Patent Publication Number: US-2002008082-A1

Title: Local etching apparatus and local etching method

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a local etching apparatus and a local etching method for spraying radicals produced by plasma discharge from a nozzle to a silicon wafer or other object to be etched to locally etch the object to be etched.  
       [0003] 2. Description of the Related Art  
       [0004] In the past, as this type of local etching apparatus, there has been a local etching apparatus which causes plasma discharge of CF 4  or another gas to produce F (fluorine) radicals or other radicals and sprays these radicals from a small diameter nozzle to a relatively thick portion of a silicon wafer or other object to be etched to locally etch the relatively thick portion so as to flatten the entire object to be etched.  
       [0005] In this art, it was necessary to prevent the reaction products between the radicals and object to be etched from contaminating the object to be etched, so an exhaust means was provided for exhausting the reaction products to the outside of the chamber of the local etching apparatus.  
       [0006] As an example of such a local etching apparatus provided with an exhaust means, there is the art disclosed in Japanese Patent Laid-Open No. 9-27482.  
       [0007] This local etching apparatus, as shown in FIG. 8, is constructed to cause plasma discharge of a mixed gas of CF 4  and O 2  by a magnetron  100  and spray the produced F radicals from a nozzle  101  to a relatively thick portion of a silicon wafer W to locally etch the same and provide an exhaust pipe  110  constituting part of the exhaust means at the outside of the nozzle  101  to draw the reaction products into the exhaust pipe  110  and exhaust them through the exhaust pipe  110  to the outside of the chamber  120 .  
       [0008] In this local etching apparatus of the related art, however, there were the following problems.  
       [0009] First, the front end  101   a  of the nozzle  101  and the front end  110   a  of the exhaust pipe  110  were set at the same plane. Further, the front end  101   a  of the nozzle  101  was structured to be recessed from the exhaust pipe  110 . Therefore, part of the F radicals sprayed from the front end  101   a  was drawn into the exhaust pipe  110  and consequently the etching rate on the silicon wafer W ended up falling.  
       [0010] Next, since the F radicals were just sprayed from the nozzle  101 , the gas of the F radicals spread outward as it proceeded downward resulting in the etching region becoming larger. Further, in the above local etching apparatus of the related art, since there was no control means for suppressing this spread of the F radicals, fine etching became impossible.  
       SUMMARY OF THE INVENTION  
       [0011] The present invention was made to solve the above problems and has as its object the provision of a local etching apparatus and local etching method giving a high etching rate and enabling fine etching.  
       [0012] To achieve the above object, according to a first aspect of the present invention, there is provided a local etching apparatus comprising: a discharge tube passing through a chamber and with a spray port of a nozzle portion facing an object to be etched in the chamber; a plasma generating means for causing plasma discharge of a predetermined gas fed to the discharge tube so as to produce radicals; and an exhaust means having an exhaust pipe arranged near the nozzle portion so that the spray port of the nozzle portion projects out to the object to be etched side from a suction port of the exhaust pipe and drawing into the suction port of the exhaust pipe the reaction products produced when locally etching the object to be etched by the radicals and exhausting them to the outside of the chamber.  
       [0013] Due to this configuration, the gas fed to the discharge tube is subjected to plasma discharge by the plasma generating means and radicals are produced. These radicals are sprayed from the spray port of the nozzle portion toward the object to be etched whereby the object to be etched is locally etched. The reaction products produced at the time of local etching are exhausted by the exhaust pipe to the outside of the chamber. At this time, since the spray port of the nozzle portion projects out from the suction port of the exhaust pipe to the object to be etched side, almost none of the radicals sprayed from the spray port are drawn into the exhaust pipe.  
       [0014] As a preferable example of the amount of projection of the nozzle portion from the exhaust pipe, according to an embodiment of the invention, the amount of projection of the spray port of the nozzle portion from the suction port of the exhaust pipe is set to a value in the range from 0.5 mm to 5.0 mm.  
