JPH04247207A - Air filter - Google Patents

Abstract

PURPOSE:To make more complete the cleanliness in a clean room by providing a high performance air filter for final filtration, capable of precisely removing gaseous negative ionic and positive ionic substances contained in the atmosphere supplied to the clean room together with particulates, in respect to the improvement of high performance air filters for particulate precision filtration used as an end(final) filter in forming clean rooms, etc. CONSTITUTION:A filter medium filtering the atmosphere consists of the first filter medium for particulate precision filtration (2) and the second filter medium for ion adsorption (4) which consists of ion exchange fiber and is put upon the first filter medium from the atmosphere inflow side, or consists of a ion exchange fiber-mixed filter medium for precision filtration made by mixing ion exchange fiber with fiber which forms a filter medium for particulate precision filtration and pressure-forming the mixture.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air filter, and more particularly to an improvement in a high-performance air filter for fine particle filtration used as a terminal (final) filter when forming a clean room or the like.

In recent years, with the miniaturization of semiconductor devices, the substances subject to cleanliness control in the manufacturing environment of semiconductor devices have expanded from fine particles to gaseous ionic substances. The reason for this is that anions directly adhere to semiconductor wafers, causing corrosion of aluminum wiring, etc. At the same time, anions adhere to equipment used in the clean room and corrode their metal parts, causing particles to be generated from them. This is because gaseous cations, ie, metal ions, are also adsorbed on the wafer surface and cause deterioration of device performance due to current leakage and the like.

[0003] Therefore, it has become necessary to precisely remove gaseous anions and cations contained in the air supplied into the clean room, as well as fine particles.

0004

[Prior Art] FIG. 3 is a diagram showing an example of the ventilation flow of a laminar flow clean room. In the figure, 51 is a clean room;
52 is a screen-shaped floor, 53 is an outside air intake, 54 is a pre-filter, 55 is a temperature/humidity control means, 56 is an intermediate filter, 57 is an intake fan, 58 is an air supply circuit, 59 is a final filter, and 60 is an exhaust fan. , 61 indicates a return air circuit.

In the laminar flow type clean room shown in the figure, outside air is taken in from an outside air intake 53 by an intake fan 57 through a pre-filter 54 for removing particles, and is adjusted to a predetermined temperature and humidity by a temperature and humidity adjustment means 55. , an intermediate filter 56, an intake fan 57, an air supply circuit 58, and a final filter 59 for fine particle filtration. A part of the air excluding the part that is discharged to the outside through the air return circuit 61 is returned to the temperature and humidity control means 55, and is sent to the intermediate filter 56, the intake fan 57, the supply air circuit 58, and the final air supply together with the newly taken in outside air. By circulating through the filter 58, the clean room 51, and the return air circuit 61, the inside of the clean room 51 is maintained in a highly dust-free state with a predetermined temperature and humidity.

In such a clean room, the final (terminal) filter that has the function of keeping the number of particulates in the clean room 51 low has conventionally used HEPA (hi
gh efficiency particulate
air) filter or ULPA (ultra
A high-performance air filter called a low penetration air filter was used.

FIG. 4 is a schematic side sectional view showing the main parts of the HEPA filter. As shown in this figure, the HEPA filter (also the ULPA filter) used in the conventional final filter is a paper-like material with a thickness of about 0.5 to 1 mm made by compressing glass fiber in an aluminum frame 1. The filter medium 2 for precise removal of particulates is fitted in a wave shape through a spacer (not shown) to increase the filtration area, and the periphery is hermetically bonded to the aluminum frame 1, and the filter medium 2 has a structure of 0.1~
It only had the ability to almost completely remove fine particles of 0.3 μm or larger.

[0008]

[Problem to be solved by the invention] Therefore, conventional HEP
A filter or ULPA filter as the final (end)
In the clean room used for the filter, the filter cannot remove gaseous (more precisely, mist) ionic substances mixed in the outside air and gaseous ionic substances generated during etching work in the clean room and mixed in the return air. As the air in the clean room circulates through the return air circuit etc., the ionic substances are sequentially concentrated, causing contamination of semiconductor wafers processed in the clean room with the ionic substances, which reduces the manufacturing yield of semiconductor devices. This may cause problems such as deterioration of reliability. Furthermore, equipment in the clean room is corroded by ionic substances and generates particulates, resulting in an increase in the concentration of particulates in the room.

Therefore, the present invention aims to provide a final (terminal) system that can precisely remove gaseous anions and cations contained in the atmosphere supplied into a clean room together with particles. The purpose is to provide air filters for filtration and to improve the cleanliness inside clean rooms.

0010

[Means for Solving the Problems] The above problem is such that the filter medium for filtering the atmosphere is composed of a first filter medium (2) for microparticle precision filtration and ion exchange fibers, and the first filter medium (2) is composed of an ion exchange fiber.
A second filter medium (4) for ion adsorption superimposed on the air inflow side of the filter medium according to the present invention, or a filter medium for filtering the air comprising fibers (4) forming a filter medium for fine particle filtration. The problem is solved by the air filter according to the present invention, which comprises an ion-exchange fiber-containing precision filtration filter material (7) which is formed by mixing ion-exchange fibers (6) into 5) and press-molding the mixture.

[0011]

[Operation] That is, in the first invention according to the present invention, HE
On the air inflow side of a filter medium for microparticle precision filtration such as a PA filter or ULPA filter, a second filter medium made by pressure forming ion exchange fiber into a coarse paper shape that does not cause a large pressure loss to the filter is layered. It has a structure arranged as follows. Then, as the atmosphere passes through the second filter medium, gaseous ionic substances are adsorbed and removed by the ion exchange fibers.
Subsequently, by passing through the first filter medium, fine particles are filtered out and supplied into the clean room in an ultra-clean state.

