JP2010071463A - Method for making polyimide thin-film diaphragm - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for making a diaphragm wherein reduction and uniformization in the thickness of a polyimide thin-film used for the diaphragm are achieved and highly strong adhesion of the polyamide thin-film to a substrate is achieved to scarcely allow separation. <P>SOLUTION: The preparation of the diaphragm includes a process for providing the substrate, a spin-coating process, a dehydration process, a masking process, and an etching process. In the spin coating process, a polyamic acid solution is supplied by the spin coating on the substrate. In the dehydration process, the polyamic acid solution is cyclodehydrated and polyimidated to form the polyimide thin-film. In the masking process, a mask is patterned on the surface opposing to the surface where the polyimide thin-film is formed in the substrate. In the etching process, the substrate is etched from the mask-forming side to the polyimide thin-film. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polyimide thin film diaphragm manufacturing method, and more particularly, to a diaphragm manufacturing method using a polyimide thin film formed by spin coating.

  Diaphragms are used in various fields such as general-purpose micropumps for transporting trace fluids and pressure sensors. As a material of the diaphragm, a metal thin film is generally used, but a polyimide film having excellent chemical resistance, heat resistance, and mechanical strength may be used.

  For example, in Patent Document 1, a diaphragm is formed by bonding a composite functional film in which a fluorine-based resin is laminated in multilayer to a commercially available polyimide film sheet having a film thickness of 30 μm (a registered trademark Kapton of Dupont). Has been disclosed.

JP 2003-227467 A

  When the diaphragm is used as a micropump, the microfluid transported by the pump is strongly influenced by surface tension, viscous force, bubbles, and the like, so that a large displacement is required for the diaphragm. In order to increase the displacement of the polyimide film diaphragm, it is conceivable to make the polyimide film thinner. However, the polyimide film used for the diaphragm described in Patent Document 1 described above has not been sufficiently thinned.

  In addition, for polyimide films used for diaphragms, if the film thickness is uneven or the film properties are not uniform, it will break when used for diaphragms, and sufficient displacement will not be obtained. There is also. Here, since the polyimide film used for the diaphragm described in Patent Document 1 uses a commercially available film sheet, it has been difficult to optimize the film thickness and film uniformity.

  Moreover, in the diaphragm of the conventional patent document 1, although the commercially available polyimide film sheet is adhere | attached on a board | substrate, it is used as a diaphragm, but when adhesiveness is weak or an adhesion spot arises, a polyimide film | membrane is from a board | substrate. In some cases, it was peeled off. In particular, when the diaphragm is applied to a micropump or the like, since the bending motion is continuously repeated, the adhesiveness of the polyimide film is important.

  Accordingly, it has been desired to develop a diaphragm that can obtain a large amount of displacement with a uniform polyimide thin film and is difficult to peel off from the substrate.

  In view of such circumstances, the present invention is intended to provide a method for manufacturing a diaphragm that can reduce the thickness and make the film thickness uniform and has high adhesion between the polyimide film and the substrate. To do.

  In order to achieve the above-described object of the present invention, a polyimide thin film diaphragm manufacturing method according to the present invention includes a step of providing a substrate, a spin coating step of applying a polyamic acid solution onto the substrate by spin coating, and a polyamic acid solution. A dehydration process of forming a polyimide thin film by dehydrating and ring-closing and forming a polyimide, a masking process of patterning a mask on a surface of the substrate facing the surface on which the polyimide thin film is formed, and a mask are formed An etching process for etching and removing the substrate from the surface side to the polyimide thin film.

  Here, the dehydration process is a pre-baking process in which the polyamic acid solution is heated using an oven, and a post-baking process in which the polyamic acid solution is heated from the surface facing the surface on which the polyimide thin film is formed using a hot plate, It may consist of.

  Further, the post-baking process may include a first post-baking and a second post-baking different from the heating time and heating temperature of the first post-baking.

  The etching process may use a chlorine-based etching gas.

  In addition, the polyimide thin film diaphragm manufacturing method according to the present invention includes a process of providing a substrate, a masking process of patterning a mask on a surface of the substrate facing the surface on which the polyimide thin film is formed, and a polyamic acid solution. Spin coating process applied to the substrate by spin coating, dehydration process to form a polyimide thin film by dehydrating and closing the polyamic acid solution to form a polyimide, and etching removal of the substrate from the surface where the mask is formed to the polyimide thin film And an etching process.

