JP2824858B2 - Purge air circulation system for particle detection cell - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a purge air circulation system for cleaning a particle detection cell.

[Prior Art] Semiconductor ICs are manufactured in a clean room in which fine particles such as dust are controlled and cleanliness is good. The cleanliness of the clean room is measured by a particle detector, and the detector is an optical detector that crosses a laser beam to the air to be inspected in the detection cell and detects particles mixed in the air to be inspected by scattered light. Is exclusive. In recent years, the pattern size of ICs has become increasingly finer, and accordingly, detection performance for finer particle diameters than ever before is required. For this reason, a method has been developed in which an external mirror type laser oscillator is configured for the detection cell and the detection performance is improved by strong laser power.

FIG. 2 is a vertical sectional view showing the structure of a particle detection cell having an external mirror type laser oscillator.
Is composed of a housing 11, a suction / discharge mechanism 12 for the air A to be inspected, and a laser oscillator 13. Suction and discharge mechanism
In 12, the air to be inspected A sucked from an inlet 121 provided at the upper center of the detection cell 11 is ejected from an ejection nozzle 122 at the lower end thereof, and is discharged from the corresponding discharge nozzle 123 to the outside via an outlet 124. Is discharged. On the other hand, the laser oscillator 13 has a screw
A mounting ring 141 is fixed by 143, a gas laser tube 131 is mounted and fixed by this and a packing 142, and an external mirror 133 is provided at a position corresponding to the Brewster window 132 on the left end of the laser tube 131, and is oscillated. The laser is orthogonal to the air A to be inspected. This orthogonal portion is defined as a detection region S, and the scattered light of the fine particles in the detection region S is received by a light receiving system (not shown) provided in the direction of arrow D, and the fine particles are detected.

Now, in the particle detection cell 1 described above, all of the particles mixed in the test air A injected from the injection nozzle 122 are not necessarily discharged from the discharge nozzle 123,
Some of them float inside the detection cell 1 and adhere to the inner wall of the detection cell. The attached fine particles float again and enter the air to be inspected, resulting in a measurement error. Further, in particular, the Brewster window 132 and the external mirror 133 have the function of charging static electricity and adsorbing fine particles due to the laser oscillation, thereby causing fogging of both and reducing the oscillation intensity of the laser. It is necessary to clean the adhesion and fogging of these fine particles, and the cleaning is performed by a cleaning hole 144 provided at a position corresponding to the Brewster window 132 of the housing 11, and the airtightness is covered by a cover 145 during operation. It has been made to be. Further, the external mirror 133 is cleaned by removing the fixture 134 for the housing. However, such cleaning operations are often not possible because they are not simple. On the other hand, as a prior art for preventing contamination of each part in the detection cell, particularly the Brewster window 132 and the external mirror 133 by the fine particles during the operation of the detector, the applicant of the present invention described in "February 1989" On the 2nd, No. 1-246313, a method for preventing contamination of a particle detection cell has been filed.

Referring to FIG. 2, a pollution prevention system according to the above patent application will be described. The external mirror 13 of the housing 11 is
Pressing holes 151 and 152 are provided in the position corresponding to 3 and the cover 145 for the cleaning hole 144, respectively, and a clean purge air P is press-fitted from these press-in holes and ejected to clean the external mirror and the Brewster window. I do. Purge air P is inspection air A
And is discharged from the discharge nozzle 123 to the outside.

[Problem to be Solved] In the above-described pollution prevention method, it is assumed that the inside of the detection cell is clean before operation, and that the contamination is caused by suspended particles of the air to be inspected A sucked during operation. It is composed. However, even when the above-described cleaning operation of the Brewster window 132 and the external mirror 133 is performed, the fine particles are not completely discharged to the outside, move inside, and remain in another place. In particular, the surroundings of the Brewster window are likely to remain due to the complicated mechanism, and due to the cleaning work, fine particles are newly generated from the packing 142 etc. and remain around, and after cleaning, the detector is activated. During operation, the remaining fine particles are carried to the inspection target air A by the purge air from the press-in hole 152 and merge there, resulting in a measurement error. However, the periphery of the external mirror 133 has a simple structure, and is removed and cleaned integrally with the mounting tool 134, so that the amount of remaining fine particles is relatively small.

As described above, it is necessary to prevent fine particles from remaining around the Brewster window. However, it is desirable to use a conventional method in which the structure is performed without changing the structure of the detection cell.

The present invention has been made in view of the above, and by keeping the structure of the detection cell 1 in FIG. 2 as it is, by changing the flow path of the purge air, it is possible to prevent particles from remaining around the Brewster window. It is an object of the present invention to provide a purge air circulation system for preventing such a situation.

