In-situ, real-time detection of particulate defects in a fluid

Examples disclosed herein generally relate to an apparatus and method for detecting particles in a fluid. A system for imaging a particle includes an imaging device. The imaging device has a lens and a detector. A laser source is configured to emit a laser beam. The detector is configured to accumulate an intensity of an accumulated light that passes through the lens. The accumulated light is scattered by the particle. The particle passes through the laser beam over a given period.

BACKGROUND

Field of Endeavor

Examples disclosed herein generally relate to an apparatus and method for detecting particles in a fluid.

DETAILED DESCRIPTION

Description of the Related Art

Purified water is often used in numerous applications during semiconductor manufacturing. For example, purified water is frequently used for cleaning substrates and other semiconductor parts in a manufacturing facility. The purified water may contain particulate contamination. Known techniques for measuring samples of the purified water to determine a contamination level, require taking the samples off-site for testing, adding to the cost of testing and maintaining purified water within process requirements.

Commercially available techniques include liquid particle counters (LPC's) used to test the concentration of unwanted particles and other contaminants in the purified water. Mass spectrometry is another approach of testing purified water for unwanted particles. In mass spectrometry, a sample contained in a test tube, is aspirated by a nebulizer that shatters the purified water into droplets. A charged ion is projected through a mass spectrometer, and the ion is measured by a detector. Conductivity of the purified water can be measured in order to determine ion concentration, where the ion concentration corresponds to the level of purity in the purified water. Because these known techniques involve off-site testing, operators are faced with increased time and cost for testing the purified water to ensure it is within process requirements. While in-line and on-line spectrometers are also known, these spectrometers are only capable of detecting particle contamination at very high concentrations, and therefore not useful for contamination in purified water at low concentrations.

Accordingly, there is a need in the art for an improved method and apparatus for in-situ monitoring for contaminants in purified water.

SUMMARY

Examples disclosed herein generally relate to an apparatus and method for detecting particles in a fluid. A system for imaging a particle includes an imaging device. The imaging device has a lens and a detector. A laser source is configured to emit a laser beam. The detector is configured to accumulate an intensity of an accumulated light that passes through the lens. The accumulated light is scattered from the particle. The particle passes through the laser beam over a given period.

In another example, a light intensity measuring system includes an imaging device. The imaging device has at least one lens and an array detector. The array detector has n rows and m columns. A laser source is configured to emit a laser beam. The detector is configured to accumulate an intensity of an accumulated light that passes through the lens. The accumulated light is scattered from the particle. The particle passes through the laser beam over a given period. A vessel is proximate the laser source. The laser beam is configured to pass through the vessel.

A method of measuring light intensity is herein disclosed. The method includes flowing a fluid through a hollow vessel. The fluid has at least one particle. A laser beam is emitted through the hollow vessel onto the at least one particle. An intensity of light scattered from the particle is accumulated over a given period.

In order to facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common features. It is contemplated that elements and features of one example may be beneficially incorporated into other examples without further recitation.

DETAILED DESCRIPTION

Disclosed herein is an apparatus and method for detecting particles in a fluid. Herein, a laser beam is focused into a vessel, the vessel disposed in a pool of flowing ultra-pure water (UPW). The presence of any foreign particles in the pool of UPW causes scattering of light from the laser beam. The scattered light is collected by an imaging device proximate a side of a vessel. The scattered light is focused onto a detector.

Analytical testing of the UPW's purity, according to embodiments disclosed herein, enables operators to determine water quality in real-time, on-site, where the UPW is being used. For example, testing of the UPW can occur in the semiconductor manufacturing facility, and does not require samples of the UPW to be obtained and sent to a laboratory for testing. Obtaining samples of the UPW using known conventional techniques can increase the overall cost of obtaining data, since the cost of testing includes maintaining a laboratory or shipping the samples to a laboratory and back to the semiconductor facility for further analysis. Furthermore, the length of time between sampling and obtaining data on the UPW, delays operator decision-making. Accordingly, decisions related to routine maintenance, cleaning, and filtering are delayed. A delay in decision-making can enable the overall quantity of contaminants in the UPW to go unmonitored and unfiltered, thus decreasing the cleaning effectiveness of the UPW.

