Patent Publication Number: US-10315426-B2

Title: Method for forming patterned film and method for producing liquid ejection head

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a method for forming a patterned film using a lift-off method. The present invention also relates to a method for producing a liquid ejection head such as an ink jet recording head. 
     Description of the Related Art 
     By forming a penetration port in a silicon substrate, various micro electro mechanical system (MEMS) devices are produced. An example thereof is a liquid ejection head that ejects a liquid. The liquid ejection head is exemplified by an ink jet recording head. 
     In the ink jet recording head, an energy generating element for applying energy to eject an ink is formed on a top surface of a silicon substrate. On the top surface of the substrate, an ejection port forming member is also formed, and an opening (ejection port) that ejects an ink is formed above the energy generating element. In the silicon substrate, a penetration port is formed, and through the penetration port, an ink is supplied from the back surface of the substrate to the top surface. 
     In recent years, the ink jet recording head is required to have higher long-term reliability, and a liquid resistant film is formed on an ink liquid contact part in some cases. The technique of patterning the liquid resistant film is exemplified by a technique called lift-off method that is a microfabrication technique for semiconductors. The lift-off method is a method for removing a mask material including a photoresist as a coating on a silicon substrate and a film formed on the mask material from the silicon substrate when a pattern or the like is formed on a plate-shaped workpiece such as a silicon substrate. A patterning method using the lift-off method is disclosed in Japanese Patent Application Laid-Open No. 2008-187164. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention provides a method for forming a patterned film on a substrate, the method including the following steps in this order
     a) patterning a mask material on the substrate, thereby covering, with the mask material, a region except a patterned film forming region on a substrate surface on which the patterned film is to be formed,   b) covering, with a protective member, at least a part of a surface of the mask material opposite to the substrate so as to allow the patterned film forming region to communicate with outside air, thereby forming a workpiece to be subjected to film formation in step c,   c) forming a film on at least the patterned film forming region of a surface of the workpiece communicating with the outside air,   d) releasing the protective member from the mask material, and   e) removing the mask material and a part of the film on the mask material.   

     Another aspect of the present invention provides a method for producing a liquid ejection head, the liquid ejection head including a substrate having a surface with an energy generating element and including a flow path forming member that defines a liquid flow path between the flow path forming member and the surface with the energy generating element of the substrate, the substrate having a penetration port, the flow path forming member having an ejection port configured to eject a liquid. The method includes a step of forming a patterned film on at least a part of a liquid flow path forming substrate surface by performing the following step a to step e in this order,
     a) patterning a mask material on the substrate, thereby covering, with the mask material, a region except a patterned film forming region on a substrate surface on which the patterned film is to be formed,   b) covering, with a protective member, at least a part of a surface of the mask material opposite to the substrate so as to allow the patterned film forming region to communicate with outside air, thereby forming a workpiece to be subjected to film formation in step c,   c) forming a film on at least the patterned film forming region of a surface of the workpiece communicating with the outside air,   d) releasing the protective member from the mask material, and   e) removing the mask material and a part of the film on the mask material.   

     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A, 1B, and 1C  are schematic cross sectional views showing sequential steps for forming a patterned film by a conventional lift-off method. 
         FIGS. 2A, 2B, 2C, 2D, 2E, and 2F  are schematic cross sectional views of a substrate for describing sequential steps of a method for forming a patterned film of a first embodiment in the present invention. 
         FIG. 3A  is a schematic top view of the substrate in the stage of  FIG. 2E ,  FIG. 3B  is a schematic cross sectional view taken along line  3 A- 3 A′ in  FIG. 3A , and  FIG. 3C  is a schematic cross sectional view taken along line  3 B- 3 B′ in  FIG. 3A . 
         FIGS. 4A, 4B, 4C, 4D, 4E, 4F, 4G, 4H, 4I, 4J, and 4K  are schematic cross sectional views showing sequential steps for producing a liquid ejection head by applying a film formation method of a second embodiment in the invention. 
         FIGS. 5A, 5B, 5C, 5D, 5E, 5F, 5G, 5H, 5I, and 5J  are schematic cross sectional views showing sequential steps for producing a liquid ejection head by applying a film formation method of a third embodiment in the invention. 
         FIGS. 6A, 6B, 6C, 6D, 6E, 6F, 6G, 6H, 6I, 6J, and 6K  are schematic cross sectional view showing sequential steps for producing a liquid ejection head by applying a film formation method of a fourth embodiment in the invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings. 
     Steps of a conventional lift-off method will be described.  FIGS. 1A to 1C  show schematic cross sectional views for describing a film formation method using the lift-off method. On a substrate  101 , a pattern (parts where a film pattern is to be formed)  103  of a mask material  102  composed of a photoresist or the like is prepared by a photolithographic method or the like ( FIG. 1A ). On the pattern  103 , a film  104  is next deposited by a highly rectilinear film formation technique such as a physical vapor deposition (PVD) method ( FIG. 1B ). Then, the mask material  102  and an unnecessary film  104  on the mask material  102  are removed ( FIG. 1C ). As the removal technique, a chemical removal technique such as immersion in a mask material removal liquid, a physical removal technique such as ultrasonic vibration, or a combination thereof is performed. Through the process, an intended pattern of the film  104  is formed on the substrate  101 . 
     By the lift-off method, the film  104  removed together with the mask material  102  can be re-attached to the substrate  101 , unfortunately, as shown in  FIG. 1C . The film re-attached in this manner (re-attached film)  105  becomes wastes to contaminate the substrate  101 . Especially in a liquid ejection head, a re-attached film  105  may clog a flow path to cause an ejection defect. 
