A method for determining particle characteristics in a fluid sample and / or for determining contamination characteristics of a fluid sample

Abstract

According to the present invention, a method for determining the characteristics of particles in a fluid sample and / or for determining the contamination characteristics of a fluid sample is provided, the method comprising the following steps: (a) depositing a metal film on the surface of a substrate to provide a smooth metal surface on the substrate; (b) bringing a fluid sample into contact with the metal surface of the substrate; (c) removing the fluid sample in contact with the metal surface from the metal surface so that only particles in the fluid sample remain on the metal surface of the substrate; (d) depositing a metal layer on the metal surface and the particles remaining on the metal surface of the substrate so that each of the particles is provided with a corresponding metal layer and areas of the metal surface without particles are provided with a metal layer, wherein, for each particle, there is a gap between the metal layer on the particle and the metal layer on the metal surface; and (e) irradiating the particles and the metal surface with electromagnetic radiation. The metal layer causes the electromagnetic radiation to be scattered by the metal layer on the particle to respectively generate scattered electromagnetic radiation; or the metal layer on the particle and the metal surface is irradiated with electromagnetic radiation, so that at least a portion of the electromagnetic radiation is absorbed by the metal layer on the particle, and another portion of the electromagnetic radiation is reflected by the metal surface on the substrate to generate reflected electromagnetic radiation; (f) receiving the scattered electromagnetic radiation at a photodiode array; or receiving the reflected electromagnetic radiation at a photodiode array; (g) forming an image including pixels, wherein each pixel in the image corresponds to a corresponding photodiode in the array, wherein the brightness of each pixel in the image corresponds to the intensity of the electromagnetic radiation received by the photodiode corresponding to the pixel; and (h) processing the formed image to determine the particle characteristics, and / or processing the formed image to determine the contamination characteristics of the fluid sample.

Description

Technical Field

[0001] The present invention relates to a method for determining the characteristics of particles in a fluid sample; and in particular, but not exclusively, to a method involving providing a metal layer on particles already adhered to a metal surface of a substrate and on the metal surface of the substrate; irradiating the particles of the substrate and the metal layer on the metal surface with electromagnetic radiation; forming an image using scattered electromagnetic radiation or reflected electromagnetic radiation; and processing the image to determine the characteristics of the particles in the fluid sample and / or determine the contamination characteristics of the fluid sample. Background Art

[0002] Existing techniques for characterizing particles that define impurities in a sample fluid are inadequate. For example, existing techniques for determining the concentration of particles in a sample fluid are inadequate.

[0003] Dark field imaging based on optical scattering is widely used to detect particles deposited on surfaces. The optical scattering cross section is proportional to the sixth power of the particle radius. Therefore, detecting small particles (e.g., particles with a radius less than 50 nm in diameter) requires a strong illumination source and a sensitive photodiode. In addition, methods using a strong illumination source and a sensitive photodiode are very sensitive to background noise from inherent defects on the surface (such as surface roughness). Disadvantageously, both deposited particles and surface roughness can scatter light with similar intensities, making it challenging to distinguish between particles deposited on the surface and surface roughness.

[0004] In another approach, brightfield imaging based on optical absorption and scattering is used to detect particles deposited on a surface; in this approach, reflected light is collected and used to form a brightfield image, and the presence of particles is then detected from the brightfield image. Particles on the surface cause the pixels in the brightfield image to appear darker due to their light absorption. In this case, the background signal is bright because the reflection from the flat surface is stronger. However, most particles have very little light absorption, making them difficult to detect using this brightfield imaging technique.

[0005] It is an object of the present invention to mitigate or eliminate the disadvantages associated with said prior art. Summary of the invention

[0006] According to the invention, these objects are achieved by means of a method having the steps stated in independent claim 1 of the present application; wherein the dependent claims recite optional features of preferred embodiments.

[0007] Advantageously, in the method of the present invention, amplified scattering and absorption of light by particles (which define impurities in a fluid sample) is achieved; therefore, more accurate detection of the particle characteristics from optical images (e.g., dark field images; and / or bright field images) can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The invention will be better understood with the aid of the description of embodiments given by way of example and illustrated by the accompanying drawings, in which:

[0009] Figure 1 a flow chart showing the steps taken when carrying out the method according to the invention;

[0010] Figure 2 A flow chart showing the steps taken when implementing a method according to an embodiment of the present invention;

[0011] Figure 3 A flow chart showing steps taken when carrying out a method according to a further embodiment of the invention. DETAILED DESCRIPTION

[0012] A method for determining particle characteristics in a fluid sample and / or for determining contamination characteristics of a fluid sample, the method comprising the following steps:

[0013] (a) depositing a metal film on a surface of a substrate to provide a smooth metal surface on the substrate;

[0014] (b) contacting a fluid sample with the metal surface of the substrate;

[0015] (c) removing the fluid sample in contact with the metal surface from the metal surface so that only particles in the fluid sample remain on the metal surface of the substrate;

[0016] (d) depositing a metal layer on the metal surface and on the particles remaining on the metal surface of the substrate, so that each of the particles is provided with a corresponding metal layer and areas of the metal surface without particles are provided with a metal layer, wherein for each particle there is a gap between the metal layer on the particle and the metal layer on the metal surface;

[0017] (e) irradiating the particle and the metal layer on the metal surface with electromagnetic rays, so that the electromagnetic rays are scattered by the metal layer on the particle to generate scattered electromagnetic rays respectively; or irradiating the particle and the metal layer on the metal surface with electromagnetic rays, so that at least a portion of the electromagnetic rays is absorbed by the metal layer on the particle, and another portion of the electromagnetic rays is reflected by the metal surface on the substrate to generate reflected electromagnetic rays;

[0018] (f) receiving the scattered electromagnetic radiation at a photodiode array; or receiving the reflected electromagnetic radiation at a photodiode array;

[0019] (g) forming an image comprising pixels, wherein each pixel in the image corresponds to a respective photodiode in the array, wherein the brightness of each pixel in the image corresponds to the intensity of electromagnetic radiation received by the photodiode corresponding to the pixel;

[0020] (h) processing the formed image to determine characteristics of the particles, and / or processing the formed image to determine contamination characteristics of the fluid sample.

[0021] In one embodiment, the method comprises the following steps:

[0022] (a) depositing a metal film on a surface of a substrate to provide a smooth metal surface on the substrate;

[0023] (b) contacting a fluid sample with the metal surface of the substrate;

[0024] (c) removing the fluid sample in contact with the metal surface from the metal surface so that only particles in the fluid sample remain on the metal surface of the substrate;

[0025] (d) depositing a metal layer on the metal surface and on the particles remaining on the metal surface of the substrate, so that each of the particles is provided with a corresponding metal layer and areas of the metal surface without particles are provided with a metal layer, wherein for each particle there is a gap between the metal layer on the particle and the metal layer on the metal surface;

[0026] (e) irradiating the particle and the metal layer on the metal surface with electromagnetic radiation, so that the electromagnetic radiation is scattered by the metal layer on the particle to generate scattered electromagnetic radiation;

[0027] (f) receiving the scattered electromagnetic radiation at a photodiode array;

[0028] (g) forming a dark field image comprising pixels, wherein each pixel in the image corresponds to a corresponding photodiode in the array, wherein the brightness of each pixel in the image corresponds to the intensity of scattered light received by the photodiode corresponding to the pixel;

[0029] (h) processing the dark field image to determine the particle characteristics and / or processing the dark field image to determine contamination characteristics of the fluid sample.

