JPS6249094B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a metal filter for screening ultrafine particles having a uniform pore size and a high porosity.

Conventionally, filters for screening dust, nonmetallic inclusions in steel, pigments, abrasives, etc., and measuring particle size distribution are made by electroplating metals such as nickel or copper onto a conductive substrate having a photolithographic resist pattern. It is manufactured by
The filter has pores of ~25μ, but filters with pores of 5μ or less are also manufactured as required.

However, with photomasks used in resist photolithography, a predetermined pattern is usually created by reducing an enlarged original image with a camera, but in order to form fine patterns over a large area with high precision, lenses There are limits to performance.

Therefore, in order to obtain a metal filter with a pore size of 5 μm or less, a resist pattern 2 is formed by photolithography on a conductive substrate 1 on which a photoresist layer has been previously provided, via a photomask having a pattern with a pore size of 5 μm or more. (Fig. 1a or 2a) and electroplating a metal 3 such as nickel or copper on the exposed part of the substrate (Fig. 1b or 2b) to produce a filter with an pore diameter of 5μ or more. After that, the filter 3 is peeled off from the substrate (first
After removing the resist film, the pore diameter is further reduced by plating (FIG. 1 d or 2 d) to produce a filter with the desired pore diameter. However, the resist pattern on the conductive substrate obtained by this method has a large pitch and the pore diameter is reduced, which has the disadvantage that the pore area ratio further decreases.

The present invention uses a photomask having a light-shielding material with an interference fringe pattern obtained by interference of laser light, and uses an electroforming method to form ultra-fine pores with a uniform diameter similar to the photomask pattern above on a conductive substrate. The present invention provides a method for manufacturing a metal sieving filter having a high porosity.

Hereinafter, the above-described present invention will be explained in detail with reference to the drawings.

FIG. 3 shows an example of an optical system for manufacturing a photomask by laser interference. In FIG. 3, 11 is a source of coherent laser light. 12 is a beam splitter for splitting the parallel beam of the laser beam into transmitted light and reflected light at a ratio of 1:1. Reference numeral 13 denotes a total reflection mirror for re-imaging the light beam split by the beam splitter 12. Reference numeral 14 denotes an objective lens of the microscope, which spreads the laser beam totally reflected by the total reflection mirror 13. 15 is a pinhole plate placed at the focal length of the lens to prevent light passing through the lens from being scattered by dirt such as dust and moisture from reaching the photosensitive material layer 16 provided on the mask original plate. .

FIG. 4 shows an example of a photoresist pattern of interference fringes printed on the photosensitive material layer 16 by the optical system shown in FIG. 3 and obtained by development.

FIG. 5 shows a diffraction grating resist pattern obtained by further rotating the mask original plate having the interference fringe pattern printed in FIG. 4 by 90 degrees, printing it, and developing it.

The pitch a of the interference fringe pattern is expressed by the following equation, where θ is the intersection angle at which the two parallel rays of FIG. 3 form an image, and λ is the wavelength of the laser beam.

For example, a diffraction grating pattern with a pitch of 1 μm or less can be easily obtained using 3250 Å light using a He-Cd laser.

The photosensitive material used may be either a negative resist or a positive resist that is sensitive to laser light. For example, as a positive resist, the product name is AZ1350.
(manufactured by Shipprey, USA), KAR (manufactured by Kodatsu, USA), and OFPR (manufactured by Tokyo Ohka Kogyo). For negative resists, the product names are KMR, KTFR,
In addition to solvent resists such as KPR (manufactured by Kodatsu, USA) and Waycoat (manufactured by Hunt, USA), there are also water-soluble resists made by adding ammonium dichromate to gelatin, casein, and gryu.

The light-shielding materials that make up the photomask include:
For example, a thin film of several hundred to several thousand angstroms of chromium, chromium oxide, iron oxide, etc. obtained by vapor deposition or sputtering is applied.

FIG. 6 is a schematic cross-sectional view showing each step of an example of a method for manufacturing a photomask used in manufacturing a metal filter for sieving according to the present invention. Figure 6a
1 shows a mask original having a transparent substrate 17 made of glass or the like and a light-shielding material layer 18 made of chromium or the like provided thereon. Figure 6b shows a photosensitive material layer 19 coated on the light-shielding material layer 18 of the mask original, and if an interference fringe pattern is printed and developed using the optical system of Figure 3, the image shown in Figure 6C is shown. As shown, a resist pattern 19A is formed. As shown in FIG. 6d, the exposed light-shielding material layer 18 is etched through this resist layer 19A, and then, as shown in FIG.
By peeling off the resist 19A as shown in FIG. 2, the desired photomask P can be obtained.

