Patent Publication Number: US-2005142885-A1

Title: Method of etching and etching apparatus

Description:
This application is a Continuation Application of PCT International Application No. PCT/JP2003/010505 filed on Aug. 20, 2003, which designated the United States. 
    
    
     FIELD OF THE INVENTION  
      The present invention relates to an etching method and an etching apparatus.  
     BACKGROUND OF THE INVENTION  
      Recently, it has become an important industrial task to develop a gate insulating film, which is capable of reducing a gate operating voltage of a MOS (metal-oxide-semiconductor) transistor while, at the same time, providing an excellent withstand voltage. To achieve this goal, attention has been paid to the formation of a gate insulating film with a high-k dielectric insulating film such as a HfO 2  film.  
      However, the use of a high-k dielectric insulating film as a gate insulating film tends to entail a reduction in a drain current during an operation of the MOS transistor. Since the decreased drain current may adversely affect the speed of a device, it is preferable that such reduction in the drain current be avoided. For such purpose, therefore, placement of a Si-containing film, such as a SiON film, between the high-k dielectric insulating film and a Si substrate has been proposed.  
      On the other hand, the high-k dielectric insulating film and the Si-containing film formed on the Si substrate need to be etched so as to shape them into a desired form. Under the present situation, a HF solution is used to etch both the high-k dielectric insulating film and the Si-containing film.  
      However, if the high-k dielectric insulating film and the Si-containing film are etched with a HF solution, a field oxide film placed beneath the Si-containing film may be partially damaged, which can be problematic.  
     SUMMARY OF THE INVENTION  
      It is, therefore, an object of the present invention to provide an etching method and an etching apparatus for reducing damages to a substrate.  
      In accordance with one aspect of the present invention, there is provided an etching method, comprising the steps of: providing a substrate with a thin film formed thereon; and etching, without generating a plasma, the thin film formed on the substrate with an etching gas containing a β-diketone and a gas containing water and/or alcohol to expose a surface of the substrate. Since the etching method of the present invention is provided with the inventive etching step, damages to the substrate can be suppressed. Further, the etching rate can be increased by using the gas containing water and/or alcohol.  
      Further, a preferred β-diketone that can be used in the present invention is hexafluoro acetyl acetone (Hhfac). By using said Hhfac, damages to the substrate can be reduced effectively.  
      Furthermore, it is preferable that the etching gas containing a β-diketone includes the gas containing water and/or alcohol. Specifically, by mixing a gas containing water and/or alcohol with the etching gas containing a β-diketone, the etching rate can be improved.  
      Further, the etching may be conducted by alternating the supply of an etching gas containing a β-diketone and that of a gas containing water and/or alcohol. The alternate supplying of the gases makes the etching performed in a more accurate fashion.  
      It is also preferable that the etching be conducted while maintaining the substrate at a temperature of 300° C. or higher, preferably, 450° C. or higher. The etching rate can be improved if the etching is performed under such condition.  
      Further, it is preferable that the etching gas containing a β-diketone be supplied in such a manner that it flows along a surface of the thin film. The etching rate can be improved with such supply of the etching gas containing a β-diketone.  
      It is preferable that the thin film include a metal film and/or a metal oxide film. The etching gas containing a β-diketone is useful in etching the metal film and/or the metal oxide film.  
      Further, it is preferable that the metal film and/or the metal oxide film include at least one element selected from the group consisting of Al, Zr, Hf, Y, La, Ce and Pr. When the metal film and/or the metal oxide film includes such element(s), damages to the substrate can be mitigated effectively.  
      Further, it is preferable that a surface of the substrate be made of a Si-containing film. By constructing the substrate to be covered with the Si-containing film, the etching of the thin film can be made to stop upon the exposure of the Si-containing film.  
      The etching method may further comprise the step of etching the Si-containing film. It is preferable that the Si-containing film is etched with an etching gas including a fluorine-containing gas or with an etching solution including a hydrogen fluoride solution. When the Si-containing film is etched as described above, the etching rate of the Si-containing film can be improved.  
      It is preferable that the etching gas including the fluorine-containing gas contains water and/or alcohol. If the etching gas including the fluorine-containing gas is provided with such component(s), the etching rate of the Si-containing film can be improved further.  
      Further, the etching of the Si-containing film may be conducted by alternating the supply of an etching gas including a fluorine-containing gas and that of a gas including water and/or alcohol. The etching of the Si-containing film can be done in a more accurate fashion with such alternate supply.  
      Furthermore, it is preferable that the etching of the Si-containing film be conducted while maintaining the substrate at a temperature of 100° C. or less. The etching rate of the Si-containing film is improved when the etching is conducted under such condition.  
      In accordance with another aspect of the present invention, there is provided an etching apparatus, comprising: a reactor for accommodating a substrate on which a first thin film and a second thin film are formed, the second thin film being disposed under the first thin film; a first supply system for feeding a first etching gas containing a β-diketone into the reactor to etch the first thin film; and a second supply system for feeding a second etching gas including a fluorine-containing gas, or an etching solution including a hydrogen fluoride solution into the reactor to etch the second thin film. Since the etching apparatus of the present invention is provided with the first supply system for feeding the etching gas containing a β-diketone, damages to the substrate can be reduced. Further, the first and second thin films can be etched in a continuous manner. In addition, the first and second thin films can be etched in a single etching apparatus.  
      In accordance with a further aspect of the present invention, there is provided an etching apparatus comprising: a first reactor for accommodating a substrate on which a first thin film and a second thin film are formed, the second thin film being disposed under the first thin film; a first supply system for feeding a first etching gas containing a β-diketone into the first reactor to etch the first thin film; a second reactor for accommodating the substrate after the first thin film is removed by etching; a second supply system for feeding a second etching gas including a fluorine-containing gas, or an etching solution including a hydrogen fluoride solution into the second reactor to etch the second thin film; and a substrate transfer system for transferring the substrate into the first and the second reactors. Since the etching apparatus of the present invention is provided with the first supply system for feeding the etching gas containing a β-diketone, damages to the substrate can be mitigated. Further, the first and second thin films can be etched in a continuous manner.  