[0030] Preferably, the scattered electromagnetic radiation is Rayleigh scattered electromagnetic radiation.

[0031] In another embodiment, the method comprises the following steps:

[0032] (a) depositing a metal layer on a surface of a substrate to provide a smooth metal surface on the substrate;

[0033] (b) contacting a fluid sample with the metal surface of the substrate;

[0034] (c) removing the fluid sample in contact with the metal surface from the metal surface so that only particles in the fluid sample remain on the metal surface of the substrate;

[0035] (d) depositing a metal layer on the metal surface and on the particles remaining on the metal surface of the substrate, so that each of the particles is provided with a corresponding metal layer and areas of the metal surface without particles are provided with a metal layer, wherein for each particle there is a gap between the metal layer on the particle and the metal layer on the metal surface;

[0036] (e) irradiating the particles and the metal layer on the metal surface with electromagnetic radiation, so that at least a portion of the electromagnetic radiation is absorbed by the metal layer on the particles and another portion of the electromagnetic radiation is reflected by the metal surface on the substrate to produce reflected electromagnetic radiation;

[0037] (f) receiving the reflected electromagnetic radiation at a photodiode array;

[0038] (g) forming a bright field image comprising pixels, wherein each pixel in the bright field image corresponds to a corresponding photodiode in the array, wherein the brightness of each pixel in the bright field image corresponds to the intensity of light received by the photodiode corresponding to the pixel;

[0039] (h) processing the bright field image to determine the particle characteristics, and / or processing the bright field image to determine contamination characteristics of the fluid sample.

[0040] In a preferred embodiment, the contamination characteristic of the fluid sample determined is the ability of the fluid sample to contaminate a surface. For example, in a preferred embodiment, the contamination characteristic of the fluid sample determined is the statistical probability of the fluid sample contaminating a surface (contaminating a surface includes, but is not limited to, depositing unwanted particles on the surface and / or generating defects on the surface).

[0041] In an embodiment of the present invention, the particles may be insoluble in the fluid sample. In an embodiment of the present invention, the particles may be soluble in the fluid sample. In yet another embodiment, the particles include particles that are insoluble in the fluid sample and particles that are soluble in the fluid sample.

[0042] Step (a) - depositing a metal film on the surface of a substrate:

[0043] Preferably, the step of depositing a metal film on the surface of a substrate to provide a smooth metal surface on said substrate comprises first providing a substrate. In a preferred embodiment, the substrate is preferably rigid; and more preferably, the surface of the substrate will be free of any foreign particles (such as dust or dirt), in other words, the surface of the substrate is preferably clean. If the surface of the substrate is clean, then the step of depositing a metal film on the surface of the substrate preferably comprises depositing a metal film having a thickness greater than 30nm, and more preferably depositing a metal film having a thickness greater than 50nm. It should be understood that the substrate may take any suitable form; in one embodiment, the substrate is a silicon wafer; or alternatively, the substrate may comprise a metal.

[0044] It will be appreciated that any suitable size of substrate may be provided; however, more preferably, the diameter of the substrate will be at least 1 cm in order to avoid edge regions with different surface energies. More preferably, the size of the substrate will be between 2.5 cm (1 inch) and 450 cm (17.7 inches). In yet another embodiment, the substrate may also be a cut portion of a larger substrate (e.g., a segment of a larger wafer). In this case, the size of the cut wafer piece will preferably be greater than 1 cm x 1 cm. The substrate may include silicon, metal, plastic, glass and / or quartz. Most preferably, the substrate will be a silicon wafer.

[0045] The metal film may include any suitable material. The metal film may include a single type of metal or a combination of different metals (such as an alloy). Generally, the composition of the metal film will depend on the composition of the fluid sample. For example, if the fluid sample includes an acid, such as H 2 SO 4 or HCl, then the metal film will preferably comprise gold or platinum; if the fluid sample comprises H 2 SO 4 and / or H 2 O 2 If the sample is a piranha solution, then the metal film will preferably include gold or platinum; if the sample includes ultrapure water (UPW), then the metal film will preferably include gold or platinum. In yet another example, if the fluid sample is not corrosive (e.g., if the sample fluid includes isopropyl alcohol), then the metal film may include a metal such as silver, copper, and / or aluminum.

[0046] Preferably, the metal film further comprises a native oxide layer.

[0047] In an embodiment, the method further includes the step of providing an adhesion layer on the surface of the substrate; and then providing the metal film on the adhesion layer. In this embodiment, the metal film is not applied directly to the surface of the substrate, but is applied to the adhesion layer; therefore, in this embodiment, the metal film is indirectly deposited on the surface of the substrate. Typically, the step of providing an adhesion layer on the surface of the substrate is performed when a metal film is used that is expected to have low adhesion to the surface of the substrate. The adhesion layer may include chromium (Cr) and / or titanium (Ti). For example, the method may further include the step of depositing an adhesion layer including Cr or Ti on the surface of the substrate; and then depositing the metal film on the Cr or Ti adhesion layer. Preferably, the adhesion layer will have a thickness greater than 5nm. It is also preferred to clean the surface of the substrate before depositing the adhesion layer; the step of cleaning the surface of the substrate may include cleaning the surface of the substrate with a glow discharge, cleaning the surface of the substrate with an oxygen plasma, by using a wet cleaning process, cleaning the surface of the substrate with UV light, or by performing any combination of the above cleaning steps.

[0048] It should be understood that the metal film may be deposited on the surface of the substrate (or on the adhesion layer) using any suitable deposition method. In an embodiment, the step of depositing the metal film may include depositing the metal film using physical vapor deposition (PVD); for example, the step of depositing the metal film may include depositing the metal film using electron beam evaporation, thermal evaporation, pulsed laser deposition, cathode arc deposition, or sputtering. In yet another embodiment, the step of depositing the metal film may include depositing the metal film using chemical vapor deposition (CVD). In yet another embodiment, the step of depositing the metal film may include depositing the metal film by electroplating the surface of the substrate with the metal film. In yet another embodiment, the step of depositing the metal film may include depositing the metal film by atomic layer deposition (ALD).

[0049] Typically, the metal film is deposited at a deposition rate between 1-3 angstroms per second; and most preferably, the metal film is deposited at a deposition rate of 2 angstroms per second.

[0050] Preferably, the substrate with the metal film is used substantially immediately after the metal film has been provided on the surface of the substrate in order to limit contamination. In other words, the next step in the process is carried out substantially immediately after the metal film has been provided on the surface of the substrate.

