Patent Publication Number: US-2005115679-A1

Title: Surface treatment apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application claims priority to Japanese Patent Applications Nos. 2003-339323 filed Sep. 30, 2003 and 2004-171944 filed Jun. 9, 2004, which are hereby expressly incorporated by reference herein in their entirety.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a surface treatment apparatus.  
      2. Description of the Prior Art  
      In recent years, semiconductor devices, quartz oscillators, and the like are manufactured through processing carried out using photolithography technology or the like, that is, so-called micromachining technology is actively employed. By employing micromachining technology, it is possible to directly process substrates. For example, after one surface of a substrate is subjected to processing, the thickness of the substrate can be reduced or holes can be provided in the substrate by subjecting the other surface of the substrate, which is opposite to the processed surface, to etching or the like.  
      In such a case where one surface of a substrate is processed (that is, in a case where one surface of a substrate is subjected to etching), there is a necessity to protect the other surface that has been processed (hereinafter, referred to as a “processed surface”) from an etchant. From such a viewpoint, an apparatus for etching capable of subjecting only a surface opposite to a processed surface (hereinafter, referred to as a “surface to be etched”) to etching while protecting the processed surface has been developed (see Japanese Patent Laid-open No. Hei. 7-111257, for example).  
      The apparatus for etching disclosed in Japanese Patent Laid-open No. Hei. 7-111257 includes a supporting jig and a pressing jig to be detachably attached to the supporting jig. When the pressing jig is attached to the supporting jig with a substrate being placed on the supporting jig, the pressing jig presses the peripheral portion of the substrate. In this way, the substrate is secured to the apparatus for etching.  
      Further, the apparatus for etching has O-rings provided at predetermined positions. While the substrate is being secured to the apparatus for etching, the O-rings are in close contact with a surface to be etched of the substrate. This makes it possible to prevent an etchant from being reached to a processed surface of the substrate. Therefore, even when the apparatus for etching to which the substrate is secured is immersed in an etchant, only the surface to be etched is subjected to etching.  
      However, in the case where such an apparatus for etching is used, the outer peripheral portion of the surface to be etched which is pressed by the pressing jig is not exposed to the etchant so that the outer peripheral portion is not treated.  
      As a result, a difference in level is developed on the etched surface at the boundary between a portion that has been in contact with the pressing jig (that is, an untreated portion) and a portion that has not been in contact with the pressing jig (that is, a treated portion). Such a difference in level causes a problem that it is difficult to evenly carry out various treatments for each area of the substrate in post-steps coming after etching.  
     SUMMARY OF THE INVENTION  
      It is therefore an object of the present invention to provide a method for surface treatment capable of evenly subjecting a substrate to surface treatment.  
      In order to achieve the above-identified objects, the present invention is directed to a surface treatment apparatus for holding a substrate that has one surface to which the surface treatment is to be carried out and the other surface opposite to the one surface when the surface treatment is carried out to the one surface of the substrate. The surface treatment apparatus includes: 
          at least one enclosed space, each being defined by a portion of the surface treatment apparatus and the other surface of the substrate; and     a contact portion surrounding the at least one enclosed space adapted to hermetically contact with the other surface of the substrate to produce negative pressure in cooperation with the enclosed space and the other surface of the substrate;     wherein the surface treatment apparatus is constructed so that the substrate is attracted onto the surface treatment apparatus by means of a difference between the negative pressure and atmospheric pressure by decompressing the enclosed space in a decompression chamber and then bringing out the substrate from the inside of the decompression chamber to environment under atmospheric pressure.        

      This makes it possible to evenly subject a substrate to surface treatment.  
      In the surface treatment apparatus of the present invention, it is preferable that the at least one enclosed space are a plurality of enclosed spaces.  
      This makes it possible to evenly hold the substrate with respect to the surface treatment apparatus.  
      It is preferable that the surface treatment apparatus of the present invention further includes a flow path communicating with the plurality of enclosed spaces.  
      This makes it possible to stably hold the substrate by means of the surface treatment apparatus.  
      In the surface treatment apparatus of the present invention, it is preferable that the surface treatment apparatus is constructed so as not to have a flow path which allows the enclosed space to communicate with the outside thereof with the substrate being in contact with the concave portion.  
      For example, in the case where wet etching is carried out as the surface treatment, it is preferable to carry out the wet etching while rotating the surface treatment apparatus. However, according to the present invention, there is no necessity to connect a suction tube for decompressing the enclosed space to the surface treatment apparatus, and therefore there is no possibility that suction tubes intertwine with each other when the surface treatment apparatuses are rotated upon wet etching. At a result, it is easy to handle the surface treatment apparatus.  
      It is preferable that the surface treatment apparatus of the present invention further includes a flow path which allows the enclosed space to communicate with the outside thereof with the substrate being in contact with the contact portion wherein the flow path is hermetically sealed when the substrate is attracted onto the surface treatment apparatus.  
      This makes it possible to easily release the substrate from the surface treatment apparatus.  
      In the surface treatment apparatus of the present invention, it is preferable that the substrate has one or more concave portions each opening to the other surface thereof; and that the contact portion is constituted so as to be able to cover the concave portions of the substrate with the substrate being contact with the contact portion.  
      This makes it possible to reliably hole the substrate having one or more concave portions onto the surface treatment apparatus.  
      It is preferable that the surface treatment apparatus of the present invention further includes a hard main body which supports the contact portion.  
      The use of a hard material for the main body makes it possible to suitably prevent the surface treatment apparatus from being deformed while the substrate is being stuck to and held by the surface treatment apparatus by suction.  
      In the surface treatment apparatus of the present invention, it is preferable that the entire surface treatment apparatus is mainly made of an elastic material.  
      This makes it possible to reduce the number of components of the surface treatment apparatus.  
      In the surface treatment apparatus of the present invention, it is preferable that the surface treatment apparatus has a flat-shaped structure having two major surfaces, and has the concave portion on the side of each of the two major surfaces.  
      This makes it possible to reduce the costs required for the surface treatment and to shorten the time required for the surface treatment.  
      In the surface treatment apparatus of the present invention, it is preferable that the surface treatment is carried out using a liquid for treatment.  
      The method for surface treatment with the use of the surface treatment apparatus of the present invention can be applied to various types of surface treatment, and in particular, the method can be applied to surface treatment using a liquid for treatment suitably.  
      In the surface treatment apparatus of the present invention, it is preferable that the liquid for treatment includes an etchant.  
      Particularly, the method for surface treatment of the present invention can be applied to wet etching more suitably.  
      In the surface treatment apparatus of the present invention, it is preferable that the surface treatment is constructed so that the substrate is released by conveying the surface treatment apparatus with the substrate to the inside of the decompression chamber again after subjecting the substrate to the surface treatment and then decompressing the inside of the decompression chamber so that the pressure within the decompression chamber becomes substantially equal to or lower than the pressure within the enclosed space.  
      This makes it possible to easily release the substrate from the surface treatment apparatus.  
      It is preferable that the surface treatment apparatus of the present invention further includes separation assisting means which assists separation of the substrate from the contact portion in the decompression chamber.  
      This makes it possible to reliably release the substrate from the surface treatment apparatus.  
      In the surface treatment apparatus of the present invention, it is preferable that the separation assisting means includes a contact member having one end portion which is adapted to contact with the other surface of the substrate when the substrate is separated from the contact portion of the surface treatment apparatus, and displacement means for displacing the contact member in a direction in which the contact member is separated from the contact portion.  
      According to the separation assisting means, it is possible to reliably release the substrate from the surface treatment apparatus even though it has a simple structure.  
      In the surface treatment apparatus of the present invention, it is preferable that the contact member has the other end portion opposite to the one end portion thereof, and the contact member can be pivotally rotated with the other end portion being used as a pivotal center.  
      This makes it possible to simplify the structure of the displacement means.  
      In the surface treatment of the present invention, it is preferable that the displacement means is constituted from any one of a spring, an elastic member having a hollow space in which the volume of the hollow space is increased by decompressing the inside of the decompression chamber, a lever and a weight, and a motor.  
      This makes it possible to prevent an increase in the number of components of the surface treatment apparatus and an increase in manufacturing costs of the surface treatment apparatus because the displacement means has a very simple structure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other objects, features, and the advantages of the invention will readily become more apparent from the following detailed description of preferred embodiments of the invention with reference to the accompanying drawings.  
       FIG. 1  is a cross-sectional view which shows a surface treatment apparatus in a first embodiment according to the present invention.  
       FIG. 2  is a plan view of the surface treatment apparatus shown in  FIG. 1 .  
       FIG. 3  is a cross-sectional view which shows a surface treatment apparatus in a second embodiment according to the present invention.  
       FIG. 4  is a plan view of the surface treatment apparatus shown in  FIG. 3 .  
       FIG. 5  is a cross-sectional view which shows a surface treatment apparatus in a third embodiment according to the present invention.  
