JPH0238842A - Monitor of particle in liquid - Google Patents

Abstract

PURPOSE:To generate an accurate alarm depending on actual generation of dust by identifying the dust accurately as being separated from bubbles using laser light. CONSTITUTION:Laser light with different frequencies from a light emitters 1a and 1b within a light source 1 is condensed into a pipeline of a transparent tube 4 through a half mirror 2 and a condenser lens 3. A liquid containing dust particles and bubble particles flows through the tube 4 and scattered light is caused in the perimeter of the particles at a specified intensity. Then, the scattered light condensed with a lens 5 is separated with a wavelength selection filter F in terms of wavelength to be condensed onto photodetectors 7 and 9 through lenses 6 and 8 and signals from the photodetectors 7 and 9 are converted 10 and 11 to current and voltage to be sampled 12 and 13 separately. Then, amplitudes of the currents and voltages are compared with a comparator 14. Thus, a dust identification signal S3 and a bubble identification signal S4 are outputted and the signal S3 is counted 15. When counts of the signal exceed a criterion reference value, an ALM is generated.

Description

[Detailed Description of the Invention] [Table of Contents] Overview Industrial Application Fields Conventional Technology Problems to be Solved by the Invention Means for Solving the Problems Action Embodiment First Embodiment of the Present Invention (Figure 1) The Present Invention Second Embodiment (Figure 2) Effect of the invention [Summary] Regarding a monitoring device for particles in liquid, to correctly separate and identify dust and air bubbles and issue an accurate alarm based on the actual dust generation situation. A laser emitting means for irradiating a liquid with light from at least two light emitting sources with different wavelengths, and a scattered light means for receiving scattered light from the liquid in contact with the liquid to determine the difference in the intensity of the scattered light for each wavelength. a light receiving means; a comparing means for comparing whether the intensity difference for each wavelength is larger than a predetermined reference value;
and is configured to identify the presence of material particles in the liquid.

[Industrial application field]

TECHNICAL FIELD The present invention relates to a monitoring device for particles in liquid, and more particularly, to a monitoring device for particles in liquid that monitors dust particles in a liquid used for cleaning etc. in a semiconductor manufacturing process. The present invention relates to a monitoring device for particles in liquid that is intended to identify and reduce the false alarm rate.

-S. In the semiconductor manufacturing process, wafers and the like are cleaned using a cleaning liquid, but if dust is mixed into this cleaning liquid, it will affect the yield of the product. In particular, in the case of modern large-scale integrated circuits that have been miniaturized, even the slightest amount of dust can cause fatal defects, so the cleaning liquid is required to be dust-free and of extremely high purity. but,
There are a wide variety of factors that cause dust to be mixed in. For example, most of the things that come into contact with the cleaning liquid, such as the pump that pumps the cleaning liquid, the walls of the pipes that guide the cleaning liquid, and various sealing materials, can be the source of the dust. Therefore, it is practically impossible to eradicate dust generation. For this reason, in order to improve product yield, it is essential to monitor the dust in the liquid and take cleaning measures for the cleaning liquid system when the amount of dust exceeds a standard value.

[Conventional technology]

Conventional monitoring devices for particles in liquid include, for example, devices that irradiate a laser beam into the liquid, detect the scattered light of dust particles, convert the detected scattered light into electrical signals, and count them. In this case, when the count value exceeds the determination reference value, it is assumed that a non-negligible amount of dust particles have been mixed into the liquid, and necessary cleaning measures are taken.

[Problem to be solved by the invention]

However, such conventional monitoring devices for particles in liquid are configured to detect dust particles simply based on the presence or absence of scattered light due to laser beam irradiation.
For example, when air bubbles are mixed into the liquid, there is a problem in that the light scattered by the air bubbles is mistakenly recognized as that caused by dust, and a false alarm is generated.

That is, although a considerable amount of bubbles are generated by the pressure pump and the like, the bubbles themselves do not have a negative effect on the product. However, if these air bubbles are mistakenly identified as dust, unnecessary cleaning procedures will be performed, resulting in an unnecessary stoppage of the manufacturing process, which poses a problem in terms of manufacturing costs.