     Such re-attachment of film residues as described above has been suppressed by rewashing a substrate  101  after the lift-off step (step of removing a mask material  102 ). However, a re-attached film  105  can be still firmly fixed onto a substrate  101  in some cases. 
     Meanwhile, the other patterning techniques not causing such re-attachment of a film  104  include a wet etching method and a dry etching method. These techniques, in which a film to be left is protected by a photoresist, and a film to be removed is etched, are unlikely to causes such a problem of re-attached films  105  as in the lift-off method. These techniques, however, may damage an underlayer of the film to be removed or may deposit an unnecessary altered layer on a surface to be etched. 
     Hence, the present invention is intended to provide a method for forming a patterned film capable of reducing a re-attached film  105  when such a lift-off method as described above is performed to form a pattern of a film  104  on a substrate  101 . 
     The present invention is also intended to provide a method for producing a liquid ejection head using the method for forming a patterned film. 
     The present invention relates to a method for forming a patterned film on a substrate. The method includes steps a to e in this order. In the present specification, a substrate surface on which a patterned film is formed is called “top surface”, and a substrate surface opposite thereto is called “back surface”. 
     [Step a] 
     In the step, a mask material is patterned on a substrate. By the patterning, the region except a patterned film forming region on a substrate surface on which the patterned film is to be formed is covered with the mask material. 
     Typically, a laminar mask material is formed on a substrate. The layer is then patterned by photolithography to give a patterned mask material. The mask material may be in direct contact with the substrate, or a layer formed for any purpose (for example, an interlayer insulating film) may be present between the mask material and the substrate. 
     [Step b] 
     In the step, at least a part of the surface of the mask material opposite to the substrate (the top surface of the mask material when the substrate is placed at the lower side and the mask material is placed at the upper side) is covered with a protective member so as to allow the patterned film forming region to communicate with outside air, forming a workpiece. In other words, at least a part or all of the surface of the patterned mask material prepared in step a, opposite to the substrate is covered with a protective member. Typically, the protective member is not in contact with the substrate. 
     The workpiece means an object to be subjected to film formation in step c. The workpiece includes the substrate, the patterned mask material, and the protective member. 
     The protective member typically has a plate shape or a film shape. 
     Typically, the whole surface of the patterned laminar mask material opposite to the substrate is covered with the protective member. Typically, the lateral surfaces of the patterned laminar mask material (surfaces except the surface of the mask material at the substrate side and the surface of the mask material opposite to the substrate) are not covered with the protective member. 
     When a mask material is formed (patterned) from a photoresist and a plate-shaped or film-shaped protective member is used, the structure in which the whole top surface of the mask material is covered with the protective member and the lateral surfaces of the mask material are not covered with the protective member can be prepared. 
     The reason why the protective member is provided so as to allow the patterned film forming region to communicate with outside air is for supplying a raw material of a film from the outside of the workpiece to the region in step c. In addition, when a mask material has a part not covered with the protective member, the mask material can be easily removed in step e. 
     [Step c] 
     In the step, a film is formed on at least the patterned film forming region of the surface of the workpiece communicating with the outside air. The surface of the workpiece communicating with the outside air is exemplified by the outer surface of the workpiece. The outer surface of the workpiece includes the end surfaces of the substrate, and the back surface of the substrate, for example. The region communicating with the outside air also includes a region present in the workpiece and communicating with the outside air through an opening of the workpiece. The film may or may not be formed on the end surfaces of the substrate or the back surface of the substrate, for example. 
     As needed, before step b or between step b and step c, a step of allowing the film forming region to communicate with the outside air can be performed. For example, a material introducing path for introducing a film forming material from an end surface of a substrate to a film forming region can be formed as described in the first embodiment. Alternatively, a penetration port through a substrate or a penetration port through a protective member can be provided and used as a material introducing path as described in the third and fourth embodiments. 
     [Step d and Step e] 
     In step d, the protective member is released from the mask material. By the releasing, an unnecessary film on the protective member is also removed. In step e, the mask material and a part of the film on the mask are removed. 
     According to the present invention, many of the unnecessary film except the patterned film can be removed by step d performed before the lift-off step (step e). Hence, film residues generated in the lift-off step can be reduced, and the re-attachment of the film residues to the substrate can be suppressed. Especially for a liquid ejection head, unnecessary substances in a liquid flow path can be reduced, and thus the failure rate of the liquid ejection head caused by flow path clogging can be reduced. 
     [First Embodiment] 
     A first embodiment will be described as a preferred embodiment for implementing the present invention.  FIGS. 2A to 2F  show schematic cross sectional views of a substrate for describing steps of the first embodiment. 
     First, a substrate  201  is prepared as shown in  FIG. 2A . The substrate  201  is exemplified by a silicon substrate, a glass substrate, a silicon nitride substrate, a gallium arsenide substrate, a gallium nitride substrate, and an alumina substrate. 
     As shown in  FIG. 2B , a layer of a mask material  202  is formed on a top surface of the substrate  201  and is patterned. In other words, on a top surface of the substrate  201 , a mask material  202  is used to cover the region except an intended patterning area of a film  204 . 
     The raw material of the mask material  202  is preferably a positive photoresist (photosensitive resin). This is because the mask material  202  is required to be released by a solvent in a subsequent step. The polymer included in such a raw material is exemplified by a novolac resin, a polyvinylphenol polymer, and a polyacrylic acid polymer. Other than the positive photoresist, a releasable negative photoresist can also be used. Such a photoresist is exemplified by an epoxy resin, and is preferably trade name: KMPR1000 manufactured by Nippon Kayaku Co., Ltd., which can give a releasable mask having a large thickness of 100 μm or more. 
