Abstract:
A dry etching method involves plasma etching an organic anti-reflecting coating film through a mask layer made of photoresist and having a predetermined pattern by using an etching gas of CF 4  and O 2 . The method allows an organic anti-reflecting coating film to be etched such that the etched film exhibits a side wall portion having a better shape as compared with that formed by a conventional technique.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a dry etching method for use in manufacturing a semiconductor device; and, more particularly, to a dry etching method for etching an organic anti-reflecting coating (ARC) film through a mask layer made of, e.g., a photoresist. 
   BACKGROUND OF THE INVENTION 
   Recently, an anti-reflecting coating (ARC) film is widely employed in a field of manufacturing semiconductor devices in order to prevent, e.g., a generation of standing waves due to multiple interferences within a resist film during an exposure process using, e.g., a stepper. Conventionally employed as such an ARC film is an organic ARC film using an organic polymer. 
     FIGS. 8A to 8C  describe an exemplary manufacturing process of a semiconductor device employing the organic ARC film. 
   As shown in  FIG. 8A , formed on a semiconductor wafer (a silicon substrate)  201  are an insulating layer  202  made of, e.g., a silicon oxide film and a conductor layer  203  formed of, e.g., polysilicon and, further, formed on the conductor layer  203  by, e.g., a spin coating method are an organic ARC film  204  and a mask layer  205  made of a photoresist. 
   The mask layer  205  made of the photoresist is shaped into a predetermined pattern, as shown in  FIG. 8B , by being exposed to light and being subsequently developed while undergoing an exposure process by, e.g., a stepper and a developing process by a developer system, respectively. Thereafter, the organic ARC film  204  is patterned to have a preset pattern, as shown in  FIG. 8C , by being etched through the mask layer  205  by plasma etching employing an etching gas containing Cl 2  and O 2  gases. 
   Subsequently, the conductor layer  203  is etched through the mask layer  205  and the organic ARC film  204  into a predetermined pattern (not shown) and then the mask layer  205  and the organic ARC film  204  are removed by ashing. 
   As described above, the plasma etching employing the etching gas containing Cl 2  and O 2  gases has been conventionally employed to etch the organic ARC film. 
   In such a conventional method, however, it is difficult to form the organic ARC film  204  to have a vertical sidewall since a sidewall  204   a  of the organic ARC film  204  is of a tapered profile as shown in  FIG. 8C . 
   Further, as illustrated in  FIG. 9 , if a shape of the pattern has a dense pattern region (a left part of the drawing) in which neighboring patterns are close to each other and a sparse pattern region (a right part of the drawing) in which neighboring patterns are spaced apart from each other, the sidewall profile tends to vary between the dense pattern region and the sparse pattern region. 
   That is, in the example provided in  FIG. 9 , a profile of the sidewall is found to be tapered more in the sparse pattern region than in the dense pattern region. 
   Further, such tapered profile of the sidewall tends to vary at a central portion and a peripheral portion even on a single wafer. 
   For this reason, it has been difficult to perform an etching such that sidewall profiles are formed to be consistently of a high quality throughout the central portion, the peripheral portion, the dense pattern region and the sparse pattern region of the semiconductor wafer, even in case of controlling the sidewall profiles by adjusting etching conditions such as a flow rate and a pressure of the etching gas, a temperature of the semiconductor wafer during the etching, a high frequency power supplied to an electrode of a parallel plate type plasma etching apparatus, and so on. 
   SUMMARY OF THE INVENTION 
   It is, therefore, an object of the present invention to provide a dry etching method capable of etching an organic ARC film to have a high-quality sidewall profile. 
   In accordance with the present invention, there is provided a dry etching method for etching an organic anti-reflecting coating film through a mask layer formed to have a pattern, wherein the organic anti-reflecting coating film is etched by plasma etching employing an etching gas containing a CF 4  gas and an O 2  gas, and a trimming of a line width is carried out by etching the mask layer and the anti-reflecting coating film in a transversal direction. 
   Further, in the above-described dry etching method, the pattern may have a dense pattern region in which neighboring patterns are close to each other and a sparse pattern region in which neighboring patterns are spaced apart from each other, and the trimming may be substantially uniformly carried out at the dense pattern region and the sparse pattern region. 
   Furthermore, in the above-described dry etching method, an amount of the trimming may be controlled by varying a flow rate of O 2 /(a flow rate of CF 4  +a flow rate of O 2 ) of the etching gas. 
   Still further, in the above-described dry etching method, an amount of the trimming may be controlled by varying a power density of a high frequency power applied to a lower electrode. 
   Moreover, in the above-described dry etching method, the mask layer may be a resist film, and a silicon oxide film is formed under the organic anti-reflecting coating film. 
   The resist film may be an ArF resist film. 
