JPH0410003B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a film thickness monitoring device for a vacuum evaporation apparatus for vacuum evaporating optical thin films such as antireflection films for photographic lenses.

Prior Art A conventionally known film thickness monitoring device for a vacuum evaporation apparatus as described above has a configuration as shown in FIG. In FIG. 1, 2 is a light source consisting of a tungsten lamp, 4 is a collimating lens, 6 is a half mirror, 8 is a vacuum chamber for vacuum evaporation, and 10 is disposed within the chamber 8, and an optical thin film is provided on the lower surface of the figure. This is monitor glass that is vacuum deposited. The light emitted from the light source 2 is collimated by a collimating lens 4 and divided into two by a half mirror 6. The light reflected by the half mirror 6 is incident on the photodetector 12, and the output of the photodetector 12 is used as a reference signal in the processing circuit 14 to detect variations in the light source.
On the other hand, the light transmitted through the half mirror 6 is perpendicularly incident on the monitor glass 10 and is reflected by the monitor glass 10 and the optical thin film being vacuum-deposited.
This light is reflected by the half mirror 6, passes through the filter 16 that transmits only a specific wavelength, and enters the photodetector 18. That is, the photodetector 1
The output of 8 corresponds to the reflectance of the optical thin film being vacuum-deposited, and the output is input to a processing circuit 14 and amplified, and the signal is sequentially recorded on a recorder 20. Reference numeral 22 denotes a power source for the light source 2, and silicon photodiodes or photomals are generally used as both the photodetectors 12 and 18.

However, in such a configuration, since the emission intensity of the tungsten lamp is weak, it is necessary to make the optical path as short as possible. On the other hand, electrical noise from the heater, power supply, control relay switch, etc. of the vacuum evaporation apparatus, and vibration noise from the rotary pump, etc., exist near the chamber 8, and due to this electrical noise and vibration noise, the photodetector 18 is transmitted to the monitor glass 10.
The disadvantage is that it is difficult to detect a stable signal that depends only on the amount of reflected light. Furthermore, in the conventional configuration shown in FIG.
0 and the tilt of the half mirror 6 must be adjusted,
Adjusting these optical systems is extremely troublesome.

Purpose The present invention has been made in view of the above-mentioned points, and its purpose is to provide a stable system that responds only to the intensity of reflected light from an optical thin film without being affected by electrical noise and vibration noise in the vicinity of a vacuum chamber. The generated signal can be detected by the photoelectric conversion detection section, and
It is an object of the present invention to provide a film thickness monitoring device for a vacuum evaporation apparatus in which adjustment of the optical system is very simple.

EXAMPLES Hereinafter, the present invention will be described in detail based on the drawings.

FIG. 2 is a schematic diagram showing an apparatus according to an embodiment of the present invention.
In the figure, 24 is a vacuum chamber, 26 is an evaporation source crucible, 28 is a dome that holds a large number of lenses on its inner surface on which optical thin films are vacuum-deposited, and in the center of the dome 28 is a monitor made of transparent parallel plane glass. Glass 30 is fixed. 32 is a heater dome, 34 is a heat shield tube, and inside the heat shield tube 34, two long optical fibers 3 made of similar components are arranged near the monitor glass 30.
6,38 are arranged. The tips of both optical fibers 36 and 38 are each covered with a stainless steel tube and sealed with resin. The rear ends of both optical fibers 36 and 38 are both connected to a control box 40,
The control box 40 is connected by a cable to a microcomputer 42 having a CRT display section 42a.

The optical and electrical configuration of this example will be explained using FIG. 3. In FIG. 3, one of the optical fibers 36, 38 has a rear end 36a connected to a light source 44 in a control box 40.
is placed so as to face the The light source 44 is composed of an electronic flash discharge tube (a xenon flash tube in this embodiment), and its light emission timing is controlled by the microcomputer 42. 46 is also an optical fiber made of the same components as both optical fibers 36 and 38, with one end facing the light source 44 and the other end facing the first photodetector 48 having a single silicon photodiode. It is located. The output of the first photodetector 48 is the light source 4
It is used as a reference signal for monitoring the emission intensity of 4. With such a configuration, the light emitted from the light source 44 is guided to the monitor glass 30 by the optical fiber 36, and is also guided to the first light detection section 48 by the optical fiber 46. In this way, by configuring the monitor glass irradiation optical path and the reference optical path to be guided by optical fibers having the same component, it is possible to easily obtain a reference signal that takes into account the transmittance of the optical fiber. be able to. Furthermore, by arranging the light source 44 and the first photodetector 48 far from each other and configuring the optical path between them by the optical fiber 46, the flash light emission of the electronic flash discharge tube constituting the light source 44 can be prevented. This makes it possible to eliminate electrical noise from being detected by the first photodetector 48 at the time.