     As for the shape of the mask material  202 , a mask material  102  for the conventional lift-off method is required to have such a reverse tapered shape that a section parallel and closer to a substrate  101  has a smaller area as shown in  FIG. 1A . This is because a combination of a reverse tapered shape and a rectilinear vapor film formation technique can prevent a film  104  from adhering to the side wall of a mask material  102  and help a solvent to infiltrate from the side wall of the mask material  102  to dissolve the mask material  102 . If a mask material  102  does not have the reverse tapered shape, the side wall of the mask material  102  is unfortunately covered with a film  104 , thus a solvent cannot reach to the mask material  102 , and the mask material  102  is difficult to remove in some cases. 
     On this account, the side wall shape of a conventional mask material  102  is required to be the above reverse tapered shape or to be improved in such a way that a mask material  102  is formed from a plurality of resist layers where upper layers are wider than lower layers, for example. However, to produce such a resist having the reverse tapered shape or the like, process conditions are required to be precisely controlled, and the resist is difficult to form. In contrast, the present invention has an advantage of a mask material  202  that may have any shape in the normal direction of the surface of a substrate  201 . For example, a mask material  202  having such a forward tapered shape that a section parallel and closer to a substrate  201  has a larger area can also be used. This is because a mask material  202  is not required to be dissolved from the side wall in the present invention as described later. 
     As shown in  FIG. 2C , a plate-shaped or film-shaped protective member  203  is attached to the surface of the mask material  202  (the surface opposite to the substrate  201 ) to form a workpiece. When the protective member  203  is attached, at least a part of the mask material  202  is covered with the protective member  203 . The part covered with the protective member  203  is a part on which a film  204  is not formed in a subsequent film formation step. On this account, the protective member  203  is brought into close contact with the mask material  202  to such a degree as to prevent a film  204  from forming in the part. 
     The protective member  203  can be a structure composed of an adhesion layer having adhesive strength and a base material. The protective member  203  is required to be removed later, and thus the protective member  203  preferably has an adhesive strength that can be reduced so as to be easily released from the mask material  202  formed on the substrate  201 . Hence, the protective member  203  is exemplified by a tape including an adhesion layer made from a resin material and a base material. The tape is exemplified by a thermally releasable tape having an adhesive strength that is reduced by heat and an ultraviolet-curable tape including an adhesive having an adhesive strength that is reduced by ultraviolet irradiation. 
     The thickness of the tape can be appropriately selected according to a purpose or the like, but the tape is required to have such a strength as to withstand each step in which the tape is used, and thus the thickness is preferably about 20 μm to 500 μm. The raw material of the base material of the tape is composed of a resin, and the resin is exemplified by polyethylene terephthalate (PET), polyolefin, polyethylene naphthalate (PEN), polypropylene (PP), and polystyrene (PS). 
     The technique of bonding such a tape to a substrate  201  is exemplified by a lamination method using a tape laminator to bond a tape to a mask material  202  on a substrate  201  by roller pressure in the atmosphere or in a vacuum. Using a tape has advantages of low cost and a simple process. 
     Another example of the protective member  203  is a structure composed of a resin material as an adhesion layer and an inorganic material as a base material. The base material is first exemplified by a glass base material. The type of the glass is exemplified by borosilicate glass and quartz glass, which are processed at high accuracy, and inexpensive soda glass. Other examples of the base material include a silicon base material and a stainless steel (SUS) base material. 
     Onto such a base material, an adhesive composed of a resin is applied. The adhesive of the protective member  203  is preferably selected from materials having an adhesive strength that can be reduced for easy release in a subsequent step. The adhesive is preferably a thermoplastic liquid adhesive having an adhesive strength that is reduced by heat or an ultraviolet-curable liquid adhesive having an adhesive strength that is reduced by ultraviolet irradiation, for example. The thickness of the protective member  203  composed of a base material and an adhesive is preferably about 100 μm to 1,000 μm because the protective member  203  is required to have such a strength as to withstand each step in which the protective member  203  is used. The technique of bonding a protective member  203  including a base material made from an inorganic material to a substrate  201  is exemplified by bonding with a wafer bonder in the atmosphere or in a vacuum. 
     As shown in  FIG. 2D , the workpiece is subjected to film formation. The material of the film  204  is exemplified by an inorganic film. The material of the inorganic film is exemplified by ceramics such as silicon oxide, silicon nitride, and silicon carbide and metals such as tantalum, gold, and nickel. Alternatively, an organic resin film  204  can also be formed and is exemplified by a parylene film and a polydimethylsiloxane film. 
     The technique of forming the film is exemplified by an atomic layer deposition (ALD) method. The ALD method, in which several molecule layers are deposited step by step in a high vacuum to form a film, has advantages of good adhesiveness and enabling easy film formation even in a narrow part. 
     Other examples of the film formation technique include a chemical vapor deposition (CVD) method, a plating method as a liquid phase film formation method, and a sputtering method and an evaporation method as a physical vapor deposition method. For example, a film formation method of heating and evaporating an organic resin in a vacuum to form a parylene film achieves good adhesiveness as with the ALD method, and thus is preferred. 