       FIG. 6  is a plan view of the surface treatment apparatus shown in  FIG. 5 .  
       FIG. 7  is a cross-sectional view which shows a surface treatment apparatus in a fourth embodiment according to the present invention.  
       FIG. 8  is a partially cross-sectional view which shows a surface treatment apparatus in a fifth embodiment according to the present invention.  
       FIG. 9  is a partially cross-sectional view to be used for explaining the usage of the surface treatment apparatus shown in  FIG. 8 .  
       FIG. 10  is a partially cross-sectional view which shows a surface treatment apparatus in a sixth embodiment according to the present invention.  
       FIG. 11  is a perspective view which shows a part (which is separation assisting means) of a surface treatment apparatus in a seventh embodiment according to the present invention.  
       FIG. 12  is a perspective view which shows a part (which is separation assisting means) of a surface treatment apparatus in an eighth embodiment according to the present invention.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Hereinbelow, a surface treatment apparatus according to the present invention will be described in detail with reference to preferred embodiments shown in the appended drawings.  
      In the present invention, substrates to be subjected to surface treatment include both of individual substrates and wafers. On one surface of such a substrate (hereinafter, referred to as a “front surface”), which is opposite to the other surface to be subjected to surface treatment (hereinafter, referred to as a “back surface”), semiconductor elements (active elements) or wiring formed of a transparent conductive film or the like may be provided. The surface treatment apparatus according to the present invention is applied to a case where the back surface of a substrate having such a processed front surface is subjected to surface treatment. Hereinbelow, a description will be made with regard to a case where the back surface of a substrate is subjected to wet etching by way of example.  
     First Embodiment  
      First, a first embodiment of a surface treatment apparatus according to the present invention will be described.  FIG. 1  is a cross-sectional view which shows the first embodiment of the surface treatment apparatus according to the present invention.  FIG. 2  is a plan view of the surface treatment apparatus shown in  FIG. 1 . In the following description, it is to be noted that the upper side and the lower side in  FIG. 1  will be referred to as the “upper side” and the “lower side”, respectively.  
      A surface treatment apparatus  1  of the first embodiment can hold a substrate  10  with the substrate  10  being stuck thereto by suction so that an entire back surface  101  of the substrate  10  (which is one surface of the substrate  10 ) is exposed to the outside and a front surface  102  of the substrate  10  (which is the other surface of the substrate  10 ) is protected from the outside.  
      The surface treatment apparatus  1  shown in  FIGS. 1 and 2  includes an O-ring (which is a contact portion)  2  to be brought into contact with the front surface  102  of the substrate  10 , and a main body  3  which supports the O-ring  2 .  
      The main body  3  is formed so as to have a disc shape (flat plate shape), and has a substrate contact surface  31 . The size of the substrate contact surface  31  when viewed from the top of the surface treatment apparatus  1  is slightly larger than that of the substrate  10  to be held (or to be secured). Further, the main body  3  has a plurality of concave portions  32  provided in an area on the inner side of a peripheral portion  311 . Each of the concave portions  32  forms an enclosed space with the front surface  102  of the substrate  10  (that is, the enclosed space is defined by the concave portion  32  and the front surface  102  of the substrate  10 ). As will be described later, the enclosed spaces are decompressed, and then the surface treatment apparatus  1  is subjected to atmospheric pressure, so that the difference between pressure within the concave portions  32  and atmospheric pressure allows the substrate  10  to be stuck to and held by the surface treatment apparatus  1  by suction.  
      In the peripheral portion  311  of the main body  3 , there is provided an annular groove  33 . The groove  33  accommodates the O-ring  2 . The O-ring  2  is a member having the function of maintaining the hermeticity of the concave portions (that is, enclosed spaces)  32  while the substrate  10  is being stuck to the surface treatment apparatus  1  by suction. In the present embodiment, by allowing the O-ring  2  and the front surface  102  of the substrate  10  to firmly stick together, the concave portions  32  are hermetically sealed.  
      The O-ring  2  is mainly made of an elastic material. Examples of such an elastic material include various rubber materials such as natural rubber, butyl rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber and silicone rubber, and various thermoplastic elastomers such as polyurethane-based thermoplastic elastomer, polyester-based thermoplastic elastomer, polyamide-based thermoplastic elastomer, olefin-based thermoplastic elastomer, and styrene-based thermoplastic elastomer. These elastic materials can be used singly or in combination of two or more of them.  
      Further, the main body  3  has a step portion  312  provided along the edge portion thereof. The step portion  312  is formed so as to be higher than the substrate contact surface  31 , and functions as a positioning guide at the time when the substrate  10  is placed at a predetermined position on the substrate contact surface  31 .  
      The main body  3  is mainly made of a hard material. As will be described later, since the substrate  10  is stuck to and held by the surface treatment apparatus  1  by suction due to the difference between pressure within the concave portions  32  and atmospheric pressure (hereinafter, simply referred to as a “pressure difference”), the use of a hard material for the main body  3  makes it possible to suitably prevent the surface treatment apparatus  1  from being deformed while the substrate  10  is being stuck to and held by the surface treatment apparatus  1  by suction.  
      Examples of such a hard material include various ceramic materials such as various glass, alumina, silica, titania, zirconia, yttria, calciumphosphate, silicon nitride, aluminum nitride, titanium nitride, boron nitride, graphite and tungsten carbide, and various metal materials such as iron, nickel, copper, aluminum, titanium, and alloys containing two or more of them. These hard materials can be used singly or in combination of two or more of them.  
      Among them, various ceramic materials are preferably used as a constituent material of the main body  3 . The use of various ceramic materials as a constituent material of the main body  3  makes it possible to impart high mechanical strength and high resistance to etchants (which are liquids for treatment) to the main body  3 . From the viewpoint of improving resistance to etchants, the surface of the main body  3  may be coated with a material having high chemical resistance such as fluorine-based resins, for example.  
      The ratio of the total opening area of the concave portions  32  with respect to the area of the substrate  10  when viewed from the top of the surface treatment apparatus  1  is preferably in the range of about {fraction (1/20)} to ¾, and more preferably it is in the range of about ¼ to ½. By setting the ratio to a value within the above range, it is possible for the substrate  10  to be stuck to and held by the surface treatment apparatus  1  by suction more reliably due to the pressure difference. If the total opening area of the concave portions  32  is too large, there is a fear that the mechanical strength of the main body  3  is extremely lowered depending on the depth of the concave portions  32  or the constituent material of the main body  3 .  
      The concave portions  32  are decompressed with the concave portions  32  being covered with the substrate  10 , and then the surface treatment apparatus  1  is subjected to atmospheric pressure. As a result, force pressing the substrate  10  toward the substrate contact surface  31  is generated due to the pressure difference so that the substrate  10  is pressed against the substrate contact surface  31 . In this way, the substrate  10  is stuck to and held by the surface treatment apparatus  1  by suction. At this time, the O-ring  2  is deformed so that repulsive force is generated in the up-and-down direction. As a result, the gap between the substrate  10  and the O-ring  2  is hermetically sealed (that is, the gap is closed), which makes it possible to keep the insides of the concave portions  32  in a reduced pressure (decompressed) state.  
      Particularly, by providing the plurality of concave portions  32  so as to be scattered, it is possible to secure the substrate  10  to the surface treatment apparatus  1  evenly. Unlike a conventional apparatus which allows a substrate to be secured by holding it between jigs, since the surface treatment apparatus  1  secures the substrate  10  by creating a negative pressure in the concave portions  32 , the entire back surface (which is a surface to be subjected to surface treatment)  101  of the substrate  10  can be exposed to the outside.  
      Therefore, it is possible to evenly subject each area of the back surface  101  of the substrate  10  to wet etching. In addition, since the gap between the front surface  102  of the substrate  10  and the main body  3  is hermetically sealed by the O-ring  2 , the front surface  102  of the substrate  10  can be reliably protected from an etchant (which is a liquid for treatment) upon wet etching of the substrate  10 . In order to hermetically seal the gap between the front surface  102  of the substrate  10  and the main body  3  with the use of the O-ring  2  as described above, the wire diameter L and the Shore hardness Hs of the O-ring  2  are preferably set so as to satisfy the following conditions. First, the repulsive force F of the O-ring  2  can be determined from the following formula (I): 
 
 F/L= 4.58×10 −7 ε 1.8   HS   4.0  ( kg/cm )  (I) 
 
 where F is repulsive force (kg), L is a wire diameter (that is, a diameter) (cm), ε is a squeeze ratio, and Hs is Shore hardness. 
 
      Here, the squeeze ratio ε means the ratio of amount of squeeze of the O-ring  2  with respect to the wire diameter L of the O-ring  2  at the time when the O-ring  2  is squeezed. For example, in a case where the O-ring  2  having a wire diameter L of 1 mm is squeezed so that the amount of squeeze becomes 0.2 mm, the squeeze ratio ε at this time is expressed by 0.2/1.  
