Film thickness measuring device and film thickness measuring method

Abstract

To provide a device that can measure the film thickness of an object with high precision. [Solution] The film thickness measuring device (1) comprises a light source (10) that irradiates a sample (100) with light, area sensors (23, 24) that detect light from the sample (100) and output a signal corresponding to the brightness information of the detected light, a spectrometer (50) that spectrally detects the light from the sample and outputs a signal corresponding to wavelength information including the spectrum of the light, and a control device (30) that estimates the film thickness of the sample based on brightness information identified from the signals output from the area sensors (23, 24) and wavelength information identified from the signals output from the spectrometer.

Description

Technical Field

[0001] One aspect of the present invention relates to a film thickness measuring apparatus and a film thickness measuring method.

Background Art

[0002] As a technique for measuring the film thickness of a measurement object, there is known a technique in which white light is irradiated onto the measurement object and the reflected light is detected by a color camera to obtain an interference color image of three wavelengths, and the film thickness distribution is measured in area units based on a predetermined algorithm (see, for example, Patent Documents 1 and 2, and Non-Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In this technical field, it is required to measure the film thickness of a measurement object with higher accuracy.

[0006] One aspect of the present invention has been made in view of the above circumstances, and an object thereof is to accurately derive the film thickness of a measurement object.

Means for Solving the Problems

[0007] A film thickness measuring device according to one aspect of the present invention comprises: a light irradiation unit that irradiates light onto an object to be measured; a first photodetector which is an area sensor or line sensor that detects light from the object to be measured and outputs a signal corresponding to the brightness information of the detected light; a spectrometer that spectrally detects light from the object to be measured and outputs a signal corresponding to wavelength information including the spectrum of the light; and an analysis unit that estimates the film thickness of the object to be measured based on brightness information identified from the signal output from the light detection unit and wavelength information identified from the signal output from the spectrometer.

[0008] In a film thickness measuring device according to one aspect of the present invention, light from the object to be measured is detected by a photodetector and spectrally detected by a spectrometer. The film thickness of the object to be measured is estimated based on luminance information identified from the signal output from the photodetector and wavelength information identified from the signal output from the spectrometer. The luminance information (reflectance of light) of the light detected by the photodetector is a value corresponding to the film thickness of the object to be measured. However, with only luminance information, only the relative distribution of film thickness is identified, and the absolute value is not identified. In this respect, in a film thickness measuring device according to one aspect of the present invention, wavelength information including the spectrum of spectrally detected light is further considered, so that the absolute value of the film thickness at the spectrally detected point can be identified. As a result, the absolute value of the film thickness in each area of ​​the object to be measured can be appropriately derived based on the relative film thickness distribution identified from the luminance information and the absolute value of the film thickness at the spectrally detected point. As described above, by calibrating the detection result in the photodetector with the detection result in the spectrometer, the film thickness of the object to be measured can be derived with high accuracy.

[0009] The above-described film thickness measuring device further comprises an optical splitting element that splits light from the object to be measured, and the optical detection unit further comprises a second photodetector which is an area sensor or a line sensor. The optical splitting element may split the light from the object to be measured and guide it to the first and second photodetectors. In this way, the light from the object to be measured is split, and the split light is detected by the two photodetectors. For example, the light can be separated by wavelength band, and the film thickness can be estimated from the brightness information in the desired wavelength band. This makes it possible to derive the film thickness of the object to be measured with higher accuracy.

[0010] The optical splitting element may have a tilted dichroic mirror whose transmittance and reflectance change according to wavelength in a predetermined wavelength range, splitting the light from the object to be measured by transmitting and reflecting it. With such a configuration, light can be appropriately split for each wavelength band.

[0011] The light splitting element may include a dichroic mirror or a half-mirror and a bandpass filter. With such a configuration, light can be appropriately split for each wavelength band.

[0012] The photodetector may output a signal corresponding to luminance information, which includes the ratio of the luminance value of the light detected by the first photodetector to the luminance value of the light detected by the second photodetector. The light detected by the photodetector may be affected by, for example, fluctuations in the light source or background light. In this case, it may not be possible to estimate the film thickness with high accuracy based on the luminance information. In this regard, by deriving the ratio of the luminance values ​​of light in two wavelength bands divided according to wavelength, it is possible to derive luminance information that is not affected by the background light mentioned above. By estimating the film thickness based on such luminance information, it is possible to achieve highly accurate film thickness estimation.

[0013] The analysis unit may decide whether or not to perform film thickness estimation of the object to be measured using luminance information and wavelength information, based on the information of the object to be measured. Since the method for estimating film thickness with high accuracy differs depending on the state of the object to be measured (e.g., thickness), by deciding whether or not to perform the "film thickness estimation using luminance information and wavelength information" described above based on the information of the object to be measured, it is possible to perform film thickness estimation that is appropriate to the state of the object to be measured. This makes it possible to achieve highly accurate film thickness estimation.

[0014] The optical splitting element has a tilted dichroic mirror whose transmittance and reflectance change according to wavelength in a predetermined wavelength range, splitting light from the object to be measured by transmitting and reflecting it. The analysis unit may estimate the film thickness of the object to be measured based on brightness information and wavelength information if the film thickness of the object to be measured is less than a predetermined value, or if the film thickness of the object to be measured is greater than a predetermined value, it may identify the wavelength centroid based on the signal output from the photodetector and estimate the film thickness of the object to be measured based on the wavelength centroid. Estimating the film thickness of the object to be measured based on the wavelength centroid allows for simpler and more accurate film thickness estimation. However, it is difficult to perform highly accurate film thickness estimation based on the wavelength centroid when the film thickness is small. In this regard, if the film thickness of the object to be measured is obtained and the film thickness is less than a predetermined value, the above-described film thickness estimation based on brightness information and wavelength information can be performed, allowing for highly accurate film thickness estimation even when the film thickness is small. Furthermore, if the film thickness is sufficiently large, film thickness estimation based on the wavelength centroid can be performed more simply, quickly, and with higher accuracy.

[0015] The analysis unit may identify a film thickness measurement range, which is the range of film thicknesses that can be measured, based on wavelength information, and estimate the film thickness of the object to be measured from one or more film thicknesses identified based on the relationship between brightness and film thickness and brightness information, that falls within the film thickness measurement range. Since a relationship holds between the brightness of light from the object to be measured and the film thickness, the relationship between brightness and film thickness can be defined in advance. Here, since the relationship between brightness and film thickness is shown by a waveform that shows periodic changes, even if brightness is identified based on brightness information, there will be multiple candidate film thicknesses corresponding to that brightness. In this respect, by using wavelength information including the spectrum, the range of film thicknesses that can be measured (film thickness measurement range) is identified, making it possible to identify one film thickness from among multiple candidate film thicknesses. By estimating the film thickness of the object identified in this way, highly accurate film thickness estimation can be achieved.

[0016] The analysis unit may estimate the film thickness of the object being measured based on corrected luminance information, which is obtained by correcting the luminance value indicated by the luminance information by the amount of change from the initial value of the spectrum in the wavelength information. The light detected by the photodetector may be affected by, for example, fluctuations of the light source or background light. In this case, there is a risk that the film thickness cannot be estimated with high accuracy based on the luminance information. In this regard, by correcting the luminance value indicated by the luminance information by the amount of change from the initial value of the spectrum, the film thickness can be estimated with high accuracy using luminance information that cancels out the effects of the original fluctuations of the light source and background light.

[0017] A method for measuring film thickness according to one aspect of the present invention includes: a light irradiation step of irradiating an object to be measured with light; a photodetection step of detecting light from the object to be measured and outputting a signal corresponding to the brightness information of the detected light; a spectral detection step of spectrally detecting the light from the object to be measured and outputting a signal corresponding to wavelength information including the spectrum of the light; and a film thickness estimation step of estimating the film thickness of the object to be measured based on brightness information identified from the signal output in the photodetection step and wavelength information identified from the signal output in the spectral step.

[0018] In the light detection step, the luminance information may be obtained by splitting the light from the measurement object and detecting each of the split lights.

[0019] In the light detection step, a signal corresponding to the luminance information including the ratio of the luminance values of each of the split lights may be output.

[0020] In the film thickness estimation step, based on the information of the measurement object, it may be determined whether to perform the film thickness estimation of the measurement object using the luminance information and the wavelength information.

[0021] In the light detection step, the light from the measurement object is split by an inclined dichroic mirror that changes the transmittance and reflectance according to the wavelength in a predetermined wavelength range and transmits and reflects the light from the measurement object. In the film thickness estimation step, when the thickness of the film thickness of the measurement object is smaller than a predetermined value, the film thickness of the measurement object is estimated based on the luminance information and the wavelength information. When the thickness of the film thickness of the measurement object is larger than a predetermined value, the wavelength centroid is specified based on the signal output in the light detection step, and the film thickness of the measurement object may be estimated based on the wavelength centroid.

[0022] In the film thickness estimation step, based on the wavelength information, the film thickness measurement range, which is the range of the film thickness that can be measured, is specified, and among the one or more film thicknesses specified based on the relational expression between the luminance and the film thickness and the luminance information, the film thickness included in the film thickness measurement range is estimated as the film thickness of the measurement object.

[0023] In the film thickness estimation step, the film thickness of the measurement object may be estimated based on the corrected luminance information obtained by correcting the luminance value indicated by the luminance information by the amount of change from the initial value of the spectrum of the wavelength information.

Advantages of the Invention

[0024] According to one aspect of the present invention, the film thickness of the measurement object can be derived with high accuracy.

Brief Description of the Drawings

[0025] [Figure 1] Figure 1 is a schematic diagram showing a film thickness measuring device according to an embodiment of the present invention. [Figure 2] Figure 2 shows the relationship between wavelength and reflectance for different film thicknesses. [Figure 3] Figure 3 is a diagram illustrating the estimation of film thickness. [Figure 4] Figure 4 is a flowchart showing the film thickness measurement flow according to an embodiment of the present invention. [Modes for carrying out the invention]

[0026] Embodiments of the present invention will be described in detail below with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions are omitted.

[0027] Figure 1 is a schematic diagram of the film thickness measuring device 1 according to this embodiment. The film thickness measuring device 1 is a device that irradiates a sample 100 (object to be measured) with light, for example, in a planar manner, and measures the thickness of a film formed on the sample 100 based on the reflected light from the sample 100. The sample 100 may be a light-emitting element such as an LED, mini-LED, μLED, SLD element, laser element, vertical-cavity-cell-scale (VCSEL), or OLED, or it may be a light-emitting element whose emission wavelength is adjusted by a fluorescent material containing nanodots, etc. The sample 100 may also be a semiconductor material such as a wafer on which a thin film has been formed.

[0028] As shown in Figure 1, the film thickness measuring device 1 comprises a light source 10 (light irradiation unit), a camera system 20, and a control device 30 (analysis unit).

[0029] The light source 10 illuminates the sample 100 with light in a planar manner, for example. The light source 10 illuminates substantially the entire surface of the sample 100 with light in a planar manner. The light source 10 is a light source capable of uniformly illuminating the surface of the sample 100 and irradiates the sample 100 with diffused light. The light source 10 may be a so-called flat dome type light source or a dome type light source. A flat dome type light source can suppress reflections while ensuring a sufficient field of view (for example, a field of view of about 300 mm). The light source 10 may be a surface illumination unit using a white LED, halogen lamp, or Xe lamp, etc.

[0030] The light source 10, for example, irradiates the sample 100 with light of a wavelength included in a predetermined wavelength range of the tilted dichroic mirror 22 (details described later) of the camera system 20. As will be described in detail later, the tilted dichroic mirror 22 is an optical element that divides the light from the sample 100 by transmitting and reflecting it according to its wavelength. The transmittance and reflectance of the tilted dichroic mirror 22 change according to the wavelength in the predetermined wavelength range mentioned above.

[0031] The camera system 20 comprises a lens 21, an inclined dichroic mirror 22 (light-splitting element), area sensors 23, 24 (light-detecting units), bandpass filters 25, 26, a half-mirror 29, and a spectrometer 50.

[0032] Lens 21 is a lens that focuses light from the incident sample 100. Lens 21 may be positioned upstream of the inclined dichroic mirror 22, or it may be positioned in the region between the inclined dichroic mirror 22 and the area sensors 23 and 24. Lens 21 may be a finite focus lens or an infinite focus lens. If lens 21 is a finite focus lens, the distance from lens 21 to the area sensors 23 and 24 is set to a predetermined value. If lens 21 is an infinite focus lens, lens 21 is a collimator lens that converts light from the sample 100 into parallel light, and aberration correction is performed so that parallel light is obtained. The light output from lens 21 is incident on the inclined dichroic mirror 22.

[0033] The tilted dichroic mirror 22 is a mirror made using a special optical material and is an optical splitting element that splits light from sample 100 by transmitting and reflecting it according to its wavelength. The tilted dichroic mirror 22 splits the light from sample 100 and guides it to area sensors 23 and 24. The tilted dichroic mirror 22 is configured so that the transmittance and reflectance of light change according to the wavelength in a predetermined wavelength range. That is, in the tilted dichroic mirror 22, the transmittance (and reflectance) of light changes gradually in accordance with the change in wavelength in a predetermined wavelength range, and the transmittance (and reflectance) of light remains constant regardless of the change in wavelength in wavelength ranges other than the predetermined wavelength range. In other words, in a specific wavelength band, the transmittance of light increases monotonically (the reflectance decreases monotonically) in accordance with the change in wavelength. Since transmittance and reflectance have a negative correlation, where when one changes in the direction of increasing, the other changes in the direction of decreasing, the term "transmittance (and reflectance)" may be used below instead of simply "transmittance". Furthermore, "constant light transmittance regardless of wavelength change" includes not only cases where it is perfectly constant, but also cases where, for example, the change in transmittance for a 1 nm change in wavelength is 0.1% or less.

[0034] Area sensors 23 and 24 image (detect) light from sample 100 (more specifically, light split by the tilted dichroic mirror 22). Area sensor 23 is a first photodetector that images light transmitted through the tilted dichroic mirror 22. Area sensor 24 is a second photodetector that images light reflected by the tilted dichroic mirror 22. The wavelength range to which area sensors 23 and 24 are sensitive corresponds to a predetermined wavelength range in which the transmittance (and reflectance) of light changes in the tilted dichroic mirror 22 according to the change in wavelength. Area sensors 23 and 24 are, for example, monochrome sensors or color sensors. Area sensors 23 and 24 output a signal corresponding to the brightness information of the detected light. More specifically, area sensors 23 and 24 may output a signal corresponding to brightness information, including the ratio of the brightness value of light detected by area sensor 23 to the brightness value of light detected by area sensor 24, to the control device 30. The signals output from area sensors 23 and 24 are, for example, imaging results (images).

[0035] The tilted dichroic mirror 22 described above may be replaced with other optical splitting elements. For example, such optical splitting elements may consist of, for example, a normal dichroic mirror (a dichroic mirror with small changes in light transmittance and reflectance depending on wavelength) or a half-mirror and a bandpass filter. Also, the area sensors 23 and 24 described above may be replaced with other photodetectors. For example, such photodetectors may be, for example, line sensors.

[0036] The bandpass filter 25 is positioned between the tilted dichroic mirror 22 and the area sensor 23. The bandpass filter 26 is positioned between the tilted dichroic mirror 22 and the area sensor 24. The bandpass filters 25 and 26 may be filters that remove light in wavelength ranges other than the predetermined wavelength range described above (the wavelength range in the tilted dichroic mirror 22 where the transmittance and reflectance of light change depending on the wavelength).

[0037] The half-mirror 29 is provided, for example, in the optical path between the lens 21 and the inclined dichroic mirror 22, and reflects light from a point on the sample 100 (for example, a point near the center of the sample 100) towards the spectrometer 50.

[0038] The spectrometer 50 spectrally detects the light from the sample 100, specifically the light from a single point on the sample 100 reflected by the half mirror 29, and obtains the spectrum of the light. Here, the spectrum refers to a spectral spectrum that shows the intensity of light at each wavelength. Using such a spectral spectrum, the control device 30 can determine the absolute value of the thickness of the single point on the sample 100 as described above. The spectrometer 50 outputs a signal to the control device 30 corresponding to the wavelength information including the spectral spectrum. Note that the spectrometer 50 may be installed outside the camera system 20 and spectrally detect the light from the sample 100 before it enters the lens 21.

[0039] The control device 30 is a computer, and physically comprises memory such as RAM and ROM, a processor (arithmetic circuit) such as a CPU, a communication interface, and a storage unit such as a hard disk. The control device 30 functions by executing a program stored in memory using the CPU of the computer system. The control device 30 may be composed of a microcontroller or an FPGA.

[0040] The control device 30 is an analysis unit that estimates the film thickness of sample 100. The control device 30 performs preprocessing, selection processing, and film thickness estimation processing. Each of these processes will be described below.

[0041] (Pre-processing) The control device 30 acquires captured images (signals corresponding to brightness information) from the area sensors 23 and 24 and performs preprocessing on the captured images. Preprocessing here refers to correction processing to estimate the film thickness of sample 100 with high accuracy based on the captured images, such as background correction and reference correction (shading correction).

[0042] Background correction is a process that subtracts the light from the atmosphere (background light) contained in the captured image to appropriately obtain the brightness value of the light from sample 100 corresponding to the irradiated light. In background correction, for example, the brightness value of the image data of sample 100 in a non-reflective state is subtracted from the brightness value of the captured image. In order to remove the effect of direct light from the light source 10, x corresponding to the brightness information of the captured image may be derived using the following equation (1). In the following equation (1), IT is the transmitted light amount, IR is the reflected light amount, ITr is the transmitted light amount at the reference, IRr is the reflected light amount at the reference, ITb is the transmitted light amount in a non-reflective state, and IRb is the reflected light amount in a non-reflective state. x={(IT-ITb) / (ITr-ITb)-(IR-IRb) / (IRr-IRb)} / 2{(IT-ITb) / (ITr-ITb)+(IR-IRb) / (IRr-IRb)} (1)

[0043] Reference correction (shading correction) is a process that corrects individual differences such as uneven brightness and aberrations caused by the optical system by acquiring difference data between the captured image and a shading image for the region corresponding to the captured image. In reference correction, for example, the captured image is divided by the image data of a reference sample. For example, x may be derived using equation (2) below, with the signal intensity of a substrate with known reflection characteristics as the reference. x=(IT / ITr-IR / IRr) / 2(IT / ITr+IR / IRr) (2)

[0044] (Selection process) The control device 30 performs a selection process following the preprocessing. The control device 30 selects a film thickness estimation method based on the information of sample 100 (specifically, the film thickness of sample 100). The film thickness of sample 100 may be pre-set in the control device 30 or entered by the user. The control device 30 selects either the wavelength shift method or the reflected light thickness conversion method (details described later) as the film thickness estimation method. If the film thickness of sample 100 is less than a predetermined value (e.g., 100 nm), the control device 30 selects the reflected light thickness conversion method, and if the film thickness of sample 100 is greater than the predetermined value, it selects the wavelength shift method.

[0045] (Film thickness estimation process) The control device 30 estimates the film thickness of sample 100 using the film thickness estimation method selected in the selection process. Specifically, the control device 30 estimates the film thickness of sample 100 using either the wavelength shift method or the reflected light amount thickness conversion method.

[0046] In the wavelength shift method, the control device 30 identifies the wavelength centroid based on the signals (imported images) output from the area sensors 23 and 24, and estimates the film thickness of the sample 100 based on the wavelength centroid. The control device 30 derives the wavelength centroid of light for each pixel based on the amount of transmitted light identified based on the image captured by the area sensor 23, the amount of reflected light identified based on the image captured by the area sensor 24, the center wavelength of the tilted dichroic mirror 22, and the width of the tilted dichroic mirror 22, and estimates the film thickness corresponding to each pixel based on the wavelength centroid. The width of the tilted dichroic mirror 22 is, for example, the wavelength range from the wavelength at which the transmittance is 0% to the wavelength at which the transmittance is 100% in the tilted dichroic mirror 22.

[0047] Specifically, the control device 30 derives the wavelength centroid of each pixel based on the following equation (3). In the following equation (3), λ is the wavelength centroid, λ0 is the center wavelength of the tilted dichroic mirror 22, W is the width of the tilted dichroic mirror 22, R is the amount of reflected light, and T is the amount of transmitted light. In this way, the wavelength centroid shifts (wavelength shift) based on the amount of transmitted light and the amount of reflected light. λ = λ0 + W(TR) / 2(T + R) (3)

[0048] The method for deriving the wavelength centroid is not limited to the above. For example, since λ (wavelength centroid) is proportional to x as follows, the wavelength centroid may also be derived from equations (4) and (5) below. In equation (5) below, IT represents the transmitted light amount and IR represents the reflected light amount. Furthermore, if the spectral shape of the object to be measured and the line formation of the tilted dichroic mirror 22 are ideal shapes, the parameters a and b in equation (4) can be determined by the optical properties of the tilted dichroic mirror 22. λ = ax + b (4) x = IT - IR / 2(IT + IR) (5)

[0049] Furthermore, in order to comprehensively implement various corrections such as film characteristics, irradiation spectrum, and nonlinearity of the tilted dichroic mirror 22, the wavelength centroid (λ) may be approximated by a polynomial such as equation (6) below. Note that each parameter (a, b, c, d, e) in equation (6) below can be determined, for example, by measuring multiple samples with different wavelength centroids (film thicknesses). λ = ax⁴ + bx³ + cx² + dx + e (6)

[0050] Furthermore, since the wavelength centroid differs depending on the film thickness, it becomes possible to estimate the film thickness by identifying the wavelength centroid. The relationship between wavelength and film thickness can be explained by the following equation (7). In the following equation (7), n is the refractive index of the film, d is the film thickness, m is a positive integer (1, 2, 3, ...), and λ is the wavelength centroid. 2nd represents the optical path difference (the optical path difference caused by the arrangement of the film). Based on the following equation (7), the control device 30 estimates the film thickness corresponding to each pixel from the wavelength centroid of each pixel. 2nd = mλ (m = 1, 2, 3, ...) (Constructive interference condition) 2nd = (m - 1 / 2)λ (m = 1, 2, 3, ...) (Condition for destructive interference) (7)

[0051] Here, the shift in the wavelength centroid value based on the transmitted and reflected light amounts (wavelength shift) described above is less likely to occur when the film thickness of sample 100 is thin. Figure 2 shows the relationship between wavelength and reflectance (reflectance of light detected by area sensors 23 and 24) for each film thickness. In Figure 2, the horizontal axis represents wavelength, and the vertical axis represents reflectance (reflectance). As shown in Figure 2, it can be seen that the thinner the film thickness, the smaller the change in wavelength becomes even when the reflectance (light amount) changes. If the wavelength does not shift sufficiently in response to the light amount, it becomes difficult to estimate the film thickness using the wavelength shift method described above. Specifically, the wavelength shift method described above becomes difficult to estimate the film thickness with high accuracy when the film thickness of sample 100 is thinner than 100 nm. Therefore, when the film thickness of sample 100 is less than a predetermined value (e.g., 100 nm), the control device 30 estimates the film thickness of sample 100 using the reflected light amount thickness conversion method.

[0052] In the reflected light thickness conversion method, the control device 30 estimates the film thickness of sample 100 based on luminance information identified from signals (imaging images) output from area sensors 23 and 24 and wavelength information identified from signals output from spectrometer 50.

[0053] Specifically, the control device 30 first derives a value of x corresponding to the brightness information of the captured image. For example, if the brightness information of the light transmitted from the tilted dichroic mirror 22 is used, x = IT (where IT is the amount of transmitted light). If the brightness information of the light reflected from the tilted dichroic mirror 22 is used, x = IR (where IR is the amount of reflected light). Furthermore, if brightness information including the ratio of the brightness value of the light detected by the area sensor 23 and the brightness value of the light detected by the area sensor 24 is used, x may be set to x = IT / IR. The light detected by the area sensors 23 and 24 may be affected by, for example, fluctuations of the light source 10 or background light (i.e., light intensity fluctuations occur), but by setting the value of x corresponding to the brightness information to a ratio value such as IT / IR, the above-mentioned light intensity fluctuations can be corrected. Note that such light intensity fluctuation correction is effective when the amount of light intensity fluctuation is extremely small compared to the detected light intensity.

[0054] The control device 30 may perform the above-mentioned light intensity fluctuation correction by correcting the values ​​of IT (IT is transmitted light) and IR (IR is reflected light) related to the derivation of x described above, based on the wavelength information identified from the signal output from the spectrometer 50. The control device 30 may also perform the light intensity fluctuation correction of IT and IR according to the following equation (8). In the following equation (8), IT' is the corrected transmitted light, IR' is the corrected reflected light, T(λ) is the transmittance in the tilted dichroic mirror 22, R(λ) is the reflectance in the tilted dichroic mirror 22, I(λ) is the spectrum included in the wavelength information (spectrum measured by the spectrometer 50), and Iini(λ) is the initial value of the spectrum measured by the spectrometer 50. Note that in the tilted dichroic mirror 22, R(λ) = 1 - T(λ). IT´=IT×(Σ(Iini(λ)T(λ)) / Σ(I(λ)T(λ)) IR´=IR×(Σ(Iini(λ)R(λ)) / Σ(I(λ)R(λ)) (8)

[0055] As shown in equation (8) above, the control device 30 derives corrected luminance information, IT' and IR', by correcting IT (or IR) corresponding to the luminance value indicated by the luminance information with the amount of change from the initial value of the spectrum measured by the spectrometer 50. In this way, by correcting the luminance value with the amount of change from the initial value of the spectrum, the effects of fluctuations of the light source 10 and background light that were originally included can be canceled. Note that, as mentioned above, when the value of x is a ratio value such as IT / IR, light intensity fluctuation correction is performed by using the ratio value, so it is not always necessary to perform light intensity fluctuation correction using equation (8). However, if there are independent light intensity fluctuations in the transmitted signal and the reflected signal, it is preferable to perform light intensity fluctuation correction using equation (8). That is, when the behavior of the light source 10 changes depending on the wavelength band, etc., light intensity fluctuation correction using equation (8) is preferable. Below, an example in which light intensity fluctuation correction is performed using equation (8) and the corrected luminance information is used will be described. In other words, the control device 30 estimates the film thickness of sample 100 based on corrected luminance information, which is obtained by correcting the luminance value indicated by the luminance information by the amount of change from the initial value of the spectrum of the wavelength information.

[0056] The control device 30 identifies a film thickness measurement range, which is the range of film thicknesses that can be measured, based on the wavelength information identified from the signal output from the spectrometer 50, and estimates the film thickness that falls within the film thickness measurement range from one or more film thicknesses identified based on the relationship between brightness and film thickness and the brightness information, as the film thickness of sample 100.

[0057] Figure 3 illustrates the film thickness estimation described above. The relationship between the luminance value (reflection intensity) of light shown in the luminance information and the film thickness is shown, for example, by equation (9) below. In equation (9) below, I is the luminance value (reflection intensity), n is the refractive index of the film, and d is the film thickness. I = Acos(2π(2nd / λ)) + B (9)

[0058] Figure 3(a) shows the relationship between the luminance value (reflection intensity) and film thickness determined by equation (9) above. In Figure 3(a), the horizontal axis is film thickness and the vertical axis is luminance value (reflection intensity). As is clear from equation (9), the relationship between luminance and film thickness is shown as a waveform that shows periodic changes (see Figure 3(a)). Therefore, even if a luminance value is identified based on luminance information, there will be multiple candidates for film thickness d corresponding to that luminance value. That is, when a luminance value (reflection intensity) shown by a dashed line in Figure 3(a) is identified, there will be multiple candidates for film thickness d that differ for each phase. In the example shown in Figure 3(a), with m being an integer, there are film thickness ranges of 2π(2nd / λ)=(m+4)π to (m+5)π, 2π(2nd / λ)=(m+2)π to (m+3)π, and 2π(2nd / λ)=mπ to (m+1)π. In this case, the control device 30 can determine which film thickness range is the measurable film thickness range (film thickness measurement range) based on the wavelength information (see Figure 3(e)) identified from the signal output from the spectrometer 50. That is, given the relationship between reflectance intensity and wavelength for (m+4)π to (m+5)π (see Figure 3(b)), the relationship between reflectance intensity and wavelength for (m+2)π to (m+3)π (see Figure 3(c)), and the relationship between reflectance intensity and wavelength for mπ to (m+1)π (see Figure 3(d)), the control device 30 determines the film thickness range to be (m+2)π to (m+3)π because the relationship between reflectance intensity and wavelength for (m+2)π to (m+3)π (see Figure 3(c)) matches the wavelength information (see Figure 3(e)).

[0059] The control device 30 may approximate the film thickness d with a polynomial such as equation (10) below in order to comprehensively perform various corrections such as film characteristics, irradiation spectrum, and nonlinearity of the tilted dichroic mirror 22. Note that each parameter (a, b, c, d, e) in equation (10) below may be set in advance for each film thickness and film type, for example, by measuring multiple samples with different film thicknesses and film types. d = ax⁴ + bx³ + cx² + dx + e (10)

[0060] Next, the film thickness measurement flow according to this embodiment will be described. Figure 4 is a flowchart of the film thickness measurement flow according to this embodiment.

[0061] In the film thickness measuring device 1, light is first shone onto the sample 100 from the light source 10 (light irradiation step), the light from the sample 100 is detected by area sensors 23 and 24, and an image is acquired by outputting a signal corresponding to the brightness information of the detected light (step S1, light detection step).

[0062] The acquired image is subjected to background correction by the control device 30 (step S2), and then reference correction is performed (step S3). The control device 30 then selects a film thickness estimation method based on the information of the sample 100 (step S4). Based on the film thickness of the sample 100, the control device 30 decides whether or not to perform film thickness estimation of the sample 100 using luminance information and wavelength information. If the film thickness is, for example, less than 100 nm, the control device 30 decides to perform film thickness estimation of the sample 100 using luminance information and wavelength information (reflected light thickness conversion method) and performs the processes in steps S5 to S10. If the film thickness is, for example, 100 nm or more, the control device 30 decides to perform the wavelength shift method without performing film thickness estimation of the sample 100 using luminance information and wavelength information (reflected light thickness conversion method) and performs the processes in steps S13 to S15.

[0063] In the reflected light thickness conversion method, first, a value of x corresponding to the brightness information of the captured image is derived (step S5). For example, if brightness information including the ratio of the brightness value of light detected by area sensor 23 and the brightness value of light detected by area sensor 24 is used, then x = IT / IR.

[0064] Next, it is determined whether or not absolute film thickness correction is performed (step S6). Absolute film thickness correction is a process that calculates the film thickness value using the measurement result of the absolute value of the film thickness by the spectrometer 50. If absolute film thickness correction is not performed, the process of step S10, which will be described later, is performed after the process of step S6.

[0065] When absolute value correction of film thickness is performed, the spectrometer 50 spectrally detects the light from the sample 100 and outputs a signal corresponding to the wavelength information including the spectrum of the light (step S7, spectral step). Then, the control device 30 identifies the film thickness measurement range, which is the range of film thickness that can be measured, based on the above wavelength information (step S8).

[0066] Furthermore, the control device 30 performs light intensity fluctuation correction (step S9). Specifically, the control device 30 performs light intensity fluctuation correction by correcting the values ​​of IT (IT is transmitted light) and IR (IR is reflected light) based on wavelength information using equation (8) described above.

[0067] Finally, the control device 30 estimates the film thickness d using the polynomial shown in equation (10) above (step S10, film thickness estimation step). Note that each parameter (correction coefficient) a, b, c, d, and e in equation (10) may be set for each film thickness and film type. In that case, correction images are acquired in advance for each film thickness and film type (step S11), and the correction coefficients a to e are determined (step S12).

[0068] On the other hand, in the wavelength shift method, first, the control device 30 derives x for deriving the wavelength centroid using equation (5) above (step S13). Then, the control device 30 derives the wavelength centroid λ using the polynomial shown in equation (6) above (step S14). Then, the control device 30 estimates the film thickness from the wavelength centroid using equation (7) above (step S15). Note that the parameters (correction coefficients) a, b, c, d, and e in equation (6) may be determined in advance by acquiring a correction image (step S16) (step S17).

[0069] Next, the effects and advantages of this embodiment will be described.

[0070] The film thickness measuring device 1 comprises a light source 10 that irradiates light onto a sample 100, an area sensor 23 that detects light from the sample 100 and outputs a signal corresponding to the brightness information of the detected light, a spectrometer 50 that spectrally detects the light from the sample 100 and outputs a signal corresponding to the wavelength information including the spectrum of the light, and a control device 30 that estimates the film thickness of the sample 100 based on the brightness information identified from the signal output from the area sensor 23 and the wavelength information identified from the signal output from the spectrometer 50.

[0071] In the film thickness measuring device 1 according to this embodiment, light from the sample 100 is detected by the area sensor 23 and spectrally detected by the spectrometer 50. The film thickness of the sample 100 is estimated based on the luminance information identified from the signal output from the area sensor 23 and the wavelength information identified from the signal output from the spectrometer 50. The luminance information (reflectance of light) of the light detected by the area sensor 23 is a value corresponding to the film thickness of the sample 100. However, with only luminance information, only the relative distribution of film thickness is identified, and the absolute value is not identified. In this respect, the film thickness measuring device 1 according to this embodiment further considers wavelength information including the spectrum of spectrally detected light, so that the absolute value of the film thickness at the spectrally detected point can be identified. As a result, the absolute value of the film thickness of each area of ​​the object to be measured can be appropriately derived based on the relative film thickness distribution identified from the luminance information and the absolute value of the film thickness at the spectrally detected point. As described above, by calibrating the detection result in the area sensor 23 with the detection result in the spectrometer 50, the film thickness of the sample 100 can be derived with high accuracy.

[0072] The above-described film thickness measuring device 1 further comprises a tilted dichroic mirror 22 (or a dichroic mirror or half mirror and bandpass filter), which is an optical splitting element for splitting light from sample 100, and further comprises an area sensor 24. The tilted dichroic mirror 22 may split the light from sample 100 and guide it to area sensors 23 and 24. In this way, the light from sample 100 is split, and the split light is detected by the two area sensors 23 and 24. For example, the light can be separated by wavelength band, and the film thickness can be estimated from the brightness information in the desired wavelength band. This makes it possible to derive the film thickness of sample 100 with higher accuracy.

[0073] Furthermore, by using a tilted dichroic mirror 22 (or a dichroic mirror or half mirror and a bandpass filter) as an optical splitting element, light can be appropriately split for each wavelength band.

[0074] Area sensors 23 and 24 may output a signal corresponding to luminance information, which includes the ratio of the luminance value of the light detected by area sensor 23 to the luminance value of the light detected by area sensor 24. The light detected by area sensors 23 and 24 may be affected by, for example, fluctuations of the light source or background light. In this case, it may not be possible to estimate the film thickness with high accuracy based on the luminance information. In this regard, by deriving the ratio of the luminance values ​​of light in two wavelength bands divided according to wavelength, it is possible to derive luminance information that is not affected by the background light, etc. mentioned above. By estimating the film thickness based on such luminance information, it is possible to achieve high-accuracy film thickness estimation.