       FIGS. 3A to 3C  show a schematic top view ( FIG. 3A ) of the substrate  201  (workpiece) after the formation of the film  204  and the subsequent removal of the protective member  203  (stage in  FIG. 2E ), a schematic cross sectional view ( FIG. 3B ) taken along line  3 A- 3 A′, and a schematic cross sectional view ( FIG. 3C ) taken along line  3 B- 3 B′. In the present embodiment, a path (material introducing path  205 ) that allows a material gas or a material liquid as the raw material of a film  204  (film forming material) to enter from an end of the substrate  201  into the workpiece in the surface direction of the substrate  201  of the workpiece is formed as a part without the mask material  202  as shown in  FIGS. 3A to 3C . In the present embodiment, a material introducing path  205  for introducing a film forming material from an end of the substrate  201  to at least a patterning area of a film  204  is prepared in this manner. Typically, the material introducing path  205  is a region surrounded by the patterned mask material  202 , the protective member  203 , and the substrate  201 . For example, in such a case as shown in  FIG. 2D , the side walls of the mask material  202  serve as the walls of the material introducing path  205 , and the protective member  203  serves as the ceiling of the material introducing path  205 . 
     Generally, in order to allow a film forming material to enter every nook and corner in a workpiece, the material introducing path  205  preferably has a larger width. However, for example, a film  204  formed by the ALD method has good adhesiveness, and thus the material introducing path  205  can have a smaller width. When the ALD method is used for a 2-inch substrate, typically, a material introducing path  205  from an end surface of the substrate  201  is preferably designed to have a width of 2.5 mm or more, and the mask material  202  is preferably designed to have a height of 50 μm or more. 
     After the film formation, the protective member  203  is released from the mask material  202  as shown in  FIG. 2E . For the release, the adhesive strength of the protective member  203  is preferably reduced first. For example, when used, a thermally releasable tape is subjected to heat treatment before release from a mask material  202 , and thus the adhesive strength of an adhesion layer of the tape is reduced. An ultraviolet-curable tape is subjected to ultraviolet irradiation before release from a mask material  202  for the same purpose. 
     The protective member  203  is released preferably after the adhesive strength is reduced. The releasing method is exemplified by a method of pulling a protective member  203  while a substrate  201  side of the workpiece is fixed by adsorption using a vacuum chuck or the like, thereby releasing the protective member  203 . A specific method is exemplified by a method in which a tape for releasing a protective member is attached to the peripheral part of a protective member  203  and the releasing tape is pulled to release the protective member. The releasing tape is exemplified by a tape with glue and a thermally fusible tape that can be thermocompression-bonded to a protective member  203 . Other examples include a method in which a protective member  203  is fixed by adsorption using another adsorption jig and only the protective member  203  is pulled upward from the workpiece and released. 
     The top surface of the mask material  202  (the surface of the laminar mask material  202  opposite to the substrate  201 ) is protected by the protective member  203  at the time of film formation, and thus no film is formed on the top surface of the mask material  202 . Hence, after the removal of the protective member  203 , a film, which is deposited on the top surface of a mask material  202  in the conventional lift-off method, is absent in the present embodiment as shown in  FIG. 2E . This greatly reduces the film to be removed in a subsequent step of removing the mask material  202  by a solvent or the like, and thus the film re-attached to the substrate  201  can be reduced. 
     As shown in  FIG. 2F , the mask material  202  and the film  204  on the mask material  202  are removed. As the removal technique, a treatment appropriate for characteristics of the mask material  202  can be performed. For example, when the mask material  202  is such a photoresist as described above, ashing by oxygen gas or immersion in an aqueous alkali solution is performed for removal. The aqueous alkali solution is exemplified by a mixture of an organic amine and a polar solvent. 
     In the present invention, no film can be present on the top surface of the mask material  202  after the step of releasing the protective member  203 . Hence, a solvent or gas can easily reach to the mask material  202  from the top surface of the mask material  202 . The embodiment therefore has an advantage over the conventional lift-off method in enabling easy removal of a mask material  202  by a solvent or an ashing gas. 
     In addition, a residual film that is a part of the film  204  formed on the side walls of a mask material  202  and has not been removed, that is, a burr is more certainly removed, and thus the production yield should be further improved. For example, when a method of removing a mask material  202  by immersion in an organic solvent is selected, burrs can be more certainly removed by a solvent at a higher temperature, sonication in a solvent, an appropriate rotation rate of a substrate  201  in a solvent, or the like. 
     The method of further reducing burrs is exemplified by a method of rewashing a substrate  201  after the above steps, by high-pressure jet washing, ultrasonic vibration washing, steam washing, supercritical carbon dioxide washing, dry ice washing, or two-fluid washing, for example. 
     By sequentially performing the above steps, a patterned film  204   a  can be formed on a substrate  201 . A film  204   b  is also formed on the end surfaces and the back surface of the substrate  201 . 
     [Second Embodiment] 
     A second embodiment will be described as a preferred embodiment for implementing the present invention. The same steps as in the first embodiment are not described basically.  FIGS. 4A to 4K  show steps of a method for producing a liquid ejection head to which the present invention is applicable. 
     First, a silicon substrate  303  having the top surface on which a circuit (not shown), an energy generating element (heater)  301 , and an optional interlayer insulating film  302  are formed is prepared as shown in  FIG. 4A . 
     As shown in  FIG. 4B , a plurality of first holes  304  (bottomed holes at this stage) functioning as individual supply ports of a liquid ejection head are formed on the top surface of the silicon substrate  303 . The formation method of the first holes  304  is exemplified by dry etching and crystal anisotropic etching. The etching method is preferably dry etching. Specifically, Bosch process excellent in depth etching of silicon is preferred. The Bosch process is a technique of alternately repeating formation of a deposit film mainly containing carbon and etching by SF 6  gas or the like, thereby anisotropically etching silicon. 
     Next, by the same procedure as in the first embodiment, a mask material  305  and a protective member  306  are formed, then a film  307  is formed, and the protective member  306  and the mask material  305  are removed, thereby forming a patterned film  307   a  on the silicon substrate  303 . These steps will next be described in detail. 
