JP2010048604A - Apparatus and method for measuring film thickness - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To quickly measure and acquire film thicknesses at a plurality of measurement points in a measurement of a film formed on an object. <P>SOLUTION: In this film-thickness measuring apparatus 1, a plurality of reflection characteristics corresponding to a plurality of inspection wavelengths are stored beforehand, concerning the film 92 whose optical constants are known. Based on the plurality of reflection characteristics and a plurality of inspection images corresponding to the plurality of inspection wavelengths acquired by imaging the film 92 while switching the inspection wavelengths, the film thicknesses at the individual measurement points are acquired by a film-thickness calculation part 73, based on the degrees of coincidences between a plurality of pixel values of the plurality of inspection images at the individual measurement points on the film 92, and a plurality of theoretical reflectivities represented by a plurality of reflection characteristics at individual film thicknesses. Accordingly, the film thicknesses at the plurality of measurement points on a substrate 9 can be quickly acquired, since the amount of calculations by the calculation part 73 only increases slightly even if the number of measurements increases. As a result, a wide-range of film-thickness distribution on the substrate 9 can be acquired with high accuracy and with high resolution. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technique for measuring the thickness of a film formed on an object.

  Conventionally, as one of apparatuses for inspecting a thin film such as a resist film formed on a main surface of a glass substrate or a semiconductor substrate (hereinafter simply referred to as “substrate”) for a display device, An apparatus for inspecting unevenness is known. In the devices of Patent Document 1 to Patent Document 10, light from a light source is irradiated onto a thin film on a substrate, and film thickness unevenness (that is, film thickness on the substrate) is performed using light interference in reflected light or transmitted light from the thin film. The distribution of relative fluctuations is detected.

On the other hand, Patent Document 11 discloses a film thickness measuring device that irradiates light toward a minute region on a substrate and obtains a film thickness of the thin film on the substrate based on the spectral intensity of reflected light from the minute region. Yes. In the film thickness measurement device of Patent Document 11, in addition to the above-described measurement unit that obtains the film thickness from the spectral intensity of the reflected light by the optical interference method, the polarized light is irradiated onto a minute region on the substrate, An ellipsometer is also provided to determine the thickness of the thin film by analyzing the polarization state of the reflected light.
JP 2006-105884 A Japanese Patent Laid-Open No. 2006-284211 JP 2006-284212 A JP 2006-292487 A JP 2006-308556 A JP 2006-313143 A JP 2007-57521 A JP 2007-322256 A JP 2007-322257 A JP 2007-322258 A JP 2004-156996 A

  By the way, in the process of forming a thin film on the substrate, in order to manage the thin film with high accuracy, the distribution of the film thickness on the substrate (that is, the distribution of the absolute value of the film thickness) is acquired with high accuracy and high resolution. It is demanded. However, with the apparatuses of Patent Document 1 to Patent Document 10, it is possible to obtain the distribution of the relative variation of the film thickness on the substrate, but it is not possible to obtain the absolute value of the film thickness. On the other hand, in the film thickness measurement apparatus of Patent Document 11, the area that can be measured by one measurement is very small in both the film thickness measurement by the optical interferometry and the film thickness measurement by the ellipsometer, and thus a wide range on the substrate. In order to perform the film thickness measurement at a high resolution, it is necessary to repeat the measurement many times, which requires a lot of measurement time.

  The present invention has been made in view of the above problems, and an object of the present invention is to quickly obtain film thicknesses at a plurality of measurement points in film thickness measurement of a film formed on an object.

  The invention according to claim 1 is a film thickness measuring device for measuring the film thickness of a film formed on an object, and holds the object on which a film having a known optical constant is formed on the main surface. And a reflection characteristic storage unit that stores in advance a plurality of reflection characteristics respectively indicating the relationship between the film thickness of the film at a plurality of inspection wavelengths and the theoretical value of the reflectivity of the film that varies according to the change in the film thickness And a light irradiating unit for irradiating the film with light, and receiving interference light reflected by the film among the light from the light irradiating unit to obtain a plurality of images of the film at the plurality of inspection wavelengths. An imaging unit, and a film thickness calculation unit that calculates a film thickness at each of a plurality of measurement points on the object based on the plurality of images and the plurality of reflection characteristics, the film thickness calculation unit, a) In each of the plurality of images, the maximum pixel value is the maximum. Obtaining a maximum pixel value and a minimum pixel value at a minimum position at which the position and the pixel value are minimum; b) a maximum in reflection characteristics corresponding to the maximum pixel value and the minimum pixel value of each image and each image; A step of associating a pixel value of each image with a reflectance based on a relationship between a reflectance and a minimum reflectance; c) a plurality of pixel values of the plurality of images at each measurement point of the plurality of measurement points; A step of obtaining a film thickness at each measurement point based on a degree of coincidence with a plurality of reflectivities indicated by the plurality of reflection characteristics at each film thickness.

  Invention of Claim 2 is a film thickness measuring apparatus of Claim 1, Comprising: Among the some optical filter which each selectively permeate | transmits the light of these test | inspection wavelength, and these optical filters An optical filter changing mechanism that changes one optical filter disposed on an optical path from the light irradiation unit to the imaging unit to another optical filter, and the light emitted from the light irradiation unit is white light. is there.

  Invention of Claim 3 is a film thickness measuring apparatus of Claim 1 or 2, Comprising: The film thickness meter which acquires the film thickness in the at least 1 measurement point on the said film | membrane is further provided, The said film thickness The film thickness acquired by the meter is used for calculation of the film thickness by the film thickness calculator.

  Invention of Claim 4 is the film thickness measuring apparatus of Claim 3, Comprising: The film thickness in the said at least 1 measurement point acquired with the said film thickness meter, and the said film thickness calculating part calculate The film thickness at each measurement point calculated by the film thickness calculator is corrected based on the difference from the film thickness at the at least one measurement point.

