JP3944693B2 - Film thickness measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical interference type film thickness measuring apparatus suitable for applications such as film thickness measurement of RGB resist films functioning as a color filter for a liquid crystal display panel, in particular, using infrared light as a measuring medium. Thus, the present invention relates to a film thickness measuring apparatus that can accurately measure the film thickness of each RGB resist film without being affected by the wavelength selection characteristics as a filter.
[0002]
[Prior art]
There is an increasing demand for cost reduction of liquid crystals. The failure of color filters currently occupies the largest percentage as a factor that hinders the cost reduction of liquid crystals. In order to reduce the price of liquid crystals, it is important to reduce the loss cost due to the failure of color filters.
[0003]
Color filter defects are found during lighting inspection in the liquid crystal manufacturing process, but lighting inspection is only possible after the color filter is manufactured and the liquid crystal is injected after bonding the TFT substrate (the final stage of the liquid crystal manufacturing process). Stage), and the loss cost when a defect is found is very large. This is because not only the loss of the liquid crystal itself in which defects are found, but also a considerable amount of time has passed until the defect is found, so if the cause of the defect is a shift in process conditions, the color produced during that time This is because the filter and the TFT substrate bonded to the filter all become defective products.
[0004]
The criterion for determining a color filter defect is the uniformity of image quality (color unevenness and brightness unevenness) at the time of completion of the liquid crystal, and there is an increasing demand for the uniformity of image quality. For this purpose, it is necessary to manage the thickness of the color filter more uniformly, and the manufacturing tolerance of the color filter thickness is becoming narrower.
[0005]
A manufacturing process of this type of color filter is performed in three stages in the order of, for example, a red (R) process, a green (G) process, and a blue (B) process. Each color process includes a coating process (1), a baking process (2), an exposure process (3), a development process (4), and a strip process (5).
[0006]
First, in the coating process (1), a resist having selective transmission characteristics of the corresponding color is coated on the surface of the glass substrate uniformly with a uniform thickness. In the subsequent baking process (2), the resist film coated in the previous process is baked and stabilized. In the subsequent exposure processing step (3), the resist film is selectively exposed so that the fine regions corresponding to the respective pixels are uniformly dispersed. In the subsequent development processing step (4), the fine filter region generated by the selective exposure appears. In the subsequent strip processing step (5), the excess resist is removed to expose the surface of the glass plate other than the fine filter region.
[0007]
At the end of the process for each color, the periphery of the filter panel region for one sheet is in a state where the glass plate surface is exposed in a frame shape. Therefore, when the resist is coated by the coating process, the film thickness of the resist film coated on the periphery of the filter panel area is measured to accurately determine the film thickness of each color resist film in the fine filter area corresponding to each pixel. Can know.
[0008]
[Problems to be solved by the invention]
The thickness control of the liquid crystal color filter is currently performed by a stylus type film thickness inspection apparatus. That is, in each of the red (R) process, the green (G) process, and the blue (B) process, the thickness of the film is measured by applying a probe to the resist film at the peripheral edge of the filter panel every time the resist film is coated. It is.
[0009]
However, in this stylus type film thickness measuring apparatus, since the inspection takes a very long time, the inspection can only be performed by sampling, and inevitably becomes an off-line inspection. This is because when all the inspections are performed, the time required for manufacturing becomes longer and the cost becomes higher. Therefore, in this method, there is a limit to the detection of defective products, and the loss cost cannot be reduced sufficiently.
[0010]
On the other hand, as an apparatus that can measure the film pressure of a thin film in a short time without contact, an optical film thickness inspection apparatus using a halogen lamp is known. This device is also called an optical interference type film thickness measuring device, which irradiates white light from a halogen lamp to the film body to be measured, and the film surface reflected light and the film back surface reflected light interfere with each other. The film thickness is obtained based on the generated interference waveform. In this film thickness measuring device, in order to sufficiently satisfy the measurement range, measurement light having almost uniform output power characteristics in a considerably wide wavelength region is prepared, and this is applied to the film body to be measured at all wavelengths. It is required to transmit uniformly over the entire area. Further, in the sampling inspection, even if a defect is found, many defective products have already been produced up to that point, so that the cost cannot be sufficiently reduced.
[0011]
However, each RGB resist film of the color filter to be measured has a unique light absorption characteristic corresponding to each of RGB as shown in FIG. 27, so that a uniform wavelength component from the halogen lamp can be obtained. Even if these resist films are irradiated with the measurement light they have, the wavelength of the transmitted light is greatly biased and non-uniform, and the optical interference effect cannot be obtained for non-transmitted wavelength light. Cause trouble.
[0012]
In addition, halogen lamps used as light sources are relatively large and bulky, have a short lifetime of about 1000 hours, require frequent replacement, and have a large heat generation and require precise temperature control. However, it is not suitable for in-line measurement in the color filter production line of the liquid crystal display panel in that the installation location is limited.
[0013]
On the other hand, as an optical interference type film thickness measuring apparatus capable of in-line measurement using a light source device that is small and has a long life and does not generate heat, the film thickness previously proposed by the present applicant in International Publication No. WO01 / 01070A1. Sensors are known.
[0014]
However, even in this film thickness sensor, when applied to each RGB resist film of a color filter, white light in a wide wavelength region from a light source device to a wavelength region of about 400 nm to 700 nm is emitted from the color filter. Since the RGB resist film cannot be uniformly transmitted through each wavelength, it is still impossible to generate an appropriate interference waveform necessary for film thickness measurement.
[0015]
Here, as a result of intensive studies to solve the above problems, the present inventors have found that the problem of selective light transmission or selective light absorption regarding the RGB resist film of the color filter is infrared light as measurement light. The knowledge that it was possible to solve by using was obtained.
