Abstract:
Etching and protective-film deposition operations E and D are in alternation repeatedly executed on a silicon substrate carried on a platform within a processing chamber. With gas inside the processing chamber having been exhausted to pump down the chamber interior, in the etching operation E, the substrate is etched by supplying etching gas into the chamber and converting it into plasma and applying a bias potential to the platform, and in the protective-film deposition operation D, a protective film is formed on the silicon substrate by supplying protective-film deposition gas into the processing chamber and converting it into plasma. When a predetermined time prior to the close of operations E and D (time intervals indicated by reference marks Ee and De) is reached, the supply of etching or protective-film deposition gas is halted, and the exhaust flow rate of gas exhausted from the chamber is made greater than that previously.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Technical Field  
         [0002]     The present invention relates to silicon-substrate etching methods and etching apparatuses structured to execute, repeatedly in alternation, an etching operation in which an etching gas is converted into plasma to etch the silicon substrate, and a protective-film deposition operation in which a protective-film deposition gas is converted into plasma to form a protective film on the silicon substrate.  
         [0003]     2. Description of the Related Art  
         [0004]     Examples of the above-mentioned etching technique known to date include the method disclosed in Japanese Unexamined Pat. App. (based on Int&#39;l. app.) Pub. No. H07-503815. This etching technique is one in which silicon substrates are etched by placing a silicon substrate on a platform in a processing chamber and then executing repeatedly in alternation, as indicated in  FIG. 8 : an etching operation E, in which etching gas is supplied into the processing chamber at a constant flow rate and converted into plasma, and at the same time a bias potential is applied to the platform; and a protective-film deposition operation D, in which a protective-film deposition gas is supplied into the processing chamber at a constant flow rate and converted into plasma to form a protective film on the silicon substrate.  
         [0005]     In the etching operation E, the etching gas is converted to plasma, generating ions, electrons, radicals, and so on. The silicon substrate is etched by the radicals chemically reacting with the silicon atoms and, as a consequence of the potential difference (bias potential) produced between the platform and the plasma, by the ions traveling toward and colliding with the silicon substrate (platform). Accordingly, in the silicon substrate, which is covered with a photoresist mask of a predetermined pattern (lines, circles, etc.), those areas not covered by the mask are etched, forming grooves and holes provided with predetermined width and depth.  
         [0006]     Meanwhile, in the protective-film deposition operation D, the protective-film deposition gas is converted to plasma, and, as is the case with the etching gas, ions, electrons, and radicals are generated. The radicals create polymers, and the polymer formation is deposited on the sidewalls and bottoms of the grooves and holes, whereby a protective film that does not react with the radicals generated by the etching gas is formed.  
         [0007]     Thus, according to the etching technique of repeating the etching operation E and the protective-film deposition operation D in alternation: in the etching operation E, along the bottoms of the grooves or holes, where the ion bombardment is heavy, protective film removal by ion bombardment and etching by radical and ion bombardment proceed, and along the sidewalls of the grooves and holes, where the ion bombardment is slight, only protective film removal by ion bombardment proceeds, with etching of the sidewalls being prevented; and in the protective film deposition operation D, polymers are deposited on the bottoms and sidewalls again to form a protective film. Accordingly, the new groove and hole sidewalls formed by the etching operation E are immediately protected by the protective film formed by the protective-film deposition operation D, whereby etching progresses only along the depth of the grooves and holes.  
         [0008]     It should be noted that the gases inside the processing chamber are exhausted to the exterior at a constant flow rate by means of a suitable exhaust device; this device reduces the pressure inside the processing chamber, and at the same time discharges outside the processing chamber the etching gas and the protective-film deposition gas consumed in etching the silicon substrate and forming the protective film.  
         [0009]     In order to execute the protective-film deposition operation D after execution of the etching operation E, it is necessary to supply the protective-film deposition gas into the processing chamber, to exchange or replace the etching gas in the processing chamber with the protective film deposition gas. Likewise, in order to execute the etching operation E after execution of the protective-film deposition operation D, it is necessary to supply the etching gas into the processing chamber, to exchange or replace the protective film deposition gas in the processing chamber with the etching gas. However, this exchanging of gases requires a certain amount of time.  
         [0010]     Consequently, for a certain time following the transition from the etching operation E to the protective-film deposition operation D and following the transition from the protective-film deposition operation D to the etching operation E, the etching gas and the protective-film deposition gas become mixed, and the etching process induced by the etching gas and the protective-film deposition process induced by the protective-film deposition gas proceed simultaneously. As a result, the etching of, and the forming of the protective film on, the silicon substrate that should be carried out by the etching operation E and the protective-film deposition operation D cannot be adequately performed.  
         [0011]     Accordingly, several problems occur in situations in which it takes a long time to replace the gases: the etch rate is lowered; high-precision etching profiles cannot be obtained because a high-quality protective film does not form, leading to inadequate protection of the sidewalls; and mask selectivity is lowered because the protective effectiveness of the mask is weakened. These problems are especially pronounced when processing times in the etching operation E and protective-film deposition operation D are short, such that the number of gas replacements is large during a given etching process time, or when the etching operation E and protective-film deposition operation D are performed under high pressure, wherein it takes time to exchange the gases.  
         [0012]     However, in the above-described conventional etching technique, the gases are exchanged by exhausting the gas within the processing chamber at a constant flow rate and at the same time supplying the etching gas or protective-film deposition gas into the processing chamber at a constant flow rate, wherein a problem with the technique has been that time required to exchange the gases is prolonged, as will be understood from the fact that, as indicated in  FIG. 9 , after the gas supply is halted it takes a long time for the pressure in the processing chamber to stabilize (until the gas in the processing chamber is completely exhausted) and from the fact that, as indicated in  FIG. 10 , after the gas supply is started it takes a long time for the pressure in the processing chamber to stabilize (until the gas completely fills the processing chamber). Herein,  FIG. 9 ( a ) and  FIG. 10 ( a ) are graphs plotting the relationship between gas-supply flow rate and time in a conventional example, while  FIG. 9 ( b ) and  FIG. 10 ( b ) are graphs plotting the relationship between pressure within the processing chamber and time in the conventional example.  