Advantageously, the methods and apparatuses disclosed herein enable water quality to be monitored in real-time, thus reducing above-noted drawbacks from reliance upon periodic testing and off-site analysis. In addition, the cleaning effectiveness of the UPW is maintained to a desired level, since operators are able to detect the number of particles having particle diameters less than 20 nm.

FIG. 1is a schematic orthogonal view of a particle imaging system100disposed within a pool104. A fluid120flows through the pool104. The fluid120may enter the pool104through an inlet108. An outlet112, fluidly coupled to the inlet108, provides a pathway for the fluid120to exit the pool104. The inlet108can be coupled to a source (not shown) of UPW. In some examples, the outlet112communicates with the inlet108via a return116. The return116directs fluid120to the inlet108, restoring fluid120that has exited the outlet112back to the pool104. The fluid120may be water, H2O. The water may be UPW treated to remove contaminants including organic and inorganic compounds, dissolved and particulate matter, and gases. The gases may be dissolved, volatile, non-volatile, reactive, inert, hydrophilic, and hydrophobic. However, it is understood that the UPW may be treated to remove contaminants not specifically recited herein.

A particle(s)124may be present in the fluid120. The particle124may be residual materials that remain in the fluid120after a manufacturing process. For example, the particle124may remain in the pool104after the fluid120has been used to remove contaminants on a surface of a substrate. The particle124may be mineral deposits, microorganisms, and trace organic and nonorganic chemicals, including other contaminants. Depending upon manufacturing process, the particle124can be from a few micrometers (mm) to a few nanometers (nm).

A vessel126may be a portion or segment of the pool104. The particles124of the fluid120passes through the vessel126. The vessel126surrounds the fluid120. The vessel126may be made of glass, quartz, plastic, or other substantially transparent material that enable light to pass therethrough. While the vessel126is shown as generally cylindrical, the shape is not limited to this geometry, and may be any geometry such that the fluid120is configured to flow therethrough.

The particle imaging system100includes an imaging device130. An imaging lens134and a detector138are included in the imaging device130. A laser source146is included in the particle imaging system100. The laser source146emits a laser beam142. A focusing lens128can be positioned between the laser source146and the vessel126. The focusing lens128focuses or narrows a diameter of the laser beam142before the laser beam142enters the vessel126. Alternatively, the focusing lens128can widen the diameter of the laser beam142.

FIG. 2is a schematic orthogonal view of an imaging system200configured to capture images of a particle124passing through the vessel126ofFIG. 1. The imaging system200includes an imaging device216, the laser source146, and a hollow prism202. The hollow prism202is shown generally as a parallelogram, however it is understood that the hollow prism202is not limited to this geometry, and may be any geometry such that fluid120is configured to flow therethrough.

The hollow prism202has a first side204. The hollow prism202has another first side204that is coplanar and substantially equal in dimension. A second side206is in contact with first side204. The hollow prism202has another second side206positioned coplanar to and substantially equal to the second side206. The second side206may be substantially perpendicular to the first side204. The hollow prism202may be substantially in the shape of a hollow cuboid.

The hollow prism202has a top208. The top208is substantially unobstructed and enables fluid120to enter the hollow prism202. The top208of the hollow prism202is substantially coaxial with the bottom212of the hollow prism202. Fluid120enters the top208of the hollow prism202in a y-direction260. The top208can have the same cross-sectional area as the bottom212. It is understood however, that the top208and the bottom212may have different cross-sectional areas. The fluid120exits the hollow prism202through a bottom212that is substantially unobstructed.

The imaging device216is disposed in proximity to the hollow prism202. The imaging device216may be partially or fully submersed in the pool104, shown inFIG. 1. Alternatively, the imaging device216may be positioned outside of the pool104. The imaging lens134and a detecting array224are included in the imaging device216.