      Furthermore, a preferred β-diketone that can be used in the present invention is Hhfac. By using Hhfac as the β-diketone, damages to the substrate can be effectively mitigated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      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:  
       FIG. 1  shows a schematic vertical sectional view of an etching apparatus in accordance with a first preferred embodiment of the present invention;  
       FIG. 2  describes a schematic top sectional view of the etching apparatus in accordance with the first preferred embodiment;  
       FIG. 3  illustrates a schematic view of a wafer before it is etched in accordance with the first preferred embodiment;  
       FIG. 4  offers a flow chart showing the steps of etching executed in the etching apparatus in accordance with the first preferred embodiment;  
       FIG. 5  delineates a schematic view of the etching performed in accordance with the first preferred embodiment;  
       FIG. 6 . outlines a schematic view of the etching performed in accordance with the first preferred embodiment;  
       FIG. 7A  exhibits a schematic view of a chemical structure of Hhfac used in the first preferred embodiment, and  FIG. 7B  shows a schematic view of a chemical structure formula of Hf complex generated in the first preferred embodiment;  
       FIG. 8A  discloses a schematic view of a wafer after a HfO 2  film is removed by etching in accordance with the first preferred embodiment, and  FIG. 8B  shows a schematic view of a wafer after a SiON film is removed by etching in accordance with the first preferred embodiment;  
       FIG. 9  reveals relationships between a wafer temperature and an etching rate of a HfO 2  film based on the results obtained in Example 2 and Reference Example 2;  
       FIG. 10  provides relationships between a wafer temperature and an etching rate of an Al 2 O 3  film based on the results obtained in Example 3 and Reference Example 3;  
       FIG. 11  records relationships between a pressure in an inner chamber and an etching rate of a HfO 2  film based on the results obtained in Example 4 and Reference Example 4;  
       FIG. 12  presents a relationship between a Hhfac flow rate and an etching rate based on the result obtained in Example 5;  
       FIG. 13  indicates relationships between an O 2  flow rate and an etching rate of a HfO 2  film based on the results obtained in Example 6 and Reference Example 6;  
       FIG. 14  demonstrates relationships between an O 2  flow rate and an etching rate of an Al 2 O 3  film based on the results obtained in Example 7 and Reference Example 7;  
       FIG. 15  represents relationships between a concentration of H 2 O and an etching rate of a HfO 2  film based on the results obtained in Example 8 and Reference Example 8;  
       FIG. 16  accords relationships between a H 2 O concentration and an etching rate of an Al 2 O 3  film based on the results obtained in Example 9 and Reference Example 9;  
       FIG. 17  introduces a relationship between a concentration of C 2 H 5 OH and an etching rate based on the result obtained in Example 10;  
       FIGS. 18A and 18B  visualize flow charts describing the steps of etching executed in the etching apparatus in accordance with a second preferred embodiment;  
       FIG. 19  relates to a schematic vertical sectional view of an etching apparatus in accordance with a third preferred embodiment;  
       FIG. 20  expresses a flow chart showing the steps of etching executed in the etching apparatus in accordance with the third preferred embodiment;  
       FIG. 21  reproduces a schematic diagram of the etching performed in accordance with the third preferred embodiment;  
       FIG. 22  exemplifies a schematic vertical sectional view of an etching apparatus in accordance with a fourth preferred embodiment;  
       FIG. 23  charts a schematic view of an etching apparatus in accordance with a fifth preferred embodiment;  
       FIG. 24  sets forth a schematic vertical sectional view of a first etching part in the fifth preferred embodiment;  
       FIG. 25  gives a schematic vertical sectional view of a second etching part in the fifth preferred embodiment; and  
       FIGS. 26A and 26B  yield flow charts showing the steps of etching executed in the etching apparatus in accordance with the fifth preferred embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     First Preferred Embodiment  
      Hereinafter, a description will be given of an etching apparatus in accordance with a first preferred embodiment of the present invention.  FIG. 1  schematically illustrates a vertical sectional view of the etching apparatus in accordance with the first preferred embodiment.  FIG. 2  shows a top sectional view thereof; and  FIG. 3  schematically illustrates a wafer before it is etched in accordance with the first preferred embodiment.  
      As shown in  FIGS. 1 and 2 , the etching apparatus  10  is equipped with a chamber  20  for housing a semiconductor wafer W. The chamber  20  includes an outer chamber  30  and an inner chamber  40 , the inner chamber  40  being placed inside the outer chamber  30 .  
      The outer chamber  30  is made of, e.g., Al. However, it can be made of hastelloy or the like and is not limited to Al in its construction. In addition, an inside wall of the outer chamber  30  may be subject to a surface treatment such as an alumite treatment or a PTFE (polytetrafluoroethylene) coating. A ledge  31  is formed on an inside wall of the outer chamber  30  to protrude inward. Openings  32 ,  33 ,  34  are provided as well at certain positions of the outer chamber  30 .  
      A gate valve  50  is installed at an outer end of the opening  32  for the purpose of separating the outer chamber  30  from the exterior environment. One end of a gas exhaust line  60  is connected to the opening  33  at an outer end thereof to exhaust the inner chamber  40 . The other end of the gas exhaust line  60  is connected to a depressurization pump  70 . The inner chamber  40  can be exhausted through the opening  33  by an operation of the depressurization pump  70 . An automatic pressure controller  80  is installed at the gas exhaust line  60  to control the pressure of the inner chamber  40 . The pressure of the inner chamber  40  can be adjusted at a desired level by changing a conductance of the automatic pressure controller  80 .  
      In addition, one end of a gas exhaust line  90  is connected to the opening  34  at an outer end thereof to exhaust a space formed between the outer chamber  30  and the inner chamber  40 . The other end of the gas exhaust line  90  is connected to a depressurization pump  100 . The space formed between the outer chamber  30  and the inner chamber  40  can be exhausted through the opening  34  by an operation of the depressurization pump  100 , thereby preventing a heat transfer between the inner chamber  40  and the outer chamber  30 . An automatic pressure controller  110  is installed at the gas exhaust line  90  to control the pressure in the space formed between the outer chamber  30  and the inner chamber  40 . The pressure in the space formed between the outer chamber  30  and the inner chamber  40  can be adjusted at a desired level by controlling a conductance of the automatic pressure controller  110 .  
      Further, a disk-shaped susceptor  120  is provided in the outer chamber  30  for loading a wafer W thereon. The susceptor  120  is made of, e.g., ceramics such as AlN or Al 2 O 3 . A further description will now be given for the wafer W which is to be loaded on the susceptor  120 .  
      As shown in  FIG. 3 , the wafer W has a P-type Si substrate  1 , a part of the P-type Si substrate  1  being covered with a N-type diffusion layer  2 . It must be noted that the substrate  1  is not limited to a P-type Si substrate but can be a N-type Si substrate instead. A SiO 2  film  3  may be formed on the substrate  1  to function as a field oxide layer, and may have a thickness of about 1000 Å.  
      Further, a SiON film  4  and a HfO 2  film  5  are formed on the P-type Si substrate  1  and the SiO 2  film  3  as gate insulating films. Specifically, the HfO 2  film  5  is placed above the SiON film  4 . The SiON film  4  has a thickness of about 10 Å or less and the HfO 2  film  5  is formed at a thickness of about 20-40 Å. Other Si-containing films may be employed in place of the SiON film  4 . A SiO 2  film and a SiN film exemplify such Si-containing film. Further, other high-k dielectric insulating films may be used in place of the HfO 2  film  5 . Examples of such high-k dielectric insulating film include a metal oxide film such as an Al 2 O 3  film, a ZrO 2  film, a La 2 O 3  film, a Y 2 O 3  film, a CeO 2  film, a Ce 2 O 3  film, a Pr 2 O 3  film, a Pr 6011  film or a PrO 2  film.  
      On the HfO 2  film  5 , a patterned W film  6  is formed to function as a gate electrode. A metal film or a polysilicon film may be used in place of the W film  6 . Examples of the metal film include a Ti film, a Mo film and a Ta film. A SiO 2  film  7  is coated over the W film  6  to work as a sidewall. Other Si-containing films can be employed as well as a sidewall, in place of SiO 2 . For instance, Si-containing film such as a Si 3 N 4  film can be used instead.  
      Three holes  121  are formed and penetrate through the susceptor  120  to help the loading/unloading of the wafer W.  
      The susceptor  120  is supported by, e.g., a ring-shaped supporting member  130  made of ceramics. An air cylinder  140  is connected to the supporting member  130 . The susceptor  120  moves upward and downward by the vertical movement of a rod  141 , the movement being triggered by the operation of the air cylinder  140 . The susceptor  120  stops at two positions: a transfer position for transferring the wafer W; and an etching position for etching the wafer W.  
      Further, the rod  141  is covered with a bellows  150  at an outside of the outer chamber  30 . By covering the rod  141  with the bellows  150  having stretchy properties (i.e., expanding and contracting freely), an air-tightness in the outer chamber  30  can be maintained.  
      Wafer elevating pins  160  are provided under the holes  121  of the susceptor  120  to be inserted thereinto. The wafer elevating pins  160  are fixed perpendicularly to a ring-shaped support  170 .  
      Further, the support  170  for elevating pins is provided with an air cylinder  180 . When a rod  181  in the air cylinder  180  moves downward, the wafer elevating pins  160  are pulled out of the holes  121  and the wafer W (which was supported by the wafer elevating pins  160 ) is placed on the susceptor  120  to be loaded thereon. Conversely, when the rod  181  of the air cylinder  180  moves upwards, the wafer elevating pins  160  are inserted into the holes  121 , thereby unloading the wafer W (which was loaded on the susceptor  120 ) therefrom.  
      The rod  181  is covered with a bellows  190  at an outside of the outer chamber  30 , by which the air tightness of the outer chamber  30  is maintained.  
      A cylindrically shaped member  200  is disposed to surround the susceptor  120  and the supporting member  130 . The cylindrically shaped member  200  is made of, e.g., quartz. At an upper part of the cylindrically shaped member  200 , a flange  201  is formed to protrude inward. An internal diameter of the formed flange  201  is set to be smaller than an outer diameter of the supporting member  130  but is large enough to receive the susceptor  120 . As such, the susceptor  120  is stopped at the etching position by the flange  201 . Also, there is provided a space between the cylindrically shaped member  200  and the outer chamber  30  for communication with the opening  33 .  