  Furthermore, before the etching process, a metal vapor deposition process in which a metal thin film is formed on the polyimide thin film by vapor deposition may be provided.

  Further, a metal thin film removal process for removing the metal thin film formed by the metal vapor deposition process after the etching process may be provided.

  Furthermore, the diaphragm of the present invention includes a substrate having a through hole, a polyimide thin film formed on the through hole of the substrate, and a metal thin film formed on the polyimide thin film.

  The polyimide thin film diaphragm manufacturing method of the present invention has the advantage that the polyimide film used for the diaphragm can be made thin and uniform in thickness. There is also an advantage that a diaphragm having high adhesion between the polyimide thin film and the substrate can be provided.

FIG. 1 is a cross-sectional view for explaining each manufacturing process of the polyimide thin film diaphragm manufacturing method of the present invention. FIG. 2 is a bottom view of the substrate for explaining a mask formed on the back side of the substrate. FIG. 3 is a bottom view of the substrate for explaining a state in which the substrate has been removed by etching. FIG. 4 is a cross-sectional view for explaining an example in which the diaphragm manufactured by the diaphragm manufacturing method of the present invention is applied to a micropump.

  The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view for explaining each manufacturing process of the polyimide thin film diaphragm manufacturing method of the present invention. As shown in the drawing, the polyimide thin film diaphragm manufacturing method of the present invention includes a process of providing a substrate (FIG. 1A), a spin coating process (FIG. 1B), and a dehydration process (FIG. 1C). And a masking process (FIG. 1D) and an etching process (FIG. 1E). Hereinafter, each of these processes will be described with reference to the drawings.

  First, as shown in FIG. 1A, a substrate 10 serving as a base of a diaphragm is prepared. The material of the substrate 10 may be any solid material that can be removed by an etching process described later and can serve as a base of a diaphragm. For example, a specific substrate material is silicon.

  Next, as shown in FIG. 1B, a polyamic acid solution 20 is applied on the substrate 10. The polyamic acid solution 20 is applied onto the substrate 10 by spin coating. Spin coating is a method of forming a film by rotating a surface to be coated with a spin coater and dropping a solution to be coated on the surface. Using this spin coating, a film is formed by dropping the polyamic acid solution 20 onto the substrate 10 while rotating the substrate 10 at a high speed. The film thickness of the polyamic acid solution 20 is adjusted by the viscosity of the polyamic acid solution 20 and the number of rotations of the substrate. Therefore, the number of rotations and the like may be adjusted as appropriate so as to obtain a desired film thickness.

  Although polyimide has strong intermolecular force and excellent mechanical properties, it has insoluble and infusible properties, so it is poor in workability. However, as in the present invention, a polyimide acid solution that is a precursor of polyimide is used as a substrate. It is possible to obtain a polyimide thin film with a desired film thickness by spin-coating and polyamidating the polyamic acid solution by dehydration and ring closure in the dehydration process described later. The polyamic acid solution can be obtained, for example, by reacting pyromellitic dianhydride and diaminodiphenyl ether in an organic polar solvent.

  Next, as shown in FIG. 1C, the polyamic acid solution 20 applied onto the substrate 10 is converted into a polyimide by dehydration ring closure, and a polyimide thin film 30 is formed on the substrate 10. Dehydration and ring closure can be performed by heating or using a dehydrating agent as long as the polyamic acid solution can be converted into a polyimide. In the present invention, considering the adhesion between the substrate and the polyimide thin film, it is preferable to include a process of heating from the substrate side using a hot plate. Hereinafter, the dehydration process will be described in detail.

