JPS62223647A - Foreign matter monitor - Google Patents

Abstract

PURPOSE:To take a real-time measurement and a temporary measurement by preparing a solution whose foreign matter number per unit volume is already known and calibrating and using the relation between the intensity of scattered light and the density of foreign matter. CONSTITUTION:A foreign matter group 1a is irradiated with a light beam 5a. This beam 5a is formed through a cylindrical lens 6a, but this irradiated light is guided through an optical fiber bundle 16. A scattered light beam 7a from the foreign matter group 1a is converged through the cylindrical lens 6b to enter a fiber bundle 17, and guided out of the solution. The lenses 6a and 6b and the tip parts of the fiber bundles 16 and 17 are fixed at positions determined optically by using a holding box. then, the part consisting of the fiber bundles 16 and 17, lenses 6a and 7b, and holding box is reducible in size, so this part is put in the object solution to discriminate plural pieces of foreign matter in the area where beams 7a and 5a cross each other. Thus, the real-time measurement and temporary measurement are both taken.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a foreign matter monitor that measures in-line and in real time foreign matter in various solutions used in wet processes in semiconductor device manufacturing processes.

[Conventional technology]

It is well known that foreign substances (miscellaneous substances commonly referred to as dust) in water and chemical solutions are harmful, not only in semiconductor processes, but in general, foreign substances in water and chemical solutions have been inspected. , measurement methods and devices have been developed and commercialized by various companies.

The basic principles of conventional foreign substance inspection devices vary depending on the purpose of use. If we summarize the basic principles of conventional equipment, the main methods are (1) optical method, (2) electrical resistance method, and (3)
) Ultrasonic methods can be roughly divided into three types.

The ultrasonic method is an application of sonar and ultrasonic flaw detection techniques to foreign objects in liquid, as described in, for example, Japanese Patent Application Laid-open No. 19653/1983. It has poor reflection efficiency and is not necessarily common.

The electrical resistance method detects an increase in the electrical resistance of a solution caused by eliminating the solution in the hole when a foreign object passes through a small hole (pinhole), as described in, for example, Japanese Patent Application Laid-open No. 58-53738. It is something to do.

This method was originally developed to measure red blood cells in blood. Since the size of red blood cells is almost constant,
If a small hole that is slightly larger than a red blood cell is used, the small hole will not become clogged.6 However, since the size of foreign substances in the solution used in the semiconductor process is not constant, the small hole used for measurement may become clogged in some cases. Therefore, it is inconvenient for regular use in semiconductor processes where the size of foreign particles is not constant.

Like the ultrasonic method, it is not necessarily common.

In the end, the optical method mentioned above is the most general foreign object inspection method and can be safely used even for foreign objects of unknown size. If the optical method is subdivided, there are several methods, but here, two methods that are closely related to the present invention will be described.

The first notable optical method is, for example, Japanese Patent Application Laid-Open No.
As described in Japanese Patent No. 136475, it detects scattered light from foreign objects. FIG. 5 shows the principle configuration of an apparatus using scattered light.

In FIG. 5, a foreign substance 1.1' (indicated by a black circle in the figure) to be detected is transferred together with a solution 2 into a specific container 3. This solution 2 is made into a narrow jet 2' through a nozzle 3a by suitable means (not shown) such as pressurization. The jet 2' enters the receiver 4 and is normally discarded. In the case of a solution with a relatively small amount of foreign matter (for example, pure water, which is most often used in semiconductor processes), if the diameter of the jet stream 2' is several 1,000 μm, the foreign matter 1,1' will be as shown in Figure 5. They are sprayed together with the solution 2 in a lined up state. Therefore, if the jet stream 2' is irradiated with the light beam 5 perpendicularly to the jet stream 2', the foreign matter 1 will be individually irradiated with the light beam 5. The light beam 5 is formed by converging light I@5' from a light source such as a laser with a lens 6.

In FIG. 5, when the light beam 5 is irradiated onto the foreign object 1,
Two different phenomena occur. The first thing is.