Although not shown, the photosensitive material layer provided on the transparent substrate is printed with the laser beam,
After developing and forming the desired resist pattern, a light-shielding material such as chromium is then layered by vapor deposition, sputtering, etc., and the photomask is completed at the same time as the resist is removed.It is also manufactured using the so-called lift-off method. be able to. In this case, it is possible to create a mask with a reversed light-shielding pattern using the same type of photosensitive material as in the above method.

Next, FIG. 7 is a cross-sectional view schematically showing each step of an example of a method for manufacturing a metal filter using the photomask P as described above. First, as shown in FIG. 7a, a fine diffraction grating pattern is printed with ultraviolet light 20 on a photoresist layer 22 provided on a conductive substrate 21 using the photomask P.
Thereafter, a resist pattern 22A is obtained by developing as shown in FIG. 7b. Next, the metal 23 is electroplated as shown in FIG. 7c by a conventional electroforming method, and then the metal 23 is electroplated as shown in FIG. 7d.
A metal filter can be manufactured by peeling off the metal 23 as shown in FIG. In addition to the above-mentioned photoresists, photoresists for deep ultraviolet rays, such as polymethyl methacrylate (PMMA) and polybutyl methacrylate, can also be used as the photoresists used above.

In the case of the present invention, since the pore diameter of the filter is matched in advance with the photomask pattern to be used, there is no need to reduce it by plating. Since the pore diameter of the metal filter manufactured according to the present invention is maintained as it is in the mask pattern, the pore diameter is extremely fine and uniform, and can be 1 μm or less. The porosity is much higher than conventional filters.

Hereinafter, the present invention will be described in more detail by showing examples while referring to the drawings.

Example 1 In FIG. 6, a light shielding material layer (chromium) layer 1 with a thickness of about 1000 Å is deposited on a transparent glass substrate 17.
Using the optical system shown in Fig. 3, a photosensitive material layer 19 was formed by applying Shippley's AZ1350 resist to a thickness of about 1000 Å on top of 8 using a spinner. The two-beam interference beam of a 1W argon laser was burned for 10 minutes. Next, after rotating 90 degrees and exposing the interference light for 10 minutes, development was performed using AZ1350 resist developer, and the exposed chromium layer was chemically etched and the resist was peeled off, resulting in a pitch of approximately 2μ as shown in Figure 5. A photomask with a diffraction grating pattern was fabricated.
Using this diffraction grating mask, as shown in Figure 7, a stainless steel substrate coated with Shipprey's AZ1350J resist (approximately 2μ thick) was baked with an ultra-high pressure mercury lamp, developed, and then nickel plated to form a metal sheet with a thickness of approximately 2μ. A filter was made.

This filter has a pitch of approximately 2μ and an pore diameter of approximately 1μ.
It has uniform pores and can be used for screening fine particles.

Example 2 A similar diffraction grating mask was produced by plasma etching the chromium of the light-shielding material layer constituting the photomask in a mixed gas atmosphere of carbon tetrachloride and oxygen in Example 1. Using this mask, a metal filter was similarly fabricated. was created.

Example 3 According to Example 1 or 2, a diffraction grating mask using a quartz glass substrate was produced. Using this diffraction grating mask, a metal filter was fabricated by plating nickel onto a stainless steel substrate provided with a polymethyl methacrylate (PMMA) resist pattern.

[Brief explanation of the drawing]

FIGS. 1 and 2 are cross-sectional views schematically showing the manufacturing process of a metal filter by the conventional electroforming method, respectively. FIG. 3 is an explanatory diagram showing an example of an optical system that causes laser interference to produce a photomask used in the present invention;
5 and 5 are plan views showing an example of a diffraction grating pattern obtained by the optical system of FIG. 3.
FIG. 6 is a schematic cross-sectional view showing each step of an example of the photomask manufacturing method used in the present invention, and FIG. 7 is a schematic cross-sectional view showing each step of an example of the method of manufacturing a metal filter by the method of the present invention. FIG. DESCRIPTION OF SYMBOLS 11... Laser light generation source, 12... Beam splitter, 13... Total reflection mirror, 14... Objective lens, 15... Pinhole plate, 16... Photosensitive material layer, 17... Transparent substrate, 18... ...Light-shielding material layer, 19... Photosensitive material layer, 19A... Resist pattern, 20... Ultraviolet light, 21... Conductive substrate,
22...Photoresist layer, 22A...Resist pattern, 23...Metal.

Claims (1)

[Claims] 1. After applying a photosensitive material onto a conductive substrate, a fine pattern is printed on the photosensitive material layer through a photomask, and then developed to form a resist pattern, and then a resist pattern is formed on the conductive substrate having the resist pattern. In the method of manufacturing a metal filter by depositing metal by electroforming and peeling the deposited metal from the substrate, the photomask is made of a light-shielding material with a laser beam interference fringe pattern on one side of the transparent substrate. A method for manufacturing a metal filter, characterized by using a photomask on its surface.