  The dehydration process preferably includes a process of heating a plurality of times under different conditions in order to prevent bubbles due to rapid heating. Specifically, the dehydration process includes a pre-bake process and a post-bake process. Here, the prebaking process heats the polyamic acid solution using an oven. In the post-baking process, the polyamic acid solution 20 is heated using a hot plate from the surface of the substrate 10 facing the surface on which the polyimide thin film 30 is formed. Since the polyamic acid solution 20 is heated from the back side of the substrate 10 through the substrate 10 by the hot plate, the polyamic acid solution 20 is thermally cured from the contact surface with the substrate 10. Accordingly, the adhesion between the polyimide thin film 30 to be formed and the substrate 10 is enhanced, and the polyimide thin film 30 is firmly fixed to the substrate 10. Furthermore, the post-baking process preferably includes a first post-baking process and a second post-baking process in which the heating time and the heating temperature are changed. Thereby, dehydration ring closure becomes possible more efficiently.

  Next, as shown in FIG. 1D, a mask 40 for removing the substrate 10 by etching is formed. The mask 40 is formed by patterning on the surface of the substrate 10 that faces the surface on which the polyimide thin film 30 is formed. Details of the mask 40 will be described with reference to FIG. FIG. 2 is a bottom view of the substrate for explaining a mask formed on the back side of the substrate. As shown in the figure, a mask 40 is formed on the back surface of the substrate 10, that is, on the surface facing the surface on which the polyimide thin film 30 is formed. The mask 40 is for protecting a portion that is not etched away by an etching process described later. The portion 11 to be removed of the substrate 10 is a portion for exposing the polyimide thin film, and the remaining portion 12 of the substrate 10 is a portion that functions as a frame of the diaphragm. In FIG. 2, the portion not covered by the mask 40 is circular, but the present invention is not limited to this, and the shape can be changed as appropriate depending on the use of the diaphragm. As a material of the mask 40, various commonly used resist films such as an aluminum film can be used.

Then, as shown in FIG. 1E, the substrate 10 is removed by etching. The substrate 10 is removed from the surface on which the mask 40 is formed to the polyimide thin film 30. That is, the substrate 10 is removed by etching so as to penetrate from the back surface side to the polyimide thin film 30. Here, the etching is preferably performed by etching and removing only the substrate 10 without damaging the polyimide thin film 30. FIG. 3 shows a bottom view of the substrate with the substrate removed by etching. As the etching method, various methods such as reactive ion etching can be applied. Further, it is preferable to use a chlorine-based gas as the etching gas. Chlorine-based gas is a gas containing chlorine atom, _{e.g., Cl 2, BCl 3, SiCl} 4, CCl 4, CClF 3, CHClF 2, CCl 2 F 2, CHCl 2 F, CHCl 3, CCl 3 F, It contains at least one gas among CH ₂ Cl _{2 and the} like. When reactive ion etching using a chlorine-based etching gas is used, the substrate can be removed by etching with little damage to the polyimide thin film formed according to the present invention. In the case of reactive ion etching using inductively coupled plasma, SF ₆ , CF ₄ , O ₂ or the like may be used as a reactive gas. If necessary, the mask 40 is removed after etching.

  In addition to dry etching such as reactive ion etching as described above, the substrate may be removed by wet etching so as to penetrate from the back surface side to the polyimide thin film. For example, when a very thin polyimide thin film of 5 μm or less, for example, 1.5 μm or less is formed, the polyimide thin film may be damaged by heat during dry etching. Therefore, when forming such a very thin thin film, it is preferable to etch away the substrate by a method that does not generate heat, such as wet etching. As the wet etching solution, for example, general KOH or the like may be used.

  According to the polyimide thin film diaphragm manufacturing method according to the present invention, the polyimide thin film and the substrate can be adhered to each other while the polyimide film is thinned and the film thickness is uniformized through the above-described process. It is possible to obtain a high diaphragm.

  In the above description, the masking process for patterning the mask is performed after the dehydration process for forming the polyimide thin film. However, the present invention is not limited to this, and a spin coating process or the like may be executed after patterning the mask after providing the substrate. The mask may be formed before the substrate is finally removed by etching.

  Hereinafter, specific examples of the method of the present invention for producing a diaphragm having a diameter of 5 mm using a polyimide thin film having a thickness of 10 μm will be described.

  First, a 16 mm square silicon substrate is prepared. The film thickness of the silicon substrate was 0.4 mm.