         [0013]     Furthermore, as a consequence of a time lag, as indicated in  FIG. 9 ( a ) and  FIG. 10 ( a ), that occurs between the controlled supply flow rate that is the control target value and the actual supply flow rate, system disturbances arise, such as the continuance of the etching-gas or protective-film-forming-gas supply even after the close of either operation (after transitioning from one operation to the other), and the occurrence of a time interval during which gas supply into the processing chamber immediately after the start of either operation does not take place. These factors also rule out the efficient exchange of gases within the processing chamber.  
         [0014]     Consequently, the conventional etching technique discussed above has not allowed the etch rate to be quickened or the mask selectivity to be heightened, nor has it allowed high-precision etching profiles to be obtained.  
       BRIEF SUMMARY OF THE INVENTION  
       [0015]     In light of the above realities, it is an object of the present invention to provide an etching method and an etching apparatus that can efficiently exchange the gases in the processing chamber to speed up the etch rate, improve the mask selectivity, and obtain high-precision etching profiles.  
         [0016]     In order to achieve the above mentioned object, the present invention involves a method of etching a silicon substrate placed on a platform in a processing chamber, comprising: an etching operation of etching the silicon substrate by supplying an etching gas into the processing chamber in a state that gas in the processing chamber is exhausted to pump down inside of the processing chamber so that the etching gas is converted to plasma and a bias potential is applied to the base; and a protective-film deposition operation of forming a protective film on the silicon substrate by supplying a protective film deposition gas into the processing chamber in a state that gas in the processing chamber is exhausted to pump down inside of the processing chamber so that the protective film deposition gas is converted to plasma; wherein the etching operation and the protective-film deposition operation are repeated alternately, the supply of the etching gas or the protective film deposition gas is stopped a predetermined time before the end of each step, and an exhaust flow rate for exhausting the gas from the processing chamber is, during a time period from the predetermined time before the end to the end of each step, set higher than an exhaust flow rate before the predetermined time before the end.  
         [0017]     This etching method can optimally be implemented with the following etching apparatus.  
         [0018]     An etching apparatus comprising: a processing chamber having a closed space; a platform disposed at a lower portion in the processing chamber and on which a silicon substrate is placed; platform power supply means for applying RF power to the base; gas supply means for supplying etching gas and protective film deposition gas into the processing chamber, the gas supply means being configured such that supply flow rates of the etching gas and the protective film deposition gas can be adjusted; a coil being disposed around the processing chamber; coil power supply means for applying RF power to the coil to convert the etching gas and the protective film deposition gas in the processing chamber to plasma; exhaust means for exhausting the gas in the processing chamber to pump down inside of the processing chamber, the exhaust means being configured such that an exhaust flow rate of the gas can be adjusted; and control means for controlling the platform power supply means, the coil power supply means, the gas supply means and the exhaust means; the control means, by controlling the gas supply means to adjust supply flow rates of the etching gas and the protective film deposition gas to be supplied into the processing chamber, alternately repeats an etching operation of supplying the etching gas into the processing chamber to etch the silicon substrate, and a protective-film deposition operation of supplying the protective film deposition gas into the processing chamber to form protective films on the silicon substrate, and the platform power supply means applies RF power to the platform when at least the etching operation is performed, the control means stops the supply of the etching gas or the protective film deposition gas from the gas supply means a predetermined time before the end of each step, and the control means controls the exhaust means to set an exhaust flow rate of the gas exhausted from the processing chamber higher than an exhaust flow rate before the predetermined time, during a time period from the predetermined time before the end to the end of the step. According to this etching apparatus, after the silicon substrate is placed on the platform in the processing chamber, the etching operation of supplying the etching gas into the processing chamber and the protective-film deposition operation of supplying the protective film deposition gas into the processing chamber are repeated alternately to etch the silicon substrate.  
         [0019]     More specifically, in the etching operation, under control of the control means, the gas supply means supplies the etching gas into the processing chamber at a constant flow rate, and the coil power supply means and the platform power supply means apply RF power to the coil and the platform, respectively. The inside gas is exhausted by the exhaust means at a constant flow rate, so that the inside of the processing chamber is pumped down to the predetermined pressure.  
         [0020]     When RF power is applied to the coil, a magnetic field is generated in the processing chamber. The magnetic field induces an electric field, and the electric field in turn converts the etching gas in the processing chamber to plasma including ions, electrons, and radicals. Meanwhile, when RF power is applied to the platform, a potential difference (bias potential) is generated between the platform and the plasma.  
         [0021]     The radicals react chemically with the silicon atoms, and the ions are moved by the bias potential toward the silicon substrate (base) to collide with it. As a result, the silicon substrate that is covered with a mask of resist having a predetermined pattern (lines or circles) is etched only at portions that are not covered with the mask, so that grooves or holes having predetermined width and depth are formed.  
         [0022]     Meanwhile, in the protective-film deposition operation, as mentioned before, under control of the control means, the gas supply means supplies the protective film deposition gas at the constant flow rate into the processing chamber, and the coil power supply means applies RF power to the coil. The gas in the processing chamber is exhausted at the constant flow rate by the exhaust means, so that the inside of the processing chamber is pumped down to the predetermined pressure.  
         [0023]     The protective film deposition gas supplied into the processing chamber is converted by the electric field to plasma including ions, electrons, and radicals. The polymer is generated from the radicals and is deposited on the sidewalls and bottom surfaces of the grooves or holes. As a result, on the sidewalls and bottom surfaces are generated protective films that do not react with the radicals generated by the etching gas.  
