BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a flowchart showing a method according to an embodiment of the invention of producing a porous plate in which micro openings with a predetermined size are arranged at a predetermined interval;
FIG. 2 is a view for explaining the method according to the embodiment of the invention of producing the porous plate in which the micro openings with a predetermined size are arranged at a predetermined interval;
FIG. 3 shows an example of a porous plate according to the invention in which micro openings with a predetermined size are arranged at a predetermined interval;
FIG. 4 shows micro openings on a porous plate;
FIG. 5 shows a configuration of a atomizer for spraying pharmaceutical; and
FIG. 6 shows a configuration of a porous plate and a vibrator.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 is a flowchart showing a method of producing a porous plate according to an embodiment of the invention, in which micro openings with a predetermined size are arranged at a predetermined interval.
FIG. 2 is a view for explaining the method of the embodiment of producing the porous plate in which the micro openings with a predetermined size are arranged at a predetermined interval.
In Step S010 shown in FIG. 1, a substrate 101 is washed in a wet washing manner. The substrate 101 is formed by a silicon wafer or the like. FIG. 2(a) shows the substrate 101.
In Step S020 shown in FIG. 1, a sacrifice layer 103 is formed on the substrate 101. FIG. 2(b) shows the sacrifice layer 103 formed on the substrate 101. As described later, the sacrifice layer 103 is used to peel off a layer formed on the sacrifice layer 103. In the embodiment, a positive type UV resist is used as the sacrifice layer 103. In forming the sacrifice layer 103, the positive type UV resist is applied on the substrate 101 by spin coating, and pre-baking is performed. The spin coating is performed at a speed of 1500 rpm. In the pre-baking, the substrate 101 is placed on a hot plate whose temperature is set at 90° C., for 90 seconds.
In Step S030 shown in FIG. 1, a UV curable resin layer 105 is formed on the sacrifice layer 103. FIG. 2(c) shows the UV curable resin layer 105 formed on the sacrifice layer 103. When the UV curable resin layer 105 is formed, a UV curable resin is applied by the spin coating. A thickness of the coated layer is 100 micrometers. The spin coating (rotation) is performed as follows. The substrate 101 is accelerated up to 500 rpm with an acceleration of 100 rpm/s, and the substrate 101 is maintained at 500 rpm for five seconds. Then, the substrate 101 is accelerated up to 1400 rpm with an acceleration of 300 rpm/s, and the substrate 101 is maintained at 1400 rpm for 50 seconds. SU-8 (a product of MicroChem, United States) which is of a negative type epoxy resist may be used as the UV curable resin.
The substrate is maintained in a horizontal position for at least one hour before soft-baking is performed, in order to decrease an edge bead and to have the UV curable resin layer 105 as flat as possible.
In Step S040 shown in FIG. 1, soft-baking is performed in order to volatilize a solvent of the UV curable resin layer 105 to harden the UV curable resin layer 105. The soft-baking may be performed using a hot plate. In this case, the substrate 101 is placed on the hot plate whose temperature is set at 95° C., for 30 seconds. After the soft-baking, the substrate 101 is cooled for 10 minutes or more.
In Step S050 shown in FIG. 1, the UV curable resin layer 105 and the sacrifice layer 103 formed by the positive type UV resist are exposed with an ultraviolet ray. The UV exposure is performed with a micro-opening pattern using a mask aligner. FIG. 2(d) shows a state in which the UV curable resin layer 105 formed on the sacrifice layer 103 is exposed with the ultraviolet ray.
The UV curable resin such as SU-8 having the thickness of 100 micrometers requires an UV irradiation amount of 400 mJ/cm2. In order to avoid heating during the exposure, it is preferable to alternately repeat a 15 second exposure period and a one minute delay period (period during which the exposure is not performed). In the embodiment, entire exposure time is 90 seconds (six 15-second exposure periods).
The substrate 101 is cooled for 10 minutes before post-exposure baking.
In Step S060 shown in FIG. 1, the post-exposure baking is performed to promote cross-linking of the exposed portion. The post-exposure baking may be performed using a hot plate. In this case, the substrate 101 is placed on the hot plate whose temperature is set at 95° C., for 15 minutes. After the post-exposure baking, the substrate 101 is cooled for 15 minutes in advance of development.
In Step S070 shown in FIG. 1, development is performed to remove portions which has not been exposed to the UV irradiation. An organic development solution is used for the development. Propylene glycol methyl ether acetate (PGMEA) may be used as the development solution. The substrate 101 is soaked in a high-purity PGMEA for eight minutes. Then, the rinsing is performed with isopropanol (IPA). FIG. 2(e) shows a state in which the UV curable resin layer 105 formed on the sacrifice layer 103 is developed.
In Step S080 shown in FIG. 1, the UV curable resin layer 105 is peeled off from the substrate 101. An inorganic alkaline development solution (for example, MF-351 development solution produced by Rohm & Haas Microelectronics) is used for peeling off the UV curable resin layer 105. The substrate 101 is soaked in a development solution vessel placed on a hot plate whose temperature is set at room temperature. The hot plate may be rotated in the range of 1000 to 1500 rpm to promote the lift-off process. FIG. 2(i) shows the cured resin layer 105 which has been peeled off from the substrate 101. The cured resin layer 105 becomes the porous plate with micro openings.
FIG. 3 shows an example of a porous plate according to the invention in which the micro openings with a predetermined size are arranged at a predetermined interval. The porous plate according to the invention is produced by the above method. The porous plate is formed in a circular shape. For example, the porous plate has a diameter of six millimeters. For example, the porous plate has a thickness of 100 micrometers. In FIG. 3, size of the micro openings is enlarged.
FIG. 4 shows micro openings on the porous plate. In the embodiment, a cross section of each opening has a circular shape and the interval between the openings is 60 micrometers. The openings may be tapered. A diameter of each opening having a circular cross section, is 30 micrometers in the upper surface of the porous plate, while a diameter of the opening may range from 3 to 5 micrometers in the lower surface.
When the porous plate is used for a pharmaceutical spraying atomizer, a diameter (minimum diameter) of openings in the porous plate is preferably several micrometers and the interval between the openings preferably ranges from 30 to 60 micrometers. The number of the openings in the porous plate is preferably not lower than 1000.
The configuration of the pharmaceutical spraying atomizer according to an embodiment of the invention is similar to that of the atomizer shown in FIG. 5. The configurations of the porous plate and vibrator of the embodiment of the invention are similar to that of the porous plate shown in FIG. 6. However, in the embodiment a porous plate 201 is produced by the producing method described above.
According to the invention, a porous plate in which micro openings with a predetermined size are arranged at a predetermined interval can be produced at low cost. Furthermore, the invention can provide an inexpensive porous plate and an inexpensive atomizer in which the porous plate of the invention is used to deliver uniform droplets having a predetermined quantity.
Patent Application
20080023572