[0051] Typically, after the metal film has been deposited on the surface of the substrate, the substrate is then stored for a period of time before it is used in the subsequent steps of the method of the present invention. When stored, foreign particles may accumulate on the metal film, so after the substrate is removed from storage, the metal film is preferably cleaned before it is used in the subsequent steps of the method of the present invention. Most preferably, after the substrate is removed from storage, the metal film is cleaned using a suitable cleaning method before it is used in the subsequent steps of the method of the present invention (i.e., before the sample fluid is brought into direct contact with the metal surface so that particles in the fluid sample can adhere to the metal surface). The cleaning step preferably does not damage or oxidize the metal film. Most preferably, the metal film on the surface of the substrate is cleaned using air or oxygen plasma; for example, if the metal (such as gold) is stable under short oxygen plasma exposure, the oxygen plasma can be applied to the metal film for 1 second to 15 seconds. It is not recommended to apply oxygen plasma to metals (such as silver) because their surfaces will be chemically altered due to the oxygen plasma.

[0052] Step (b) - contacting the fluid sample with the metal surface of the substrate:

[0053] After the metal film has been deposited directly on the surface of the substrate (or indirectly on the surface of the substrate by depositing the metal film on an adhesion layer provided on the surface of the substrate) to provide a smooth metal surface on the substrate, the step of contacting the fluid sample with the metal surface of the substrate is then carried out. As will be described in more detail below, the step of contacting the fluid sample with the metal surface of the substrate can be carried out in a variety of different ways; for example, a predefined amount of the fluid sample can be dispensed on the metal surface when the metal surface is stationary; or a predefined amount of the fluid sample can be dispensed on the metal surface when the metal surface is rotating; or the substrate can be provided in a chamber containing a gas that defines the fluid sample, so that the metal surface of the substrate is exposed to the gaseous fluid sample (preferably for a predefined length of time).

[0054] The fluid sample may include any suitable composition; the fluid sample may include a gas, a liquid, or a photoresist (a polymer resin that can be dissolved in a solvent). For example, if the fluid sample is a liquid, it may include any one or more of ultrapure water (UPW), alcohol, an acid, an ionic solution, an oxidant, and / or any mixture of these. For example, if the fluid sample is a gas, it may include any one or more of N2, O2, CO2, argon, helium, NH3, or any process gas used in the semiconductor industry. The manner in which the step of contacting the fluid sample with the metal surface of the substrate is carried out may vary depending on whether the fluid sample is a liquid, a photoresist, or a gas.

[0055] In one embodiment, wherein the fluid sample comprises a liquid, the substrate is rotated, and the fluid sample is dispensed onto the metal surface of the substrate while the substrate is rotating. Preferably, the substrate is rotated at a non-zero speed of less than 400 rpm. Most preferably, the sample fluid is dispersed over the entire metal surface of the substrate (typically the rotation of the substrate will disperse the sample fluid over the entire metal surface of the substrate). When the fluid sample contacts the metal surface of the substrate, particles (which define impurities) present in the fluid sample adhere to the metal surface of the substrate. In another embodiment, wherein the fluid sample comprises a liquid, the substrate is stationary (i.e., has a fixed position and does not rotate), and the fluid sample is dispensed onto the metal surface of the substrate. Preferably, the fluid sample dispensed onto the metal surface of the substrate is arranged to cover the entire surface of the metal surface. When the fluid sample contacts the metal surface of the substrate, particles (which define impurities) present in the fluid sample adhere to the metal surface of the substrate.

[0056] In one embodiment, where the fluid sample comprises a gas, the substrate is simply placed in an enclosure containing the gas sample for a predefined length of time. The length of time the substrate is exposed to the gas should preferably reflect the length of time an object in production (such as a silicon wafer for the semiconductor industry) is exposed to the gas sample in the enclosure. In the enclosure, when the metal surface of the substrate is exposed to the gaseous fluid sample, particles (which define impurities) present in the gaseous fluid sample will deposit on the metal surface of the substrate during the predefined time. In another embodiment, in addition to the particles adhering to the metal surface, other molecules may condense or resolidify on the metal surface of the substrate.

[0057] In another embodiment, where the fluid sample comprises a liquid, the substrate is simply immersed in a container containing the fluid sample for a predefined length of time. The predefined length of time that the substrate is exposed to the liquid should preferably reflect the length of time that an object in production (such as a silicon wafer for the semiconductor industry) is exposed to said liquid sample in said container; ideally, the predefined length of time depends on the application, the purity of the liquid and / or the metal surface; most preferably, the predefined length of time will maximize the correlation between particles on the surface and particles in the liquid; most preferably, the predefined length of time is not so short as to have large variations for the same liquid, and not so long that it results in the same number of particles on the metal surface for liquids of different purity levels. During the predefined time that the metal surface of the substrate is immersed in the liquid fluid sample in the container, particles (which define impurities) present in the liquid fluid sample will adhere to the metal surface of the substrate.

[0058] In another embodiment, wherein the fluid sample comprises a liquid, the method comprises the step of arranging the substrate in an inclined orientation; and the step of contacting the fluid sample with the metal surface of the substrate is performed while the substrate is maintained in its inclined orientation. In this embodiment, the fluid sample is dispensed onto the metal surface of the substrate; when the substrate is in the inclined orientation, the fluid sample dispensed onto the metal surface will flow off the metal surface under the influence of gravity.

[0059] In one embodiment, where the fluid sample comprises a photoresist (e.g., a polymer resin preferably dissolved in a solvent), the substrate is rotated and the photoresist is dispensed onto the metal surface of the substrate while the substrate is rotating. Preferably, the substrate is rotated at a non-zero speed of less than 400 rpm. Most preferably, the photoresist is spread over the entire metal surface of the substrate (typically, the rotation of the substrate will cause the photoresist to be spread over the entire metal surface of the substrate).

[0060] In another embodiment, where the fluid sample comprises a photoresist (a polymer resin, preferably dissolved in a solvent), the substrate is stationary (i.e. has a fixed position and does not rotate), and the photoresist is dispensed onto the metal surface of the substrate. Preferably, the photoresist dispensed onto the metal surface of the substrate is arranged to cover the entire surface of the metal surface.

[0061] In another embodiment, wherein the sample fluid comprises a liquid, the step of contacting the fluid sample with the metal surface of the substrate comprises providing the fluid sample onto the metal surface of the substrate by dispensing the fluid sample dropwise from a dispenser tip that is free of contamination (preferably the dispenser tip is composed of a chemically stable plastic such as, for example, perfluoroalkoxyalkane (PFA) or polytetrafluoroethylene (PTFE)). Most preferably, the volume of each droplet dispensed from the tip is within a predefined range (preferably, the predefined range is 1-100 microliters); the volume of each droplet may be controlled using any suitable means known in the art, such as, for example, using a pump (e.g., a syringe pump), a flow meter, a camera to image the droplets, a balance to measure the weight of the droplets, etc. Most preferably, the rate at which successive droplets are dispensed from the dispenser tip onto the metal surface of the substrate is within a predefined range (preferably, the predefined range is 1-240 seconds).