      Therefore, it is preferred that the wire diameter L and the Shore hardness Hs of the O-ring  2  are set so that the repulsive force F determined from the formula (I) becomes smaller than force pressing the substrate  10  generated due to the pressure difference (hereinafter, referred to as a “condition A”). By setting the wire diameter L and the Shore hardness Hs of the O-ring  2  so that the condition A can be satisfied, the O-ring  2 , the front surface  102  of the substrate  10 , and the main body  3  can stick together more firmly, thereby enabling the substrate  10  to be stuck to and held by the surface treatment apparatus  1  by suction more reliably.  
      Further, average pressure P generated by the repulsive force of the O-ring  2  can be determined from the following formula (II): 
 
 P=F/S ( kg/cm   2 )  (II) 
 
 where P is average pressure (kg/cm 2 ), F is repulsive force (kg), and S is the area of the groove  33  when viewed from the top of the surface treatment apparatus  1  (cm 2 ). 
 
      Therefore, it is preferred that the wire diameter L and the Shore hardness Hs of the O-ring  2  are set so that the average pressure P determined from the formula (II) becomes higher than the water pressure of an etchant to be used in wet etching (especially, so that the average pressure P becomes about 1.5 to 3.5 times as high as the water pressure of an etchant to be used in wet etching) (hereinafter, referred to as a “condition B”). By setting the wire diameter L and the Shore hardness Hs of the O-ring  2  so that the condition B can be satisfied, it is possible to more reliably prevent the O-ring  2  from being deformed due to the water pressure of the etchant so that intrusion of the etchant into the concave portions  32  is prevented.  
      In this regard, it should be noted that it is more preferred that the wire diameter L and the Shore hardness Hs of the O-ring  2  are set so that both of the conditions A and B can be satisfied. By setting the wire diameter L and the Shore hardness Hs of the O-ring  2  so that both of the conditions A and B can be satisfied, it is possible for the substrate  10  to be stuck to and held by the surface treatment apparatus  1  by suction more reliably as well as it is possible to prevent an etchant from intruding the concave portions  32  more reliably.  
      Next, a method of subjecting a substrate to surface treatment with the use of the surface treatment apparatus  1  of the first embodiment (that is, a first method for surface treatment) will be described.  
      &lt;1A&gt; Decompression Step (First Step)  
      First, the substrate  10  is brought into contact with the surface treatment apparatus  1  shown in  FIGS. 1 and 2  so that the front surface  102  of the substrate  10  can come into contact with the O-ring  2  and so that the substrate  10  can be placed on the inner side of the step portion  312 .  
      In the case where the front surface  102  of the substrate  10  has been already processed, that is, in the case where wiring, semiconductor elements (active elements) or the like have been already provided on the front surface  102  of the substrate  10 , a protective layer may be formed on the front surface  102  of the substrate  10  prior to the step &lt;1A&gt;. By forming the protective layer on the front surface  102  of the substrate  10 , it is possible to prevent such wiring or semiconductor elements provided on the front surface  102  of the substrate  10  from being damaged when coming into contact with (abutting on) the substrate contact surface  31 . The protective layer can be formed (or provided) by application of a resist, attachment of a polymeric sheet, or the like. The average thickness of the protective layer is preferably in the range of about 0.1 to 5 μm, and more preferably in the range of about 0.1 to 2 am.  
      Next, the surface treatment apparatus  1  which is in contact with the substrate  10  is conveyed to the inside of a vacuum chamber (decompression chamber), and then the vacuum chamber is decompressed. Air within the concave portions  32  escapes (leaks out) little by little through the gap between the substrate  10  and the O-ring  2  so that the pressure within the concave portions  32  becomes substantially equal to the pressure within the vacuum chamber. At this time, the pressure within the vacuum chamber is preferably in the range of about 30,000 to 10,000 Pa, and more preferably in the range of about 20,000 to 10,000 Pa. By setting the pressure within the vacuum chamber to a value within the above range, it is possible for the substrate  10  to be stuck to and held by the surface treatment apparatus  1  by suction while the substrate  10  is more reliably prevented from being damaged in the next step &lt;2A&gt;.  
      &lt;2A&gt; Step in which the Substrate is Stuck to and Held by the Surface Treatment Apparatus by Suction (Second Step)  
      Next, decompression of the vacuum chamber is terminated, and the pressure within the vacuum chamber is returned to atmospheric pressure. As a result, a pressure difference is generated between the pressure within the concave portions  32  and the external pressure (that is, atmospheric pressure), and pressing force is exerted on the substrate  10  toward the substrate contact surface  31  so that the substrate  10  is pressed against the substrate contact surface  31  (that is, the substrate  10  is stuck to the surface treatment apparatus  1  by suction) and is held by the surface treatment apparatus  1 .  
      At this time, the O-ring  2  is squeezed in the up-and-down direction so that repulsive force is generated in the up-and-down direction. As a result, the gap between the substrate  10  and the O-ring  2  is hermetically sealed, which makes it possible to reliably keep the insides of the concave portions  32  in a reduced pressure (decompression) state.  
      &lt;3A&gt; Etching Step (Third Step)  
      Next, the surface treatment apparatus  1  by which the substrate  10  is held by suction is immersed in a desired etchant (which is a liquid for treatment) stored in a bath to subject the back surface  101  of the substrate  10  to surface treatment. An etchant to be used is not limited to any specific one, and is appropriately selected according to a purpose. Examples of such an etchant include an aqueous hydrofluoric acid solution, an aqueous hydrogen peroxide solution, an aqueous ammonium bifluoride solution, an aqueous potassium hydroxide solution, and TMH (tetramethyl ammonium hydroxide), and they can be used singly or in combination of two or more of them. In wet etching, it is preferred that the substrate  10  is subjected to surface treatment while the surface treatment apparatus  1  is rotated. By doing so, it is possible to subject each area of the back surface  101  to surface treatment evenly.  
      As described above, the surface treatment apparatus  1  of the present embodiment allows the substrate  10  to be held (secured) thereto due to the pressure difference, but the surface treatment apparatus  1  does not have a flow path which allows the concave portions  32  to communicate with the outside while the substrate  10  is in contact with the O-ring  2  (or with the substrate  10  being firmly stuck to the O-ring  2 ). That is, in the present embodiment, there is no necessity to connect a suction tube for decompressing the concave portions  32  to the surface treatment apparatus  1 , and therefore there is no possibility that suction tubes intertwine with each other when the surface treatment apparatuses  1  are rotated upon wet etching. Namely, the surface treatment apparatus  1  is easy to handle. From such a viewpoint, such a surface treatment apparatus is suitably used in subjecting a substrate to wet etching.  
      In the present embodiment, it is to be noted that pressure at the time when surface treatment is carried out is higher than atmospheric pressure (atmospheric pressure or higher), because the substrate  10  is subjected to surface treatment with the surface treatment apparatus  1  being immersed in an etchant so that water pressure is further applied. Pressure at the time when the step &lt;3A&gt; is carried out varies depending on the type of surface treatment, but this pressure is preferably atmospheric pressure or higher. Therefore, in the present embodiment, since it is not necessary to precisely set pressure at the time when the step &lt;3A&gt; is carried out, pressure within the vacuum chamber in the step &lt;1A&gt; is easily set.  
      &lt;4A&gt; Step of Releasing the Substrate (Fourth Step)  
      Next, the surface treatment apparatus  1  is taken out of the bath, and is then conveyed to the vacuum chamber (decompression chamber) again. The vacuum chamber is decompressed so that pressure within the vacuum chamber becomes substantially equal to or lower than the pressure within the vacuum chamber in the step &lt;1A&gt;. By doing so, pressure within the concave portions  32  becomes substantially equal to or higher than the external pressure (that is, the pressure within the concave portions  32  becomes substantially equal to or higher than the pressure within the vacuum chamber). As a result, pressing force is exerted on the substrate  10  in the direction in which the substrate  10  is separated from the substrate contact surface  31  (that is, in the upward direction in  FIG. 1 ) due to the pressure difference so that the substrate  10  is detached from the substrate contact surface  31 . That is, the substrate  10  is released (removed) from the surface treatment apparatus  1 .  
      Here, when the pressure within the vacuum chamber in the step &lt;1A&gt; is defined as A (Pa) and the pressure within the vacuum chamber in the step &lt;4A&gt; is defined as B (Pa), it is preferable that the relationship that B/A is 0.5 or less is satisfied, and more preferably it is 0.2 or less. If B/A exceeds the above range, there is a fear that the pressing force exerted on the substrate  10  is so small that it becomes difficult to release the substrate  10  from the surface treatment apparatus  1 . Specifically, the pressure within the vacuum chamber in the step &lt;4A&gt; (that is, B) is preferably in the range of about 20,000 to 5,000 Pa, and more preferably it is in the range of about 10,000 to 5,000 Pa. By setting the pressure within the vacuum chamber in the step &lt;4A&gt; (that is, B) to a value within the above range, it is possible to more reliably release the substrate  10  from the surface treatment apparatus  1 .  
