Method for determining which of a plurality of liquids is most likely to cause deposition of particulate impurities on a wafer surface - Patents.com

Abstract

In accordance with the present invention, various methods are provided for determining which of a plurality of liquids has the greatest risk of depositing particulate impurities on the surface of a wafer. The methods include, for a plurality of different test liquids, placing a drop of the test liquid on the surface of a wafer, then spin-drying the wafer, and repeating these steps to increase the number of particulate impurities on the surface of a second wafer. Additionally, a method is provided for determining which of a plurality of filters is best suited for filtering particulate impurities from a liquid.

Description

[Technical field]

[0001] Technical area The present invention relates to a method for determining which of a plurality of liquids has the greatest risk of depositing particulate impurities on a wafer surface, the method comprising, for a plurality of different test liquids, placing a drop of the test liquid on the wafer surface, then spinning the wafer dry, and repeating these steps to increase the number of particulate impurities on the wafer surface. Additionally, a method is provided for determining which of a plurality of filters is best suited for filtering particulate impurities from liquids used in wafer processing. [Background technology]

[0002] 2. Background of the Invention In the processing of wafers, the surface of each wafer typically undergoes multiple cleaning steps. These cleaning steps typically involve depositing a liquid onto the surface of the wafer that is used to clean the surface of the wafer. However, all liquids, including liquids used to clean the surface of the wafer, contain particulate impurities. When such liquids are deposited onto the wafer surface, at least a portion of the particulate impurities in the liquid typically remain on the wafer surface after the wafer is dried. It is desirable to use a liquid that leaves fewer particulate impurities on the wafer surface. For example, two different types of liquids (e.g., two liquids of different compositions) may be used in a cleaning step to clean the surface of the wafer, and when deciding which of the two liquids to use, it is desirable to use the liquid that leaves the fewest number of particulate impurities on the wafer surface. There is no satisfactory method in the prior art for identifying a liquid from among multiple liquids that is likely to leave the fewest number of particulate impurities on the wafer surface.

[0003] Additionally, existing techniques for testing the number of particle impurities deposited on a wafer generally require the use of a wafer that has a low number of particle impurities on its surface to begin with; for example, 12-inch wafers tend to have a low baseline of particle impurities. By using a wafer with a low baseline of particle impurities, any particle impurities found on the wafer surface after applying a liquid to the wafer surface can be attributed to the liquid. However, a problem with this approach is that wafers with a low baseline of particle impurities are very expensive; the high cost of these wafers limits the number of times the technique can be performed. Wafers with a high baseline number of particle impurities on their surface are inexpensive, but existing techniques are not adapted to be performed on wafers with a high baseline number of particle impurities on their surface.

[0004] Additionally, some particulate impurities in the liquid have a high tendency to deposit on the surface of the wafer, while other particulate impurities in the liquid have a low tendency to deposit on the surface of the wafer and therefore remain mobile on the surface of the wafer. In wafer processing, it is desirable to use a liquid having particulate impurities that have a low tendency to deposit on the wafer surface. This is because wafer processing typically includes more than one cleaning step, and if particulate impurities that have deposited on the wafer surface are mobile, they are more likely to be removed in subsequent cleaning steps.

[0005] Furthermore, some liquids used in wafer processing steps will undergo treatment before use. For example, some liquids are filtered using a filter before using the liquid to process a wafer; there are many different types of filters to choose from. When filtering a liquid before using it for wafer processing, it is usually best to use a filter that removes the most particulate impurities from the liquid. The prior art does not provide a satisfactory method for identifying which filter from a plurality of filters will remove the most particulate impurities from the liquid. In other cases, it is necessary to identify which of a plurality of filters will remove a particular type of particulate impurity (e.g., particulate impurities having a size equal to or greater than a predefined threshold; or particulate impurities having a particular composition, e.g., metallic particulate impurities); the prior art does not provide a satisfactory method for identifying which of a plurality of filters will remove the most particulate impurities from the liquid. JP2016-075920 discloses a method for producing an organic process liquid for patterning a chemically amplified resist film. The method includes a step of passing a liquid containing an organic solvent through a filtration device including a liquid inlet, a liquid outlet, and a filtration membrane arranged in a flow path connecting the liquid inlet and the liquid outlet. The absolute value of the difference between the temperature of the liquid at the liquid inlet and the temperature of the liquid at the liquid outlet is 3°C or less, the filtration speed of the liquid in the filtration device is 0.5 L / min / m or more, and the filtration pressure of the liquid in the filtration device is 0.1 MPa or less. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] WO2020 / 229876 [Patent Document 2] JP2016-075920 Summary of the Invention [Problem to be solved by the invention]

[0007] It is an object of the present invention to mitigate or avoid at least some of the disadvantages associated with the prior art. [Means for solving the problem]

[0008] Summary of the Invention According to the invention, this object is achieved by a method comprising the steps as recited in claim 1 and / or by any of the other independent claims. The dependent claims describe advantageous, optional steps which can be implemented in various embodiments of the invention. [Brief description of the drawings]

[0009] BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the present invention will now be described with reference to the following drawings: FIG. 1 is a flow chart illustrating the steps of a method according to an embodiment of the present invention; Figure 2 shows a wafer with four distinct predefined portions of the wafer surface represented by respective boxes; FIG. 3 is a flow chart illustrating steps of a method according to an embodiment of the present invention; FIG. 4a is a table showing the number of particulate impurities measured for each wafer, FIG. 4b is a graph of the measurements shown in the table of FIG. 4a, and FIG. 4c is a table showing the number of particulate impurities added by the liquid sample per drop of test liquid; FIG. 5 shows a wafer having particulate impurities deposited on its surface, along with an image and a Raman spectrum of the particulate impurities, and FIG. 5 shows a first wafer having particulate impurities deposited on its surface derived from a first test liquid, along with an image and a Raman spectrum of the particulate impurities. FIG. 6 is a flow chart illustrating steps of a method according to a further aspect of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Detailed Description of the Invention Embodiments 1 is a flow chart illustrating steps of a method according to an embodiment of the present invention for determining which of a plurality of liquids has the highest risk of depositing particulate impurities on a wafer surface. The method includes the steps of: (a) depositing a droplet of a first test liquid on a surface of a first wafer; (b) performing a spin-dry step that includes spinning the first wafer until the droplet of the first test liquid has dried from the first wafer, leaving any particulate impurities that were in the droplet on a surface of the first wafer; (c) repeating steps (a) and (b) a predetermined number of times to increase the number of particle impurities on the surface of the first wafer, the predetermined number being greater than two; (d) depositing a droplet of a second test liquid on a surface of a second wafer, the second wafer being of the same type as the first wafer; (e) performing a spin-dry step that includes spinning the second wafer until the droplet of the second test liquid has dried from the second wafer, leaving any particulate impurities that were in the droplet on the surface of the second wafer; (f) repeating steps (d) and (e) a predetermined number of times to increase the number of particle impurities on the surface of the second wafer; (g) obtaining measurements indicative of the number of particle impurities on the first wafer and obtaining measurements indicative of the number of particle impurities on the second wafer; (h) First wafer Ha-jo comparing a measurement indicative of the number of particle impurities on the first wafer to a measurement indicative of the number of particle impurities on the second wafer; (i) First wafer Ha-jo If the measured number of particulate impurities on the first wafer is greater than the measured number of particulate impurities on the second wafer, the first liquid is determined to be at greatest risk of depositing particulate impurities on the wafer surface or the second wafer is determined to be at greatest risk of depositing particulate impurities on the wafer surface. Ha-jo A measurement indicating the number of particle impurities on the first wafer is obtained. Number If the measured value is greater than the indicated value, determining that the second liquid poses the greatest risk of depositing particle impurities on the wafer surface.

[0011] In one embodiment, the first test liquid and the second test liquid are different from one another; for example, in one embodiment, the first test liquid has a composition that is different from the composition of the second test liquid; in another embodiment, the first and second test liquids have the same composition but may have been subjected to different processes, e.g., the first test liquid is filtered and the second test liquid is unfiltered, or the first test liquid is filtered through a first filter and the second test liquid is filtered through a second filter (wherein the first filter may be a different type of filter than the second filter).

[0012] In this embodiment, the first test liquid has a composition different from the composition of the second test liquid; the first test liquid corresponds to a first liquid that may be applied to a surface of a wafer (e.g., a 12-inch wafer, etc.) at a wafer processing assembly to clean the wafer surface; and the second test liquid corresponds to a second liquid that may be applied to a surface of a wafer (e.g., a 12-inch wafer, etc.) at a wafer processing assembly to clean the wafer surface. The method illustrated in FIG. 1 may be used to determine whether a liquid corresponding to the first test liquid or a liquid corresponding to the second test liquid should be used to clean a wafer surface at a wafer processing assembly. In general, it is preferred to use a liquid that is likely to deposit only minimal particulate impurities on the wafer surface.