  And the polyamic acid solution which is a precursor is apply | coated on a board | substrate. As the polyamic acid solution, PIX-3400 manufactured by Hitachi Chemical DuPont was used. This solution has a viscosity of 13 Pa · s. Since the viscosity affects the film thickness and properties after film formation, the polyamic acid solution was applied onto the substrate in a clean room set at room temperature 20 ° C. and humidity 40%.

  Moreover, the application conditions of the polyamic acid solution by a spin coater vary depending on the film thickness desired to be obtained after film formation. The rotational speed of the spin coater is preferably changed in two stages. More specifically, first, 800 rpm is performed for 8 seconds as the rotation speed in the first stage. Next, regarding the rotation speed of the second stage, the film thickness can be adjusted by changing the rotation speed of the second stage. The number of rotations in the second stage is determined according to the desired film thickness, and this is performed for 30 seconds. For example, when PIX-3400 is used as the polyamic acid solution, the polyamic acid solution may be applied at a second rotational speed of 2500 rpm in order to obtain a 10 μm polyimide thin film. In addition, when obtaining a 6 micrometer polyimide thin film, what is necessary is just about 4500 rpm. As the rotation speed of the spin coater increases, the film thickness uniformity increases. Further, although depending on the viscosity of the polyamic acid solution to be used, when PIX-3400 (viscosity 13 Pa · s) is used, the range of film thickness is more preferably about 2 μm to 15 μm from the viewpoint of workability and film thickness characteristics. Is about 3 μm to 12 μm.

  Next, after applying the polyamic acid solution, the polyamic acid solution is heated to be polyimideized. First, it is heated in an oven at 120 ° C. for 5 minutes as a pre-bake. Next, as a first post-bake, the substrate is heated from the back of the substrate with a hot plate at 200 ° C. for 5 minutes. The temperature is further raised, and the second post-bake is heated from 350 ° C. for 10 minutes using the same hot plate from the back side of the substrate. In order to prevent insufficient heating, the post-baking was performed for a slightly longer time. However, heating with a hot plate is more efficient than heating with an oven, and polyimide formation is possible in a shorter time.

  Next, a mask is formed by patterning on the back side of the substrate. Since it is necessary to remove by etching so as to penetrate a 0.4 mm silicon substrate, an aluminum film that is more durable than a normal resist film was used as a mask material.

Then, the substrate is etched away to the polyimide thin film from the masked side. Etching was performed by reactive ion etching, specifically, reactive ion etching using inductively coupled plasma. The etching gas is SF ₆ , the gas flow rate is 550 sccm, 1 cycle 10 seconds, the deposition gas is C ₄ F ₈ , the gas flow rate is 330 sccm, 1 cycle 3 seconds, and these are alternately sprayed onto the surface on which the mask is formed for etching. went. In the diaphragm manufacturing method of the present invention, since the diaphragm is manufactured by penetrating the substrate, it is not necessary to use a special technique such as controlling the etching film thickness.

  In this way, it is possible to produce a polyimide thin film diaphragm. The manufactured polyimide thin film of the diaphragm was highly uniform, and it was confirmed in the stud pull test that the polyimide thin film was adhered to a very large load without peeling off from the substrate.

  Further, when the air pressure was applied to the diaphragm with a cylinder and the displacement of the polyimide thin film with respect to the pressure was measured, a large displacement of 100 μm was confirmed at ± 20 kPa. Moreover, the displacement with respect to this pressure had substantially linearity. Furthermore, when the hysteresis of the polyimide thin film at the time of restoration by pressurization and suction is calculated, the average is 2.3% at the time of pressurization and 2.9% at the time of suction, and the polyimide thin film manufactured by the present invention is excellent. It has been found that it has good restoration characteristics.

  In addition, the displacement was kept within a relatively small variation with respect to the continuous load, and even when a static load of 10 kPa was repeatedly applied 10,000 times, there was no breakage.

  Further, when a laser Doppler vibrometer was applied to the center of the diaphragm, vibration was applied and measurement was performed with an FFT analyzer, the average resonance frequency was 27.5 kHz. In general, a bulk polyimide thin film has a low elastic modulus (for example, 3 GPa) and thus has a low frequency. However, in the polyimide thin film produced by the diaphragm manufacturing method of the present invention, a high frequency was obtained by reducing the film thickness. Therefore, it can be seen that the membrane response of the diaphragm is high.

