                               O 2     Ar       CF 3 C≡CC 2 F 5                     CF 3 C≡CC 2 F 5     flow   flow       partial   Selectivity           flow rate   rate   rate   pressure   pressure   to resist   etching       No.   (×10 −3  L/min)   (×10 −3  L/min)   (×10 −3  L/min)   (Pa)   (×10 −2  Pa)   (−)   penetrability                                11   13   19   380   2.00   6.26   3.4   ◯       12   13   19   500   2.67   6.53   3.4   ◯       13   15   19   500   2.67   7.46   3.8   ◯       14   17   19   500   2.67   8.40   4.7   ◯       15   19   19   500   2.67   9.46   5.0   ◯       16   21   19   800   4.00   10.0   4.8   ◯       17   21   19   500   2.67   10.4   6.2   X       18   25   19   800   4.00   11.9   8.1   X                  
 
         [0060]     Based on TABLE 2, it can be confirmed that in an area where the CF 3 C≡CC 2 F 5  partial pressure is in the range from about 0.0746 to about 0.105 Pa, the selectivity to resist is high and the etch stop is likely to occur. Further, in case where the CF 3 C≡CC 2 F 5  partial pressure is about 0.119 Pa, even though the etch stop is unlikely to occur, given that the selectivity to resist is high, it is possible to apply the condition to etch a film which has a small aspect ratio [thickness of film subject to etching]/[distance across area subject to etching]. In addition, in case where the CF 3 C≡CC 2 F 5  partial pressure is about 0.0626 Pa, even though the selectivity to resist is not high, given that an etch stop is unlikely to occur, a thick resist film having a high aspect ratio can be sufficiently etched.  
         [0061]     As mentioned above, in accordance with the present invention, a film to be etched, e.g., a SiO 2  film having patterns formed by a resist mask, is etched by the etching gas plasma in which the aliphatic C 5 F 8  is the major component. Therefore, it is possible to perform plasma etching having a high selectivity to resist and/or suppressing the etch stop.  
         [0062]     While the invention has been shown and described with respect to the preferred embodiment, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.