         [0024]     As a result, in the etching operation, removing the protective film by the ion bombardment and etching by the radical and ion bombardment are progressed on the bottom surfaces of the grooves or holes because of heavy ion bombardment, and only removing the protective film by the ion bombardment is progressed on the sidewalls of the grooves or holes, i.e., the sidewalls are prevented from being etched because of light ion bombardment. In the protective-film deposition operation, the polymer is deposited again on the bottom surfaces and sidewalls to make protective films so that new sidewalls formed in the etching operation can be protected immediately. Thus, the etching is progressed in the grooves or holes only along the depth.  
         [0025]     As described above, since it takes a certain time for exchange (replacement) of the gases in the processing chamber when shifting from the etching operation to the protective-film deposition operation or shifting from the protective-film deposition operation to the etching operation, the etching gas and the protective film deposition gas are mixed until the certain time elapses since the start of each step. Consequently, etching of the silicon substrate or forming of the protective film can not be sufficiently performed, which should be performed in the etching operation or the protective-film deposition operation. Accordingly, if the time of exchanges of the gases becomes long, some problems occur such as lowering of the etch rate, form accuracy of etching, and mask selectivity.  
         [0026]     Therefore, in the etching apparatus according to the present invention, the control means controls the gas supply flow rate from the gas supply means and the exhaust flow rate by the exhaust means such that the supply of the etching gas or the protective film deposition gas is stopped the predetermined time before the end of each step, and the exhaust flow rate out of the processing chamber is set higher than that before the predetermined time before the end of each step (than the constant flow rate) during a time period from the predetermined time before the end to the end of the step.  
         [0027]     As a result, when shifting from the etching operation to the protective-film deposition operation, the protective film deposition gas is supplied into the processing chamber at the high flow rate during the predetermined time, while exhausting an amount of the etching gas in the processing chamber at the high flow rate. When shifting from the protective-film deposition operation to the etching operation, the etching gas is supplied into the processing chamber at the high flow rate during the predetermined time while exhausting an amount of the protective film deposition gas in the processing chamber at the high flow rate, so that it is possible to efficiently exchange the gases in the processing chamber to achieve an etching gas or protective film deposition gas atmosphere in the processing chamber in a short period of time.  
         [0028]     Even if the control means controls the gas supply means to stop the gas supply when shifting the steps, a delay (time lag) occurs from an instant when the gas supply is stopped to an instant when the flow rate of the gas to be supplied into the processing chamber becomes zero in reality. By controlling the control means to stop the gas supply the predetermined time before the end of the each step, it is possible to prevent inconveniences such as supplying the etching gas or the protective film deposition gas continuously after the end of the step (after the step shifting). This contributes to an efficient exchange of the gases in the processing chamber, too.  
         [0029]     As a result, it is possible to shorten the time during which the etching gas and the protective film deposition gas are mixed, so that the etching in the etching operation or the forming of the protective film in the protective-film deposition operation can be performed sufficiently to raise the etch rate, and to form the high quality protective films for obtaining the high-precision etching profiles and high mask selectivity.  
         [0030]     The control means may control the gas supply means to start to supply the etching gas in advance of the end of the protective-film deposition operation, and to start to supply the protective film deposition gas in advance of the end of the etching operation. A supply flow rate of the etching gas or the protective film deposition gas to be supplied into the processing chamber is, during a time period from the supply start to an instant when a predetermined time elapses since the start of the etching operation or the protective-film deposition operation, set higher than a supply flow rate after the predetermined time elapses (the constant flow rate).  
         [0031]     Accordingly, because the etching gas or the protective film deposition gas is supplied into the processing chamber at a high flow rate in advance of the end of the protective-film deposition operation or the etching operation, i.e., during a time period from an instant before the start of the etching operation or the protective-film deposition operation to an instant when the predetermined time elapses since the start of the step, it is possible to efficiently exchange the gases in the processing chamber to make an atmosphere of the etching gas or the protective film deposition gas in a short period of time.  
         [0032]     Furthermore, as at the stop of the gas supply, even if the control means controls the gas supply means to start the gas supply, when shifting the steps, a delay (time lag) occurs from an instant when the gas supply is started to an instant when the gas is started to be supplied into the processing chamber at the predetermined flow rate in reality. By starting to supply the etching gas or the protective film deposition gas before the start of the protective-film deposition operation or the etching operation, it is possible to prevent a time period from being generated during which the gas is not supplied into the processing chamber immediately after the start of the step. This contributes to an efficient exchange of the gases in the processing chamber, too.  
         [0033]     As a result, as described above, by shortening the time during which the etching gas and the protective film deposition gas are mixed, it is possible to raise the etch rate, and to form high quality protective films to obtain high mask selectivity and high-precision etching profiles.  
         [0034]     The control means may control the gas supply means such that a supply flow rate of the etching gas or the protective film deposition gas to be supplied into the processing chamber is, during a time period from the start of each step to an instant when a predetermined time elapses, set higher than a supply flow rate after the predetermined time elapses (the constant flow rate).  
         [0035]     In this operation, too, since the etching gas or the protective film deposition gas is supplied at a high flow rate into the processing chamber within the predetermined time after the start of each step, it is possible to efficiently exchange the gases in the processing chamber. i.e., obtaining the same effect as the above-mentioned one.  
         [0036]     The present invention is a method for etching a silicon substrate placed on a platform in a processing chamber, comprising: an etching operation of etching the silicon substrate by supplying an etching gas into the processing chamber so that etching gas is converted to plasma and a bias potential is applied to the base; and a protective-film deposition operation of forming a protective film on the silicon substrate by supplying a protective film deposition gas into the processing chamber so that the protective film deposition gas is converted to plasma; wherein the etching operation and the protective-film deposition operation are repeated alternately, a supply flow rate of the etching gas or the protective film deposition gas to be supplied into the processing chamber is, during a time period from the start of the each step to an instant when a predetermined time elapses since the start of each step, set higher than a supply flow rate after the predetermined time elapses.  
         [0037]     This etching method can optimally be implemented with the following etching apparatus.  