[0062] Step (c) - removing the fluid sample in contact with the metal surface from the metal surface so that only the Particles in the fluid sample are retained on the metal surface of the substrate:

[0063] In one embodiment, wherein the fluid sample is in contact with a metal surface of a substrate while the substrate is rotating (e.g., at a non-zero speed of less than 400 rpm), the step of removing the fluid sample in contact with the metal surface from the metal surface such that only particles in the fluid sample remain on the metal surface of the substrate comprises increasing the rotation speed. Most preferably, the rotation speed of the substrate is increased to a speed in the range of 1000 rpm and 4000 rpm. In this embodiment, most of the liquid fluid sample is removed from the metal surface by centrifugal force, and some is removed by evaporation. After removal of the sample fluid, only particles (which define impurities in the fluid sample) remain adhered to the metal surface of the substrate.

[0064] In another embodiment, wherein the fluid sample is in contact with the metal surface of the substrate when the substrate is stationary (i.e. not rotating), the step of removing the fluid sample in contact with the metal surface from the metal surface so that only particles in the fluid sample remain on the metal surface of the substrate comprises rotating the substrate. Most preferably, the rotational speed of the substrate is increased to a speed within the range of 1000rpm and 4000rpm. This drying method is known as spin drying. During this process, most of the liquid fluid sample is driven out of the metal surface by centrifugal force, and some is evaporated. In this embodiment, most of the liquid fluid sample is removed from the metal surface by centrifugal force, and some is removed by evaporation. After removing the sample fluid, only particles (which define impurities in the fluid sample) remain adhered to the metal surface of the substrate.

[0065] As already mentioned above, in another embodiment, the substrate is arranged in an inclined orientation; and the step of removing the fluid sample in contact with the metal surface from the metal surface so that only particles in the fluid sample remain on the metal surface of the substrate comprises allowing the fluid sample in contact with the metal surface of the substrate to flow out of the metal surface under the influence of gravity. In a variation of this embodiment, the method further comprises providing a dry air flow that blows the fluid sample off the metal surface; preferably a pressurized air gun is used to provide the dry air flow.

[0066] In one embodiment in which the fluid sample comprises photoresist, the step of removing the fluid sample in contact with the metal surface of the substrate comprises removing a majority of the photoresist in contact with the metal surface. The step of removing a majority of the photoresist in contact with the metal surface comprises rotating the substrate at a speed within a predefined range, for example, rotating the substrate at a speed between 1000 rpm and 4000 rpm (either the substrate is rotated from a stationary position to a speed within the predefined range, or the substrate is already rotating and the rotation speed is increased to a speed within the predefined range). After the photoresist has contacted the metal surface of the substrate, rotating the substrate at a speed within the predefined range will ensure that the photoresist is spread over the entire metal surface of the substrate, thereby forming a photoresist layer on the metal surface of the substrate; preferably, the photoresist layer will have a uniform thickness. Most preferably, the photoresist layer will comprise a photoresist resin (which is preferably free of any solvent). In an embodiment, the photoresist layer can be baked on a hot plate to remove solvent from the photoresist layer (the hot plate temperature is preferably between 60 and 160 degrees Celsius).

[0067] The method may further include the step of curing the photoresist layer (curing the photoresist layer changes the chemical structure of the photoresist, such as for example polymerizing the photoresist); the step of curing the photoresist layer may include providing or heating the photoresist layer using electromagnetic radiation incident on the photoresist layer.

[0068] The spinning and curing steps depend on the type of photoresist. Ideally, the same spinning and curing parameters of the semiconductor manufacturing process actually used for the photoresist sample are applied to estimate the contamination of the spinning and curing process used.

[0069] Preferably, the cured layer of photoresist is then removed. In one embodiment, the photoresist layer is removed using a dry process such as applying an oxygen plasma to the photoresist layer. The photoresist layer will include a polymer matrix, and applying an oxygen plasma to the photoresist layer will remove the polymer matrix.

[0070] After the polymer matrix of the photoresist layer has been removed, particles (which define impurities in the photoresist) remain on the metal surface of the substrate. The remaining particles represent the contamination capacity of the original fluid sample (i.e. the original photoresist in contact with the metal surface of the substrate).

[0071] In one embodiment, due to chemical degradation of the polymer structure of the photoresist during its production or storage, particle residues can remain on the metal surface of the substrate after the photoresist layer has been cured (e.g., UV treatment) and subsequently removed (e.g., using TMAH, acetone, or another wet cleaning process to remove the photoresist layer). The most likely cause of such defects originates from unsuccessful cross-linking of the polymer during the UV treatment. In this case, most of the particles deposited on the surface after the overall process are not from particle impurities in the photoresist, but simply the defective polymer structure of the photoresist.

[0072] In another embodiment, a photoresist layer on a metal surface of a substrate is stripped (or removed) using a wet cleaning process; for example, TMAH (tetramethylammonium hydroxide) is applied to the photoresist layer, or acetone is applied to the photoresist layer. Applying TMAH or acetone to the photoresist layer will remove the polymer matrix. After the polymer matrix of the photoresist layer has been removed, particles (which define impurities in the photoresist) remain on the metal surface of the substrate. The remaining particles represent the contamination capacity of the original fluid sample (i.e., the original photoresist in contact with the metal surface of the substrate) and TMAH or acetone.

[0073] In an embodiment, wherein the sample fluid is a gas and the metal surface is exposed to the gas in the housing, the step of removing the fluid sample in contact with the metal surface of the substrate comprises removing the substrate from the housing. Most preferably, the substrate is removed from the housing after a predefined period of time. After the substrate is removed from the housing, particles (which define impurities in the gas) will remain on the metal surface of the substrate; the particles will include particles that have adhered to the metal surface and molecules that have condensed or resolidified onto the metal surface.

[0074] In the embodiment described, wherein the fluid sample comprises a liquid, and the substrate is simply immersed in a container containing the fluid sample for a predefined length of time, the step of removing the fluid sample in contact with the metal surface of the substrate comprises removing the substrate from the container of the fluid sample. After the substrate is removed from the container, particles (which define impurities in the fluid sample) will remain on the metal surface of the substrate. Most preferably, the method further comprises the step of providing a flow of drying gas across the metal surface after the substrate has been removed from the container, so as to dry the metal surface. For example, the drying gas may comprise nitrogen and / or argon. And a pressurized air gun may be used to provide the flow of drying gas.

[0075] In yet another embodiment, the sample fluid comprises a liquid. In this embodiment, the step of contacting the fluid sample with the metal surface of the substrate comprises providing the fluid sample onto the metal surface of the substrate by dispensing the fluid sample dropwise from a dispenser tip that is free of contamination (preferably, the dispenser tip is composed of a chemically stable plastic, such as perfluoroalkoxyalkane (PFA) or polytetrafluoroethylene (PTFE)). Most preferably, the volume of each droplet dispensed from the tip is within a predefined range (preferably, the predefined range is 1-100 microliters); the volume of each droplet can be controlled using any suitable component known in the art, such as, for example, using a pump (e.g., a syringe pump), a flow meter, a camera that images the droplets, a balance that measures the weight of the droplets, etc. Most preferably, the rate at which continuous droplets are dispensed from the dispenser tip onto the metal surface of the substrate is within a predefined range (preferably, the predefined range is 1-240 seconds).

