JP2006184060A - Instrument and method for measuring film thickness - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an instrument and a method for measuring a film thickness prevented from affecting color measurement in a cell domain by performing accurate measurement positioning when measuring the film thickness of an object under measurement with a thin film formed in the minute cellular domain of a color filter, etc. by a spectral reflection interference method. <P>SOLUTION: A measurement head is disposed in the vicinity of a cell to be measured to image the vicinity while performing illumination by a light source for photographing. Minute displacement is calculated from photographed image data to perform positional correction. Then, the illumination light source is switched to a light source of infrared light with wavelengths of 900nm or more for minute spot measurement. Its reflected light is measured to measure a film thickness. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to an apparatus and a measurement method for measuring a film thickness in a minute thin film cell such as a color filter in a non-contact manner by spectral interference.

  The film thicknesses of the R, G, and B films of the color filter on which the minute cell-like RGB thin film pattern is formed are factors that greatly affect the display characteristics of the liquid crystal display, and thus are strictly controlled within the manufacturing process. . The film thickness is measured by scraping a part of the film with a sharp blade to create a step between the film surface and the substrate surface, and measuring with a stylus type step gauge. In the production of color filters by the photolithographic method, film thickness measurement in minute RGB cells is performed in a plurality of steps. However, such a method is troublesome to prepare for measurement, takes time, and destroys the object to be measured. Therefore, there is a problem that there is a lot of loss accompanying the measurement.

  On the other hand, as a non-destructive inspection method, the film thickness measurement target is irradiated with light, the light reflected from the sample is dispersed, the spectral reflectance is measured, and the spectral reflectance when no film is formed. There is known a measuring method using a method of obtaining a spectral reflection ratio by taking the ratio of the above and obtaining a film thickness from this data and previously obtained calibration curve data.

  Furthermore, as an improvement of the above-described measurement apparatus and measurement method, Patent Document 1 discloses a method and apparatus for correcting an error that occurs when the numerical aperture of an objective lens used for measurement is large.

  However, although both the above-described two methods and apparatuses are non-destructive, it is necessary to perform complicated calculations in order to obtain true data from measurement data, and there is a problem that measurement accuracy is reduced due to a calculation error in correction.

JP-A-6-249620 JP 2002-318106 A

  The present invention has been made in view of the above-mentioned problems, and the problem is that the inner cell thickness of a minute cell can be measured nondestructively, and accurate measurement can be performed without requiring complicated data processing. It is in providing a film thickness measuring apparatus and a film thickness measuring method.

  According to the first aspect of the present invention, illumination light is incident on the surface of an object to be measured on which a microcellular thin film pattern is formed on a substrate, the reflected light is dispersed to obtain a spectral reflectance, and the spectral interference is obtained. A spectral reflection interference type film thickness measuring device that calculates a film thickness from a waveform, including a spectroscope, a moving mechanism for placing a measurement head at a predetermined measurement position on a substrate, and an image near the measurement position. An imaging device for imaging, an imaging illumination optical system that uniformly illuminates the entire imaging area, an image processing unit that processes captured image data, and a measurement illumination optical system in which the illumination area is in a minute cell A film thickness measuring apparatus having a mechanism for switching between an imaging illumination optical system and a measurement illumination optical system. By switching between the illumination for positioning and the illumination for measurement, it is possible to perform measurement with high accuracy without being affected by uneven illumination.

  According to a second aspect of the present invention, the measurement illumination optical system includes a light source that irradiates visible light and light in the near infrared region having a wavelength of 900 nm or more, a condensing optical system, and an optical fiber that transmits near infrared light. A 50% beam splitter that transmits and reflects infrared light, a hot mirror that transmits visible light and reflects near-infrared light, and an infrared objective lens. The infrared light component is reflected by the hot mirror sequentially through an optical optical system, the optical fiber, and the beam splitter, guided to the infrared objective lens, and irradiated on the object to be measured. It is a film thickness measuring device. By narrowing the measurement light with an optical fiber, it is possible to eliminate an error in a measurement value due to an optical path difference, or it is possible to eliminate a complicated calculation for correcting the error. Moreover, the influence by absorption of the visible light part of a to-be-measured object can be eliminated by using infrared light.

  The invention according to claim 3 of the present invention is the film thickness measuring apparatus according to claim 2, wherein the core diameter of the optical fiber is 0.8 mm to 0.2 mm. A suitable irradiation spot diameter can be obtained for a minute cell of the object to be measured.