[Means for Solving the Problems] The present invention provides a method for inspecting an intermediate laser between a Brewster window of a gas laser tube constituting a laser oscillator of an external mirror type and an external mirror corresponding to the Brewster window. This is a purge air circulation system that cleans the inside of a particle detection cell that detects particles by making air orthogonal. A press-fit hole for press-fitting and ejecting clean purge air at a position corresponding to the external mirror of the housing of the detection cell, and a discharge hole for discharging the purge air ejected by the above to the outside at a position corresponding to the Brewster window. Are provided, and after the injected purge air cleans the external mirror and its surroundings, it passes through the inside of the detection cell, cleans the Brewster window and its surroundings, and is discharged from the discharge holes to the outside.

[Operation] In the purge air circulation system according to the present invention having the above-described configuration, the purge air injected and injected from the injection hole prevents the fine particles floating around from adhering to the external mirror. This is the same as the conventional one. However, the flow path of the purge air thereafter is different from the conventional one, and the purge air that has passed through the inside of the detection cell is cleaned around the Brewster window and discharged to the outside through the discharge hole. In this case, since the purge air P is irrelevant to the discharge nozzle 123, the purge air P does not merge with the air A to be inspected, but instead bypasses the surroundings and proceeds in the direction of the Brewster window. No measurement error occurs. As described above, the fine particles remaining around the Brewster window due to the cleaning operation are discharged to the outside without entering the detection area, and the occurrence of the measurement error as in the related art can be avoided.

[Embodiment] FIG. 1 shows an embodiment of a purge air flow system of a particle detector according to the present invention. The structure of a detection cell 1 is exactly the same as that of the conventional cell shown in FIG. The description of the detection principle will be omitted, and the changed flow path of the purge air will be described. In the figure, clean purge air P is press-fitted and injected from a press-fitting hole 151 provided at a position corresponding to the external mirror 133 of the housing 11 of the detection cell 1,
Cleaning the external mirror 133 and its surroundings is the same as in the related art. Next, the cleaning lid 1 for the Brewster window 132
In the present invention, a conventional press-in hole 152 (see FIG. 2) provided in 45 is used as a discharge hole 152 '. The purge air P passes around the detection area S in the detection cell and cleans the Brewster window 132 and its surroundings.
It is discharged outside from 52 '. The influence of the fine particles of the purge air P on the measurement error is conventionally caused by the fact that the purge air P joins the air A to be inspected and is discharged from the discharge nozzle 123. According to the present invention, the air does not merge with the air A to be inspected, but proceeds toward the Brewster window 132. In this case, by making the flow velocity of the purge air P sufficiently smaller than the flow velocity of the test air A, the purge air P passes around the test air A so to speak, so as not to join the test air A. Therefore, it does not cause a measurement error.

[Effects of the Invention] As is clear from the above description, according to the purge air circulation system for a particle detector according to the present invention, particles remaining around the Brewster window can enter the detection region due to a cleaning operation of the Brewster window or the like. No measurement error is caused by discharging to the outside through the discharge hole corresponding to the Brewster window, and at the same time, both the external mirror and the Brewster window are cleaned. It can be easily executed only by changing the route, and there is a great point that contributes to the improvement of the reliability of the measurement data of the particle detector.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a detection cell illustrating a flow path of purge air in an embodiment of a purge air flow system of a particle detector according to the present invention. FIG. 2 is a diagram showing a structure of the particle detection cell and a conventional pollution prevention method according to a patent application. It is explanatory drawing of a system. DESCRIPTION OF SYMBOLS 1 ... Particle detection cell, 11 ... Housing, 12 ... Suction / discharge mechanism, 121 ... Inlet, 122 ... Injection nozzle, 123 ... Discharge nozzle, 124 ... Outlet, 13 ... Laser oscillator, 131 ... … Gas laser tube, 132… Brewster window, 133… external mirror, 134… mounting fixture, 141… mounting ring, 142… packing, 143… screw, 144… cleaning hole, 145… lid, 151,152… Press-in hole, 152 ′… Discharge hole.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yukio Kawakami 2-6-2 Otemachi, Chiyoda-ku, Tokyo Hitachi Electronics Engineering Co., Ltd. (56) References JP-A-61-278734 (JP, A) (58) ) Surveyed field (Int.Cl. ⁶ , DB name) G01N 15/00-15/14

Claims (1)

(57) [Claims] An air to be inspected is made orthogonal to a laser located between a Brewster window of a gas laser tube constituting a laser oscillator of an external mirror type and an external mirror corresponding to the Brewster window, thereby causing fine particles to be generated. In the particle detection cell to be detected, a press-in hole for press-in and injection of clean purge air is provided at a position corresponding to the external mirror of the housing of the detection cell, and the injection hole is provided at a position corresponding to the Brewster window. Discharge holes are provided for discharging the purge air to the outside, and the injected purge air cleans the external mirror and its periphery, then passes through the inside of the detection cell, and cleans the Brewster window and its periphery. A purge air circulation method for a particle detection cell, wherein the purge air is discharged outside through the discharge hole.