JP2011237355A - Film thickness measuring method and film thickness measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure a film thickness of a film to be measured which is formed on a substrate having a small difference in refraction factor with respect to the film to be measured.SOLUTION: A film thickness measuring apparatus includes a light source 42 for irradiating a surface of a protection film 16, which is a film to be measured, with pulse light 41 at an incident angle of 45 degrees or greater, a spectrometer 44 for dispersing interference light generated by surface reflection light reflected at a surface and interface reflection light reflected at an interface between a dielectric layer 15 and the protection layer 16, a separator 47 for separating signals from the light source 42 from noise due to disturbance light based on information on phase and cycles of pulse light 41, and a light detector 46 for detecting light dispersed by the spectrometer 44.

Description

  The present invention relates to a film thickness measuring apparatus that measures the film thickness of a film to be measured formed on a substrate in a non-destructive and non-contact manner, and in particular, a film thickness measuring method suitable for measuring a film thickness of a protective film of a plasma display panel and The present invention relates to a film thickness measuring device.

  In recent years, an image display device using a plasma display panel (hereinafter abbreviated as “PDP”) is developed and produced as a large-screen, high-definition screen display device. A typical AC surface discharge type PDP as a PDP is composed of a front substrate and a back substrate, which are arranged to face each other and sealed around each other, and a large number of discharge cells are formed inside.

  A dielectric layer is formed on a front substrate made of a glass substrate of PDP, and a protective film is further formed to cover the dielectric layer. The protective film has a function of protecting the dielectric layer from ion bombardment caused by electric discharge and reducing the driving voltage by emitting secondary electrons. As a material of the protective film, a magnesium oxide (MgO) film having high ion impact resistance is used, and is generally formed by a vacuum deposition method or the like. In film formation by such a vacuum deposition method, the deposited film thickness has a great influence on the discharge characteristics. Therefore, the film thickness of the protective film formed on the dielectric layer is automatically measured with high accuracy and the product quality Is required to ensure.

  As a method for measuring the thickness of such a protective film in-line in a manufacturing process, a method using a spectral interference method is generally used. For example, in Patent Document 1, light is irradiated perpendicularly to a film to be measured, and interference light of light reflected at the surface of the film to be measured and the interface between the film to be measured and its substrate is measured by a spectroscope. And a film thickness measuring apparatus for measuring the film thickness from the interference wavelength obtained by separating through the film.

Japanese Patent Laid-Open No. 2003-130614

  However, in recent PDPs, further improvement in light emission efficiency is required. For this purpose, the dielectric constant of the dielectric layer formed under the protective film is reduced. As a result, the difference in refractive index between the dielectric layer and the magnesium oxide protective film formed on the dielectric layer has become very small. For this reason, when measuring the film thickness of the protective film that is a non-measurement target film, the difference in reflection intensity at the interface between the protective film and the dielectric layer is weakened, and the intensity of the interference signal is reduced. The problem that thickness cannot be measured accurately occurs.

  The present invention solves such problems, and a film thickness measuring method capable of accurately measuring in-line the film thickness of a non-measurement target film formed on a substrate having a small difference in refractive index from the non-measurement target film. And an apparatus for measuring the film thickness.

  In order to achieve the above object, a film thickness measuring method of the present invention is a film thickness measuring method for measuring a film thickness of a film to be measured formed on a substrate, and is provided on the surface of the film to be measured. Interference formed by a light irradiation step of irradiating pulsed light from a light source with an incident angle of more than 90 degrees, and surface reflected light reflected from the surface and interface reflected light reflected from the interface between the substrate and the film to be measured A spectroscopic step for splitting light; a separation step for separating a signal from the light source and noise due to disturbance light based on information on the phase and period of the pulsed light; and a light detection step for detecting light dispersed in the spectroscopic step; It has.

  According to such a method, the reflection intensity from the interface between the substrate and the film to be measured can be increased, and the non-measurement object formed on the substrate having a small difference in refractive index from the non-measurement object film. The film thickness can be measured with high measurement accuracy while reducing the influence of noise.

