JPH04132936A - Method and apparatus for monitoring particle using backscattered light interfered by no bubble - Google Patents

Abstract

PURPOSE: To detect a submicron particle under presence of a bubble by irradiating a sample of a medium to be processed with a light beam and determining the size and the quantity of the particle and a bubble based on the features of the backscattering light component unique to the bubble. CONSTITUTION: When a sample of a medium 2 to be processed drawn into a cell 8 in a sensor housing 10 is irradiated with laser light from a light source 18, the laser light is scattered by particles or bubbles in the sample to produce a light beam of a known wavelength. The scattering light is collected by means of a fiber optical unit 22 and separated into forward, perpendicular and back scattering components which are detected 12, 14, 16, respectively, and converted into electric signals corresponding to the optical level and then delivered through a cable 24 to an electronic module 26. The module 26 detects a signal caused by backscattering from a bubble and determines the size and the quantity of the particle and/or the bubble in the medium 2. This arrangement prevents the medium 2 to be processed from being discarded too early while reducing the processing cost and enhancing the production yield.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates generally to optical methods and apparatus for determining the size and amount of particles and bubbles in liquid media. In particular, the present invention relates to monitoring and/or analysis, either real-time or offline, for detecting and identifying particles and bubbles in processing fluids used in manufacturing processes where the purity of the liquid media is important, such as in the semiconductor or medical fields. .

BACKGROUND OF THE INVENTION Particles are generated during the manufacture of semiconductor devices and contaminate liquids used during wafer fabrication that generate particles, such as chemical etch solutions, photoresist deionized water, and solvents. It is known that defects and therefore manufacturing yield numbers are directly proportional to the presence and number of particles in the liquid medium used for processing.

Current wafer processing methods require minimizing the amount of particles in all liquids that contact the wafer. Such processing media are monitored for particulate contamination, and various filter methods are used to remove particles.

Bubbles are measured and counted as particles because they emit a signal that is indistinguishable from particles in conventional methods of monitoring semiconductor fluids during processing.

Although particles larger than 1 micron can be successfully filtered, reliable removal of particles becomes much more difficult as the particles are smaller than 1 micron. As wafer processing technology advances, purity standards for processing media become more stringent, with detection of particles of 0.1 microns or smaller desired.

No satisfactory in-line method has been found to physically separate bubbles from submicron particles for wafer processing.

(Problem to be solved by the invention) Since it is difficult to distinguish between particles and bubbles, conventional devices can distinguish between particles and bubbles.
Count particles and indistinguishable bubbles.

Therefore, the count is the number of false particles rather than the number of real particles. Because of this number of spurious particles, the processing media is prematurely determined to be exhausted and to be discarded.

In many applications, the processing fluids used are environmentally hazardous and, in many cases, appropriate disposal methods require costly special handling. Premature disposal of processing fluids also , increasing the cost of processing.

When the particle count exceeds an acceptable level, the number of defects increases and manufacturing yield decreases.

Although there are particle monitors that measure off-line samples of processing media or are placed in processing solution recirculation lines, due to particle mechanics, such monitors actually measure filter efficiency and monitor on-line solution conditions. Not measured. Furthermore, such monitors do not distinguish between particles and bubbles.

What is needed for a sampling device that is on-line and in contact with the processing media is a sampling system that does not generate or introduce additional particles. Materials that come into contact with the processing media must be non-reactive in the media.

The object of the present invention is a method and apparatus for reliably detecting the presence and quantity of submicron particles in the presence of foam.

Another object of the invention is the detection of particles of 0.1 micron or smaller in liquid media.

Another object of the present invention is to more efficiently detect the point at which the number of particles exhausts the effectiveness of the media, thereby eliminating premature disposal and reducing disposal problems.

Yet another object of the present invention is to accurately detect the point at which the amount of particles causes unacceptable yield and send a signal to a process controller to change the media.

Yet another object of the invention is to provide real-time online measurements of particles.

Another object of the invention is to monitor the number of bacteria in the presence of particles and foam.

Yet another object of the invention is to provide a submerge handling apparatus and method that is unobtrusive, does not generate additional particles, is protected from toxic substances in solution, and ensures representative samples. It is.

Hatton and Plaws
U.S. Pat. . Tatsuno
U.S. Pat. No. 4,595,291, "Particle Size Measuring Apparatus," discloses the use of laser light and optical fibers to direct a power source and monitor light scattered by particles for particle measurements. There is. Philip H. Hall
Lip H, Paul) and Di1-Zikichakov (Ge
``Compact optical fiber detector for optical measurement of particle size'' by J.
nalof Lightwave Technology
Vol. LT-5, No. 7. July 1987 discusses the use of laser light and detection of forward or right-angle scattered light to measure particle size.