   Further, the silicon oxide film may be etched by using a gaseous mixture containing a CF 4  gas and a CHF 3  after etching the organic anti-reflecting coating film. 
   In accordance with the present invention, there is provided a dry etching method for etching an organic anti-reflecting coating film through a mask layer formed to have a pattern, wherein the organic anti-reflecting coating film is etched by plasma etching employing an etching gas containing an N 2  gas and an O 2  gas, and a trimming of a line width is carried out by etching the mask layer and the anti-reflecting coating film in a transversal direction. 
   The pattern may be a dense pattern region in which neighboring patterns are close to each other and a sparse pattern region in which neighboring patterns are spaced apart from each other, and the trimming is substantially uniformly carried out at the dense pattern region and the sparse pattern region. 
   Preferably, a flow rate of the N 2  gas is substantially identical to that of the O 2  gas. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1A to 1C  provide schematic cross sectional views of a wafer explaining a preferred embodiment of the present invention; 
       FIG. 2  exemplifies a configuration of an apparatus for use in the embodiment of the present invention; 
       FIG. 3  describes a pattern structure in the embodiment of the present invention; 
       FIG. 4  shows a measurement result of a CD shift in a first example; 
       FIG. 5  provides a measurement result of a CD shift in a second example; 
       FIGS. 6A to 6C  depict schematic cross sectional views of a wafer explaining another preferred embodiment of the present invention; 
       FIG. 7  describes a measurement result of a relationship between a gas flow ratio and a trimming amount; 
       FIGS. 8A to 8C  set forth schematic cross sectional views of a wafer explaining the prior art; 
       FIG. 9  explains the prior art pattern structure; and 
       FIG. 10  charts a measurement result of a CD shift in a comparative example. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Referring to  FIGS. 1A to 1C , there are illustrated partially enlarged schematic longitudinal cross sectional views of a semiconductor wafer (silicon substrate) for explaining a preferred embodiment of the present invention. 
   As shown in  FIG. 1A , formed on a semiconductor wafer (silicon substrate)  101  are an insulating layer  102  made of, e.g., a silicon oxide film and a conductor layer  103  formed of, e.g., polysilicon and, further, formed on the conductor layer  103  by, for example, a spin coating method are an organic ARC film  104  and a mask layer  105  made of a (?:“a” inserted) photoresist. 
   The mask layer  105  is first exposed to light and developed while undergoing an exposure process by a stepper and a developing process by a developer, respectively, to be formed into a predetermined pattern as shown in  FIG. 1B . Thereafter, the organic ARC film  104  is etched through the mask layer  105  by plasma etching employing an etching gas including CF 4  and O 2  gases from a state shown in  FIG. 1B , so that the organic ARC film  104  is patterned to have a preset pattern as illustrated in  FIG. 1C . Further, after completing the etching of the organic ARC film  104 , the conductor layer  103  is etched through the mask layer  105  and the organic ARC film  104  into a predetermined pattern. Then, the mask layer  105  and the organic ARC film  104  are removed by ashing. 
     FIG. 2  schematically illustrates an exemplary configuration of a plasma processing apparatus (etching apparatus)  1  for use in the preferred embodiment of the present invention. As shown therein, the etching apparatus  1  is a capacitively coupled parallel plate type etching apparatus having an upper and a lower electrode plate placed to face each other in parallel, one side of each plate being connected to a power supply for plasma generation. 
   The etching apparatus  1  includes, for example, a cylindrical chamber  2  which is grounded and made of aluminum whose surface is treated by anodic oxidation (alumite-treated). Installed on a bottom portion of the chamber  2  via an insulating plate  3  such as ceramic is a substantially columnar susceptor support  4  for mounting thereon a wafer W. Disposed on the susceptor support  4  is a susceptor  5  serving as a lower electrode. Connected to the susceptor  5  is a high pass filter (HPF)  6 . 
   Formed within the susceptor support  4  is a temperature control medium path  7 . A temperature control medium is introduced into the temperature control medium path  7  via an inlet line  8  to circulate therethrough and is exhausted via an outlet line  9 . By the circulation of the temperature control medium, the temperature of the susceptor  5  is maintained at a desired level. 
   The susceptor  5  is of a disk shape with a central topmost portion being protruded. Mounted on the central topmost portion of the susceptor  5  is an electrostatic chuck  11  shaped similar to the wafer W. The electrostatic chuck  11  includes an electrode  12  embedded in an insulating material. The electrostatic chuck  11  electrostatically adsorbs the wafer W by a Coulombic force generated by, e.g., a DC voltage of 1.5 kV supplied from a DC power supply  13  coupled to the electrode  12 . 
   Further, formed through the insulating plate  3 , the susceptor support  4 , the susceptor  5  and the electrostatic chuck  11  is a gas channel  14  for supplying a heat transfer medium (for example, a He gas) to a backside of the wafer W to be processed. Heat is transferred between the susceptor  5  and the wafer W through the heat transfer medium, so that the wafer W is maintained at a predetermined temperature. 