         [0038]     An etching apparatus comprising: a processing chamber having a closed space; a platform disposed at a lower portion in the processing chamber and on which a silicon substrate is placed; platform power supply means for applying RF power to the base; gas supply means for supplying an etching gas and a protective film deposition gas into the processing chamber, the gas supply means being configured such that supply flow rates of the etching gas and the protective film deposition gas can be adjusted; a coil being disposed around the processing chamber; coil power supply means for applying RF power to the coil to convert the etching gas and the protective film deposition gas in the processing chamber to plasma; and control means for controlling the platform power supply means, the coil power supply means and the gas supply means; the control means, by controlling the gas supply means to adjust supply flow rates of the etching gas and the protective film deposition gas to be supplied into the processing chamber, alternately repeats an etching operation of supplying the etching gas into the processing chamber to etch the silicon substrate, and a protective-film deposition operation of supplying the protective film deposition gas into the processing chamber to form a protective film on the silicon substrate, and the platform power supply means applies RF power to the platform when at least the etching operation is performed, the control means controls the gas supply means to, during a time period from the start of each step to an instant when a predetermined time elapses since the start of each step, set a supply flow rate of the etching gas or the protective film deposition gas to be supplied into the processing chamber higher than a supply flow rate after the predetermined time elapses. In this case, too, as mentioned before, in the etching operation, removing the protective film by the ion bombardment and etching by the radical and ion bombardment are progressed on the bottom surfaces of the grooves or holes because of heavy ion bombardment, and only removing the protective film by the ion bombardment is progressed on the sidewalls of the grooves or holes, i.e., the sidewalls are prevented from being etched because of light ion bombardment. In the protective-film deposition operation, the polymer is deposited again on the bottom surfaces and sidewalls to make protective films so that new sidewalls formed in the etching operation can be protected immediately. Thus, the etching is progressed in the grooves or holes only along the depth.  
         [0039]     In this etching apparatus, because the control means controls the gas supply means such that the etching gas or the protective film deposition gas is supplied into the processing chamber during a time period from the start of each step to an instant when the predetermined time elapses, it is possible to efficiently exchange the gases, i.e., obtaining the same effect as the above-mentioned one.  
         [0040]     In this case too, the control means may control the gas supply means to start to supply the etching gas in advance of the end of the protective-film deposition operation at the flow rate higher than the supply flow rate after the predetermine time elapses in the etching operation, and to start to supply the protective film deposition gas in advance of the end of the etching operation at the flow rate higher than the supply flow rate after the predetermined time elapses in the protective-film deposition operation, thereby obtaining the same effect as the above-mentioned one.  
         [0041]     As mentioned above, according to the etching method and the etching apparatus of the present invention, since the gases in the processing chamber can be efficiently exchanged when shifting from the etching operation to the protective-film deposition operation and shifting from the protective-film deposition operation to the etching operation, it is possible to progress the etching in the etching operation and the forming of the protective film in the protective-film deposition operation well. As a result, it is possible to raise the etch rate, improve the mask selectivity and obtain the high-precision etching profiles.  
         [0042]     From the following detailed description in conjunction with the accompanying drawings, the foregoing and other objects, features, aspects and advantages of the present invention will become readily apparent to those skilled in the art.  
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0043]      FIG. 1  is a partially block-diagrammed, sectional view illustrating the configurational outline of an etching apparatus involving one embodiment of the present invention;  
         [0044]      FIG. 2  is a timing chart representing controlled conditions of the supply flow rates of SF 6  gas and C 4 F 8  gas and the gas exhaust flow rates in the processing chamber according to the present invention;  
         [0045]      FIG. 3  is a timing chart representing controlled conditions of RF power to be applied to a platform and a coil according to the present invention;  
         [0046]      FIG. 4  is a graph representing a relationship between the gas supply flow rate and the time, and a relationship between the pressure in the processing chamber and the time according to the present invention;  
         [0047]      FIG. 5  is a graph representing a relationship between the gas supply flow rate and the time, and a relationship between the pressure in the processing chamber and the time according to the present invention;  
         [0048]      FIG. 6  is a timing chart representing controlled conditions of the supply flow rates of SF 6  gas and C 4 F 8  gas and the gas exhaust flow rates in the processing chamber in another embodiment according to the present invention;  
         [0049]      FIG. 7  is an illustrative picture for explaining the cross-sectional shape of the silicon substrate;  
         [0050]      FIG. 8  is a timing chart representing controlled conditions of the supply flow rate of the etching gas and the protective film deposition gas according to a conventional example;  
         [0051]      FIG. 9  is a graph representing a relationship between the gas supply flow rate and the time, and a relationship between the pressure in the processing chamber and the time according to the conventional example; and  
         [0052]      FIG. 10  is a graph representing a relationship between the gas supply flow rate and the time, and a relationship between the pressure in the processing chamber and the time according to the conventional example. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0053]     Hereinafter, with reference to attached drawings a description will be made of a preferable embodiment of the present invention.  
         [0054]     As shown in  FIG. 1 , an etching apparatus  1  of the present embodiment comprises a processing chamber  11  having a closed space, a platform  12  displaced on the lower side in the processing chamber  11  and on which a silicon substrate K as a thing to be etched is placed, an exhaust device  14  for exhausting the gas in the processing chamber  11  to pump the inside down, a gas supply device  20  for supplying etching gas and protective film deposition gas into the processing chamber  11 , a plasma generating device  30  for converting the etching gas and the protective film deposition gas supplied into the processing chamber  11  to plasma, a first high-frequency power source  13  for applying RF power to the platform  12  to generate a potential difference (bias potential) between the platform  12  and the plasma, and a control device  40  for controlling operations of the exhaust device  14 , the gas supply device  20 , the plasma generating device  30  and the first high-frequency power source  13 .  
         [0055]     The processing chamber  11  is made up of a plasma generating chamber  11   a  and a reaction chamber  11   b  below the chamber  11   a . The platform  12  includes an electrode  12   a  to which RF power is applied by the first high-frequency power source  13 , and is disposed in the reaction chamber  11   b.    