      In the step &lt;4A&gt;, it is to be noted that external force may be applied to the substrate  10  to assist the detachment of the substrate  10  from the surface treatment apparatus  1 . Examples of a method of applying such external force include a method where the outer peripheral portion (edge portion) of the substrate  10  is pressed in the direction in which the substrate  10  is separated from the substrate contact surface  31  (that is, in the upward direction in  FIG. 1 ) with the use of a pin (which will be described later in fifth to eighth embodiments), a method in which a magnetic field is applied to a magnet attached to the main body  3  in advance so as to act as repulsive force, and the like.  
      According to such a method for surface treatment, since the back surface  101  of the substrate  10  is evenly subjected to etching (surface treatment), it is possible to accurately carry out operations such as application of a resist, exposure using a contact aligner, and the like in post-steps coming after the step &lt;4A&gt;.  
     Second Embodiment  
      Next, a second embodiment of the surface treatment apparatus according to the present invention will be described.  
       FIG. 3  is a cross-sectional view which shows the second embodiment of the surface treatment apparatus according to the present invention, and  FIG. 4  is a plan view of the surface treatment apparatus shown in  FIG. 3 . In the following description, it is to be noted that the upper side and the lower side in  FIG. 3  will be referred to as the “upper side” and the “lower side”, respectively.  
      Hereinbelow, the second embodiment of the surface treatment apparatus will be described by focusing the difference between the first and second embodiments, and a description with regard to the overlapping points will be omitted.  
      A surface treatment apparatus  4  of the second embodiment is constituted from a flat-shaped member having two major surfaces, and has a contact portion on each of the two surfaces thereof to which a substrate is stuck by suction. That is, the surface treatment apparatus  4  shown in  FIGS. 3 and 4  can hold substrates  20  and  30  with the substrates  20  and  30  being stuck thereto by suction so that entire back surfaces  201  and  301  of the substrates  20  and  30  are exposed to the outside and front surfaces  202  and  302  of the substrates  20  and  30  are protected from the outside.  
      The surface treatment apparatus  4  is formed so as to have a disc shape (flat plate shape), and has substrate contact surfaces  41   a  and  41   b . The sizes of the substrate contact surfaces  41   a  and  41   b  when viewed from the top of the surface treatment apparatus  4  are substantially equal to the sizes of the substrates  20  and  30  to be held (or to be secured), respectively. In the present embodiment, the almost entire surface treatment apparatus  4  is mainly made of an elastic material. As such an elastic material, the same elastic materials as those mentioned above with reference to the first embodiment can be used.  
      Further, the surface treatment apparatus  4  has a plurality of through holes  42  and a plurality of concave portions  43 . The through holes  42  pass through the surface treatment apparatus  4  in the thickness direction thereof, and the concave portions  43  are provided in the substrate contact surface  41   a  on the lower side of the surface treatment apparatus  4  and in the substrate contact surface  41   b  on the upper side of the surface treatment apparatus  4 . Each of the through holes  42  forms (defines) an enclosed space together with the front surface  202  of the substrate  20  and the front surface  302  of the substrate  30 . Each of the concave portions  43  forms (defines) an enclosed space together with the front surface  202  of the substrate  20  or together with the front surface  302  of the substrate  30 . As will be described later, the enclosed spaces are decompressed, and then the surface treatment apparatus  4  is subjected to atmospheric pressure, so that the difference between pressure within the through holes  42  and the concave portions  43  and atmospheric pressure (hereinafter, simply referred to as the “pressure difference”) allows the substrates  20  and  30  to be stuck to and held by the surface treatment apparatus  4  by suction.  
      In the present embodiment, some of the enclosed spaces to be decompressed are formed from the concave portions  43 , which makes it possible to prevent lowering of the mechanical strength of the surface treatment apparatus  4  compared with a case where all of the enclosed spaces are formed from the through holes  42 . According to such a structure, it is possible to increase the number of substrates to be subjected to surface treatment while reducing the number of components of the surface treatment apparatus  4 . As a result, costs and time to be spent on etching (surface treatment) can be reduced.  
      The through holes  42  and the concave portions  43  are decompressed with the through holes  42  and the concave portions  43  being covered with the substrates  20  and  30 , and then the surface treatment apparatus  4  is subjected to atmospheric pressure. As a result, force pressing the substrate  20  toward the substrate contact surfaces  41   a  and force pressing the substrate  30  toward the substrate contact surface  41   b  are generated due to the pressure difference so that the substrates  20  and  30  are pressed against the substrate contact surfaces  41   a  and  41   b , respectively. In this way, the substrates  20  and  30  can be stuck to and held by the surface treatment apparatus  4  by suction.  
      At this time, the surface treatment apparatus  4  is compressed in the up-and-down direction so that repulsive force is generated in the up-and-down direction. As a result, the gap between the substrate  20  and the substrate contact surface  41   a  and the gap between the substrate  30  and the substrate contact surface  41   b  are hermetically sealed (that is, the gaps are closed), which makes it possible to keep the insides of the through holes  42  and the concave portions  43  in a reduced pressure state.  
      As shown in  FIG. 3 , the substrates  20  and  30  have concave portions  203  and  303  having openings in the front surfaces  202  and  302 , respectively. The surface treatment apparatus  4  is formed so as to have a structure capable of covering the openings of the concave portions  203  and  303  when the substrates  20  and  30  are brought into contact with the surface treatment apparatus  4 , which makes it possible to reliably keep the insides of the through holes  42  and the concave portions  43  in a reduced pressure state. Therefore, the surface treatment apparatus  4  can hold the substrates  20  and  30  with stability even when the front surfaces of the substrates  20  and  30  have a complicate structure containing the concave portions  203  and  303 .  
      As for substrates having such concave portions, a multilayer semiconductor substrate having through holes as concave portions, an ink-jet head substrate having ink chambers as concave portions, and a glass substrate having through holes as concave portions can be mentioned, for example. The surface treatment apparatus  4  of the second embodiment will provide the same effects as those described above with reference to the surface treatment apparatus  1  of the first embodiment.  
      Next, a method of subjecting a substrate to surface treatment with the use of the surface treatment apparatus  4  of the second embodiment (that is, a second method for surface treatment) will be described. It is to be noted that the second method for surface treatment will be described by focusing the difference between the first and second methods, and a description with regard to the overlapping points will be omitted.  
      &lt;1B&gt; Decompression Step (First Step)  
      First, the substrates  20  and  30  are brought into contact with the surface treatment apparatus  4  shown in  FIGS. 3 and 4 .  
      Specifically, the substrate  20  is brought into contact with the surface treatment apparatus  4  so that the front surface  202  of the substrate  20  can come into contact with the substrate contact surface  41   a  and so that the front surface  202  can be superposed on the substrate contact surface  41   a . Similarly, the substrate  30  is also brought into contact with the surface treatment apparatus  4  so that the front surface  302  of the substrate  30  can come into contact with the substrate contact surface  41   b  and so that the front surface  302  can be superposed on the substrate contact surface  41   b . Further, at this time, the substrates  20  and  30  are brought into contact with the surface treatment apparatus  4  so that the openings of the concave portions  203  and  303  can be covered with the substrate contact surfaces  41   a  and  41   b , respectively.  
      In this regard, it is to be noted that a sheet-shaped material may be attached to (or provided on) each of the front surface  202  of the substrate  20  and the front surface  302  of the substrate  30  to cover the concave portions  203  and  303  prior to the step &lt;1B&gt;. This makes it possible to prevent washing fluid from intruding into the concave portions  203  and  303  even when the substrates  20  and  30  are washed for the purpose of removing an etchant (which is a liquid for treatment) after the substrates  20  and  30  are released from the surface treatment apparatus  4 .  
      Next, the surface treatment apparatus  4  which is in contact with the substrates  20  and  30  is conveyed to a vacuum chamber (decompression chamber), and then the vacuum chamber is decompressed. As a result, air within the through holes  42  and the concave portions  43  leaks out little by little through the gap between the substrate  20  and the substrate contact surface  41   a  and the gap between the substrate  30  and the substrate contact surface  41   b  so that the pressure within the through holes  42  and the concave portions  43  becomes substantially equal to the pressure within the vacuum chamber. In this regard, it is to be noted that a preferred range of the pressure within the vacuum chamber is the same as that described above with reference to the first method for surface treatment.  
      &lt;2B&gt; Step in which the Substrate is Stuck to and Held by the Surface Treatment Apparatus by Suction (Second Step)  
      Next, the same step as the step &lt;2A&gt; described above is carried out.  
      &lt;3B&gt; Etching Step (Third Step)  
      Next, the same step as the step &lt;3A&gt; described above is carried out.  
      &lt;4B&gt; Step of Releasing the Substrate (Fourth Step)  
      Next, the same step as the step &lt;4A&gt; described above is carried out.  