   An annular focus ring  15  is disposed on an upper peripheral portion of the susceptor  5  to surround the wafer W mounted on the electrostatic chuck  11 . The focus ring  15  is made of an insulating material, e.g., ceramic or quartz, or a conductive material, and serves to improve an etching uniformity. 
   Further, installed above the susceptor  5  to face thereto in parallel is an upper electrode  21 . The upper electrode  21  is supported within the chamber  2  via an insulating member  22 . The upper electrode  21  includes an electrode plate  24  (made of, e.g., quartz) facing toward the susceptor  5  and provided with a plurality of injection openings  23  and an electrode support  25  (made of a conductive material, e.g., aluminum whose surface is alumite treated) that serves to support the electrode plate  24 . Further, the distance between the susceptor  5  and the upper electrode  21  is adjustable. 
   Formed at a center of the electrode support  25  of the upper electrode  21  is a gas inlet opening  26  communicating with a gas supply line  27 , which in turn is connected to a process gas supply unit  30  via a valve  28  and a mass flow controller  29 . An etching gas for plasma etching is supplied from the process gas supply unit  30 . Though there is illustrated in  FIG. 2  only one process gas supplying system including the process gas supply unit  30  and the like, the plasma processing apparatus is provided with a plurality of process gas supplying systems capable of supplying gases for example, CF 4 , O 2 , N 2 , CHF 3 , and the like, into the chamber  2  by independently controlling flow rates thereof. 
   Connected to a bottom portion of the chamber  2  is a gas exhaust line  31 , which in turn is coupled to a gas exhaust unit  35 . The gas exhaust unit  35  includes a vacuum pump such as a turbo molecular pump or the like, and serves to reduce an inner pressure of the chamber  2  down to a predetermined vacuum level (e.g., 0.67 Pa or less). Further, installed on a sidewall of the chamber  2  is a gate valve  32 . The wafer W is transferred between the chamber  2  and an adjacent load lock chamber (not shown) while the gate valve  32  is opened. 
   Connected to the upper electrode  21  via a matching unit  41  is a first high frequency power supply  40 . Further connected to the upper electrode  21  is a low pass filter (LPF)  42 . The first high frequency power supply  40  has a frequency ranging from 50 to 150 MHz. By applying a high frequency power in such a range, a plasma of high density in a desired dissociation state can be generated within the chamber  2 , which makes it possible to execute a plasma etching under a pressure lower than that in conventional cases. The frequency of the first high frequency power supply  40  preferably ranges from 50 to 80 MHz. Typically, its frequency is 60 MHz as illustrated in  FIG. 2  or thereabouts. 
   Connected to the susceptor  5  serving as the lower electrode via a matching unit  51  is a second high frequency power supply  50  whose frequency ranges from several hundred KHz to less than twenty MHz. By applying a power of a frequency in such a range, a proper ionic action can be facilitated without causing any damage on the wafer W to be processed. Typically, the frequency of the second frequency power supply  50  is, e.g., 13.56 MHz as shown in  FIG. 2  or 800 KHz. 
   In the following, there will be explained a process for etching the organic ARC film  104  formed on the wafer W into a predetermined pattern through the mask layer  105  made of the photoresist by employing the etching apparatus  1  configured as described above. 
   As described above, the gate valve  32  is opened first, and then the wafer W, on which the organic ARC film  104  and the mask layer  105  patterned into the predetermined pattern are formed, is carried into the chamber  2  from the load lock chamber (not shown) to be mounted on the electrostatic chuck  11 . A DC voltage is then supplied from the DC power supply  13  to the electrostatic chuck  11 , so that the wafer W is adsorbed thereto electrostatically 
   Then, the gate valve  32  is closed and the chamber  2  is evacuated to a predetermined vacuum level by the gas exhaust unit  35 . Then, the valve  28  is opened, and an etching gas containing Cl 4 +O 2  is supplied from the process gas supply unit  30  onto the wafer W. The etching gas, a flow rate of which is controlled by the mass flow controller  29 , is discharged uniformly towards the wafer W as indicated by arrows in  FIG. 2  via the process gas supply line  27 , the gas inlet opening  26 , a hollow central space of the upper electrode  21  and the injection openings  23  of the electrode plate  24 . At the same time, the inner pressure of the chamber  2  is maintained at a predetermined pressure level. Thereafter, by applying high frequency powers to the upper electrode  21  and the susceptor  5  serving as the lower electrode from the first and the second high frequency power supply  40  and  50 , respectively, the etching gas is converted into a plasma to thereby perform the etching on the organic ARC film  104  on the wafer W. Such an etching process is terminated at the moment the state shown in  FIG. 1C  is obtained. 
   As illustrated in  FIG. 3 , a wafer of 200 mm, which is provided with a pattern shaped to have a dense pattern region (a left part of  FIG. 3 , line:space=1:1) in which neighboring patterns are placed close to each other and a sparse pattern region (a right part of  FIG. 3 , line:space=1:10 or greater) in which neighboring patterns are spaced apart from each other, was etched as a first example through the processes described above under the following condition: 
   