[0013] In the embodiment shown in Figure 1, most preferably the first wafer is a 2 inch wafer and the second wafer is also a 2 inch wafer. In a preferred embodiment, the first wafer is an unpatterned (flat) wafer and the second wafer is also an unpatterned (flat) wafer.

[0014] Step (a) preferably comprises depositing a drop of the first test liquid on the surface of the first wafer, preferably having a volume between 10 μl and 300 μl, most preferably a volume of 50 μl; step (b) performing a spin-drying step preferably comprises spinning the first wafer at a speed between 500 rpm and 10000 rpm, most preferably at a speed of 5000 rpm. Step (c) comprises repeating steps (a) and (b) a predetermined number of times, most preferably at a rate at which steps (a) and (b) are repeated such that there is a time duration between 5 seconds and 60 seconds, most preferably 10 seconds, between each repetition of step (a), i.e. most preferably there is 10 seconds between a drop of the first test liquid arriving at the surface of the first wafer and the next drop of the first test liquid arriving at the surface of the first wafer. Most preferably, step (a) involves depositing a droplet near the center of the first wafer, but offset from the center; i.e., step (a) involves depositing a droplet near the center of the first wafer, but not at the exact direct center of the first wafer (this is so that centrifugal forces will not act on a droplet that is exactly at the center of the first wafer during the spin drying step, thereby allowing the subsequent spin drying step (b) to be performed successfully, as is well understood in the art).

[0015] Step (d) preferably comprises depositing a droplet of a second test liquid on the second wafer, the droplet having a volume equal to the volume of the droplet of the first test liquid deposited on the first wafer in step (a); in other words, in this embodiment, step (d) preferably comprises depositing a droplet of the second test liquid on the surface of the second wafer, the droplet having a volume between 10 and 300 μl, most preferably a volume of 50 μl; and step (e) of performing a spin drying step preferably comprises spinning the second wafer at a speed between 500 and 10,000 rpm, most preferably at a speed of 5,000 rpm. Step (f) comprises repeating steps (d) and (e) a predetermined number of times, most preferably at a rate at which steps (d) and (e) are repeated such that there is a time period between each repetition of step (d) of 5 to 60 seconds, most preferably 10 seconds, i.e., most preferably 10 seconds between the time when a droplet of the second test liquid reaches the surface of the second wafer and the time when the next droplet of the second test liquid reaches the surface of the second wafer. Most preferably, step (d) comprises depositing a droplet close to the center of the second wafer but offset from the center. In other words, step (d) comprises depositing a droplet close to the center of the second wafer but not directly at the exact center of the second wafer (this is to allow the subsequent spin drying step (e) to be performed successfully since centrifugal forces will not act on the droplets that are exactly at the center of the second wafer during the spin drying step, as is well understood in the art).

[0016] Step (g) includes obtaining a measurement indicative of the number of particle impurities on the first wafer and obtaining a measurement indicative of the number of particle impurities on the second wafer. It should be understood that any suitable measurement may be obtained. In one embodiment, step (g) includes predefining a portion of the wafer surface, the number of particle impurities within the predefined portion being indicative of a total number of particle impurities on the wafer surface. Most preferably, the predefined portion of the wafer surface is a portion of the wafer surface that is indicative of the total number of particle impurities on the wafer. Surface2 shows a wafer 20 with four separate predefined portions 24a-24d of the surface of the wafer 20 represented by respective boxes 24a-24d. In this embodiment, each of the predefined portions 24a-24d has an area of ​​7 mm by 7 mm (preferably, each of the predefined portions 24a-24d has an area of ​​at least 10 mm 2 most preferably, each of the predefined portions 24a-24d has an area of ​​100 mm 2 2, the predefined portions 24a-24d include a first portion 24a adjacent to an edge 25 of the wafer 20, a second portion 24b adjacent to but offset from a center 26 of the wafer 20, and two portions 24c, 24d located between the edge 25 of the wafer 20 and the center 26 of the wafer 20. However, it should be understood that while the predefined portions 24a-24d can have any suitable locations, it is important that the locations of the predefined portions 24a-24d remain the same for each wafer.

[0017] In this embodiment, the total number of particle impurities present only in these four distinct predefined portions 24a-24d of the first wafer is measured to obtain a measurement indicative of the number of particle impurities on the first wafer, and similarly, the total number of particle impurities present only in these four distinct predefined portions 24a-24d of the second wafer is measured to obtain a measurement indicative of the number of particle impurities on the second wafer. Therefore, what is important is that the number of particle impurities present in equivalent portions of the first and second wafers is measured. Advantageously, in this embodiment, measuring the total number of particle impurities present only in the four distinct predefined portions 24a-24d of the wafer is quicker and cheaper than measuring the total number of particle impurities present across the entire surface of the wafer, so this embodiment allows for a more cost-effective and faster method.

[0018] There are many methods for measuring the number of particle impurities present on the surface of a wafer known in the art; any of these known methods can be used to measure the number of particle impurities present within the four separate predefined portions 24a-24d of the first and second wafers. For example, WO2020 / 229876 discloses a technique that can be used to measure the number of particle impurities on the surface of a wafer; the technique disclosed in WO2020 / 229876 can be used to measure the number of particle impurities within the four separate predefined portions 24a-24d of the first and second wafers.

[0019] In this embodiment, step (h) may include comparing a measured total number of particle impurities present only in these four distinct predefined portions 24a-24d of the first wafer with a measured total number of particle impurities present only in these four distinct predefined portions 24a-24d of the second wafer; step (i) may include determining that the first liquid has a highest risk of depositing particle impurities on the surface of the wafer if the total number of particle impurities present in these four distinct predefined portions 24a-24d of the first wafer is greater than the total number of particle impurities present in these four distinct predefined portions 24a-24d of the second wafer, or may include determining that the second liquid has a highest risk of depositing particle impurities on the surface of the wafer if the total number of particle impurities present in these four distinct predefined portions 24a-24d of the second wafer is greater than the total number of particle impurities present in these four distinct predefined portions 24a-24d of the first wafer.

[0020] In another embodiment, the step (g) of obtaining a measurement indicative of the number of particle impurities on the first wafer includes measuring the total number of particle impurities present on the entire surface of the first wafer, and the step of obtaining a measurement indicative of the number of particle impurities on the second wafer includes measuring the total number of particle impurities present on the entire surface of the second wafer. There are many methods for measuring the number of particle impurities present on the surface of a wafer known in the art, and any of these known methods can be used to measure the number of particle impurities present on the surfaces of the first and second wafers. For example, WO2020 / 229876 discloses a technique that can be used to measure the number of particle impurities on the surface of a wafer; the technique disclosed in WO2020 / 229876 can be used to measure the total number of particle impurities on the entire surface of each of the first and second wafers.

[0021] In this other embodiment, step (h) may include comparing a measured total number of particle impurities present on the entire surface of the first wafer with a measured total number of particle impurities present on the entire surface of the second wafer; step (i) may include determining that the first liquid poses the highest risk of depositing particle impurities on the surface of the wafer when the total number of particle impurities present on the entire surface of the first wafer is greater than the total number of particle impurities present on the entire surface of the second wafer, or may include determining that the second liquid poses the highest risk of depositing particle impurities on the surface of the wafer when the total number of particle impurities present on the entire surface of the second wafer is greater than the total number of particle impurities present on the entire surface of the first wafer.

[0022] In another embodiment, the method further includes determining whether the concentration of particulate impurities is greater in a first predetermined area adjacent to the center of the wafer than in a second predetermined area adjacent to the edge of the wafer. If the concentration of particulate impurities is greater in the first predetermined area adjacent to the center of the wafer than in the second predetermined area adjacent to the edge of the wafer, this indicates that the test liquid dispensed on the surface of the wafer has a higher proportion of particulate impurities that tend to deposit on the surface of the wafer than particulate impurities that are mobile on the surface of the wafer. Similarly, if the concentration of particulate impurities is greater in the second predetermined area adjacent to the edge of the wafer than in the first predetermined area adjacent to the center of the wafer, this indicates that the test liquid dispensed on the surface of the wafer has deposited a higher proportion of particulate impurities that are mobile on the surface of the wafer than particulate impurities that deposit on the surface of the wafer. This is because it indicates that those particulate impurities present in the second predetermined area adjacent to the center of the wafer have been centrifugal-force-mobilized to their location on the surface of the wafer during the spin-dry step. In a wafer cleaning process, it is often preferred to use a liquid that has a lower deposition of particulate impurities that tend to deposit on the surface of the wafer than particulate impurities that are mobile on the surface of the wafer; this is because wafer cleaning processes often include multiple cleaning steps, and particulate impurities that are mobile on the surface of the wafer are more likely to be removed in a subsequent cleaning step. It will be appreciated that the exact location of the first predetermined area proximate the center of the wafer, and the exact location of the second predetermined area proximate the edge of the wafer, can be selected at the discretion of the user. Most preferably, the first predetermined area proximate the center of the wafer is not located exactly at the center of the wafer, but rather is offset from the exact center of the wafer - since there are no centrifugal forces at the exact center of the wafer during the spin drying step; what is important is that the locations of the first and second predetermined areas remain the same for each wafer, to allow for accurate comparison of different liquids during testing.Most preferably, for wafers having a diameter of 100 mm or more, the first predetermined area is located within 20 mm of the edge of the wafer, and for wafers having a diameter of less than 100 mm. , No. The first predetermined area is located within 10 mm of the edge of the wafer. Most preferably, for wafers with a diameter of 100 mm or more, the second predetermined area is located somewhere between 10 mm from the center of the wafer and 20 mm from the edge of the wafer, and for wafers with a diameter of less than 100 mm, the second predetermined area is located somewhere between 10 mm from the center of the wafer and 10 mm from the edge of the wafer.