For this reason, conventional monitoring devices for particles in liquid are equipped with a defoaming device that eliminates air bubbles in the middle of the cleaning fluid flow path in an effort to improve false alarms, but the defoaming device uses a vacuum pump. This vacuum pump becomes a new source of dust,
This is unfavorable in terms of cleaning of cleaning fluids, etc.

Therefore, an object of the present invention is to correctly separate and identify air bubbles and dust, and to generate an accurate warning based on the actual state of dust contamination.

[Means to solve the problem]

In order to achieve the above object, the present invention includes a laser emitting means that irradiates light from at least two light emitting sources with different wavelengths into a liquid, and a laser emitting means that receives scattered light from the cough liquid and scatters it at each wavelength. A scattered light receiving means for determining the difference in light intensity, and a comparison means for comparing whether the difference in intensity for each wavelength is larger than a predetermined reference value, and identifying the presence of material particles in the liquid. It is configured as follows.

[Effect]

In the present invention, at least two lights with different wavelengths are irradiated into a liquid, and bubbles and material particles (
Only dust can be identified from the difference in scattered light intensity between bubbles and dust, which is caused by the difference in relative refractive index with respect to the liquid layer refractive index.

Therefore, false alarms due to air bubbles are avoided, unnecessary cleaning procedures are not performed, and manufacturing costs are improved.

In addition, since there is no need to purposely extinguish air bubbles, a defoaming device is not required, and the causes of dust generation can be reduced.

〔Example〕

Hereinafter, the present invention will be explained based on the drawings.

FIG. 1 is a diagram showing a first embodiment of a monitoring device for particles in liquid according to the present invention.

In FIG. 1, l is a light source (laser emitting means),
The light source 1 has two laser emitters 1a and lb that emit laser beams of different wavelengths λ. Laser emitter 1a
is, for example, a Ne-Ne laser, and the wavelength λ=633r
The laser emitter 1 emits a single wavelength laser beam of
b is, for example) f e -Cd laser, and λ-441
, 3nn+ single wavelength laser light is emitted. Light 7! lX
After the optical axes of the two laser beams from 1 are aligned by a half mirror 2, the beams are condensed into a conduit of a transparent tube 4 by a condenser lens 3. The transparent tube 4 is used to flow a liquid for cleaning semiconductor devices, etc., and its outer wall is made of a translucent material in whole or in part, so that the laser beam from the condenser lens 3 is not transmitted through the transparent tube 4. It's designed to be easy. It should be noted that in the liquid flowing inside the transparent tube 4, there are material particles (for example, dust particles made of Si particles) indicated by .
and bubble particles indicated by O are included. However, the dust particles and air bubble particles in the diagram are shown in larger numbers than their actual amounts.

The laser light irradiated onto the dust particles and bubble particles becomes scattered light, which is emitted around the dust particles and bubble particles with a predetermined scattered light intensity.

Here, assuming that the dust particles and bubble particles are isotropic homogeneous spherical particles, the intensity of light scattered by these particles is determined by Mie as an exact solution of electromagnetic wave scattering in Maxwell's electromagnetic equation. , scattering angle dependence, particle size dependence, and refractive index dependence. Among these, refractive index dependence is a phenomenon in which a difference appears in the intensity of scattered light depending on the refractive index of the particle.The larger the value of the refractive index, the stronger the intensity of scattered light. The rate is approximately monotonic.

Now, assuming that the dust particles are Si particles, and looking at the tendency of the dependence of the relative refractive index of these Si particles and bubble particles (considered as particles that treat air as a substance), we can see that the refractive index of the liquid depends on the wavelength. Assuming that z is close to a constant value of 1, the refractive index m of Si particles is:
m'' for λ = 633 nm.

3.9, mL for λ-441.6nm: 5.6
It is.