The laser beam142is on an upstream side of the focusing lens128. A focused beam232is formed on a downstream side of the focusing lens128. The focused beam232is part of the laser beam142that has been narrowed by the focusing lens128. Narrowing of the focused beam232reduces a cross-sectional area (A) of the laser beam142. Alternatively, the focused beam232can be expanded. A cross-sectional area (A) of the focused beam232may be increased in a manner that corresponds to the cross-sectional area (A) of the laser beam142.

The focused beam232passes through the first side204of the hollow prism202. The focused beam232can be substantially orthogonal to the flow of fluid120. As fluid120flows through the hollow prism202, the focused beam232illuminates the fluid120, as the fluid120passes through the vessel126. Particles124travelling in the fluid120(shown inFIG. 1) are illuminated by the focused beam232. Light from the focused beam232is scattered by the particles124that are disposed in the fluid120. Scattered light of the focused beam232passes through the hollow prism202. The scattered light may be photons that scatter from the particle124. Collected light228is a portion of the scattered light of the focused beam232. Collected light228includes the scattered light from the focused beam232. The collected light228is the portion of the scattered light that has passed through the second side206of the hollow prism202. Alternatively, the collected light228can pass through the first side204of the hollow prism202.

Collected light228from the laser beam142is received by the imaging device216after passing through a second side206of the hollow prism202. It is understood that the first side204and the second side206are relative terms. For illustrative purposes, the collected light228is shown passing through the second side206. However, it is understood that the collected light228may take several paths out of the hollow prism202. For example, the imaging device216can be configured so that collected light228is received after passing through the first side204. The collected light228discussed herein includes light that is refracted, scattered, reflected from the surface of the particle124, and background light. Collected light228may also include light emitted from the laser beam142, as the laser beam142passes through the fluid120and/or hollow prism202. Collected light228is stored with a corresponding value on an n×m pixel of the detecting array224. The detecting array224is an n×m array, having n pixel rows and m pixel columns.

As fluid120flows through the hollow prism202, the laser beam142is focused through the first side204of the hollow prism202. The presence of the particle124in the fluid120will cause a certain amount of scattering of the focused beam232as collected light228. The collected light228is collated by imaging lens134on the second side206of hollow prism202. The collected light228thus collected is focused onto the detecting array224. The scattering of light by the particle124in the Rayleigh regime can be formulated as that due to a dipole, whose maximum radiation value is given by the following expression 1:

An illumination intensity is represented by I0; n is a refractive index of the particle124; n0is a refractive index of the fluid120; λ is a wavelength of light in a vacuum. The wavelength λ may be any range between the x-ray to far-infrared range. A diameter of the particle124is represented by d. The illumination intensity I0is equal a power (P) of the laser beam142divided by the cross-sectional area (A) of laser beam142, and I is the accumulated or actual intensity of the laser beam142.

An area A is the cross-sectional area (A) of the laser beam142. A=πD2/4, where D is the diameter of laser beam142at a point where the particle124intersects the laser beam142. Alternatively, the D may be a diameter of the focused beam232at a point where the particle124intersects the focused beam232. The illumination intensity I0is proportional to 1/D2. On a downstream side of the focusing lens128, the focused beam232has a cross-sectional diameter D1. An interrogation volume of the fluid120increases as the cross-sectional diameter D1increases. The interrogation volume of the fluid is represented by

l*π*(D12)2,
where l is a length of the laser beam142image captured by the imaging device216. An overall sensitivity of the imaging device216is inversely proportional to the cross-sectional diameter D1of focused beam232.

The appearance of the term (n/n0) in expression 1 results in a reduction of the relative scattering of the particle124in fluid120compared with relative scattering of the particle124in atmospheric air. However, this reduction in scattering is compensated by the term (λ/n0), representing refraction in liquid.