     Third Embodiment  
      Next, a third embodiment of the surface treatment apparatus according to the present invention will be described.  FIG. 5  is a cross-sectional view which shows the third embodiment of the surface treatment apparatus according to the present invention.  FIG. 6  is a plan view of the surface treatment apparatus shown in  FIG. 5 . In the following description, it is to be noted that the upper side and the lower side in  FIG. 5  will be referred to as the “upper side” and the “lower side”, respectively.  
      Hereinbelow, the surface treatment apparatus of the third embodiment will be described by focusing the difference between the surface treatment apparatuses of the first and third embodiments, and a description with regard to the overlapping points will be omitted.  
      A main difference between the first and third embodiments is in the structure of the contact portion, and other structures of the third embodiment are the same as those of the first embodiment. Specifically, a surface treatment apparatus  5  shown in  FIGS. 5 and 6  has an elastic plate  6  having a disc shape as the contact portion. The elastic plate  6  is provided on a main body  7 .  
      The elastic plate  6  has a substrate contact surface  61 . The size of the substrate contact surface  61  when viewed from the top of the surface treatment apparatus  5  is substantially equal to the size of the substrate  10  to be held (or to be secured). The elastic plate  6  may be mainly made of an elastic material. Examples of such an elastic material include the same elastic materials as those mentioned above with reference to the first embodiment.  
      Further, the elastic plate  6  has a plurality of through holes (spaces)  62  passing through the elastic plate  6  in the thickness direction thereof. Each of the through holes  62  forms an enclosed space with the front surface  102  of the substrate  10 . As will be described later, the enclosed spaces are decompressed, and then the surface treatment apparatus  5  is subjected to atmospheric pressure, so that the difference between the pressure within the through holes  62  and atmospheric pressure (hereinafter, simply referred to as a “pressure difference”) allows the substrate  10  to be stuck to and held by the surface treatment apparatus  5  by suction.  
      Such an elastic plate  6  is supported by the main body  7 . The main body  7  has a flow path  72  which allows the through holes  62  to communicate with each other. The flow path  72  is formed so as to have a pattern shown in  FIG. 6 .  
      The through holes  62  are decompressed while the through holes  62  are covered with the substrate  10 , and then the surface treatment apparatus  5  is subjected to atmospheric pressure. As a result, force pressing the substrate  10  toward the substrate contact surface  61  is generated due to the pressure difference so that the substrate  10  is pressed against the substrate contact surface  61 .  
      In this way, the substrate  10  is stuck to and held by the surface treatment apparatus  5  by suction. Particularly, in the present embodiment, since the flow path  72  which allows the through holes  62  to communicate with each other is provided, air can be moved among the through holes  62  so that the pressure within each of the through holes  62  becomes substantially even. This makes it possible for the surface treatment apparatus  5  to secure (or hold) the substrate  10  more stably.  
      Further, at this time, the elastic plate  6  is compressed in the up-and-down direction in  FIG. 5  so that repulsive force is generated in the up-and-down direction. As a result, the gap between the substrate  10  and the substrate contact surface  61  is hermetically sealed (that is, the gap is closed), which makes it possible to keep the insides of the through holes  62  in a reduced pressure state. The surface treatment apparatus  5  of the third embodiment will provide the same effects as those described above with reference to the surface treatment apparatus  1  of the first embodiment.  
      Next, a method of subjecting a substrate to surface treatment with the use of the surface treatment apparatus of the third embodiment (that is, a third method for surface treatment) will be described. In this regard, it is to be noted that the third method for surface treatment will be described by focusing the difference between the first and third methods, and a description with regard to the overlapping points will be omitted.  
      &lt;1C&gt; Decompression Step (First Step)  
      First, the substrate  10  is brought into contact with the surface treatment apparatus  5  shown in  FIGS. 5 and 6  so that the front surface  102  of the substrate  10  can come into contact with the substrate contact surface  61  and so that the front surface  102  can be superposed on the substrate contact surface  61 .  
      Next, the surface treatment apparatus  5  which is in contact with the substrate  10  is conveyed to a vacuum chamber (decompression chamber), and then the vacuum chamber is decompressed. As a result, air within the through holes  62  and the flow path  72  leaks out little by little through the gap between the substrate  10  and the substrate contact surface  61  so that the pressure within the through holes  62  becomes substantially equal to the pressure within the vacuum chamber. Further, at this time, since air within each of the through holes  62  evenly leaks out by virtue of the flow path  72 , the pressure within each of the through holes  62  becomes substantially even. In this regard, it is to be noted that a preferred range of the pressure within the vacuum chamber is the same as that described above with reference to the first method for surface treatment.  
      &lt;2C&gt; Step in which the Substrate is Stuck to and Held by the Surface Treatment Apparatus by Suction (Second Step)  
      Next, the same step as the step &lt;2A&gt; described above is carried out.  
      &lt;3C&gt; Etching Step (Third Step)  
      Next, the same step as the step &lt;3A&gt; described above is carried out.  
      &lt;4C&gt; Step of Releasing the Substrate (Fourth step)  
      Next, the same step as the step &lt;4A&gt; described above is carried out.  
     Fourth Embodiment  
      Next, a fourth embodiment of the surface treatment apparatus according to the present invention will be described.  FIG. 7  is a cross-sectional view which shows the fourth embodiment of the surface treatment apparatus according to the present invention. In the following description, it is to be noted that the upper side and the lower side in  FIG. 7  will be referred to as the “upper side” and the “lower side”, respectively. Hereinbelow, the fourth embodiment of the surface treatment apparatus will be described by focusing the differences between the first and third embodiments and the fourth embodiment, and a description with regard to the overlapping points will be omitted.  
      The surface treatment apparatus of the fourth embodiment is the same as the surface treatment apparatus of the third embodiment except that the surface treatment apparatus of the fourth embodiment has a flow path which allows spaces, which are to be decompressed, to communicate with the outside while a substrate is in contact with the contact portion (or while a substrate is firmly stuck to the contact portion). Specifically, the surface treatment apparatus  5  shown in  FIG. 7  has a flow path  73  provided at almost the center of the main body  7 . The flow path  73  communicates with both of the flow path  72  and the outside. That is, each of the through holes  62  communicates with the outside of the surface treatment apparatus  5  through the flow paths  72  and  73  while the substrate  10  is in contact with the substrate contact surface  61  (that is, while the substrate  10  is in contact with the elastic plate  6 ).  
      In the inner circumferential surface of the flow path  73 , there is provided a thread groove so that a screw  81  (which is a sealing member) can be threadedly engaged in the flow path  73 . Further, an O-ring  82  having elasticity is provided so as to be positioned between the screw  81  and the main body  7  when the screw  81  is attached to the main body  7 . By providing the O-ring  82 , it is possible to hermetically seal the flow path  73  when the screw  81  is attached to the flow path  73 .  
      As will be described later, the through holes  62  are decompressed with the through holes  62  being covered with the substrate  10  and the screw  81  being attached to the flow path  73 , and then the surface treatment apparatus  5  is subjected to atmospheric pressure. As a result, force pressing the substrate  10  toward the substrate contact surface  61  is generated due to the pressure difference so that the substrate  10  is pressed against the substrate contact surface  61 . In this way, the substrate  10  is stuck to and held by the surface treatment apparatus  5  by suction. Then, when the screw  81  is removed from the flow path  73 , air flows into the flow path  72  and the through holes  62  through the flow path  73  so that the pressure within the through holes  62  and the flow path  72  becomes substantially equal to the pressure outside the surface treatment apparatus  5 . Therefore, the pressing force that has been exerted on the substrate  10  is eliminated, and then the substrate  10  is detached from the substrate contact surface  61 .  
      As described above, according to the surface treatment apparatus  5  of the present embodiment, by removing the screw  81  from the flow path  73  after the substrate  10  is subjected to etching, it is possible to easily release the substrate  10  from the surface treatment apparatus  5 . The surface treatment apparatus  5  of the fourth embodiment will provide the same effects as those described above with reference to the surface treatment apparatuses  1  and  5  of the first and third embodiments.  
      Next, a method of subjecting a substrate to surface treatment with the use of the surface treatment apparatus of the fourth embodiment (that is, a fourth method for surface treatment) will be described. In this regard, it is to be noted that the fourth method for surface treatment will be described by focusing the difference between the third and fourth methods, and a description with regard to the overlapping points will be omitted.  
      &lt;1D&gt; Decompression Step (First Step)  
      First, the screw  81  is attached to the flow path  73  of the surface treatment apparatus  5  shown in  FIG. 7  to hermetically seal the flow path  73 . Subsequently, the same step as the step &lt;1C&gt; described above is carried out.  
      &lt;2D&gt; Step in which the Substrate is Stuck to and Held by the Surface Treatment Apparatus by Suction (Second Step)  
      Next, the same step as the step &lt;2C&gt; described above is carried out.  