         [0056]     The exhaust device  14  includes an exhaust pipe  15  connected to a sidewall of the reaction chamber  11   b  of the processing chamber  11 , a vacuum pump  16  connected to the exhaust pipe  15 , and a flow rate adjust mechanism  17  for adjusting gas flow rate flowing in the exhaust pipe  15 . When the vacuum pump  16  exhausts the gas out of the processing chamber  11 , the pressure in the processing chamber  11  is pumped down to a predetermined pressure.  
         [0057]     The gas supply device  20  is made up of a supply pipe  21  connected to a ceiling portion of the plasma generating chamber  11   a  of the processing chamber  11  and gas cylinders  22  and  23  connected to the supply pipe  21  via flow rate adjust mechanisms  25  and  26 , respectively. The gases whose flow rates are adjusted by the flow rate adjust mechanisms  25  and  26  are supplied into the plasma generating chamber  11   a  via the gas cylinders  22  and  23 , respectively.  
         [0058]     Although SF 6  gas for etching is filled in the gas cylinder  22  and C 4 F 8  gas for forming the protective film is filled in the gas cylinder  23 , the etching gas and the protective film deposition gas are not limited to SF 6  gas and C 4 F 8  gas, respectively.  
         [0059]     The plasma generating device  30  is made up of a coil  31  disposed around the outer circumference of the plasma generating chamber  11   a  of the processing chamber  11  and a second high-frequency power source  32  for applying RF power to the coil  31 . When the second high-frequency power source  32  applies RF power to the coil  31 , a magnetic field is generated in the plasma generating chamber  11   a , which induces an electric field to convert the gas in the plasma generating chamber  11   a  to plasma.  
         [0060]     The function of the control device  40  is to repeat etching operations E of etching the silicon substrate K and protective-film deposition operations D of forming protective films on the silicon substrate K alternately for predetermined times, as shown in  FIG. 2  and  FIG. 3 . The control device  40  is made up of a supply flow rate controller  41  for controlling the flow rate adjust mechanisms  25  and  26  to adjust flow rates of SF 6  gas and C 4 F 8  gas to be supplied into the plasma generating chamber  11   a  of the processing chamber  11  from the gas cylinders  22  and  23 , an exhaust flow rate controller  42  for controlling the flow rate adjust mechanism  17  to adjust the flow rate of the gas to be exhausted from the processing chamber  11  by the vacuum pump  16 , a platform power controller  43  for controlling the first high-frequency power source  13  to adjust RF power to be applied to the platform  12  (the electrode  12   a ), and a coil power controller  44  for controlling the second high-frequency power source  32  to adjust RF power to be applied to the coil  31 .  
         [0061]     The supply flow rate controller  41  changes the flow rates of SF 6  gas and C 4 F 8  gas supplied from the gas cylinder  22  and  23  into the plasma generating chamber  11   a  as shown in  FIG. 2 ( a ) and  FIG. 2 ( b ) so that SF 6  gas is mainly supplied when the etching operation E is performed and C 4 F 8  gas is mainly supplied when the protective film deposition operation D is performed.  
         [0062]     More specifically, SF 6  gas is started to be supplied in advance of the start of the etching operation E, i.e., at an instant when it reaches a predetermined time before the end of the protective film deposition operation D (entering a processing time period indicated by reference mark De). SF 6  gas is continued to be supplied until a predetermined time before the end of the etching operation E (until it reaches a processing time period indicated by reference mark Ee). During a time period from the supply start to an instant a predetermined time elapses since the start of the etching operation E (until the end of the processing time period indicated by reference mark Es), SF 6  gas is supplied at flow rate V E1  higher than flow rate V E2  after the predetermined time elapses.  
         [0063]     Meanwhile, C 4 F 8  gas is started to be supplied in advance of the start of the protective film deposition operation D, i.e., when it reaches a predetermined time before the end of the etching operation E (entering the processing time period indicated by reference mark Ee). C 4 F 8  gas is continued to be supplied until a predetermined time before the end of the protective film deposition operation D (until the processing time period indicated by reference mark De). During a time period from the supply start to an instant when a predetermined time elapses since the start of the protective film deposition operation D (until the end of the processing time period indicated by reference mark Ds), C 4 F 8  is continued to be supplied at flow rate V D1  higher than flow rate V D2  after the predetermined time elapses.  
         [0064]     The exhaust flow rate controller  42  continuously exhausts the gas in the processing chamber  11  while the etching operation E and the protective film deposition operation D are performed as shown in  FIG. 2 ( c ). The exhaust flow rate controller  42  exhausts the gases at flow rate V H1  higher than previous flow rate V H2  during a time period from a predetermined time before the end of the etching operation E to the end of the etching operation E (the processing time period indicated by reference mark Ee), and a time period from a predetermined time before the end of the protective film deposition operation D to the end of the protective film deposition operation D (the processing time period indicated by reference mark De). The flow rate V H1  and the flow rate V H2  may be different between performing the etching operation E and performing the protective film deposition operation D.  
         [0065]     The reason why the supply flow rates V E1  and V D1  are set higher during a time period from the supply start of SF 6  gas and C 4 F 8  gas to the instant the predetermined time elapses since the start of the etching operation E or the protective film deposition operation D is that it is necessary to fill SF 6  gas and C 4 F 8  gas into the processing chamber  11  quickly (to stabilize the pressure in the processing chamber  11  quickly) as shown in  FIG. 4 . The reason why the exhaust flow rate V H1  is set higher the predetermined time before the end of the etching operation E or the protective film deposition operation D is that it is necessary to exhaust the gas in the processing chamber  11  quickly not to leave the gas of the previous step for the next step, as shown in  FIG. 5 .  