  Next, manufacturing conditions for a polyimide thin film diaphragm having a film thickness of 10 μm or less, for example, 5 μm or less will be described. The main conditions for controlling the film thickness are the viscosity of the polyamic acid solution and the rotational speed of the spin coater. In the above example of obtaining a 10 μm polyimide thin film, a polyamic acid solution having a viscosity of 13 Pa · s was used and spin coating was performed at a rotational speed of 2500 rpm. However, for example, when a polyamic acid solution having a viscosity of 13 Pa · s was spin-coated at about 6000 rpm, a polyimide thin film having a thickness of about 3 μm was obtained. When a polyamic acid solution having a viscosity diluted to about 1 Pa · s is used, a polyimide thin film having a thickness of about 1 μm can be obtained by spin coating at a rotational speed of 6000 rpm. Further, by increasing the rotational speed, a polyimide thin film having a thickness of less than 1 μm can be produced.

  In the case of manufacturing a diaphragm by etching and removing the substrate from the back surface of the substrate to the polyimide thin film by dry etching, when a very thin polyimide thin film of 5 μm or less, particularly 1.5 μm or less is formed, heat generated during dry etching is used. The polyimide thin film may be damaged. In this case, wet etching may be used as described above.

  As described above, since the diaphragm formed by the diaphragm manufacturing method of the present invention can form a very thin thin film with a uniform film thickness, a large displacement required for a micropump can be realized. In addition, there is an advantage that the hysteresis is small, the film has excellent recoverability, and the response of the film to the operation is good. Furthermore, since the diaphragm formed by the diaphragm manufacturing method of the present invention has excellent adhesion between the substrate and the polyimide film, it also has an advantage of excellent durability.

  Next, the example which applied the diaphragm manufactured by the diaphragm manufacturing method of this invention to the micropump is demonstrated using FIG. FIG. 4 is a transverse cross-sectional view for explaining an example in which the diaphragm manufactured by the diaphragm manufacturing method of the present invention is applied to a micropump. FIG. 4 (a) shows the state of the diaphragm during discharge of the micropump. FIG. 4B shows the state of the diaphragm during the suction of the micropump. In the figure, the same reference numerals as those in FIG. 1 denote the same parts. As shown in the figure, the micropump has a diaphragm provided with a valve element 50 having a discharge valve 51 and a suction valve 52. The valve element 50 is made of, for example, two acrylic plates having a thickness of 0.5 mm, and, for example, holes having a diameter of 0.5 mm and a diameter of 1.2 mm are formed and bonded asymmetrically to the diaphragm. That is, a 1.2 mm hole is formed in the diaphragm side acrylic plate, and a 0.5 mm hole is formed in the discharge side acrylic plate. On the other hand, a 0.5 mm hole is formed in the diaphragm-side acrylic plate, and a 1.2-mm hole is formed in the suction-side acrylic plate. With this configuration, it is possible to realize a valve element using the resistance difference of the flow path. The valve element 50 having such a configuration is attached to a surface of the diaphragm substrate 10 opposite to the surface on which the polyimide thin film 30 is formed to constitute a micropump.

  Then, an air pump is connected to the side of the diaphragm substrate 10 where the polyimide thin film 30 is provided so that air pressure can be applied (not shown). When the diaphragm is pressurized by the air pump, the polyimide thin film is recessed as shown in FIG. 4A, and the liquid in the diaphragm is discharged. Further, when the diaphragm is sucked by the air pump, as shown in FIG. 4B, the polyimide thin film protrudes, and liquid or the like is sucked into the diaphragm.

  If the diaphragm manufactured by the diaphragm manufacturing method of the present invention is used for such a micropump, it is possible to provide an excellent micropump having a large displacement, high durability, and high reaction speed.

  Next, a diaphragm using a composite film of a polyimide thin film and a metal thin film will be described. In the above-described example of the micropump, the diaphragm is driven by air pressure. However, the diaphragm using a composite film of a polyimide thin film and a metal thin film can be applied to a micropump that can be driven by electrostatic force.