  Further, it is desirable that the pulsed light is light including near ultraviolet light. According to such a method, the film thickness can be measured with higher accuracy.

  Furthermore, it is desirable to provide a correction step of correcting the light intensity for each wavelength using the reference light by dividing the light before entering the light detection step with a beam splitter to be the reference light. According to such a method, since the peak of the interference signal can be recognized with high accuracy, the measurement accuracy can be further improved.

  Furthermore, it further includes a conversion step of converting the relationship between the wavelength and the light intensity detected in the light detection step into a relationship between the wave number and the light intensity, and then converting the relationship into period information, and the period information obtained by measuring the measurement target film and the substrate It is desirable to include a calculation step for calculating a difference from the period information obtained by measuring the. According to such a configuration, the measurement accuracy can be further improved by reducing the influence of noise caused by disturbance light or the like.

  The film thickness measuring apparatus of the present invention is a film thickness measuring apparatus for measuring the film thickness of a film to be measured formed on a substrate, and has an incident angle of 45 degrees or more on the surface of the film to be measured. A light source that emits pulsed light, a spectroscope that separates interference light formed by the surface reflected light reflected from the surface and the interface reflected light reflected from the interface between the substrate and the film to be measured, A noise separator that separates a signal from the light source and noise caused by disturbance light based on phase and period information, and a photodetector that detects light dispersed by the spectroscope.

  According to such a configuration, the reflection intensity from the interface between the substrate and the film to be measured can be increased, and the non-measurement target formed on the substrate having a small difference in refractive index from the non-measurement target film. The film thickness can be measured with high measurement accuracy while reducing the influence of noise.

  Furthermore, it is desirable that the light source is a light source that emits light including near-ultraviolet light. According to such a configuration, the film thickness can be measured with higher accuracy.

  Furthermore, it is desirable to include a beam splitter that divides the light before entering the photodetector to obtain reference light, and a correction unit that corrects the light intensity for each wavelength using the reference light. According to such a configuration, since the peak of the interference signal can be recognized with high accuracy, the measurement accuracy can be further improved.

  Further, the substrate further includes a conversion unit that converts the relationship between the wavelength and the light intensity acquired by the photodetector into the relationship between the wave number and the light intensity and then converts the relationship into the period information, and the period information and the substrate obtained by measuring the film to be measured It is desirable to include a calculation unit that calculates the difference from the period information obtained by measuring the. According to such a configuration, the measurement accuracy can be further improved by reducing the influence of noise caused by disturbance light or the like.

  As described above, according to the film thickness measuring method and the film thickness measuring apparatus of the present invention, the non-measurement formed on the substrate having a small difference in refractive index from the non-measurement target film having a small difference in refractive index from the substrate. The film thickness of the target film can be measured with high accuracy.

It is a fragmentary perspective view of AC surface discharge type PDP. It is a figure which shows the vacuum evaporation system for forming the protective film of the PDP. It is a figure which shows the film thickness measuring apparatus in embodiment. It is a figure which shows the relationship between the wavelength of the interference signal in the film thickness measuring apparatus in embodiment, and light intensity. It is a figure which shows the relationship between the wave number of the interference signal and light intensity in the film thickness measuring apparatus in embodiment.

  Hereinafter, a film thickness measuring method and a film thickness measuring apparatus according to an embodiment of the present invention will be described with reference to the drawings using a PDP protective film as a film to be measured.

  First, a PDP having a protective film that is a film to be measured will be described. FIG. 1 is a partial perspective view of an AC surface discharge type PDP. As shown in FIG. 1, the PDP 10 has a configuration in which a front substrate 11 and a rear substrate 17 are arranged to face each other. On the glass front substrate 11, a plurality of display electrode pairs 14 are formed in parallel with each other with the scanning electrodes 12 and the sustain electrodes 13. Scan electrode 12 and sustain electrode 13 have a width including a metal such as silver (Ag) on a wide transparent electrode made of a conductive metal oxide such as indium tin oxide (ITO) in order to enhance conductivity. It is formed by stacking narrow bus electrodes. A black stripe 21 for preventing crosstalk is formed between the display electrode pair 14. A dielectric layer 15 made of low melting point glass having a film thickness of about 40 μm is formed so as to cover the display electrode pair 14. Further, a protective film 16 made of magnesium oxide (MgO) having a thickness of about 0.8 μm, which is a film to be measured in the present embodiment, is formed on the dielectric layer 15. The protective film 16 is provided to protect the dielectric layer 15 from ion sputtering and stabilize discharge characteristics such as a discharge start voltage.

  A plurality of parallel data electrodes 18 made of a conductive material mainly composed of silver are formed on the glass back substrate 17 so as to be orthogonal to the display electrode pair 14 so as to cover the data electrodes 18. A base dielectric layer 19 made of low-melting glass is formed. A partition wall 20 made of low-melting glass is formed on the base dielectric layer 19 so as to sandwich the data electrode 18, and red (R) and green (G) are formed on the surface of the base dielectric layer 19 and the side surfaces of the partition wall 20. ) And blue (B) phosphor layers 23 of the respective colors are formed.

  The front substrate 11 and the back substrate 17 are sealed at the periphery (outside of the image display area) with a sealing material made of glass frit to form a discharge space inside. A discharge gas containing xenon (Xe) or the like is sealed in the discharge space at a pressure of about 60 kPa. A discharge cell is formed at a portion where the display electrode pair 14 and the data electrode 18 intersect in the discharge space, and these discharge cells are discharged to emit light, thereby displaying an image.

  The film thickness measuring method and the film thickness measuring apparatus 60 in the present embodiment are used for measuring the film thickness in-line when the protective film 16 of the PDP 10 is formed by vacuum deposition. FIG. 2 is a view showing a vacuum deposition apparatus 30 for forming the protective film 16.

  The vacuum deposition apparatus 30 includes an inside of a vacuum chamber 32 to which a vacuum pump 31 is connected, a hearth 34 that holds a protective film raw material 33 made of magnesium oxide (MgO), and an electron gun that irradiates the protective film raw material 33 with an electron beam 35. 36. A vacuum chamber 32 is provided with a tray 38 provided with an opening 37 for transferring the front substrate 11 and a heater 39 for heating the front substrate 11 to a predetermined temperature. On the tray 38, the front substrate 11 on which the dielectric layer 15 is formed is placed so that the surface of the dielectric layer 15 is the lower surface.

  In such a vacuum deposition apparatus 30, the vacuum chamber 32 is maintained at a predetermined degree of vacuum in an oxygen atmosphere, and the protective film material 33 is irradiated with the electron beam 35 to evaporate, and the evaporated particles 40 are the dielectric of the front substrate 11. A protective film 16 of magnesium oxide (MgO) is deposited on the layer 15. The tray 38 on which the front substrate 11 on which the protective film 16 is formed is placed is discharged from the vacuum chamber 32, and the tray 38 on which the next front substrate 11 is placed is transferred again to the vacuum deposition apparatus 30 to form a film. The During the process of repeating such a process, the thickness of the protective film 16 after vacuum deposition is measured in-line.

  FIG. 3 is a diagram showing a film thickness measuring device 60 in the present embodiment. In addition, when measuring the film thickness in-line, the top and bottom of FIG. 3 are reversed. As shown in FIG. 3, the protective film 16 that is a film to be measured is formed on a dielectric layer 15 formed on a glass front substrate 11.

  As shown in FIG. 3, a light source 42 that irradiates pulsed light 41 at an incident angle θ of 45 degrees or more with respect to the surface of the protective film 16 is provided. The spectroscope 44 generates interference light 43 formed by the reflected light reflected from the surface of the protective film 16 by the pulsed light 41 and the interface reflected light reflected at the interface between the protective film 16 and the dielectric layer 15 serving as the substrate. Spectroscopy. As the spectroscope 44, a known grating or prism can be used. The split interference light 45 is detected by a multi-array photodetector 46. That is, in the film thickness measuring device 60, the light irradiation step, the spectroscopic step, and the light detection step in the film thickness measuring method are performed.

