Abstract:
A method of plasma etching which comprises introducing a gas containing C x F y  (X≧2) and CF 4  into a treatment chamber, and forming a plasma of the gas, to thereby subject a coating film in an article to be treated (W) being present in the treatment chamber to plasma etching through a pattern having openings placed on the coating film. The method can be used for carrying out plasma etching with the suppression of etching-stop phenomenon and without the formation of deposits in an etching hole.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a plasma etching method to be used in the manufacturing process of semiconductor devices.  
       BACKGROUND OF THE INVENTION  
       [0002]     Conventionally, a gas containing fluorocarbon as a major component has been used as etching gas to plasma etch a SiO 2  film disposed on a substrate to be processed through a pattern of openings in a photoresist.  
         [0003]     However, when the gas having fluorocarbon as a major component is used, by-products tend to accumulate in the holes during an etching process and the etching rate would slow down, thereby inducing a so-called etch stop at which point the etching process is finally terminated. Such tendency to induce an etch stop significantly increases when the hole has a diameter in the order of submicrons and thereby failing to provide microprocessing capability in accordance with the recent demands.  
         [0004]     Therefore, in order to prevent such an etch stop, adding oxygen to etching gas has been attempted to suppress the formation of by-products in the hole.  
         [0005]     However, recently, instead of photoresist, hard mask etching by using metal or metal nitride mask has been employed widely. When a gas containing fluorocarbon and oxygen is used in etching SiO 2  with metal or metal nitride as a mask, it is problematic that metal oxide deposits are formed in etching holes. Such deposits cannot be removed even by a wet cleaning process. Further, when plasma processing is performed by using a gas containing Cl, the deposits can be removed but the hard mask is etched at the same time.  
       SUMMARY OF THE INVENTION  
       [0006]     It is, therefore, an object of the present invention to provide a plasma etching method for performing a plasma etching without generation of deposits in an etching hole while preventing the etching stop.  
         [0007]     In accordance with the present invention, there is provided a plasma etching method including the step of plasma etching a film on an article to be treated accommodated in a treatment chamber through a pattern of openings of a mask made of a metal compound formed on the film by converting a gas containing C x F y (X≧2) and CF 4  introduced into the treatment chamber to a plasma.  
         [0008]     The metal compound may be a metal nitride. The metal nitride may be TiN or TaN.  
         [0009]     The gas containing C x F y  (X≧2) and CF 4  may also include N 2 . Further, the gas may also include Ar.  
         [0010]     The film on the article to be treated may be a SiO 2  film, a SiC film or a SiOC film. SiOC used herein represents a so-called organic silicon oxide which includes a main chain of —Si—O— and has an organic functional group such as a methyl group at least at a portion of side chains.  
         [0011]     C x F y  (X≧2) of the gas may be C 4 F 6 . In such a case, the gas preferably has a ratio of C 4 F 6  flow rate to CF 4  flow rate (C 4 F 6  flow rate/CF 4  flow rate) in the range from 0.12 to 0.20. That is because etching stop occurs if the ratio is greater than 0.20, and deposits (even a few) are formed in a hole or selectivity of an etching target film to a mask (etching rate of the film/etching rate of the mask) becomes decreased if the ratio is less than 0.12. C x F y  (X≧2) of the gas may be C 4 F 8  or C 5 F 8 .  
         [0012]     In accordance with the present invention, there is provided a plasma etching method including the step of plasma etching a SiO 2  film disposed on an article to be treated accommodated in a treatment chamber through a pattern of openings of a mask made of a metal compound formed on the SiO 2  film by converting a gas containing C 4 F 6  and N 2  introduced into the treatment chamber to a plasma.  
         [0013]     Further, in accordance with the present invention, there is provided a plasma etching method including the step of plasma etching a SiC film disposed on an article to be treated accommodated in a treatment chamber through a pattern of openings of a mask made of a metal compound formed on the SiC film by converting a gas containing C 4 F 6  and N 2  introduced into the treatment chamber to a plasma.  
         [0014]     Furthermore, in accordance with the present invention, there is provided a plasma etching method including the step of plasma etching a SiOC film disposed on an article to be treated accommodated in a treatment chamber through a pattern of openings of a mask made of a metal compound formed on the SiOC film by converting a gas containing C 4 F 6  and N 2  introduced into the treatment chamber to a plasma.  
         [0015]     The metal compound may be a metal nitride. The metal nitride may be TiN or TaN. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  shows a schematic cross sectional view of a plasma etching apparatus to which the present invention can be applied; and  
         [0017]      FIG. 2  shows a cross sectional view of an etching target portion of an article to be treated. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]     Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.  
         [0019]      FIG. 1  shows a schematic cross sectional view of a plasma etching apparatus  1  to which the present invention is applied. A frame grounded treatment chamber  2  is formed of metal, e.g., aluminum of which surface is oxidized. Inside the treatment chamber  2 , installed on the bottom portion thereof is a susceptor  5 , which functions as a lower electrode of parallel plate electrodes via an insulator  3 . A high pass filter (HPF)  6  is connected to the susceptor  5 .  
         [0020]     Installed on the susceptor  5  is an electrostatic chuck  11  on which an article W to be treated such as a semiconductor wafer is mounted. The electrostatic chuck  11  has an electrode  12  embedded in an insulator, wherein the electrode  12  is connected to a DC power supply  13  which applies a DC voltage to the electrode  12  so that the electrostatic chuck  11  electrostatically attracts and holds the article W to be treated thereon. Further, a focus ring  15  is placed to surround the article to be treated W. The focus ring  15  is made of Si, SiO 2  or the like, and improves etching uniformity.  