[0023] For example, any of the above-described method embodiments may further include defining a first predefined region proximate the center of the wafer and defining a second predefined region proximate the edge of the wafer. Any of the above-described method embodiments may further include measuring a number of particle impurities present in an area on the surface of the first wafer corresponding to the first predefined region to obtain a first center value, and measuring a number of particle impurities present in an area on the surface of the first wafer corresponding to the second predefined region to obtain a first edge value; and comparing the first center value to the first edge value, determining that the first test liquid deposit has a higher proportion of sticky particle impurities than mobile particle impurities if the first center value is greater than the first edge value, and determining that the first test liquid deposit has a higher proportion of mobile particle impurities than sticky particle impurities if the first edge value is greater than the first center value.

[0024] Similarly, any of the embodiments of the method described above may further include measuring the number of particle impurities present in an area on the surface of the second wafer corresponding to the first predetermined area to obtain a second center value; measuring the number of particle impurities present in an area on the surface of the second wafer corresponding to the second predetermined area to obtain a second edge value; and comparing the second center value with the second edge value, and determining that the deposit of the second test liquid has a higher proportion of sticky particle impurities than mobile particle impurities if the second center value is greater than the second edge value, and determining that the deposit of the second test liquid has a higher proportion of mobile particle impurities than sticky particle impurities if the second edge value is greater than the second center value.

[0025] In further embodiments, the method may further include comparing the first central value to the second central value, and / or comparing the first edge value to the second edge value, and / or comparing the first edge value to the second central value, and / or comparing the first edge value to the second central value, and / or comparing the first central value to the second edge value; any one or more of these comparisons may enable additional comparison of characteristics of the particulate impurities from the first and second liquids (in particular the tendency of the particulate impurities to deposit on the wafer surface).

[0026] In another embodiment, the method further includes obtaining an image of the particle impurity on the surface of the first wafer; and obtaining an image of the particle impurity on the surface of the second wafer. Most preferably, the method further includes obtaining a plurality of images, each image being an image of a respective particle impurity on the surface of the first wafer, the images depicting a particle impurity contained in the first test sample, and obtaining a plurality of images, each image being an image of a respective particle impurity on the surface of the second wafer, the images depicting a particle impurity contained in the second test sample. The images are preferably stored in a memory and form a library. A first portion of the library includes an image of each particle impurity contained in the first test sample, and a second portion of the library includes an image of each particle impurity contained in the second test sample. These images can be used as a reference to determine the likely source of particles on the wafer (e.g., a 12-inch wafer): for example, if a test wafer (e.g., a 12-inch wafer) has undergone a cleaning process that includes applying a number of different liquids to the surface of the test wafer, including liquids equivalent to the first and second test liquids (i.e., having the same / similar composition as the first and second test liquids), an image of the particles on the surface of the test wafer can then be captured and the image of the particles can be compared to the images in the library. If the comparison results in the captured image being similar to the image contained in the first part of the library, it can be inferred that the source of the particles was a liquid having the same / similar composition as the first test liquid and applied to the surface of the test wafer during the cleaning process. If the comparison results in the captured image being similar to the image contained in the second part of the library, it can be inferred that the source of the particles was a liquid having the same / similar composition as the second test liquid and applied to the surface of the test wafer during the cleaning process. Thus, the library of images can be used as a reference to identify the likely source of particle impurities on the wafer surface.

[0027] In one embodiment, an image depicting particle impurities in a first test sample is obtained from memory and the image of particles on the surface of the test wafer is compared to the obtained image; if the comparison indicates that the image of particles on the surface of the test wafer is similar to the obtained image, it can be inferred that the source of the particles is a liquid having the same / similar composition as the first test liquid and applied to the surface of the test wafer during the cleaning process. If the comparison indicates that the image of particles on the surface of the test wafer is not similar to the obtained image, an image depicting particle impurities in a second test sample is obtained from memory and the image of particles on the surface of the test wafer is compared to the obtained image; if the comparison indicates that the image of particles on the surface of the test wafer is similar to the obtained image, it can be inferred that the source of the particles is a liquid having the same / similar composition as the second test liquid and applied to the surface of the test wafer during the cleaning process.

[0028] In a further embodiment, the method further comprises obtaining a Raman spectrum of the particle impurities on the surface of the first wafer; and obtaining a Raman spectrum of the particle impurities on the surface of the second wafer. Most preferably, the method further comprises obtaining a plurality of Raman spectra of each particle impurity on the surface of the first wafer, the Raman spectra being indicative of the Raman spectrum of the particle impurities contained in the first test sample, and obtaining a plurality of Raman spectra of each particle impurity on the surface of the second wafer, the Raman spectra being indicative of the Raman spectrum of the particle impurities contained in the second test sample. The Raman spectra are preferably stored in a memory, a first portion of the memory storing the Raman spectrum of each particle impurity contained in the first test sample and a second portion of the memory storing the Raman spectrum of each particle impurity contained in the second test sample. These Raman spectra can be used as a reference to determine the possible source of particles on the wafer: for example, if a test wafer undergoes a cleaning process that includes applying a number of different liquids to the surface of the test wafer, including liquids equivalent to the first and second test liquids (i.e., having the same / similar composition as the first and second test liquids), a Raman spectrum of particle impurities on the surface of the test wafer can then be obtained and the obtained Raman spectrum can be compared to the Raman spectrum stored in the memory. If the comparison shows that the obtained Raman spectrum is similar to the Raman spectrum stored in the first portion of the memory, it can be inferred that the source of the particles is a liquid having the same / similar composition as the first test liquid and applied to the surface of the test wafer during the cleaning process. Similarly, if the comparison shows that the obtained Raman spectrum is similar to the Raman spectrum contained in the second portion of the memory, it can be inferred that the source of the particles is a liquid having the same / similar composition as the second test liquid and applied to the surface of the test wafer during the cleaning process. Thus, the Raman spectrum stored in the memory can be used as a reference to identify the likely source of particle impurities on the wafer surface.

[0029] In a more preferred embodiment, both the image stored in the memory and the Raman spectrum are used to identify a possible source of particle impurities on a surface of a wafer (e.g., a 12-inch wafer). For example, a preferred embodiment can include providing a wafer (e.g., a 12-inch wafer) having particle impurities on a surface of the wafer. In this preferred embodiment, a first liquid corresponding to a first test liquid (i.e., the first liquid has the same composition as, or a very similar composition to, the first test liquid) is applied to the surface of the wafer, and a second liquid corresponding to a second test liquid (i.e., the second liquid has the same composition as, or a very similar composition to, the first test liquid) is applied to the surface of the wafer; the first and second liquids are applied to the surface of the wafer prior to the step of providing the wafer. After the wafer is provided, an image of at least one particle on a surface of the wafer is obtained; a Raman spectrum of the at least one particle is obtained; the obtained image is compared to one or more images of particle impurities on the surface of a first wafer and one or more images of particle impurities on the surface of a second wafer; and the obtained Raman spectrum is compared to the Raman spectrum of the one or more particle impurities on the surface of the first wafer and the Raman spectrum of the one or more particle impurities on the surface of a second wafer (it should be understood that the one or more images of particle impurities on the surface of the first wafer and the one or more images of particle impurities on the surface of the second wafer may be stored in a memory and the method may include the step of obtaining these images from the memory for comparison with the obtained image; it should be understood that the one or more Raman spectra of particle impurities on the surface of the first wafer and the one or more Raman spectra of particle impurities on the surface of the second wafer may be stored in a memory and the method may include the step of obtaining these Raman spectra from the memory for comparison with the obtained Raman spectrum).Then, determining that particles have been deposited on the surface of the wafer by the first liquid if the obtained image and obtained Raman spectrum are more similar to the image and Raman spectrum for particle impurities on the surface of the first wafer than to the image and Raman spectrum for particle impurities on the surface of the second wafer, or determining that particles have been deposited on the surface of the wafer by the second liquid if the obtained image and obtained Raman spectrum are more similar to the image and Raman spectrum for particle impurities on the surface of the second wafer than to the image and Raman spectrum for particle impurities on the surface of the first wafer.