      &lt;3D&gt; Etching Step (Third Step)  
      Next, the same step as the step &lt;3C&gt; described above is carried out.  
      &lt;4D&gt; Step of Releasing the Substrate (Fourth Step)  
      Next, the screw  81  is removed from the flow path  73  under, for example, atmospheric pressure to open the flow path  73  to the outside. As a result, air flows into the flow path  72  and the through holes  62  through the flow path  73  so that the pressure within the through holes  62  and the flow path  72  is returned to atmospheric pressure (that is, so that the pressure within the through holes  62  and the flow path  72  becomes substantially equal to the pressure outside the surface treatment apparatus  5 ). Therefore, the pressing force that has been exerted on the substrate  10  (that is, a load that has been applied on the substrate  10 ) is eliminated, and then the substrate  10  is detached from the substrate contact surface  61 .  
     Fifth Embodiment  
      Next, a fifth embodiment of the surface treatment apparatus according to the present invention will be described.  FIGS. 8A and 8B  are fragmentally cross-sectional views which show the fifth embodiment of the surface treatment apparatus according to the present invention.  FIGS. 9A  to  9 C are fragmentally cross-sectional views to be used for explaining the usage of the surface treatment apparatus shown in  FIGS. 8A and 8B . In the following description, it is to be noted that the upper side and the lower side in  FIGS. 8A and 8B  and  FIGS. 9A  to  9 C will be referred to as the “upper side” and the “lower side”, respectively.  
      Hereinbelow, the surface treatment apparatus of the fifth embodiment will be described by focusing the difference between the first and fifth embodiments, and a description with regard to the overlapping points will be omitted. The surface treatment apparatus of the fifth embodiment is obtained by adding separation assisting means to the surface treatment apparatus of the first embodiment. The separation assisting means is used for assisting the separation of a substrate from the O-ring (which is a contact portion) in the step of releasing the substrate (that is, in the fourth step). It is preferred that the separation assisting means can be separated from the surface treatment apparatus so as to be used in only the step of releasing the substrate (that is, in only the fourth step).  
      A surface treatment apparatus  100  shown in  FIGS. 8A and 8B  includes a base  110  to be used for supporting the main body  3 , and a fixing portion  120  to be used for fixing the main body  3  to the base  110 . The main body  3  is placed on the base  110 , and then the main body  3  is fixed to the base  110  by allowing the fixing portion  120  to come into contact with the edge portion of the main body  3 . In this way, the main body  3  can be fixed to the base  110 .  
      In this regard, it is to be noted that two or more of the fixing portions  120  are preferably provided so that the outer periphery of the main body  3  can be fixed at two or more positions. In this case, for example, three fixing portions  120  may be provided so that the main body  3  is fixed to the base  110  at a position shown in  FIGS. 8A and 8B  and positions on the both sides of a pin  131  (which will be described later) at the time when the pin  131  is in a first position (that is, in a position shown in  FIG. 8A ).  
      Further, as shown in  FIGS. 8A and 9A , the surface treatment apparatus  100  of the present embodiment is formed so as to have a gap  34  between the peripheral portion  311  of the main body  3  and the substrate  10  with the substrate  10  being stuck to and held by the surface treatment apparatus  100  by suction. The pin  131  (described later) is inserted in this gap  34 .  
      On an area of the base  110  other than an area where the main body  3  is to be placed, separation assisting means  130  is provided. The separation assisting means  130  includes the pin  131  (which is a part of a contact member having a cylindrical shape or a prismatic shape) to be inserted in the gap  34  between the substrate  10  and the main body  3 , and a coil spring (which is displacement means)  132  to displace the pin  131  in the direction in which the pin  131  is separated from the main body  3  (that is, in the direction in which the pin  131  is separated from the O-ring  2 ).  
      One end portion of the pin  131 , which is opposite to the other end portion positioned on the side of the O-ring  2  (that is, opposite to the other end portion positioned on the side of the main body  3 ), that is, the end portion of the pin  131  on the right side in  FIGS. 8A and 8B  is fixed to one end portion of a supporting portion  133  (which is a part of the contact member). In the other end portion of the supporting portion  133  (that is, in the end portion of the supporting portion  133  on the right side in  FIGS. 8A and 8B ), there is provided a rotation central shaft  134  (pivotal center). The rotation central shaft  134  (that is, the supporting portion  133 ) is rotatably supported by a bearing  135  provided on the base  110 . Therefore, the pin  131  can be rotated (displaced) about the center which is positioned on the opposite side of the O-ring  2  (that is, the rotation central shaft  134 ) so as to be displaced between the first position (that is, a position shown in  FIG. 8A ) where the end portion of the pin  131  on the side of the O-ring  2  is close to the main body  3  (or close to the base  110 ) and a second position (that is, a position shown in  FIG. 8B ) where the end portion of the pin  131  on the side of the O-ring  2  is separated from the main body  3  (or separated from the base  110 ). In other words, the contact member constituted from the pin  131  and the supporting member  133  can be pivotally rotated with the rotation central shaft  134  being used as a pivotal center.  
      The coil spring  132  is provided between the supporting portion  133  and the base  110 , and is positioned on the side close to the pin  131 . The lower end portion of the coil spring  132  is fixed to the base  110 . At least when the pin  131  is in the first position, the coil spring  132  is compressed so that the upper end portion thereof comes into contact with the supporting portion  133 . Therefore, the coil spring  132  urges (biases) the pin  131  positioned in the first position upwardly (that is, the coil spring  132  urges (biases) the pin  131  positioned in the first position toward the second position).  
      By providing such separation assisting means  130 , it is possible to reliably detach (release) the substrate  10  from the surface treatment apparatus  100  in the step of releasing the substrate (that is, in the fourth step) even in the case where the substrate  10  is relatively firmly stuck to the O-ring  2  due to, for example, elution of a plasticizer from the O-ring  2  in the etching step (that is, in the third step). In this regard, it is to be noted that the separation assisting means  130  may be formed so that the entire pin  131  can come close to or be separated from the base  110  (that is, so that the entire pin  131  can be displaced). However, as described above, by forming the separation assisting means  130  so that the pin  131  can be rotated about the center positioned on the side of one end of the pin  131  (that is, about the rotation central shaft  134 ), it is possible to simplify the structure of the displacement means.  
      Further, the surface treatment apparatus  100  has a screw (which is locking means)  136  to lock (keep) the pin  131  in the second position. The supporting portion  133  has a through hole  133   a  which passes through the supporting portion  133  in the thickness direction of the supporting portion  133 . The base  110  has a threadedly engaging portion  110   a  in which the tip end portion of the screw  136  is to be threadedly engaged. The pin  131  is set in the first position by moving the pin  131  against the urging force (biasing force) of the coil spring  132 , and then the screw  136  is inserted in the through hole  133   a  of the supporting portion  133 . Then, the tip end portion of the screw  136  is threadedly engaged in the threadedly engaging portion  110   a  until slightly before the lower portion of a head of the screw  136  comes into contact with the supporting portion  133 , and the screw  136  is slackened so that the head of the screw  136  gets away from the supporting portion  133  (see  FIGS. 9A and 9B ). This makes it possible to lock the pin  131  in the second position when the substrate  10  is detached from the surface treatment apparatus  100 .  
      In this regard, it is to be noted that by adjusting the amount (depth) of the screw  136  to be inserted in the threadedly engaging portion  110   a , it is possible to arbitrarily set the second position of the pin  131 . That is, the distance that the pin  131  is displaced between the first position and the second position (that is, the rotation angle of the pin  131 ) can be arbitrarily set.  
      The surface treatment apparatus  100  of the fifth embodiment will provide the same effects as those described above with reference to the surface treatment apparatus  1  of the first embodiment. In particular, according to the surface treatment apparatus  100  of the present embodiment, it is possible to more reliably release (detach) the substrate  10  from the surface treatment apparatus  100  by virtue of the actions of both of the O-ring  2  and the separation assisting means  130 . In this regard, it is to be noted that a leaf spring may also be used instead of the coil spring  132 .  
      Next, a method of subjecting a substrate to surface treatment with the use of the surface treatment apparatus of the fifth embodiment (that is, a fifth method for surface treatment) will be described. In this regard, it is to be noted that the fifth method for surface treatment will be described by focusing the difference between the first and fifth methods, and a description with regard to the overlapping points will be omitted.  
      &lt;1E&gt; Decompression Step (First Step)  
      First, as described above, the main body  3  is separated from the base  110 . Subsequently, the front surface  102  of the substrate  10  is brought into contact with the O-ring  2 , and then the same step as the step &lt;1A&gt; described above is carried out.  
      &lt;2E&gt; Step in which the Substrate is Stuck to and Held by the Surface Treatment Apparatus by Suction (Second Step)  
      Next, the same step as the step &lt;2A&gt; described above is carried out. As a result, the substrate  10  is stuck to and held by the surface treatment apparatus  100  by suction.  