       [0015] According to a second aspect of the present invention, there is provided a local etching apparatus comprising: a discharge tube passing through a chamber and with a spray port of a nozzle portion facing an object to be etched in the chamber; a plasma generating means for causing plasma discharge of a predetermined gas fed to the discharge tube so as to produce radicals; an exhaust means having an exhaust pipe arranged near the nozzle portion and drawing into the suction port of the exhaust pipe the reaction products produced when locally etching the object to be etched by the radicals and exhausting them to the outside of the chamber; and an etching region limiting means for feeding into the chamber a gas of a predetermined pressure for suppressing the dispersion of the radicals sprayed from the spray port of the nozzle portion toward the object to be etched.  
       [0016] Due to this configuration, since the dispersion of the radicals sprayed from the spray port toward the object to be etched is suppressed by the gas of a predetermined pressure fed from the etching region limiting means, the sectional area of the flux of the radicals becomes smaller.  
       [0017] Further, according to an embodiment of the invention, the spray port of the nozzle portion is made to project out from the suction port of the exhaust pipe by exactly a value in the range from 0.5 mm to 5.0 mm.  
       [0018] Further, according to an embodiment of the invention, a distance between the spray port of the nozzle portion and the object to be etched is set to a value in the range from 1 mm to 10 mm.  
       [0019] Further, as a preferable example of the pressure of the gas fed by the etching region limiting means, according to an embodiment of the invention, the pressure of the gas fed around the object to be etched by the etching region limiting means is set to 40 percent to 80 percent of the gas pressure inside the nozzle portion.  
       [0020] The gas fed by the etching region limiting means is for limiting the etching region of the object to be etched, so preferably is a gas of a nature not reacting with the radicals sprayed from the nozzle portion or the object to be etched.  
       [0021] Therefore, according to an embodiment of the invention, the gas fed to the chamber by the etching region limiting means is one of nitrogen gas, argon gas, and the predetermined gas fed to the discharge tube.  
       [0022] The steps executed by the local etching apparatuses in their operation also stand as method inventions.  
       [0023] Therefore, according to a third aspect of the present invention, there is provided a local etching method comprising: a plasma generating step for causing plasma discharge of a predetermined gas fed to a discharge tube passing through a chamber and with a spray port of a nozzle portion facing an object to be etched in the chamber so as to produce radicals; a local etching step for directing the radicals sprayed from the spray port of the nozzle portion to a relatively thick portion of the object to be etched to locally etch that relatively thick portion; and a reaction product exhaust step using an exhaust pipe arranged near the nozzle portion so that the spray port of the nozzle portion projects out to the object to be etched side so as to exhaust the reaction products produced in the local etching step outside of the chamber.  
       [0024] Further, according to an embodiment of the invention, the spray port of the nozzle portion is made to project out from the suction port of the exhaust pipe by exactly a value in the range from 0.5 mm to 5.0 mm for the spraying of the radicals.  
       [0025] Further, according to a fourth aspect of the present invention, there is provided a local etching method comprising: a plasma generating step for causing plasma discharge of a predetermined gas fed to a discharge tube passing through a chamber and with a spray port of a nozzle portion facing an object to be etched in the chamber so as to produce radicals; a local etching step for directing the radicals sprayed from the spray port of the nozzle portion to a relatively thick portion of the object to be etched to locally etch that relatively thick portion; a reaction product exhaust step using an exhaust pipe arranged near the nozzle portion so as to exhaust the reaction products produced in the local etching step outside of the chamber; and an etching region limiting step for feeding into the chamber a gas of a predetermined pressure for suppressing the dispersion of the radicals sprayed from the spray port of the nozzle portion toward the object to be etched.  