[0030] A user can simply visually inspect the image and Raman spectrum to determine whether the resulting image and the resulting Raman spectrum are more similar to the image and Raman spectrum for the particle impurities on the surface of the first wafer than to the image and Raman spectrum for the particle impurities on the surface of the second wafer, or more similar to the image and Raman spectrum for the particle impurities on the surface of the second wafer than to the image and Raman spectrum for the particle impurities on the surface of the first wafer. Typically, the image and Raman spectrum for the particle impurities on the first wafer will look significantly different from the image and Raman spectrum for the particle impurities on the second wafer, and these differences are very apparent to the naked eye. For example, typical similarities or differences a user may look for when comparing images include, but are not limited to, the following: do the images show a single particle or an aggregate of multiple particles; do the particles in each image have an organic film (an organic film is detected by a local increase in background signal around the particle); what shape are the particles in each image (e.g., do both images depict rod-shaped particles or spherical particles); do the images being compared have similar deposition of watermarks due to evaporation of droplets. For example, if an image of particle impurities on a first wafer surface shows a single rod-shaped particle with an organic film and an image of particle impurities on a second wafer surface shows an aggregate of multiple spherical particles without an organic film, and the resulting image shows a single rod-shaped particle with an organic film, it is clear that the resulting image is more similar to the image of particle impurities on the first wafer surface.In one embodiment, the Raman spectra can be easily compared by overlaying them; for example, the obtained Raman spectrum is overlaid with the Raman spectrum for particulate impurities on the surface of a first wafer, and the obtained Raman spectrum is overlaid with the Raman spectrum for particulate impurities on the surface of a second wafer, and thus a user can determine whether the obtained Raman spectrum is more similar to the Raman spectrum for particulate impurities on the surface of the first wafer or the Raman spectrum for particulate impurities on the surface of the second wafer. As a result, it can be determined by the naked eye whether the obtained image and the obtained Raman spectrum are more similar to the image and Raman spectrum for particulate impurities on the first wafer surface than to the image and Raman spectrum for particulate impurities on the second wafer surface, or more similar to the image and Raman spectrum for particulate impurities on the second wafer surface than to the image and Raman spectrum for particulate impurities on the first wafer surface.

[0031] FIG. 5 shows a wafer 50 having a first particle impurity 51 and a second particle impurity 52 on a surface 53 of the wafer 50. An image of the first particle impurity 51 was obtained to provide a first image 51a, and a Raman spectrum of the first particle impurity was obtained to provide a first Raman spectrum 51b. An image of the second particle impurity 52 was obtained to provide a second image 52a, and a Raman spectrum of the second particle impurity was obtained to provide a second Raman spectrum 52b. To determine the likely source of these particle impurities, the first and second images 51a, 52a and the first and second Raman spectra 52b, 52b are compared to the images and Raman spectra of impurity particles from the first and second test liquids stored in memory.

[0032] 5 also shows a first image 54a, which is an image of a first particle impurity 54 that was on the surface 58 of a first wafer 55, and a first Raman spectrum 54b of said first particle impurity that was on the surface of the first wafer 55. The first image 54a and the first Raman spectrum 54b were obtained from memory. Figure 5 also includes a second image 57a, which is an image of a second particle impurity 56 that was on the surface 58 of the first wafer 55, and a second Raman spectrum of the second particle impurity that was on the surface 58 of the first wafer 55. 57b A second image 57a and a second Raman spectrum 57b are also obtained from memory.

[0033] First and second images 51a, 52a and first and second Raman spectra 51b , 52b with the images 54a, 57a and Raman spectra 54b, 57b obtained from the memory, thereby obtaining the first and second images 51a, 52a and the first and second Raman spectra. 51b It can be seen by the naked eye that the images 54a, 57a and Raman spectra 54b, 57b obtained from memory are similar to the images 54a, 57a and Raman spectra 54b, 57b obtained from memory. It can therefore be concluded that the source of the first particle impurity 51 and the second particle impurity 52 on the surface 53 of the wafer 50 was a liquid that was applied to the surface 53 of the wafer 50 during a processing step and that had a composition equal to or similar to that of the first test liquid.

[0034] 3 is a flow chart illustrating steps in a method according to a further embodiment of the invention for determining which of a plurality of liquids is at greatest risk of depositing particulate impurities on a wafer surface, the method including the steps of: (a) depositing a droplet of a first test liquid on a surface of a first wafer; (b) performing a spin-dry step that includes spinning the first wafer until the droplet of the first test liquid has dried from the first wafer, leaving any particulate impurities that were in the droplet on a surface of the first wafer; (c) repeating steps (a) and (b) a first predetermined number of times to increase the number of particle impurities on the surface of the first wafer, the predetermined number being greater than two. (d) placing a droplet of the first test liquid on a surface of a second wafer, the second wafer being of the same type as the first wafer; (e) performing a spin-dry step including spinning the second wafer until the droplet of the first test liquid has dried from the second wafer, and any particulate impurities that were in the droplet are removed from the second wafer. Second steps remaining on the surface of the wafer; (f) repeating steps (d) and (e) a second predetermined number of times to increase the number of particle impurities on the surface of the second wafer, the second predetermined number being greater than the first predetermined number of times. (g) depositing a droplet of the second test liquid on a surface of a third wafer, the third wafer being of the same type as the first wafer; (h) performing a spin-dry step that includes spinning the third wafer until the droplet of the second test liquid has dried from the third wafer, with any particulate impurities that were in the droplet remaining on the surface of the third wafer; (i) repeating steps (g) and (h) the first predetermined number of times to increase the number of particle impurities on the surface of the third wafer; (j) depositing a droplet of the second test liquid on a surface of a fourth wafer, the fourth wafer being of the same type as the first wafer; (k) performing a spin-dry step that includes spinning the fourth wafer until the droplet of the second test liquid has dried from the fourth wafer, leaving any particulate impurities that were in the droplet on the surface of the fourth wafer; (l) repeating steps (j) and (k) a second predetermined number of times; Fourth increasing the number of particle impurities on a surface of the wafer; (m) obtaining a measurement indicative of the number of particle impurities on a first wafer; obtaining a measurement indicative of the number of particle impurities on a second wafer; obtaining a measurement indicative of the number of particle impurities on a third wafer; and obtaining a measurement indicative of the number of particle impurities on a fourth wafer.

[0035] In one embodiment, the first test liquid and the second test liquid are different from each other. For example, in some embodiments, the first test liquid has a different composition than the composition of the second test liquid; in other embodiments, the first and second test liquids have the same composition but may be subjected to different processing, e.g., the first test liquid is filtered and the second test liquid is unfiltered, or the first test liquid is filtered through a first filter and the second test liquid is filtered through a second filter.

[0036] In this embodiment, the first test liquid has a composition different from that of the second test liquid; the first test liquid corresponds to a first liquid that can be applied to a surface of a wafer (e.g., a 12-inch wafer, etc.) in a wafer-processing-assembly to clean the wafer surface; and the second test liquid corresponds to a second liquid that can be applied to a surface of a wafer (e.g., a 12-inch wafer, etc.) in a wafer-processing-assembly to clean the wafer surface. For example, processing of a wafer (e.g., a 12-inch wafer, etc.) in a wafer-processing-assembly can include one or more cleaning steps that include applying a liquid to the surface of the wafer to clean the wafer surface; the cleaning step can be performed in one of two ways, namely, by applying the first liquid to the surface of the wafer or by applying the second liquid to the surface of the wafer. The method shown in FIG. 3 can be used, for example, to determine whether the first liquid or the second liquid should be used to clean the surface of a test wafer. Typically, it is preferable to use a liquid that is most likely to cause the least deposition of particulate impurities on the wafer surface.

[0037] It should be understood that the first and second test liquids may be equivalent to any liquid that is applied to the surface of the wafer at any stage in the processing of the wafer, and the first and second test liquids are not limited to being equivalent only to liquids used to clean the surface of the wafer.

[0038] In the embodiment shown in Figure 3, most preferably, each of the first, second, third and fourth wafers is a respective 2 inch wafer. In a preferred embodiment, each of the first, second, third and fourth wafers is an unpatterned (flat) wafer.

[0039] Step (a) preferably comprises depositing a droplet of the first test liquid, having a volume between 10 μl and 300 μl, most preferably a volume of 50 μl, on the surface of the first wafer; step (b) of performing a spin-drying step preferably comprises spinning the first wafer at a speed between 500 rpm and 10,000 rpm, most preferably at a speed of 5,000 rpm. Step (c) comprises repeating steps (a) and (b) a first predetermined number of times. In this embodiment, step (c) comprises repeating steps (a) and (b) "49" times (i.e., the first predetermined number is "49"), so that a total of "50" droplets of the first test liquid are deposited (and spin-dried) on the surface of the first wafer.