     As shown in  FIG. 4C , a layer of a mask material  305  is formed on the top surface of the silicon substrate  303 , and then is patterned. The region except an intended patterning area of a film  307  is covered with the mask material  305 . The area covered with the mask material  305  is exemplified by the area of the energy generating element  301  and the attachment area of a flow path forming member. 
     As shown in  FIG. 4D , a plate-shaped or film-shaped protective member  306  is bonded to the surface of the mask material  305  (the surface opposite to the silicon substrate  303 ) to form a workpiece. 
     As shown in  FIG. 4E , a film  307  is formed on the workpiece. The material and the formation method of the film  307  are the same as in the first embodiment. Of the materials and the formation methods described in the first embodiment, a material and a method enabling film formation in a condition of 100 to 300° C. are particularly preferred. This is because a transistor or a wiring of the energy generating element  301  is not damaged. 
     As shown in  FIG. 4F , the protective member  306  is released from the mask material  305 . Then, the mask material  305  and the film  307  on the mask material  305  are removed to complete patterning of the film  307  as shown in  FIG. 4G . 
     Next, the surface without the energy generating element  301  (back surface) of the silicon substrate  303  is etched to form a second hole  308  as shown in  FIG. 4H . The second hole  308  reaches the first holes  304 , and the first holes  304  and the second hole  308  communicate with each other to form penetration ports through the silicon substrate  303 . One second hole  308  communicates with a plurality of first holes  304 , and the second hole  308  functions as a common liquid chamber of a liquid ejection head. The etching method can be such a technique as described in the step in  FIG. 4B . After stopping the etching, deposited substances on the inner walls of the penetration ports are removed, and then the top and back surfaces of the silicon substrate  303  and the inner walls of the penetration ports are washed. 
     At this stage, a patterned film  307   a  is formed on the top surface of the silicon substrate  303 . In addition, a film  307   b  is formed on the end surfaces and the back surface of the silicon substrate  303 , and a film  307   c  is formed on the inner walls of the first holes  304 . 
     Then, a flow path forming member is formed. The flow path forming member can be formed by a method known in the field of liquid ejection head production. As shown in  FIG. 4I , walls  309  of the flow path forming member are first formed. The formation method is exemplified by patterning of a dry film resist. Specifically, a dry film resist prepared by coating a film base material with a photosensitive resin is bonded to the silicon substrate  303 . Then, exposure and development are performed to pattern the walls  309  of the flow path forming member. 
     Next, a photosensitive resin is placed on the walls  309  of the flow path forming member as a cover to form a top plate  310  of the flow path forming member as shown in  FIG. 4J  by a similar method. Specifically, a dry film resist is bonded onto the walls  309  of the flow path forming member, and patterning is performed by exposure and development, completing a liquid ejection head. During the patterning, an ejection port  311  is formed at a position that is on the top plate  310  of the flow path forming member and corresponds to the energy generating element  301 . The completed liquid ejection head is shown in  FIG. 4K  (in  FIG. 4K , the top and bottom of the liquid ejection head in  FIGS. 4A to 4J  are inverted). 
     The present embodiment is characterized by forming the second hole  308  through the silicon substrate  303  in a later step ( FIG. 4H ). The embodiment thus has an advantage of maintaining the substrate strength of a silicon substrate  303  to later steps. This process can easily prevent a substrate from cracking in each step before the step to  FIG. 4H . In addition, the workpiece is prevented from warping, and this facilitates proper conveyance of the workpiece. 
     The flow path forming member has a liquid ejection port  311  and defines a liquid flow path  312  for supplying a liquid to the ejection port  311 , between the flow path forming member and the silicon substrate  303  (especially, the substrate surface with the energy generating element  301 ). A liquid such as an ink is supplied from the back side of the silicon substrate  303  to the second hole  308  (common liquid chamber), passes through the first holes (individual supply ports)  304  and the liquid flow path  312 , and is ejected from the ejection port  311 . 
     [Third Embodiment] 
     A third embodiment will be described as another preferred embodiment for implementing the present invention.  FIGS. 5A to 5J  show steps of a method for producing a liquid ejection head to which the present invention is applicable. The present embodiment is characterized by providing penetration ports (including first holes  304  and a second hole  308 ) through a silicon substrate  303  before film formation or step c. The penetration ports pass through the silicon substrate  303  and communicate with a patterned film  307   a  forming region on the silicon substrate  303 . 
     First, a silicon substrate  303  having a top surface on which a circuit (not shown), an energy generating element  301 , and an optional interlayer insulating film  302  are formed is prepared as described in the second embodiment ( FIG. 4A ). On the back surface without these members of the silicon substrate  303 , a second hole  308  (a bottomed hole at this stage) functioning as a common liquid chamber is formed as shown in  FIG. 5A . 
     Next, first holes  304  are formed from the top surface with the circuit and the energy generating element  301  of the silicon substrate  303  as shown in  FIG. 5B . The first holes  304  reach the second hole  308 , and the first holes  304  and the second hole  308  communicate with each other to form penetration ports through the silicon substrate  303 . In this manner, penetration ports are formed in the silicon substrate  303  before film formation. The method of forming holes, specifically the etching method is in accordance with the second embodiment. The steps shown in  FIG. 5C  and  FIG. 5D  are the same as in the second embodiment, but a material introducing path communicating with an end of the silicon substrate  303  is not necessarily formed on the surface of the silicon substrate  303 . 