Photons forming the light beam 5 are scattered on the surface of the foreign object 1, and so-called 6-scattered light 7 is emitted in a direction different from the traveling direction of the light beam 5. Second, the light beam 5 is prevented from traveling, ie is blocked, and cannot pass to the right of the jet stream 2'.

Since the above-mentioned scattered light 7 is generated by the presence of the foreign object 1, when the foreign object 1 flows away toward the receptor 4, the scattered light 7 disappears. Therefore, if the scattered light 7 is detected by the photodetector 8, it means that the passage of the foreign object 1 has been detected.

FIG. 6(,) shows an example in which the scattered light signal from the foreign object 1 obtained as described above is converted into an electrical signal waveform. As shown in the figure, which shows an example in which three foreign objects 1 are detected, if the scattered light intensity is converted into electrical pulses, the number of pulses can be counted using well-known electrical signal processing technology, and the foreign objects can be detected. 1 can be measured. If only a specific volume of solution 2 is used, the number of foreign substances per unit volume can be quantitatively determined.

The second optical method is called a light blocking method and detects transmitted light. The principle of this method will be described again using FIG.

In FIG. 5, assuming that there is no foreign object 1 in the jet stream 2', the light beam 5 passes through the jet stream 2' and forms a light beam 5' since there is no obstacle. When the transmitted light beam 5' is detected using the photodetector 9, a foreign object 1 is detected.
It is clear that the light intensity of the light beam 5'' decreases or the light beam 51 is blocked by the appearance of the light beam 5''.In other words, the output waveform of the detector 9 is as shown in FIG. 6(b).
It decreases in response to the generation of scattered light. In Figure 6(b),
This corresponds to the case where three foreign objects cross the light beam 5. This transmitted light signal is clearly equivalent to the scattered light signal waveform shown in FIG. 6(a), and as understood from the previous explanation, the number of foreign substances in the solution 2 can also be determined from the transmitted light signal. I can do it.

FIG. 7(a) shows another conventional example in which foreign objects are detected using transmitted light. This is applied to a sedimentation tank for purifying sewage, as described in Japanese Patent Application Laid-Open No. 50-11290. The method shown in Figure 5 extracts only a small amount of the target solution and measures it away from the actual process, so-called off-line (off-1, tne), but it naturally has the drawback that it is not a real-time measurement. ing. On the other hand, the method shown in FIG. 7(a) enables real-time measurement.

In FIG. 7(a), there is a solution 2 in the settling tank 10,
With the passage of time 0 when foreign substances 1 and 1' exist, tank 1
The foreign matter 1' that was in the upper layer of the tank 10 falls to the bottom of the tank 10 and settles.

Since the tank 10 is usually made of an opaque material such as reinforced resin or metal, a light beam cannot be introduced from the outside.Therefore, a hole is made in a part of the side wall of the tank 10 and filled with a transparent material (for example, acrylic). and window 11.11'
Form it. In this way, the light beam 5 can be
If the light beam 5 intersects with the foreign object 1, the amount of transmitted light beam 5' decreases. As a result, as shown in FIG. 7(b), the output from the photodetector 9 is reduced in response to the presence of foreign objects, and the number of foreign objects can be measured according to the principle already explained. Note that the light beam 5 is transmitted to the vicinity of the tank 10 through an optical fiber 12, and is formed by a lens 6.

[Problem that the invention seeks to solve]

Although conventional methods and devices for measuring foreign matter in solutions are used at key points in industry, they have several drawbacks when applied to semiconductor processes.

The first drawback is that it is not a real-time measurement.

For example, in the case of the light scattering method or light blocking method shown in FIG.
Put it in and measure. During this time, the number of foreign substances in the solution itself changes moment by moment, and by the time the measurement of foreign substances has been completed, the number of foreign substances in the process has already changed.

Although the light blocking method shown in Fig. 7(a) is a real-time measurement, it is meaningful when applied to precipitation phenomena, and when a solution is stirred, such as in a semiconductor process, it is possible to detect the same foreign matter. It cannot be used because it requires multiple measurements.In any case, it is clear that the conventional method of identifying one foreign object 1 in time series and converting it into an electric pulse cannot perform real-time measurement in JM theory. It is.