     
       
             
             
           
         
             
                 
             
           
           
             
               an etching gas: 
               CF 4  (a flow rate of 35 sccm) + O 2   
             
             
                 
               (a flow rate of 5 sccm) 
             
             
               a flow rate of CF 4 : 
               a flow rate of O 2  = 7:1 
             
             
               a pressure: 
               0.67 Pa (5 mTorr) 
             
             
               a high frequency power applied 
               325 W 
             
             
               to the upper electrode: 
             
             
               a high frequency power applied 
                30 W 
             
             
               to the lower electrode: 
             
             
               a distance between the electrodes: 
               80 mm 
             
             
               a susceptor temperature: 
               80° C. 
             
             
                 
             
           
        
       
     
   
   The pattern of the organic ARC film obtained by the above etching process in accordance with the first embodiment was investigated by a scanning electron microscope (SEM) to find that a sidewall profile of the organic ARC film  104  was substantially vertical as shown in  FIG. 3 . Moreover, such a high quality sidewall profile was found throughout the dense pattern region and the sparse pattern region and, further, the central portion and the peripheral portion of the wafer. Further, for the pattern of the organic ARC film thus obtained, a deviation of a line with of the pattern actually formed by etching from a designed line width (i.e., CD (critical dimension) shift) was measured in both of the dense pattern region and the sparse pattern region of respective parts on the surface of the wafer (the central portion and the peripheral portion thereof). 
     FIG. 4  provides a graph showing a measurement result of the CD shift, wherein a vertical axis represents a CD shift while a horizontal axis stands for a radial position on the surface of the wafer (a distance from a center of the wafer) (mm). 
   Further, in  FIG. 4 , a solid line A indicates a measurement result of an X-directional line width in the dense pattern region; a solid line B represents a measurement result of an X-directional line width in the sparse pattern region; a solid line C shows a measurement result of a Y-directional line width in the dense pattern region; and a solid line D describes a measurement result of a Y-directional line width in the sparse pattern region. 
   As shown in  FIG. 4 , in the first embodiment, a difference between a line width in the dense pattern region and that in the sparse pattern region and a difference between line widths within the surface of the wafer were both small. An average of the CD shifts was −19.8 nm and the difference between a line width in the dense pattern region and that in the sparse pattern region was 4.4 nm. 
   For comparison, an etching of an organic ARC film having the same pattern as illustrated above was carried out by employing a conventional etching gas containing Cl 2 +O 2  under the following condition: 
   