An amount of light collected can be a function of the numerical aperture (NA) of the imaging lens134. The amount of light collated may also be a function of the integration time of the detecting array224. The integration time of the detecting array224corresponds to the velocity of the particle(s)124passing through the fluid120. A total detected energy per particle124is I(δt). The integration time δt is the time it takes for particle124to pass through the laser beam142. Alternatively, the integration time δt can be the time it takes for particle124to pass through the focused beam232. The integration time δt=D/v, where v is velocity of particle124. As such, integration time is proportional to the diameter D1of focused beam232.

As the NA increases, the amount of collected light228increases. By increasing the amount of collected light228, a certain amount of background noise (i.e., radiation) is also collected by the detecting array224. This background noise originates in collected light228due to the molecular level fluctuations in the fluid120. Collected light228passing through the second side206of the hollow prism202can also contribute to the background noise. The background noise manifests as a “DC” signal in the output of the detecting array224.

In detecting the particle(s)124, a shot noise associated with the background noise is an important factor to consider. The imaging device216has the ability to substantially collect all the light within its NA. The dynamic range of the detecting array224should be high enough to be able to accommodate the background noise. Additionally the shot noise associated with the background light should be low enough for small particle(s)124to be detected.

The detecting array224is configured to substantially eliminate background noise associated with the collected light228. As stated above, the detecting array224is an n×m array, having n pixel rows and m pixel columns. The detecting array224can include 1,000 or more rows n. The number of columns m can be up to 8,000. In some examples, the detecting array224can be a linear array, where the number of rows is equal to about 1. The detecting array224, is a device such as a charge-coupled device (CCD), or complementary metal-oxide-semiconductor (CMOS) array, onto which falls the collected light228from an illuminated region (i.e., the illumination volume of the focused beam232). In an example when the focusing lens128is not used, the illuminated region includes the illumination volume of the laser beam142.

Alternative methods of performing this task include the use of a linear CMOS array, and a static mode CCD array. When the particle124passes the focused beam232within a field of view of the imaging lens134, the collected light228from the particle124is imaged onto a corresponding position on the detecting array224(FIG. 2), as the particle124travels downward in a vertical direction (i.e., the y-direction260). The y-direction260is perpendicular to both an x-direction250and a z-direction270.

The detecting array224may be configured to perform time delay integration (TDI). An image of the particle124also moves along a column (m) of the detecting array224. The image of the particle124moves in synchronicity with a position of the particle124. Otherwise stated, the image of the particle124on a given n×m pixel corresponds to the vertical position of the particle124as it travels through the focused beam232. A given n×m pixel of detecting array224generates a charge. The charge moves in synchrony with the movement of the particle124sequentially along a column (m column) of detecting array224. The charge generated in each pixel along the row (n) accumulates successively through each corresponding column (m), as the particle124moves in the vertical direction. In addition, as the image of the particle124moves in the vertical direction, the charge generated in each n×m pixel along the row (n) accumulates successively through each corresponding column (m). Thus, an accumulated charge at the end of each column m corresponds to the collected light228throughout a position of the particle124as it passes the focused beam232. Advantageously, the illumination intensity I0, stored as a signal in detecting array224, increases in a traveling direction of the particle124.

The TDI operation accumulates charge throughout the travel time of the particle124in the focused beam232. The TDI operation increases the total amount of collected scattered photons stored as signals in the column (m) of the detecting array224. Narrowing a field of view of the imaging device216reduces the background noise that is stored onto a given n×m pixel. Advantageously, the TDI operation provides averaging of any spatial variation of the background noise that is imaged onto a given column (m) of the detecting array224. In this manner, sensitivity of the imaging device216is enhanced.

In some examples, the plurality of columns (m) of the detecting array224may be several thousand. Accordingly, imaging device216is enabled to detect the simultaneous passage of a plurality of particle(s)124. By acquiring data on several particles124simultaneously, the imaging device216is configured to reduce miscounting of the particle(s)124. Miscounting of the particles can be the result of a coincidence of arrival into the illuminated region. For example, the illuminated region can be the illumination volume of the focused beam232.