Although the second drawback is closely related to the first.

The conventional method is not an "in situ" (tn 5 itu) measurement. For example, in FIG. 7(a), the density of foreign matter 1 is greater as it is closer to the bottom of the settling tank 10. Finally, there are almost no foreign substances 1 near the upper surface of the settling tank 10, and a relatively clean solution 2 with so-called turbidity is thickened. Therefore, in order to detect the foreign matter 1 at the bottom of the tank 1o, it is necessary to provide a transmitted light detection section as shown in FIG. 7(a) also at the bottom of the tank 10. This means that the sedimentation tank 10 must be additionally processed, resulting in a large industrial loss. In this way, "on-the-spot" measurement at any part is virtually impossible as long as conventional methods are used. The solution collected from any part is
Although it is possible to measure using the method shown in the figure, in the case of a subject whose state changes from moment to moment, such as precipitation, it is necessary to collect multiple types of sample solutions corresponding to each time. It takes a lot of time and effort to change the results and is not practical. Therefore, the purpose of the present invention is to eliminate the two serious drawbacks of the above-mentioned conventional methods and to provide real-time measurement and in-situ measurement. The object of the present invention is to provide a foreign substance monitor that makes it possible.

[Means for solving problems]

In order to achieve real-time measurement, which is the first problem with the conventional method, it is necessary to abandon the individual counting of foreign objects used in the conventional method and adopt a new counting method. In the invention, a large number of foreign objects can be measured simultaneously6.
That is, light scattering signals from a plurality of foreign objects present in a specific volume are optically added, and the added signal is detected by one photodetector.

Regarding in-situ measurement, which is the second problem with the conventional method,
The purpose is achieved by irradiating light onto a plurality of foreign substances, integrating and miniaturizing the part that collects the scattered light from the foreign substances, and placing this in the target solution. To achieve this objective, the present invention employs optical fibers. That is, in order to introduce irradiation light into the target solution and take out the number of scatterings from foreign substances out of the solution, an optical fiber bundle (multiple optical fiber strands) is used.
Use.

For better understanding, the basic principle of the present invention will be described using FIG. 4. In the same figure, arrow 13 indicates the traveling direction of the irradiation light beam for irradiating the foreign object, and the number of arrows indicates the relative light amount, 0 plane ABCD and the opposite plane A'
The rectangular solid line defined by B'C'D' indicates the area where the irradiation light beam exists. The irradiation light beam travels in the direction of arrow 14, but if a foreign object is present in the rectangular parallelepiped, the light is blocked, and the amount of light decreases (as shown by arrow 1).
The fact that there are only two 4's represents a decrease; note that there are three arrows 13). If the foreign object is on the surface E'F
Assuming that the foreign object exists between 'G'H' and the plane E'F'G'H', the scattered light from the foreign object is emitted in the direction of arrow 15.

Naturally, if there are many foreign objects in the space, the amount of scattered light will increase. Therefore, by measuring the intensity of the scattered light traveling in the direction of arrow 15 with a photodetector, it is possible to know the number of foreign objects in the space of interest, and if the volume of that space is known, the number of foreign objects per unit volume can be determined. becomes possible.

The angle O between the irradiation light direction and the scattered light direction is, for example, 901
is effective, but it can be selected within the range of 0° to 180@.

[Effect]

The first technical means of the present invention is to simultaneously measure the scattered light from a plurality of foreign objects, so there is no need for the time-series arrangement of foreign objects as in the conventional method. For example, 100
Since multiple foreign objects are recognized simultaneously, the response time can be reduced, for example.
Using a 1 μs photodetector (a conventional photomultiplier tube is a good example), the measurement is completed virtually instantaneously.

The second technical means of the present invention is that the light irradiation part and the scattered light condensing part are integrated in a small size, so this part can be installed in any part of the target solution, for example, in the upper part or middle part of the precipitation tank. ,
The bottom barrel does not matter. Alternatively, it can be set in a recess that is not visible from the outside.

As described above, the effect of the present invention that it can be set in any case is due to the fact that the irradiated light and the scattered light are transmitted through optical fibers. As is well known, since optical fibers can be bent freely, light can be transported in any direction.

