JP2824857B2 - Error correction method for particle measurement system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an error correction method in a particle measurement system, and more particularly to a measurement error generated by an air pipe of a centralized particle measurement system.

[Prior Art] With an increase in the integration density of semiconductor ICs, clean rooms for manufacturing semiconductor ICs are required to have an even higher degree of cleanliness. The cleanliness is evaluated by measuring the size and number of fine particles such as dust contained in air in the clean room using a fine particle detector.

FIG. 2A shows a basic configuration of the particle detector. The particle detector 1 includes a detection cell 11, a suction / discharge mechanism 12 for the air to be inspected, and a detection optical system 13. The air to be inspected is sucked into the detection cell 11 from the inlet 121, and is discharged from the outlet 122 by suction of the exhaust pump 123. On the other hand, the laser from the light source 131 is
The light is projected into the detection cell by 32 and is orthogonal to the air to be inspected.
The scattered light of the fine particles in the orthogonal portion S is
The light is condensed by 3 and is received by the light receiving device 135 through the slit of the slit plate 134 to detect the fine particles.

By the way, the distribution of fine particles in the clean room is not uniform, varies from place to place, and fluctuates over time. It is necessary to measure. However, providing a particle detector at each location for this purpose has a problem in arrangement,
In addition, since it is not efficient in terms of cost, a centralized particle measurement system using one particle detector in common is applied.

FIG. 2 (b) shows the configuration of the centralized particle measurement system. A switch 2 for the air pipe is provided for the particle detector 1, and the output side is connected to the inlet 121. On the other hand, a plurality of measurement points p ₁ , p ₂ …… p in the clean room
and laying the air pipe 21,22 ...... 2 _n than _n, connected to the input side of the switch 2. The switching device 2 is operated by the driving mechanism 4 controlled by the microprocessor 3, and the air pipe is operated.
21,22 ...... 2 _n is switched sequentially, each measurement point p _1, p ₂ ......
The air to be inspected sucked from _pn is introduced into the detection cell 11 from the inlet 121 to detect fine particles, and the detection signal is processed by the microprocessor 3 to measure the diameter φ and the number of fine particles at each measurement point. Are output to the output unit 5.

[Problem to be solved] The air pipe used in the above particle measurement system is
It is necessary that the fine particles are not adsorbed on the inner surface of the pipe, but in reality, there is adsorption, and the loss reduces the number of fine particles sucked into the detection cell, causing measurement errors at each measurement point and reducing the reliability of the measurement system. Sex has declined. Since such adsorption is mainly generated by static electricity on the inner surface of the pipe, a semiconductive plastic pipe is used to prevent this, but it is not always perfect. That is, the adsorption of fine particles is caused not only by static electricity but also by other causes, and the degree varies depending on the speed of the air to be inspected in the pipe and the diameter φ of the fine particles. The smaller the φ, the less the adsorption. Therefore, it is conceivable to reduce the loss by increasing the flow velocity by making the air pipe thinner, and there is a direction in which this is being carried out, but the increase in the flow velocity is naturally limited, and even those with a large diameter are completely absorbed. Is difficult to prevent. Further, when increasing the flow velocity, it is necessary to increase the intake pressure of the exhaust pump at the same time. on the other hand,
It is desirable for the particle detector to measure by inhaling as much air as possible to be inspected into a large clean room.
Corresponding to this, the intake pressure of the exhaust pump has already been set high, and the air pipe also has a sufficiently large diameter. Therefore, it is difficult to further increase the intake pressure of the exhaust pump. On the other hand, it is more effective to correct the measurement error than to prevent the loss due to the increase in the flow velocity, and it is considered to be advantageous to maintain the reliability of the measurement data.

The present invention has been made in view of the above, and an object of the present invention is to provide a method of correcting a measurement data error caused by a loss of an air pipe in a centralized particle measurement system at a data processing stage.

[Means for Solving the Problems] According to the present invention, an air pipe is laid between a particle detector and a plurality of measurement points, and the air pipes are sequentially switched by a switch and connected to an inlet of the particle detector. This is an error correction method in a centralized particle measurement system that introduces air to be inspected that is sucked in at a plurality of measurement points and guided by an air pipe into a detection cell from an inlet, and measures particles included in air at a plurality of measurement points.
The loss ratio R (φ) of the fine particles adhering to the inner surface of each of the plurality of air pipes with respect to the diameter φ is measured, or the loss coefficient K (φ) with respect to the unit length of the air pipe is measured.
The loss ratio R (φ) of each air pipe is calculated from (φ) and the length L of the air pipe, and the measurement error of the fine particles at each measurement point caused by the loss ratio R (φ) is corrected by data processing.