     Next, film formation is performed as shown in  FIG. 5E . The film  307  is formed on the back surface of the silicon substrate  303  and the end surfaces of the silicon substrate  303 . Through the penetration ports, a material gas or a material liquid as the film forming material can be supplied from the back surface of the silicon substrate  303  to the top surface of the silicon substrate  303 , and thus the film  307  is also formed on the inner walls of the penetration ports and the top surface of the silicon substrate  303 . 
     In the present embodiment, the penetration ports (including the first hole  304  and the second hole  308 ) function as a material introducing path unlike the first and second embodiments. This structure has an advantage of enabling film formation also on the inner wall of the second hole  308 , that is, on the whole inner walls of the penetration ports. For example, a liquid resistant film can be continuously formed on a liquid contact part of penetration ports through which an ejecting liquid flows. This structure can further suppress damage to a silicon substrate  303  by a liquid, and can improve the reliability of a liquid ejection head. Especially when applied to production of an ink jet recording head, this structure can suppress ink erosion in an ink flow path and the like and thus is preferred. 
     In the present embodiment, the length of the penetration port functioning as the material introducing path is as small as the thickness of the silicon substrate  303 , and thus the embodiment has an advantage of allowing a film forming material to readily reach a film pattern region as compared with the first and second embodiments. The film formation technique can be the same as in the first embodiment. Especially when the second hole  308  or the first holes  304 , on which a film is to be formed, have a high aspect ratio, the ALD method is preferred. In order to allow a film forming material gas to reach a film pattern forming region on the top surface of a silicon substrate  303  by the ALD method, typically, the second hole  308  is preferably designed to have a width of 8 μm or more, for example, for an 8-inch substrate having a thickness of 725 μm. For example, when the second hole  308  has a rectangular opening, the shortest distance between the facing hole walls can be designed to be 8 μm or more. 
     Next, the protective member  306  is removed as shown in  FIG. 5F , and then the mask material  305  is removed to complete the patterning of the film  307  ( FIG. 5G ). In the present embodiment, in addition to a patterned film  307   a  on the top surface of the silicon substrate  303 , films  307   b  on the end surfaces and the back surface of the silicon substrate  303 , and films  307   c  on the inner walls of the first holes  304 , films  307   d  are also formed on the inner wall of the second hole  308 . 
     Then, a flow path forming member is formed by the same method as in the second embodiment ( FIG. 5H  and  FIG. 5I ). A liquid ejection head shown in  FIG. 5K  is completed. 
     [Fourth Embodiment] 
     A fourth embodiment will be described as another embodiment for implementing the present invention.  FIGS. 6A to 6K  show steps of a method for producing a liquid ejection head to which the present invention is applicable. The present embodiment is characterized by providing penetration ports  320  in a protective member  306 . 
     The steps in  FIGS. 6A to 6C  are the same as in the second embodiment ( FIGS. 4A to 4C ). 
     In  FIG. 6D , a protective member  306  is bonded to the surface of the mask material  305  (the surface opposite to the silicon substrate  303 ). Here, the protective member  306  has penetration ports  320 , and the penetration ports  320  function as the material introducing path for introducing a film forming material. The penetration ports  320  are provided so as to communicate with a region on which a film  307  is intended to be formed, except the back surface of the silicon substrate  303  and the end surfaces of the silicon substrate  303  (a film pattern forming region on the top surface of the silicon substrate  303  and the inner wall of the first holes  304 ). 
     The protective member  306  is exemplified by a silicon substrate having penetration ports  320  formed by etching. The other examples include a glass substrate having penetration ports  320  processed by laser or sandblast, a stainless steel plate having penetration ports  320  processed by punching, and a plastic substrate having penetration ports  320  processed with a mold. 
     In order to bond the protective member  306  to the mask material  305 , an adhesive is applied to the surface of the protective member  306  having these penetration ports  320 , for example. The adhesive is exemplified by a thermoplastic resin having an adhesive strength that is reduced by heat and an ultraviolet curable resin that is cured by ultraviolet irradiation. The method of applying the adhesive to the protective member  306  is exemplified by spin coating, slit coating, and spray coating. 
     A film base material coated with the adhesive may be laminated on the protective member  306  (a silicon substrate having penetration ports, for example). In such a case, an adhesion layer can be laminated on a protective member  306 , and then penetration ports can be formed through the adhesion layer. The method of forming the penetration ports is exemplified by etching or asking the adhesion layer from the penetration port  320  side of the protective member  306  (the side opposite to the adhesion layer). 
     As shown in  FIG. 6E , film formation is performed. At this film formation, a film  307  is formed from the protective member  306  side through the penetration ports  320 . The film formation method can be the same method as in the first embodiment. In the present embodiment, it is easy to directly arrange penetration ports  320  (functioning as the material introducing path) just above the regions on which a film is intended to be formed, and a large opening shape can be designed. This is because the case of providing penetration ports  320  in a protective member  306  is unlikely to be limited by the design size of an intended device structure and thus has high degree of freedom for formation of the penetration ports  320 . The present embodiment thus has an advantage of good adhesiveness of a film  307  to the surface of a silicon substrate  303  as compared with the first to third embodiments. On this account, the embodiment advantageously enables use of various film formation methods and film formation conditions and can reduce the film formation time, for example. The opening shape and the thickness of the protective member  306  can be designed in consideration of the adhesion of a film  307 . A protective member  306  having a smaller thickness can reduce the length of a penetration port  320  to improve the adhesiveness of a film  307  and thus is advantageous. The thickness of the protective member  306  is typically, preferably 5 to 1,000 μm. 
     The protective member  306  is removed as shown in  FIG. 6F , and then the mask material  305  is removed as shown in  FIG. 6G , completing the patterning of the film  307 . The removed protective member  306  can be reused after the surface is washed, and this can reduce the cost. 