〔Example〕

FIG. 1 shows the main part of one embodiment of the present invention, and FIG. 2 shows the main part of another embodiment of the invention.

In FIG. 1, a group of foreign substances 1a in the target solution is shown as a set of dots. Although foreign substances exist throughout the solution, the detection area is optically limited, so for the sake of simplicity, FIG. 1 shows only a group of foreign substances 1a within the measurement target area.

The foreign matter group 1a is irradiated with a light beam 5a having a rectangular cross section. This light beam 5a is formed by a so-called cylindrical lens 6a, and the irradiation light is supplied by an optical fiber bundle 16. The scattered light beam 7a from the foreign object group 1a is transmitted through the cylindrical lens 6.
The light is focused at b, enters the fiber bundle 17, and is transmitted out of the solution. Cylindrical lenses 6a, 6b and optical fiber bundle 16.1
The distal end of 7 is optically fixed at a predetermined position using a holding box 18.

As shown in FIG.
Since it can be downsized to about a cubic inch, if this part (hereinafter referred to as the monitor head or simply head) is placed in the target solution, it will be located in the area where the trajectories of the scattered light beam 7a and the irradiated light beam 5a intersect. Multiple foreign objects can be identified. Needless to say, the amount of scattered light is zero if no foreign matter is present.

In the present invention, unlike the conventional method, foreign objects are not counted individually6. Therefore, the number of foreign objects in the region of interest cannot be immediately determined from the scattered light intensity.

Therefore, a solution with a known number of foreign substances per unit volume is prepared, and the relationship between the scattered light intensity and the density of foreign substances is calibrated and used. There is no particular problem with this calibration since the force can be applied to any monitor head as long as the shape of the monitor head is not affected.

Another embodiment of the present invention shown in FIG. 2 is basically the same as the embodiment shown in FIG. 1, but the difference between the two lies in the difference in measurement sensitivity. In the embodiment shown in FIG. 2, the measurement sensitivity is approximately twice as high as in the example shown in FIG. That is, the scattered light generated by the irradiation light beam 5a is reflected not only by the mirror 19a but also by the mirror 19b, and the fiber bundle 1
74. =Introduced. Although this embodiment can operate without fi 119b, in that case the scattered light directed in the direction of fi 19b is lost without being introduced into the fiber bundle 17. But II! 19b, the scattered light that would otherwise be lost is reflected and enters the mirror 19a, and at 90'
It is reflected and enters the cylindrical lens 6b, effectively forming the fiber bundle 1.
Guided by 7.

In both of the above-mentioned examples, scattered light was detected. However, for the purpose of foreign object detection, transmitted light may be used, and since this can be easily implemented by simply changing the head, the details will be omitted.

In order to speed up understanding, the present invention has been described with the tacit understanding that the wavelengths of the irradiated light and the scattered light are the same. However, it is clear that the present invention can also be used for fluorescence detection6. For example, by detecting fluorescence of about 600 nm using irradiated light with a wavelength of about 400 nm,
It is possible to detect particles of fetresist.

Although the present invention has been described with reference to foreign matter in a solution, it is clear that it can also be applied to foreign matter inspection in gases or solids.

Regardless of whether fluorescence is detected, scattered light, or transmitted light is used, measurements often span visible wavelengths, and therefore, in some cases, extraneous light (indoor light, sunlight, etc.) may be mixed in. be.

In such a case, an appropriate filter can be used to eliminate the influence of extraneous light.

The irradiation light may be continuous light, but in order to remove the influence of continuous light such as sunlight, the irradiation light is modulated at an appropriate frequency, for example 2 KHz, and the signal light such as scattered light is well-known. Detection may also be performed by amplifying the detected phase. By doing so, the effect of extraneous light other than the irradiation light can be minimized, and the S/N ratio can be significantly improved.