         [0066]     The reason why the supply of SF 6  gas and C 4 F 8  gas are started before the starts of the etching operation E and the protective film deposition operation D and are stopped before the ends of the etching operation E and the protective film deposition operation D is that a time delay occurs between a controlled supply flow rate as a control objective value and a real supply flow rate as shown in  FIG. 4  and  FIG. 5 .  FIG. 4 ( a ) and  FIG. 5 ( a ) are graphs showing a relationship between the gas supply flow rate and the time in the present embodiment.  FIG. 4 ( b ) and  FIG. 5 ( b ) are graphs showing relationships between the pressure and the time in the processing chamber in the present embodiment and the conventional example.  
         [0067]     The platform power controller  43  controls the first high-frequency power source  13  to continuously apply RF power Wp to the platform  12  during a time period from the start of the etching operation E to a predetermined time before the end of the etching operation E (until the processing time period indicated by reference mark Ee) as shown in  FIG. 3 ( a ). The coil power controller  44  controls the second high-frequency power source  32  to apply RF power Wc to the coil  31  when the etching operation E and the protective film deposition operation D are performed.  
         [0068]     According to the etching apparatus  1  having the above-described configuration in the present embodiment, after the silicon substrate K is placed on the platform  12  in the reaction chamber  11   b , the etching operation E and the protective film deposition operation D are repeated alternately to etch the silicon substrate K.  
         [0069]     More specifically, in order to perform the etching operation E, first, under control of the control device  40 , SF 6  gas which is adjusted by the flow rate adjust mechanism  25  to have flow rate V E1  is supplied from the gas cylinder  22  into the plasma generating chamber  11   a  and certain RF power is applied by the high-frequency power sources  13  and  32  to the platform  12  and the coil  31 , respectively. The gas which is adjusted by the flow rate adjust mechanism  17  to have the flow rate V H2  is exhausted from the processing chamber  11  by the vacuum pump  16  under control of the control device  40 , so that the inside of the processing chamber  11  is pumped down to a certain pressure.  
         [0070]     When the predetermined time elapses since the start of the etching operation E, i.e., the processing time period indicated by reference mark Es is finished, the flow rate of SF 6  gas is lowered to flow rate V E2  and SF 6  gas is supplied. After that, the supply of SF 6  gas and application of RF power to the platform  12  are stopped and the gas in the processing chamber  11  is exhausted at flow rate V H1  which heightened compared to the previous one at the predetermined time before the end of the etching operation E (entering the processing time period indicated by reference mark Ee).  
         [0071]     At this time, in order to shift steps from the etching operation E to the protective film deposition operation D, C 4 F 8  gas which is adjusted by the flow rate adjust mechanism  26  to have flow rate V D1  is supplied from the gas cylinder  23  into the plasma generating chamber  11   a , in advance of the start of the protective film deposition operation D, under control of the control device  40 .  
         [0072]     When shifting from the etching operation E to the protective film deposition operation D, the gas in the processing chamber  11  is exhausted at flow rate V H2  which is lowered compared to the previous one and the inside of the processing chamber  11  is pumped down to a certain pressure. When a predetermined time elapses since the start of the protective film deposition operation D and the processing time period indicated by reference mark Ds is finished, C 4 F 8  gas is supplied at flow rate V D2  which is lowered compared to the previous one. After that, the supply of C 4 F 8  gas is stopped and the gas in the processing chamber  11  is exhausted at flow rate V H1  which is heightened compared to the previous one a predetermined time before the end of the protective film deposition operation D (entering the processing time period indicated by reference mark De).  
         [0073]     Furthermore, at this time, in order to shift steps from the protective film deposition operation D to the etching operation E, SF 6  gas adjusted to have flow rate V E1  is supplied from the gas cylinder  22  to the plasma generating chamber  11   a  in advance of the start of the etching operation E.  
         [0074]     When shifting from the protective film deposition operation D to the etching operation E, the gas in the processing chamber  11  is exhausted at flow rate V H2  which is lowered compared to the previous one to pump inside of the processing chamber  11  down to a certain pressure and the high-frequency power source  13  applies certain RF power to the platform  12 . After that, when a predetermined time elapses since the start of the etching operation E and the processing time period indicated by reference mark Es is finished, SF 6  gas is supplied at flow rate V E2  which is lowered compared to the previous one.  
         [0075]     Hereinafter, theses processes or operations are subsequently repeated to repeat the etching operations E and the protective-film deposition operations D alternately. In the etching operation E, SF 6  gas in the plasma generating chamber  11   a  is converted to plasma including ions, electrons, and F radicals by an electric field formed by the coil  31 , wherein F radicals react chemically with silicon atoms and the ions are moved toward and collide with the platform  12  (the silicon substrate K) by a potential difference (a bias potential) between the platform  12  and the plasma so that the silicon substrate K is etched and grooves or holes are formed in the silicon substrate K patterned by the mask.  
         [0076]     Meanwhile, in the protective film deposition operation D, C 4 F 8  gas in the plasma generating chamber  11   a  is converted to plasma including ions, electrons, and radicals by the electric field, wherein the radicals form the polymer to be deposited on sidewalls and bottom surfaces of the grooves or holes, so that the protective film (fluorocarbon film) is formed on the sidewalls and bottom surfaces, which does not react with F radicals.  
         [0077]     As a result, in the etching operation E, removing the protective film by the ion bombardment and etching by F radical and ion bombardment are progressed on the bottom surfaces of the grooves or holes because of the heavy ion bombardment, and only removing the protective film by the ion bombardment is progressed on the sidewalls of the grooves or holes, i.e., the sidewalls are prevented from being etched because of the light ion bombardment. In the protective film deposition operation D, the polymer is deposited again on the bottom surfaces and sidewalls to make protective films so that new sidewalls formed in the etching operation E can be protected immediately. Thus, the etching is progressed in the grooves or holes only along the depth.  
         [0078]     As described above, since it takes a certain time for the exchange (replacement) of the gases in the processing chamber  11  when shifting from the etching operation E to the protective film deposition operation D or shifting from the protective film deposition operation D to the etching operation E, SF 6  gas and C 4 F 8  gas are mixed until the certain time elapses since the start of each operation E and D. Consequently, etching of the silicon substrate K or forming of the protective film on the silicon substrate K can not be sufficiently, which should be performed in the etching operation E or the protective film deposition operation D. Accordingly, if the time of exchanges of the gases becomes long, some problems occur such as lowering the etch rate, form accuracy of etching, and mask selectivity.  