[0076] With reference to the embodiment, wherein the sample fluid comprises a liquid, and wherein the step of contacting the fluid sample with the metal surface of the substrate comprises providing the fluid sample onto the metal surface of the substrate by dispensing the fluid sample dropwise from a dispenser tip (each droplet preferably having a predefined volume), the step of removing the fluid sample in contact with the metal surface of the substrate comprises, evaporating each respective droplet after each respective droplet contacts the metal surface, or allowing a plurality of sample fluid droplets to contact the metal surface and then collectively evaporating the plurality of droplets. In other words, in one embodiment, after each successive droplet is dispensed onto the metal surface of the substrate, the fluid in the droplet evaporates from the metal surface of the substrate. In another embodiment, after each successive droplet is dispensed onto the metal surface of the substrate, the fluid in the droplet is partially evaporated from the metal surface of the substrate (preferably, 65%-90% of the droplet volume is evaporated) before the next droplet is dispensed onto the metal surface of the substrate and partially evaporated (these steps are preferably repeated for each successive droplet dispensed onto the metal surface). Alternatively, in yet another embodiment, after all of the droplets have been dispensed onto the metal surface of the substrate, the fluid in those droplets evaporates from the metal surface of the substrate. In other words, the evaporation of the fluid on the metal surface of the substrate can be completed either after each successive droplet has been dispensed from the dispenser tip onto the metal surface of the substrate, or after all of the droplets have been dispensed from the dispenser tip onto the metal surface of the substrate. After the fluid has evaporated, particles (which in this embodiment are non-volatile particles and molecules; and which define impurities) present in the liquid fluid sample remain adhered to the metal surface of the substrate. The step of evaporating each respective droplet or collectively evaporating a plurality of droplets after each respective droplet contacts the metal surface includes heating the droplet / collective droplets on the metal surface using any suitable heating component. In summary, as described in this paragraph, there are at least three variations of bringing the fluid sample into contact with the metal surface of the substrate dropwise: depositing all droplets and evaporating all droplets together; depositing one droplet, partially evaporating the droplet and then depositing the next droplet, and repeating multiple times; depositing one droplet, completely evaporating the droplet, and then depositing the next droplet, and repeating multiple times.

[0077] In order to promote rapid evaporation of each drop of sample fluid that has been dispensed onto the metal surface of the substrate, or evaporation of the collective droplets of sample fluid that have been dispensed onto the metal surface of the substrate, the temperature of the metal surface is increased (preferably to a value below the boiling point of the liquid sample). The temperature is preferably increased by heat transfer from a heat source located below the substrate; the heat source is preferably arranged in mechanical contact with the surface of the substrate relative to the metal surface. In one embodiment, the heat source comprises a resistive heater. Most preferably, the temperature of the heat source is below the boiling temperature of the fluid sample. In another embodiment, the heat source is configured to emit electromagnetic radiation incident on the metal surface to heat the metal surface and / or the droplets. In one embodiment, the electromagnetic radiation is radiation in the infrared region of the spectrum. In a further embodiment, faster evaporation is achieved by further implementing the step of providing a gas flow on the metal surface of the substrate; the gas preferably comprises dry air, dry N2 or dry argon.

[0078] Most preferably, after a drop of sample fluid has been dispensed onto the metal surface of the substrate, the rate at which the drop evaporates is preferably such that the drop is prevented from contacting the edge of the metal surface. The area of ​​the metal surface over which the dispensed sample fluid drop(s) are spread depends on the total volume of the drop(s) present on the metal surface of the substrate. Preferably, the volume of each drop dispensed and the rate of successive drop dispenses are tuned to ensure that the sample fluid will not spread over more than 80% of the metal surface of the substrate and contact the edge of the metal surface.

[0079] Step (d) - depositing gold on the metal surface and the particles remaining on the metal surface of the substrate The metal layer is provided so that each of the particles is provided with a corresponding metal layer and the areas of the metal surface without particles are provided with A metal layer is provided, wherein for each particle, there exists between the metal layer on the particle and the metal layer on the metal surface gap:

[0080] After the steps of contacting the fluid sample with the metal surface of the substrate and removing the fluid sample from the metal surface so that particles in the sample fluid remain on the metal surface have been performed, a step of depositing a metal layer on the metal surface and the particles already retained on the metal film so that each of the particles already retained on the metal film is provided with a corresponding metal layer, and the area of ​​the metal surface without particles is provided with a metal layer, wherein for each particle, a gap exists between the metal layer on the particle and the metal layer on the metal surface. The gap between each metal layer on each particle and the metal layer on the metal surface will advantageously be used to provide amplified light scattering and / or amplified light absorption. Most preferably, the step (c) of depositing a metal layer on the metal surface and the particles retained on the metal surface of the substrate includes using physical vapor deposition, such as sputtering, pulsed laser deposition, electron beam evaporation or thermal evaporation, to deposit a metal layer on the metal surface and the particles on the metal surface.

[0081] It is important that the thickness of the metal layer provided on the metal surface does not extend above a predefined thickness; the predefined thickness defines the minimum size of a particle that can be detected. For example, if a particle has a radius of 5 nm, and the metal layer provided on the metal surface has a thickness greater than 5 nm, then the particle in question may be completely buried within the metal layer provided on the metal surface of the substrate; as a result, the particle in question will not extend above the metal layer provided on the metal surface of the substrate, and therefore will not scatter light and / or absorb light, and therefore will ultimately not be detected. In order to detect a particle, a portion of the particle must extend above the metal layer provided on the metal surface of the substrate, so that this portion of the particle can be provided with its own corresponding metal layer, and there will be a gap between the metal layer on the particle and the metal layer provided on the metal surface of the substrate. Therefore, the user selects the minimum particle size they wish to detect and ensures that the predefined thickness of the metal layer provided on the metal surface of the substrate is lower than the selected minimum particle size; this will ensure that all particles with a size above the selected minimum particle size will protrude above the metal layer provided on the metal surface of the substrate and may therefore be provided with a corresponding metal layer, and that there will be a gap between the corresponding metal layer on the particles and the metal layer on the metal surface of the substrate.

[0082] Therefore, the thickness of the metal layer provided on the metal surface of the substrate is preferably less than the selected minimum particle size. However, it is preferred that the gap between the metal layer on the corresponding particle and the metal layer on the metal surface of the substrate is small (preferably between 1-5 nm), because a smaller gap leads to a strong hybrid plasma resonance at a lower frequency, with a stronger electric field enhancement at the gap, and ultimately leads to amplified light absorption and scattering, which in turn facilitates particle detection.

[0083] Most preferably, the thickness of the metal layer provided on the metal surface of the substrate will be at most half the smallest particle size; this will ensure that the particles to be detected do not become completely buried in the metal layer provided on the metal surface, and also facilitate the formation of gaps small enough to achieve good amplification of light scattering, thereby allowing more reliable particle detection. For example, a metal layer provided on the metal surface of the substrate having a thickness of between 3-7 nm allows the detection of particles with a size of 10 nm or more.