[0016]
That is, as shown in FIG. 1, the spectral transmittance characteristics of the RGB resist films constituting the color filter of the liquid crystal display panel are selectively transmitted as RGB register films in the visible light region from about 400 nm to about 700 nm. In contrast, in the near-infrared region to infrared region exceeding about 800 nm, it is hardly attenuated in any of the resist films of RGB (almost transparent state), but in the entire wavelength region. Uniform transmission characteristics can be obtained. Therefore, if near infrared light or infrared light is used as the measurement light, a clear optical interference waveform can be obtained by interference between the front surface reflected light and the back surface reflected light regardless of the resist film of RGB. Based on this, the film thicknesses of the RGB resist films can be accurately measured by a known calculation method.
[0017]
The present invention has been made on the basis of the above-mentioned knowledge, and its object is to provide an optical interference film capable of accurately measuring the thickness of each of the RGB resist films constituting the color filter of the liquid crystal display panel. It is to provide a thickness measuring device.
[0018]
Another object of the present invention is to provide an optical interference type film thickness measuring apparatus capable of accurately measuring the film thickness of a silicon-based thin film having visible light absorption characteristics such as polysilicon.
[0019]
Another object of the present invention is to provide an optical interference type film thickness measuring device that can be incorporated in a color filter manufacturing line of a liquid crystal display panel and can measure the film thickness of each of the RGB resist films constituting the color filter at high speed without contact. It is to provide.
[0020]
Another object of the present invention is to reduce the loss cost as much as possible by performing high-quality inspection of all products in the color filter production line of the liquid crystal display panel, thereby enabling the quality improvement and cost reduction of the liquid crystal panel. An object of the present invention is to provide an optical interference type film thickness measuring device.
[0021]
Other objects and operational effects of the present invention will be easily understood by those skilled in the art by referring to the description of the following specification.
[0022]
[Means for Solving the Problems]
The optical interference type film thickness measuring apparatus of the present invention is characterized in that infrared light is used as measurement light. As long as the interference waveform appears clearly, there is no positive reason for limiting the upper and lower limits of the usable infrared light wavelength region. However, the shorter the wavelength, the thinner the film can be measured, and the wider the wavelength band, the more accurately the film thickness can be calculated from the interference waveform, and the light receiving of the CCD element used as a photoelectric conversion element. Considering that the sensitivity characteristic decreases as the wavelength increases, the infrared light used as the measurement light preferably has a continuous wavelength band in a wavelength region of about 800 nm to 1000 nm.
[0023]
As a film to be measured suitable for the optical interference type film thickness measuring apparatus of the present invention, first, RGB resist films functioning as a color filter for a liquid crystal display panel can be mentioned. In other words, as described above, each of the RGB resist films has a unique light absorption characteristic in the visible light region, but has almost no light absorption property in the infrared light region, and light transmission almost nearly transparent. Has characteristics. Therefore, in an optical interference type film thickness measuring device, if infrared light is used as measurement light, a clear optical interference waveform can appear in the RGB resist film. Based on this, a curve fitting method or Their film thickness can be accurately measured by a known calculation method such as an extreme value search method.
[0024]
Other suitable measurement target film bodies include silicon-based thin films such as polysilicon. Since such a silicon-based film body also has visible light absorption characteristics, when visible light is used as measurement light, a clear optical interference waveform cannot be produced. According to the optical interference type film thickness measuring apparatus using infrared light of the present invention, a clear optical interference waveform can be obtained by sufficiently transmitting infrared light into a film body, even in a silicon film body. , The film thickness can be accurately measured.
[0025]
The film thickness measuring device of the present invention viewed from another aspect is a light source unit that emits infrared light, and the infrared light emitted from the light source unit is emitted toward the film body that is a measurement object and the reflected light is emitted. A transmission / reception optical system that is incident and guided to the spectroscopic unit, a series of component light obtained from the spectroscopic unit and a photoelectric conversion unit that performs photoelectric conversion individually and an electrical signal corresponding to an interference waveform obtained from the photoelectric conversion unit And a calculation unit for obtaining a film thickness based on the above. According to such a configuration, it is possible to accurately measure the thickness of each RGB film functioning as a color filter for a liquid crystal display panel and the film thickness of a silicon-based film body such as polysilicon based on the optical interference waveform. Here, as the photoelectric conversion unit, an element including a plurality of independent photoelectric elements such as a line CCD, a two-dimensional CCD, and a photodiode array can be used.
[0026]
In a preferred embodiment of the present invention, a monitor spectroscopic unit for monitoring infrared light emitted from the light source unit and a monitor photoelectric conversion unit may be further provided. According to such a configuration, the wavelength characteristic of the original infrared light emitted from the light source and the wavelength characteristic of the modulated infrared light interfered with the measurement object can be acquired at the same time. A pre-measurement process for acquisition is not required.
[0027]
In a preferred embodiment of the present invention, a mirror tube can be further interposed in the incident path to the spectroscopic unit. According to such a configuration, since the shift of the interference waveform due to the inclination of the measurement object is suppressed, the measurement accuracy can be maintained even if the measurement target panel is warped or distorted.
[0028]
In a preferred embodiment of the present invention, the light source unit includes a plurality of semiconductor infrared light emitting elements having different output waveform characteristics, an optical element for extracting light in a partial wavelength region from each semiconductor infrared light emitting element, and each semiconductor. Means for individually setting the output power of the infrared light emitting element, and the light extracted from each semiconductor infrared light emitting element may be superimposed and emitted. According to such a configuration, measurement infrared light having a continuous wavelength band can be generated in a relatively wide constant wavelength region, and the light source can be reduced in size, extended in life (maintenance-free), and cooled light source. For example, the incorporation of the film thickness measuring device into the production line can be facilitated.
[0029]
In a preferred embodiment of the present invention, a transmission / reception coaxial optical system including a beam splitter may be adopted as the transmission / reception optical system. According to such a configuration, it is possible to improve the detection sensitivity by minimizing the light power loss in the light projecting and light receiving paths while facilitating the incorporation into the production line by downsizing the transmission / reception optical system.