         [0079]     Therefore, in the etching apparatus  1  of the present example, the supply of SF 6  gas or C 4 F 8  gas is stopped the predetermined time before the end of the etching operation E or the protective film deposition operation D (entering the processing time periods indicated by reference marks Ee or De). C 4 F 8  gas or SF 6  gas is started to be supplied to perform the next step and is supplied until the predetermined time elapses since the start of the protective film deposition operation D or the etching operation E as next steps (until the end of the processing time periods indicated by reference mark Ds or Es) at the flow rate V D1  or V E1  higher than the next flow rate V D2  or V E2 . Furthermore, the gas in the processing chamber  11  is exhausted at the flow rate V H1  higher than the previous flow rate V H2  during a time period from the predetermined time before the end of the etching operation E or the protective film deposition operation D to the end of the etching operation E or protective film deposition operation D (a processing time period indicated by reference mark Ee or De).  
         [0080]     As a result, when shifting from the etching operation E to the protective film deposition operation D, C 4 F 8  gas is supplied into the processing chamber  11  at the high flow rate for a predetermined time, while exhausting SF 6  gas in the processing chamber  11  at the high flow rate. When shifting from the protective film deposition operation D to the etching operation E, SF 6  gas is supplied into the processing chamber  11  at the high flow rate for the predetermined time while exhausting C 4 F 8  gas in the processing chamber  11  at the high flow rate, so that it is possible to efficiently exchange gases in the processing chamber  11  to achieve SF 6  gas or C 4 F 8  atmosphere in the processing chamber  11  in a short period of time.  
         [0081]     Even if the supply flow rate controller  41  controls the flow rate adjust mechanisms  25  and  26  to stop the gas supply, a delay (time lag) occurs from an instant when the gas supply is stopped to an instant when the flow rate of the gas to be supplied into the processing chamber  11  becomes zero in reality, due to the gases existing in the supply pipe  21  between the flow rate adjust mechanisms  25  and  26  and the plasma generating chamber  11   a . By controlling the supply flow rate controller  41  to stop the gas supply the predetermined time before the end of the each operation E and D, it is possible to prevent inconveniences such that SF 6  gas or C 4 F 8  gas is continuously supplied after the end of the operation E or D (after the step shifting). This contributes to an efficient exchange of the gases in the processing chamber  11 , too.  
         [0082]     Furthermore, as at the stop of the gas supply, even if the supply flow rate controller  41  controls the flow rate adjust mechanisms  25  and  26  to start the gas supply, a delay (time lag) occurs from an instant when the gas supply is started to an instant when the gas is started to be supplied into the processing chamber  11  at the predetermined flow rate in reality, due to a length of the supply pipe  21  from the flow rate adjust mechanisms  25  and  26  to the plasma generating chamber  11   a . By starting to supply SF 6  gas or C 4 F 8  gas before each operation E and D, it is possible to prevent a time period during which the gas is not supplied into the processing chamber  11  immediately after the start of the operation E or D. This contributes to an efficient exchange of the gases in the processing chamber  11 .  
         [0083]     As a result, the time during which SF 6  gas and C 4 F 8  gas are mixed is short so that the etching in the etching operation E and the forming of the protective film in the protective film deposition operation D can be performed well. Furthermore, it is possible to raise the etch rate and to form high quality protective films for obtaining high-precision etching profiles and high mask selectivity.  
         [0084]     Although one embodiment of the present invention was described in the above-described description, specific embodiments which can be employed by the present invention are not limited to the embodiment.  
         [0085]     Although the supply flow rate controller  41  starts to supply SF 6  gas the predetermined time before the end of the protective film deposition operation D and starts to supply C 4 F 8  gas predetermined time before the end of the etching operation E in the above-described embodiment, operations are not limited to this one. As shown in  FIG. 6 ( a ) and  FIG. 6 ( b ), SF 6  gas and C 4 F 8  gas may be started to be supplied simultaneously at the start of the etching operation E and protective film deposition operation D and the gases are supplied from the supply start to an instant when the predetermined time elapses (until the end of the processing time period indicated by reference mark Es and Ds) at the flow rates V E1  and V D1  higher than the flow rates V E2  and V D2  after the predetermined time elapses, respectively. In this case, too, the exhaust flow rate controller  42  controls the exhaust flow rate of the gas in the processing chamber  11  as described above, as shown in  FIG. 6 ( c ).  
         [0086]     In this case, due to SF 6  gas or C 4 F 8  gas having a high flow rate to be supplied into the processing chamber  11  within the predetermined time after the start of each operation D and E, it is possible to efficiently exchange the gases in the processing chamber  11  and making SF 6  gas or C 4 F 8  gas atmosphere in the processing chamber  11  in a short period of time, thereby achieving the same effect as one in the above-described embodiment.  
         [0087]     Although the time to stop the supply of SF 6  gas and the time to start the supply of C 4 F 8  gas are set to be the same as the time to stop the supply of C 4 F 8  gas and the time to stop the supply of SF 6  gas, respectively, in the above-described embodiment, they can be set as different from each other. In addition, the processing times of the etching operation E and the protective film deposition operation D, the processing times indicated by reference mark Es and reference mark Ds, and the processing times indicated by reference mark Ee and reference mark De may be the same as each other or different from each other.  