[0075] The control device 30 may decide whether or not to perform film thickness estimation of sample 100 using brightness information and wavelength information, based on the information of sample 100. Since the method for estimating film thickness with high accuracy differs depending on the state of sample 100 (e.g., thickness), by deciding whether or not to perform the "film thickness estimation using brightness information and wavelength information" described above based on the information of sample 100, it is possible to perform film thickness estimation that is appropriate to the state of sample 100. This makes it possible to achieve highly accurate film thickness estimation.

[0076] The control device 30 may estimate the film thickness of sample 100 based on brightness information and wavelength information if the film thickness of sample 100 is less than a predetermined value, or it may identify the wavelength centroid based on the signals output from area sensors 23 and 24 and estimate the film thickness of sample 100 based on the wavelength centroid if the film thickness of sample 100 is greater than a predetermined value. The method of estimating the film thickness of sample 100 based on the wavelength centroid allows for simpler and more accurate film thickness estimation. However, as described above, it is difficult to perform highly accurate film thickness estimation based on the wavelength centroid when the film thickness is small. In this regard, if the film thickness of sample 100 is obtained and the film thickness is less than a predetermined value, the film thickness estimation based on brightness information and wavelength information described above can be performed, thereby enabling highly accurate film thickness estimation even when the film thickness is small. Furthermore, if the film thickness is sufficiently large, the film thickness estimation based on the wavelength centroid can be performed more simply, quickly, and with higher accuracy.

[0077] The control device 30 may identify a film thickness measurement range, which is the range of film thicknesses that can be measured, based on wavelength information, and estimate the film thickness within the film thickness measurement range from one or more film thicknesses identified based on the relationship between brightness and film thickness and brightness information, as the film thickness of sample 100. Since a relationship holds for the brightness and film thickness of light from sample 100, the relationship between brightness and film thickness can be defined in advance. Here, since the relationship between brightness and film thickness is shown by a waveform that shows periodic changes, even if brightness is identified based on brightness information, there will be multiple candidate film thicknesses corresponding to that brightness. In this respect, by using wavelength information including the spectrum, the range of film thicknesses that can be measured (film thickness measurement range) is identified, making it possible to identify one film thickness from among multiple candidate film thicknesses. By estimating the film thickness identified in this way as the film thickness of sample 100, highly accurate film thickness estimation can be achieved.

[0078] The control device 30 may estimate the film thickness of sample 100 based on corrected luminance information obtained by correcting the luminance value indicated by the luminance information by the amount of change from the initial value of the spectrum of the wavelength information. The light detected by the photodetector may be affected by, for example, fluctuations of the light source or background light. In this case, it may not be possible to estimate the film thickness with high accuracy based on the luminance information. In this regard, by correcting the luminance value indicated by the luminance information by the amount of change from the initial value of the spectrum, the film thickness can be estimated with high accuracy using luminance information that cancels out the effects of fluctuations of the light source and background light that were originally included. [Explanation of Symbols]

[0079] 1…Film thickness measuring device, 10…Light source (light irradiation unit), 22…Inclined dichroic mirror, 23,24…Area sensor (photodetector, light detection unit), 30…Control device (analysis unit), 50…Spectrometer, 100…Sample (object to be measured).

Claims

1. A light irradiation unit that irradiates light onto the object to be measured, A light-dividing element that divides light from the object to be measured, A light detection unit having a first area sensor and a second area sensor that detect light from the light splitting element, and outputting a signal corresponding to the brightness information of the detected light, A spectrometer that spectrally detects light from the object to be measured and outputs a signal corresponding to wavelength information including the spectrum of said light, A film thickness measuring device comprising: an analysis unit that derives the absolute value of the film thickness of each area of ​​the object to be measured based on the luminance information identified from the signal output from the light detection unit and the wavelength information identified from the signal output from the spectrometer.

2. The film thickness measuring apparatus according to claim 1, wherein the light source irradiates light onto the object to be measured in a planar manner.

3. The film thickness measuring apparatus according to claim 1, wherein the optical splitting element has a dichroic mirror, and the first area sensor and the second area sensor are monochrome sensors.

4. The film thickness measuring apparatus according to claim 1, wherein the optical splitting element has a half mirror and a bandpass filter, and the first area sensor and the second area sensor are monochrome sensors.

5. The film thickness measuring apparatus according to claim 1, wherein the light splitting element has a half mirror, and the first area sensor and the second area sensor are color sensors.

6. The film thickness measuring apparatus according to any one of claims 1 to 5, wherein the light detection unit outputs a signal corresponding to the brightness information, which includes the ratio of the brightness value of light detected by the first photodetector to the brightness value of light detected by the second photodetector.

7. The film thickness measuring apparatus according to any one of claims 1 to 5, wherein the analysis unit identifies a film thickness measurement range, which is a range of film thicknesses that can be measured, based on the wavelength information, and derives, as the absolute value of the film thickness of the object to be measured, one or more film thicknesses identified based on the relationship between brightness and film thickness and the brightness information, the film thickness included in the film thickness measurement range.

8. The film thickness measuring apparatus according to any one of claims 1 to 5, wherein the analysis unit derives the absolute value of the film thickness of the object to be measured based on corrected luminance information obtained by correcting the luminance value indicated by the luminance information by the amount of change from the initial value of the spectrum of the wavelength information.

Images