  The invention according to claim 5 is a film thickness measuring method for measuring a thickness of a film formed on an object, and a) an object in which a film having a known optical constant is formed on a main surface. And b) storing in advance a plurality of reflection characteristics respectively indicating the relationship between the film thickness of the film at a plurality of inspection wavelengths and the theoretical value of the reflectivity of the film that varies according to the change in the film thickness. And c) irradiating the film with light from the light irradiating unit, and receiving interference light reflected by the film among the light from the light irradiating unit by the imaging unit, and the film at the plurality of inspection wavelengths. Obtaining a plurality of images; and d) obtaining a maximum pixel value and a minimum pixel value at a maximum position where the pixel value is maximum and a minimum position where the pixel value is minimum in each of the plurality of images. E) the maximum pixel value and the minimum of each image Associating a pixel value and a reflectance of each image based on a relationship between an elementary value and a maximum reflectance and a minimum reflectance in a reflection characteristic corresponding to each image; and f) a plurality of measurements on the object. Obtaining a film thickness at each measurement point based on a degree of coincidence between a plurality of pixel values of the plurality of images at each measurement point and a plurality of reflectances indicated by the plurality of reflection characteristics at each film thickness; Is provided.

  Invention of Claim 6 is a film thickness measuring method of Claim 5, Comprising: The light radiate | emitted from the said light irradiation part in the said c) process is white light, The said c) process is c1. ) One optical filter among a plurality of optical filters that selectively transmit light of the plurality of inspection wavelengths is disposed on an optical path from the light irradiation unit to the imaging unit, and corresponds to the one optical filter. And c2) a step of changing the one optical filter to another optical filter and returning to the step c1) until the plurality of images are acquired.

  The invention according to claim 7 is the film thickness measuring method according to claim 5 or 6, further comprising: g) obtaining a film thickness at at least one measurement point on the film with a film thickness meter. The film thickness obtained in the step g) is used for calculating the film thickness in the step f).

  The invention according to claim 8 is the film thickness measuring method according to claim 7, wherein the film thickness at the at least one measurement point acquired in the step g) is calculated in the step f). Based on the difference from the film thickness at the at least one measurement point, the film thickness at each measurement point calculated in the step f) is corrected.

  In the present invention, film thicknesses at a plurality of measurement points can be quickly obtained. In the inventions of claims 3 and 7, the accuracy of film thickness measurement can be improved.

  FIG. 1 is a diagram showing a configuration of a film thickness measuring apparatus 1 according to the first embodiment of the present invention. The film thickness measuring device 1 is a resist film (hereinafter referred to as a pattern forming resist film) formed on one main surface 91 of a glass substrate (hereinafter simply referred to as “substrate”) 9 used in a display device such as a liquid crystal display device. , Simply referred to as “film”). The film 92 on the substrate 9 is formed by applying a resist solution on the main surface 91 of the substrate 9, and the optical constant of the film 92 is known.

  As shown in FIG. 1, the film thickness measuring apparatus 1 includes a substrate 9 on which a film 92 is formed on a main surface 91 (hereinafter referred to as “upper surface 91”), with the upper surface 91 on the upper side ((+ Z) in FIG. 1). Of the light emitted from the light irradiation unit 3, the light irradiation unit 3 that irradiates light onto the film 92 on the upper surface 91 of the substrate 9 held by the stage 2. The imaging unit 4 that receives light after being reflected by the film 92 to acquire an image of the film 92, and the wavelength band of light that is disposed between the substrate 9 and the imaging unit 4 and is received by the imaging unit 4 Based on the wavelength band switching mechanism 5 for switching between, the moving mechanism 21 for moving the stage 2 relative to the light irradiation unit 3, the imaging unit 4 and the wavelength band switching mechanism 5, and the image acquired by the imaging unit 4. The inspection unit 7 for determining the film thickness of the film 92 is provided.

  The (+ Z) side surface of the stage 2 is preferably black matte. The moving mechanism 21 has a configuration in which a ball screw (not shown) is connected to a motor 211, and the stage 211 moves along the upper surface 91 of the substrate 9 along the guide 212 by rotating the motor 211 in FIG. Move in the direction.

  The light irradiation unit 3 is a halogen lamp 31 that is a light source that emits white light (that is, light in a wavelength band that includes all of a plurality of inspection wavelengths described later), and the Y direction in FIG. 1 perpendicular to the moving direction of the stage 2. Columnar quartz rod 32 extending in the vertical direction and a cylindrical lens 33 extending in the Y direction. In the light irradiation unit 3, a halogen lamp 31 is attached to an end portion on the (+ Y) side of the quartz rod 32, and light incident on the quartz rod 32 from the halogen lamp 31 is linear light extending in the Y direction (that is, The light beam cross-section is converted to light that is long in the Y direction), is emitted from the side surface of the quartz rod 32, and is guided to the upper surface 91 of the substrate 9 through the cylindrical lens 33. In other words, the quartz rod 32 and the cylindrical lens 33 convert the light from the halogen lamp 31 into linear light along the upper surface 91 of the stage 2 and perpendicular to the moving direction to convert the film 92 on the upper surface 91 of the substrate 9. It is an illumination optical system that leads to The length of the linear light irradiated onto the upper surface 91 of the substrate 9 in the Y direction is larger than the width of the substrate 9 in the Y direction.

  In FIG. 1, the optical path from the light irradiation unit 3 to the substrate 9 is indicated by a one-dot chain line (the same applies to the optical path from the substrate 9 to the imaging unit 4). A part of the light that is emitted from the halogen lamp 31 of the light irradiation unit 3 and is inclined with respect to the film 92 on the upper surface 91 of the substrate 9 (that is, at an incident angle greater than 0 °) Is reflected on the (+ Z) side upper surface of the film 92 on the upper surface 91. The film 92 is light transmissive to the light from the light irradiation unit 3, and the light that has not been reflected by the upper surface of the film 92 out of the light from the light irradiation unit 3 passes through the film 92. Reflected by the upper surface 91 of the substrate 9 (that is, the lower surface of the film 92). In the film thickness measuring device 1, interference light (hereinafter simply referred to as “reflected light”) between the light reflected by the upper surface of the film 92 and the light reflected by the upper surface 91 of the substrate 9 is a wavelength band switching mechanism. Then, the light enters the imaging unit 4 via 5.

  The wavelength band switching mechanism 5 includes a plurality of optical filters (for example, interference filters having a half-value width of 10 nm) 51 and a plurality of optical filters that selectively transmit light of a plurality of different narrow wavelength bands used for film thickness measurement. A disc-shaped filter wheel 52 that holds 51, and a filter rotation motor 53 that is attached to the center of the filter wheel 52 and rotates the filter wheel 52. The filter wheel 52 is arranged so that the normal direction thereof is parallel to the optical path from the substrate 9 to the imaging unit 4.