     
       
             
             
           
         
             
                 
             
           
           
             
               an etching gas: 
               Cl 2  (a flow rate of 10 sccm) + O 2   
             
             
                 
               (a flow rate of 30 sccm) 
             
             
               a pressure: 
               0.67 Pa (5 mTorr) 
             
             
               a high frequency power applied 
               325 W 
             
             
               to the upper electrode: 
             
             
               a high frequency power applied 
                30 W 
             
             
               to the lower electrode: 
             
             
               a distance between the electrodes: 
               80 mm 
             
             
               a susceptor temperature: 
               80° C. 
             
             
                 
             
           
        
       
     
   
   The pattern of the organic ARC film obtained by the above etching process was investigated by the SEM to find that a sidewall of the organic ARC film  204  had a tapered profile as shown in  FIG. 9 . 
   Further, for the pattern of the organic ARC film thus formed, a deviation of a line width of the pattern actually formed by etching (CD shift) from a designed line width was measured, and the result is provided in a graph of  FIG. 10  charted in a similar manner as in the graph of  FIG. 4 . 
   As shown in  FIG. 10 , in the comparative example, a difference between a line width in a dense pattern region and that in a sparse pattern region and a difference between line widths within the surface of a wafer were found to be greater than those in the case of the example described in  FIG. 4 . An average of CD shifts was −29.9 nm and the difference between the line width from the dense pattern region and that from the sparse pattern region was 14.6 nm. 
   Next, as a second example, the etching gas including CF 4 +O 2  mentioned above was replaced with a gas of N 2 +O 2 , and a wafer with a predetermined pattern having a dense pattern region (a left part in  FIG. 3 ) and a sparse pattern region (a right part in  FIG. 3 ), as illustrated in  FIG. 3 , was etched under the following condition: 
   
     
       
             
             
           
         
             
                 
             
           
           
             
               an etching gas: 
               N 2  (a flow rate of 20 sccm) + O 2   
             
             
                 
               (a flow rate of 20 sccm) 
             
             
               a high frequency power applied 
               325 W 
             
             
               to the upper electrode: 
             
             
               a high frequency power applied 
                30 W 
             
             
               to the lower electrode: 
             
             
               a distance between the electrodes: 
               80 mm 
             
             
               a susceptor temperature: 
               80° C. 
             
             
                 
             
           
        
       
     
   