On the other hand, m of bubble particles is the same as m of air, and λ=
Approximately m5 at both 633nm and λ-441.6nm
It is 1. Therefore, the scattered light intensity of Si particles is λ=
The difference between different wavelengths such as 633 nm and λ = 441.6 nm corresponds to mLi 3.9 and m4 = i 5.6, while for bubble particles, λ = 633 nm and λ = 4
There is almost no difference between this and 41°Gnm. In this example, we focused on the fact that the dependence of m on the wavelength of the irradiated light is different for dust particles and air bubbles. It is identified as a bubble.

That is, the scattered light collected by the condenser lens 5 is wavelength-separated by the wavelength selection filter F, and for example, λ=633r+
The +++ scattered light P is condensed onto the light receiver 7 via the condenser lens 6, and the λ-441,3 nm scattered light Pz is condensed onto the light receiver 9 via the condenser lens 8. Ru. The current signal 11 whose thickness corresponds to the intensity of Pl from the light receiver 7 is
The current/voltage converter 10 converts the current signal E1 into a voltage signal E1 proportional to the current value. Similarly, the current signal +2 from the light receiver 9 is converted into the voltage signal E1 by the current/voltage converter 11.
is converted to

These El and EZ are each connected to the sampling circuit 12.
．． 13, sampled at the same sampling timing, and having the voltage levels of E + and E z as pulse amplitudes. , S2 and output. These signals s, , S2 are input to a comparator (comparison means) 14, and their amplitudes are compared. In addition, the above-mentioned condensing lens 6.8, light receiver 7.9, current/voltage converter 10
．． 11 and sampling circuits 12 and 13 collectively constitute a scattered light receiving means.

Here, the magnitude (level) of S, S2 is the above-mentioned P+,
Since it corresponds to the size of Pz, if P8 and P2 are caused by dust particles, there is a relationship such as Pl<P2, and the difference is relatively large. On the other hand, P,,P,
If it is caused by bubble particles, P, #P, or even if PI < P8, the difference is small. In other words, the signal S from the output terminal A of the comparator 14 indicates that dust is identified. A signal S4 from output terminal B is output when a bubble is identified. The pulse counter 15 counts S, and when this count value exceeds a predetermined determination reference value, it determines that a non-negligible amount of dust is present in the liquid and generates an alarm signal ALM.

In such a configuration, a unique tendency appears between the scattered light of dust particles and the scattered light of bubble particles flowing in the transparent tube 4, characterized by a difference in wavelength and a difference in refractive index between the two laser beams. . That is, according to Mie's scattering theory, the intensity of light scattered by particles (2) is expressed according to the following equation (2).

2, where Io : Incident light intensity r : Distance from the particle center λ : Wavelength ■ In the formula (il+i), 11 and ia are called the vertical and horizontal polarized component scattered light intensity distribution functions, respectively, and the scattered light It is a function determined by the angle θ, the wavelength λ, the particle diameter DP, and the refractive index m. Now dust particles (e.g. St
Consider a case in which a particle) is irradiated with two laser beams of different wavelengths.

In this case, if the scattered light is observed at the same location, θ and RI do not change. For example, in this example, the value of λ takes two different values, λ = 663 nm and λ = 441.6 nm, and based on these two values, m and mζ
It takes two values: 3.9 and m:=i5.6. Therefore, l calculated using the above formula (■) is λ=663n11 and λ-
441.6 nm, there is a difference depending on λ and m. On the other hand, in the case of bubble particles, m is almost constant 1 even if λ changes, and in this case, I calculated by the above equation Not affected. Therefore, the current/voltage converter 10.11
By setting the transfer characteristics corresponding to the case of bubble particles, and making El and E2 outputted from the current/voltage converter 10.11 almost the same in the case of bubble particles,
In the case of dust, a difference value corresponding to the difference of , mζ3.9 and m:5.9 can be provided between E, and E. As a result, the comparator 14 can output S only in the case of dust, and the pulse counter 15 can count the occurrence of correct dust and generate ALM without being affected by air bubbles. can.