  The diaphragm is composed of a substrate having a through hole, a polyimide thin film formed on the through hole of the substrate, and a metal thin film formed on the polyimide thin film. For example, a metal thin film is formed by vapor deposition on the polyimide thin film manufactured as described above. The metal is aluminum, for example, and is provided on the polyimide thin film by vacuum deposition. The film thickness of the aluminum thin film may be about 0.1 μm, for example, in order to act on the electrostatic force. In addition, the polyimide thin film was not damaged by the heat | fever by vacuum evaporation. The timing for depositing the metal thin film on the polyimide thin film may be any time after the polyimide thin film is formed. Of course, the metal thin film may be formed on the entire surface of the polyimide thin film. However, the metal thin film may be formed in the inner region where the through hole is located on the polyimide thin film provided on the through hole of the substrate. preferable. This is because the portion of the polyimide thin film located near the periphery of the through hole is the portion most deformed by the pump operation.

  The thus-produced composite film diaphragm of polyimide thin film and metal thin film can be driven by electrostatic force. That is, by sucking or repelling the composite film by electrostatic force, the diaphragm can be sucked and discharged, and the control of the diaphragm becomes easier.

  In addition, when the substrate is etched away after forming the composite film of the polyimide thin film and the metal thin film, heat generated during dry etching can be conducted to the metal thin film to suppress damage to the polyimide thin film. Thereby, a polyimide thin film can be formed still thinner. Therefore, if dry etching is performed, the metal thin film deposition process is preferably performed before the substrate etching process. Further, the metal thin film may be removed after the substrate is etched away. Thereby, even when the polyimide thin film is used as a single film, it is possible to further reduce the thickness even by dry etching. For removing the metal thin film, for example, the polyimide thin film may be immersed in an acidic solution to dissolve only the metal thin film without affecting the polyimide thin film.

  In addition, the diaphragm manufacturing method of the polyimide thin film of this invention is not limited only to the above-mentioned example of illustration, Of course, various changes can be added within the range which does not deviate from the summary of this invention.

10 Substrate 20 Polyamide acid thin film 30 Polyimide thin film 40 Mask 50 Valve element 51 Discharge valve 52 Suction valve

Claims (8)

A method for producing a diaphragm for a polyimide thin film, the method for producing a diaphragm comprising:
Providing a substrate; and
A spin coating process of applying a polyamic acid solution onto the substrate by spin coating;
A dehydration process for forming a polyimide thin film by dehydrating and ring-closing the polyamic acid solution to form a polyimide;
A masking process for patterning a mask on a surface of the substrate facing the surface on which the polyimide thin film is formed;
An etching process for etching and removing the substrate from the surface side on which the mask is formed to the polyimide thin film;
A diaphragm manufacturing method comprising:   2. The diaphragm manufacturing method according to claim 1, wherein the dehydration process is opposed to a pre-bake process of heating the polyamic acid solution using an oven and a surface of the substrate on which the polyimide thin film is formed using a hot plate. And a post-baking process of heating the polyamic acid solution from the surface.   3. The diaphragm manufacturing method according to claim 2, wherein the post-baking process includes a first post-baking and a second post-baking different from the heating time and heating temperature of the first post-baking.   4. The diaphragm manufacturing method according to claim 1, wherein the etching process uses a chlorine-based etching gas. A method for producing a diaphragm for a polyimide thin film, the method for producing a diaphragm comprising:
Providing a substrate; and
A masking process for patterning a mask on the surface of the substrate opposite to the surface on which the polyimide thin film is formed;
A spin coating process of applying a polyamic acid solution onto the substrate by spin coating;
A dehydration process for forming a polyimide thin film by dehydrating and ring-closing the polyamic acid solution to form a polyimide;
An etching process for etching and removing the substrate from the surface side on which the mask is formed to the polyimide thin film;
A diaphragm manufacturing method comprising:   The diaphragm manufacturing method according to any one of claims 1 to 5, further comprising a metal vapor deposition step of forming a metal thin film on the polyimide thin film by vapor deposition before the etching step. Diaphragm manufacturing method   The diaphragm manufacturing method according to claim 6, further comprising a metal thin film removing process of removing the metal thin film formed by the metal vapor deposition process after the etching process. A substrate having a through hole;
A polyimide thin film formed on the through hole of the substrate;
A metal thin film formed on the polyimide thin film;
A diaphragm characterized by comprising: