Liquid composition determination method

Abstract

To provide a spectral photometer which is used for measuring the amounts of components in a process liquid on a rotating substrate, and with which it is possible to simultaneously measure optical intensities in a plurality of wavelengths.SOLUTION: Provided is a spectral photometer 26 comprising: a housing 46; an optical fiber connection part 47 which is disposed in the housing, and to which an optical fiber 28a for guiding light having passed through a process liquid to the inside of the housing is connected; collimating means 41 for collimating light radiated from the optical fiber to the inside of the housing into a bundle of parallel rays; a shielding member 42 which is disposed in the optical path of the bundle of parallel rays, and in which a plurality of openings 43 of the same area and of the same shape are formed rotationally symmetrically around the optical axis of the bundle of parallel rays; a bandpass filter 44 which closes each of the openings and allows light to pass through prescribed mutually different wavelength bands; and an optical detection element 45 for detecting the intensity of light having passed through each of the bandpass filters.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a spectrophotometer used for measuring the amount of components contained in a processing liquid on a substrate in the single-wafer processing of substrates such as semiconductor wafers.

Background Art

[0002] In the single-wafer process in the semiconductor industry, processes such as etching and cleaning are carried out by horizontally holding a semiconductor wafer and rotating it while supplying a processing liquid to its surface. The cleaning process consists of a rinse process and a drying process. After performing a rinse process of washing away a chemical solution such as an etching solution with pure water, a drying process of replacing the pure water on the wafer with 2-propanol (IPA) is carried out. If unintended components remain on the substrate in these processes, it may cause defects in subsequent processes. For example, the substance to be cleaned may remain due to insufficient rinse processing. Also, if water remains due to insufficient replacement of pure water with IPA, it may cause watermarks (drying marks). In recent years, fine and high aspect ratio patterns are often formed on the wafer surface. If the replacement with IPA is insufficient, the pattern may collapse due to the remaining water with a large surface tension.

[0003] As a countermeasure to such problems, excess supply of the processing liquid has been carried out by increasing the supply amount of the processing liquid or lengthening the supply time. However, there is a problem that the cost of waste liquid treatment increases as the usage amount of the processing liquid increases. In order to reduce the usage amount of the processing liquid and efficiently perform substrate processing, it is preferable to process the substrate while checking the amount of components to be focused on, such as components for which residual concerns exist. By monitoring the component change of water on the substrate during the rinse process or monitoring the progress of replacement of pure water with IPA during the drying process with IPA, the amount of the processing liquid used wastefully can be reduced.

[0004] Patent Document 1 describes a method for measuring the amount of components present on a substrate while processing it, by supplying a processing solution onto a rotating substrate, irradiating the liquid film of the processing solution formed on the substrate's surface with infrared light, receiving the reflected light, and measuring the amount of one or more components contained in the processing solution film from the absorbance at a predetermined wavelength. It also describes that, in order to average out the effect of surface irregularities on the wafer, the measurement time for calculating the absorbance is preferably set to a natural number multiple of the wafer's rotation period. The examples describe the results of quantifying H2O and IPA on a wafer while supplying an IPA-water mixture onto a rotating silicon wafer.

[0005] Patent Document 2 describes a substrate processing method that aims to effectively remove pure water from the surface of a substrate without wasting time or using a low surface tension liquid such as IPA. This method involves supplying pure water to the substrate surface, followed by supplying a low surface tension liquid. In parallel with the low surface tension liquid supply process, the water concentration in the liquid on the substrate surface is detected, and based on the detected water concentration, it is determined whether the low surface tension liquid supply process should be terminated. The water concentration is detected by irradiating the IPA liquid surface on the substrate with light passing through a prism in contact with the liquid, receiving the light that has been multiple-reflected between the substrate and the prism, and determining the intensity of the received light. This allows the light to pass through the liquid multiple times, effectively attenuating light of a specific wavelength with the water in the liquid, thus enabling accurate detection of the water concentration in the liquid.

[0006] For the quantitative determination of substances such as H2O and IPA, methods utilizing the absorption of infrared radiation by the substance being measured have been conventionally employed. Furthermore, measuring absorption at multiple wavelengths is also practiced. Using multiple wavelengths allows for more accurate quantitative determination of component amounts and enables the simultaneous determination of multiple substances present in a mixture. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2016-070669 [Patent Document 2] Japanese Patent Publication No. 2009-218402 [Overview of the project] [Problems that the invention aims to solve]

[0008] When performing absorbance analysis on a dynamic (not stationary) liquid, it is common practice to calculate the absorbance by integrating the received light intensity over a certain period of time. This allows for averaging out the effects of various scattering factors and suppressing variability in the measured values. As mentioned above, Patent Document 1 also describes averaging out the effects of wafer surface irregularities by setting the measurement time for calculating absorbance to a natural number multiple of the wafer's rotation period. However, even when measuring the amount of components in the processing liquid using the method described in Patent Document 1, the variability in the measured values ​​was large, making it sometimes difficult to determine whether the replacement from pure water to IPA was complete. The inventors conducted experiments by changing the integration time of the received light intensity and discovered that the undulation of the processing liquid surface greatly affected the variability in the measured values. Therefore, it was considered that when the undulation of the processing liquid surface increased due to conditions such as the substrate rotation speed and the processing liquid supply speed, the variability in the measured values ​​increased even when using the method in Patent Document 1.

[0009] According to the method described in Patent Document 2, the prism is in contact with the processing liquid, so the undulation of the processing liquid surface may not affect the measurement. However, in the method of Patent Document 2, the substrate is rotated at high speed with the prism close to the processing liquid film thickness of tens to hundreds of micrometers, which presents a problem in that it is difficult to control the position of the prism so that it does not collide with the substrate.

[0010] One method for measuring absorption at multiple wavelengths involves inserting a bandpass filter (BPF) that transmits only a predetermined wavelength band into the optical path from the light source through the sample to the photometer, and then measuring the light intensity with the photometer while replacing the BPF. In this method, the measurement of light intensity at multiple wavelengths is strictly speaking performed with slight time delays. However, when measuring a processing liquid on a rotating substrate, the amount of light reaching the photometer constantly changes due to the undulation of the processing liquid surface, making it necessary to precisely measure the light intensity at multiple wavelengths simultaneously.

[0011] The present invention has been made in consideration of the above, and aims to provide a spectrophotometer used to measure the amount of components in a processing solution on a rotating substrate while processing the substrate, which can simultaneously measure light intensity at multiple wavelengths. [Means for solving the problem]

[0012] The spectrophotometer of the present invention is used to measure the amount of one or more components contained in a processing liquid supplied onto a rotating substrate, and comprises: a housing; an optical fiber connection part provided in the housing to which an optical fiber that guides light passing through the processing liquid into the housing is connected; a collimating means that makes the light emitted from the optical fiber into the housing into a parallel beam of light; a shielding member provided in the optical path of the parallel beam of light, wherein a plurality of openings of the same area and shape are formed rotationally symmetrically around the optical axis of the parallel beam of light; a bandpass filter that closes each of the openings and transmits different predetermined wavelength bands from each other; and a photodetector that detects the intensity of the light transmitted through each of the bandpass filters.

[0013] The spectrophotometer set of the present invention is configured by arranging multiple spectrophotometers in parallel. [Effects of the Invention]

[0014] According to the spectrophotometer of the present invention, since the plurality of openings formed in the shielding member have the same area, the same shape, and are rotationally symmetrically located around the optical axis of the fiber optic parallel light beam, the intensity of the light reaching all the openings is equal. The light reaching each opening is detected by a light detection element after the light of different wavelengths passes through the BPF according to the characteristics of the BPF. As a result, the light intensities at a plurality of wavelengths are measured simultaneously.

Brief Description of the Drawings

[0015] [Figure 1] It is a diagram showing the device configuration for measuring the components of the treatment liquid. [Figure 2] It is a diagram showing an example of the structure of a probe that also serves as a light projecting unit and a light receiving unit. [Figure 3] A: Diagram showing the structure of a photometric unit equipped with the spectrophotometer according to an embodiment of the present invention, B: Cross-sectional view taken along the line B-B of FIG. 3A. [Figure 4] It is a diagram for explaining the variation in the received light intensity. [Figure 5] It is a diagram for explaining the variation in the received light intensity. [Figure 6] It is a diagram for explaining the variation in the received light intensity. [[ID=2...]] [Figure 7] It is a diagram showing an example of the frequency distribution of absorbance [Figure 8] It is a diagram showing the relationship between the allowable error of absorbance and the sample size. [Figure 9] It is a diagram showing the change in the IPA concentration in the example.

Embodiments for Carrying Out the Invention

[0016] An embodiment of the spectrophotometer of the present invention will be described by taking as an example the case of analyzing the components of a treatment liquid while cleaning a silicon wafer.

[0017] Referring to FIG. 1, the single wafer substrate processing apparatus 10 has a rotary table 11 that holds and rotates a wafer W horizontally or at a desired angle, and a nozzle 12 that supplies a processing liquid S onto the wafer. A plurality of nozzles 12 are provided for each type of processing liquid, and each is connected by a pipe 13 to a processing liquid supply source (not shown). The nozzle 12 is movable in the radial direction from the center to the outer edge of the wafer. When the processing liquid S is supplied onto the upper surface of the wafer W while the wafer W is rotated, the processing liquid moves toward the outer edge of the wafer by centrifugal force, and forms a processing liquid film F having a film thickness in which the moving amount and the supply amount are balanced. When the supply of the processing liquid stops, the processing liquid is discharged from the outer edge of the wafer, and the processing liquid film reduces its film thickness and eventually disappears.

[0018] The type of the processing liquid is not particularly limited, and examples thereof include water; functional water such as ozone water, radical water, and electrolytic ion water; organic solvents such as IPA; mixed solutions of ammonia and hydrogen peroxide, hydrochloric acid and hydrogen peroxide, sulfuric acid and hydrogen peroxide, nitric acid and hydrofluoric acid, hydrofluoric acid, sulfuric acid, phosphoric acid, nitric acid, buffered hydrofluoric acid, ammonia, hydrogen peroxide, hydrochloric acid, tetramethylammonium hydroxide, and mixtures of these with water.

[0019] The liquid component measuring device 20 includes a light source 21, a probe 22, a photometry unit 25, and an arithmetic unit 27. The photometry unit 25 includes a spectrophotometer 26 of the present embodiment. The probe 22 is disposed on the wafer W inside the substrate processing apparatus 10. In the present embodiment, the probe 22 also serves as a light projecting unit 23 that irradiates a light beam toward the wafer W and a light receiving unit 24 that receives the reflected light passing through the processing liquid on the wafer. In the following description of light projection, the probe 22 may be referred to as the light projecting unit 23, and in the description of light reception, the probe 22 may be referred to as the light receiving unit 24. The light source 21, the photometry unit 25, and the arithmetic unit 27 are disposed outside the substrate processing apparatus. The light projecting unit 23 is connected to the light source 21, and the light receiving unit 24 is connected to the photometry unit 25 by an optical fiber cable 28. The photometry unit 25 and the arithmetic unit 27 are electrically connected.

[0020] The light source 21 emits light containing wavelengths absorbed by the component to be measured (hereinafter referred to as "specific component"). Preferably, the light source 21 generates light in a continuous wavelength range. This makes it possible to measure absorption at multiple wavelengths included in the continuous light. For example, to measure H2O and 2-propanol, the light source 21 preferably irradiates with light in a wavelength range including 1350 to 1720 nm. To analyze other practically important components, the light source more preferably irradiates with light in a wavelength range including 1200 to 1800 nm. The light source 21 may combine an optical filter with the lamp to cut out wavelengths that are not necessary for measurement. As the light source, commercially available lamps such as halogen tungsten lamps can be used.

[0021] Referring to Figure 2, the probe 22 combines a light-emitting unit 23 that irradiates a light ray B toward the processing liquid film F on the wafer W, and a light-receiving unit 24 that receives the light reflected after passing through the processing liquid. The probe 22 has a single optical path P inside its housing. Light introduced from one end of the probe (the right end in Figure 2) through the optical fiber 28 travels horizontally toward the left side of Figure 2, is collimated by the lens 31, reflected downward by the mirror 32, passes through the lens 33, and is irradiated vertically toward the wafer W. The light ray that has passed through the processing liquid film F on the wafer and been reflected by the wafer W travels through the lens 33 into the probe, and is guided back to the optical fiber 28 by retracing the optical path P.

[0022] The light-emitting unit 23 and the light-receiving unit 24 may be provided separately. When the light-emitting unit and the light-receiving unit are provided separately, the angle of incidence to the processing liquid film F can be selected. For example, by setting the incidence angle to the Brewster angle and irradiating with P-polarized light, reflection at the processing liquid surface can be suppressed. On the other hand, as shown in Figure 2, if the light-emitting unit and the light-receiving unit are used together and the light beam is irradiated perpendicularly to the wafer, it becomes easier to control the distance between the probe and the wafer. Also, if the optical path P is made L-shaped as shown in Figure 2, the height of the probe can be reduced, which has the advantage of making it easier to install inside the substrate processing apparatus 10.

[0023] Returning to Figure 1, the probe 22 is movable radially above the wafer W, from the center to the outer edge. This allows for measurement of components in the processing liquid film at any position on the wafer.

[0024] The light received by the light receiving unit 24 is branched midway through the optical fiber 28 and guided to the photometric unit 25. An optical filter may be provided at the entrance of the photometric unit 25 to cut out wavelengths that are not needed for measurement. The photometric unit 25 measures the received light intensity at multiple wavelengths, amplifies the electrical signal corresponding to the measured received light intensity as needed, and outputs it to the calculation unit 27.

[0025] The photometric unit 25 includes one spectrophotometer 26, or a spectrophotometer set in which two or more spectrophotometers 26 are arranged in parallel. The photometric unit 25 shown in Figure 1 includes a set consisting of two spectrophotometers 26. Arranging the spectrophotometers in parallel means that all spectrophotometers are arranged under the same conditions for light that has passed through the processing solution. Specifically, the light from a single optical fiber 28 is equally divided and introduced into each spectrophotometer.

[0026] Referring to Figure 3, the spectrophotometer 26 has a housing 46 made of an opaque material, for example, a roughly cylindrical shape, and one optical fiber 28a is connected to an optical fiber connection part 47 provided at one end of the housing (the left end in Figure 3). This optical fiber 28a is a branch of the optical fiber 28 from the light receiving unit 24. The light introduced into the spectrophotometer 26 from the optical fiber 28a is emitted from the end of the optical fiber 28a inside the housing 46 and is collimated by the lens 41 into a beam of light parallel to the optical axis X of the optical fiber.

[0027] In the optical path, an opaque partition 42 is provided perpendicular to the optical axis X, and openings 43 of the same shape and area are formed in the partition 42 rotationally symmetrically around the optical axis X. In Figure 3, a total of four openings are formed around the optical axis X at positions that are four rotationally symmetrical. Since the openings are arranged rotationally symmetrically with respect to the optical axis X, they are all at the same distance from the optical axis, and the intensity of light incident on each opening is equal. A BPF 44 is placed in each opening 43 so as to completely block the opening, and a photodetector element 45 is placed behind the BPF (on the opposite side from the optical fiber). Each BPF is made of a material that transmits light of a different wavelength. The collimated light passes through the BPF 44 and reaches the photodetector element 45. In this way, by arranging a set of BPF 44 and photodetector element 45 with different transmission wavelengths for each opening 43, the received light intensity at multiple wavelengths transmitted through each BPF can be measured simultaneously.

[0028] The number of BPF 44 and photodetector 45 pairs in a single spectrophotometer 26 is not particularly limited, but is preferably 3 or 4. This is because it allows for the utilization of more light that is close to the optical axis X and has high intensity. The photometric unit 25 can measure the received light intensity at multiple desired wavelengths by arranging multiple spectrophotometers 26 in parallel as needed.

[0029] The multiple wavelengths at which the photometric unit 25 measures the received light intensity do not need to be aligned with the absorption peak wavelength of a specific component; it is sufficient that any of the wavelengths are included in the absorption bandwidth of that specific component.

[0030] It is preferable that the multiple wavelengths for which the photometric unit 25 measures the received light intensity are separated from each other to a certain extent. From this point of view, it is preferable that the BPF has a full width at half maximum of 20 nm to 40 nm in the transmitted wavelength band, and that the interval between the medians of the transmitted wavelength bands is at least twice the full width at half maximum. Here, the median of the transmitted wavelength band is the median in terms of full width at half maximum. In this specification, the median of the transmitted wavelength band may also be simply referred to as the "transmitted wavelength".

[0031] Furthermore, it is preferable that the multiple wavelengths used to measure the received light intensity are dispersed across the entire wavelength range, for example, 1200 to 1800 nm. If the photometric unit 25 consists of one spectrophotometer 26, it is preferable that the median of at least one transmission wavelength band of the BPF provided by the spectrophotometer is in the range of 1200 nm to 1500 nm, and the median of at least one transmission wavelength band is in the range of 1600 nm to 1800 nm. If the photometric unit 25 consists of two or more spectrophotometers 26, it is preferable that the median of at least one transmission wavelength band of the entire set of BPFs provided by the multiple spectrophotometers is in the range of 1200 nm to 1500 nm, and the median of at least one transmission wavelength band is in the range of 1600 nm to 1800 nm.

[0032] The number of wavelengths for which the photometric unit 25 measures the received light intensity is preferably 4 or more, more preferably 8 or more. This is because a larger number of wavelengths improves the accuracy of calculating the amount of a specific component from multiple received light intensities using the least squares method or the like. On the other hand, the number of wavelengths for which the received light intensity is measured is not particularly limited, but is preferably 256 or less, more preferably 128 or less, and even more preferably 64 or less. When the sampling rate for measuring the received light intensity is high, absorption due to molecular vibrations observed in the near-infrared region is generally weak, so if the number of wavelengths is too large, the measurement error of the received light intensity at each wavelength becomes negligible.

[0033] The sampling rate at which the photometric unit 25 measures the received light intensity needs to be high enough to distinguish fluctuations in received light intensity caused by ripples in the treated liquid surface. Details regarding the sampling rate will be described in the explanation of the liquid component measurement method and in the examples.

[0034] The calculation unit 27 receives the light intensity as an electrical signal from the photometric unit 25 and performs various calculations, such as determining whether the ripple of the processed liquid surface affects the light intensity, determining whether the light intensity is normal or abnormal, calculating the absorbance from the light intensity, and calculating the amount of specific components present. Specific examples of the calculations will be described in the explanation of the liquid component measurement method and in the examples.

[0035] Next, we will explain the method for measuring the components of the processed liquid.

[0036] As the wafer W is rotated, a processing liquid S is supplied to its upper surface. The processing liquid moves toward the periphery of the wafer due to centrifugal force, forming a processing liquid film F on the wafer. A light ray B is shone from the light-emitting unit 23 toward this processing liquid film. The light ray passes through the processing liquid, is reflected off the wafer surface, received by the light-receiving unit 24, and sent through the optical fiber 28 to the photometric unit 25.

[0037] The photometric unit 25 measures the received light intensity at multiple wavelengths and sends an electrical signal corresponding to the received light intensity to the calculation unit 27. The frequency at which the received light intensity is measured and transmitted to the calculation unit is the sampling rate. The sampling rate must be high enough to distinguish fluctuations in the received light intensity due to undulation of the processing liquid surface. Since the undulation of the processing liquid surface moves at high speed from the center to the periphery of the wafer W, if the sampling rate is slow, the effect of the undulation of the processing liquid surface is smoothed out, making it difficult to determine whether or not there was a fluctuation in the received light intensity due to the undulation of the processing liquid surface.

[0038] The inventors conducted experiments under different conditions for substrate rotation speed and processing liquid supply speed, varying the sampling rate of the received light intensity. The results showed that, in order to distinguish fluctuations in received light intensity due to undulation of the processing liquid surface, a sampling rate of 400 times / second or higher is preferable, and 750 times / second or higher is even more preferable. On the other hand, there is no particular upper limit to the sampling rate. Since commercially available photodetectors often have sampling time intervals of several μm, the sampling rate is preferably 100,000 times / second or less. Furthermore, the sampling rate is more preferably 10,000 times / second or less. There is no particular advantage to a higher sampling rate, as it increases the cost in order to provide the arithmetic unit 27 with high-speed processing capability.

[0039] Conventionally, when performing absorbance analysis on dynamic liquids, it has been common practice to calculate absorbance by integrating the received light intensity over a certain period of time in order to average out the effects of various scattering factors and suppress variability in the measured values. Even when measuring and displaying liquid components in real time, if the measurement results can be displayed at an interval of about 0.1 to 0.5 seconds, the purpose of "real-time" monitoring can be achieved, so a sampling interval of about 0.1 to 0.5 seconds was sufficient. When using a charge-type photodetector, the received light intensity was sometimes sampled once every few milliseconds to tens of milliseconds and sent to the calculation unit in order to prevent photodetector overflow, but even in that case, the calculation unit calculated absorbance by integrating the received light intensity over a period of about 0.1 to 0.5 seconds. In contrast, in this embodiment, it is possible to determine whether or not the measured received light intensity is affected by the undulation of the treated liquid surface based on the received light intensity measured at a higher sampling rate.

[0040] Furthermore, it is preferable to synchronize the sampling by the photometric unit 25 with the rotation of the rotary table 11 of the substrate processing apparatus 10. This allows the light intensity to be measured at the same position or in the same range each time the wafer W rotates. To synchronize the sampling with the rotation of the substrate, the substrate processing apparatus 10 can transmit a signal synchronized with the rotation to the liquid component measuring device 20. Also, if the rotation speed is changed during wafer processing, the sampling rate may be changed in accordance with the wafer rotation speed, as long as the sampling rate is within a range that allows for the discrimination of fluctuations in light intensity due to undulation of the processing liquid surface.

[0041] The calculation unit 27, which receives the light intensity from the photometric unit 25, performs two main tasks. One is to calculate the amount of a specific component based on the received light intensity, and the other is to determine whether the received light intensity is an abnormal value that has fluctuated due to the influence of ripples in the processing liquid surface.

[0042] First, the method by which the calculation unit 27 calculates the amount of a specific component will be explained. Here, the concept of the amount of a component includes both the absolute amount, such as the mass of the component, and the relative amount, such as the concentration of the component in the processing liquid.

[0043] Absorbance A is, A = -log(I / I0) ... (Equation 1) It is determined by the following: Here, I is the measured light intensity, and I0 is the light intensity when the specific component is absent. I0 can be measured in advance. Absorbance A is given by Lambert-Beer's law, A = αLC ... (Equation 2) The following relationship exists: Here, α is the absorption coefficient of the specific component at that wavelength, L is the optical path length, and C is the concentration of the specific component. C corresponds to the relative amount of the specific component, and LC corresponds to the absolute amount of the specific component.

[0044] To calculate the abundance of a specific component from the light intensity at multiple wavelengths, the abundance of that component can be determined using the least squares method or similar techniques based on a set of absorbance data previously measured with varying concentrations of the component. Furthermore, if there are multiple specific components to be measured, and a set of absorbance data previously measured with varying concentrations of each component is available, the abundance of each component can be determined by performing multivariate analysis using principal component regression or partial least squares regression. Moreover, if a set of absorbance data previously measured with varying liquid film thickness and concentration of the specific component is available, the thickness of the treated liquid film and the concentration of the specific component in the treated liquid can be simultaneously determined by multivariate analysis with liquid film thickness and concentration as independent variables.

[0045] The amount of a specific component (LC or C) is preferably calculated based on a series of light intensity readings received over a predetermined period. This is to average out the effects of various scattering factors, such as surface irregularities of the wafer, and suppress variations in the measured values, similar to conventional methods. The period during which the amount of this specific component is calculated once will be called the "integration period." The integration period is preferably 0.05 seconds or more, more preferably 0.1 seconds or more. On the other hand, when calculating the amount of a specific component in real time, The integration period is preferably 0.5 seconds or less, more preferably 0.25 seconds or less, and particularly preferably 0.1 seconds or less, in accordance with the display interval for monitoring specific components in real time. For each integration period, the calculation unit 27 calculates the amount of the specific component by integrating the received light intensity measured by the photometric unit 25 during that integration period and received from the photometric unit.

[0046] The calculation unit 27 determines whether the received light intensity is an abnormal value that has fluctuated due to the influence of ripple on the surface of the processing liquid, either in parallel with or prior to calculating the amount of a specific component. Whether the received light intensity is affected by ripple on the surface of the processing liquid can be determined by looking at the variation in the received light intensity received during a predetermined period. For example, the calculation unit finds the median value of the received light intensity received during the integration period, and if there is a received light intensity whose difference from the median value exceeds a predetermined value, it can be determined that the received light intensity is an abnormal value affected by ripple on the surface of the processing liquid, and that abnormal values ​​are mixed in the received light intensity measured during that integration period. Alternatively, the calculation unit may calculate the absorbance from the received light intensity each time it receives light intensity from the photometric unit, and determine whether or not there is an influence of ripple on the surface of the processing liquid based on the variation in absorbance. It is preferable to determine the influence of ripple on the surface of the processing liquid based on the variation in absorbance because it makes it easier to identify abnormal values ​​affected by ripple on the surface of the processing liquid.

[0047] Furthermore, abnormal values ​​caused by malfunctions in the device, such as the lamp of the light source 21 not being lit or the optical fiber 28 being broken, have been detected in conventional hypothetical devices, and it is preferable that the liquid component measuring device of this embodiment also be able to detect them.

[0048] Next, regarding the calculation of the abundance of a specific component by the calculation unit 27, two different methods for selecting the light-receiving intensity data used in the calculation will be explained.

[0049] The first method performed by the calculation unit 27 is a method for calculating the amount of a specific component using all of the received light intensity values ​​received during a certain integration period. At the same time, it is determined whether or not each individual received light intensity value is affected by the undulation of the processing liquid surface.

[0050] The calculation unit 27 may calculate the absorbance or the amount of a specific component present each time it receives a light intensity and determine the average over the integration period, or it may integrate the light intensity measured during that integration period and determine the absorbance or the amount of a specific component present from the integrated value. At the same time, the calculation unit 27 determines whether the light intensity is an abnormal value affected by the undulation of the processing liquid surface.

[0051] This method allows for the determination of whether the calculated amount of a specific component is affected by fluctuations in the processing liquid surface, and the measurement results can be used to control the processing conditions of the wafer. For example, in the drying process following the rinsing process, the IPA supply time is set to be longer in order to reliably replace the pure water on the wafer with IPA. However, if the calculated amount of IPA is stable over multiple accumulation periods and it is determined that the amount is not affected by fluctuations in the processing liquid surface, the supply of IPA can be stopped immediately to shorten the drying process time. On the other hand, even if the calculated amount of IPA is stable over multiple accumulation periods, if it is determined that the amount is affected by fluctuations in the processing liquid surface, the supply of IPA can be continued for a predetermined time with a margin of safety, and the drying process can be continued.

[0052] The second method by the calculation unit 27 involves determining whether each received light intensity received during a certain integration period is an abnormal value affected by the undulation of the treated liquid surface, and calculating the amount of a specific component using only the received light intensities that are determined not to be abnormal values. This makes it possible to determine the amount of a specific component while eliminating the effect of undulation of the treated liquid surface. Details of this method will be described later based on experimental results. [Examples]

[0053] First, we will show an example of light reception intensity measurement in a preliminary experiment.

[0054] In the preliminary experiment, an unpatterned silicon wafer with a diameter of 200 mm was rotated at 500 rpm, and pure water was supplied to the center of the wafer at a rate of 1.0 L / min. At a position 50 mm from the center of the wafer, light from a tungsten lamp (15 W) was shone perpendicularly from the probe (light emitter) toward the wafer surface, and the reflected light was received by the probe (light receiver), and the received light intensity was measured by the photometer. The photometer consisted of three units in parallel, each equipped with three sets of BPFs and photodetectors (InGaAs) by branching an optical fiber, and the received light intensity was measured at nine wavelengths in the near-infrared region at a sampling rate of 1000 times / second. The measured received light intensity was defined as I, and the received light intensity without pure water supply was defined as I0. The absorbance A was calculated using Equation 1 described above.

[0055] Figure 4 shows the absorbance calculated from the received light intensity at a wavelength of 1300 nm. Figure 4 plots 1000 received light intensities over one second. In Figure 4, the absorbance varied greatly, with exceptionally large values ​​being observed occasionally. From this, it was confirmed that the fluctuation in received light intensity due to the undulation of the treated liquid surface was not simply due to changes in the thickness of the treated liquid film, but rather due to the scattering of light irradiated onto the treated liquid, which reduced the amount of light returning to the light-receiving unit. Furthermore, it was confirmed that the fluctuation in received light intensity due to the undulation of the treated liquid surface could be distinguished when the sampling rate was 1000 times / second.

[0056] Figures 5 and 6 show the absorbance calculated by integrating the received light intensity two or three times, respectively, in the experiment in Figure 4. Figures 5 and 6 correspond to the results when the sampling rates were 500 times / second and 333 times / second, respectively. Comparing Figures 4 to 6, it can be seen that it is possible to determine the effect of the undulation of the treated liquid surface on the received light intensity in Figures 4 and 5, but not so easy in Figure 6. From this, it was considered that a sampling rate of 400 times / second or higher is preferable for measuring the received light intensity, and even more preferable is 750 times / second or higher.

[0057] Furthermore, the inventors conducted preliminary experiments in which the rotation speed of the silicon wafer was varied from 100 to 1000 rpm and the supply rate of pure water from 0.1 to 1.0 L / min. The results of these experiments also showed similar results regarding the preferred range of the sampling rate.

[0058] Furthermore, a reasonably fast sampling rate is necessary to calculate the amount of specific components present in real time. Whether or not the received light intensity is affected by fluctuations in the surface of the treated liquid is determined by observing the variation in the received light intensity received during a predetermined period. Due to the requirement of real-time measurement, the integration period is preferably 0.5 seconds or less, more preferably 0.25 seconds or less, and particularly preferably 0.1 seconds or less, and it is necessary to measure a certain number of received light intensities during this integration period.

[0059] Similar to the preliminary experiment described above, absorbance was calculated from the received light intensity measured with a silicon wafer rotation speed of 300 rpm, a pure water supply rate of 1 L / min, and a sampling rate of 1000 times / second. Figure 7 shows the absorbance over 1 second at 1450 nm, where absorption by H2O is significant and absorbance variability is large. The standard deviation of the data in Figure 7 was 0.15.

[0060] The relationship between the acceptable error δ and the sample size n is: δ = zσ / √(n) ... (Equation 3) This is expressed as follows: Here, z is a constant, for example, 1.96 for a 95% confidence interval and 2.63 for a 99% confidence interval, σ is the standard deviation, and √(n) is the square root of the sample size n. Figure 8 is a graph showing the relationship between the sample size n and the acceptable error δ in Equation 3. From Figure 8, it can be seen that to reduce the acceptable error δ to a certain extent, a sample size n of 50 or more is necessary, and more stably, 100 or more is necessary.

[0061] The above calculations show that, for example, if the integration period for calculating the amount of a specific component in real time is 0.1 seconds, in order to determine whether the received light intensity is an abnormal value affected by the undulation of the treated liquid surface, based on the variation in received light intensity within that integration period, it is preferable to have 50 or more, and more preferably 100 or more, received light intensity data points per 0.1 seconds, considering the relationship with the acceptable error. From these results, it is preferable that the sampling rate for measuring received light intensity be 500 times / second or more, and more preferably 1000 times / second or more.

[0062] Next, embodiments of the present invention will be described.

[0063] The photometric unit branched the optical fiber and installed three parallel units, each equipped with three sets of BPFs and photodetectors (InGaAs), to measure the received light intensity at nine near-infrared wavelengths.

[0064] In the experiment, an unpatterned silicon wafer with a diameter of 200 mm was rotated at 1000 rpm, and pure water was supplied to the center of the wafer at a rate of 50 mL / min for 18 seconds. After stopping the supply of pure water, IPA was supplied at a rate of 50 mL / min for approximately 20 seconds. Light from a tungsten lamp (15 W) was shone perpendicularly from the probe (light emitter) toward the wafer surface at a position 50 mm from the center of the wafer, and the reflected light was received by the probe (light receiver), and the received light intensity was measured by the photometer. The sampling rate of the photometer was set to 1000 times / second. It was determined whether the measured received light intensity value was an abnormal value caused by wavering of the processing liquid surface, and for the received light intensities determined not to be abnormal values, multivariate analysis was performed using a group of absorbance data measured in advance with varying liquid film thickness and IPA-water mixing ratio, with an integration period of 0.1 seconds, to determine the IPA concentration in the processing liquid on the wafer.

[0065] The determination of outliers was performed as follows: Absorbance was calculated from 100 light reception intensities for each cumulative period, and the 10 data points with the smallest values ​​were unconditionally judged as outliers and excluded. Then, the smallest value among the remaining 90 was judged to be the normal absorbance value and set as the reference value. The reference value is a value that is considered to be extremely certain to be a normal value, and it is acceptable if the 10 excluded data points include normal values.

[0066] Next, using a threshold of the reference value + 0.2, data exceeding the threshold among the 90 absorbance data points were identified as abnormal values, while data below the threshold were retained as normal values. The threshold can be set in advance by pre-determining a fixed value, for example, the expected maximum absorbance, or, as in this embodiment, by determining it according to a reference value and a predetermined calculation formula.

[0067] Other methods can also be used to determine whether a value is an outlier. For example, based on an absorbance histogram, values ​​outside a predetermined range including the median can be identified as outliers.