[0012] Also, in the second invention according to the present invention,
Ion-exchange fibers are mixed into glass fibers used for filter media such as HEPA filters and ULPA filters in a proportion that does not impair precision filtration performance, and the mixture is pressure-formed into paper and used as a filter media. The entire filter medium removes fine particles, and at the same time, the ion exchange fibers mixed in the filter medium adsorb and remove gaseous ionic substances, supplying an ultra-clean atmosphere within the clean room.

[0013]

EXAMPLES The present invention will be specifically explained below with reference to illustrated examples. FIG. 1 is a schematic diagram of the first embodiment of the present invention (a)
2 is a plan view, (b) is a sectional view taken along the line A-A, and FIG. 2 is a schematic diagram of the second embodiment of the present invention, (a) is a plan view, (b)
is a sectional view taken along line A-A. Identical objects are indicated by the same reference numerals throughout the figures.

[0014] The air filter of the first invention according to the present invention, as shown in FIGS. 1(a) and 1(b), is made by pressure-molding glass fiber similar to the conventional filter, and has a thickness of 0.5 to 0.5 mm.
It has a paper shape of 1mm and can be used with a HEPA filter or ULP.
First filter medium 2 for fine particle filtration used in A filter
is fixed in the aluminum frame 1 in a corrugated manner with the periphery airtightly adhered to the aluminum frame 1 via a spacer (not shown), as in the conventional case, and the air circulation shown by the arrow 3 of the filter. For example, a thickness of several tens of μm is placed on the first filter medium 2 on the upstream side of the direction along its surface.
A second paper for ion exchange is made by mixing approximately 1 mm of anion exchange fibers and cation exchange fibers in a ratio of 6:4, and forming the paper into a coarse paper with a thickness of approximately 1 mm to the extent that the pressure drop does not increase too much. It has a structure in which filter media 4 are placed one on top of the other, and the periphery thereof is adhesively fixed to an aluminum frame 1.

[0015] In the air filter having the structure of the first embodiment, when passing through the second filter medium 4, the ionic substances contained in the atmosphere, which are in the form of a gas or more precisely in the form of a mist, pass through the second filter medium. After being adsorbed and removed by the constituent ion exchange fibers, fine particles of 0.1 to 0.3 μm or more are filtered and removed by a first filter medium 2 similar to conventional HEPA and ULPA. Therefore, by using this air filter as the final filter, the interior of the clean room can be made into an ultra-clean space with extremely low amounts of ionic substances and fine particles.

[0016] Furthermore, the air filter of the second aspect of the present invention has a thickness of several μm to 100 μm, which is used when forming the filter medium of a HEPA filter or a ULPA filter, as shown in FIGS. 2(a) and 2(b), for example. For example, about 20% of ion exchange fibers 6 made of anion exchange fibers and cation exchange fibers and formed to the same thickness as the glass fibers are mixed into glass fibers 5 of several tens of micrometers to have a predetermined fine particle filtration ability. A precision filter medium 7 mixed with ion exchange fibers compressed and shaped to a certain density is placed in an aluminum frame 1 as before.
It has a structure in which it is assembled and fixed in a corrugated manner with the periphery thereof airtightly adhered to the aluminum frame 1 via a spacer (not shown).

In the air filter having the structure of this second embodiment, fine particles of 0.1 to 0.3 μm or more in the atmosphere are filtered and removed by the entire filter medium of the ion exchange fiber-containing precision filter medium 7. When this air passes through the filter medium 7, the mist-like ionic substances contained in the air are adsorbed and removed by the ion exchange fibers 6 contained in the filter medium 7, so this air filter can be used as the final filter. This makes it possible to make the inside of the clean room an ultra-clean space, similar to the embodiment described above.

[0018]

Effects of the Invention As explained above, according to the air filter of the present invention, 0.1 to 0.3
It is possible to simultaneously remove not only fine particles with a size of μm or larger, but also mist-like ionic substances, which were conventionally impossible to remove.

Therefore, by using the air filter according to the present invention as the final (terminal) filter of a clean room, it is possible to avoid contamination of fine semiconductor devices manufactured in the clean room with fine particles and ionic substances. It greatly contributes to improving the manufacturing yield and reliability of LSIs and the like.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a first embodiment of the present invention, in which (a) is a plan view and (b) is a sectional view taken along the line A-A.

FIG. 2 is a schematic diagram of a second embodiment of the present invention, in which (a) is a plan view and (b) is a sectional view taken along the line A-A.

[Figure 3] Diagram showing an example of ventilation flow in a laminar flow clean room

[Figure 4] Schematic cross-sectional view showing the main parts of a HEPA filter

[Explanation of symbols]

1 Aluminum frame 2 First filter medium for microparticle precision filtration 3 Atmospheric flow direction 4 Second filter medium for ion exchange 5 Glass fiber 6 Ion exchange fiber 7 Ion exchange fiber mixed precision filter media

Claims (2)

[Claims] Claim 1: A filter medium for filtering the atmosphere is composed of a first filter medium (2) for fine particle filtration and an ion exchange fiber, and a filter medium (2) for filtering the air is composed of a first filter medium (2) for fine particle filtration and an ion exchange fiber, and a filter medium (2) for filtering the air is provided on the side of the first filter medium into which the atmosphere flows. An air filter comprising: a second filter medium (4) for adsorbing ions which are superimposed on each other. Claim 2: The filter medium for filtering the air is made by adding ion exchange fibers (6) to the fibers (5) forming the filter medium for microparticle microfiltration.
1.) An air filter characterized by comprising an ion-exchange fiber-containing precision filtration filter material (7) which is mixed with ion-exchange fibers and press-molded.