      A heat-ray penetration window  210  made of, e.g., quartz is provided under the susceptor  120  to allow heat radiation passing through it. The heat-ray penetration window  210  is fitted into the outer chamber  30  to be fixed therein. A heating chamber  220  is disposed under the heat-ray penetration window  210  to enclose it.  
      Further, heating lamps  230  are provided in the heating chamber  220  for the purpose of heating the susceptor  120 . Once the heating lamps  230  are turned on, the heat-rays radiating therefrom pass through the heat-ray penetration window  210  to heat the susceptor  120 , which is disposed above the heat-ray penetration window  210 . Heating means in the heating chamber  220  can be other heating devices such as a resistance-heating unit and is not limited to the heating lamps  230 .  
      In addition, a motor  240  is connected to the heating lamps  230  so as to rotate the heating lamps  230 . The motor  240  spins a rotating shaft  241  to turn around the heating lamps  230 , thereby entailing a uniform application of heat to the wafer W.  
      The inner chamber  40  is placed on the ledge  31  of the outer chamber  30 . The inner chamber is made of, e.g., quartz. An opening  41  for receiving the wafer W and an exhaust port  42  for exhausting the inner chamber  40  are formed at the bottom of the inner chamber  40 . The exhaust port  42  is located so that it is in communication with the space formed between the outer chamber  30  and the cylindrically shaped member  200 . By placing an exhaust port like this, the inner chamber  40  can be exhausted when the depressurization pump  70  operates.  
      A nozzle  250  is provided in the inner chamber  40  to supply a Hhfac-containing etching gas into the inner chamber  40 . The nozzle  250  is placed in a direction to face the exhaust port  42  and the wafer W is disposed therebetween. As the nozzle  250  is close to the bottom of the inner chamber  40 , the Hhfac-containing etching gas flows along a surface of the wafer W. The nozzle  250  is connected to a gas supply line  260  which has a five-forked end.  
      A first end of the gas supply line  260  is connected to a Hhfac supply source  270  having hexafluoro acetyl acetone (CF 3 COCH 2 COCF 3 : Hhfac) therein. The supply source  270  is not limited to Hhfac but other β-diketone may be employed as well such as tetramethyl heptanedion ((CH 3 ) 3 CCOCH 2 COC(CH 3 ) 3 : Hthd) or acetyl acetone (CH 3 COCH 2 COCH 3 ). An opening/closing valve  280  and a mass flow controller  290  for controlling a Hhfac flow rate are provided at the gas supply line  260  to regulate the feeding of Hhfac. By adjusting the mass flow controller  290 , the Hhfac flow rate can be controlled at a desired level when the valve  280  is opened and Hhfac in the supply source  270  is released into the inner chamber  40 .  
      A second end of the gas supply line  260  is connected to a HF supply source  300  containing absolute HF. An opening/closing valve  310  and a mass flow controller  320  for controlling a HF flow rate are provided at the gas supply line  260  to regulate the feeding of HF. By adjusting the mass flow controller  320 , the HF flow rate can be controlled at a desired level when the valve  310  is opened and HF in the supply source  300  is released into the inner chamber  40 .  
      A third end of the gas supply line  260  is connected to an O 2  supply source  330  containing O 2 . An opening/closing valve  340  and a mass flow controller  350  for controlling an O 2  flow rate are provided at the gas supply line  260  to regulate the feeding of O 2 . By adjusting the mass flow controller  350 , the O 2  flow rate can be controlled at a desired level when the valve  340  is opened and O 2  in the supply source  330  is released into the inner chamber  40 .  
      A fourth end of the gas supply line  260  is connected to a H 2 O supply source  360  containing H 2 O. Alcohol such as ethanol (C 2 H 5 OH) may also be used in place of H 2 O. An opening/closing valve  370  and a mass flow controller  380  for controlling a flow rate of H 2 O are provided at the gas supply line  260  to regulate the feeding of H 2 O. By adjusting the mass flow controller  380 , the H 2 O flow rate can be controlled at a desired level when the valve  370  is opened and H 2 O in the supply source  360  is released into the inner chamber  40 .  
      A fifth end of the gas supply line  260  is connected to a N 2  supply source  390  containing N 2 . An opening/closing valve  400  and a mass flow controller  410  for controlling a flow rate of N 2  are provided at the gas supply line  260  to regulate the feeding of N 2 . By adjusting the mass flow controller  410 , N 2  flow rate can be controlled at a desired level when the valve  400  is opened and N 2  in the supply source  390  is released into the inner chamber  40 .  
      Hereinafter, a description will be given for the etching implemented in the etching apparatus  10  with reference to FIGS.  4  to  8 B.  FIG. 4  is a flow chart showing the etching steps conducted in the etching apparatus  10  in accordance with the first preferred embodiment, and  FIGS. 5 and 6  schematically illustrate the etching performed in accordance with the first preferred embodiment.  FIG. 7A  illustrates a structural formula of Hhfac used in the first preferred embodiment, and  FIG. 7B  shows a structural formula of a Hf complex generated in the first preferred embodiment.  FIG. 8A  delineates a wafer W after a HfO 2  film  5  is etched away in accordance with the first preferred embodiment, and  FIG. 8B  describes a wafer W after a SiON film  4  is removed by etching in accordance with the first preferred embodiment.  
      First, by the operation of the depressurization pump  70 , the inner chamber  40  is exhausted and vacuumized. Also, the depressurization pump  100  exhausts the space formed between the outer chamber  30  and the inner chamber  40  (step  1 A).  
      Subsequently, the heating lamps  230  are turned on to heat the susceptor  120  (step  2 A). Once a pressure in the inner chamber  40  is reduced to 9.31×10 3 -1.33×10 4  Pa and a temperature of the susceptor  120  is elevated to reach 300° C. or higher, the gate valve  50  is opened and a transfer arm (not shown in the drawing), with a wafer W being mounted thereon, is extended to transfer the wafer W into the outer chamber  30  (step  3 A).  
      Next, the transfer arm is pulled out leaving the wafer W therein to be supported by the wafer elevating pins  160 . Once the wafer W is left on the wafer elevating pins  160 , the air cylinder  180  operates to move the wafer elevating pins  160  downward, thereby placing the wafer W on the susceptor  120  to be loaded thereon (step  4 A). Subsequent to the loading of the wafer W on the susceptor  120 , the air cylinder  140  lifts the susceptor  120  in an upward direction to transfer the wafer W into the inner chamber  40  (step  5 A).  
      Once the wafer W is heated and a temperature of the wafer W reaches 300° C. or higher, preferably 450° C. or higher, the opening/closing valves  280 ,  340 ,  370 ,  400  are opened and the Hhfac-containing etching gas is supplied from the nozzle  250  into the inner chamber  40  as shown in  FIG. 5  (step  6 A). The main components in the Hhfac-containing etching gas are Hhfac, O 2 , H 2 O and N 2 . The flow rates of Hhfac, O 2  and N 2  are set at 320-380 sccm, 50-250 sccm and 100-300 sccm, respectively. H 2 O is supplied into the inner chamber  40  with its concentration being about 2000 ppm or less (0 ppm inclusive). The Hhfac-containing etching gas supplied from the nozzle  250  flows along the surface of the wafer W in a laminar flow state. When the Hhfac-containing etching gas comes into contact with the HfO 2  film  5 , Hhfac etches the HfO 2  film  5  through a reaction therewith while the SiO 2  film  7  is functioning as a mask. A reaction mechanism is as follows. Since Hhfac is a tautomeric material, Hhfac can exist in two forms, i.e., structure I and structure II as shown in  FIG. 7A . In structure II, shared electrons between a C═O bond and a C—C bond become delocalized, thereby weakening an O—H bond. If the O—H bond is broken, Hhfac can coordinate with Hf from the HfO 2  film  5  to form a Hf complex as shown in  FIG. 7B . The Hf complex so formed is vaporized and separated from a surface of the HfO 2  film  5 . The reaction mechanism described so far shows how the HfO 2  film  5  is etched away with Hhfac. Once separated from the surface of the HfO 2  film  5 , the Hf complex is exhausted from the outer chamber  30  through the gas exhaust line  60 .  