In particular, a desired signal from the collected light228accumulated from the particle124increases directly with the strength of the laser beam142. Correspondingly, the background signal also increases directly with the strength of the laser beam142. However, since the shot noise is proportional to the square root of the background signal, the signal to noise ratio increases with additional light. Accordingly, a sensitivity of the imaging device216is also increased. Focusing of the laser beam124has a similar effect. The sensitivity of the imaging device216improves linearly (i.e., proportional to 1/D) with the reduction in diameter D of the laser beam142.

The imaging device216can be configured to enhance sensitivity and maintain a counting efficiency of the particle124. The sensitivity of particle imaging system100also corresponds to the NA of the imaging device216. However, the larger the NA, the shorter is the depth of focus of the collected light228. Widening the laser beam142diameter D will result in the narrowing of the focused beam232. The integration time δt of the particle(s)124for a given flow rate of the fluid120is correspondingly reduced. Furthermore, the reduction in the diameter D of the focused beam232corresponds to a smaller interrogation volume of the fluid120(e.g., the illumination volume of the focused beam232).

FIG. 3is a schematic orthogonal view of another imaging system300configured to capture particles124passing through the vessel ofFIG. 1. The imaging system300includes the imaging device216, the laser source146, and a hollow prism302. As mentioned above, the hollow prism302is shown generally as a parallelogram, however it is understood that the hollow prism302is not limited to this geometry, and may be any geometry such that fluid120is configured to flow therethrough.

The hollow prism302includes the first side(s)204, second side(s)206, and third side(s)304. The hollow prism302has another third side304that is opposite and coplanar to the third side304depicted inFIG. 3. Collectively the sides may be referred to as third sides304. The top208of the hollow prism302is not coaxial with the bottom212of the hollow prism302. In an example, the cross-section of the top208is within a plane that is substantially perpendicular to another plane in which the cross-section of the bottom212is disposed. Fluid120enters the hollow prism302in the z-direction270through the top208. The bottom212provides an exit for the fluid120to escape the hollow prism302in the y-direction260.

The laser source146is positioned substantially orthogonal to the third side304. The laser beam142, emitted by the laser source146, enters the hollow prism302through the third side304. The laser beam142may be substantially parallel to the flow of the fluid120in the hollow prism302.

The imaging lens134of the imaging device216is positioned substantially orthogonal to the second side206of the hollow prism302. Collected light228passes through the imaging lens134. Collected light228is stored with a corresponding value on an n×m pixel of the detecting array224.

FIG. 4is a schematic orthogonal view of an exemplary imaging system400configured to capture particles124passing through the vessel ofFIG. 1. The imaging system400includes the imaging device216, the laser source146, and the hollow prism302. Fluid120flows through the top208of the hollow prism302and exits through the bottom212of the hollow prism302.

The imaging device216is oriented along the y-direction260. The detecting array224may be substantially coplanar to the third side304. Collected light228from hollow prism302travels along the y-direction260toward the imaging lens134. The collected light228is stored with a corresponding value on the n×m pixel of the detecting array224.

The laser source146is substantially perpendicular to the second side206of the hollow prism302. A focusing lens420is disposed between the hollow prism302and the laser source146. The focusing lens420focuses the laser beam142. On a downstream side of the focusing lens420, a focused beam432has a cross-sectional diameter D2. As the cross-sectional diameter D2increases, the interrogation volume of the fluid120increases. The cross-sectional diameter D1of the focused beam232is less than the cross-sectional diameter D2of the focused beam432. An overall sensitivity of the imaging device216is inversely proportional to the cross-sectional diameter D2of focused beam432.

FIG. 5is a schematic orthogonal view of obscured edges500of the hollow prism202depicted inFIG. 2. Herein, it is understood that obscured edges500may also be applied to hollow prism302, illustrated inFIGS. 3-4. The hollow prism202has first side(s)204and second side(s)206. The laser beam142emitted from the laser source146enters the hollow prism202through a first side204.