  FIG. 2 is a view of the wavelength band switching mechanism 5 as viewed from the substrate 9 side along the direction perpendicular to the filter wheel 52. As shown in FIG. 2, the filter wheel 52 has six circular openings 521 formed at equal intervals in the circumferential direction, and five of these openings 521 have five types of optical filters having different transmission wavelength bands. 51 is attached. The transmission wavelength band of each optical filter 51 is a narrow wavelength band centered on a predetermined wavelength of light (hereinafter referred to as “inspection wavelength”) used in film thickness measurement by the film thickness measuring apparatus 1. In the following description, the light in the transmission wavelength band that passes through each optical filter 51 is referred to as “light at the inspection wavelength” as a representative of the center wavelength of the transmission wavelength band. That is, the description “light having an inspection wavelength of 550 nm” means light having a narrow transmission wavelength band centered on the inspection wavelength of 550 nm.

  In the wavelength band switching mechanism 5 shown in FIG. 1, the filter wheel 52 is rotated by the filter rotation motor 53, so that one of the five optical filters 51 (see FIG. 2) (hereinafter, different from the other optical filters 51). (Referred to as “selected optical filter 51a”), and is disposed on the optical path from the substrate 9 to the imaging unit 4. Thereby, among the reflected light from the substrate 9 (that is, reflected light of white light including light of five inspection wavelengths corresponding to the five optical filters 51), it corresponds to the selected optical filter 51a arranged on the optical path. Only light of a specific inspection wavelength passes through the selective optical filter 51a and is guided to the imaging unit 4.

  When the filter wheel 52 is rotated by the filter rotating motor 53, the selected optical filter 51a arranged on the optical path from the substrate 9 to the imaging unit 4 among the plurality of optical filters 51 is changed to another optical filter 51, and imaging is performed. The wavelength band of the light received by the unit 4 is changed. In the film thickness measuring apparatus 1, the filter rotation motor 53 is an optical filter changing mechanism that changes the optical filter 51 on the optical path. In the film thickness measurement device 1, the selection optical filter 51 a may be disposed on the optical path from the light irradiation unit 43 to the imaging unit 4, and is disposed on the optical path from the light irradiation unit 3 to the substrate 9. Also good.

  The imaging unit 4 includes a line sensor 41 in which CCD (Charge Coupled Device) elements, which are a plurality of light receiving elements, are linearly arranged in the Y direction, and an optical path from the substrate 9 to the line sensor 41. And a condensing lens 42 disposed between the selection optical filter 51 a of the wavelength band switching mechanism 5. The condenser lens 42 is reflected by a film 92 in a linear irradiation region (hereinafter referred to as “linear irradiation region”) that is emitted from the light irradiation unit 3 and extends in the Y direction on the upper surface 91 of the substrate 9. Of the subsequent linear light, the light having the inspection wavelength transmitted through the selection optical filter 51 a is condensed toward the line sensor 41. The line sensor 41 collects the light having the inspection wavelength while being condensed by the condenser lens 42, acquires the intensity distribution of the received light (that is, the distribution in the Y direction of the output value from each light receiving element), and inspects it. Output to unit 7. In the film thickness measuring apparatus 1, the intensity distribution of reflected light from the film 92 formed on the upper surface 91 of the substrate 9 is repeatedly acquired by the line sensor 41 while the substrate 9 and the stage 2 are moving in the X direction. In the film thickness measuring apparatus 1, the length of the linear irradiation region on the upper surface 91 of the substrate 9 in the Y direction may be smaller than the width of the substrate 9 in the Y direction. When the linear irradiation area is scanned relative to the substrate 9 in the Y direction during the movement to, the intensity distribution of the reflected light over the entire width of the substrate 9 is acquired.

  The inspection unit 7 receives an output from the line sensor 41 and generates an image generation unit 71 that generates a two-dimensional image of the upper surface 91 of the substrate 9, a reflection characteristic storage unit 72 that stores in advance a theoretical value of the reflection characteristic of the film 92, and And a film thickness calculation unit 73 that calculates the film thickness of the film 92 from the two-dimensional image generated by the image generation unit 71 and the reflection characteristics stored in the reflection characteristic storage unit 72. FIG. 3 is a diagram illustrating the reflection characteristics of the film 92 stored in the reflection characteristic storage unit 72. In FIG. 3, the horizontal axis indicates the film thickness of the film 92, and the vertical axis indicates the theoretical value of the reflectivity of the film 92 (hereinafter referred to as "theoretical reflectivity") that varies with periodicity as the film thickness changes. Show. The theoretical reflectance of the film 92 is obtained based on a known optical constant of the film 92 (for example, the refractive index of the film 92). In the film thickness measuring device 1, the optical constant of the film 92 necessary for obtaining the reflection characteristic of the film 92 stored in the reflection characteristic storage unit 72 is known.

  As shown in FIG. 3, the reflection characteristic storage unit 72 has a plurality of reflection characteristics indicating the relationship between the film thickness of the film 92 and the theoretical reflectance of the film 92 at a plurality of inspection wavelengths corresponding to the plurality of optical filters 51. Is stored. In the present embodiment, there are five inspection wavelengths, 550 nm, 580 nm, 600 nm, 620 nm, and 650 nm. In FIG. While indicated by a broken line, a thin one-dot chain line, a solid line, a thick one-dot chain line, and a thick broken line, reference numerals 801 to 805 are given to these reflection characteristics.

  Next, the flow of film thickness measurement by the film thickness measuring device 1 will be described with reference to FIGS. When film thickness measurement of the film 92 on the upper surface 91 of the substrate 9 is performed by the film thickness measuring device 1, first, the substrate 9 is held on the stage 2 located at the imaging start position indicated by the solid line in FIG. (Step S11). Further, the reflection characteristic storage unit 72 stores a plurality of reflection characteristics at a plurality of inspection wavelengths shown in FIG. 3 (step S12). Either step S11 or step S12 may be performed first or may be performed in parallel.

  Subsequently, the movement of the substrate 9 and the stage 2 in the (+ X) direction is started (step S13), and the linear shape that is emitted from the light irradiation unit 3 and incident on the upper surface 91 of the substrate 9 at an incident angle of 60 °. Light is irradiated to the linear irradiation region on the film 92 on the upper surface 91 of the substrate 9 (step S14), and the linear irradiation region moves relative to the substrate 9. At this time, in the wavelength band switching mechanism 5, one optical filter 51 corresponding to one inspection wavelength (for example, 550 nm) is disposed on the optical path between the substrate 9 and the imaging unit 4 as the selection optical filter 51a. .

  The light from the light irradiation unit 3 is reflected by the film 92 on the upper surface 91 of the substrate 9 and passes through the selective optical filter 51a of the wavelength band switching mechanism 5, so that only the light having the inspection wavelength is reflected from the reflected light (actually , Only light in a narrow wavelength band centered on the inspection wavelength) is taken out and guided to the imaging unit 4. In the imaging unit 4, the interference light having the inspection wavelength after being reflected by the film 92 is condensed toward the line sensor 41 by the condenser lens 42 and is received by the line sensor 41, and from the linear irradiation region on the film 92. Of the reflected light, the intensity distribution at the inspection wavelength is acquired (step S15). Output values from the respective light receiving elements of the line sensor 41 are sent to the image generation unit 71 of the inspection unit 7.

  In the film thickness measuring apparatus 1, whether or not the substrate 9 and the stage 2 have moved to the imaging end position indicated by a two-dot chain line in FIG. 1 is repeatedly confirmed during the movement of the substrate 9 (step S16). If it has not moved to the end position, the process returns to step S15 and the acquisition of the intensity distribution of the interference light of the inspection wavelength in the linear irradiation region on the film 92 is repeated (steps S15 and S16). In the film thickness measuring device 1, while the stage 2 is moving in the (+ X) direction, the operations of steps S15 and S16 are repeated, and the intensity distribution of the reflected light from the linear irradiation region is repeatedly acquired. An image showing the intensity distribution at the inspection wavelength of the reflected light from the film 92 for the entire substrate 9 (that is, an image of the film 92 at the inspection wavelength, hereinafter referred to as “inspection image”) is acquired. And if the board | substrate 9 and the stage 2 move to an imaging completion position, the movement of the board | substrate 9 and the stage 2 by the moving mechanism 21 will be stopped (step S17).

  When the inspection image of the film 92 at one inspection wavelength is acquired, the presence or absence of the next inspection wavelength is confirmed (step S18), and the substrate 9 and the stage 2 are returned to the imaging start position (step S19). Further, when the filter wheel 52 is rotated by a predetermined angle by the filter rotation motor 53, the optical filter 51 corresponding to the second inspection wavelength becomes a new selection optical filter 51a between the substrate 9 and the imaging unit 4. It arrange | positions on an optical path and a test | inspection wavelength is changed (step S20).

  Subsequently, returning to step S13, the movement of the substrate 9 in the (+ X) direction is started, and the linear light from the light irradiation unit 3 is irradiated to the linear irradiation region on the film 92 on the upper surface 91 of the substrate 9. (Step S14) Of the reflected light from the film 92, only the light of the second inspection wavelength (for example, 580 nm) is received by the line sensor 41 of the imaging unit 4, and the intensity distribution at the inspection wavelength is acquired (Step S15). ). Then, step S15 is repeated until the substrate 9 reaches the imaging end position (step S16), and the inspection image of the film 92 at the second inspection wavelength is acquired, and the movement of the substrate 9 is stopped (step S17). Thereafter, the presence / absence of the next inspection wavelength is confirmed again (step S18). If the next inspection wavelength exists, the substrate 9 is returned to the imaging start position and the filter wheel 52 is rotated to change the inspection wavelength. After that (steps S19 and S20), the process returns to step S13.

  In the film thickness measurement device 1, the above-described steps S13 to S20 are repeated, whereby a plurality of inspection images of the film 92 at a plurality of (in this embodiment, five) inspection wavelengths are acquired. Irradiation is stopped (step S21). FIG. 6 shows each pixel value distribution indicating the relationship between the position in the X direction on a straight line passing through the center of the substrate 9 and parallel to the X direction (that is, the moving direction of the substrate 9), and the pixel value at each position. It is a figure shown about an image (namely, about each test | inspection wavelength). The horizontal axis in FIG. 6 indicates the position in the X direction, and the vertical axis indicates the reflectance obtained based on the pixel value at each position (that is, the ratio of the intensity of the reflected light obtained based on the pixel value to the incident light). ). In FIG. 6, pixel value distributions corresponding to inspection wavelengths of 550 nm, 580 nm, 600 nm, 620 nm, and 650 nm, respectively, are indicated by thin broken lines, fine one-dot chain lines, solid lines, thick one-dot chain lines, and thick broken lines, and these pixel values. Reference numerals 811 to 815 are attached to the distribution.

  When a plurality of (in the present embodiment, five) inspection images of the film 92 are acquired, the film thickness calculator 73 causes the maximum pixel value and the pixel at the maximum position where the pixel value is maximum in each inspection image. The minimum pixel value at the minimum position where the value is minimum is acquired (step S22). For example, assuming that the pixel value distribution 813 corresponding to the inspection wavelength 600 nm in FIG. 6 includes the maximum pixel value and the minimum pixel value in the inspection image at the inspection wavelength 600 nm, the maximum value on the left side of the pixel value distribution 813. Is obtained as the maximum pixel value, and the pixel value corresponding to the minimum value adjacent to the right side of the maximum value is acquired as the minimum pixel value.

  When the maximum pixel value and the minimum pixel value are acquired, each inspection image is based on the relationship between the maximum and minimum pixel values of each inspection image and the maximum reflectance and the minimum reflectance in the reflection characteristics corresponding to each inspection image. The pixel value in each pixel and the theoretical reflectance are associated with each other (step S23). For example, at the inspection wavelength of 600 nm, the maximum pixel value of the inspection image is associated with the maximum reflectance (about 0.25) near the film thickness of 1420 nm and the film thickness of 1630 nm in the reflection characteristic 803 in FIG. The minimum pixel value is associated with the minimum reflectance (about 0.19) in the reflection characteristics 803 near the film thickness of 1310 nm and the film thickness of about 1520 nm. Assuming that the pixel value and the theoretical reflectance are in a directly proportional relationship, in each pixel of the inspection image, the pixel value of each pixel based on the pixel value of each pixel and the maximum and minimum pixel values of the inspection image The theoretical reflectance corresponding to is required. For example, when the pixel value of one pixel is equal to the average value of the maximum pixel value and the minimum pixel value, the theoretical reflectance associated with the pixel value of the pixel is the average value of the maximum reflectance and the minimum reflectance. It is about 0.22.

  When the pixel value and the theoretical reflectance are associated with each pixel of each inspection image, one inspection image is obtained at one measurement point among a plurality of measurement points set on the substrate 9 by the film thickness calculator 73. The film thickness at the measurement point is estimated based on the theoretical reflectance associated with the pixel value and the reflection characteristic in FIG. 3 corresponding to the inspection image (that is, the reflection characteristic of the same inspection wavelength). A film thickness candidate value is obtained. For example, when the theoretical reflectance associated with the pixel value of the measurement point in the inspection image is 0.22 at the inspection wavelength of 600 nm, the film having the theoretical reflectance of 0.22 in the reflection characteristic 803 in FIG. Thicknesses of 1360 nm, 1470 nm, and 1580 nm are obtained as film thickness candidate values. Similarly, when the theoretical reflectance associated with the pixel value at the measurement point of the inspection image is 0.195 at the inspection wavelength of 550 nm, the film having the theoretical reflectance of 0.195 in the reflection characteristic 801 in FIG. Thicknesses of 1370 nm, 1420 nm, and 1580 nm are obtained as film thickness candidate values.

  In the film thickness calculation unit 73, for one measurement point, based on the theoretical reflectance associated with the pixel values of the five inspection images and the reflection characteristics in FIG. 3 respectively corresponding to the five inspection images, A film thickness candidate value estimated as the film thickness of the measurement point is obtained for each of the five inspection wavelengths. Subsequently, for a predetermined film thickness range centered on the respective film thickness candidate values of the five inspection wavelengths, the number of points to which the gradient distribution is applied so as to decrease as the distance from the film thickness candidate value is voted.

  FIG. 7 is a diagram showing the voting results for the above-mentioned film thickness range together with the graph of the reflection characteristics at each inspection wavelength. In FIG. 7, the voting results for the film thickness ranges centered on the film thickness candidate values obtained for the inspection wavelengths of 550 nm, 580 nm, 600 nm, 620 nm, and 650 nm, respectively, are shown as a thin broken line, a fine dotted line, a solid line, and a thick dashed line These voting results are indicated by reference numerals 821 to 825. In FIG. 7, voting is performed on a film thickness range centering on a film thickness of 1580 nm at five inspection wavelengths, and the voting results for the film thickness range show only those relating to the inspection wavelength of 600 nm denoted by reference numeral 823. . In addition, the total number of voting results for the film thickness range is drawn with a two-dot chain line denoted by reference numeral 826. In the film thickness calculator 73, a film thickness of 1580 nm having the largest number of votes in the voting result shown in FIG. 7 is obtained as the film thickness of the measurement point.

  In other words, the calculation of the film thickness at one measurement point is indicated by five pixel values of five inspection wavelengths at the measurement point and five reflection characteristics 801 to 805 (see FIG. 3) at one film thickness. The degree of coincidence with two theoretical reflectances (more precisely, the coincidence between the five theoretical reflectances associated with the five pixel values at the measurement point in step S23 and the five theoretical reflectances at one film thickness) Degree) for each film thickness, and the film thickness having the highest degree of coincidence is obtained as the film thickness at the measurement point.

  In the film thickness calculator 73, the above-described film thickness calculation is performed at each of a plurality of measurement points on the substrate 9. That is, a plurality of pixel values of a plurality of inspection images at a plurality of measurement points (a plurality of theoretical reflectances associated with each other), and a plurality of theoretical reflectances indicated by a plurality of reflection characteristics at each film thickness Based on the degree of coincidence, the film thickness at each measurement point is obtained (step S24).

  When film thickness measurement is continuously performed on a plurality of substrates 9 in the film thickness measuring device 1, the reflection characteristic storage unit 72 stores the reflection characteristics (step S12). This is performed only at the time of measurement, and step S12 is omitted in the film thickness measurement of the second and subsequent substrates 9.

  As described above, in the film thickness measuring apparatus 1, a plurality of reflection characteristics 801 to 805 (see FIG. 3) corresponding to a plurality of inspection wavelengths are stored in advance for the film 92 whose optical constant is known. Based on a plurality of inspection images corresponding to a plurality of inspection wavelengths acquired by imaging the film 92 while switching the inspection wavelengths and the plurality of reflection characteristics 801 to 805, the film thickness calculation unit 73 performs a plurality of operations on the substrate 9. The film thickness at each of the measurement points is calculated.

  By the way, a film thickness meter that irradiates light onto a minute region on a substrate from a light irradiation unit and receives reflected light from the minute region by a light receiving unit to measure the film thickness (hereinafter referred to as “thickness meter of comparative example”). Then, when measuring the film thickness at each of a plurality of measurement points on the substrate, the process of measuring the film thickness after moving the light irradiation part and the light receiving part relative to one measurement point is measured. It is necessary to do as many times as the number of points. In addition, since a large amount of calculation is required to calculate the film thickness at one measurement point, a long time is required for measurement as the number of measurement points increases. Therefore, since it takes a long time to measure a wide range of film thickness on the substrate with high resolution, a wide range of film thickness distribution must be acquired with high resolution using the film thickness meter of the comparative example. Is very difficult in practice.

  On the other hand, in the film thickness measuring apparatus 1 according to the present embodiment, the image of the film 92 on the substrate 9 is switched five times (that is, the number of inspection wavelengths is changed) by switching the inspection wavelength by relative scanning of the line sensor 41. After obtaining the same number of times), the film thickness calculation unit 73 performs calculation at each of a plurality of measurement points on the substrate 9 based on the five inspection images and the reflection characteristics of the film 92 stored in advance. The film thickness (if necessary, the film thickness at the position corresponding to all the pixels of the inspection image) is obtained. Further, as described above, since the film thickness is obtained by voting on the film thickness range, the amount of calculation by the film thickness calculator 73 is relatively small. For this reason, even when the number of measurement points is increased, the amount of calculation by the film thickness calculator 73 is only slightly increased, and the time required for film thickness measurement is much shorter than that of the film thickness meter of the comparative example. can do. As described above, the film thickness measuring apparatus 1 can quickly determine the film thickness at a plurality of measurement points on the substrate 9 as compared with the film thickness meter of the comparative example, and a wide range of film thickness distribution on the substrate 9 can be obtained. It can be acquired with high accuracy and high resolution.