      After the etching of the HfO 2  film  5  is conducted to expose a surface of the SiON film  4  as shown in  FIG. 8A , the opening/closing valves  280 ,  340 ,  370  are closed and the supply of the Hhfac-containing etching gas is stopped. The heating lamps  230  are also turned off to stop the heating of the susceptor  120 , thereby finishing the etching of the HfO 2  film  5 . However, since the opening/closing valve  400  is still open, N 2  keeps flowing into the inner chamber  40  and cools down the wafer W (step  7 A). Although the wafer W is shown to be cooled with N 2  in the first preferred embodiment, cooling can be achieved with any non-reactive gas and is not limited to N 2 . The wafer W may also be cooled with a separate cooling device installed at the susceptor  120 . The cooling device is, e.g., a peltier device or a water-cooled jacket.  
      After the wafer W is cooled and the temperature of the wafer W lowered to about 100° C. or less, preferably 10-50° C., the opening/closing valves  310 ,  370  are opened and the HF-containing etching gas is supplied from the nozzle  250  into the inner chamber  40  as shown in  FIG. 6  (step  8 A). The main components in the HF-containing etching gas are HF, H 2 O and N 2 . The HF-containing etching gas supplied from the nozzle  250  flows along the surface of the wafer W in a laminar flow state. When the HF-containing etching gas comes into contact with the SiON film  4 , HF reacts therewith to etch the SiON film  4  while the SiO 2  film  7  functions as a mask.  
      The etching of the SiON film  4  is conducted until the surfaces of the P-type Si substrate  1  and SiO 2  film  3  are exposed as shown in  FIG. 8B . Next, the opening/closing valves  310 ,  370 ,  400  are closed and the supply of the HF-containing etching gas is stopped (step  9 A), thereby finishing the etching of the SiON film  4 . After the stoppage of the supply of the HF-containing etching gas, the susceptor  120  moves downward by the operation of the air cylinder  140  and the wafer W is carried out of the inner chamber  40  (step  10 A).  
      Subsequently, the wafer elevating pins  160  are raised by the operation of the air cylinder  180 , whereby the wafer W is taken away from the susceptor  120  (step  11 A). The gate valve  50  is opened and the transfer arm (not shown in the drawing) is extended to keep the wafer W thereon. Next, the transfer arm is retracted to carry the wafer W out of the outer chamber  30  (step  12 A).  
      In the first preferred embodiment, since the Hhfac-containing etching gas is employed for the etching of the HfO 2  film  5  formed on the SiON film  4 , damages to the SiO 2  film  3  can be reduced: for it is believed that a HF solution inflicts damages on the field oxide film due to a non-uniform etching rate in the uneven susceptibility of the film to the etching solution. Through the use of Hhfac having high etching selectivity, etching can be stopped once a SiON film  4  is exposed in etching the HfO 2  film  5  formed on the SiON film  4  in accordance with the first preferred embodiment. Accordingly, the differences in the etching between the part which is more amenable to the etching and the part which is less amenable can be reduced because the etching with the HF-containing etching gas is conducted on the SiON film  4  after the removal of the HfO 2  film  5 . Therefore, damages to the SiO 2  film  3  can be mitigated.  
      In the first preferred embodiment, by the inclusion of O 2  and H 2 O in the Hhfac-containing etching gas, the etching rate can be raised when etching the HfO 2  film  5 . Furthermore, since the etching apparatus  10  is provided with the Hhfac supply source  270  and HF supply source  300 , the HfO 2  film  5  and SiON film  4  can be etched in a single etching apparatus, thereby entailing a heightened throughput.  
      In the first preferred embodiment, since the Hhfac-containing etching gas and HF-containing etching gas are supplied to the wafer in such a way that they flow along a surface of the wafer W, the etching rate thereof can be improved.  
      In the first preferred embodiment, corrosion of the inner chamber  40  can be reduced since the materials fed thereinto are the Hhfac-containing etching gas and HF-containing etching gas. In contrast, if the HF solution was employed instead, it would be hard to remove the HF solution adhered to the chamber and the like therefrom. In the first preferred embodiment, since the Hhfac-containing etching gas, etc. is employed, cleaning can be done simply by exhausting the inner chamber  40  and the corrosion of the inner chamber  40  can be suppressed.  
      In the first preferred embodiment, the inner chamber  40  is made of quartz and the susceptor  120  is made of ceramics. However, the inner chamber  40  may also be made of SiC. The susceptor  120  and other members contacting the gas may also be made of, e.g., quartz, a PTFE (polytetrafluoro ethylene) coated metal, hastelloy or titanium. In such case, corrosion of the inner chamber  40  may be further suppressed.  
     EXAMPLE 1; COMPARATIVE EXAMPLE 1  
      Hereinafter, a description will be given for Example 1 and Comparative Example 1. Subsequent to the etching of a HfO 2  film and an Al 2 O 3  film formed on SiON films, their conditions were checked.  
      The test conditions were as follows. The etching apparatus of the first preferred embodiment was used to etch the HfO 2  film and the Al 2 O 3  film formed on the wafers. The HfO 2  and Al 2 O 3  films were formed on the wafers while the wafers were maintained at a temperature of about 300° C. The etching gas contained Hhfac and O 2 , the respective flow rates thereof being 375 sccm and  100  scam. But H 2 O was not included in the etching gas. The pressure in the inner chamber was about 1.13×10 4  Pa. Such conditions were maintained during the etching of the HfO 2  and Al 2 O 3  films.  
      For comparison, the conditions of HfO 2 , Al 2 O 3  and SiON films were checked in Comparative Example 1 after etching them with a HF solution.  
      Results were as follows. The HfO 2  and Al 2 O 3  films formed on the SiON film were completely removed by etching them in both Example 1 and Comparative Example 1. Meantime, the SiON film in Comparative Example 1 underwent etching while that in Example 1 remained nearly intact.  
      From these observations, it can be ascertained that the etching of the SiON films can be prevented if the etching gas of Example 1 is employed when etching HfO 2  and Al 2 O 3  films.  
     EXAMPLE 2; REFERENCE EXAMPLE 2  
      Hereinafter, a description will be given for Example 2 and Reference Example 2. An optimum temperature of a wafer when etching a HfO 2  film was sought after.  
      The test conditions were as follows. The etching apparatus of the first preferred embodiment was used to etch the HfO 2  film formed on a wafer. The HfO 2  film was formed on the wafer while the wafer was maintained at a temperature of about 300° C. The etching gas contained Hhfac and O 2 , the flow rates thereof being 375 scam and 100 sccm, respectively. But H 2 O was not included in the etching gas. The pressure in the inner chamber was about 1.13×10 4  Pa. While maintaining these conditions, the HfO 2  films were etched at various wafer temperatures.  
      As Reference Example 2, HfO 2  films formed at 150° C. were etched at various wafer temperatures. The HfO 2  film formed at 300° C. is known to be denser than that formed at 150° C.  
      Results are summarized in  FIG. 9  which shows the relationship between the etching rate of the HfO 2  film and the temperature of the wafer. As indicated in  FIG. 9 , the high etching rate was achieved when the temperature of the wafer was 400° C. or higher in etching the HfO 2  film in accordance with Example 2. Meanwhile, the high etching rate was achieved for Reference Example 2 when the temperature of the wafer was 350° C. or higher.  
      Based on the above, it is believed to be preferable to maintain the temperature of the wafer at 400° C. or higher when etching the HfO 2  film in accordance with Example 2. When etching the HfO 2  film in accordance with Reference Example 2, it is believed to be preferable to maintain the temperature of the wafer at 350° C. or higher.  
     EXAMPLE 3; REFERENCE EXAMPLE 3  
      Hereinafter, a description will be given for Example 3 and Reference Example 3. An optimum temperature of a wafer when etching an Al 2 O 3  film was sought after.  