[0040] Most preferably, the rate at which steps (a) and (b) are repeated is such that there is a time duration between each repetition of step (a) of 5 seconds to 60 seconds, most preferably 10 seconds, i.e., preferably 10 seconds between a droplet of the first test liquid arriving on the surface of the first wafer and the next droplet of the first test liquid arriving on the surface of the first wafer. Most preferably, step (a) involves depositing a droplet close to the center of the first wafer but offset from the center; in other words, step (a) involves depositing a droplet close to the center of the first wafer but not directly at the exact center of the first wafer (this is so that centrifugal forces will not act on a droplet that is exactly at the center of the first wafer during the spin drying step, allowing the subsequent spin drying step (b) to be performed successfully, as is well understood in the art).

[0041] Step (d) preferably comprises depositing a droplet of the first test liquid on the second wafer, the droplet having a volume equal to the volume of the droplet of the first test liquid deposited on the first wafer in step (a); in other words, in this embodiment, step (d) preferably comprises depositing a droplet of the first test liquid on the surface of the second wafer, the droplet having a volume between 10 μl and 300 μl, most preferably a volume of 50 μl. Step (e) of performing a spin drying step comprises spinning the second wafer at a speed between 500 rpm and 10000 rpm, most preferably 5000 rpm. Step (f) comprises repeating steps (d) and (e) a second predetermined number of times, and in this embodiment, step (f) comprises: (d) and (e) a total of 150 drops of the first test liquid are deposited (and spun-dried) on the surface of the second wafer, thereby including repeating the above process 149 times (i.e., the second predetermined number is 149 times).

[0042] Most preferably, the rate at which steps (d) and (e) are repeated is such that there is a time duration between each repetition of step (d) of 5 seconds to 60 seconds, most preferably 10 seconds. Most preferably, step (d) includes depositing a droplet close to but offset from the center of the second wafer. In other words, step (d) includes depositing a droplet close to but not directly at the exact center of the second wafer.

[0043] Step (g) preferably comprises depositing a droplet of a second test liquid on the third wafer, the droplet having a volume equal to the volume of the droplet of the first test liquid deposited on the first wafer in step (a); in other words, in this embodiment, step (g) preferably comprises depositing a droplet of the second test liquid on the surface of the third wafer, the droplet having a volume between 10 μl and 300 μl, most preferably a volume of 50 μl. Step (h) of performing a spin drying step comprises spinning the third wafer at a speed between 500 rpm and 10000 rpm, most preferably 5000 rpm. Step (i) includes repeating steps (g) and (h) the first predetermined number of times, which in this embodiment is 49 times, and therefore step (i) includes repeating steps (g) and (h) a further 49 times, resulting in a total of 50 drops of the second test liquid being deposited (and spun-dried) onto the surface of the third wafer.

[0044] Most preferably, the rate at which steps (g) and (h) are repeated is such that there is a time duration between each repetition of step (g) of 5 seconds to 60 seconds, most preferably 10 seconds, i.e., preferably 10 seconds from when a droplet of the second test liquid arrives on the surface of the third wafer to when the next droplet of the second test liquid arrives on the surface of the third wafer. Most preferably, step (g) includes depositing a droplet close to but offset from the center of the third wafer. In other words, step (g) includes depositing a droplet close to but not directly on the exact center of the third wafer.

[0045] Step (j) preferably comprises depositing on the fourth wafer a droplet of the second test liquid having a volume equal to the volume of the droplet of the first test liquid deposited on the first wafer in step (a); in other words, in this embodiment, step (j) preferably comprises depositing on the surface of the fourth wafer a droplet of the second test liquid having a volume between 10 μl and 300 μl, most preferably 50μl Step (k) of performing a spin drying step includes spinning the fourth wafer at a speed between 500 rpm and 10,000 rpm, most preferably at a speed of 5,000 rpm.

[0046] Step (l) includes repeating steps (j) and (k) a second predetermined number of times, which in this embodiment is 149 times, and thus step (l) includes repeating steps (j) and (k) a further 149 times, resulting in a total of 150 drops of the second test liquid being deposited (and spun-dried) on the surface of the fourth wafer.

[0047] Most preferably, the rate at which steps (j) and (k) are repeated is such that there is a time duration between each repetition of step (j) of between 5 seconds and 60 seconds, most preferably 10 seconds, i.e., preferably 10 seconds between when a droplet of the second test liquid arrives on the surface of the fourth wafer and when the next droplet of the second test liquid arrives on the surface of the fourth wafer. Most preferably, step (j) involves depositing a droplet close to but offset from the center of the fourth wafer. In other words, step (j) involves depositing a droplet close to but not directly at the exact center of the fourth wafer.

[0048] At this stage, the wafer includes: a first wafer having a total of "50" drops of the first test liquid deposited on its surface and spun dry; a second wafer having a total of "150" drops of the first test liquid deposited on its surface and spun dry; a third wafer having a total of "50" drops of the second test liquid deposited on its surface and spun dry; and a fourth wafer having a total of "150" drops of the second test liquid deposited on its surface and spun dry.

[0049] Step (m) is then performed, and measurements indicative of the number of particle impurities on the first wafer are obtained, measurements indicative of the number of particle impurities on the second wafer are obtained, measurements indicative of the number of particle impurities on the third wafer are obtained, and measurements indicative of the number of particle impurities on the fourth wafer are obtained. It should be understood that these measurements can be obtained at any suitable step of the method; for example, the measurements indicative of the number of particle impurities on the first wafer can be obtained after step (c) before performing step (d), the measurements indicative of the number of particle impurities on the second wafer can be obtained after step (f) before performing step (g), the measurements indicative of the number of particle impurities on the third wafer can be obtained after step (i) before performing step (j), and the measurements indicative of the number of particle impurities on the fourth wafer can be obtained after step (l). It should also be understood that the measurements indicative of the number of particle impurities on the first wafer, the measurements indicative of the number of particle impurities on the second wafer, the measurements indicative of the number of particle impurities on the third wafer, and the measurements indicative of the number of particle impurities on the fourth wafer can be obtained using any suitable technique known in the art. There are many methods for measuring the number of particle impurities present on the surface of a wafer known in the art, and any of these known techniques can be used to obtain said measurements.For example, WO2020 / 229876 discloses a technique that can be used to measure the number of particle impurities on the surface of a wafer; the technique disclosed in WO2020 / 229876 can be used to obtain said measurements.

[0050] In a preferred embodiment, step (m) includes predefining a portion of the wafer surface, the number of particle impurities within the predefined portion being indicative of the total number of particle impurities on the wafer surface. Most preferably, the predefined portion of the wafer surface is a portion of the wafer surface that is indicative of the total number of particle impurities on the wafer surface. Surface 2 shows a wafer 20 with four distinct predefined portions 24a-24d of the surface of the wafer 20 represented by respective boxes 24a-24d. In this embodiment, each of the predefined portions 24a-24d has an area of ​​7 mm by 7 mm (preferably, each of the predefined portions 24a-24d has an area of ​​at least 10 mm 2 most preferably, each of the predefined portions 24a-24d has an area of ​​100 mm 2 2, the predefined portions 24a-24d include a first portion 24a adjacent to an edge 25 of the wafer 20, a second portion 24b adjacent to but offset from a center 26 of the wafer 20, and two portions 24c, 24d located between the edge 25 of the wafer 20 and the center 26 of the wafer 20. However, it should be understood that while the predefined portions 24a-24d can have any suitable locations, it is important that the locations of the predefined portions 24a-24d remain the same for each wafer.

[0051] In this embodiment, to obtain a measurement indicative of the number of particulate impurities on a first wafer, the total number of particulate impurities present only in these four distinct predefined portions 24a-24d of the first wafer is determined; to obtain a measurement indicative of the number of particulate impurities on a second wafer, the total number of particulate impurities present only in these four distinct predefined portions 24a-24d of the second wafer is determined; to obtain a measurement indicative of the number of particulate impurities on a third wafer, the total number of particulate impurities present only in these four distinct predefined portions 24a-24d of the third wafer is determined; to obtain a measurement indicative of the number of particulate impurities on a fourth wafer, the total number of particulate impurities present only in these four distinct predefined portions 24a-24d of the fourth wafer is determined. What is important is that the number of particulate impurities present in a substantial portion of the first, second, third and fourth wafers is determined. Advantageously, measuring the number of particle impurities present within four separate predefined portions 24a-24d of the wafer is quicker and cheaper than measuring the total number of particle impurities present across the entire surface of the wafer, thereby enabling a more cost-effective and faster methodology.

[0052] There are many methods for measuring the number of particle impurities present on the surface of a wafer known in the art; any of these known methods can be used to measure the number of particle impurities present within the four separate predefined portions 24a-24d of the first, second, third and fourth wafers. For example, WO2020 / 229876 discloses a technique that can be used to measure the number of particle impurities on the surface of a wafer; the technique disclosed in WO2020 / 229876 can be used to measure the number of particle impurities within the four separate predefined portions 24a-24d of the first, second, third and fourth wafers.