  Further, in the film thickness measuring device 1, in the wavelength band switching mechanism 5, by positioning any one of the plurality of optical filters 51 corresponding to the plurality of inspection wavelengths on the optical path between the substrate 9 and the imaging unit 4, The inspection wavelength can be easily switched. As a result, the structure of the film thickness measuring device 1 is simplified.

  Next, a film thickness measuring apparatus according to the second embodiment of the present invention will be described. FIG. 8 is a diagram showing a configuration of a film thickness measuring apparatus 1a according to the second embodiment. As shown in FIG. 8, the film thickness measuring device 1 a is an epi-illuminating type that is a film thickness meter that acquires the film thickness at one measurement point on the film 92 in addition to the components of the film thickness measuring device 1 shown in FIG. 1. The optical interference unit 6 is further provided, and the inspection unit 7 includes a reference film thickness calculation unit 74 and a film thickness correction unit 731. Other configurations are the same as those of the film thickness measuring apparatus 1 shown in FIG. 1, and the same reference numerals are given in the following description.

  As shown in FIG. 8, the optical interference unit 6 includes a light source 61 that emits white light as illumination light, a spectroscope 62 that splits reflected light from the substrate 9, and an optical system 65. The illumination light from 61 is guided onto the upper surface 91 of the substrate 9 and the reflected light from the substrate 9 is guided to the spectroscope 62.

  Specifically, illumination light from the light source 61 is introduced into one end of the optical fiber 651, and illumination light is derived from a lens 652 provided at the other end. The derived illumination light is guided to the half mirror 653 by the lens group 650a, and the reflected illumination light is irradiated to a measurement point which is a minute region on the film 92 via the objective lens 654. The reflected light from the measurement point is guided to the half mirror 653 through the objective lens 654. The light transmitted through the half mirror 653 is guided to the spectroscope 62 through the lens 650b, and the spectroscopic intensity of the reflected light is acquired by the spectroscope 62. The spectral intensity data is sent to the reference film thickness calculator 74 of the inspection unit 7. As described above, the optical system 65 is configured by the lens group 650a, the lenses 650b and 652, the optical fiber 651, the half mirror 653, and the objective lens 654.

  In the film thickness measuring device 1 a, the film thickness acquired by the optical interference unit 6 is used for the calculation of the film thickness at a plurality of measurement points by the film thickness calculator 73. 9 and 10 are diagrams showing a part of the flow of film thickness measurement by the film thickness measuring apparatus 1a according to the second embodiment. The flow of film thickness measurement by the film thickness measurement device 1a is substantially the same as the flow of film thickness measurement by the film thickness measurement device 1 according to the first embodiment shown in FIG. 4: Steps S31 and S32 shown in FIG. 9 are performed between the step S13) and the movement stop (step S17). After the film thickness is calculated by the film thickness calculator 73 (step S24), FIG. The difference is that step S41 shown is performed.

  When the film thickness is measured by the film thickness measuring apparatus 1a shown in FIG. 8, the substrate 9 is held on the stage 2 in the (+ X) direction from the movement start position, as in the first embodiment. The move starts. The reflection characteristic storage unit 72 stores in advance a plurality of reflection characteristics at a plurality of inspection wavelengths shown in FIG. 3 (steps S11 to S13).

  Subsequently, the linear light from the light irradiation unit 3 is irradiated to the linear irradiation region on the film 92 on the upper surface 91 of the substrate 9 (step S14), and the selection light filter 51a out of the reflected light from the film 92 is transmitted. The light having the inspection wavelength is received by the line sensor 41 of the imaging unit 4 and the intensity distribution is acquired (step S15). In the film thickness measuring apparatus 1a, as in the first embodiment, steps S14 and S15 are repeated until the substrate 9 is positioned at the imaging end position, and an inspection image of the film 92 corresponding to one inspection wavelength is acquired. After that, the movement of the substrate 9 is stopped (steps S16 and S17).

  In the film thickness measuring device 1a, the illumination light is emitted from the light source 61 of the optical interference unit 6 in parallel with the irradiation of the linear light onto the film 92 and the acquisition of the intensity distribution of the reflected light (steps S14 and S15). A predetermined measurement point (hereinafter referred to as “specific measurement point”) out of a plurality of measurement points on 92 is guided. The reflected light from the specific measurement point is guided to the spectroscope 62 of the optical interference unit 6, and the spectroscopic intensity of the reflected light is acquired by the spectroscope 62 (step S31), and the spectral intensity data is sent to the reference film thickness calculator 74. Is output. In the reference film thickness calculator 74, the relationship between the spectral intensity and the spectral reflectance of another substrate whose spectral reflectance is known is prepared in advance, and from the spectral intensity acquired by the spectroscope 62 based on the relationship. The spectral reflectance of the film 92 is obtained. The reference film thickness calculator 74 obtains the film thickness (hereinafter referred to as “reference film thickness”) of the film 92 at the specific measurement point based on the acquired spectral reflectance (step S32).

  In the film thickness measuring device 1a, as in the first embodiment, the presence or absence of the next inspection wavelength is confirmed, the substrate 9 is returned to the imaging start position, and the inspection wavelength is changed (steps S18 to S20). Subsequently, by repeating steps S13 to S20, a plurality of inspection images of the film 92 at a plurality of (in this embodiment, five) inspection wavelengths are acquired, and then irradiation of illumination light is stopped ( Step S21). Note that steps S31 and S32 are not performed when acquiring inspection images corresponding to the second and subsequent inspection wavelengths.

  When a plurality of images (five in this embodiment) of the film 92 are acquired, the film thickness calculator 73 acquires the maximum pixel value and the minimum pixel value in each inspection image, and the maximum pixel value in each inspection image. The pixel value and the theoretical reflectance at each pixel of each inspection image are associated with each other based on the relationship between the value and the minimum pixel value and the maximum reflectance and the minimum reflectance in the reflection characteristics corresponding to each inspection image (Step S22, S23). Then, by the film thickness calculator 73, a plurality of pixel values (five theoretical reflectances associated with each other) of a plurality of inspection images at each measurement point of a plurality of measurement points, and a plurality of reflection characteristics at each film thickness. Based on the degree of coincidence with the plurality of theoretical reflectances shown, the film thickness at each measurement point is obtained (step S24).