[0030]
In a preferred embodiment of the present invention, a spectroscopic element in which an optical multilayer film in which a transmission wavelength region continuously changes depending on an incident position may be adopted as a spectroscopic portion on the surface of a transparent substrate. According to such a configuration, it is possible to facilitate the incorporation of the film thickness measuring device into the production line by reducing the size of the spectroscopic unit and extending the life thereof.
[0031]
In a preferred embodiment of the present invention, the light source emits light including at least infrared light, and the spectroscopic unit may transmit only infrared light and split it. According to such a configuration, even if visible light is included in the light from the light source, the measurement operation can be performed normally.
[0032]
In a preferred embodiment of the present invention, a calculation unit that calculates a film thickness by calculating only the infrared wavelength region by a curve fitting method or an extreme value method can be employed. According to such a configuration, the film thickness can be quickly and accurately obtained by computer calculation based on the spectral wavelength data obtained from the photoelectric conversion unit.
[0033]
The film thickness measuring device of the present invention viewed from another aspect is configured to be separated into a sensor head that can be mounted close to the measurement object and a signal processing unit that can be mounted apart from the measurement object, and both are connected by an electric wire. It is. The sensor head includes a light source unit, a transmission / reception optical system, a spectroscopic unit, and a photoelectric conversion unit, and the signal processing unit includes a calculation unit. According to such a configuration, the sensor head can be easily incorporated into the production line due to the downsizing of the sensor head.
[0034]
In a preferred embodiment, the signal processing unit may have a form of a PCI board that can be mounted in an internal slot of a personal computer. According to such a configuration, it is possible to easily link with a measurement application by incorporating a PCI board into a personal computer.
[0035]
Further, in a preferred embodiment, the sensor head is incorporated in the production line of the color filter for the liquid crystal panel so that the film pressures of the RGB resist films constituting the color filter can be continuously measured. Good. According to such a configuration, the loss cost is reduced and the quality of the product is improved by early detection of a defective product based on continuously measured film thickness data and feedback processing to the process of continuously measured film thickness data. be able to.
[0036]
DETAILED DESCRIPTION OF THE INVENTION
In the following, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.
[0037]
A block diagram showing an electrical configuration of the film thickness measuring apparatus according to the first embodiment is shown in FIG. As shown in the figure, this film thickness measuring apparatus includes a small sensor head 1 that can be mounted in the vicinity of a measurement object 7 (for example, a color filter plate flowing through a production line), and a measurement object. And a PCI board 3 that can be mounted in an internal slot of a personal computer (PC) 5 that is set apart from the object 7.
[0038]
A cable (electric wire) 2 is connected between the sensor head 1 and the PCI board 3. A PCI bus 4 is connected between the PCI board 3 and a CPU (not shown) of a personal computer (PC) 5. Reference numeral 5a in the figure is application software incorporated in the personal computer (PC) 5, and reference numeral 6 outputs film thickness measurement data and film thickness determination output (LOW, HIGH, PASS, etc.) to the outside, or from the outside. This is an external interface for inputting various digital command signals. The application software 5a includes various functional processes that control film thickness measurement data processing, display, determination processing, and the like.
[0039]
The sensor head 1 includes a light projecting unit 11 and a light receiving unit 12. The light projecting unit 11 includes a light source unit that emits infrared light and a light transmission side optical system that emits infrared light emitted from the light source unit toward the measurement object 7. In the light receiving unit 12, the light receiving side optical system that receives the reflected light from the measurement object 7 and guides it to the spectroscopic unit and the series of component light obtained from the spectroscopic unit are appropriately classified and individually photoelectrically converted. And a photoelectric conversion unit. Note that specific configurations of the light source unit, the light transmission side optical system, the light reception side optical system, the spectroscopic unit, and the photoelectric conversion unit will be described in detail later.
[0040]
FIG. 3 shows a schematic configuration diagram of the optical system in the sensor head of the film thickness measuring apparatus according to the first embodiment. As shown in the figure, in the sensor head 1, an infrared LED 111 functioning as a light source unit, a lens 101 having both functions of a light transmitting side optical system and a light receiving side optical system, and a half mirror 102, , A spectroscopic element 121 that functions as a spectroscopic unit that splits reflected light from a measurement object, and a CCD that functions as a photoelectric conversion unit that appropriately photoelectrically converts a series of component light obtained from the spectroscopic unit and separately Contains.
[0041]
That is, the infrared LED 111 emits infrared light as measurement light. As infrared light used as measurement light, for example, one having a continuous wavelength band in a wavelength region of 800 nm to 1000 nm is preferable. The wavelength region of 800 nm to 1000 nm is not necessarily the entire region. If the film to be measured is thick, the number of waves of the interference waveform increases, so that sufficient measurement accuracy can be obtained even if the wavelength region is short. In such a case, it may be 800 nm to 900 nm.
[0042]
Of course, the light itself emitted from the light source unit may contain components in the visible light wavelength region of 400 nm to 700 nm, but these visible light components adversely affect the film thickness measurement of the color filter. That is, when the visible light wavelength region of 400 nm to 700 nm is included, only a specific wavelength region (visible) is absorbed when measuring the film thickness of the color filter, which is different from the theoretically required interference waveform. . Then, it becomes impossible to derive a correct film thickness because fitting cannot be performed at the time of calculation, or an extreme value that should be really disappeared. Therefore, when the visible light wavelength region of 400 nm to 700 nm is included, it is necessary to consider that only the infrared light wavelength region is selected by the spectroscopic unit, or that the calculation unit calculates only the infrared wavelength region. .
[0043]
Needless to say, ideally, it is preferable that the LED, the spectroscopic unit, and the calculation wavelength region are all infrared light. At this time, the reason why the LED is infrared light is to maximize light utilization efficiency. Moreover, the reason why the transmitted light of the spectroscopic unit is infrared light is for maximizing the light utilization efficiency and maximizing the resolution. Furthermore, in the calculation wavelength region, if infrared light is not used, appropriate measurement cannot be performed. Because.