[0053] In a preferred embodiment, the method further includes measuring an average number of particle impurities deposited on the wafer surface per drop for each of the first and second test liquids. The step of measuring the average number of particle impurities deposited on the wafer surface per drop may include, for each wafer, subtracting a baseline (which is a value representative of the number of particles already present on the wafer surface before the test liquid is dropped onto the wafer surface) from the obtained measurements indicating the number of particle impurities on the wafer surface by dividing by the number of drops of test liquid placed on the wafer to provide a median average value; then, averaging all of the median averages for the wafer.

[0054] Specifically, in the above embodiment, the method may include determining an average number of particle impurities deposited on the surface of the wafer per drop for the first test liquid by: subtracting a baseline (which is a number representative of the number of particles already present on the surface of the first wafer before the test liquid is applied to the surface of the first wafer) from the resulting measurements indicative of the number of particle impurities on the first wafer to provide a first intermediate value, and dividing the first intermediate value by "50" (the total number of drops of the first test liquid applied to the first wafer) to obtain a first intermediate average value; and The first intermediate mean is then calculated by subtracting the first intermediate mean (which is a number representative of the number of particles already present on the surface of the second wafer before the test liquid was dropped onto the surface of the second wafer) from the resulting measurement indicating the number of particle impurities on the second wafer to provide a second intermediate value; the second intermediate value is divided by "150" (the total number of droplets of the first test liquid dropped onto the second wafer) to obtain a second intermediate average; and the average of the first intermediate average and the second intermediate average is then calculated to obtain the average number of particle impurities that the first test liquid will deposit on the wafer surface, i.e., ("first intermediate mean" + "second intermediate average") / 2).

[0055] Similarly, the method can include determining an average number of particle impurities deposited on the surface of the wafer per drop for the second test liquid by: subtracting a baseline (which is a number representative of the number of particles already present on the surface of the third wafer before the test liquid is dropped onto the surface of the third wafer) from the resulting measurements indicative of the number of particle impurities on the third wafer to provide a third intermediate value; and dividing the third intermediate value by "50" (the total number of drops of the second test liquid placed on the third wafer) to obtain a third intermediate average; and dividing the fourth wafer by "50" (the total number of drops of the second test liquid placed on the third wafer) to obtain a third intermediate average. Subtract the baseline (which is a number representative of the number of particles already present on the surface of the fourth wafer before the test liquid was dropped onto the surface of the fourth wafer) from the resulting measurement showing the number of particle impurities on the fourth wafer to provide a fourth intermediate value, and divide the fourth intermediate value by "150" (the total number of droplets of the second test liquid dropped onto the fourth wafer) to obtain a fourth intermediate average; then obtain the average number of particle impurities deposited on the wafer surface by the second test liquid by taking the average of the third and fourth intermediate averages, i.e., ("third intermediate average" + "fourth intermediate average") / 2). It is understood that in the present invention, there can be different baseline values ​​for different wafers; in this embodiment, the first, second, third and fourth wafers are all of the same type, and therefore, in this embodiment, the baseline value for each wafer was considered to be the same; however, in another embodiment, the baseline value can differ between wafers (e.g., where the first, second, third and fourth are of different types), in which case the appropriate baseline value would be used when performing the above calculations to determine the average number of particle impurities.

[0056] Most preferably, the method further comprises determining that the first liquid has a high risk of depositing particulate impurities on the surface of the wafer if the average number of particulate impurities deposited on the surface of the wafer by the first test liquid per drop is greater than the average number of particulate impurities deposited on the surface of the wafer by the second test liquid per drop, or determining that the second liquid has a high risk of depositing particulate impurities on the wafer surface if the average number of particulate impurities deposited on the wafer surface by the second test liquid per drop is greater than the average number of particulate impurities deposited on the wafer surface by the first test liquid per drop.

[0057] Although the above embodiment tests a first and a second test liquid, it should be understood that any number of liquids can be used in the embodiments of the present invention. For example, the embodiment shown in FIG. 3 is used to determine whether the first test liquid or the second test liquid poses the highest risk of depositing particle impurities on the surface of the wafer, but it should be understood that the method can be performed for any number of test liquids. For example, in the embodiment of FIG. 3, if it is desired to test a third test liquid, the method further includes placing one drop of the third test liquid on a fifth wafer and spin-drying the fifth wafer, and repeating these steps until a total of 50 drops of the third liquid have been placed on the surface of the fifth wafer; and further includes placing one drop of the third test liquid on a sixth wafer, spin-drying the sixth wafer, and repeating these steps until a total of 250 drops of the third liquid have been placed on the surface of the sixth wafer. The same steps described above for the first and second test liquids are then performed for the third test liquid, and the same steps described above for the first, second, third and fourth wafers are then performed for the fifth and sixth wafers.

[0058] Also, most preferably, in the embodiment shown in Figure 3, the number of wafers used corresponds to the number of different sets of droplets deposited on the wafer; for example, in the embodiment shown in Figure 3, for each test liquid, two different sets of droplets of the test liquid are deposited on the surface of the wafer. For example, in the embodiment shown in Figure 3, for each test liquid, two different sets of droplets of the test liquid are deposited on the wafer surface; i.e., a first set of 50 droplets and a second set of 150 droplets, and thus, for each test liquid, two wafers are used; one wafer receives 50 droplets of that test liquid and a second wafer receives 150 droplets of that test liquid. It should be understood that the method of the present invention can include any number of sets of drops; for example, in the embodiment of Figure 3, if the third set of drops (e.g., 250 drops) is used, the method would further include depositing 250 drops of the first test liquid on the fifth wafer and spin-drying the fifth wafer after each drop, and depositing 250 drops of the second test liquid on the sixth wafer and spin-drying the sixth wafer after each drop. The same steps as described above for the first, second, third and fourth wafers would then be performed for the fifth and sixth wafers.

[0059] FIG. 4a is a table showing measurements indicating the number of particle impurities measured in step (m) for each wafer: a first wafer received "50" drops of the first test liquid on its surface, and when step (m) was performed, a measurement of "1891" particle impurities was obtained; a second wafer received "150" drops of the first test liquid on its surface, and when step (m) was performed, a measurement of "3517" particle impurities was obtained; a third wafer received "50" drops of the second test liquid on its surface, and when step (m) was performed, a measurement of "826" particle impurities was obtained; and a fourth wafer received "150" drops of the second test liquid on its surface, and when step (m) was performed, a measurement of "1631" particle impurities was obtained.

[0060] FIG. 4b is a graph of measurements showing the number of particle impurities measured (along the y-axis) in step (m) versus the number of droplets (along the x-axis); in other words, FIG. 4b is a graph of the measurements shown in the table of FIG. 4a: in the graph of FIG. 4b, a first square 41a shown on the graph shows the number of particle impurities (i.e., "1891") measured on the first wafer surface in step (m) after "50" drops of the first test liquid were placed on the first wafer and spun dry; a second square 41b shown on the graph shows the number of particle impurities (i.e., "1891") measured on the first wafer surface in step (m) after "10" drops of the first test liquid were placed on the first wafer and spun dry; a first circle 41c shown on the graph represents the number of particle impurities measured to be present on the surface of a second wafer after "50" drops of the second test liquid are deposited on the third wafer and spun dry in step (m) ("3517"); a first circle 41b shown on the graph represents the number of particle impurities measured to be present on the surface of a third wafer after "50" drops of the second test liquid are deposited on the third wafer and spun dry in step (m) ("826"); a second circle 41d shown on the graph represents the number of particle impurities measured to be present on the surface of a fourth wafer after "150" drops of the second test liquid are deposited on the fourth wafer and spun dry in step (m) ("1631").

[0061] The graph of FIG. 4b also shows a baseline 42, which may be an estimate of the number of particle impurities that were present on the surface of the first and / or second test wafers before any of the first and / or second test liquids were deposited. The baseline 42 may be obtained from measurements of the number of particle impurities performed in a calibration step. The baseline 42 may be determined in a calibration step, which involves measuring the number of particle impurities over a 1 cm area on the surfaces of a number of different wafers (e.g., a number of 2 inch wafers, and / or a number of unpatterned (flat) wafers) that have no liquid deposited on their respective surfaces. 2 The number of particle impurities per cm 2 This involves determining the average number of particle impurities per cm 2The average number of particle impurities per cm 2 can define a baseline 42. For example, in one embodiment, the baseline 42 can be determined by providing 10 wafers; measuring the number of particle impurities on the surface of each of the "10" wafers; then measuring the number of particle impurities on the surface of each of the "10" wafers; 2 determining the average number of particle impurities per cm 2 The average number of particle impurities per cm 2 of the surface of the respective wafer is defined as the baseline 42. In another embodiment, the baseline 42 is determined by providing ten wafers, each of which is measured over a 1 cm 2 area of ​​the surface of the respective wafer. 2 This is determined in a calibration step that involves determining the number of particle impurities per cm 2 The determined maximum number of particle impurities per cm 2 defines the baseline 42. In another embodiment, the baseline 42 is determined by providing ten wafers, each of which is measured over a 1 cm 2 area of ​​the surface of the respective wafer. 2 This is determined in a calibration step that involves determining the number of particle impurities per cm 2 The determined minimum number of particle impurities per cm of the wafer surface defines the baseline 42. 2 It should be understood that the number of particle impurities per unit area can be determined using any suitable technique known in the art (such as the techniques disclosed in WO2020 / 229876).