[0084] The metal layer on the corresponding particle may consist of a single metal particle or a plurality of metal particles (eg, a plurality of closely packed metal nanoparticles).

[0085] Steps (e) to (g): (e) irradiating the particles and the metal layer on the metal surface with electromagnetic radiation so that the particles The electromagnetic rays are scattered by the metal layer on the particles to generate scattered electromagnetic rays respectively; or irradiating with electromagnetic rays The particles and the metal layer on the metal surface enable at least a portion of the electromagnetic radiation to be reflected by the metal on the particles. The metal layer absorbs the electromagnetic radiation, and another part of the electromagnetic radiation is reflected by the metal surface on the substrate to generate reflected electromagnetic radiation. (f) receiving the scattered electromagnetic radiation at a photodiode array; or receiving the reflected electromagnetic radiation at a photodiode array (g) forming an image comprising pixels, wherein each pixel in the image corresponds to a corresponding light in the array The brightness of each pixel in the image corresponds to the brightness of the photodiode corresponding to the pixel. Intensity of electromagnetic radiation:

[0086] Next, the corresponding metal layer on each of the corresponding particles and on the metal surface is irradiated with electromagnetic radiation, so that the electromagnetic radiation is scattered by the metal layer on the particles to generate scattered electromagnetic radiation (preferably, the scattered electromagnetic radiation includes Rayleigh scattered electromagnetic radiation); or the corresponding metal layer on each of the corresponding particles and on the metal surface is irradiated with electromagnetic radiation, so that at least a portion of the electromagnetic radiation is absorbed by the metal layer on the particles, and another portion of the electromagnetic radiation is reflected by the metal surface on the substrate to generate reflected electromagnetic radiation. Then, the scattered electromagnetic radiation is received at the photodiode array; or the reflected electromagnetic radiation is received at the photodiode array. Then there is an image, wherein each pixel in the image corresponds to a corresponding photodiode in the array, wherein the brightness of each pixel in the image corresponds to the intensity of the electromagnetic radiation received by the photodiode corresponding to the pixel.

[0087] In one embodiment, the particles and the metal layer on the metal surface are illuminated with electromagnetic radiation in a dark field setting, and at least a portion of the electromagnetic radiation is scattered by the metal layer on the particles to produce scattered electromagnetic radiation (e.g., Rayleigh scattering). The scattered electromagnetic radiation is received at a photodiode array, and then a dark field image comprising pixels is formed, wherein each pixel in the dark field image corresponds to a corresponding photodiode in the array. The color of each pixel in the dark field image corresponds to the intensity of the scattered electromagnetic radiation received by the photodiode corresponding to the pixel. Photodiodes that receive a higher proportion of scattered electromagnetic radiation will appear brighter than pixels corresponding to photodiodes that receive a smaller proportion of scattered electromagnetic radiation. In other words, each pixel in the dark field image has a color corresponding to the intensity of the scattered electromagnetic radiation received by the corresponding photodiode in the array. Electromagnetic radiation that has been scattered by the metal layer on the particles produces brightly colored pixels in the dark field image. In one embodiment, the dark field image comprises a monochrome image; in another embodiment, the dark field image comprises a multi-color image. The use of a polychromatic image allows information about the resonance frequency of the particle related to the particle size to be determined (the particle has its metal layer on top and has its gap between the metal layer on top of the particle and the metal layer on the metal surface of the substrate). Alternatively, to generate a polychromatic image, the electromagnetic waves, either scattered or reflected, pass through (one or more) wavelength filters before being incident on a photodiode; preferably, a diffraction grating can be used to separate the wavelengths before using a photodiode or a polychromatic photosensor.

[0088] In the above embodiments using dark field images, preferably the electromagnetic radiation is incident on the particles and the metal layer on the metal surface at an angle offset by 90 degrees from the surface plane of the metal layer on the metal surface of the substrate. Preferably, the electromagnetic radiation is provided by illuminating the particles and the metal layer on the metal surface with broadband illumination, for example with white light.

[0089] In another embodiment, the metal layer on the particle and the metal surface is irradiated with electromagnetic radiation in a set bright field, and at least a portion of the electromagnetic radiation is absorbed by the metal layer on the particle, and another portion of the electromagnetic radiation is reflected by the metal surface on the substrate to produce reflected electromagnetic radiation. The reflected electromagnetic radiation is received at a photodiode array, and then a bright field image including pixels is formed, wherein each pixel in the bright field image corresponds to a corresponding photodiode in the array. The color of each pixel in the bright field image corresponds to the intensity of the reflected electromagnetic radiation received by the photodiode corresponding to the pixel. Photodiodes that receive a higher proportion of reflected electromagnetic radiation will have corresponding pixels that will appear brighter than pixels corresponding to photodiodes that receive a lower proportion of reflected electromagnetic radiation. In this embodiment, since a portion of the electromagnetic radiation is absorbed by the metal layer on the particle, this will result in a reduction in the amount of electromagnetic radiation received by some photodiodes.

[0090] Each pixel in the bright field image has a color corresponding to the intensity of reflected electromagnetic radiation received by the corresponding photodiode in the array. Electromagnetic radiation that has been absorbed by the metal layer on the particle will result in darker colored pixels in the bright field image because the photodiodes corresponding to those pixels will have received less electromagnetic radiation due to the absorption of those electromagnetic radiation by the metal layer on the particle. In one embodiment, the bright field image comprises a monochrome image; in another embodiment, the bright field image comprises a multi-color image. The use of a multi-color image allows information about the resonance frequency of the particle to be determined that is related to the particle size. Alternatively, to generate a multi-color image, any electromagnetic wave passes through (one or more) wavelength filters before being incident on the photodiode; preferably, a diffraction grating can be used to separate the wavelengths before using the photodiode or multi-color photosensor.

[0091] In said above embodiments using bright field images, electromagnetic radiation is incident on said particles and said metal layer on said metal surface at an angle preferably substantially 90 degrees to the surface plane of the metal layer on said metal surface of the substrate. Preferably, the electromagnetic radiation is provided by illuminating said particles and said metal layer on said metal surface with broadband illumination, for example with white light.

[0092] In each of the above embodiments, the particles and the metal layer on the metal surface are preferably irradiated with electromagnetic radiation by irradiating the particles and the metal layer on the metal surface with broadband illumination, for example with white light.

[0093] In yet another embodiment, the particles and the metal layer on the metal surface are illuminated with electromagnetic radiation in both a bright field setting and a dark field setting so that a bright field image and a dark field image are formed.

[0094] In a variation of any of the above embodiments, in order to capture a dark field image or a bright field image, the particles and the metal layer on the metal surface are illuminated with electromagnetic radiation, using a plurality of different light sources; in other words, the electromagnetic radiation illuminating the particles and the metal layer on the metal surface is provided by a plurality of different light sources. Most preferably, the plurality of different light sources comprises a plurality of different light sources, each light source having a different frequency band; this allows determining information about the resonance frequency of the particles that is related to the particle size.