      The test conditions were as follows. The etching apparatus of the first preferred embodiment was used to etch the Al 2 O 3  film formed on the wafer. The Al 2 O 3  film was formed on the wafer while the wafer was maintained at a temperature of about 300° C. The etching gas contained Hhfac and O 2 , the flow rates thereof being 375 sccm and 100 sccm, respectively. But H 2 O was not included in the etching gas. The pressure in the inner chamber was about 1.13×10 4  Pa. While maintaining these conditions, the Al 2 O 3  films were etched at various wafer temperatures.  
      As Reference Example 3, the Al 2 O 3  film formed at 150° C. was etched at various wafer temperatures.  
      The results are summarized in  FIG. 10  which shows the relationship between the etching rate of the Al 2 O 3  film and the temperature of the wafer. As indicated in  FIG. 10 , a high etching rate was achieved when the temperature of the wafer was 400° C. or higher in etching the Al 2 O 3  film in accordance with Example 3; meanwhile, a high etching rate was achieved in case of Reference Example 3 when the temperature of the wafer was 350° C. or higher.  
      Based on the above results, it is believed to be preferable to maintain the wafer at a temperature of 400° C. or higher when etching the Al 2 O 3  film in accordance with Example 3. When etching the Al 2 O 3  film in accordance with Reference Example 3, it is believed to be preferable to maintain the temperature of the wafer at 350° C. or higher.  
     EXAMPLE 4; REFERENCE EXAMPLE 4  
      Hereinafter, a description will be given for Example 4 and Reference Example 4, wherein an optimum pressure in the inner chamber was sought after.  
      The test conditions were as follows. The etching apparatus of the first preferred embodiment was used to etch a HfO 2  film formed on a wafer. The HfO 2  film was formed on the wafer while the wafer was maintained at a temperature of about 300° C. The etching gas contained Hhfac and O 2 , the flow rates thereof being 375 sccm and 100 sccm, respectively. But H 2 O was not included in the etching gas. The etching temperature of the wafer was 450° C. While maintaining these conditions, the HfO 2  film was etched at various inner chamber pressures.  
      As Reference Example 4, the HfO 2  film formed at 150° C. was etched at various inner chamber pressures.  
      The results are summarized in  FIG. 11  which shows the relationship between the etching rate of the HfO 2  film and the pressure in the inner chamber. As indicated in  FIG. 11 , the high etching rate was achieved when the pressure in the inner chamber was 1.06×10 4 -1.20×10 4  Pa in etching the HfO 2  film in accordance with Example 4; meanwhile, the high etching rate was achieved for Reference Example 4 when the pressure in the inner chamber was 0.95×10 4 -1.20×10 4  Pa.  
      Based on the above results, it is believed to be preferable to maintain the pressure in the inner chamber at 1.06×10 4 -1.20×10 4  Pa when etching the HfO 2  film in accordance with Example 4. When etching the HfO 2  film in accordance with Reference Example 4, it is believed to be preferable to maintain the pressure in the inner chamber at 0.95×10 4 -1.20×10 4  Pa.  
     EXAMPLE 5  
      Hereinafter, a description will be given for Example 5, wherein an optimum flow rate of Hhfac was sought after.  
      The test conditions were as follows. The etching apparatus of the first preferred embodiment was used to etch a HfO 2  film formed on a wafer. The etching gas contained Hhfac and O 2 , N 2  and H 2 O. The ratios of Hhfac, O 2  and N 2  in the etching gas were 15:2:8 and the H 2 O concentration therein was 1000 ppm. The pressure in the inner chamber was about 6.65×10 3  Pa and the temperature of the wafer was about 400° C. While maintaining these conditions, the HfO 2  film was etched at various Hhfac flow rates.  
      The results are summarized in  FIG. 12  which shows the relationship between the etching rate and the Hhfac flow rate. As indicated in  FIG. 12 , a high etching rate was achieved when the Hhfac flow rate was 320-380 sccm.  
      Based on the above results, it is believed to be preferable to maintain the Hhfac flow rate at 320-380 sccm when etching a HfO 2  film in accordance with Example 5.  
     EXAMPLE 6; REFERENCE EXAMPLE 6  
      Hereinafter, a description will be given for Example 6 and Reference Example 6, wherein an optimum O 2  concentration when etching a HfO 2  film was sought after.  
      The test conditions were as follows. The etching apparatus of the first preferred embodiment was used to etch a HfO 2  film formed on a wafer. The HfO 2  film was formed on the wafer while the wafer was maintained at a temperature of about 300° C. The etching gas contained Hhfac, O 2  and H 2 O. The flow rate of Hhfac was 375 sccm and the concentration of H 2 O therein was 700 ppm. The pressure in the inner chamber was about 9.31×10 3  Pa and the etching temperature of the wafer was about 450° C. While maintaining these conditions, the HfO 2  film was etched at various O 2  flow rates.  
      As Reference Example 6, HfO 2  film formed at 150° C. was etched at various O 2  flow rates.  
      The results are summarized in  FIG. 13  which shows the relationship between the etching rate of the HfO 2  film and the O 2  flow rate. As indicated in  FIG. 13 , a high etching rate was achieved when the O 2  flow rate was 50-250 sccm in etching the HfO 2  film in accordance with Example 6. Similar results were obtained in case the HfO 2  film was etched in accordance with Reference Example 6 (i.e., high etching rate was achieved when the O 2  flow rate was 50-250 sccm).  
      Based on the above results, it is believed to be preferable to maintain the O 2  flow rate at 50-250 scam when etching a HfO 2  film in accordance with Example 6 and Reference Example 6.  
     EXAMPLE 7; REFERENCE EXAMPLE 7  
      Hereinafter, a description will be given for Example 7 and Reference Example 7, wherein an optimum O 2  concentration when etching an Al 2 O 3  film was sought after.  
      The test conditions were as follows. The etching apparatus of the first preferred embodiment was used to etch an Al 2 O 3  film formed on a wafer. The Al 2 O 3  film was formed on the wafer while the wafer was maintained at a temperature of about 300° C. The etching gas contained Hhfac, O 2  and H 2 O. The flow rate of Hhfac was 375 scam and the concentration of H 2 O therein was 700 ppm. The pressure in the inner chamber was about 9.31×10 3  Pa and the temperature of the wafer was about 450° C. While maintaining these conditions, the Al 2 O 3  film was etched at various O 2  flow rates.  
      As Reference Example 7, Al 2 O 3  film formed at 150° C. was etched at various O 2  flow rates.  
      The results are summarized in  FIG. 14  which shows the relationship between the etching rate of the Al 2 O 3  film and the O 2  flow rate. As indicated in  FIG. 13 , a high etching rate was achieved when the O 2  flow rate was maintained at a range of 50-250 scam in etching the Al 2 O 3  film in accordance with Example 7. A similar result was obtained in case of Reference Example 7 (high etching rate was achieved when the O 2  flow rate was 50-250 sccm).  
      Based on the above results, it is believed to be preferable to maintain the O 2  flow rates at 50-250 sccm when etching the Al 2 O 3  films in accordance with Example 7 and Reference Example 7.  
     EXAMPLE 8; REFERENCE EXAMPLE 8  
      Hereinafter, a description will be given for Example 8 and Reference Example 8, wherein an optimum H 2 O concentration when etching a HfO 2  film was sought after.  
      The test conditions were as follows. The etching apparatus of the first preferred embodiment was used to etch the HfO 2  film formed on a wafer. The HfO 2  film was formed on the wafer while the wafer was maintained at a temperature of about 300° C. The etching gas contained Hhfac, O 2  and H 2 O. The flow rates of Hhfac and O 2  were 375 sccm and 50 sccm, respectively. The pressure in the inner chamber was about 9.31×10 3  Pa and the temperature of the wafer was about 450° C. While maintaining these conditions, the HfO 2  film was etched at various H 2 O concentrations.  
      As Reference Example 8, the HfO 2  film formed at 150° C. was etched at various H 2 O concentrations.  