     Then, by the same procedure as in the second embodiment ( FIGS. 4H to 4J ), a second hole  308  is formed from the back surface ( FIG. 6H ), and a flow path forming member is formed ( FIG. 6I  and  FIG. 6J ), completing a liquid ejection head shown in  FIG. 6K . 
     The structures shown the first to fourth embodiments are not necessarily performed independently, and a plurality of embodiments can be appropriately combined and performed. 
     By any of the methods for producing a liquid ejection head described in the second to fourth embodiments, a patterned film, for example, a patterned liquid resistant film can be formed on a liquid flow path  312  formed area on the surface of a silicon substrate  303 , except the region on an energy generating element  301 . 
     By the methods for producing a liquid ejection head described in the second and fourth embodiments, a film  307   c , for example, a liquid resistant film can be formed on a part of the inner wall of penetration ports through a silicon substrate  303 , that is, on the inner walls of first holes  304  (no film is formed on the inner wall of a second hole  308 ). A similar film  307   b  can also be formed on the end surfaces of a silicon substrate  303  and the back surface of the silicon substrate  303 . 
     By the method for producing a liquid ejection head described in the third embodiment, films  307   c  and  307   d , especially a liquid resistant film can be formed on the whole inner walls of penetration ports through a silicon substrate  303  (including first holes  304  and a second hole  308 ). A similar film  307   b  can also be formed on the end surfaces of a silicon substrate  303  and the back surface of the silicon substrate  303 . 
     EXAMPLES 
     Example 1 
     As Example 1, the production method described in the third embodiment ( FIGS. 5A to 5J ) was used to produce a liquid ejection head. By a photolithographic method, the following members were formed on an 8-inch silicon substrate (thickness: 625 μm)  303 . In other words, aluminum wirings (not shown), an interlayer insulating film  302  of a silicon oxide thin film, a heater thin film pattern of tantalum nitride (energy generating element  301 ), and a contact pad for electrical connection to an external controller (not shown) were formed. 
     Onto the top surface of the silicon substrate  303 , a positive photoresist (TZNR (trade name) manufactured by Tokyo Ohka Kogyo Co., Ltd.) (hereinafter, the resist is also called “TZNR resist”) was applied by spinning so as to give a thickness of 10 μm to protect the top surface of the silicon substrate  303 . Then, a resist was applied onto the back surface of the silicon substrate  303  by the same technique, and photolithographic process was performed to pattern the resist having a thickness of 5 μm. 
     The back surface of the silicon substrate  303  was etched using the resist pattern as a mask with a silicon dry etching apparatus by the Bosch process to a depth of 475 μm, and the etching was stopped. By the etching, a second hole  308  was formed. After the completion of silicon etching, the resist on the silicon substrate  303  was removed with a stripping liquid ( FIG. 5A ). 
     Then, an ultraviolet releasable tape including polyethylene terephthalate as a base material was bonded to the back surface of the silicon substrate  303  by a laminator to protect the back surface of the silicon substrate  303 . 
     Next, the same procedure as above (patterning of the positive photoresist and the Bosch process using a silicon dry etching apparatus) was performed to etch the silicon substrate  303  from the top surface, forming first holes  304  having a depth of about 150 μm. In this manner, penetration ports (including the first holes  304  and the second hole  308 ) serving as an ink supply port were formed in the silicon substrate  303 . Here, the opening shape on the top surface of the silicon substrate  303  was a 50×50 μm 2  square. The protective tape on the back surface was then released, and the etching mask and deposited substances by etching in the penetration ports were removed by combination of washing with a stripping liquid and oxygen plasma asking ( FIG. 5B ). 
     Next, a mask material  305  was formed on the top surface of the silicon substrate  303 . A TZNR resist applied by spinning onto a polyethylene terephthalate base material was bonded to the top surface of the silicon substrate  303  by using a laminator and transferred. The resist had a thickness of 15 μm. Next, an exposure machine was used to perform pattern exposure, and the product was immersed in a developer in a developer tank, forming a pattern of the mask material  305  ( FIG. 5C ). 
     On the mask material  305 , a thermally releasable tape having a thickness of 228 μm (manufactured by Mitsui Chemicals Tohcello, Inc., trade name: Icros Tape) as a protective member  306  was bonded to the mask material  305  by using a laminator with pressure, preparing a workpiece ( FIG. 5D ). 
     An atom layer deposition (ALD) film forming apparatus was used to form a metal oxide film, a Ta 2 O 5  (tantalum pentoxide) film, having a thickness of 50 nm as an ink resistant film  307  on a region of the workpiece communicating with outside air ( FIG. 5E ). 
     Next, the workpiece was fixed onto a chuck capable of being warmed. By heating the workpiece to 50° C., the adhesive strength of the thermally releasable tape (protective member  306 ) was reduced, then a tape with glue as a releasing tape was attached to the peripheral part of the silicon substrate  303 , and the tape as the protective member  306  was mechanically peeled off from the silicon substrate  303  ( FIG. 5F ). 
     The mask material  305  on the silicon substrate  303  and unnecessary metal oxide films (the unnecessary film on the mask material  305  and films re-attached onto the surface of the silicon substrate  303 ) were removed by using a running water ultrasonic cleaner nozzle (W-357-1MPD (trade name) manufactured by Honda Electronics Co., Ltd.). As the liquid for removing the mask material  305 , a photoresist stripping liquid mainly containing a polyhydric alcohol (trade name: EKC1112A manufactured by DuPont) was used. The removing liquid was warmed at 40° C., then was sonicated at 1 MHz in the ultrasonic cleaner nozzle, and was sprayed to the surface of the silicon substrate  303  in conditions of a flow rate of 1.2 l/min and an output power of 10 W, thereby removing the substance to be removed ( FIG. 5G ). 