[0062] As is evident from the graph of FIG. 4b, the method of the present invention allows the number of particulate impurities deposited by the test liquid being tested to be orders of magnitude greater than the baseline number of particulate impurities, which makes the test liquids easier to compare with each other and allows for more accurate comparison of the test liquids; for example, prior art techniques only provide particle impurity measurement numbers that are close to the baseline, making comparison of the test liquids more difficult as differences in measured particle impurities for different test liquids may be due to variations in the baseline number of particle impurities present on the wafer rather than due to particle impurities originating from the test liquid.

[0063] 4c is a table showing the number of particle impurities per drop (i.e., the number of particle impurities added to the surface of the first and second wafers by the first and second test liquids per drop). Each of said number of particle impurities per drop is determined by the following general formula: ("Total number of particles detected on the wafer (shown in FIG. 4a)"-"Baseline 42") / "Number of droplets"). In this embodiment, baseline 42 has a value of "131" (as shown in FIG. 4b). Specifically, the table in FIG. 4c shows: a first intermediate average value of “35.2” (determined by (“1891” - “131”) / 50 = “35.2”); a second intermediate average value of “22.5” (determined by (“3517” - “131”) / 150 = “22.5”); and an average number per drop of particulate impurities deposited by the first test liquid on the wafer surface of “29.8” (determined by (“35.2” + “22.5”) / 2 (i.e., (“first intermediate average” + “second intermediate average”) / 2). The table of FIG. 4c further shows the third intermediate average "13.6" (determined by ("826"-"131") / 50="13.9"), and the fourth intermediate average "10" (determined by ("1631"-"131") / 150="10"), and the average number of particle impurities per drop that the second test liquid deposits on the wafer surface "12" as determined by ("13.9"+"10") / 2 (i.e., ("third intermediate average"+"fourth intermediate average") / 2). From these values ​​in the table of FIG. 4c, the user can determine that the first test liquid and / or a liquid having a composition the same as or similar to that of the first test liquid has a higher risk of depositing particle impurities on the wafer surface than the second test liquid and / or a liquid having a composition the same as or similar to that of the second test liquid.It should be understood that in the present invention, the baseline 42 value may be different for different wafers; in this embodiment, the first, second, third and fourth wafers are all of the same type, and therefore, in this embodiment, the baseline 42 value for each wafer is considered to be the same ("131"); however, in other embodiments, the baseline 42 value may vary between wafers (such as different types of wafers), and the appropriate baseline 42 value is used when performing the above calculations to determine the average number of particle impurities.

[0064] As mentioned above, the first test liquid and the second test liquid can take any suitable form. In one embodiment, the first test liquid and the second test liquid have the same composition, but the first test liquid is filtered before performing the method of the present invention, whereas the second test liquid is not filtered (i.e., unfiltered) before performing the method of the present invention. The method of the present invention can also be used to evaluate different types of filters to determine which filter filters the most particulate impurities from the liquid and / or to determine which filter is best for filtering a predefined type of particle (e.g., particles having a predefined size). Thus, in a further aspect of the invention, there is provided a method of determining which of a plurality of filters is most effective at filtering particulate impurities from a liquid; in this aspect of the invention, first and second liquids having the same or very similar composition are provided; the method preferably comprises passing the first liquid through the first filter and recovering the filtered liquid, wherein the filtered liquid defines a first test liquid; the method comprises passing the second liquid through a second filter and recovering the filtered liquid, wherein the filtered liquid defines a second test liquid; and then performing a method according to any of the method embodiments described above (e.g. the method embodiment shown in FIG. 1 ).

[0065] In one embodiment (particularly when the method embodiment of FIG. 1 is implemented), the method comprises the steps of: Ha-jo The method may further include determining that the second filter is better at filtering particulate impurities from the liquid than the first filter if the measurements indicating the number of particulate impurities on the first filter are greater than the measurements indicating the number of particulate impurities on the second wafer obtained in step (g), or determining that the second filter is better at filtering particulate impurities from the liquid than the first filter if the measurements indicating the number of particulate impurities on the second wafer obtained in step (g) are greater than the measurements indicating the number of particulate impurities on the second wafer obtained in step (g). Ha-jo The method may further include a step of determining that the first filter is better at filtering particulate impurities from the liquid than the second filter if the measurement indicating the number of impurities on the first wafer is greater than the measurements obtained in step (g) indicating the number of particulate impurities on the first wafer.

[0066] In another embodiment (particularly when the method embodiment of FIG. 3 is implemented), the method may include determining that the second filter is better at filtering particulate impurities from the liquid than the first filter if the number of particulate impurities per drop determined for the first test liquid is greater than the number of particulate impurities per drop determined for the second test liquid, or may include determining that the first filter is better at filtering particulate impurities from the liquid than the second filter if the number of particulate impurities per drop determined for the second test liquid is greater than the number of particulate impurities per drop determined for the first test liquid.

[0067] Thus, according to one embodiment of the present invention, a method is provided for determining which of a plurality of filters is best suited to filter impurities from a liquid - a flow chart illustrating steps in an exemplary embodiment is shown in Figure 6. This method embodiment includes the steps of providing a first liquid and a second liquid, where the first and second liquids have the same composition; providing a first filter and a second filter; passing the first liquid through the first filter and collecting the filtered liquid, where the filtered liquid defines a first test liquid, and passing the second test liquid through the second filter and collecting the filtered liquid, where the filtered liquid defines a second test liquid.

[0068] Next, steps (a)-(h) of the method embodiment shown in FIG. 1 are performed, i.e.; (a) depositing a droplet of a first test liquid on a surface of a first wafer; (b) performing a spin-dry step including spinning the first wafer until the droplet of the first test liquid dries off the first wafer, leaving any particulate impurities that were in the droplet on the surface of the first wafer; (c) repeating steps (a) and (b) a predetermined number of times to increase the number of particle impurities on the surface of the first wafer, the predetermined number being greater than two; (d) depositing a droplet of a second test liquid on a surface of a second wafer, the second wafer being of the same type as the first wafer; (e) performing a spin-dry step including spinning the second wafer until the droplet of the second test liquid dries off the second wafer, leaving any particulate impurities that were in the droplet on the surface of the second wafer; (f) repeating steps (d) and (e) the predetermined number of times to increase the number of particle impurities on the surface of the second wafer; (g) obtaining measurements indicative of the number of particle impurities on the first wafer and obtaining measurements indicative of the number of particle impurities on the second wafer; (h) First wafer Ha-jo comparing a measurement indicative of the number of particle impurities on the first wafer to a measurement indicative of the number of particle impurities on the second wafer.

[0069] If, after step (h) is performed, the measurement indicating the number of particulate impurities on the first wafer is greater than the measurement indicating the number of particulate impurities on the second wafer, it is determined that the second filter is better than the first filter at filtering out particulate impurities from a liquid having a composition similar to that of the first and second liquids, or if the measurement indicating the number of particulate impurities on the second wafer is greater than the measurement indicating the number of particulate impurities on the first wafer, it is determined that the first filter is better than the second filter at filtering out particulate impurities from a liquid having a composition similar to that of the first and second liquids.

[0070] Various modifications and variations to the described embodiments of the invention 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 connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments.

Claims

1. 1. A method for determining which of a plurality of liquids poses the greatest risk of depositing particulate contaminants on a wafer surface, comprising: (a) depositing a droplet of a first test liquid on a surface of a first wafer; (b) performing a spin-dry step that includes spinning the first wafer until the droplet of the first test liquid has dried from the first wafer, with any particulate impurities that were in the droplet remaining on the surface of the first wafer; (c) repeating steps (a) and (b) a predetermined number of times to increase the number of particle impurities on the surface of the first wafer, the predetermined number being greater than two; (d) depositing a droplet of a second test liquid on a surface of a second wafer, the second wafer being of the same type as the first wafer; (e) performing a spin-dry step that includes spinning the second wafer until the droplet of the second test liquid has dried from the second wafer, leaving any particulate impurities that were in the droplet on the surface of the second wafer; (f) repeating steps (d) and (e) the predetermined number of times to increase the number of particle impurities on the surface of the second wafer; (g) obtaining measurements indicative of the number of particle impurities on the first wafer and obtaining measurements indicative of the number of particle impurities on the second wafer; (h) comparing a measurement indicative of the number of particle impurities on the first wafer number to a measurement indicative of the number of particle impurities on the second wafer; And, (i) determining that the first liquid has the highest risk of depositing particulate impurities on the wafer surface if the measurement indicating the number of particulate impurities on the first wafer number is greater than the measurement indicating the number of particulate impurities on the second wafer, or determining that the second liquid has the highest risk of depositing particulate impurities on the wafer surface if the measurement indicating the number of particulate impurities on the second wafer number is greater than the measurement indicating the number of particulate impurities on the first wafer. The method comprising:

2. (a) depositing a droplet of a first test liquid on a surface of a first wafer; (b) performing a spin-dry step of spinning the first wafer until the droplet of the first test liquid dries from the first wafer, leaving any particulate impurities that were in the droplet on the surface of the first wafer; (c) repeating steps (a) and (b) a first predetermined number of times to increase the number of particle impurities on the surface of the first wafer, the first predetermined number being greater than two. (d) depositing a droplet of the first test liquid on a surface of a second wafer, the second wafer being of the same type as the first wafer; (e) performing a spin-dry step including spinning the second wafer until the droplet of the first test liquid has dried from the second wafer, leaving any particulate impurities that were in the droplet on the surface of the first wafer; (f) repeating steps (d) and (e) a second predetermined number of times to increase the number of particle impurities on the surface of the second wafer, the second predetermined number being greater than the first predetermined number; (g) depositing a droplet of the second test liquid on a surface of a third wafer, the third wafer being of the same type as the first wafer; (h) performing a spin-dry step including spinning the third wafer until the droplet of the second test liquid has dried from the third wafer, with any particulate impurities that were in the droplet remaining on the surface of the third wafer; (i) repeating steps (g) and (h) the first predetermined number of times to increase the number of particulate impurities on the surface of the third wafer; (j) depositing a droplet of the second test liquid on a surface of a fourth wafer, the fourth wafer being of the same type as the first wafer; (k) performing a spin-dry step including spinning the fourth wafer until the droplet of the second test liquid has dried from the fourth wafer, with any particulate impurities that were in the droplet remaining on the surface of the fourth wafer; (l) repeating steps (j) and (k) a second predetermined number of times to increase the number of particulate impurities on the surface of the second wafer; (m) obtaining measurements indicative of the number of particle impurities on a first wafer; obtaining measurements indicative of the number of particle impurities on a second wafer; obtaining measurements indicative of the number of particle impurities on a third wafer; and obtaining measurements indicative of the number of particle impurities on a fourth wafer. The method of claim 1 , comprising:

3. 3. The method of claim 2, further comprising the step of determining particulate impurities per drop for each of the first and second test liquids.

4. said step of determining particulate impurities per drop for each of the first and second test liquids further comprising: subtracting a baseline value from the measurements indicative of the number of particle impurities on the first wafer to provide a first intermediate value, and dividing the first intermediate value by the total number of droplets of the first test liquid dispensed on the first wafer to obtain a first intermediate average value; subtracting the baseline value from the measurements indicative of the number of particle impurities on the second wafer to provide a second intermediate value, and dividing the second intermediate value by the total number of droplets of the first test liquid dispensed on the second wafer to obtain a second intermediate average value; adding the first intermediate average value and the second intermediate average value and dividing by "2" to obtain an average particle impurity per drop for the first test liquid; subtracting the baseline value from the measurements indicative of the number of particle impurities on the third wafer to provide a third intermediate value, and dividing the third intermediate value by the total number of droplets of the second test liquid dispensed on the third wafer to obtain a third intermediate average; subtracting the baseline value from the measurements indicative of the number of particle impurities on the fourth wafer to provide a fourth intermediate value, and dividing the fourth intermediate value by the total number of droplets of the second test liquid dispensed on the fourth wafer to obtain a fourth intermediate average; 4. The method of claim 3, further comprising adding the third and fourth intermediate average values ​​and dividing by "2" to obtain an average particle impurity per drop of the second test liquid.

5. 5. The method of claim 3 or 4, further comprising determining that the first test liquid has a higher risk of depositing particle impurities on the surface of the wafer if the average particle impurity per drop of the first test liquid is greater than the average particle impurity per drop of the second test liquid, or determining that the second test liquid has a higher risk of depositing particle impurities on the surface of the wafer if the average particle impurity per drop of the second test liquid is greater than the average particle impurity per drop of the first test liquid.

6. the step of obtaining measurements indicative of a number of particle impurities on the first wafer includes measuring a number of particle impurities present at a plurality of predefined portions of a surface of the first wafer; the step of obtaining measurements indicative of a number of particle impurities on the second wafer includes measuring a number of particle impurities present at a plurality of predefined portions of a surface of the second wafer; The method of any one of claims 1 to 5, wherein the predefined portion of the surface of the first wafer and the predefined portion of the surface of the second wafer are at corresponding locations on the respective wafers.

7. Each of the predefined portions is at least 10 mm ２ The method of claim 6, wherein the area of ​​the surface is

8. 8. The method of claim 6, wherein the plurality of predefined portions includes a portion proximate an edge of the wafer, a portion adjacent to but offset from a center of the wafer, and at least one portion between the edge of the wafer and the center of the wafer.

9. 6. The method of claim 1, wherein the step of obtaining measurements indicative of the number of particle impurities on the first wafer comprises measuring the number of particle impurities present across a surface of the first wafer, and the step of obtaining measurements indicative of the number of particle impurities on the second wafer comprises measuring the number of particle impurities present across a surface of the second wafer.

10. 10. The method of claim 1, further comprising determining, for at least one of the first and / or second wafers, whether a concentration of particle impurities is greater in a first predefined region adjacent a center of the wafer than in a second predefined region adjacent an edge of the wafer.

11. obtaining an image of particles on a surface of the first wafer; obtaining an image of the particles on the surface of the second wafer; The method of any one of claims 1 to 10, further comprising:

12. obtaining a Raman spectrum for particles on a surface of the first wafer; obtaining a Raman spectrum for particles on the surface of the second wafer; The method of any one of claims 1 to 11, further comprising:

13. providing a wafer having particle impurities on a surface thereof; obtaining an image of particulate impurities on a surface of the wafer; obtaining a Raman spectrum of the particulate impurities; and comparing the obtained image with an image of particle impurities on a surface of a first wafer and comparing the obtained image with an image of particle impurities on a surface of a second wafer; and comparing the obtained Raman spectrum to a Raman spectrum of particulate impurities on the surface of the first wafer and comparing the obtained Raman spectrum to a Raman spectrum of particulate impurities on the surface of the second wafer; determining that the particle impurities were deposited on the surface of the wafer by a liquid equivalent to the first test liquid if the obtained image and obtained Raman spectrum are more similar to the image and Raman spectrum of the particle impurities on the surface of the first wafer than to the image and Raman spectrum of the particle impurities on the surface of the second wafer, or determining that the particle impurities were deposited on the surface of the wafer by a liquid equivalent to the second liquid if the obtained image and obtained Raman spectrum are more similar to the image and Raman spectrum of the particle impurities on the surface of the second wafer than to the image and Raman spectrum of the particle impurities on the surface of the first wafer; The method of any one of claims 1 to 12, further comprising:

14. The method of claim 13 , wherein the wafer provided is a 12 inch wafer.

15. 1. A method for determining which of a plurality of filters is best suited for filtering impurities from a liquid, comprising the steps of providing a first liquid and a second liquid, wherein the first liquid and the second liquid have the same composition; providing a first filter and a second filter; passing a first liquid through a first filter and collecting a filtered liquid, said filtered liquid defining a first test liquid; and passing a second test liquid through a second filter and collecting a filtered liquid, the filtered liquid defining the second test liquid; Then, the following steps: (a) depositing a droplet of a first test liquid on a surface of a first wafer; (b) performing a spin-dry step that includes spinning the first wafer until the droplet of the first test liquid has dried from the first wafer, with any particulate impurities that were in the droplet remaining on the surface of the first wafer; (c) repeating steps (a) and (b) a predetermined number of times to increase the number of particle impurities on the surface of the first wafer, the predetermined number being greater than two; (d) depositing a droplet of a second test liquid on a surface of a second wafer, the second wafer being of the same type as the first wafer; (e) performing a spin-dry step that includes spinning the second wafer until the droplet of the second test liquid has dried from the second wafer, leaving any particulate impurities that were in the droplet on the surface of the second wafer; (f) repeating steps (d) and (e) the predetermined number of times to increase the number of particulate impurities on the surface of the second wafer; (g) obtaining measurements indicative of the number of particle impurities on the first wafer and obtaining measurements indicative of the number of particle impurities on the second wafer; (h) comparing a measurement indicative of the number of particle impurities on the first wafer number to a measurement indicative of the number of particle impurities on the second wafer number; determining that the second filter is better than the first filter at filtering out particulate impurities from a liquid having an equivalent composition to the first and second liquids if the measurement indicative of the number of particulate impurities on the first wafer is greater than the measurement indicative of the number of particulate impurities on the second wafer, or determining that the first filter is better than the second filter at filtering out particulate impurities from a liquid having an equivalent composition to the first and second liquids if the measurement indicative of the number of particulate impurities on the second wafer is greater than the measurement indicative of the number of particulate impurities on the first wafer; The method for carrying out the above.

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