       [0026] According to an embodiment of the invention, the spray port of the nozzle portion is made to project out from the suction port of the exhaust pipe by exactly a value in the range from 0.5 mm to 5.0 mm for spraying the radicals. According to an embodiment of the invention, the spray port of the nozzle portion is brought close to the object to be etched up to a distance in the range from 1 mm to 10 mm for spraying the radicals. According to an embodiment of the invention, the pressure of the gas fed around the object to be etched in the etching region limiting step is set to 40 percent to 80 percent of the gas pressure inside the nozzle portion. Further, according to an embodiment of the invention, the gas fed to the chamber in the etching region limiting step is one of nitrogen gas, argon gas, and the predetermined gas fed to the discharge tube. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0027] The above and other objects, features, and advantages of the present invention will become more readily apparent from the following detailed description of a presently preferred embodiment of the invention taken in conjunction with the accompanying drawings, in which:  
     [0028]FIG. 1 is a schematic sectional view of a local etching apparatus according to a first embodiment of the present invention;  
     [0029]FIG. 2 is a sectional view of an exhaust mechanism;  
     [0030]FIG. 3 is a sectional view for explaining the dispersion suppressing action of F radicals by an etching region limiting gas feeder;  
     [0031]FIG. 4 is a graph of the relationship between a projecting distance of a nozzle portion and a depth of etching of a silicon wafer;  
     [0032]FIG. 5 is a graph of the relationship between the width of an etching region and the pressure of N 2  gas;  
     [0033]FIG. 6 is a graph of the relationship between the distance between the spray port and wafer and the width of the etching region;  
     [0034]FIG. 7 is a graph of the relationship between the distance between the spray port and wafer and the pressure inside the nozzle; and  
     [0035]FIG. 8 is a sectional view of an example of a local etching apparatus of the related art provided with an exhaust means. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0036] A preferred embodiment of the present invention will be explained next with reference to the drawings.  
     [0037]FIG. 1 is a schematic sectional view of a local etching apparatus according to an embodiment of the present invention.  
     [0038] The local etching apparatus is provided with a plasma generator  1  as a plasma generating means, a quartz discharge tube  2 , a gas feeder  3 , an X-Y drive  4 , a Z-drive  5 , an exhaust portion  6  as an exhaust means, and an etching region limiting gas feeder  7  as an etching region limiting means.  
     [0039] The plasma generator  1  is a device for causing plasma discharge of gas inside the quartz discharge tube  2  to produce radicals and is comprised of a microwave generator  10  and a waveguide  11 .  
     [0040] The microwave generator  10  is a magnetron and can generate a microwave M of a predetermined frequency.  
     [0041] The waveguide  11  is for guiding the microwave M generated by the microwave generator  10  and is fit over the quartz discharge tube  2  through a hole  12 .  
     [0042] At the inside of the left end of the waveguide  11  is attached a reflection plate (short plunger)  13  for reflecting the microwave M to form a standing wave. Further, in the middle of the waveguide  11  are attached a 3-stub tuner  14  for positioning the microwave M and an isolator  15  for bending the reflected microwave M heading toward the microwave generator  10  90° in direction (surface direction of FIG. 1).  
     [0043] The quartz discharge tube  2  is a cylinder having a nozzle portion  20  at its lower end, passes through the upper wall  90  of a chamber  9 , and has a spray port  21  facing the surface of the silicon wafer W.  
     [0044] Specifically, a hole  91  is made at the center of the upper wall  90  of the chamber  9 . The nozzle portion  20  of the quartz discharge tube  2  is inserted into the chamber  9  through this hole  91 . An O-ring  92  is fit between the hole  91  and the quartz discharge tube  2  so as to keep the space between the hole  91  and the quartz discharge tube  2  airtight. The outside diameter and inside diameter (diameter of spray port  21 ) of the quartz discharge tube  2  of this embodiment are set to 13 mm and 9 mm, respectively.  
     [0045] At the upper end of this quartz discharge tube  2  is connected a feed pipe  30  of the gas feeder  3 .  
     [0046] The gas feeder  3  is a device for feeding gas into the quartz discharge tube  2  and has a CF 4  (carbon tetrachloride) gas bomb  31  and an O 2  (oxygen) bomb  32 . The bombs  31 ,  32  are connected to the feed pipe  30  through valves  37  and flow controllers  34 ,  35 .  
     [0047] By adopting this configuration for the plasma generator  1 , a mixed gas of CF 4  and O 2  is fed from the gas feeder  3  to the quartz discharge tube  2 , plasma discharge is caused upon generation of the microwave M from the microwave generator  10 , and F (fluorine) radicals R produced by the plasma discharge are sprayed from the spray port  21  of the nozzle portion  20 .  
     [0048] The X-Y drive  4  is arranged inside the chamber  9  and supports a chuck  93  from below.  
     [0049] The X-Y drive  4  makes the chuck  93  move in the lateral direction in FIG. 1 by an X-drive motor  40  and makes the chuck  93  and the X-drive motor  40  move in the direction perpendicular to the surface of the paper on which FIG. 1 is drawn by a Y-drive motor  41 . That is, it is possible to make the nozzle portion  20  move in the X-Y direction relative to the silicon wafer W by the X-Y drive  4 .  
     [0050] The drive operations of the X-drive motor  40  and Y-drive motor  41  of the X-Y drive  4  are controlled by a control computer  8  based on a predetermined program.  
     [0051] The chamber  9  as a whole is designed to be able to move vertically with respect to the quartz discharge tube  2 . The Z-drive  5  supports the chamber  9  from below. The Z-drive  5  makes the chamber  9  as a whole move in the vertical direction by a Z-drive motor  50  and enables the distance between the spray port  21  of the nozzle portion  20  and the surface of the silicon wafer W to be adjusted. In this embodiment, as shown in FIG. 2, the distance L 2  between the spray port  21  of the nozzle portion  20  and the silicon wafer W is set to a value in the range of 1 mm to 10 mm.  
     [0052] The exhaust portion  6  is a mechanism for exhausting reaction products G produced at the time of etching the silicon wafer W by the F radicals R to the outside of the chamber  9 .  
     [0053] The exhaust portion  6 , as shown in FIG. 2, is provided with an exhaust pipe  60 , a tube  61 , and an exhaust pump  62 .  
     [0054] The exhaust pipe  60  is designed to surround the nozzle portion  20  as a whole from the outside and is attached airtightly to the inside surface of the upper wall  90  of the chamber  9 . It has at its lower end a suction port  60   a  with a diameter of 30 mm. The length of the exhaust pipe  60  is set to be shorter than the length of the nozzle portion  20 . The front end of the nozzle portion  20  therefore projects out from the suction port  60   a  of the exhaust pipe  60  to the silicon wafer W side. The amount of projection, that is, the distance L 1  between the suction port  60   a  of the exhaust pipe  60  and the spray port  21  of the nozzle portion  20 , is set to a value in the range from 0.5 mm to 5.0 mm.  
     [0055] The tube  61  connects the inside of the exhaust pipe  60  and the exhaust pump  62 . Due to this, by actuating the exhaust pump  62 , the reaction products G inside the chamber  9  are drawn into the suction port  60   a  of the exhaust pipe  60 . The reaction products G then pass through the tube  61  and can be exhausted to the outside of the chamber  9 .  
     [0056] Note that reference numeral  94  in FIG. 1 is a vacuum pump. This vacuum pump  60  may be used to create a state of vacuum inside the chamber  9 .  
     [0057] The etching region limiting gas feeder  7  is a device for feeding into the chamber  9  a gas of a predetermined pressure suppressing the dispersion of the F radicals R sprayed from the nozzle portion  20  and is provided with a N 2  (nitrogen) gas S bomb  70 , a flow controller  71 , and a nozzle  72  attached to the side wall  95  of the chamber  9 .  
     [0058] Due to this, by opening the valve  73  of the bomb  70  and controlling the pressure of the N 2  gas S sprayed from the nozzle  72  to the inside of the chamber  9  by the flow controller  71 , it is possible to suppress the dispersion of the F radicals R as shown in FIG. 3.  
     [0059] That is, when the chamber  9  is close to a vacuum, as shown by the two-dot chain line, the flux of the F radicals R spreads outward as it proceeds downward and the etching region E 1  of the silicon wafer W becomes larger. As opposed to this, when N 2  gas S is fed into the chamber  9 , the pressure of the N 2  gas S causes the flux of the F radicals R to be reduced and therefore, as shown by the solid line, the etching region E 2  of the silicon wafer W by the F radicals R becomes smaller. Therefore, it becomes possible to control the etching region E 2  by the pressure of the N 2  gas S. In this embodiment, the pressure of the N 2  gas S is set to a percentage in the range from 40 percent to 80 percent of the gas pressure inside the nozzle portion  20 .  
     [0060] Next, an explanation will be given of the operation of the local etching apparatus of this embodiment. Note that since it is possible to execute the local etching method according to the aspect of the present invention by operating the local etching apparatus, the explanation will be given along with the steps of that method.  
     [0061] First, the plasma generation step is executed.  
     [0062] That is, in FIG. 1, the vacuum pump  94  is driven in the state with the silicon wafer W held by suction against the chuck  93  so as to bring the inside of the chamber  9  to a low air pressure state of 0.1 Torr to 5.0 Torr and the Z-drive  5  is driven to raise the chamber  9  as a whole so as to bring the silicon wafer W to a distance in the range from 1 mm to 10 mm below the nozzle portion  20 .  
     [0063] In this state, the valves  37  of the gas feeder  3  are opened, the CF 4  gas and O 2  gas inside the bombs  31 ,  32  are made to flow into the feed pipe  30 , and the mixed gas of the two is fed into the quartz discharge tube  2 .  
     [0064] At this time, the opening degrees of the valves  37  are adjusted to maintain the CF 4  gas and O 2  gas at predetermined pressures and the flow controller  34  is used to adjust the flow rate of the CF 4  gas.  
     [0065] In parallel with the feeding of the CF 4  gas, the microwave generator  10  is driven. The microwave M causes plasma discharge of the CF 4  gas present at the discharge position and production of F radicals R. Due to this, the F radicals R are guided into the nozzle portion  20  of the quartz discharge tube  2  and sprayed from the spray port  21  of the nozzle portion  20  to the silicon wafer W side.  
     [0066] Suitably thereafter, the X-Y drive  4  is used to position the silicon wafer W directly under the nozzle portion  20 , then the etching region limiting step is executed.  
     [0067] That is, the pressure of the N 2  gas S sprayed from the nozzle  72  to the inside of the chamber  9  is controlled by the flow controller  71  to make the pressure of the N 2  gas S around the silicon wafer W a percentage in the range from 40 percent to 80 percent of the gas pressure inside the nozzle portion  20 .  
     [0068] Due to this, the flux of the F radicals R is reduced and, as shown in FIG. 3, the etching region of the silicon wafer W is limited to the small etching region E 2 .  
     [0069] The local etching step is executed in this state.  
     [0070] That is, the chuck  93  is made to move zigzag in the X-Y direction to make the nozzle portion  20  scan the silicon wafer W in a zigzag pattern. At this time, the relative speed of the nozzle portion  20  with respect to the silicon wafer W is set so as to be substantially inversely proportional to the thickness of the relatively thick portion so the etching time of the relatively thick portion of the silicon wafer W becomes longer and the relatively thick portion is shaved flat. Further, as explained above, since the etching region E 2  by the F radicals R is small, it is possible to sequentially etch small relatively thick portions and possible to achieve fine local etching. By etching the entire surface of the silicon wafer W in this way, the local etching step is completed.  
     [0071] A reaction product exhausting step is executed in parallel with the above local etching step.  
     [0072] That is, the exhaust pump  62  of the exhaust portion  6  is operated while executing the above local etching step.  
     [0073] The local etching step, as shown in FIG. 2, causes the production of reaction products G due to the reaction between the F radicals R sprayed from the nozzle portion  20  and the silicon wafer W. The reaction products G would fill the inside of the chamber  9 . The reaction products G, however, are drawn into the suction port  60   a  of the exhaust pipe  60  by the operation of the exhaust pump  62  and are exhausted through the tube  61  to the outside of the chamber  9 . The F radicals R sprayed from the nozzle portion  20 , however, are also liable to be exhausted by the exhaust portion  6 . As explained above, however, the front end of the nozzle portion  20  projects out from- the suction port  60   a  of the exhaust pipe  60  to the silicon wafer W side by exactly a value in the range from 0.5 mm to 5.0 mm. Further, the F radicals R are sprayed from the nozzle portion  20  at a considerable pressure. Therefore, almost none of the F radicals R sprayed from the nozzle portion  20  are drawn in by the exhaust portion  6 . Substantially all of F radicals R contribute to the etching of the silicon wafer W. As a result, the etching rate becomes far greater than the etching rate by the local etching apparatus of the related art explained above.  
     [0074] In this way, according to the local etching apparatus of this embodiment, since the nozzle portion  20  is made to project out from the exhaust pipe  60  to prevent the F radicals R from being drawn in by the exhaust portion  6  and the flux of F radicals R sprayed from the nozzle portion  20  can be reduced to make the etching region smaller, it is possible to improve the etching rate of the silicon wafer W and finely etch the silicon wafer W.  
     [0075] The present inventors conducted the following experiments to provide evidence of this point.  
     [0076] First, a first experiment was conducted to determine the relationship between the amount of projection of the nozzle portion  20  from the exhaust pipe  60 , that is, the distance L 1  between the spray port  21  of the nozzle portion  20  and the suction port  60   a  of the exhaust pipe  60 , and the etching rate of the silicon wafer W.  
     [0077] In this experiment, the flow controllers  34 ,  35  were controlled to make the flow rate of the CF 4  gas and the flow rate of the O 2  gas fed to the quartz discharge tube  2  1000 sccm and 60 sccm, respectively, and the pressure inside the nozzle portion  20  was set to 3.0 Torr. Further, the depth of etching of the silicon wafer W per second was measured while changing the above distance L 1 . Due to this, the results shown in FIG. 4 was obtained.  
     [0078]FIG. 4 is a graph of the relationship between a projecting distance L 1  of the nozzle portion  20  and the depth of etching of the silicon wafer W.  
     [0079] As shown in FIG. 4, when the projecting distance L 1  of the nozzle portion  20  is 0 mm or less, that is, when the spray port  21  of the nozzle portion  20  and the suction port  60   a  of the exhaust pipe  60  are on the same plane or the nozzle portion  20  is pulled back inside the exhaust pipe  60 , the depth of etching of the silicon wafer W becomes smaller in proportion to the amount of recess of the nozzle portion  20 .  
     [0080] This is considered to be because the more than nozzle portion  20  is recessed in the exhaust pipe  60 , the higher the probability of the F radicals R sprayed from the nozzle portion  20  being exhausted by the exhaust portion  6 .  
     [0081] As opposed to this, when the projecting distance L 1  of the nozzle portion  20  is in the range from 0.5 mm to 5.0 mm, a large depth of etching of 0.2 μm is maintained. This is considered to be because substantially all of the F radicals R sprayed from the nozzle  20  contribute to the etching of the silicon wafer W without being sucked into the exhaust portion  6 .  
     [0082] Further, when the projecting distance L 1  of the nozzle portion  20  exceeds 5.0 mm, the depth of etching becomes smaller in accordance with this.  
     [0083] From this viewpoint, the inventors reached the conclusion that setting the projecting distance L 1  of the nozzle portion  20  to a range from 0.5 mm to 5.0 mm is preferable in improving the etching rate of the silicon wafer W.  
     [0084] Next, the inventors conducted a second experiment to investigate the relationship between the width (diameter) of the etching region by the F radicals R and the pressure of the N 2  gas fed by the etching region limiting gas feeder  7 .  
     [0085] In this experiment, the flow controller  71  was controlled under the same conditions as the above first experiment so as to increase the pressure of the N 2  gas S around the silicon wafer W. Due to this, the results shown in FIG. 5 were obtained.  
     [0086]FIG. 5 is a graph of the relationship between the width of the etching region by the F radicals R and the pressure of the N 2  gas S fed by the etching region limiting gas feeder  7 .  
     [0087] As shown in FIG. 5, when the pressure of the N 2  gas S was increased up to 40 percent (1.2 Torr) of the pressure inside the nozzle portion  20 , the width of the etching region by the F radicals R spreading out downward was reduced to up to 30 mm. When the pressure of the N 2  gas S was increased to 80 percent of the pressure inside the nozzle portion  20 , the width of the etching region was maintained at a substantially constant value. When the pressure of the N 2  gas S was increased to over 80 percent of the pressure inside the nozzle portion  20 , however, the fall in the etching rate was remarkable. Note that to limit the width of the etching region to 30 mm, the distance L 2  between the spray port  21  of the nozzle portion  20  and the surface of the silicon wafer W becomes an issue.  
     [0088]FIG. 6 is a graph of the relationship between the distance L 2  between the spray port and wafer and the width of the etching region, while FIG. 7 is a graph of the relationship between the distance L 2  between the spray port and wafer and the pressure inside the nozzle portion.  
     [0089] The pressure of the N 2  gas S was set to 40 percent of the pressure inside the nozzle portion  20  and the distance L 2  between the spray port and wafer was changed. When the distance L 2  between the spray port and wafer was set larger than 10 mm, as shown in FIG. 6, the width of the etching region ended up become larger rapidly. To deal with this, it is necessary to increase the pressure of the N 2  gas S, but if set too large, the N 2  gas S inhibits the F radicals R from reaching the silicon wafer W and the etching rate ends up falling.  
     [0090] On the other hand, when the distance L 2  between the spray port and wafer was set smaller than 1 mm, as shown in FIG. 7, the pressure inside the nozzle portion could not be maintained at 3.0 Torr, but rapidly increased and stable etching became impossible. This is considered to have been due to the silicon wafer W itself blocking the F radicals R when the nozzle portion  20  is brought too close to the silicon wafer W and the F radicals R inside the nozzle portion  20  being inhibited from being sprayed from the spray port  21 .  
     [0091] From this viewpoint, the inventors reached the conclusion that setting the pressure of the N 2  gas S to 40 percent to 80 percent of the pressure inside the nozzle portion  20  and setting the distance L 2  between the spray port and wafer to a range from 1 mm to 10 mm are preferable for stable, fine local etching.  
     [0092] Note that the invention is not limited to the above embodiment. Various modifications and changes may be made within the scope of the gist of the invention.  
     [0093] For example, in the above embodiment, CF 4  and O 2  gas were used as the plasma discharge gas, but CF 4  gas alone is also possible. Further, instead of CF 4  gas, SF 6  (sulfur hexafluoride) gas or NF 3  (nitrogen trifluoride) gas may also be used.  
     [0094] Further, in the above embodiment, N 2  gas S was used as the gas for limiting the etching region, but it is also possible to use Ar gas or the CF 4  gas fed to the quartz discharge tube  2  (SF 6  gas etc. when using SF 6  gas etc.). The point is that any gas not inhibiting the etching of the silicon wafer W may be used as the gas for limiting the etching region.  
     [0095] Further, in the above embodiment, a quartz discharge tube  2  was used as the discharge tube, but an alumina discharge tube may also be used.  
     [0096] Further, in the above embodiment, a plasma generator  1  for generating plasma by generation of microwaves was used as the plasma generating means, but any means able to produce F radicals R may be used. For example, it is of course also possible to use various other types of plasma generators such as plasma generators which produce F radicals R by generation of plasma by high frequency.  
     [0097] As explained in detail above, according to the aspects of the invention, since almost none of the radicals sprayed from the spray port of the nozzle portion are drawn into the suction port of the exhaust pipe, almost all of the radicals sprayed from the spray port contribute to the local etching of the object to be etched and as a result there is the superior effect of improvement of the etching rate.  
     [0098] Further, according to the aspects of the invention, since it is possible to reduce the sectional area of the flux of radicals sprayed from the spray port of the nozzle portion, the etching region of the object to be etched becomes smaller and finer etching of the object to be etched becomes possible to that extent.