Although FIGS. 1 and 2 only show the monitor head, which is the main part of the present invention, FIG. 3(a) shows an example in which it is applied to an actual process. Although there are many types of cleaning processes, FIG. 3(a) shows a typical example of a cleaning process using pure water.Pure water is supplied from the direction of a wave arrow 22 through a water supply pipe 21 to a cleaning tank 2o for cleaning wafers. Ru. The water from the cleaning tank 2o is arrow 2
3. Overflows in the direction of 23', falls into the sink 24, and is eventually drained. Washing tank 2o has one leg 25 and sink 2
It is fixed at 4. At a predetermined location in the cleaning tank 2°, the monitor head 26 shown in FIGS. 1 and 2 is already suspended by an optical fiber bundle 16.17. Six optical fiber bundles 16.1 are used.
7 is a light source.

It is directly connected to a measurement section 26 that includes elements and devices such as a photodetector, signal display, and signal recording.

FIG. 3(b) shows an example of measuring the intensity of scattered light.

When a wafer (not shown) is placed in the cleaning tank 2o at time ti, the scattering intensity increases due to foreign matter brought in by the wafer.

On the other hand, foreign matter brought in is discharged outside the tank 20 by the supply of pure water, so the amount of foreign matter in the tank 20 starts to decrease from time tz. In this way, according to the invention, the tank 2o
Changes in the number of foreign objects inside can be measured in real time.

〔Effect of the invention〕

As described above, according to the present invention, FIG. 3(a).

As shown in (b), changes in the density of foreign substances in the target solution can be measured in real time. Therefore, for example, the end of wafer cleaning can be determined quantitatively by determining the limit number of foreign particles. Furthermore, the optimum flow rate of pure water to be supplied can be determined from the measurement results. Therefore, using the present invention, it is possible to automatically control the water supply flow rate (eg, increase the water supply amount as foreign particles increase). The above-mentioned real-time performance and immediate response are clearly impossible with conventional methods.

During wafer cleaning, if there are many foreign substances in the solution near the wafer, these foreign substances will re-adhere to the wafer.

Therefore, there is no point in measuring at a portion far from the wafer.

According to the present invention, the objective can be easily achieved by moving the monitor head close to the wafer.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a foreign object monitor according to the present invention, FIG. 2 is a schematic configuration diagram of another implementation side according to the present invention, and FIG. 3 (a)
is a device configuration diagram showing an example of application of the foreign object monitor according to the present invention;
FIG. 3(b) is a graph showing the measurement results, FIG. 4 is an explanatory diagram of the principle of the foreign object monitor according to the present invention, FIG. 5 is an explanatory diagram of the principle of the conventional method, and FIGS. 6(a) and (b) are Scattered light due to passage of foreign matter. FIG. 7(a) is a graph showing the time dependence of transmitted light intensity, and FIG. 7(b) is a graph showing the time dependence of transmitted light intensity. 1a... Foreign matter group, 5a... Irradiation light (beam), 6a
. 6b... Cylindrical lens, 7a... Scattered light (beam). 16... Optical fiber bundle (for irradiation light), 17... Optical fiber bundle (for scattered light), 1B... Holding box, 19a, 1
9b No. 1/α, foreign body group sL:L:! '! , 7 mountains 1 & tL /l,, /7: Onifiber warehouse Milyu, lb with cylindrical lens / 8 stitches, packing box 2nd figure 3 times Cb) 1, 12 Kyotozuzumon 7 figure (of) (b)

Claims (1)

[Scope of Claims] 1. Means for irradiating a subject with a light beam having a predetermined cross-sectional area, and a change caused by the foreign matter that occurs when the foreign matter contained in the subject is irradiated with the light beam. A foreign matter monitor comprising: means for detecting light; and means for measuring the amount of foreign matter contained in the subject from the changing amount of light. 2. The foreign object monitor according to item 1, wherein the light beam is a light beam whose intensity is modulated at a specific frequency, and the detection means includes means for phase-detecting the changed light at the frequency. 3. The foreign object monitor according to item 1, wherein the light beam irradiation means and the changed light detection means are comprised of an optical fiber bundle and a lens. 4. The foreign object monitor according to item 1, wherein the object to be examined is a liquid. 5. The foreign object monitor according to item 1, wherein the changed light is scattered light from the foreign object, fluorescence, or transmitted light that is blocked and attenuated by the foreign object.