  Next, the reference film thickness at the specific measurement point obtained by the reference film thickness computation unit 74 by the film thickness correction unit 731 of the film thickness computation unit 73 and the film at the plurality of measurement points obtained by the film thickness computation unit 73. Based on the film thickness at the specific measurement point among the thicknesses, the film thickness at each measurement point obtained in step S24 is corrected (step S41). In the present embodiment, the difference between the reference film thickness at the specific measurement point obtained by the reference film thickness calculation unit 74 and the film thickness before correction at the specific measurement point obtained by the film thickness calculation unit 73 is the film thickness correction value. The film thickness correction at each measurement point is corrected by adding the film thickness correction value to the film thickness at each measurement point calculated by the film thickness calculation unit 73.

  In the film thickness measuring device 1a according to the second embodiment, the film thickness calculator 73 can quickly obtain the film thickness at a plurality of measurement points on the substrate 9 as in the first embodiment. Further, by correcting the film thickness at the plurality of measurement points using the reference film thickness acquired by the optical interference unit 6, the film thickness at the plurality of measurement points on the substrate 9 can be obtained with high accuracy. As a result, a wide range of film thickness distribution on the substrate 9 can be obtained with higher accuracy and higher resolution. Further, the film thickness correction by the film thickness correction unit 731 is performed based on the difference between the reference film thickness at the specific measurement point and the film thickness calculated by the film thickness calculation unit 73 (that is, the film thickness before correction). Thus, the calculation related to the correction of the film thickness can be simplified, and the acquisition of the film thickness distribution on the substrate 9 can be speeded up.

  In the above embodiment, in the film thickness measuring device 1a, when acquiring an inspection image corresponding to the first inspection wavelength, steps S31 and S32 are performed to measure the reference film thickness at a specific measurement point. The measurement of the film thickness may be performed in parallel with acquisition of any of the five inspection images. Further, the reference film thickness may be measured a plurality of times in parallel with the acquisition of a plurality of inspection images among the five inspection images. For example, an average value of a plurality of measurement results is used as the reference film thickness. Also good.

  Alternatively, a plurality of specific measurement points are set on the film 92, and the reference film thickness at the plurality of specific measurement points is set to the optical interference unit 6 in parallel with acquisition of one inspection image (or acquisition of a plurality of inspection images). May be measured sequentially. In this case, the film thickness correction value (that is, the difference between the reference film thickness and the film thickness before correction obtained by the film thickness calculation unit 73 in step S24) at each of the plurality of specific measurement points is obtained. Based on the film thickness correction value, the film thickness at each measurement point is corrected. For example, the relationship between the film thickness before correction and the film thickness correction value is obtained from the film thickness before correction and the film thickness correction value at a plurality of specific measurement points, and at each measurement point, the relationship and the film thickness before correction are calculated. The film thickness is corrected by the film thickness correction value obtained based on the above. As described above, in the film thickness measuring device 1a, the optical interference unit 6 obtains the reference film thickness at at least one specific measurement point on the film 92, and the reference film thickness is used for the film thickness calculation unit 73 to calculate the film thickness. Used.

  In the film thickness measuring device 1a, a plurality of optical interference units 6 arranged in the Y direction (that is, a direction perpendicular to the moving direction of the substrate 9) are provided, and a plurality (however, The reference film thickness of the specific measurement points (the number smaller than the number of measurement points at which the film thickness is measured by the film thickness calculation unit 73) is measured, and the plurality of reference film thicknesses are the film thicknesses at the plurality of measurement points on the film 92. It may be used for calculation. For example, in a rectangular region having four specific measurement points as vertices, the film thickness correction value is calculated based on the film thickness correction value that is the difference between the reference film thickness at each of the four specific measurement points and the film thickness before correction. The distribution is obtained, and the film thickness before correction at the plurality of measurement points in the rectangular area is corrected by the film thickness correction value obtained from the distribution of the film thickness correction value. Thereby, when the film thickness correction value varies depending on the position on the film 92, the film thickness at each measurement point can be obtained with higher accuracy.

  As mentioned above, although embodiment of this invention has been described, this invention is not limited to the said embodiment, A various change is possible.

  In the film thickness measuring apparatus according to the above embodiment, as shown in FIG. 7, in the voting for the film thickness range centering on the film thickness candidate value, the score voted for each film thickness is 0 or more. For example, a negative score may be voted for a film thickness range far away from the film thickness candidate value. Further, in the film thickness measurement device, an inspection image may be acquired by a two-dimensional CCD camera or the like instead of the line sensor 41.

  The number of inspection wavelengths used for film thickness measurement in the film thickness measurement device is not necessarily limited to five. For example, when the approximate film thickness of the film 92 is known in advance, reflection near the film thickness is performed. The film thickness may be measured using only two inspection wavelengths whose characteristic phase difference (that is, the phase of change in theoretical reflectance) is shifted by approximately π / 2. As a result, the time required to acquire the image of the film 92 can be shortened, and the film thickness can be measured more rapidly.

  In the film thickness measuring device 1a according to the second embodiment, the reference film thickness acquired by the optical interference unit 6 and the reference film thickness calculator 74 is used for the calculation of the film thickness by the film thickness calculator 73. If there is, it is not necessarily required to be used for correcting the film thickness calculated by the film thickness calculator 73. For example, when it is previously known that the film thicknesses of all the measurement points on the substrate 9 are included in a narrow range, the voting range is used when voting in the calculation of the film thickness of each measurement point (step S24). Is limited to a relatively narrow film thickness range including the reference film thickness (for example, the maximum voting film thickness is set to a value 100 nm larger than the reference film thickness, and the minimum value is a value 100 nm smaller than the reference film thickness). Thus, the calculation of the film thickness at each measurement point can be simplified, and the acquisition of the film thickness distribution on the substrate 9 can be speeded up.