[0095] Step (h) - Processing the formed image to determine the particle characteristics and / or processing the formed image to Determine the contamination characteristics of a fluid sample:

[0096] Next, the image (i.e., dark field image and / or bright field image) formed in the above steps is processed. Generally speaking, the step of processing the image is implemented by inputting the image into a predefined model; wherein the predefined model defines different combinations of predefined image characteristics and any predefined characteristics of particles (in the sample fluid or on the surface) associated with each of the different combinations of predefined image characteristics (e.g., size; concentration; type). The model receives an image; extracts characteristics from the received image; and identifies a combination of predefined image characteristics that matches the extracted characteristics; and outputs a specified characteristic associated with the identified combination of predefined image characteristics that matches the extracted characteristics. It should be understood that the predefined model can take any suitable form; in particular, the predefined characteristics of the particles can be any suitable characteristics (e.g., size; concentration; type).

[0097] For example, in one embodiment, the formed image is processed to determine the particle concentration in the fluid sample: In this embodiment, the captured image is input to a predefined model, wherein the predefined model defines different combinations of predefined image characteristics and particle concentrations associated with each of the different combinations of predefined image characteristics. The model receives the image; extracts characteristics from the received image; and identifies a combination of predefined image characteristics that matches the extracted characteristics; and outputs a particle concentration associated with the identified combination of predefined image characteristics that matches the extracted characteristics. The output particle concentration defines the particle concentration on the surface. In another embodiment, the output particle concentration defines the particle concentration in the fluid sample.

[0098] For example, in one embodiment, the model extracts from the received image a characteristic of the number of pixels having a grayscale value above a predefined threshold grayscale value; and determines from the number of pixels above the predefined threshold grayscale value an area occupied by a metal layer on the corresponding particle. The model then derives the particle concentration in the fluid sample from the area.

[0099] In another example, a formed image is processed to determine the size of particles adhered to a metal surface of a substrate: In this embodiment, a captured image is input to a predefined model, wherein the predefined model defines different combinations of predefined image characteristics and particle sizes associated with each of the different combinations of predefined image characteristics. The model receives an image; extracts characteristics from the received image; and identifies a combination of predefined image characteristics that matches the extracted characteristics; and outputs a particle size associated with the identified combination of predefined image characteristics that matches the extracted characteristics. The output particle size defines the size of particles in a fluid sample. Specifically, the output particle size defines the particle size on the metal surface, which defines the particle size in the fluid sample in contact with the metal surface.

[0100] In another example, a formed image is processed to determine the type of particles adhered to a metal surface of a substrate: In this embodiment, a captured image is input to a predefined model, wherein the predefined model defines different combinations of predefined image characteristics and particle types associated with each of the different combinations of predefined image characteristics. The model receives an image; extracts characteristics from the received image; and identifies a combination of predefined image characteristics that matches the extracted characteristics; and outputs a particle type associated with the identified combination of predefined image characteristics that matches the extracted characteristics. The output particle type defines the type of particles in a fluid sample. Specifically, the output particle size defines the particle size on the metal surface, which defines the particle size in the fluid sample in contact with the metal surface.

[0101] In yet another example, a formed image is processed to determine a particle count in a fluid sample: In this embodiment, a captured image is input to a predefined model, wherein the predefined model defines different combinations of predefined image characteristics and a particle count associated with each of the different combinations of predefined image characteristics. The model receives an image; extracts characteristics from the received image; and identifies a combination of predefined image characteristics that matches the extracted characteristics; and outputs a particle count associated with the identified combination of predefined image characteristics that matches the extracted characteristics. The output particle count defines a particle count on a surface. In another embodiment, the output particle concentration defines a particle concentration in a fluid sample.

[0102] In a preferred embodiment, the formed image is processed to estimate the contamination characteristics of the fluid sample. In this embodiment, the captured image is input to a predefined model, wherein the predefined model defines different combinations of predefined image characteristics and contamination characteristics of the fluid sample. The model receives an image; extracts characteristics from the received image; and identifies a combination of predefined image characteristics that matches the extracted characteristics; and outputs the contamination characteristics of the fluid sample associated with the identified combination of predefined image characteristics that matches the extracted characteristics. From the contamination characteristics of the fluid sample, the ability of the fluid sample to contaminate a surface is preferred. Most preferably, the ability of the fluid sample to contaminate a surface is the statistical probability that the fluid sample contaminates a surface (e.g., the surface of a silicon wafer) when the fluid sample contacts the surface.

[0103] Optional reuse of substrate:

[0104] Alternatively, the substrate used in the above steps can be reused. In order to prepare the substrate for reuse to perform the above steps on another fluid sample. However, before the substrate can be reused, the substrate must first be prepared. In order to prepare the substrate for reuse, a further metal film is deposited on the metal layer on the metal surface of the substrate and the corresponding particles that have adhered to the metal surface of the substrate. The new metal film will be used to provide a new metal surface for the substrate, and then steps (b)-(g) can be performed for the another fluid sample.

[0105] According to a further aspect of the present invention, there is further provided an assembly which is operable to perform any of the method embodiments described above, the assembly comprising: a first station comprising a component for depositing a metal film on the surface of a substrate to provide a smooth metal surface on the substrate; a second station comprising a component for causing the fluid sample to flow on the metal surface so that particles in the fluid sample can adhere to the metal surface; a station comprising a component for depositing a metal layer on the metal surface and on particles already adhered to the metal film so that each of the particles already adhered to the metal film is provided with a corresponding metal layer, and the area on the metal surface without particles is provided There is a metal layer, wherein, for each particle, there is a gap between the metal layer on the particle and the metal layer on the metal surface; and a fourth station, comprising a component for irradiating the particle and the metal layer on the metal surface with electromagnetic rays, so that the electromagnetic rays can be scattered by the metal layer on the particle to produce Rayleigh scattering; a photodiode array, which can receive the scattered electromagnetic rays; a component for forming an image including pixels, wherein each pixel in the image corresponds to a corresponding photodiode in the array, and wherein the color of each pixel corresponds to the intensity of the electromagnetic rays received by the corresponding diode; and a component for processing the formed image to determine the characteristics of the particles in the fluid sample.

[0106] Various modifications and variations to the embodiments described herein will be apparent to those skilled in the art without departing from the scope of the invention as defined in the appended claims. Although the invention has been described in conjunction with specific preferred embodiments, it should be understood that the invention claimed should not be unduly limited to such specific embodiments.