In this example, two laser beams with different wavelengths are irradiated into the liquid, and only the dust particles can be accurately identified from the difference in the intensity of the scattered light of the dust particles and bubble particles caused by the laser beams. There is. Therefore, since it is not affected by air bubble particles, a correct alarm can be issued and unnecessary cleaning measures can be avoided. Further, since dust particles can be detected even when air bubbles are generated, there is no need to provide a special defoaming device, and there is no need to increase the number of dust generation sources. Moreover, the liquid is only irradiated with laser light,
There are no parts that come into direct contact with cleaning liquid, etc.

Therefore, the sources of dust generation can also be minimized.

Furthermore, in this embodiment, since the liquid in the transparent tube 4 is constantly monitored, the dust generation status can be monitored from beginning to end, which greatly contributes to improving the product yield.

FIG. 2 is a diagram showing a second embodiment of a monitoring device for particles in liquid according to the present invention.

In FIG. 2, 20 is a light source (laser emitting means), and the light source 20 has a Ne-Ne laser 20a and a He-Cd laser 20b similar to those in the first embodiment.

The two laser beams from the light source 20 are input to the optical axis switch 21, and the optical axis switch 21 switches the optical path according to the timing signal sr and alternately selects the two laser beams. The selected laser beam is focused into the liquid in the transparent tube 23 via the condensing lens 22 . Light scattered by dust particles or bubble particles in the liquid is focused onto a light receiver 25 via a condenser lens 24, and converted by the light receiver 25 into a current signal I3. The current/voltage converter 26 changes the transfer characteristic according to the gain control signal SG (so as to balance the difference in the intensity of scattered light of the bubble particles due to the wavelengths of the two laser beams), and converts I to the voltage signal E.

Convert and output. E is sampled by the sampling circuit 27 according to the sampling signal S, and this sampled pulse signal S is held in the buffer for two days. The condensing lens 24, the light receiver 25, the current/voltage converter 26, and the sampling circuit 27 collectively constitute a scattered light receiving means.

A comparator (comparison means) 29 receives the S held in the buffer 28 and the S directly from the sampling circuit 27.

If the levels do not match, a signal SA indicating the occurrence of dust is output to the pulse counter 30 and counted.

Note that 31 is a reference signal generation circuit, and the reference signal generation circuit 31 generates St that continues at equal intervals and S that instructs the current/voltage converter 26 to an appropriate gain value every half cycle of this ST.
6 and a clock signal SCK synchronized with SA. ScK is divided by 1/2 by the frequency dividing circuit 32 and becomes S,
The signal S& synchronized with S is delayed by half a cycle by the phase delay circuit 33 to become the control signal S for controlling the buffer 28.

With this configuration, the same effects as in the first embodiment can be obtained, and according to the second embodiment, the number of parts can be reduced, and since only one optical system is required, variations in the optical system can be avoided. It has the advantage that it can be avoided.

Note that in each of the above embodiments, the laser light is
Although the number is three, the number is not limited to this, and the number may be three or more, for example. In short, it is sufficient that the wavelengths of the respective laser beams differ to such an extent that the refractive index of the observed particle is clearly different.

〔Effect of the invention〕

According to the present invention, bubbles and dust can be correctly separated and identified. Therefore, it is possible to generate an accurate warning based on the actual dust contamination situation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of a particle-in-liquid monitoring device according to the present invention, and FIG. 2 is a block diagram showing a second embodiment of a particle-in-liquid monitoring device according to the present invention. be. l...Light*<laser emitting means), 14...
...Comparator (comparison means), 20...Light m<laser emitting means) 29...Comparator (comparison means)

Claims (1)

[Scope of Claims] Laser emitting means for irradiating light from at least two light emitting sources with different wavelengths into a liquid, and receiving scattered light from the liquid to determine the difference in the intensity of the scattered light for each wavelength. A liquid characterized in that it has a scattered light receiving means and a comparison means for comparing whether the intensity difference for each wavelength is larger than a predetermined reference value, and is characterized in that the presence of substance particles in the liquid is identified. Medium particle monitoring device.