      The results are summarized in  FIG. 15  which shows the relationship between the etching rate of the HfO 2  film and the H 2 O concentration. As indicated in  FIG. 15 , a high etching rate was achieved when the H 2 O concentration was 1000 ppm or lower in etching the HfO 2  film in accordance with Example 8. A similar result was achieved in case of Reference Example 8 (i.e., the high etching rate was achieved when the H 2 O concentration was 1000 ppm or lower). Furthermore, in both Reference Example 8 and Example 8, a high etching rate could be achieved even when H 2 O was not included.  
      Based on the above results, it is believed to be preferable to maintain the H 2 O concentration at 1000 ppm or less (0 ppm inclusive) when etching a HfO 2  film in accordance with Example 8 and Reference Example 8.  
     EXAMPLE 9; REFERENCE EXAMPLE 9  
      Hereinafter, a description will be given for Example 9 and Reference Example 9, wherein an optimum H 2 O concentration when etching an Al 2 O 3  film was sought after.  
      The test conditions were as follows. The etching apparatus of the first preferred embodiment was used to etch an Al 2 O 3  film formed on a wafer. The Al 2 O 3  film was formed on the wafer while the wafer was maintained at a temperature of about 300° C. The etching gas contained Hhfac, O 2  and H 2 O. The flow rates of Hhfac and O 2  were 375 sccm and 50 sccm, respectively. The pressure in the inner chamber was about 9.31×10 3  Pa and the temperature of the wafer was about 450° C. While maintaining these conditions, the Al 2 O 3  film was etched at various H 2 O concentrations.  
      As Reference Example 9, an Al 2 O 3  film formed at 150° C. was etched at various H 2 O concentrations.  
      The results are summarized in  FIG. 16  which shows the relationship between the etching rate of the Al 2 O 3  film and the H 2 O concentration. As indicated in  FIG. 16 , a high etching rate was achieved when the H 2 O concentration was 1000 ppm or lower in etching the Al 2 O 3  film in accordance with Example 9. A similar result was obtained in case of Reference Example 9 as well (i.e., high etching rate was achieved when the H 2 O concentration was 1000 ppm or lower). In both Example 9 and Reference Example 9, high etching rate could be achieved even when H 2 O was not included.  
      Based on the above results, it is believed to be preferable to maintain the H 2 O concentration at 1000 ppm or less (0 ppm inclusive) when etching an Al 2 O 3  film in accordance with Example 9 and Reference Example 9.  
     EXAMPLE 10  
      Hereinafter, a description will be given for Example 10, wherein an optimum C 2 H 5 OH concentration was sought after.  
      The test conditions were as follows. The etching apparatus of the first preferred embodiment was used to etch a HfO 2  film formed on a wafer. The etching gas contained Hhfac, O 2 , N 2  and C 2 H 5 OH. The flow rates of Hhfac, O 2  and N 2  were 375 scam, 50 scam and 200 scam, respectively. The pressure in the inner chamber was about 6.65×10 3  Pa and the temperature of the wafer was about 400° C. While maintaining these conditions, the HfO 2  film was etched at various C 2 H 5 OH concentrations.  
      The results are summarized in  FIG. 17  which shows the relationship between the etching rate of the HfO 2  film and the C 2 H 5 OH concentration. As indicated in  FIG. 17 , a high etching rate was achieved when the C 2 H 5 OH concentration was 500-1000 ppm.  
      Based on the above results, it is believed to be preferable to maintain the C 2 H 5 OH concentration at 500-1000 ppm when etching a HfO 2  film in accordance with Example 10.  
     Second Preferred Embodiment  
      Hereinafter, a second preferred embodiment of the present invention will be explained. Some of the common expressions between the first and the following preferred embodiments will be omitted for the sake of simplicity. In the second preferred embodiment, explanations will be given on alternating the supply of a Hhfac-containing etching gas and a H 2 O-containing gas; and alternating the supply of a HF-containing etching gas and a H 2 O-containing gas.  
       FIGS. 18A and 18B  represent the flow charts showing the etching implemented in the etching apparatus  10  in accordance with the second preferred embodiment.  
      First, a depressurization pump  70  is operated to exhaust an inner chamber  40 . And a depressurization pump  100  is operated as well to create a vacuum in a space formed between an outer chamber  30  and an inner chamber  40  (step  1 B).  
      Next, heating lamps  230  are turned on to heat a susceptor  120  (step  2 B). Once the pressure in the inner chamber  40  is reduced to 9.31×10 3 -1.33×10 4  Pa and the temperature of the susceptor  120  is elevated to a certain level, a gate valve  50  is opened and a transfer arm (not shown in the drawing), with a wafer W being mounted thereon, is extended to transfer the wafer W into the outer chamber  30  (step  3 B).  
      Next, the transfer arm is pulled out leaving the wafer W therein to be supported by the wafer elevating pins  160 . Once the wafer W is left on the wafer elevating pins  160 , an air cylinder  180  operates to move the wafer elevating pins  160  downward, thereby placing the wafer W on the susceptor  120  to be loaded thereon (step  4 B). Subsequent to the loading of the wafer W on the susceptor  120 , another air cylinder  140  lifts the susceptor  120  in an upward direction to transfer the wafer W into the inner chamber  40  (step  5 B).  
      Once the wafer W is heated, the opening/closing valves  280 ,  340 ,  400  are opened and a Hhfac-containing etching gas is supplied (step  6 B). The Hhfac-containing etching gas includes Hhfac, O 2  and N 2 . When the Hhfac-containing etching gas comes into contact with a surface of a HfO 2  film  5 , Hhfac is adsorbed onto the surface of the HfO 2  film  5 . The remainder of the Hhfac-containing etching gas which remains unadsorbed on the surface of the HfO 2  film  5  is exhausted from the inner chamber  40 .  
      After an elapse of a predetermined time, the valves  280 ,  340  are closed and the supply of the Hhfac-containing etching gas is stopped. However, since the valve  400  is still open, N 2  keeps flowing into the inner chamber  40 , thereby purging the inner chamber  40 . Accordingly, the remaining Hhfac except what has been adsorbed on the surface of the HfO 2  film  5  is exhausted from the inner chamber  40  (step  7 B).  
      After an elapse of a predetermined time, an opening/closing valve  370  is opened and a H 2 O-containing gas is supplied into the inner chamber  40  (step  8 B). The H 2 O-containing gas may include H 2 O and N 2 —Once the H 2 O-containing gas reaches the surface of the HfO 2  film  5 , a reaction between the HfO 2  film  5  and the portion of Hhfac adsorbed thereon is triggered and the HfO 2  film  5  is etched.  
      After an elapse of a predetermined time, the valve  370  is closed and the supply of the H 2 O-containing gas is stopped, thereby ending the etching of the HfO 2  film  5 . Since the valve  400  is still open, N 2  keeps flowing into the inner chamber  40  to purge the inner chamber  40  and exhaust the H 2 O remaining therein (step  9 B).  
      Next, a series of steps  6 B to  9 B is set as one cycle and a central controller (not shown in the drawing) determines whether or not to proceed to a next step based on the number of cycles (step  10 B). If it is determined that a predetermined number has not been reached (i.e., the etching has not been conducted enough), the series of steps  6 B to  9 B will be repeated.  
      Once the etching of the HfO 2  film  5  is estimated to have been conducted for the predetermined number of cycles, the heating of the susceptor  120  is stopped. And N 2  is supplied into the inner chamber  40  for a certain duration to cool down the wafer W (step  11 B). A surface of a SiON film  4  is in an exposed state when the HfO 2  film  5  is subject to etching for the predetermined number of cycles.  
      After the cooling of the wafer W, an opening/closing valve  310  is opened and a HF-containing etching gas is supplied into the inner chamber  40  (step  12 B). Main components in the HF-containing etching gas are HF and N 2 . When the HF-containing etching gas comes into contact with a surface of a SiON film  4 , HF is adsorbed onto the surface of the SiON film  4 . The HF-containing etching gas other than what has been adsorbed on the surface of the SiON film  4  is exhausted from the inner chamber  40 .  