         [0021]     Further, placed above the susceptor  5  is an upper electrode  21  facing the susceptor  5 . The upper electrode  21  is installed at the upper portion of the treatment chamber  2  through an insulator  22  and includes a showerhead-shaped electrode plate  24  and a supporting body  25  for holding the electrode plate  24  in place.  
         [0022]     A gas inlet opening  26  is provided in the central portion of the supporting body  25  and is connected to a gas supply line  27 , a valve  28 , a mass flow controller  29  and an etching gas source  30  in the order provided. The etching gas source  30  supplies a gas, for example, C x F y  (X≧2), CF 4 , N 2 , Ar and the like. C x F y  (X≧2) is C 4 F 6 , C 4 F 8 , C 5 F 8 , and the like. Further, in case of using C 4 F 6 , it is preferable that a ratio of C 4 F 6  flow rate to CF 4  flow rate (C 4 F 6  flow rate/CF 4  flow rate) is 0.12 to 0.20. In case of using C 4 F 6 , N 2  can be used in lieu of CF 4 .  
         [0023]     In this case, connected to the bottom portion of the treatment chamber  2  is a gas exhaust line  31  which is connected to a gas exhaust unit  35 . Further, a gate valve  32  is disposed in a sidewall of the treatment chamber  2 , wherein the article W to be treated is transported between the treatment chamber  2  and a neighboring load-lock chamber (not shown) through the valve.  
         [0024]     Connected to the upper electrode  21  are a low pass filter (LPF)  42  and a first high frequency power supply  40  via a matching unit  41 , respectively. A second high frequency power supply  50  is connected to the susceptor  5  serving as the lower electrode via a matching unit  51 .  
         [0025]     Hereinafter, a plasma etching process using the aforementioned plasma etching apparatus  1  will be described in detail, wherein a SiO 2  film on the article to be treated is plasma etched through a pattern of openings of a mask. In this case, as shown in  FIG. 2 , there will be described a case where a SiO 2  film  62  formed on a SiN film  61  is plasma etched through a pattern of openings of a TiN mask  63 .  
         [0026]     Upon opening the gate valve  32 , the article W to be treated is loaded into the treatment chamber  2  and mounted on the electrostatic chuck  11 . Next, the gate valve  32  is closed and the treatment chamber  2  is depressurized by the gas exhaust unit  35 . Then, after opening the valve  28 , from the etching gas source  30 , the above etching gas, e.g., an etching gas containing C 4 F 6 , CF 4 , and Ar or an etching gas containing C 4 F 6 , N 2 , and Ar, is supplied.  
         [0027]     Under such conditions, a high frequency power is supplied from the high frequency power supply to the upper electrode  21  and to the susceptor serving as the lower electrode, and the SiO 2  film  62  on the article W to be treated is etched by converting the etching gas into a plasma. In this case, before or after applying the high frequency power to the upper and the lower electrode, a DC voltage is applied from the DC power supply  13  to the electrode  12  inside the electrostatic chuck  11  to thereby electrostatically attracts and holds the article W to be treated on the electrostatic chuck  11 .  
         [0028]     During the etching process, a predetermined emission intensity is detected by an endpoint detector (not shown) and the etching process is terminated based on the detected value.  
         [0029]     In the present embodiment, as described above, by using a gas containing C x F y  (X≧2) and CF 4 , or a gas-containing C 4 F 6  for C x F y  and N 2  instead of CF 4 , the SiO 2  film  62  is etched through the TiN mask  63  such that it is possible to form etching holes without the generation of deposits in the etching holes and without the occurrence of an etching stop.  
         [0030]     Further, an etching target is not limited to a SiO 2  film and, particularly, in case the film is formed of at least one component from SiO 2 , SiC and SiOC, the above results are more readily obtainable. Further, instead of using TiN as the mask, TaN or other metal nitride is also acceptable as a mask material. In addition, the configuration of the etching apparatus is not limited to that shown in  FIG. 1 .  
       Embodiments  
       [0031]     Hereinafter, preferred embodiments of the present invention will be described. 
        Frequency of high frequency power supply applied to upper electrode: 60 MHz     High frequency power applied to upper electrode: 1000 W     Frequency of high frequency power supply applied to lower electrode: 2 MHz     High frequency power applied to lower electrode: 800     Temperature of susceptor: 40° C.     Pressure in treatment chamber: 6.65 Pa (50 mTorr)     Flow rate of etching gas: C 4 F 6  is 0.018 L/min(18 sccm); CF 4  is 0.1 L/min (100 sccm); and Ar is 0.6 L/min (600 sccm).        
 
         [0039]     Under the above process conditions, as shown in  FIG. 2 , a SiO 2  film formed on a silicon wafer was etched through a pattern of openings of a TiN mask.  
         [0040]     As a result, deposits were not formed in etching holes and, further, an etching stop did not occur.  
         [0041]     Further, in case of etching with C 5 F 8  substituting C 4 F 6  in the etching gas in the above embodiment, likewise, it was possible to perform etching without the formation of deposits in etching holes and without the occurrence of etching stop as well.  
         [0042]     Further, in case of etching with N 2  substituting CF 4  in the etching gas and doubling the flow rate, i.e., 0.2 L/min (200 sccm) in the above embodiment, similarly, it was possible to perform etching without the formation of deposits in etching holes and the occurrence of etching stop.  
         [0043]     As described above, in accordance with the present invention, a film such as a SiO 2  film patterned by metal compound such as metal nitride is etched by a plasma generated from a gas containing C x F y  (X≧2) and CF 4 , or a gas containing C 4 F 6  and N 2 , whereby it is possible to prevent etching stop and form etching holes without the generation of deposits in the etching holes.  
         [0044]     While the invention has been shown and described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be without departing from the spirit and scope of the invention as defined in the following claims.