Means for Solving the Problems The detection system for measuring and identifying particles and bubbles in a liquid medium of the present invention includes: (a) a light source that generates a light beam;
(b) includes a sampling volume to be analyzed and located;
the sampling volume is illuminated by the light beam to scatter the light; (C) a cell for collecting the scattered light and separating the scattered light into forward and/or orthogonal scattered components and backscattered components; detection means; (d) a separate detector arranged to separately receive each scattered light component and convert each said component into an electrical signal proportional to the intensity of the detected light; and (e) Signal processing means are provided for determining the size and amount of particles and bubbles in the sampling volume based on the unique characteristics caused by bubbles in the backscatter channel, thereby achieving the above object.

Further, the light source may be a collimated laser diode.

Furthermore, the detection means may be a fiber optic device.

Further, the detection means may be a lens imaging device.

Further, the detection means may be a reflective optical device.

The detection means may also comprise a light pipe defining a collection aperture and transferring the collected light to each detector.

The particles may also be enhanced by ultrasound means for easier detection.

Furthermore, when the present invention is applied to a device for detecting and measuring bacteria in the presence of particulates and bubbles, the light source may be of a wavelength that causes the bacteria to emit light.

The present invention is a method and apparatus for detecting, sizing and monitoring particles, in which a light source of known wavelength is configured to separate and collect forward scattered light, right angle scattered light, and back scattered light. The sensor housing is arranged within a sensor housing having an optical device configured and directed to illuminate a sampling volume in a cell. The light from each direction is then
The light is sent to a detector, such as a photodiode, which converts it into a separate electrical signal proportional to the level of light detected.

The electrical signal is then sent to an electronic decoder that detects and processes the signal into information. An electronic decoder using the principles described below allows determination of the size and amount of particles and/or bubbles in the medium being tested.

The invention is based on the premise that optically the backscattering level of bubbles is very different from that of particles and that particles can be distinguished from bubbles by their significantly different scattering. Also, the coefficient of scattering is a direct function of the concentration of the medium.

Thus, the amount of backscatter by a liquid medium containing bubbles is
Decreased in the presence of bubbles. Therefore, the total energy detected by the backscatter detector with the presence of bubbles in the cell is
Gives a negative pulse when compared to the backscatter reference level.

In contrast, particles give a small positive signal on the backscatter detector and positive signals on the forward and right-angle detectors. Analyzing the combination of these signals with conventional signal processing techniques increases the sensitivity of particle detection and the ability to discriminate between bubbles and particles.

The method and apparatus of the present invention determine the amount and size of particles and bubbles in a liquid processing medium. The present invention provides a collimated light source to generate a light beam of known wavelength, and directs the light source to collect light scattered by particles and/or bubbles in the sample caused by impact erosion of the light beam. irradiating a liquid sampling volume in a cell disposed within the configured sensor housing. The scattered light is then separated into forward and/or right angle and backscatter sections and converted into separate electrical signals for each scattering direction. Since the coefficient of scattering is a direct function of the concentration of the sampling volume, the presence of bubbles reduces the concentration and the amount of radiation that is backscattered. Using the scattering levels obtained from liquid media alone as an example, particles and bubbles in the sampling volume each scatter radiation into the forward and/or right-angle scattering channels at levels that result in significant and approximately similar positive signals. . As a result, bubbles and particles are not discernible in the forward or right-angle scattering channels. Previously, backscatter was known to exist in sample volumes containing bubbles and particles, but the presence and amount of backscatter had not been correlated to the presence or absence of bubbles. In the present invention, for forward and/or right-angle scattering characteristics, the presence of bubbles in the sampling volume results in a large (51gn1f 1cant) negative signal in the backscattering channel, while the presence of particles in the opposite sampling volume results in a backscattered It has been found that this results in only a small positive signal in the channel. This difference in the scattering properties of bubbles and particles allows separate signals from both forward and/or right-angle scattering and backscatter to determine the size and amount of particles and/or bubbles associated with the monitored medium. will be processed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a detailed illustration of the invention, in which a sample of liquid processing medium 2 is pumped through a tube 4 by a pump 6 into a cell 8 of known volume placed within a sensor housing 10. I'm drawn into it. Cell 8 is placed in close proximity to forward scatter detector 12, right angle scatter detector 14 and back scatter detector 16. Sampling can be either real-time or offline. The cells 8 are made of a material such as quartz or sapphire and do not react with the processing medium 2 and do not introduce particles to the medium.