      After an elapse of a predetermined time, the valve  310  is closed and the supply of the HF-containing etching gas is stopped. However, since the valve  400  is still open, N 2  keeps flowing into the inner chamber  40 , thereby purging the inner chamber  40 . Accordingly, the remaining HF except what has been adsorbed on the surface of the SiON film  4  is exhausted from the inner chamber  40  (step  13 B).  
      After an elapse of a predetermined time, the valve  370  is opened and a H 2 O-containing gas is supplied into the inner chamber  40  (step  14 B). Once the H 2 O-containing gas reaches the surface of the SiON film  4 , a reaction between the SiON film  4  and HF adsorbed thereon is triggered and the SiON film  4  is etched.  
      After an elapse of a predetermined time, the valve  370  is closed and the supply of the H 2 O-containing gas is stopped, thereby ending the etching of the SiON film  4 . Since the valve  400  is still open, N 2  keeps flowing into the inner chamber  40  to purge the inner chamber  40  and exhaust H 2 O remaining therein (step  15 B).  
      Next, a series of steps  12 B to  15 B is set as one cycle and a central controller (not shown in the drawing) determines whether or not to proceed to a next step based on the number of cycles (step  16 B). If it is deemed that the predetermined number has not been reached (i.e., the etching has not been conducted enough), the series of steps  12 B to  15 B will be repeated.  
      If the etching of the SiON film  4  is estimated to have been conducted for a predetermined number of cycles, the susceptor  120  descends by the operation of an air cylinder  140  to transfer the wafer W out of the inner chamber  40  (step  17 B). Surfaces of a P-type Si substrate  1  and a SiO 2  film  3  are in exposed states if the SiON film  4  was subjected to etching for a predetermined number of cycles.  
      Next, wafer elevating pins  160  move upwards by the operation of an air cylinder  180 , whereby the wafer W is unloaded from the susceptor  120  (step  18 B). Finally, a gate valve  50  is opened and the wafer W is carried out of the outer chamber  30  (step  19 B).  
      In the second preferred embodiment, by alternating the supply of the Hhfac-containing etching gas and that of the H 2 O-containing gas, the HfO 2  film  5  can be etched more accurately.  
      In addition, by alternating the supply of the HF-containing etching gas and that of the H 2 O-containing gas, the SiON film  4  can be etched in a more accurate fashion.  
     Third Preferred Embodiment  
      In accordance with a third preferred embodiment of the present invention, a SiON film will be etched using F radicals.  FIG. 19  illustrates a schematic vertical sectional view of an etching apparatus employed in the third preferred embodiment.  
      As shown in  FIG. 19 , a gas supply line  260  is connected to a F 2  supply source  510  (containing F 2 ) instead of a HF supply source  300 . A recess is formed near a nozzle  250  in an outer chamber  30  and a UV lamp  520  for emitting a UV light is provided therein. After the UV lamp  520  is turned on, the UV light generated from the UV lamp  520  is applied to the inner chamber  40  through the bottom thereof.  
      Hereinafter, a description will be given for the etching implemented in the etching apparatus  10 ′ with reference to  FIGS. 20 and 21 .  FIG. 20  is a flow chart showing the etching implemented in the etching apparatus  10 ′ in accordance with the third preferred embodiment, and  FIG. 21  illustrates a schematic view of the etching in accordance with the third preferred embodiment.  
      First, by the operation of the depressurization pump  70 , the inner chamber  40  is exhausted and evacuated. Also, the depressurization pump  100  exhausts a space formed between the outer chamber  30  and the inner chamber  40  (step  1 C).  
      Subsequently, the heating lamps  230  are turned on to heat the susceptor  120  (step  2 C). Once the pressure in the inner chamber  40  is reduced to 9.31×10 3 -1.33×10 4  Pa and the temperature of the susceptor  120  is elevated to reach 300° C. or higher, the gate valve  50  is opened and a transfer arm (not shown in the drawing), with a wafer W being mounted thereon, is extended to transfer the wafer W into the outer chamber  30  (step  3 C).  
      Next, the transfer arm is pulled out leaving the wafer W therein to be supported by the wafer elevating pins  160 . Once the wafer W is left on the wafer elevating pins  160 , the air cylinder  180  operates to move the wafer elevating pins  160  downward, thereby placing the wafer W on the susceptor  120  to be loaded thereon (step  4 C). Subsequent to the loading of the wafer W on the susceptor  120 , the air cylinder  140  lifts the susceptor  120  in an upward direction to transfer the wafer W into the inner chamber  40  (step  5 C).  
      After the wafer W is heated and the temperature of the wafer W reaches 300° C. or higher, preferably 450° C. or higher, the opening/closing valves  280 ,  340 ,  370 ,  400  are opened and a Hhfac-containing etching gas is supplied into the inner chamber  40  (step  6 C), thereby initiating the etching of a HfO 2  film  5 .  
      The etching of the HfO 2  film  5  is conducted and a surface of a SiON film  4  is exposed. Next, the valves  280 ,  340 ,  370  are closed while leaving the valve  400  in an opened state, whereby the supply of the Hhfac-containing etching gas is stopped. And the heating lamps  230  are turned off to stop the heating of the susceptor  120 . This finishes the etching of the HfO 2  film  5 . At the same time, the wafer W is cooled down by N 2  (step  7 C).  
      After the wafer W is cooled and the temperature of the wafer W is stabilized at about 100° C. or less, preferably at 10-50° C., the opening/closing valves  310 ,  370  are opened and a F 2 -containing etching gas is supplied into the inner chamber  40 . The UV lamp  520  is turned on and the UV light is applied to the inner chamber  40  as shown in  FIG. 21  (step  8 C). The main components in the F 2 -containing etching gas are F 2 , N 2  and H 2 O. When the F 2 -containing etching gas is supplied into the inner chamber  40 , F 2  is excited by UV light and F radicals are generated. The F radicals etch the SiON film  4  by reacting therewith.  
      The etching of the SiON film  4  is conducted until a surface of a P-type Si substrate  1  and a SiO 2  film  3  is exposed whereby the opening/closing valves  310 ,  370 ,  400  are closed to stop the supply of the F 2 -containing etching gas. Furthermore, the UV lamp  520  is turned off and thus the generation of UV light is stopped (step  9 C). This finishes the etching of the SiON film  4 . After the supply of the F 2 -containing etching gas is stopped, the susceptor  120  moves downward by the operation of the air cylinder  140  and the wafer W is carried out of the inner chamber  40  (step  10 C).  
      Subsequently, the wafer elevating pins  160  move upward by the operation of the air cylinder  180  and the wafer W is unloaded from the susceptor  120  (step  11 C). Finally, the gate valve  50  is opened and the wafer W is transferred out of the outer chamber  30  (step  12 C).  
     Fourth Preferred Embodiment  
      Hereinafter, a fourth preferred embodiment of the present invention will exemplify a showerhead for use in supplying a Hhfac-containing etching gas.  FIG. 22  illustrates a schematic vertical sectional view of the etching apparatus in accordance with the fourth preferred embodiment.  
      As shown in  FIG. 22 , the etching apparatus  10 ″ is provided with a chamber  610  made of, e.g., Al. The chamber may be made of SiC, hastelloy or the like and is not limited to Al in its construction. An inside wall of the chamber  610  may be subject to a surface treatment such as an alumite treatment or a PTFE (polytetrafluoroethylene) coating. Openings  611 ,  612  are formed on predetermined positions of the chamber  610 .  
      A gate valve  50  is attached to an outer end of the opening  611  and a gas exhaust line  60  is connected to an outer end of the opening  612 . A cylindrical reflector  620  is provided in the chamber  610  to reflect light radiated from the heating lamps  230 . The reflector  620  is made of, e.g., Al. A supporting member  630  is fixed to an upper part of the reflector  620  to support a susceptor  120 , the supporting member  630  being made of, e.g., quartz.  
      The showerhead  640  is disposed on top of the chamber  610  in such a manner that the Hhfac-containing etching gas can be directed towards the susceptor  120 . The showerhead  640  includes a gas feed unit  641  for supplying Hhfac and HF and a gas feed unit  642  for supplying O 2 , H 2 O and N 2 . A plurality of gas supply holes are formed at the gas feed units  641 ,  642  to supply gases, such as Hhfac, therethrough.  