      &lt;3E&gt; Etching Step (Third Step)  
      Next, the same step as the step &lt;3A&gt; described above is carried out.  
      &lt;4E&gt; Step of Releasing the Substrate (Fourth Step)  
      First, the main body  3  is taken out of the bath, and is then placed on the base  110 . Subsequently, as described above, the main body  3  is fixed to the base  110  by allowing the fixing portions  120  to come into contact with the edge portion of the main body  3 . In this way, the main body  3  is fixed to the base  110  as shown in  FIG. 9A . Further, the screw  136  is rotated (so that the tip end portion of the screw  136  is threadedly engaged in the threadedly engaging portion  110   a  and then the screw  136  is slightly slackened) to appropriately adjust the second position of the pin  131 .  
      At this time, since one end portion of the pin  131  is being inserted in the gap  34 , the pin  131  is slightly rotated toward the second position due to the action of the coil spring  132  (that is, due to the urging force of the coil spring  132 ), but the pin  131  is kept in a state where the one end portion thereof is in contact with the edge portion of the front surface  102  of the substrate  10  (that is, the pin  131  is kept in the first position) as shown in  FIG. 9B .  
      Next, the surface treatment apparatus  100  by which the substrate  10  is held is again conveyed to the vacuum chamber (decompression chamber), and then the vacuum chamber is decompressed. As a result, the pressure within the concave portions  32  becomes substantially equal to or higher than the external pressure (that is, the pressure within the concave portions  32  becomes substantially equal to or higher than the pressure within the vacuum chamber) so that pressing force is exerted on the substrate  10  in the direction in which the substrate  10  is separated from the substrate contact surface  31  (that is, in the upward direction in  FIG. 9 ) due to the pressure difference.  
      Further, as described above, since one end portion of the pin  131  is in contact with the edge portion of the front surface  102  of the substrate  10 , the edge portion of the substrate  10  is being pressed in the direction in which the pin  131  is displaced from the first position to the second position (that is, in the upward direction in  FIG. 9 ).  
      According to the surface treatment apparatus  100  of the present embodiment, as shown in  FIG. 9C , it is possible to more reliably release (detach) the substrate  10  from the surface treatment apparatus  100  due to the pressing force caused by both of the pressure difference and the separation assisting means  130 .  
      In this regard, it is to be noted that since the pin  131  is kept in the second position by virtue of the screw  136 , there is no possibility that too much force is exerted on the substrate  10  upon the detachment of the substrate  10  so that the substrate  10  is thrown up. Further, the distance between the first position and the second position, that is, the distance that the one end portion of the pin  131  on the side of the O-ring  2  (which is the end portion that is in contact with the substrate  10 ) is displaced between the first position and the second position is not limited to any specific value, but it is preferably in the range of about 1 to 5 mm.  
     Sixth Embodiment  
      Next, a sixth embodiment of the surface treatment apparatus according to the present invention will be described.  FIGS. 10A and 10B  are fragmentally cross-sectional views which show the sixth embodiment of the surface treatment apparatus according to the present invention. In the following description, it is to be noted that the upper side and the lower side in  FIGS. 10A and 10B  will be referred to as the “upper side” and the “lower side”, respectively.  
      Hereinbelow, the surface treatment apparatus of the sixth embodiment will be described by focusing differences between the first and fifth embodiments and the sixth embodiment, and a description with regard to the overlapping points will be omitted.  
      The surface treatment apparatus of the sixth embodiment is the same as the surface treatment apparatus of the fifth embodiment except for the structure of the displacement means. The surface treatment apparatus  100  shown in  FIGS. 10A and 10B  has an elastic member  137  having a spherical shape as the displacement means. The elastic member  137  includes a hollow space  137   a  which in increased in volume when the elastic member  137  is subjected to a reduced pressure by decompressing a decompression chamber. The elastic member  137  is formed so as to have an outer diameter substantially the same as the distance between the supporting portion  133  and the base  110  at about atmospheric pressure (that is, at normal pressure). When the elastic member  137  is subjected to a reduce pressure by decompressing the decompression chamber, the volume of the hollow space  137   a  is increased so that the outer diameter of the elastic member  137  is also increased. As a result, the supporting portion  133  is rotated about the rotation central shaft  134  so that the pin  131  is rotated (displaced) from the first position (that is, a position shown in  FIG. 10A ) to the second position (that is, a position shown in  FIG. 10B ).  
      As a constituent material of the elastic member  137 , the same materials as those mentioned above with reference to the O-ring  2  can be used. The surface treatment apparatus  100  of the sixth embodiment will provide the same effects as those of the surface treatment apparatus  100  of the fifth embodiment. In this regard, it is to be noted that the outer shape (entire shape) of the elastic member  137  is not limited to a spherical shape. The elastic member  137  may have any shape such as a cube, a rectangular parallelepiped, or the like.  
      Next, a method of subjecting a substrate to surface treatment with the use of the surface treatment apparatus of the sixth embodiment (that is, a sixth method for surface treatment) will be described. In this regard, it is to be noted that the sixth method for surface treatment will be described by focusing the difference between the fifth and sixth methods, and a description with regard to the overlapping points will be omitted.  
      &lt;1F&gt; Decompression Step (First Step)  
      First, the same step as the step &lt;1E&gt; described above is carried out.  
      &lt;2F&gt; Step in which the Substrate is Stuck to and Held by the Surface Treatment Apparatus by Suction (Second Step)  
      Next, the same step as the step &lt;2E&gt; described above is carried out.  
      &lt;3F&gt; Etching Step (Third Step)  
      Next, the same step as the step &lt;3E&gt; described above is carried out.  
      &lt;4F&gt; Step of Releasing the Substrate (Fourth Step)  
      First, the main body  3  is taken out of the bath, and is then placed on the base  110 . Subsequently, as described above, the main body  3  is fixed to the base  110  by allowing the fixing portions  120  to come into contact with the edge portion of the main body  3 . In this way, the main body  3  is fixed to the base  110 . Further, the screw  136  is rotated (so that the tip end portion of the screw  136  is threadedly engaged in the threadedly engaging portion  110   a  and then the screw  136  is slightly slackened) to appropriately adjust the second position of the pin  131 .  
      Next, the surface treatment apparatus  100  by which the substrate  10  is held is again conveyed to the vacuum chamber (decompression chamber), and then the vacuum chamber is decompressed. As a result, the pressure within the concave portions  32  becomes substantially equal to or higher than the external pressure (that is, the pressure within the concave portions  32  becomes substantially equal to or higher than the pressure within the vacuum chamber) so that pressing force is exerted on the substrate  10  in the direction in which the substrate  10  is separated from the substrate contact surface  31  (that is, in the upward direction in  FIG. 10 ) due to the pressure difference. Further, at this time, as the vacuum chamber is decompressed, the volume of the hollow space  137   a  is increased so that the outer diameter of the elastic member  137  is increased. As a result, the elastic member  137  presses the supporting portion  133  upwardly, and then the pin  131  is started to rotate (displace) toward the second position so that the one end portion of the pin  131  comes into contact with the edge portion of the front surface  102  of the substrate  10  to press the edge portion of the substrate  10  upwardly. According to the surface treatment apparatus  100  of the present embodiment, it is possible to more reliably release (detach) the substrate  10  from the surface treatment apparatus  100  due to the pressing force caused by both of the pressure difference and the separation assisting means  130 .  
     Seventh Embodiment  
      Next, a seventh embodiment of the surface treatment apparatus according to the present invention will be described.  FIG. 11  is a perspective view which shows a part (which is separation assisting means) of the seventh embodiment of the surface treatment apparatus according to the present invention. In the following description, it is to be noted that the upper side and the lower side in  FIG. 11  will be referred to as the “upper side” and the “lower side”, respectively.  
      Hereinbelow, the surface treatment apparatus of the seventh embodiment will be described by focusing differences between the first and fifth embodiments and the seventh embodiment, and a description with regard to the overlapping points will be omitted. The surface treatment apparatus of the seventh embodiment is the same as the surface treatment apparatus of the fifth embodiment except for the structure of the displacement means. The displacement means of the surface treatment apparatus  100  shown in  FIG. 11  includes a lever  138   a  and a weight  138   b.    
      One end portion of the lever  138   a  is inserted in the space between the base  110  and the supporting portion  133 . The weight  138   b  is attached to the other end portion of the lever  138   a . Since the weight  138   b  is attached to the other end portion of the lever  138   a , force is exerted on the one end portion of the lever  138   a  in the upward direction in  FIG. 11 . Therefore, the supporting portion  133  is pressed in the upward direction so that the pin  131  is rotated (displaced) toward the second position. The surface treatment apparatus  100  of the seventh embodiment will provide the same effects as those described above with reference to the surface treatment apparatus  100  of the fifth embodiment. In this regard, it is to be noted that, in the present embodiment, the lever  138   a  and the weight  138   b  are separate members, but they may be combined into a single member. Further, the pin  131  may be directly used as a lever.  