  In recent years, further improvement in the light emission efficiency of the PDP 10 has been demanded. For this purpose, the relative dielectric constant of the dielectric layer 15 is reduced. As a result, the difference in refractive index between the dielectric layer 15 and the protective film 16 formed on the dielectric layer 15 has become very small. For this reason, when measuring the film thickness of the protective film 16 that is a non-measurement target film, the difference in reflection intensity at the interface between the protective film 16 and the dielectric layer 15 is weakened, and the intensity of the interference signal is reduced. In particular, the conventional method of irradiating light perpendicularly to the protective film 16 has a problem that the intensity of the interference signal becomes small and the film thickness of the protective film 16 cannot be measured accurately.

  Therefore, in the present embodiment, the intensity of the interface reflected light is increased by setting the incident angle of the pulsed light 41 to 45 degrees or more. Therefore, even if the difference in refractive index between the protective film 16 and the dielectric layer 15 is small, the film thickness of the protective film 16 can be accurately measured. For example, when the incident angle is 45 degrees, the reflectance is about 1.4 times, and when the incident angle is 60 degrees, the reflectance at the interface can be about twice.

  On the other hand, the reason for conventional vertical incidence is that the light source, the spectroscope, the photodetector, etc. can be integrated, and there is little deviation of the light path due to vibration caused by substrate transport, and the amount of light incident on the photodetector is constant. Thus, there is an advantage that stable signal processing can be performed.

  On the other hand, although the interface reflectance can be increased by increasing the incident angle as described above, noise due to reflected light and scattered light from the vacuum deposition apparatus 30 and the substrate transport path also increases. It is desirable to remove. Therefore, in the present embodiment, the light source 42 is caused to flash periodically or mechanically using a chopper or the like to form the periodic pulsed light 41. Further, the phase and period of the pulsed light 41 and the output from the photodetector 46 are phase-compared and detected using a separator 47 such as a lock-in amplifier, and a periodic component different from that of the pulsed light 41 is removed, thereby causing disturbance. The component light is removed.

  Further, in the present embodiment, the interference light 45 split by the spectroscope 44 is split as reference light 49 by a beam splitter 48 placed in front of the photodetector 46. The reference light 49 is detected by the reference light detector 50, amplified by the multiplication mechanism 51, and enters the separator 47. With such a configuration, the light intensity for each wavelength is corrected using the reference light 49, the peak of the interference signal can be recognized with high accuracy, and the film thickness measurement accuracy can be further increased. In the present embodiment, a correction unit that corrects the light intensity for each wavelength is provided in the separator 47 and is electrically processed. That is, the correction step of the film thickness measurement method is performed by this correction.

  The spectroscope 44 may be provided with a rotation mechanism or a movement mechanism. That is, the wavelength of the light incident on the photodetector 46 can be changed by slightly rotating or moving the spectroscope 44, thereby increasing the number of data points in the wavelength direction. According to the sampling theorem, when the number of measurement points in the wavelength direction is doubled, the error can be reduced by about a square root of about 1/2. Therefore, the peak of the interference signal can be detected with higher accuracy, and the film thickness measurement accuracy can be further increased.

  In the present embodiment, the light source 42 emits light including near ultraviolet light, and the photodetector 46 can detect the near ultraviolet light. By including the near ultraviolet region in the wavelength region to be used in this way, it is possible to improve the measurement accuracy as the film thickness. The reason for this will be described below.

  FIG. 4 is a diagram showing the relationship between the wavelength of the interference signal and the light intensity in the film thickness measuring device 60 according to the embodiment of the present invention. As shown in FIG. 4, the wavelength and the light intensity are that the signal intensity periodically has a maximum value and a minimum value, and the intensity decreases and the period increases as the wavelength increases. For this reason, the number of extreme values, that is, the number of fringes increases on the short wavelength side. Therefore, it is possible to increase the reference data, and as a result, it is possible to further increase the accuracy when converting the film thickness.

  In this case, the spectroscope 44 also needs to support near ultraviolet light. When the spectroscope 44 is a grating, the dispersion can be reduced so that the short wavelength corresponds to the same emission angle, or the angle of the grating can be changed. On the other hand, when the spectroscope 44 is a prism, this can be dealt with by increasing the refractive index of the prism or changing the installation angle of the prism.