      A gas supply line  650  with a two-forked end is connected to the gas feed unit  641  and a gas supply line  660  with a three-forked end is connected to the gas feed unit  642 . The gas supply line  650  is connected to a Hhfac supply source  270  and a HF supply source  300  while the gas supply line  660  is connected to an O 2  supply source  330 , a H 2 O supply source  360  and a N 2  supply source  390  with their forked ends.  
     Fifth Preferred Embodiment  
      Hereinafter, a fifth preferred embodiment of the present invention will be explained for the employment of separate chambers in etching a HfO 2  film and a SiON film.  FIG. 23  illustrates a schematic view of an etching apparatus in accordance with the fifth preferred embodiment.  FIG. 24  shows a schematic vertical sectional view of a first etching part in accordance with the fifth preferred embodiment; and  FIG. 25  illustrates a schematic vertical sectional view of a second etching part in accordance therewith.  
      As shown in FIGS.  23  to  25 , main constituents of the etching apparatus  10 ″′ are the first etching part  10 A for etching the HfO 2  film  5 , the second etching part  10 B for etching the SiON film  4  and a transfer system  11  for transferring a wafer W.  
      The structure of the first etching part  10 A is almost identical to that of the etching apparatus  10  in  FIG. 1 . Only the HF supply source  300  is lacking in the first etching part  10 A. Likewise, the second etching part  10 B has almost the same structure as given in the etching apparatus  10  of  FIG. 1 . However, heating lamps  230 , Hhfac supply source  270  and O 2  supply source  330  are not provided in the second etching part  10 B.  
      The transfer system  11  is provided with a transfer chamber  12  which is connected to gate valves  50 A,  50 B. A transfer arm  13  is provided in the transfer chamber  12  to carry the wafer W into the first etching part  10 A or its counterpart. The transfer chamber  12 A is connected to a load-lock chamber  14  via a gate valve  15 , the load-lock chamber  14  being used to receive a carrier cassette storing about 25 wafers W therein.  
      Hereinafter, a description will be given for the etching implemented in the etching apparatus  10 ″′ with reference to  FIGS. 26A and 26B .  FIGS. 26A and 26B  are flow charts showing the etching implemented in the etching apparatus  10 ″′ in accordance with the fifth preferred embodiment.  
      First, depressurization pumps  70 A,  70 B are operated to exhaust inner chambers  40 A,  40 B. And depressurization pumps  100 A,  100 B are operated as well to evacuate: a space formed between an outer chamber  30 A and the inner chamber  40 A; and a space formed between an outer chamber  30 B and the inner chamber  40 B (step  1 D).  
      Subsequently, heating lamps  230 A are turned on to heat a susceptor  120 A (step  2 D). Once the pressures in both inner chambers  40 A,  40 B are reduced to 9.31×10 3 -1.33×10 4  Pa and the temperature of the susceptor  120 A is elevated to reach 300° C. or higher, a gate valve  15  is opened and the transfer arm  13  takes the wafer W out of the carrier cassette placed in the load-lock chamber  14 . Next, the gate valve  50 A is opened and the transfer arm  13  is extended therein to transfer the wafer W into the outer chamber  30 A (step  3 D).  
      Thereafter, the transfer arm  13  is pulled out leaving the wafer W therein to be supported by the wafer elevating pins  160 A. Once the wafer W is left on the wafer elevating pins  160 A, an air cylinder  180 A operates to move the wafer elevating pins  160 A downward, thereby placing the wafer W on the susceptor  120 A to be loaded thereon (step  4 D). Subsequent to the loading of the wafer W on the susceptor  120 A, the air cylinder  140 A lifts the susceptor  120 A in an upward direction to transfer the wafer W into the inner chamber  40 A (step  5 D).  
      Once the wafer W is heated and the temperature of the wafer W reaches 300° C. or higher, preferably 450° C. or higher, the opening/closing valves  280 A,  340 A,  370 A,  400 A are opened and the Hhfac-containing etching gas is supplied into the inner chamber  40 A (step  6 D), thereby initiating the etching of a HfO 2  film  5 .  
      The etching of the HfO 2  film  5  is conducted and a surface of a SiON film  4  is exposed. Next, the valves  280 A,  340 A,  370 A and  400 A are closed to stop the supply of the Hhfac-containing etching gas. (step  7 D). This finishes the etching of the HfO 2  film  5 .  
      After the stoppage of the supply of the Hhfac-containing etching gas, the susceptor  120 A moves downward by the operation of the air cylinder  140 A and the wafer W is transferred out of the inner chamber  40 A (step  8 D).  
      Subsequently, the wafer elevating pins  160 A move upward by the operation of the air cylinder  180 A and the wafer W is unloaded from the susceptor  120 A (step  9 D). Finally, the gate valve  50 A is opened and the wafer W is transferred out of the outer chamber  30 A (step  10 D).  
      Thereafter, the gate valve  50 B is opened and the transfer arm  13  extends to feed the wafer W into the outer chamber  30 B (step  11 D).  
      Next, the transfer arm  13  is pulled out leaving the wafer W therein to be supported by the wafer elevating pins  160 B. Once the wafer W is left on the wafer elevating pins  160 B, an air cylinder  180 B operates to move the wafer elevating pins  160 B downward, thereby placing the wafer W on the susceptor  120 B to be loaded thereon (step  12 D). Subsequent to the loading of the wafer W on the susceptor  120 B, another air cylinder  140 B lifts the susceptor  120 B in an upward direction to transfer the wafer W into the inner chamber  40 B (step  13 D).  
      After the wafer W is transferred into the inner chamber  40 B, opening/closing valves  310 B,  370 B,  400 B are opened and a HF-containing etching gas is supplied into the inner chamber  40  (step  14 D), thereby initiating the etching of a SiON film  4 .  
      After the etching of the SiON film  4  is conducted to expose surfaces of a P-type Si substrate  1  and a SiO 2  film  3 , the opening/closing valves  310 B,  370 B,  400 B are closed and the supply of the HF-containing etching gas is stopped (step  15 D). This finishes the etching of the SiON film  4 .  
      After the supply of the HF-containing etching gas is stopped, the susceptor  120 B descends by the operation of the air cylinder  140 B and the wafer W is carried out of the inner chamber  40 B (step  16 D). Subsequently, the wafer elevating pins  160 B move upward by the operation of the air cylinder  180 B and the wafer W is unloaded from the susceptor  120 B (step  17 D).  
      Once the wafer W is unloaded from the susceptor  120 B, the gate valve SOB is opened and the transfer arm  13  takes the wafer W out of the outer chamber  30 B (step  18 D).  
      The present invention has been described in an illustrative manner and it is to 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 present invention. Proper modifications of structures, materials and arrangements of members in accordance with the present invention are possible. In the first to fifth preferred embodiments, a Hhfac-etching (etching with the Hhfac-containing etching gas) is conducted on the HfO 2  film  5 . However, a metal film may be a subject of the Hhfac-etching as well. Examples of the metal film may include Al, Zr, Hf, Y, La, Ce and Pr. Furthermore, a glass substrate may be used instead of the wafer W.  
      The first, second, fourth and fifth preferred embodiments employ a HF-containing etching gas. However, an etching solution, such as a HF solution, may be used in place of the HF-containing etching gas.  
      In the first, third, fourth and fifth preferred embodiments, the main components in the Hhfac-containing etching gas are Hhfac, O 2 , H 2 O and N 2  and those in the second preferred embodiment are Hhfac, O 2  and N 2 . However, components other than Hhfac may be removed from the Hhfac-containing etching gas.  
      In the first, fourth and fifth preferred embodiments, main components in the HF-containing etching gas are HF, H 2 O and N 2  and those in the second preferred embodiment are HF and N 2 . However, components other than HF may be removed from the HF-containing etching gas. Additionally, even though the main components in the F 2 -containing etching gas of the third preferred embodiment are F 2 , H 2 O and N 2 , components other than F 2  may be removed from the F 2 -containing etching gas.  
     Industrial Applicability  
      It is possible to apply the etching method and the etching apparatus in accordance with the present invention to the semiconductor fabrication industry.