      Next, a method of subjecting a substrate to surface treatment with the use of the surface treatment apparatus of the seventh embodiment (that is, a seventh method for surface treatment) will be described. In this regard, it is to be noted that the seventh method for surface treatment will be described by focusing the difference between the fifth and seventh methods, and a description with regard to the overlapping points will be omitted.  
      &lt;1G&gt; Decompression Step (First Step)  
      First, the same step as the step &lt;1E&gt; described above is carried out.  
      &lt;2G&gt; Step in which the Substrate is Stuck to and Held by the Surface Treatment Apparatus by Suction (Second Step)  
      Next, the same step as the step &lt;2E&gt; described above is carried out.  
      &lt;3G&gt; Etching Step (Third Step)  
      Next, the same step as the step &lt;3E&gt; described above is carried out.  
      &lt;4G&gt; Step of Releasing the Substrate (Fourth Step)  
      First, the main body  3  is taken out of the bath, and is then placed on the base  110 . Subsequently, as described above, the main body  3  is fixed to the base  110  by allowing the fixing portions  120  to come into contact with the edge portion of the main body  3 . In this way, the main body  3  is fixed to the base  110 . Further, the screw  136  is rotated (so that the tip end portion of the screw  136  is threadedly engaged in the threadedly engaging portion  110   a  and then the screw  136  is slightly slackened) to appropriately adjust the second position of the pin  131 .  
      At this time, since one end portion of the pin  131  is being inserted in the gap  34 , the pin  131  is slightly rotated toward the second position due to the action of the displacement means constituted from the lever  138   a  and the weight  138   b , but the pin  131  is kept in a state where the one end portion thereof is in contact with the edge portion of the front surface  102  of the substrate  10  (that is, the pin  131  is kept in the first position).  
      Next, the surface treatment apparatus  100  by which the substrate  10  is held is again conveyed to the vacuum chamber (decompression chamber), and then the vacuum chamber is decompressed. As a result, the pressure within the concave portions  32  becomes substantially equal to or higher than the external pressure (that is, the pressure within the concave portions  32  becomes substantially equal to or higher than the pressure within the vacuum chamber) so that pressing force is exerted on the substrate  10  in the direction in which the substrate  10  is separated from the substrate contact surface  31  (that is, in the upward direction in  FIG. 11 ) due to the pressure difference. Further, as described above, since the one end portion of the pin  131  is in contact with the edge portion of the front surface  102  of the substrate  10 , the edge portion of the substrate  10  is being pressed in the direction in which the pin  131  is displaced from the first position to the second position (that is, in the upward direction). According to the surface treatment apparatus  100  of the present embodiment, it is possible to more reliably release (detach) the substrate  10  from the surface treatment apparatus  100  due to the pressing force caused by both of the pressure difference and the separation assisting means  130 .  
     Eighth Embodiment  
      Next, an eighth embodiment of the surface treatment apparatus according to the present invention will be described.  FIG. 12  is a perspective view which shows a part (which is separation assisting means) of the eighth embodiment of the surface treatment apparatus according to the present invention. In the following description, it is to be noted that the upper side and the lower side in  FIG. 12  will be referred to as the “upper side” and the “lower side”, respectively.  
      Hereinbelow, the surface treatment apparatus of the eighth embodiment will be described by focusing differences between the first and fifth embodiments and the eighth embodiment, and a description with regard to the overlapping points will be omitted. The surface treatment apparatus of the eighth embodiment is the same as the surface treatment apparatus of the fifth embodiment except for the structure of the displacement means. The surface treatment apparatus  100  shown in  FIG. 12  has a motor  139  as the displacement means.  
      The motor  139  includes a rotation shaft  139   a  and a main body  139   b . In the present embodiment, the rotation shaft  139   a  also serves as the rotation central shaft  134  of the supporting portion  133 . Alternatively, the rotation shaft  139   a  may be engaged with the rotation central shaft  134   a  of the supporting portion  133  via a gear or the like. The main body  139   b  is fixed to the base  110 . The surface treatment apparatus  100  of the eighth embodiment will provide the same effects as those described above with reference to the surface treatment apparatus  100  of the fifth embodiment.  
      Next, a method of subjecting a substrate to surface treatment with the use of the surface treatment apparatus of the eighth embodiment (that is, an eighth method for surface treatment) will be described. In this regard, it is to be noted that the eighth method for surface treatment will be described by focusing the difference between the fifth and eighth methods, and a description with regard to the overlapping points will be omitted.  
      &lt;1H&gt; Decompression Step (First Step)  
      First, the same step as the step &lt;1E&gt; described above is carried out.  
      &lt;2H&gt; Step in which the Substrate is Stuck to and Held by the Surface Treatment Apparatus by Suction (Second Step)  
      Next, the same step as the step &lt;2E&gt; described above is carried out.  
      &lt;3H&gt; Etching Step (Third Step)  
      Next, the same step as the step &lt;3E&gt; described above is carried out.  
      &lt;4H&gt; Step of Releasing the Substrate (Fourth Step)  
      First, the main body  3  is taken out of the bath, and is then placed on the base  110 . Subsequently, as described above, the main body  3  is fixed to the base  110  by allowing the fixing portions  120  to come into contact with the edge portion of the main body  3 . In this way, the main body  3  is fixed to the base  110 .  
      Further, the screw  136  is rotated (so that the tip end portion of the screw  136  is threadedly engaged in the threadedly engaging portion  110   a  and then the screw  136  is slightly slackened) to appropriately adjust the second position of the pin  131 . Then, the motor  139  is driven. At this time, since one end portion of the pin  131  is being inserted in the gap  34 , the pin  131  is slightly rotated toward the second position due to the driving force of the motor  139 , but the pin  131  is kept in a state where the one end portion thereof is in contact with the edge portion of the front surface  102  of the substrate  10  (that is, the pin  131  is kept in the first position).   
      Next, the surface treatment apparatus  100  by which the substrate  10  is held is again conveyed to the vacuum chamber (decompression chamber), and then the vacuum chamber is decompressed. As a result, the pressure within the concave portions  32  becomes substantially equal to or higher than the external pressure (that is, the pressure within the concave portions  32  becomes substantially equal to or higher than the pressure within the vacuum chamber) so that pressing force is exerted on the substrate  10  in the direction in which the substrate  10  is separated from the substrate contact surface  31  (that is, in the upward direction in  FIG. 12 ) due to the pressure difference. Further, as described above, since the one end portion of the pin  131  is in contact with the edge portion of the front surface  102  of the substrate  10 , the edge portion of the substrate  10  is being pressed in the direction in which the pin  131  is displaced from the first position to the second position (that is, in the upward direction).  
      According to the surface treatment apparatus  100  of the present embodiment, it is possible to more reliably release (detach) the substrate  10  from the surface treatment apparatus  100  due to the pressing force caused by both of the pressure difference and the separation assisting means  130 .  
      As described above, each of the above-described separation assisting means  130  constituted from the contact member (that is, the pin  131 ) and the displacement means has a simple structure, and the use of such separation assisting means  130  makes it possible to reliably release the substrate  10  from the surface treatment apparatus  100 . Further, since the structure of each of the displacement means described above with reference to the fifth to eighth embodiments is very simple, it is possible to prevent an increase in the number of components of the surface treatment apparatus  100  and an increase in manufacturing costs of the surface treatment apparatus  100 .  
      Since each of the surface treatment apparatuses of the invention described above can hermetically secure (hold) a substrate, it is possible to reliably prevent various liquids from intruding into the inside of the substrate while the substrate is being secured to the surface treatment apparatus. Therefore, in particular, the surface treatment apparatuses of the present invention are suitably used in subjecting a substrate to surface treatment with the use of a liquid for treatment. As for surface treatment with the use of a liquid for surface treatment, for example, plating or ion exchange employed in manufacture of tempered glass can be mentioned in addition to wet etching mentioned above.  
      The surface treatment apparatuses of the present invention have been described with reference to the embodiments shown in the drawings, but the present invention is not limited thereto. For example, in the present invention, any two or more of the structures of the first to eighth embodiments may be combined into a single surface treatment apparatus. Further, so long as the same or similar functions are achieved, it is possible to make various changes and additions to each portion of the surface treatment apparatus according to the present invention.  
      Furthermore, the method for surface treatment may include steps other than the steps described above depending on particular objectives, as necessary. Moreover, in each of the embodiments described above, a description has been made with reference to a case where the surface treatment apparatus is conveyed to the decompression chamber while the enclosed spaces are covered with the substrate (that is, while the substrate is in contact with the surface treatment apparatus), and then the decompression chamber is decompressed. However, in the method for surface treatment described above, the enclosed spaces may be covered with the substrate after the decompression chamber is decompressed while the substrate is separated from the surface treatment apparatus (that is, while the enclosed spaces are not covered with the substrate).