Cell 8 is illuminated by a light source 18, such as a solid state laser. The light source 8 has a collimator 20 and illuminates the sampling volume of the liquid processing medium 2 with a known wavelength that impinges and scatters any particles or bubbles found in the sampling volume of the cell. emits a beam of

Within the sensor housing 10, a fiber optic 22 or reflector collects and separates the scattered light into forward, normal or backscatter, which are detected by detectors 12, 14 and 16, respectively, and determine the level of detected light. is converted into an electrical signal proportional to . The detector can be a photodiode. Electrical signals are sent through cable 24 to electronic module 26 .

The electronic module 26 is capable of processing the signals and determining the size and amount of particles and/or bubbles in the processing medium 2 based on the presence or absence of a signal that corresponds to a signal due to backscatter from bubbles. It has a conventional circuit configuration.

FIG. 2 explains the phenomenon that makes it possible to distinguish between bubbles and particles. Lines A and B represent the forward/orthogonal and backscattered signals, respectively.

In the figure, particles are first bombarded in the sampling volume over time. The particles cause a positive impulse to be emitted in the forward/right-angle scattered signal and a smaller positive impulse to be emitted in the backscattered signal. Bubbles are collided over time. The bubble causes a positive impulse to be emitted in the forward/right angle signal, which is similar to the positive impulse caused by a previous collision with a particle. However, bubbles cause relatively narrow bandwidth negative impulses to be emitted in the backscattered signal. The most important aspect of the present invention is the recognition of the importance of this negative impulse, which has hitherto been treated as background chatter.

Once the significance of this negative impulse emitted by backscatter is known, the processed signal can be compared to predetermined limits and used for monitoring and processing in applications such as medicine and manufacturing processes where particle quantity and size are important. Can be used for control. The present invention allows many important processing factors to be measured.

(a) For a given volume and concentration of liquid, the change in the signal emitted by backscatter can be used to measure the presence and relative size of bubbles.

(1+) For a given volume and concentration of liquid, the change in the signal emitted by forward and/or orthogonal scattering and backscattering can be used to determine the presence and relative size of particles.

(c) For a given flow rate, a given cell volume, a given sample time and the number of bubbles in the sample counted, the number of bubbles in a given volume of processing media can be determined statistically.

(d) For a given flow rate, a given cell volume, a given sample time, and the number and size of particles counted, the number and size of particles in a given processing volume are statistically related to interference from bubble detection. Using the above correct reasoning,
It can be statistically inferred.

Although the present invention has been described for use in a semiconductor manufacturing process, the ability to discriminate between particles and bubbles in a liquid medium is applicable to any process where process control is important or desirable.

The optical sensor was described as a laser-generated fiber optic system. However, it is within the skill of the art that configurations using optical components of light guides and reflectors or equivalent configurations may be used.

The above process, which is particularly useful for distinguishing between bubbles and particles in the submicron range, is accomplished by the use of ultrasonic waves that generate concentrated changes in concentration near the particles. In this way, the sensitivity of the detector can be increased by making the particles appear relatively larger as a function of the controlled ultrasound energy applied to the sampling volume.

Other embodiments of the invention use short wavelength light sources to stimulate bacteria in a liquid medium to emit light.

In connection with the system described herein, the use of luminescence can be used to detect bacteria in the presence of bubbles and particles.

The present invention provides a unique method and apparatus for the measurement of particles and bubbles in liquid media. Variations and modifications to the disclosed embodiments may be made without departing from the scope of the invention.

FIG. 1 is a schematic diagram of the apparatus according to the present invention, and FIG. 2 is a diagram illustrating the output of the monitor apparatus according to the present invention.

Engraving of drawings (no changes to content)

Claims (1)

Claims: 1. A detection system for measuring and identifying particles and bubbles in a liquid medium, comprising: (a) a light source generating a light beam; (b) a sampling volume to be analyzed and placed; including;
the sampling volume is illuminated by the light beam to scatter the light; (c) a cell for collecting the scattered light and separating the scattered light into forward and/or orthogonal scattered components and backscattered components; detection means; (d) a separate detector arranged to separately receive each scattered light component and convert each said component into an electrical signal proportional to the intensity of the detected light; and (e) A detection system comprising: signal processing means for determining the size and amount of particles and bubbles in the sampling volume based on the unique characteristics produced by the bubbles in the backscatter channel. 2. The apparatus of claim 1, wherein the light source is a collimated laser diode. 3. Claim 1, wherein the detection means is a fiber optic device.
The device described in. 4. The apparatus of claim 1, wherein the detection means is a lens imaging device. 5. The apparatus according to claim 1, wherein the detection means is a reflective optical device. 6. The detection means comprises a light pipe defining a collection aperture and transporting collected light to each detector.
The device described in. 7. The device according to claim 1, wherein the particles are enhanced by ultrasound means for easier detection. 8. The light source is of a wavelength that causes the bacteria to emit light;
Device according to claim 1 for the detection and measurement of bacteria in the presence of particulates and foam.