Claims

1. A method for determining particle characteristics in a fluid sample and / or for determining contamination characteristics of a fluid sample, the method comprising the following steps, (a) depositing a metal film on a surface of a substrate to provide a smooth metal surface on the substrate; (b) contacting a fluid sample with the metal surface of the substrate; (c) removing the fluid sample in contact with the metal surface from the metal surface so that only particles in the fluid sample remain on the metal surface of the substrate; (d) depositing a metal layer on the metal surface and on the particles remaining on the metal surface of the substrate, so that each of the particles is provided with a corresponding metal layer and areas of the metal surface without particles are provided with a metal layer, wherein for each particle there is a gap between the metal layer on the particle and the metal layer on the metal surface; (e) irradiating the particle and the metal layer on the metal surface with electromagnetic rays, so that the electromagnetic rays are scattered by the metal layer on the particle to generate scattered electromagnetic rays respectively; or irradiating the particle and the metal layer on the metal surface with electromagnetic rays, so that at least a portion of the electromagnetic rays is absorbed by the metal layer on the particle, and another portion of the electromagnetic rays is reflected by the metal surface on the substrate to generate reflected electromagnetic rays; (f) receiving the scattered electromagnetic radiation at a photodiode array; or receiving the reflected electromagnetic radiation at a photodiode array; (g) forming an image comprising pixels, wherein each pixel in the image corresponds to a respective photodiode in the array, wherein the brightness of each pixel in the image corresponds to the intensity of electromagnetic radiation received by the photodiode corresponding to the pixel; (h) processing the formed image to determine characteristics of the particles, and / or processing the formed image to determine contamination characteristics of the fluid sample.

2. The method according to claim 1, wherein the method comprises the following steps, (a) depositing a metal film on a surface of a substrate to provide a smooth metal surface on the substrate; (b) contacting a fluid sample with the metal surface of the substrate; (c) removing the fluid sample in contact with the metal surface from the metal surface so that only particles in the fluid sample remain on the metal surface of the substrate; (d) depositing a metal layer on the metal surface and on the particles remaining on the metal surface of the substrate, so that each of the particles is provided with a corresponding metal layer and areas of the metal surface without particles are provided with a metal layer, wherein for each particle there is a gap between the metal layer on the particle and the metal layer on the metal surface; (e) irradiating the particle and the metal layer on the metal surface with electromagnetic radiation, so that the electromagnetic radiation is scattered by the metal layer on the particle to generate scattered electromagnetic radiation; (f) receiving the scattered electromagnetic radiation at a photodiode array; (g) forming a dark field image comprising pixels, wherein each pixel in the image corresponds to a corresponding photodiode in the array, wherein the brightness of each pixel in the image corresponds to the intensity of scattered light received by the photodiode corresponding to the pixel; (h) processing the dark field image to determine the particle characteristics and / or processing the dark field image to determine contamination characteristics of the fluid sample.

3. The method of claim 2, wherein the scattered electromagnetic radiation comprises Rayleigh scattered electromagnetic radiation.

4. The method according to claim 1, wherein the method comprises the following steps: (a) depositing a metal layer on a surface of a substrate to provide a smooth metal surface on the substrate; (b) contacting a fluid sample with the metal surface of the substrate; (c) removing the fluid sample in contact with the metal surface from the metal surface so that only particles in the fluid sample remain on the metal surface of the substrate; (d) depositing a metal layer on the metal surface and on the particles remaining on the metal surface of the substrate, so that each of the particles is provided with a corresponding metal layer and areas of the metal surface without particles are provided with a metal layer, wherein for each particle there is a gap between the metal layer on the particle and the metal layer on the metal surface; (e) irradiating the particles and the metal layer on the metal surface with electromagnetic radiation, so that at least a portion of the electromagnetic radiation is absorbed by the metal layer on the particles and another portion of the electromagnetic radiation is reflected by the metal surface on the substrate to produce reflected electromagnetic radiation; (f) receiving the reflected electromagnetic radiation at a photodiode array; (g) forming a bright field image comprising pixels, wherein each pixel in the bright field image corresponds to a corresponding photodiode in the array, wherein the brightness of each pixel in the bright field image corresponds to the intensity of light received by the photodiode corresponding to the pixel; (h) processing the bright field image to determine the particle characteristics, and / or processing the bright field image to determine contamination characteristics of the fluid sample.

5. The method of claim 1, wherein the contamination characteristic of the fluid sample is the ability of the fluid sample to contaminate a surface when the fluid sample contacts the surface.

6. A method according to claim 1, wherein the step of processing the formed image to determine the characteristics of particles in the fluid sample includes processing the formed image to determine one or more of the number of particles in the fluid sample; the concentration of particles in the fluid sample; the type of particles in the fluid sample; and / or the size of particles in the fluid sample.

7. The method of claim 1, further comprising the step of rotating the substrate while the fluid sample is in contact with the metal surface of the substrate.

8. The method of claim 1, further comprising the step of evaporating the fluid sample from the metal surface.

9. The method according to claim 1 further includes selecting a minimum size of particles whose characteristics are to be determined; and wherein the step of depositing a metal layer on the particles on the metal surface and the metal film includes depositing a metal layer on the metal surface and the particles, the metal layer having a thickness less than the selected minimum size of the particles.

10. A method according to claim 1, wherein the step of processing the formed image to determine the characteristics of particles in the fluid sample includes inputting the image into a predefined model; wherein the predefined model defines different combinations of predefined image characteristics and predefined characteristics of particles associated with each of the different combinations of predefined image characteristics; extracting characteristics from the image; and identifying combinations of predefined image characteristics that match the extracted characteristics; and outputting the predefined characteristics associated with the identified combinations of predefined image characteristics that match the extracted characteristics.

11. The method of claim 1, further comprising the step of depositing an adhesion layer on the surface of the substrate, and wherein step (a) comprises depositing the metal film on the adhesion layer.

12. The method according to claim 1, wherein the method further comprises depositing a further metal film on the metal layer on the particles and the metal surface of the substrate to provide a new metal surface on the substrate so that the substrate can be reused.

13. The method of claim 12, wherein the method further comprises repeating at least steps (b)-(h) with another fluid sample using the substrate.

14. An assembly operable to perform the method of claim 1, comprising: a first station comprising means for contacting a fluid sample with said metal surface of a substrate; a second station including means for removing said fluid sample in contact with said metal surface from said metal surface such that only particles in said fluid sample remain on the metal surface of the substrate; a third station comprising means for depositing a metal layer on said metal surface and on said particles remaining on said metal surface of the substrate, so that each of said particles is provided with a respective metal layer and areas on said metal surface without particles are provided with a metal layer, wherein for each particle there is a gap between the metal layer on the particle and the metal layer on said metal surface; a fourth station, comprising means for irradiating the particles and the metal layer on the metal surface with electromagnetic rays so that the electromagnetic rays are scattered by the metal layer on the particles to respectively generate scattered electromagnetic rays; or irradiating the particles and the metal layer on the metal surface with electromagnetic rays so that at least a portion of the electromagnetic rays is absorbed by the metal layer on the particles and another portion of the electromagnetic rays is reflected by the metal surface on the substrate to generate reflected electromagnetic rays; A fifth station includes a photodiode array, the photodiode array receiving the scattered electromagnetic radiation; or the photodiode array receiving the reflected electromagnetic radiation; a sixth station comprising means for forming an image comprising pixels, wherein each pixel in the image corresponds to a respective photodiode in the array, wherein a brightness of each pixel in the image corresponds to an intensity of electromagnetic radiation received by the photodiode corresponding to the pixel; A seventh station includes components for processing the formed image to determine characteristics of the particles.

Images