[0044]
The reason why the lower limit of the wavelength range of infrared light is set to 800 nm is that, in a wavelength range shorter than that, it is absorbed by the color filter resist film, which is a measurement object, and does not contribute to the appearance of an optical interference waveform. In addition, the upper limit of the wavelength region of infrared light is set to 1000 nm because the light receiving sensitivity of the CCD constituting the photoelectric conversion unit is lower in the wavelength region longer than that, and in the optical interference type film thickness measurement, the wavelength is lower than that. This is because when applied to the film thickness measurement of the color filter, the measurement accuracy is lowered.
[0045]
The lens 101 and the half mirror 102 constitute a coaxial transmission / reception optical system. In other words, the infrared light emitted from the infrared light LED 111 is reflected downward in the figure by the half mirror 102 and then irradiates the measurement object 7 vertically through the lens 101. If the measurement object 7 is an RGB resist film of a color filter, for example, the irradiated infrared light is reflected on the front surface and the back surface, and the surface reflected light and the back surface reflected light are combined and then again. , It is returned vertically upward through the lens 101, and then transmitted through the half mirror 102 and guided to the spectroscopic element 121. The infrared light incident on the spectroscopic element 121 includes optical interference waveform information corresponding to the film thickness of the measurement object 7.
[0046]
The spectroscopic element 121 transmits incident infrared light separately for each wavelength component included therein. A conceptual diagram for explaining the operating characteristics of the spectroscopic element 121 is shown in FIG. As shown in the figure, the spectroscopic element 121 is obtained by forming an optical multilayer film 121a whose transmission wavelength region continuously changes depending on the incident position on the surface of a glass substrate 121b which is a transparent substrate. More specifically, the transmission wavelength characteristic of the optical multilayer film is continuously changed by continuously changing the optical film thickness of each layer constituting the optical multilayer film in a one-dimensional direction. The light transmitted through each position of the spectroscopic element 121 is received by an element having a plurality of independent light receiving elements such as a line CCD, a two-dimensional CCD, a photodiode array, etc., thereby detecting the light intensity at each wavelength. Data can be obtained. According to such a multilayer film structure, it is possible to greatly reduce the size of the spectroscopic element as compared with a conventional structure using a diffraction grating, and as a result, the sensor head can be easily incorporated into a production line.
[0047]
The CCD 122 receives the light transmitted through each position of the spectroscopic element 121 and outputs a serial light reception signal corresponding to each pixel. This serial light reception signal includes interference waveform information necessary for film thickness measurement.
[0048]
Returning to FIG. 2, the PCI board 3 includes a light projection / reception control unit 31, an A / D conversion unit 32, and a signal processing unit 33 configured by a firmware 33 a as a microcomputer. The A / D conversion unit 32 performs A / D conversion on the output signal of the CCD 122 included in the sensor head 1, and then delivers it to the signal processing unit 33. The digital signal delivered to the signal processing unit 33 includes interference waveform information corresponding to the film thickness to be measured. The light projecting / receiving control unit 31 controls the lighting power and lighting timing of the infrared LED 111 included in the light projecting unit 11. In order to control the lighting power of the infrared LED 111, for example, a process of adjusting the drive current of the LED 111 with a variable resistor is performed. In order to control the lighting power, the light projecting / receiving control unit 31 controls the photographing or video signal reading operation of the CCD 122 included in the light receiving unit 12.
[0049]
Based on the interference waveform information obtained from the A / D conversion unit 32, the signal processing unit 33 calculates the film thickness of the target film body by using a known method such as a curve fitting method or an extreme value exploration method. This is obtained and transferred to the CPU of the personal computer (PC) 5 via the PCI bus 4. The arithmetic processing for measuring the film thickness will be described in detail later with reference to the drawings.
[0050]
The film thickness measurement value thus passed is displayed on the screen of the personal computer by executing the application software 5a on the personal computer (PC) 5, or binarized by comparison with a prescribed threshold value. After that, it is sent out from the external interface 6 to the outside as a judgment output (PASS, LOW, HIGH, etc.). On the other hand, when a predetermined application software 5a is executed in the personal computer (PC) 5, a command generated by an operation of a keyboard, a mouse, or the like is sent to the signal processing unit 33 via the PCI bus 4, and thereby a signal is transmitted. Various instructions or commands for the processing unit are realized.
[0051]
Examples of interference waveforms of color filters obtained by a film thickness measuring device using infrared light as measurement light are shown in FIGS. As shown in FIG. 5, for the R (red) resist film constituting the color filter for the liquid crystal display panel, a clear interference waveform was obtained in a wavelength region of about 600 nm or more. As shown in FIG. 6, for the G (green) resist film constituting the color filter for the liquid crystal display panel, a clear interference waveform was obtained in a wavelength region of about 800 nm or more. As shown in FIG. 7, for the B (blue) resist film constituting the color filter for the liquid crystal display panel, a clear interference waveform was obtained in a wavelength region of about 800 nm or more. As a result, if infrared light (light in a wavelength region of about 800 nm or more) is used as measurement light, an interference waveform corresponding to the filter film thickness is clearly displayed regardless of RGB, based on this. It was confirmed that the film thickness can be measured accurately.
[0052]
According to the film thickness measuring apparatus according to the first embodiment described above, even if the resist film of the color filter having the light absorption characteristic in the visible light region is adopted by using the infrared light as the measurement light, the light selective transmission property is obtained. In addition to being able to accurately measure the film thickness without being affected by the above, the entire apparatus is separated into the sensor head 1 and the PCI board 3 and both are connected by the cable 2. Because the light source unit (infrared light LED 111), the optical system (lens 101, half mirror 102), the spectroscopic unit (spectral element 121), and the photoelectric conversion unit (CCD 122) to be incorporated all employ element parts that can be miniaturized. By incorporating the sensor head 1 into the color filter production line, so-called in-line measurement can be realized.
[0053]
Next, a block diagram showing an electrical configuration of the film thickness measuring apparatus according to the second embodiment is shown in FIG. In the figure, the same components as those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.
[0054]
The feature of this embodiment is that the PCI board 3A includes a light receiving unit 35 and a light projecting unit 34, and the fiber head 8 is used as a detection end that can be mounted close to the measurement object. In addition, the fiber head 8 and the PCI board 3A are connected by an optical fiber 9 made of a bundle fiber having high light transmittance and good flexibility.
[0055]
That is, an infrared light LED 111 similar to that shown in FIG. 3 is built in the light projecting unit 34, and infrared light emitted from the LED 111 is introduced into the incident end of the fiber 9 and passes through the fiber 9. The measurement object 7 is irradiated from the tip of the fiber head 8. On the other hand, the reflected light from the measurement object 7 is introduced into the fiber 9 from the tip of the fiber head 8, and then introduced into the light receiving unit 35 through the fiber 9. The introduced light is irradiated to a spectral element 121 similar to that shown in FIG. Thereafter, similarly to the first embodiment, the transmitted light of the spectroscopic element 121 is received by the CCD 122, and spectroscopic data including interference waveform information is generated.
[0056]
According to the film thickness measuring apparatus according to the second embodiment described above, the fiber head 8 serving as the detection end can be remarkably reduced in size as compared with the sensor head 1 incorporating an optical component or various electronic components. Incorporated easily in a narrow space of the color filter production line, and because the fiber 9 is a bundle fiber with good light transmittance or flexibility, the sensitivity of the CCD in the infrared region is insufficient ( Regardless of (see FIG. 9), accurate film thickness measurement can be performed without degrading the detection response. Since the transmittance of the bundle fiber is about 60%, it was confirmed that a total transmittance of 36% was obtained on the light projecting side and the light receiving side.
[0057]
Next, a block diagram showing an electrical configuration of the film thickness measuring apparatus according to the third embodiment is shown in FIG. In the figure, the same components as those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.
[0058]
The feature of this embodiment is that the monitor light receiving unit 13 is provided in the sensor head 1A, the A / D converter 36 is provided in the PCI5 board 3, and the light projecting / receiving control unit 31 in the PCI board 3 is used. The monitor light-receiving unit 13 in the sensor head 1A is driven and controlled, and the video signal obtained from the monitor light-receiving unit 13 is converted into a digital signal via the A / D converter 36, and then transferred to the signal processing unit 33A. It is in the point which did.
[0059]
FIG. 11 shows a schematic configuration diagram of an optical system in the sensor head of the film thickness measuring apparatus according to the third embodiment. In the figure, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted. The new point of the optical system in the sensor head is that a monitor spectral element 131 and a monitor CCD 132 are newly provided.
[0060]
That is, in the figure, the infrared light emitted from the infrared light LED 111 is reflected vertically downward in the figure on the lower surface of the half mirror 102 in the same manner as in the first embodiment, and then passes through the lens 101. The surface of the measurement object 7 is irradiated. On the other hand, the reflected light reflected from the front surface and the back surface of the measurement object 7 reaches the half mirror 102 via the lens 101, further passes through the half mirror 102, and is guided to the spectroscopic element 121. As a result, each wavelength component included in the reflected light from the measurement object 7 is spectrally separated by the spectroscopic element 121, whereby an electric signal corresponding to the interference waveform is output from the CCD 122.
[0061]
In addition, in this embodiment, a part of the light emitted from the infrared light LED 111 passes through the half mirror 102 and is guided to the monitoring spectroscopic element 131 disposed in front of the half mirror 102. The function of the monitor spectral element 131 is the same as that of the measurement spectral element 121. Therefore, each wavelength component included in the current infrared light emitted from the infrared light LED 111 is dispersed in the monitor spectral element 131, and from the CCD 132, the current infrared light emitted from the infrared light LED 111 as a light source. It is obtained with an electric signal including the wavelength characteristics of
[0062]
As described above, according to the novel configuration including the monitoring spectral element 131 and the monitoring CCD 123 in addition to the measuring spectral element 121 and the measuring CCD shown in FIG. It becomes possible to simultaneously acquire the wavelength characteristics of the current infrared light and the wavelength characteristics of the modulated infrared light interfered by the measurement object 7.
[0063]
In order to stabilize the film thickness measurement value, the measurement accuracy of the optical interference waveform is important. The optical interference waveform is a ratio for each wavelength of the light projecting beam and the light receiving beam. In the case of a method in which a projected beam waveform measured in advance is stored and a ratio with the received beam waveform is calculated, a correct interference waveform cannot be obtained if the wavelength distribution of the projected beam intensity varies during detection of the received beam. In a conventional halogen lamp type film thickness measuring apparatus, in order to suppress such an influence, it is necessary to always obtain a reference with a quartz plate or the like prior to film thickness measurement. This is a factor that reduces the throughput of the process. On the other hand, in the embodiment shown in FIG. 11, the spectroscopic element 131 and the CCD 132 are arranged for monitoring and the wavelength distribution of the projection beam is fed back in real time. By adopting a small number of LED light sources and adding this light amount feedback method, the frequency of reference acquisition can be reduced, and maintenance can be improved.
[0064]
Next, FIG. 12 shows a schematic configuration diagram of an optical system of a sensor head including a multi-LED light source device. In the figure, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.
[0065]
This multi-LED light source device is characterized by a plurality of semiconductor infrared light emitting elements having different output waveform characteristics, an optical element for extracting light in a partial wavelength region from each semiconductor infrared light emitting element, and each semiconductor infrared light emitting Means for individually setting the output power of the element, and the light extracted from each semiconductor infrared light emitting element is superimposed and emitted.
[0066]
That is, in the sensor head 1, the first infrared light LED 111, the second infrared light LED 112, the third infrared light LED 113, the first dichroic mirror (DCM) 114, and the second The dichroic mirror (DCM) 115 is included.
[0067]
In this example, the first infrared LED 111 is LN151L (Matsushita), the second infrared LED 112 is L1915-01 (Hamamatsu Photonics), and the third infrared LED 113 is L3989-01 (Hamamatsu). Photonics) is used.
[0068]
Each of these three infrared LEDs (LED1, LED2, LED3) has a peak waveform centered on a specific wavelength. The two dichroic mirrors (DCM1 and DCM2) combine these three peak waveforms to achieve continuous wavelength characteristics in the region of about 800 nm to 1000 nm.
[0069]
In order to measure with high accuracy using the film thickness optical interference method, it is necessary to obtain an interference waveform obtained by light in a wide wavelength range. Therefore, as in this embodiment, by using a plurality of infrared LEDs having different peak wavelengths to obtain a wide wavelength range without interruption, the film thickness can be measured with high accuracy.
[0070]
Next, FIG. 14 shows a schematic configuration diagram of an optical system of a sensor head including a mirror cylinder. In the figure, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted. A feature of this embodiment is that a mirror cylinder 123 is interposed in the incident path to the spectroscopic element 121, thereby suppressing the shift of the interference waveform due to the tilt of the measurement object 7.
[0071]
As shown in the figure, a mirror tube 123 is arranged in a state in which the axis thereof is perpendicular to the spectroscopic element 121 in the path of the reflected light reflected by the measurement object 7 to the spectroscopic element 121. As shown in FIG. 15, the mirror tube is provided with a cylindrical passage 123a, and the inner surface of the cylindrical passage is mirror-finished. Therefore, the light introduced into the cylindrical passage 123a is finally emitted from the exit of the passage to the outside while repeating multiple reflection on the inner surface of the passage. In addition, as a mirror surface cylinder said here, what has a function equivalent to it like a glass rod etc. is contained. That is, when light is incident on the mirror tube 123 obliquely, the emitted light can be expanded by multiple reflection inside the mirror tube 123. If the same function as a glass rod is performed, another member may be used instead of the mirror tube 123.
[0072]
According to such a configuration, the following special effects can be obtained. That is, when measuring in-line, the target object 7 may be tilted due to the warp of the glass substrate that is the target object 7, and the measurement can be performed stably even in such a state.
[0073]
An explanatory diagram showing the optical power distribution in the state where the mirror cylinder 123 does not exist is shown in FIG. As shown in the figure, when the mirror cylinder 123 is not present, the optical power distribution is symmetrical with respect to the center of the pixel column in the normal state of the measurement object shown in FIG. It becomes. On the other hand, in the state where the measurement object shown in FIG. 5B is tilted, the optical power distribution is biased to one of the centers of the pixel positions, and as a result, erroneous interference waveform data is generated. Will be obtained.
[0074]
FIG. 17 is an explanatory diagram showing the relationship between the mirror cylinder and the optical power distribution when the measurement object is tilted. In the state without the mirror cylinder shown in FIG. 16A, as described above with reference to FIG. 16, when the target object 7 is tilted, the optical power distribution deviates from the center of the pixel row and exhibits a biased spread. Become. On the other hand, in the state with the mirror tube shown in FIG. 5B, even if the measurement object 7 is tilted and light is incident on the mirror tube 123 obliquely, the light emitted from the mirror tube 123 is not reflected. The optical power distribution is a symmetric distribution with the center of the pixel column as a reference, and the interference waveform data obtained in this state is normal.
[0075]
As described above, when the mirror cylinder 123 is arranged, even if the target object 7 is tilted, the change in the distribution of the optical power can be reduced on the CCD 122, thereby enabling accurate in-line measurement.
[0076]
Next, a graph showing comparison of interference waveforms in the infrared light region and the visible light region is shown in FIG. The interference waveform has a characteristic that the cycle becomes smaller as the film thickness increases, and the interference waveform is destroyed when the wavelength resolution of the spectroscopic element is exceeded. The period of the interference waveform becomes longer as the wavelength becomes longer. Therefore, when measuring a measurement object having a large film thickness, the interference waveform is crushed in the visible light region, making measurement difficult, as shown in FIG. As shown in FIG. 5, the interference waveform is relatively easy to measure in the infrared light region. Also from this fact, since infrared light is used as the measurement light in the present invention, there is an effect that the measurement range can be expanded to a thicker one.
[0077]
Next, a graph showing the interference waveform of polysilicon on a glass substrate is shown in FIG. Since silicon (Si) absorbs light in the visible light region, an interference waveform cannot be measured. On the other hand, in the infrared region, since light passes, the interference waveform can be measured. Also from this, in the present invention, since infrared light is used as the measurement light, there is an effect that it is possible to measure a Si-based film thickness such as polysilicon (Poly-Si).
[0078]
Finally, a specific method for calculating the film thickness based on the interference waveform will be described with reference to FIGS. As a calculation method of the film thickness in the calculation unit constituting the signal processing unit 33, for example, a curve fitting method, an extreme value search method, or the like can be used.
[0079]
As shown in FIG. 22, the curve fitting method compares the waveform data (table data) for each film thickness calculated in advance and stored as a table with the measured light reception data, and compares the light reception data with the least square method. This is a method of extracting waveform data with the smallest error (that is, the area of the hatched portion in FIG. 22), and setting the film thickness of the waveform data as the film thickness of the thin film 72 to be measured. The film thickness is obtained from the difference in wavelength corresponding to the maximum value and the minimum value of the received light data, both of which are general methods.
[0080]
The curve fitting method will be described in detail as follows. As shown in FIG. 20, an interference waveform (transmittance R) when light having a wavelength λ is incident on a thin film 72 having a film thickness d and a refractive index n is expressed by the following equation. Here, the constants A, B, and C are determined from the refractive indexes of the substrate 71 and the thin film 72.
[Expression 1]
R = 1−A / [B + C · cos [(4π / λ) nd]] (1)
[0081]
When the refractive index n and constants A, B, and C of the thin film 72 to be measured are input in advance from a keyboard of a personal computer or the like, the arithmetic unit constituting the signal processing device determines the film thickness d and the wavelength λ within the measurement range. The value of reflectance R for each value of film thickness d and wavelength λ is calculated by equation (1), and these are stored as a table in a memory (not shown) in the calculation unit.