  Further, in the film thickness measuring device 1a, instead of the epi-illumination type optical interference unit 6, the minute region on the film 92 is irradiated with light inclined with respect to the film 92 and the polarization state of the reflected light from the minute region is changed. An ellipsometer may be provided as a film thickness meter that acquires the film thickness in the minute region by acquiring and performing polarization analysis.

  The film thickness measurement apparatus according to the above embodiment may be used for film thickness measurement of a film other than a resist film, for example, an insulating film or a conductive film formed on the substrate 9. It may be formed by a method other than coating, for example, vapor deposition, chemical vapor deposition (CVD), sputtering, or the like. The film thickness measuring device may be used for measuring the film thickness of a film formed on another substrate such as a semiconductor substrate or various objects other than the substrate.

It is a figure which shows the film thickness measuring apparatus which concerns on 1st Embodiment. It is a figure which shows a wavelength band switching mechanism. It is a figure which shows the reflective characteristic of a film | membrane. It is a figure which shows the flow of a film thickness measurement. It is a figure which shows the flow of a film thickness measurement. It is a figure which shows pixel value distribution. It is a figure which shows the voting result in a film thickness measurement with the reflective characteristic of a film | membrane. It is a figure which shows the film thickness measuring apparatus which concerns on 2nd Embodiment. It is a figure which shows a part of flow of a film thickness measurement. It is a figure which shows a part of flow of a film thickness measurement.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,1a Film thickness measuring apparatus 2 Stage 3 Light irradiation part 4 Imaging part 6 Optical interference unit 9 Substrate 51 Optical filter 51a Selection optical filter 53 Filter rotation motor 72 Reflection characteristic memory | storage part 73 Film thickness calculating part 91 Upper surface 92 Film | membrane 801-805 Reflection characteristics S11 to S24, S31, S32, S41 Steps

Claims (8)

A film thickness measuring device for measuring a film thickness of a film formed on an object,
A holding unit for holding an object in which a film having a known optical constant is formed on the main surface;
A reflection characteristic storage unit that stores in advance a plurality of reflection characteristics respectively indicating the relationship between the film thickness of the film at a plurality of inspection wavelengths and the theoretical value of the reflectivity of the film that varies according to the change in the film thickness;
A light irradiation section for irradiating the film with light;
An imaging unit that receives interference light reflected by the film from the light irradiation unit and acquires a plurality of images of the film at the plurality of inspection wavelengths;
A film thickness calculator that calculates the film thickness at each of a plurality of measurement points on the object based on the plurality of images and the plurality of reflection characteristics;
With
The film thickness calculator is
a) obtaining a maximum pixel value and a minimum pixel value at a minimum position where the pixel value is maximum and a minimum position where the pixel value is minimum in each of the plurality of images;
b) Associating the pixel value of each image with the reflectance based on the relationship between the maximum pixel value and the minimum pixel value of each image and the maximum reflectance and minimum reflectance in the reflection characteristics corresponding to each image. Process,
c) Based on the degree of coincidence between the plurality of pixel values of the plurality of images at each measurement point of the plurality of measurement points and the plurality of reflectances indicated by the plurality of reflection characteristics at each film thickness, A step of obtaining a film thickness;
The film thickness measuring apparatus characterized by performing. The film thickness measuring device according to claim 1,
A plurality of optical filters that selectively transmit light of the plurality of inspection wavelengths respectively;
An optical filter changing mechanism that changes one optical filter arranged on the optical path from the light irradiation unit to the imaging unit among the plurality of optical filters to another optical filter;
Further comprising
The film thickness measuring apparatus, wherein the light emitted from the light irradiation unit is white light. The film thickness measuring device according to claim 1 or 2,
A film thickness meter for obtaining a film thickness at at least one measurement point on the film;
The film thickness measurement apparatus characterized in that the film thickness acquired by the film thickness meter is used for calculation of the film thickness by the film thickness calculator. The film thickness measuring device according to claim 3,
Based on the difference between the film thickness at the at least one measurement point acquired by the film thickness meter and the film thickness at the at least one measurement point calculated by the film thickness calculation unit, the film thickness calculation unit A film thickness measuring apparatus, wherein the calculated film thickness at each measurement point is corrected. A film thickness measuring method for measuring the thickness of a film formed on an object,
a) a step of holding an object on which a film having a known optical constant is formed on the main surface;
b) preliminarily storing a plurality of reflection characteristics respectively indicating a relationship between a film thickness of the film at a plurality of inspection wavelengths and a theoretical value of the reflectivity of the film that varies according to a change in the film thickness;
c) irradiating the film with light from the light irradiating unit, and receiving interference light reflected by the film among the light from the light irradiating unit by the imaging unit, and a plurality of the films at the plurality of inspection wavelengths. Acquiring an image;
d) obtaining a maximum pixel value and a minimum pixel value at a maximum position where the pixel value is maximum and a minimum position where the pixel value is minimum in each of the plurality of images;
e) correlating the pixel value of each image with the reflectance based on the relationship between the maximum pixel value and the minimum pixel value of each image and the maximum reflectance and minimum reflectance in the reflection characteristics corresponding to each image. Process,
f) based on a degree of coincidence between a plurality of pixel values of the plurality of images at each of the plurality of measurement points on the object and a plurality of reflectances indicated by the plurality of reflection characteristics at each film thickness. A step of obtaining a film thickness at each measurement point;
A film thickness measuring method comprising: The film thickness measuring method according to claim 5,
The light emitted from the light irradiation unit in the step c) is white light,
Step c)
c1) Corresponding to the one optical filter by arranging one optical filter among the plurality of optical filters that selectively transmit the light of the plurality of inspection wavelengths on the optical path from the light irradiation unit to the imaging unit. Acquiring an image of an inspection wavelength to be performed;
c2) changing the one optical filter to another optical filter until the plurality of images are acquired, and returning to the c1) step;
A film thickness measuring method comprising: The film thickness measuring method according to claim 5 or 6,
g) further comprising a step of obtaining a film thickness at at least one measurement point on the film by a film thickness meter;
The film thickness measurement method, wherein the film thickness obtained in the step g) is used for calculation of the film thickness in the step f). The film thickness measuring method according to claim 7,
In the step f) based on the difference between the film thickness at the at least one measurement point acquired in the step g) and the film thickness at the at least one measurement point calculated in the step f). A film thickness measuring method, wherein the calculated film thickness at each measurement point is corrected.

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