  In order to increase the reference data, it is desirable to shift the wavelength to the short wavelength side as much as possible. However, the transmittance in the atmosphere, the transmittance of a metal oxide such as magnesium oxide (MgO), the detector 46 Considering characteristics and the like, it is desirable to use a near ultraviolet region of 350 nm or more.

  In the present embodiment, a conversion unit that converts the relationship between the wavelength and the light intensity acquired by the photodetector 46 into the relationship between the wave number and the light intensity and then converts the relationship into periodic information by Fourier transform or the like is provided. As the period information, an arithmetic unit such as a computer that calculates a difference between the period information obtained by measuring the protective film 16 as the measurement target film and the period information obtained by measuring the dielectric layer 15 as the substrate. 52. The conversion unit is provided in the calculation unit 52. That is, the conversion step and the calculation step of the film thickness measurement method are performed by this conversion and calculation.

  The interference signal is an interference signal due to reflection at the surface of the protective film 16 and the interface between the protective film 16 and the dielectric layer 15. In addition to this, the interference signal is glass as the dielectric layer 15 and the front substrate 11. A total of six interference signals are observed as a combination of reflections at a total of four locations, the substrate interface and the back surface of the glass substrate. All of these signals have a maximum value at an integral multiple of the integral value of the refractive index in the thickness direction (in the case of oblique incidence, the integrated value at the optical path length), and a signal having a minimum value at an intermediate point therebetween. Therefore, when the interference signal is obtained as a relationship between the wave number that is the reciprocal of the wavelength and the light intensity from the relationship between the wavelength and the light intensity, the interference signal has maximum and minimum values at equal intervals.

  FIG. 5 is a diagram showing the relationship between the wave number of the interference signal and the light intensity in the film thickness measuring device 60 according to the embodiment of the present invention. Here, when frequency components (here, the dimension is the length dimension) are separated by Fourier transforming the relationship between the wave number and the light intensity, a large signal peak is generated in the reciprocal part of the wave number interval. For this reason, even in the case of six interference signals, a peak occurs in the reciprocal part of the interval of each wave number, and each component can be separated.

  Therefore, in the film thickness measuring method and film thickness measuring apparatus 60 in the present embodiment, first, measurement is performed using the front substrate 11 in which only the dielectric layer 15 is formed and the protective film 16 is not formed, and the arithmetic unit 52 performs the measurement. Periodic components are calculated from a total of three combinations of interference signals. Thereafter, measurement is performed using the front substrate 11 on which the protective film 16 and the dielectric layer 15 are formed, and a periodic component is calculated from a total of six combinations of interference signals using the calculation unit 52. When the difference between these periodic components is taken, only three types of interference signals involving the protective film 16 remain. Among these, since the interference signal at the surface of the protective film 16 and the interface between the protective film 16 and the dielectric layer 15 has the highest intensity, the remaining signal can be removed as noise. Thereby, the measurement precision of the film thickness of the protective film 16 can be improved more.

  Thus, when forming the protective film 16 of the PDP 10 using the film thickness measuring device 60 and the film thickness measuring method according to the present embodiment, the film thickness of the protective film 16 can be measured in-line with high accuracy. . In particular, even when a material having a dielectric constant as low as that of the material of the protective film 16 is used as the material of the dielectric layer 15, a highly accurate film thickness measurement can be realized, and the result is formed into a film. It is possible to provide feedback without time delay in the process. As a result, variations in the film thickness of the protective film 16 for each substrate can be suppressed, and the production yield can be improved.