[0082]
An example of such a table is shown in FIG. In this example, the measured film thickness range is from Δx to dy in increments of Δd = 1 nm, and the wavelength range is from λp to λq in increments of Δλ = 10 nm.
[0083]
Next, the curve fitting method is executed according to the processing flow shown in FIG. When the measurement unit obtains measurement data (transmittance measurement data) M (λ) obtained by A / D conversion (S1), the calculation unit starts the calculation. First, the film thickness d is set to the minimum film thickness dx (S2), and the transmittance at the film thickness d = dx is the square of the difference between the theoretical data Rdx (λ) and the measurement data M (λ) using the theoretical table of FIG. [Rdx (λ) −M (λ)]²Is calculated in increments of Δλ (for example, 10 nm) from the wavelength range λp to λq, and the sum
[Expression 2]
P (dx) = Σ [Rdx (λ) −M (λ)]²
(S3) and stored in the memory.
[0084]
Next, the film thickness d is increased by Δd (for example, 1 nm) (S4). Similarly, the square of the difference between the theoretical data Rdx + Δd (λ) and the measurement data M (λ) at the film thickness d = dx + Δd [Rdx + 1 (λ ) -M (λ)]²Is calculated in increments of Δλ from the wavelength range λp to λq, and the sum
[Equation 3]
P (dx + Δd) = Σ [Rdx + Δd (λ) −M (λ)]²
(S3) and stored in the memory.
[0085]
In this way, the value of the film thickness d is sequentially increased by Δd until the film thickness d reaches the maximum film thickness dy (S5), and the square sum of the difference between the theoretical data and the measurement data at that time is obtained. (S3) Store in the memory.
[0086]
When the calculation of the sum of squares up to the maximum film thickness dy is completed in this way (YES in S5), the minimum of the sums of squares P (dx) to P (dy) in the film thickness range dx to dy stored in the memory is determined. The sum of squares P (dz) taking the above value is extracted (S6), and the film thickness dz at this time is taken as the measured film thickness (S7).
[0087]
Next, a method of calculating the film thickness by the extreme value search method will be described with reference to FIG. In the extreme value search method, the arithmetic unit differentiates the digitized measurement data and obtains a local maximum value from a position where the differential value changes from plus to 0 (or minus) when the wavelength λ increases. If the wavelengths corresponding to the adjacent maximum values thus obtained are λ1 and λ2 (where λ1 <λ2) as shown in FIG. 25, the film thickness d of the thin film 72 is obtained by using the refractive index n of the thin film 72. ,
[Expression 4]
d = (λ1 × λ2) / [2n (λ2−λ1)]
The thin film d can be obtained by giving the refractive index n of the thin film 72. Alternatively, even if the minimum value is obtained from the position where the differential value changes from minus to 0 (or plus), the film thickness d can be obtained by the same calculation.
[0088]
Next, the case where the film thickness measuring apparatus according to the present invention is actually incorporated in a color filter production line of a liquid crystal panel will be described. An example of a cross-sectional view of an active matrix TFT including a color filter to be inspected is shown in FIG.
[0089]
As shown in the figure, the active matrix TFT is configured by laminating a deflecting plate, glass, liquid crystal, alignment film, ITO, glass, and deflecting plate in this order. In a fine region corresponding to each pixel, an active element, a liquid crystal driving electrode, a bus line, and the like are provided. In this example, the color filter to be inspected is manufactured using a color resist. There are three types of color resists, RGB, and these three types of resist films are arranged in a mosaic pattern so that three filter elements of RGB are uniformly distributed for each pixel, as shown in a partially enlarged view in the figure. Is done.
[0090]
The color resist process is shown in FIG. This color resist process includes a BM process, an R process, a G process, a B process, and an OC process. Each RGB process includes a coating process, a baking process, an exposure process, a development process, and a strip process.
[0091]
These processes are performed while conveying the glass substrate onto the production line. The glass substrate shown in the figure is divided into four parts vertically and horizontally, and four color filter plates are obtained by one glass substrate. A marginal area is provided in a rectangular frame shape on the outer peripheral edge of the four color filter plates. The thickness of the color resist film coated on the marginal area is determined by the thickness sensor (sensor head 1) of the present invention. Equivalent). The film thickness sensors are arranged in three rows along the margin line on the glass substrate in the width direction, and each sensor head emits infrared light vertically downward in the figure, and the reflected light is received.
[0092]
As described above, in the film thickness measuring apparatus of the present invention, since the small sensor head 1 or the fiber head 8 is used, it can be easily attached even in a narrow space on the conveyance line of the glass substrate. In addition, since a semiconductor element is used as the light source, the problem of heat generation can be ignored, and as a result, in-line continuous measurement is possible in the color resist process.
[0093]
With this continuous measurement, defective products can be found and removed immediately after each process. In addition to reducing the loss cost, the film quality data continuously measured is immediately fed back to the process, so that the product quality is always optimized. The value can be controlled. As a result, by adopting the film thickness measuring apparatus of the present invention for the color resist process, it is possible to improve the quality and reduce the cost of the liquid crystal display panel.
[0094]
【The invention's effect】
As is apparent from the above description, the optical interference type film thickness measuring apparatus of the present invention uses infrared light as measurement light, and therefore is affected by wavelength selection characteristics as a filter. In addition, the film thickness of each of the RGB resist films functioning as a color filter for a liquid crystal display panel can be accurately measured.
[Brief description of the drawings]
FIG. 1 shows spectral transmittance characteristics (3 types of B, G, and R) of a color filter.
FIG. 2 is a block diagram showing an electrical configuration of the film thickness measuring apparatus according to the first embodiment.
FIG. 3 is a schematic configuration diagram of an optical system in the sensor head of the film thickness measuring apparatus according to the first embodiment.
FIG. 4 is a conceptual diagram for explaining operating characteristics of a spectroscopic element.
FIG. 5 is an example of an interference waveform of a color filter (in the case of R).
FIG. 6 is an example of an interference waveform of a color filter (in the case of G).
FIG. 7 is an example of an interference waveform of a color filter (in the case of B).
FIG. 8 is a block diagram showing an electrical configuration of a film thickness measuring apparatus according to a second embodiment.
FIG. 9 is a graph showing an example of spectral sensitivity characteristics of a general CCD.
FIG. 10 is a block diagram showing an electrical configuration of a film thickness measuring apparatus according to a third embodiment.
FIG. 11 is a schematic configuration diagram of an optical system in a sensor head of a film thickness measuring device according to a third embodiment.
FIG. 12 is a schematic configuration diagram of an optical system of a sensor head including a multi-LED light source device.
FIG. 13 is a graph showing wavelength characteristics of an infrared light LED and a dichroic mirror.
FIG. 14 is a schematic configuration diagram of an optical system of a sensor head including a mirror cylinder.
FIG. 15 is a conceptual diagram for explaining the operation of a mirror tube.
FIG. 16 is an explanatory diagram showing an optical power distribution in a state where no mirror tube is present.
FIG. 17 is an explanatory diagram showing the relationship between the presence / absence of a specular cylinder and the optical power distribution when a measurement object is tilted.
FIG. 18 is a graph showing a comparison of interference waveforms in an infrared light region and a visible light region.
FIG. 19 is a graph showing an interference waveform of Poly-Si on a glass substrate.
FIG. 20 is a conceptual diagram for explaining an interference waveform calculation principle.
FIG. 21 is a graph showing a specific example of a spectrum.
FIG. 22 is an explanatory diagram of a curve fitting method.
FIG. 23 is a diagram showing an example of a theoretical table of reflectivity R with respect to each value of a film thickness d and a light wavelength λ.
FIG. 24 is a flowchart showing an execution procedure of a curve fitting method.
FIG. 25 is an explanatory diagram of an extreme value search method;
FIG. 26 is a cross-sectional view of an active matrix TFT.
FIG. 27 is a process diagram showing a color resist process.
FIG. 28 is a graph showing a transmission spectrum of each color element constituting the color filter.
[Explanation of symbols]
1 Sensor head
1A Sensor head
2 Cable
2A cable
3 PCI board
3a PCI board
4 PCI bus
5 PC
5a Application software
6 External interface
7 Measurement object
8 Fiber head
9 Fiber
11 Floodlight
12 Light receiver
13 Light receiver for monitor
31 Emitter / Receiver Controller
32 A / D converter
33 Signal processor
33A Signal processor
33a Firmware
34 Floodlight
35 Light receiver
101 lens
102 half mirror
111 1st infrared light LED (LED1)
112 2nd infrared light LED (LED2)
113 3rd infrared light LED (LED3)
114 First dichroic mirror (DCM1)
115 Second dichroic mirror (DCM2)
121 Spectroscopic element
122 CCD
123 mirror tube
123a Cylindrical passage
131 Spectral element for monitoring
132 CCD for monitor

Claims (10)

A light source unit that emits infrared light, a transmission / reception optical system that emits infrared light emitted from the light source unit toward a film body that is a measurement object, and that receives the reflected light to the spectroscopic unit, and a spectroscopic unit A series of component light obtained from the above, a photoelectric conversion unit that individually photoelectrically converts, a calculation unit that obtains a film thickness based on an electrical signal corresponding to an interference waveform obtained from the photoelectric conversion unit, and a surface of the transparent substrate And a spectroscopic portion composed of a spectroscopic element formed with an optical multilayer film in which the transmission wavelength region continuously changes depending on the incident position, and the wavelength of infrared light used as measurement light exceeds 800 nm, And a film thickness measuring apparatus having a continuous wavelength band in a wavelength region of about 800 nm to 1000 nm, and the film body to be measured is an RGB resist film functioning as a color filter for a liquid crystal display panel . It further has a monitoring spectroscopic unit for monitoring infrared light emitted from the light source unit and a photoelectric conversion unit for monitoring, thereby interfering with the wavelength characteristic of the original infrared light emitted from the light source and the measurement object 2. The film thickness measuring apparatus according to claim 1 , wherein the wavelength characteristics of the modulated infrared light can be acquired simultaneously. 2. The film thickness measuring apparatus according to claim 1 , wherein a mirror tube is further interposed in an incident path to the spectroscopic unit, thereby suppressing a shift in an interference waveform due to an inclination of a measurement object. The light source unit individually controls a plurality of semiconductor infrared light emitting elements having different output waveform characteristics, an optical element that extracts light in a partial wavelength region from each semiconductor infrared light emitting element, and an output power of each semiconductor infrared light emitting element. and means for setting the film thickness measurement according to any one of claims 1 to 3, characterized in that it is configured to emit by overlapping light extracted from the semiconductor infrared emitting device apparatus. The film thickness measuring apparatus according to any one of claims 1 to 3 , wherein the transmission / reception optical system is a transmission / reception coaxial optical system including a beam splitter. 2. The film thickness measuring apparatus according to claim 1 , wherein the light source emits light including at least infrared light, and the spectroscopic unit transmits only infrared light and separates it. The film thickness measuring apparatus according to any one of claims 1 to 3 , wherein the calculation unit calculates the film thickness by calculating only the infrared wavelength region by a curve fitting method or an extreme value method. The sensor head that can be mounted close to the measurement object and the signal processing unit that can be mounted separately from the measurement object are separated, and both are connected by electric wires.
The sensor head, a light source unit, and the transmitting and receiving optics, and the spectroscopic portion, includes a photoelectric conversion unit, the signal processing unit, according to claim 1, arithmetic unit is included, characterized in that thickness measuring system according to any one of 1 to 7. 9. The film thickness measuring apparatus according to claim 8 , wherein the signal processing unit has a form of a PCI board that can be mounted in an internal slot of a personal computer. Sensor head is incorporated in the production line of a color liquid crystal panel filter, whereby any of claims 8 or 9, characterized in that the thickness of each RGB resist film constituting the color filter is continuously measured The film thickness measuring apparatus described in 1.

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