A loss ratio K (φ) with respect to the diameter φ of the fine particles per unit length of the air pipe obtained by the above measurement;
From the length L of each air pipe, the loss ratio R of each air pipe
(Φ) is calculated by the following equation: R (φ) = (1−K ^L ) × 100% (1)

[Operation] In the above-described measurement error correction method of the particle measurement system according to the present invention, the loss ratio R (φ) to the diameter φ of the particles adsorbed on the inner surface of each air pipe is actually measured, or the unit length of the air pipe is measured. Loss factor K (φ) with respect to diameter φ measured for each and length L of each air pipe
This is calculated by equation (1). Here, since the flow rate of the air to be inspected is not included in Expression (1), the flow rate data is not necessary for the calculation. Equation (1) is the loss ratio R (φ)
Is represented by an exponential function of a loss coefficient K (φ) having the length L as an exponent. For example, the exponential function changes in the same manner as a current decay phenomenon in a conductor, and its validity has been confirmed by experiments. . However, the loss coefficient K (φ) or the loss ratio R (φ) is specific to the measurement system depending on the type and diameter of the air pipe and the flow rate of the air to be inspected. It is necessary to measure the diameter φ of the fine particles as a parameter.

The loss ratio R (φ) obtained as described above is applied to the measurement data at each measurement point, and the measurement error is corrected for each particle diameter by data processing.

[Embodiment] FIG. 1 shows a particle diameter φ of an example of a particle measurement system to which a measurement error correction method according to the present invention is applied.
FIG. 9 is a curve diagram showing actual measurement results of a loss ratio R (φ) with respect to a diameter φ of a fine particle with respect to a length L (m) of an air pipe, with as a parameter. The particle detector of this system inhales 28 liters per minute, and the air pipe is a semiconductor plastic pipe with an inner diameter of 8 mm, and the air flow rate in the pipe is about 9.3 m per second. Each curve has reliability based on an average value of a large number of measurements, whereby a measurement error is corrected for each particle diameter, thereby improving the reliability of measurement data. By substituting the length L of each air pipe and the loss ratio R (φ) into the above equation (1), the loss coefficient K (φ) attached on the right side of the figure can be obtained, and at the same time, the equation (1) Has been confirmed to hold. This allows
By measuring the loss coefficient K (φ) with respect to the diameter φ per unit length of the air pipe used for an arbitrary measurement system, the loss ratio R (φ) which can be sufficiently satisfied by the length L of each air pipe is calculated. It was confirmed that it could be obtained. Such a calculation method is easier than a method of measuring each of the air pipes.

By applying the loss ratio R (φ) obtained as described above to each air pipe, a measurement error for each measurement point is corrected for each particle diameter by data processing. Since the correction calculation is a normal data processing technique, the description is omitted.

[Effects of the Invention] As is clear from the above description, in the centralized particle measuring system to which the error correction method according to the present invention is applied, the measurement error caused by the loss of the fine particles adsorbed to each air pipe is reduced by the data processing. It is corrected for each diameter of the air, and the replacement of the air pipe required to increase the flow rate of the air to be inspected and the cost and trouble of increasing the intake pressure of the exhaust pump are omitted.
There is a significant contribution to the improvement of the reliability of the measurement data of the fine particles.

[Brief description of the drawings]

FIG. 1 shows an actual measurement curve of a particle loss ratio R (φ) with respect to an air pipe length L in an embodiment to which a measurement error correction method of a particle measurement system according to the present invention is applied;
FIGS. 2A and 2B are diagrams showing the numerical values of the loss coefficient K (φ) obtained by the calculation, and FIG. 2A and FIG. 2B are a basic configuration diagram of the particle detector and a configuration diagram of the centralized particle measurement system. DESCRIPTION OF SYMBOLS 1 ... Particle detector, 11 ... Detection cell, 12 ... Suction / discharge mechanism, 121 ... Inlet, 122 ... Outlet, 123 ... Exhaust pump, 13 ... Detection optical system, 131 ... Light source, 132 ... ... light projecting lens, 133 ...... condensing lens, 134 ...... slit plate, 134 ...... optical receiver, 2 ...... air pipe switch, twenty-one to two _n ...... air pipe, 3 ...... microprocessor, 4 ...... drive mechanism 5, an output unit.

Continuation of the front page (72) Inventor Tsuneyoshi Suzuki 2-6-2 Otemachi, Chiyoda-ku, Tokyo Hitachi Electronics Engineering Co., Ltd. (56) References JP-A-60-200145 (JP, A) (58) Survey Field (Int.Cl. ⁶ , DB name) G01N 15/00-15/14

Claims (1)

(57) [Claims] 1. An air pipe is laid between a particle detector and a plurality of measurement points, and the air pipes are sequentially switched by a switch and connected to an inlet of the particle detector. In the centralized particle measuring system for introducing the air to be inspected sucked and guided by the air pipe into the detection cell for detecting the fine particles from the inlet and measuring the fine particles contained in the air at the plurality of measurement points, Loss ratio R of the fine particles adhering to the inner surface of each air pipe with respect to the diameter φ
(Φ) or a loss coefficient K (φ) with respect to the diameter φ of the fine particles per unit length of the air pipe,
The loss ratio R (φ) is calculated from the loss coefficient K (φ) and the length L of the air pipe, and the measurement error of the fine particles at each of the measurement points caused by the loss ratio R (φ) is calculated as follows:
An error correction method for a particle measurement system, wherein the correction is performed by data processing for each particle diameter φ.