         [0088]     In embodiment example 1, conditions were as follows. In the etching operation E, the overall processing time was 4.3 seconds, the processing time indicated by reference mark Es was 0.4 seconds, the processing time indicated by reference mark Ee was 0.3 seconds, the pressure in the processing chamber  11  was 13 Pa, RF power applied to the coil  31  was 2.5 kW, RF power applied to the platform  12  was 170 W, the supply flow rate of SF 6  gas indicated by reference mark Es was 600 ml/min, the supply flow rate of SF 6  gas indicated between reference mark Es and reference mark Ee was 400 ml/min, the supply flow rate of C 4 F 8  gas indicated by reference mark Ee was 400 ml/min, the degree of opening of the exhaust valve constituting the flow rate adjust mechanism  17  was 8% except for reference mark Ee, and the degree of opening of the exhaust valve in the reference mark Ee was 30%. In the protective film deposition operation D, the whole processing time was 3.3 seconds, the processing time indicated by reference mark Ds was 0.4 seconds, the processing time indicated by reference mark De was 0.3 seconds, the pressure in the processing chamber  11  was 8 Pa, RF power to be applied to the coil  31  was 2.5 kW, RF power to be applied to the platform  12  was 0 W, the supply flow rate of C 4 F 8  gas indicated by reference mark Ds was 400 ml/min, the supply flow rate C 4 F 8  gas between reference mark Ds and reference mark De was 200 ml/min, the supply flow rate of SF 6  gas indicated by reference mark De was 600 ml/min, the degree of opening of the exhaust valve except for reference mark De was 8%, the degree of opening of the exhaust valve in reference mark De was 30%. The silicon substrate K was etched for a predetermined time as shown in  FIG. 2 , wherein opening width B 1  of the mask M was 2 μm shown in  FIG. 7 . As a result, the etch rate was 4.94 μm/min, the mask selectivity was 57, the maximum value of the groove width B 2  was 2.55 μm, an upper portion etched angle θ 1  was 89.8°, and a lower portion etched angle θ 2  was 89.7°. As a result, perpendicular etched sidewalls were obtained, i.e., there was no etched shape of the sidewall whose sidewall protective film was damaged as shown in  FIG. 7 . As shown in  FIG. 7 , the lower portion etched angle θ 2  is an angle between the bottom surface and the sidewall of the groove or hole T, and the upper portion etched angle θ 1  is an angle between a surface in parallel with the bottom surface and the sidewall of the groove or hole T in the middle along the depth.  
         [0089]     In embodiment example 2, conditions were as follows. In the etching operation E, the whole processing time was 4 seconds, the processing time indicated by reference mark Es was 0.7 seconds, the processing time indicated by reference mark Ee was 0.3 seconds, the pressure in the processing chamber  11  was 13 Pa, RF power to be applied to the coil  31  was 2.5 kW, RF power to be applied to the platform  12  was 170 W, the supply flow rate of SF 6  gas indicated by reference mark Es was 600 ml/min, the supply flow rate of SF 6  gas between reference mark Es and reference mark Ee was 400 ml/min, the degree of opening of the exhaust valve except for reference mark Ee was 8%, the degree of opening of the exhaust valve in reference mark Ee was 30%. In the protective film deposition operation D, the whole process time was 3 seconds, the processing time indicated by reference mark Ds was 0.7 seconds, the processing time indicated by reference mark De was 0.3 seconds, the pressure in the processing chamber  11  was 8 Pa, RF power to be applied to the coil  31  was 2.5 kW, RF power to be applied to the platform  12  was 0 W, the supply flow rate of C 4 F 8  gas indicated by reference mark Ds was 400 ml/min, the supply flow rate of C 4 F 8  gas between reference mark Ds and reference mark De was 200 ml/min, the degree of opening of the exhaust valve except for reference mark De was 8%, and the degree of opening the exhaust valve in reference mark De was 30%. The silicon substrate K was etched for a predetermined time as shown in  FIG. 6 , wherein opening width B 1  of the mask M was 2 μm as shown in  FIG. 7 , the etch rate was 5.08 μm/min, the mask selectivity was 68, the maximum value of the groove width B 2  was 2.22 μm, the upper portion etched angle θ 1  was 89.7°, the lower portion etched angle θ 2  was 89.1°. As a result, forward tapered etching shape was obtained, i.e., there was no etched shape P of the sidewall whose sidewall protective film was damaged as shown in  FIG. 7 .  
         [0090]     In contrast, as a comparison example, conditions were as follows. In the etching operation E, the processing time was 4 seconds, the pressure in the processing chamber  11  was 13 Pa, RF power to be applied to the coil  31  was 2.5 kW, RF power to be applied to the platform  12  was 170 W, the supply flow rate of SF 6  gas was 400 ml/min, the degree of opening of the exhaust valve was 8%. In the protective film deposition operation D, the processing time was 3 seconds, the pressure in the processing chamber  11  was 8 Pa, RF power to be applied to the coil  31  was 2.5 kW, RF power to be applied to the platform  12  was 0 W, the supply flow rate of C 4 F 8  gas was 200 ml/min, the degree of opening of the exhaust valve was 8%. The silicon substrate Kwhose mask M had opening width B 1  of 2 μm as shown in  FIG. 7  was etched for a predetermined time as shown in  FIG. 8 , wherein the etch rate was 4.46 μm/min, the mask selectivity was 48, the maximum value of the groove width B 2  was 3.11 μm, the upper portion etched angle θ 1  was 90.9°, the lower portion etched angle θ 2  was 89.2°. As a result, the sidewall had etched shape P as shown in  FIG. 7  due to damages to the sidewall protective films, and had a bowed profile.  
         [0091]     Comparing the embodiment examples 1 and 2 with the comparison example, according to the etching apparatus  1  of the present examples, it is apparent that the etch rate is raised, the mask selectivity is improved, and sidewalls having an etched profile P or bowed profile, as illustrated in  FIG. 7 , do not arise. By these effects, the conclusion is that the etch rate can be raised, the mask selectivity can be improved, and etching accuracy can be improved with the etching apparatus  1  of the present embodiment.  
         [0092]     Only selected embodiments have been chosen to illustrate the present invention. To those skilled in the art, however, it will be apparent from the foregoing disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. Furthermore, the foregoing description of the embodiments according to the present invention is provided for illustration only, and not for limiting the invention as defined by the appended claims and their equivalents.