   The pattern of the organic ARC film obtained by the etching in accordance with the second example was investigated by the SEM to find that a high quality sidewall profile of the organic ARC film could be made to be virtually vertical in both of the dense pattern region and the sparse pattern region, as in the first example. 
   Further, a deviation of a line width of the pattern actually fabricated by etching (CD shift) from a designed line width was measured, and the result is provided in a graph of  FIG. 5  presented similarly to the graph in  FIG. 4 . 
   As shown in  FIG. 5 , in the second example, a difference between a line width in the dense pattern region and that in the sparse pattern region and a difference between line widths within the surface of the wafer were both small as in the first example. An average of CD shifts was −50.3 nm and the difference between a line in the dense pattern region and that in the sparse pattern region was 2.6 nm. 
   As mentioned above, the average of the CD shifts was as large as −50.3 nm in the second example. For this reason, an actual line width becomes narrower than a designed line width. Thus, by designing a line width of the mask layer to be large in advance and reducing (trimming) it through the etching process, a wiring with a minute line width or the like, can be resultantly formed without having to set the line width of the mask layer to be excessively small in exposure and developing processes of the mask layer. 
   That is, by setting in advance the line width of the photoresist mask layer formed in the exposure and the developing process to be wider than the actual line width by 50 nm, a wiring with a desired fine line width can be obtained by the trimming carried out during the etching process of the second example. 
   Recently, a so-called ArF resist, which is a resist, the exposure process thereof being carried out by a laser beam using an ArF gas as a light source, is widely employed. The ArF resist is adequate for forming a minuter pattern than that formed by a conventional KrF resist. Since, however, the ArF resist has a low plasma-resistance, there exist certain disadvantages in that a surface of the resist may be roughened, selectivity against a to-be-etched portion (a ratio of etching rates) is small, and the resist may not be sustained. Further, main substances forming the ArF resist are, e.g., a cycloolefin resin, an acrylic resin containing alicyclic structure, a cyclooefin-maleic anhydride resin, and so on. 
   The present invention can be equally applied to such a case of using the ArF resist. A preferred embodiment using the ArF resist will now be described. 
   Referring to  FIGS. 6A to 6C , there are illustrated partially enlarged schematic longitudinal cross sectional views of a semiconductor wafer (silicon substrate) for explaining the preferred embodiment using the ArF resist. 
   In the semiconductor wafer shown in  FIGS. 6A to 6C , formed on a polysilicon film  121  is a silicon oxide film  122  having a predetermined thickness (in this embodiment, 50 nm) and, further, formed on the silicon oxide film  122  is an organic ARC film  123  having a certain predetermined thickness (80 nm in this embodiment), as illustrated in  FIG. 6A . Further, formed on the organic ARC film  123  is an ArF resist  124  having a specific thickness (240 nm in this embodiment) and patterned in a predetermined pattern by an exposure process and a developing process as described above. Further, a line width of the ArF resist  124  (referred to as “d” in the drawing) is set to be 80 nm in this embodiment. 
   From a state shown in  FIG. 6A , the organic ARC film  123  is etched first through the ArF resist  124  (mask layer) by plasma etching employing an etching gas containing a CF 4  gas and an O 2  gas, so that the organic ARC film  123  is patterned to have a predetermined pattern, as illustrated in  FIG. 6B . 
   Thereafter, from a state shown in  FIG. 6B , the silicon oxide film  122  is patterned into a preset pattern, as illustrated in  FIG. 6C , by being plasma etched through the ArF resist  124  (mask layer) and the organic ARC film  123  by way of employing an etching gas containing a CF 4  gas and a CHF 3  gas. 
   Then, the ArF resist  124  and the organic ARC film  123  are removed by, e.g., ashing. 
   By etching the organic ARC film  123  and the silicon oxide film  122  through the above-described processes, the silicon oxide film  122  can be etched without causing a surface roughening and deterioration of the ArF resist  124 . 
   Furthermore, in the etching process of the organic ARC film  123 , a trimming described above can be carried out under a strict control over a trimming amount, and, further, an etching can be performed without changing a trimmed line width in the etching process of the silicon oxide film  122 . 
   A wafer of a diameter of 200 mm was etched by following the above-described etching process as a third example. The etching was performed plural times while changing the value of a ratio [a flow rate of O 2 /a flow rate of (CF 4 +O 2 )] in order to examine a variation in a trimming amount as a function of the ratio of the flow rate of O 2  to the total flow rate of an etching gas (CF 4 +O 2 ). The etching condition was as follows: 
   
     
       
             
           
             
             
           
             
           
             
             
           
         
             
                 
             
           
           
             
               (Etching of the organic ARC film) 
             
           
        
         
             
               an etching gas: 
               CF 4  + O 2   
             
             
                 
               (a total flow rate of 40 sccm) 
             
             
               a pressure: 
               0.67 Pa (5 mTorr) 
             
             
               a high frequency power applied 
               300 W 
             
             
               to the upper electrode: 
             
             
               a high frequency power applied 
                60 W 
             
             
               to the lower electrode: 
             
             
               a distance between the electrodes: 
               140 mm 
             
             
               a temperature (top/wall/bottom): 
               80/60/75° C. 
             
             
               a He gas pressure (center/edge): 
               400/400 Pa (3 Torr) 
             
             
               an overetching: 
               10% 
             
           
        
         
             
               (Etching of the silicon oxide film) 
             
           
        
         
             
               an etching gas: 
               CF 4  (a flow rate of 20 sccm) + CHF 3   
             
             
                 
               (a flow rate of 20 sccm) 
             
             
               a pressure: 
               5.3 Pa (40 mTorr) 
             
             
               a high frequency power applied 
               600 W 
             
             
               to the upper electrode: 
             
             
               a high frequency power applied 
               100 W 
             
             
               to the lower electrode: 
             
             
               a distance between the electrodes: 
               140 mm 
             
             
               a temperature (top/wall/bottom): 
               80/30/65° C. 
             
             
               a He gas pressure (center/edge): 
               1300/1300 Pa (10 Torr) 
             
             
               an overetching: 
               10%. 
             
             
                 
             
           
        
       
     
   
   A pattern obtained by the etching process of the third example was investigated by the SEM to find that the organic ARC film and the silicon oxide film could be etched without causing a surface roughening and deterioration of the ArF resist. 
   Furthermore, the trimming amount of the organic ARC film can be readily controlled by adjusting [the flow rate of O 2 /the flow rate of (CF 4 +O 2 )] as shown in  FIG. 7 .  FIG. 7  describes a relationship between the trimming amount and the ratio of [a flow rate of O 2 /a flow rate of (CF 4 +O 2 )], wherein the result of the third example is represented by triangles and a vertical and a horizontal axes represent the trimming amount (nm) and the ratio (%) of [the flow rate of O 2 /the flow rate of (CF 4 +O 2 )]. And, an amount of a high frequency power per unit area (a RF power density) applied to the lower electrode was 0.19 W/cm 2  in this case. As can be seen from  FIG. 7 , the trimming amount could be changed almost linearly by varying [the flow rate of O 2 /the flow rate of (CF 4 +O 2 )]. 
   In addition, the etching of the silicon oxide film could be carried out while substantially maintaining the line width (i.e., involving a small amount of trimming). An average of the trimming amounts (decrements in the line width) was −0.2 nm in the etching process of the silicon oxide film. 
   Next, an organic ARC film identical with that employed in the third example was etched by using a wafer having a diameter of 300 mm as a fourth example. The etching condition was as follows: 
   
     
       
             
           
             
             
             
           
         
             
                 
             
             
               (Etching of the organic ARC film) 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                 
               an etching gas: 
               CF 4  + O 2  (a total flow 
             
             
                 
                 
               rate of 80 sccm) 
             
             
                 
               a pressure: 
               0.93 Pa (7 mTorr) 
             
             
                 
               a high frequency power applied 
               100 W 
             
             
                 
               to the upper electrode: 
             
             
                 
               a high frequency power applied 
                40 W 
             
             
                 
               to the lower electrode: 
             
             
                 
               a distance between the electrodes: 
               170 mm 
             
             
                 
               a temperature (top/wall/bottom): 
               80/60/75° C. 
             
             
                 
               a He gas pressure (center/edge): 
               670/670 Pa (5 Torr) 
             
             
                 
               an overetching: 
               10%. 
             
             
                 
                 
             
           
        
       
     
   
   Circular dots in  FIG. 7  describe a relationship between a trimming amount and a ratio (%) of [a flow rate of O 2 /a flow rate of (CF 4 +O 2 )] in the fourth example. As shown in  FIG. 7 , the trimming amount could also be changed almost linearly by changing [the flow rate of O 2 /the flow rate of (CF 4 +O 2 )] in the fourth example as well. 
   In the fourth example, an amount of a high frequency power per unit area (a RF power density) applied to the lower electrode was 0.57 W/cm 2 , which is greater than 0.19 W/cm 2  in the third example. As a result, trimming amounts are found to be relatively increased compared to those in the third example, as shown in  FIG. 7 , which appears to be due to the fact that an etching in a transversal direction (trimming) progresses as the power density applied to the lower electrode increases because ionic energy is increased with the increase of the power density. 
   Therefore, by changing the amount of the high frequency power (power density) applied to the lower electrode while maintaining [the flow rate of O 2 /the flow rate of (CF 4 +O 2 )] at a constant level, the trimming amount can be controlled. 
   Furthermore, though the preferred embodiments have been described for the case of employing the parallel plate type plasma etching apparatus for performing etching by applying high frequency powers to both the upper electrode and the lower electrode, the present invention is not limited thereto. That is, the present invention can be applied to any type of plasma etching apparatuses, for example, an etching apparatus for supplying a high frequency power to either one of the upper and the lower electrode, an etching apparatus for controlling the plasma by using a magnetic field, and so on. 
   INDUSTRIAL APPLICABILITY 
   The dry etching method in accordance with the present invention can be employed in the semiconductor industry manufacturing semiconductor devices. Thus, it has an industrial applicability.