     A negative dry film resist having a thickness of 20 μm (TMMF (trade name) manufactured by Tokyo Ohka Kogyo Co., Ltd.) was bonded to the top surface of the silicon substrate  303  by using a tape laminator. Next, an exposure machine was used to perform exposure, and developing was performed to pattern walls  309  of a flow path forming member. The walls  309  of the flow path forming member were formed on the top surface of the silicon substrate  303  in a region from which the Ta 2 O 5  film had been removed. 
     On the walls  309  of the flow path forming member, the dry film resist was laminated, exposed, and developed, forming a top plate  310  having an ejection port  311  of the flow path forming member. Then, the product was baked in an oven (200° C., 1 hour) ( FIG. 5I ). 
     As described above, a liquid ejection head shown in  FIG. 5J  was produced. 
     The substrate of the produced liquid ejection head was observed under an electron microscope, and film re-attachment or the like was not identified. 
     Example 2 
     As Example 2, the production method described in the fourth embodiment ( FIGS. 6A to 6K ) was used to produce a liquid ejection head. By a photolithographic method, the following members were formed on an 8-inch silicon substrate (thickness: 625 μm)  303 . In other words, aluminum wirings (not shown), an interlayer insulating film  302  of a silicon oxide thin film, a heater thin film pattern of tantalum nitride (energy generating element  301 ), and a contact pad for electrical connection to an external controller (not shown) are formed ( FIG. 6A ). 
     In order to form first holes  304 , a positive photoresist (TZNR (trade name) manufactured by Tokyo Ohka Kogyo Co., Ltd.) was patterned on the top surface of the silicon substrate  303 , and the silicon substrate  303  was etched from the top surface to a depth of about 150 μm. After etching, the resist was removed, and the substrate was washed with a stripping liquid to remove deposited substances in the first holes  304  ( FIG. 6B ). The opening shape of the first hole  304  was a 50×50 μm 2  square. 
     On the top surface of the silicon substrate  303 , a mask material  305  was formed. As with the formation of the mask material  305  in Example 1, a TZNR resist applied by spinning onto a polyethylene terephthalate base material was bonded to the top surface of the silicon substrate  303  and transferred. Pattern exposure and development were then performed in the same manner as in Example 1, forming a pattern of the mask material  305  (a thickness of 15 μm) ( FIG. 6C ). 
     Separately, a protective member  306  was prepared by the following procedure. A silicon substrate having a thickness of 400 μm was prepared, then a TZNR resist was patterned, and etching was performed by the Bosch process to form penetration ports  320 . Onto a polyethylene terephthalate base material, a thermoplastic adhesive (trade name: Spaceliquid TR2 60412 manufactured by Nikka Seiko Co., Ltd.) was applied. To the silicon substrate having the penetration ports  320 , the polyethylene terephthalate base material and the adhesive layer were bonded by using a laminator. Next, the silicon substrate having the penetration ports  320  was used as a mask, and the adhesive layer was etched by oxygen plasma from the surface of the silicon substrate opposite to the adhesive layer through the penetration ports  320 , forming penetration ports  320 . Then, only the polyethylene terephthalate base material was removed. 
     The protective member  306  prepared by the above procedure was bonded to the silicon substrate  303  with the mask material  305  by using a wafer bonder while heated at 140° C. ( FIG. 6D ). Before bonding, the protective member  306  and the silicon substrate  303  were arranged and temporarily fixed by using a bonding alignment apparatus so that the penetration ports  320  of the protective member  306  would communicate with the parts without the mask material  305  on the silicon substrate  303 . 
     From the top surface of the protective member  306  (the surface opposite to the substrate), a metal oxide film, a Ta 2 O 5  (tantalum pentoxide) film, having a thickness of 50 nm was formed as an ink resistant film  307  by using an ALD film forming apparatus on a region of the silicon substrate  303  communicating with outside air ( FIG. 6E ). 
     Next, the workpiece was fixed to a chuck capable of being warmed. While the workpiece was heated at 140° C., the protective member  306  was adsorbed by an adsorption jig and pulled up, thereby peeling off the protective member  306  (the silicon substrate with the penetration ports) ( FIG. 6F ). 
     Then, the adhesive of the protective member  306 , the TZNR resist as the mask material  305 , and the unnecessary Ta 2 O 5  film adhering to the resist side wall were removed by using a solvent and an ultrasonic cleaner nozzle in the same manner as in Example 1 ( FIG. 6G ). 
     Then, the top surface of the silicon substrate  303  was protected by laminating a thermally releasable tape having a thickness of 228 μm (trade name: Icros Tape manufactured by Mitsui Chemicals Tohcello, Inc.). On the back surface of the silicon substrate  303 , a mask is formed from a TZNR resist, and the silicon substrate  303  was processed to a depth of 475 μm by the Bosch process, forming a second hole  308 . The second hole  308  communicated with the first holes  304  on the top surface of the silicon substrate  303 , thereby forming penetration ports serving as an ink supply port. Then, the thermally releasable protective tape was removed ( FIG. 6H ). 
     Next, a flow path forming member was formed on the top surface of the silicon substrate  303  in the same manner as in Example 1 ( FIG. 6I  and  FIG. 6J ), and a liquid ejection head shown in  FIG. 6K  was produced. 
     The substrate of the produced liquid ejection head was observed under an electron microscope, and film re-attachment or the like was not identified. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2016-243419, filed Dec. 15, 2016, which is hereby incorporated by reference herein in its entirety.