The laser beam142may be refracted upon contact with the first side204of the hollow prism202. Refraction of the laser beam142causes scattered light504. The scattered light504can travel radially on a surface of the first side204. The scattered light504may also travel through a thickness of the first side204. Upon entering the hollow prism202, the scattered light504contributes to the background signal detected by the imaging device216(shown inFIG. 2-4).

Obscured edges500are provided on a surface of the hollow prism202. Each obscured edge500absorbs scattered light504. The obscured edge500may be coated with paint, an adhesive, a polymer strip, particulate granules, or other means by which light (i.e., photons) are absorbed into the obscured edge500. The obscured edge(s)500absorb refracted light, reducing background signal, and shot noise thereof, in the collected light228(shown inFIG. 2)

FIG. 6is a flow diagram of a method600of measuring light reflected within the particle imaging system ofFIG. 1. At block604, a laser beam142is projected through the vessel126. The vessel126may be any one of the hollow prisms inFIGS. 2-5. The particles124of the fluid120passes through the vessel126. At block608a focused beam232of light is collated as collected light228from the vessel126. The collected light228is stored as a signal on a detecting array224. The illumination intensity I0, stored as a signal on the n×m pixel of the detecting array224. Background noise from the focused beam232of light is filtered within the imaging device216at block612. The method600continues at block616where a charge is accumulated throughout a travel time of a particle passing through the laser beam142. The background signal, and shot noise thereof, is reduced to a quantity of light that falls onto a given pixel of the n×m detecting array224at block620. At block624, the charge is accumulated at the end of each column (m) of the detecting array224, having n×m pixels. Scattering of the laser beam142is reduced by obscuring a portion of the vessel126at block628.

FIG. 7is a plan view of the imaging device216used to measure light scattered from the particle imaging system ofFIG. 1. The imaging device216in some examples is a camera701that is coupled to a controller700. The controller700includes a processor704, a memory708, and support circuits712that are coupled to one another. The controller700may be on-board the camera701, or in an alternative example, the controller700may be on-board a remote device (not shown) that receives images from the camera701. The camera701has at least one lens702that is configured to capture images of the particle imaging system100, disclosed herein.

The imaging device216includes an input control unit, such as power supplies, clocks, cache, input/output (I/O) circuits, coupled to the various components of the imaging device216to facilitate control thereof. Optionally, imaging device216can include a display unit (not shown). The processor704may be one of any form of general purpose microprocessor, or a general purpose central processing unit (CPU), each of which can be used in an industrial setting, such as a programmable logic controller (PLC).

The memory708is non-transitory and may be one or more of readily available memory such as random access memory (RAM), read only memory (ROM), or any other form of digital storage, local or remote. The memory708contains instructions, that when executed by the processor704, facilitates the operation of the imaging device216. The instructions in the memory708are in the form of a program product such as a program that implements the method of the present disclosure. The program code of the program product may conform to any one of a number of different programming languages. Illustrative computer-readable storage media include, but are not limited to: (i) non-writable storage media (e.g., read-only memory devices within a computer such as CD-ROM disks readable by a CD-ROM drive, flash memory, ROM chips, or any type of solid-state non-volatile semiconductor memory) on which information is permanently stored; and (ii) writable storage media (e.g., floppy disks within a diskette drive or hard-disk drive or any type of solid-state random-access semiconductor memory) on which alterable information is stored. Such computer-readable storage media, when carrying computer-readable instructions that direct the functions of the methods described herein, are examples of the present disclosure.

In one example, the disclosure may be implemented as the program product stored on a computer-readable storage media (e.g.708) for use with a computer system (not shown). The program(s) of the program product define functions of the disclosure, described herein. The programs/instructions include algorithms that are configured to process light collected from particle imaging systems shown inFIGS. 1-5.

Herein, an apparatus and method are disclosed for detecting particles in a fluid. While the foregoing is directed to specific examples, other examples may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.