[0068] Furthermore, in this embodiment, absorbance was calculated each time the light intensity was measured, and a determination was made as to whether the calculated absorbance was an abnormal value. However, since absorbance and light intensity have a one-to-one correspondence, the determination of whether the light intensity is an abnormal value could also be made based on the light intensity. However, it is important to note that absorbance and light intensity have inverse relationships.

[0069] Figure 9 shows the measurement results of the amount of IPA present on the wafer before and after switching the processing solution from pure water to IPA. The horizontal axis represents time, and the vertical axis represents the IPA concentration. The white circles represent the IPA concentration every 0.1 seconds, calculated based on absorbance values ​​that were determined not to be abnormal. The black circles are an indicator of the time change in IPA concentration, and in Figure 9, they are the absolute value of the difference between the maximum and minimum concentrations of the previous five measurements. The indicator of the time change in the amount of IPA present can also be expressed as the first derivative of the amount present.

[0070] In Figure 9, while pure water is supplied to the wafer, both the IPA concentration and its indicator of change (hereinafter referred to as "variation amount") are close to 0. When the supply of pure water is stopped and the supply of IPA is started at 18 seconds on the horizontal axis, both increase. When the variation amount exceeds the replacement threshold, it is determined that replacement has started (S). After the variation amount exceeds the replacement threshold, when the variation amount continuously falls within the stable range by a number of convergence judgment points, it is determined that replacement is complete (E). Appropriate values ​​are set in advance for the replacement threshold, stable range, and convergence judgment points. In Figure 9, the replacement threshold is set to 40%, the stable range to ±15%, and the convergence judgment points to 5.

[0071] The measurement results in Figure 9 indicate that the water replacement was completed approximately 1.4 seconds after the start of IPA supply. When the amount of IPA present is not determined in real time, the IPA supply time is often set to around 10-20 seconds to allow for some leeway. However, if it can be determined from the concentration and fluctuation of IPA determined in real time that the water replacement by IPA is completed in approximately 1.4 seconds, the amount of IPA used can be reduced and the drying time shortened by stopping the IPA supply at that point.

[0072] The present invention is not limited to the embodiments or examples described above, and various modifications are possible within the scope of its technical concept.

[0073] For example, measurements using the spectrophotometer or spectrophotometer set of the present invention are not limited to those performed on a silicon wafer; the substrate may be a compound semiconductor such as silicon carbide or gallium arsenide, or a crystalline wafer such as sapphire. Furthermore, the substrate may be a glass substrate for flat panel displays, or a ceramic wafer for manufacturing electronic components. In all of these substrates, the success or failure of the processing with the processing solution significantly affects the defect rate of the product. [Explanation of symbols]

[0074] 10 Substrate Processing Equipment 11 Rotating Table 12 nozzles 13 Piping 20 Liquid component measuring device 21 Light source 22 probes 23. Lighting Unit 24 Light receiving part 25. Photometric unit (spectrophotometer set) 26 Spectrophotometer 27 Arithmetic section 28, 28a, 28b optical fibers 31, 33 lenses 32 Mirror 41. Lens (Collimating mechanism) 42 Partition wall (shielding member) 43 Opening 44 Bandpass Filter 45 Photodetector 46 cabinets 47 Optical fiber connection section B ray F Treatment liquid film P Probe's optical path S Treatment Solution W wafer (substrate) X-ray photometric unit optical axis

Claims

[Claim 1] A process of irradiating a light beam onto a processing liquid supplied onto a rotating substrate, The process involves guiding the light that has passed through the processing liquid to a spectrophotometer using an optical fiber, A step of measuring the intensity of light guided to the spectrophotometer at a sampling rate of 400 times / second or more and calculating the absorbance, A step of calculating the amount of water or 2-propanol in the processing solution based on the absorbance, The process includes determining whether the intensity of the light guided to the spectrophotometer is an abnormal value that has fluctuated due to the influence of ripples in the liquid surface of the processing solution, The aforementioned spectrophotometer is The casing and The housing is provided with an optical fiber connection section to which the optical fiber is connected, A collimating means that converts the light emitted from the optical fiber into the housing into a parallel beam, A shielding member provided in the optical path of the parallel light beam, having a plurality of openings of the same area and shape formed rotationally symmetrically around the optical axis of the parallel light beam, A bandpass filter that blocks each of the aforementioned openings and transmits different predetermined wavelength bands from each other, Each of the bandpass filters has a photodetector that detects the intensity of light transmitted through it, The plurality of bandpass filters have a full width at half maximum of 20 nm to 40 nm in the transmitted wavelength band, and the interval between the medians of the transmitted wavelength bands is at least twice the full width at half maximum. Among the plurality of bandpass filters, the median of at least one transmission wavelength band is in the range of 1200 nm to 1500 nm, and the median of at least one transmission wavelength band is in the range of 1600 nm to 1800 nm. Liquid component measurement method.

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