  According to a fourth aspect of the present invention, the imaging illumination optical system includes a Keller illumination system and a 50% beam splitter that transmits and reflects visible light, and the object to be measured is passed through the infrared objective lens. The film thickness measuring device according to any one of claims 1 to 3, wherein irradiation is performed. Uniform illumination can be easily obtained in the imaging region.

  According to a fifth aspect of the present invention, the hot mirror transmits the irradiation light from the imaging optical system, irradiates the object to be measured through the infrared objective lens, and transmits the reflected light. Guide to the imaging device, reflect the infrared light component of the irradiation light from the measurement illumination optical system, irradiate the object to be measured through the infrared objective lens, reflect the reflected light and reflect the spectral light 5. The apparatus according to claim 1, wherein the measurement illumination optical system and the imaging illumination optical system are arranged so as to perform coaxial epi-illumination. It is a film thickness measuring device. The light source can be easily switched so that imaging can be performed with visible light and measurement with infrared light.

  The invention according to claim 6 of the present invention is the color filter in which the object to be measured is a color filter in which a microcellular thin film pattern of RGB colors is formed on a substrate. This is a film thickness measuring apparatus. It is possible to accurately measure the film thickness of a minute region without being affected by the color even in the measurement target parts of different colors.

  The invention according to claim 7 of the present invention uses the film thickness measuring device according to any one of claims 1 to 6 and illuminates with an imaging illumination optical system after the measurement head portion is arranged in the vicinity of a predetermined measurement position on the substrate. Then, from the obtained image, the image processing unit calculates the minute positional deviation between the position of the measurement head unit and the measurement position, and the illumination area of the measurement illumination optical system is the central part of the minute cell. The film thickness measurement method is characterized in that after the measurement head portion is moved slightly so as to become, the illumination is switched to the measurement illumination optical system and the reflected light is input to the spectroscope. It is possible to measure at an accurate measurement position without being affected by the surroundings.

  According to the film thickness measurement apparatus and the film thickness measurement method of the present invention, for example, in a product that requires precise film thickness management in a minute area such as a color filter, the film thickness can be reduced in a minute cell. Since destructive measurement is possible, it is possible to reduce the loss due to measurement, and it is not necessary to prepare before measurement as in the case of a conventional stylus type step meter, and the measurement work can be made more efficient. In addition, complicated data calculation is unnecessary, and results with good measurement accuracy can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of the apparatus of the present invention. First, the wavelength of light used for measurement will be described. In the spectral interference type film thickness measurement, light is incident on the film surface of the object to be measured. A phase difference occurs between the component reflected on the film surface of the object to be measured and the component transmitted through the film and reflected at the boundary with the substrate. The phase difference is strengthened by exactly 2π, attenuated by π, and interference occurs. Observed. Since the phase difference is determined by the optical constants and film thicknesses of air, film, and substrate, the reflected light is dispersed and the film thickness can be calculated from the spectral reflectance. If the amount of light transmitted through the film and reflected at the substrate interface is significantly smaller than the reflection at the film surface, no interference is observed. That is, it is necessary to select a wavelength that is transmitted without being absorbed by the film. For color resist film thickness measurement, absorption occurs in each of the R, G, and B films in visible light, whereas absorption is not observed in the near infrared region of about 900 nm or more, so light in the near infrared region is used. Is preferred. Needless to say, it is also suitable for measuring a film having absorption in the visible region other than the color resist. Although there is no upper limit of the wavelength, it is practically about 1600 nm.

  The substrate size of the color filter has been increased in recent years, and the length of one side exceeds 1 m. Therefore, an XY stage as shown in FIG. 3 is provided, the object to be measured 6 is placed, and the measuring head 26 is moved. The measurement spot is moved to a desired measurement location. Although FIG. 3 shows the case where the measurement head 26 is moved, the measurement head 26 may be fixed, and an XY stage that moves the object 6 to be measured, or an XY stage that can move both the measurement head and the stage may be used.

  A halogen lamp or the like is used as the imaging illumination light source 22. The light emitted from the imaging illumination light source 22 passes through the cut filter 17 that cuts 500 nm or less, passes through the single lens 10, the brightness stop 14, the single lens 9, and the field stop 13 and reaches the beam splitter 2. Here, the cut filter 17 is installed in preparation for the case where the film of the object to be measured is photosensitive. The single lens 10 to the single lens 8 have the same configuration as an illumination mechanism generally called a microscopic Keller illumination, and uniform illumination can be obtained by appropriately adjusting the brightness stop 14 and the field stop 13.

  The beam splitter 2 is designed so that visible light is reflected and transmitted by 50% at 45 degrees, and the incident light from the imaging illumination light source 22 reaches the hot mirror 3 when the incident surface is installed at a position of 45 degrees. The hot mirror 3 is designed to transmit visible light and reflect near-infrared light when incident at 45 degrees. Therefore, the visible light transmitted through the hot mirror 3 passes through the infrared objective lens 5 and the object to be measured 6 is illuminated.

  The reflected light passes through the objective lens 5, the hot mirror 3, the beam splitter 2, and the single lens 7 and reaches the color CCD camera 1, and an image in the vicinity of the measurement position of the object to be measured 6 can be picked up. . With respect to the imaging range, a captured image as shown in FIG. 2 can be obtained by appropriately selecting the magnification of the infrared objective lens 5 and the CCD element size of the color CCD camera 1. FIG. 2 is a diagram schematically showing a case where an RGB color filter with a pitch of 100 μm is imaged with a 10 × infrared objective lens and a 1/3 inch color CCD camera. Further, the measurement spot 101 showed a size corresponding to the case where a core diameter of 0.8 mm was used as the optical fiber 20 of FIG.

  The video signal of the color CCD camera 1 is sent to the computer 24 and taken into the memory from the image input unit. The positional relationship between the imaging area and the measurement spot is mechanically determined. Usually, the measurement spot is positioned at the center of the imaging area. Processing for finely moving the measurement head unit 26 is performed so that the center of the captured image coincides with the center of the cell to be measured. Recognizing the black matrix pattern portion, R portion, G portion, and B portion, which are low in reflectance and arranged in parallel at equal pitches, from the ratios of the R, G, and B components of the captured image, and determine the boundary between the regions Then, the center position of the cell to be measured is obtained, the amount of movement from the current position is calculated from the number of pixels and the spatial resolution, the amount of movement is set in the XY stage control unit 25, and fine movement is performed. FIG. 3 is a diagram schematically showing a state where the alignment of the measurement spot 101 is completed. The measurement spot may be a position suitable for measuring the film thickness in the cell, but usually the center of the cell to be measured is preferable.

  Subsequently, in order to measure the film thickness, the shutter 15 after the imaging illumination light source 22 is closed, and the shutter 16 after the measurement light source 21 is opened. The measurement light source 21 may be, for example, a halogen light bulb provided with a gold coat reflector so as to efficiently emit near-infrared light, but is not limited thereto. This is condensed by the condensing optical system 27 and incident on the optical fiber 20. The optical fiber is preferably one that transmits near-infrared light. For example, germanium-doped quartz fiber is used. The light emitted from the tip of the optical fiber 20 reaches the beam splitter 4 through the single lens 12. Here, the beam splitter 4 is designed so as to reflect and transmit near-infrared light by 50% when incident at 45 degrees.

  The light that has passed through the beam splitter 4 passes through the hot mirror 3 so that visible light is transmitted. Therefore, only infrared light is reflected, and the object to be measured 6 is illuminated through the infrared objective lens 5 by turning 90 degrees. The spot size irradiated at this time is a diameter obtained by dividing the core diameter of the optical fiber 20 by the magnification of the objective lens 5. Therefore, when the entrance pupil diameter is fully used, the incident angle of the illumination light ranges from 0 ° to an angle corresponding to the numerical aperture of the infrared objective lens 5. In this case, the optical path difference that generates the phase difference between the reflected light from the film surface and the reflected light from the boundary surface between the film and the substrate is different from that at the time of strict vertical incidence. Therefore, when an objective lens having a relatively large numerical aperture is used, for example, correction calculation is required as in the film thickness measurement method described in Patent Document 1, and accurate measurement cannot be expected. On the other hand, in the method of the present invention, the light source for measurement is limited to the core diameter of the optical fiber 20, and the entrance pupil diameter to the objective lens 5 is limited to the center of the lens so that the incident angle on the film surface can be treated as vertical. This enables measurement with high accuracy without the need for correction calculation.

  In addition, devices that use the illumination attached to a normal microscope as a light source for measurement are commercially available, but when measuring with an object to be measured with a pattern such as a color filter, light other than the spot is incident, There is also a phenomenon that the interference waveform changes, which again causes a drop in measurement accuracy. Therefore, it is necessary to prepare a separate measurement light source as in the method of the present invention.

  The reflected light reflected and interfered by the film surface and the interface between the film and the substrate is reflected by the hot mirror 3 through the objective lens 5, reflected by the beam splitter 4, and incident on the tip of the optical fiber 19 through the single lens 11. The optical fiber 19 is connected to the spectroscope 23, and spectral data is obtained by an internal diffraction grating, and the data is sent to the computer 24.

  There are various methods for calculating the film thickness from the obtained spectral data, and there is no particular limitation, but the method disclosed in Patent Document 2 can be applied.

  The micro cell film thickness measuring apparatus of the present invention can be suitably used for measuring the film thickness of a thin film formed in a micro cell area such as a color filter for a display or an image sensor.

1 is a schematic diagram of a device configuration showing an embodiment of the present invention. The schematic diagram of the captured image example before positioning. The schematic diagram of the captured image example at the time of completion of positioning. Diagram of XY stage.

Explanation of symbols

1 Color CCD camera 2 Beam splitter 3 Hot mirror 4 Beam splitter 5 Objective lens 6 Object to be measured 7, 8, 9, 10, 11, 12
Single lens 13 Field diaphragm 14 Brightness diaphragm 15, 16 Shutter 17 Cut filter 19, 20 Optical fiber 21 Measurement light source 22 Imaging light source 23 Spectrometer 24 · · Computer 25 · · XY stage controller 26 · · Measurement head 27 · · Condensing optical system

Claims (7)

  Spectral reflection interference where incident light is incident on the surface of the object to be measured on which a microcellular thin film pattern is formed on a substrate, the reflected light is dispersed to obtain the spectral reflectance, and the film thickness is calculated from the spectral interference waveform Type film thickness measuring device, a spectroscope, a moving mechanism for disposing a measuring head portion at a predetermined measurement position on a substrate, an imaging device for imaging an image near the measurement position, and an imaging region An imaging illumination optical system that uniformly illuminates the entire image, an image processing unit that processes captured image data, a measurement illumination optical system in which an illumination area is in a minute cell, an imaging illumination optical system, and a measurement illumination A film thickness measuring apparatus having a mechanism for switching between an optical system and an optical system.   The illumination optical system for measurement includes a light source that irradiates visible light and near-infrared light having a wavelength of 900 nm or more, a condensing optical system, an optical fiber that transmits near-infrared light, and infrared light transmission / reflection 50 each. % Beam splitter, a hot mirror that transmits visible light and reflects near-infrared light, and an infrared objective lens, and irradiates light from the light source with the condensing optical system, the optical fiber, and the beam splitter. The film thickness measuring apparatus according to claim 1, wherein an infrared light component is reflected by the hot mirror, guided to the infrared objective lens, and irradiated on the object to be measured.   The film thickness measuring apparatus according to claim 2, wherein the core diameter of the optical fiber is 0.8 mm to 0.2 mm.   The imaging optical system for imaging has a Keller illumination system and a 50% beam splitter for visible light transmission and reflection, respectively, and irradiates the object to be measured through the infrared objective lens. To 4. The film thickness measuring apparatus according to any one of 3 to 4.   The hot mirror transmits the irradiation light from the imaging optical system, irradiates the object to be measured through the infrared objective lens, transmits the reflected light to the imaging apparatus, and performs the measurement. The infrared light component of the irradiation light from the illumination optical system is reflected to irradiate the object to be measured through the infrared objective lens, and the reflected light is arranged to be reflected and guided to the spectrometer. 5. The film thickness measuring apparatus according to claim 1, wherein the measurement illumination optical system and the imaging illumination optical system are arranged so as to perform coaxial epi-illumination.   6. The film thickness measuring apparatus according to claim 1, wherein the object to be measured is a color filter in which a minute cellular thin film pattern composed of RGB colors is formed on a substrate.   Using the film thickness measuring device according to any one of claims 1 to 6, the measurement head portion was arranged in the vicinity of a predetermined measurement position on the substrate, and then illuminated with an imaging optical system and imaged with the imaging device. After the image processing unit calculates a small amount of misalignment between the position of the measurement head and the measurement position from the image, and finely moves the measurement head so that the illumination area of the measurement illumination optical system becomes the center of the small cell A method for measuring a film thickness, wherein the illumination is switched to an illumination optical system for measurement and the reflected light is input to a spectrometer.