In this embodiment, an example in which the protective film 16 of the PDP 10 made of magnesium oxide (MgO) is measured has been shown. As the material of the protective film 16, aluminum oxide (Al ₂ O ₃ ), calcium oxide (CaO) ), Barium oxide (BaO), titanium oxide (TiO ₂ ), yttrium oxide (Y ₂ O ₃ ), lanthanum oxide (La ₂ O ₃ ), cerium oxide (CeO ₂ ), hafnium oxide (HfO ₂ ), etc. The same applies to the protective film 16 made of a material, mixed oxide, excellent in ion bombardment resistance, and thereby has a large secondary electron emission coefficient. Furthermore, the film thickness measuring apparatus of the present invention is not limited to the protective film of the PDP, and the film thickness of the film to be measured formed on the substrate having a small difference in refractive index from the film to be measured can be accurately in-line. It is possible to measure.

  According to the film thickness measuring apparatus and the film thickness measuring method according to the present invention, it is possible to accurately measure the film thickness of the measurement target film formed on the substrate having a small difference in refractive index from the non-measurement target film. It is useful for thin film formation processes such as display devices and other electronic devices.

10 PDP
DESCRIPTION OF SYMBOLS 11 Front substrate 12 Scan electrode 13 Sustain electrode 14 Display electrode pair 15 Dielectric layer 16 Protective film 17 Back substrate 18 Data electrode 19 Underlying dielectric layer 20 Bulkhead 21 Black stripe 23 Phosphor layer 30 Vacuum evaporation apparatus 31 Vacuum pump 32 Vacuum chamber 33 Protective Film Raw Material 34 Hearth 35 Electron Beam 36 Electron Gun 37 Opening 38 Tray 39 Heater 40 Evaporating Particles 41 Pulsed Light 42 Light Source 43 Interference Light 44 Spectrometer 45 Interference Light 46 Photodetector 47 Separator 48 Beam Splitter 49 Reference Light 50 Reference light detector 51 Multiplication mechanism 52 Calculation unit 60 Film thickness measuring device

Claims (8)

A film thickness measuring method for measuring a film thickness of a film to be measured formed on a substrate, the light having an incident angle of 45 degrees or more on the surface of the film to be measured and irradiating pulsed light from a light source An irradiating step, a spectroscopic step for separating interference light formed by the surface reflected light reflected from the surface and the interface reflected light reflected from the interface between the substrate and the film to be measured, and the phase of the pulsed light A film thickness measurement comprising: a separation step that separates a signal from the light source and noise caused by disturbance light based on period information; and a light detection step that detects light dispersed in the spectroscopic step. Method. The film thickness measuring method according to claim 1, wherein the pulsed light is light including near ultraviolet light. 2. The method according to claim 1, further comprising a correction step of dividing the light before entering the light detection step with a beam splitter to be a reference light, and correcting the light intensity for each wavelength using the reference light. Item 3. A method for measuring a film thickness according to Item 2. A conversion step of converting the relationship between the wavelength detected in the light detection step and the light intensity into a relationship between the wave number and the light intensity and then converting the relationship into the period information, and the period information obtained by measuring the film to be measured; The film thickness measuring method according to any one of claims 1 to 3, further comprising a calculation step of calculating a difference from the period information obtained by measuring the substrate. A film thickness measuring apparatus for measuring a film thickness of a film to be measured formed on a substrate, the light source for irradiating pulsed light with an incident angle of 45 degrees or more on the surface of the film to be measured; A spectroscope that splits interference light formed by surface reflected light reflected from the surface and interface reflected light reflected from the interface between the substrate and the film to be measured, and information on the phase and period of the pulsed light A film thickness measuring apparatus comprising: a separator for separating a signal from the light source and noise caused by disturbance light based on the light source; and a photodetector for detecting light dispersed by the spectroscope. The film thickness measuring apparatus according to claim 5, wherein the light source is a light source that irradiates light including near ultraviolet light. 6. The apparatus according to claim 5, further comprising: a beam splitter that divides the light before entering the photodetector to make reference light; and a correction unit that corrects light intensity for each wavelength using the reference light. Or the film thickness measuring apparatus of Claim 6. A conversion unit that converts the relationship between the wavelength and the light intensity acquired by the photodetector into a relationship between the wave number and the light intensity and then converts the relationship into period information; and the period information obtained by measuring the measurement target film; The film thickness measuring apparatus according to claim 5, further comprising an arithmetic unit that calculates a difference from the period information obtained by measuring the substrate.

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