On the other hand, the rear end 38 of the other optical fiber 38 whose tip 38b faces the monitor glass 30
a is arranged to face the second photodetector 50. The configuration of the second photodetector 50 will be described later. The outputs of the first and second photodetectors 48 and 50 are both input to the processing circuit 52.
2 and inputs information corresponding to the outputs of the respective detection sections 48 and 50 to the microcomputer 42.

With the above configuration, according to this embodiment, the monitor glass 30 in the vacuum chamber 24 and the second detection section 50 that detects the reflected light are placed apart from each other, and the optical path therebetween is connected to the long optical fiber 38. Therefore, the electrical noise of the vacuum evaporation apparatus is not detected by the second detection unit 50,
A half mirror is not required, and the optical system can be made into a cylinder. If a longer optical fiber is used, the optical loss will increase and the amount of light reaching the monitor glass 30 and the amount of light received by the second photodetector 50 will tend to decrease; however, in this embodiment, as a light source, Since an electronic flash discharge tube with strong emission intensity is used, a sufficient amount of light can be obtained.

Next, the arrangement relationship between the tips 36b, 38b of both optical fibers 36, 38 and the monitor glass 30 will be explained using FIG. 4. As shown in FIG. 4, the tips 36b and 38b of both optical fibers are fixed such that the angle θ therebetween is within 5°. The monitor glass 30 is placed at a distance l of approximately 20 mm from the tip surfaces of both optical fibers 36, 38.
The bisector P of the angle θ formed by 8 is the monitor glass 30
It is placed perpendicular to. The light emitted from the tip surface of the optical fiber 36 for light irradiation is
As shown by the optical paths d ₁ and d ₂ in the figure, it spreads to about 60°, but the optical fiber 3 for receiving reflected light
8 aims within an angle range of about 60° as shown by optical paths β ₁ and β ₂ , so one optical fiber 3
The light emitted from the monitor glass 30 and incident on the other fiber 38 is
As shown by diagonal lines in the figure, the light is almost parallel, and there is almost no difference from detecting the reflected light of the light that is perpendicularly incident on the monitor glass 30. This is because the tip surfaces of both optical fibers 36 and 38 are small and the angles of the emitted and incident light are well regulated. In addition, both optical fibers 36,
If the angle between the tips of 38 is configured to be variable, it is possible to detect reflected light not only for vertical incidence but also for obliquely incident light.

Incidentally, the tips of both the optical fibers 36 and 38 may be combined into one as shown in FIGS. 5a and 5b. Figure 5a shows the optical fiber 3 for light irradiation.
6 is an optical fiber 38 for receiving reflected light on the outside.
Fig. 5b shows a configuration in which the tips of the optical fibers 36 and 38 are subdivided and mixed to form a mosaic configuration. Both subdivided optical fibers 3
The space between 6 and 38 is sealed with resin. The tip of the optical fiber is
As shown in FIG. 5c, it is covered with a single stainless steel tube and placed perpendicularly to the monitor glass 30. By combining the optical fibers into one fiber in this manner, the positioning of the optical fibers can be further simplified.

In this embodiment, the reflectance of the monitor glass 30 can be detected simultaneously for a large number of wavelengths,
The configuration of the second photodetector 50 for this purpose will be described below with reference to FIGS. 6 to 8. FIG. 6 is a cross-sectional view showing an optical sensor arranged to face the rear end surface of the optical fiber 38 of FIG. 3. FIG. In FIG. 6, 54 is an IC ceramic package, and 56 is an array sensor consisting of a large number of minute silicon photodiodes fixed on the package 54. In FIG. Each silicon photodiode is wire-bonded to each output pin 58 fixed to the package 54 using gold wire. Reference numeral 60 denotes a mask plate having slits 60a for regulating the light flux incident on the array sensor 56, which can be easily manufactured by forming a metal film 64 on a glass plate 62 and creating the slits 60a by etching. be done. glass plate 6
An interference filter 66 for differentiating the wavelength of light detected by each silicon photodiode of the array sensor 56 is attached to the back surface of the sensor 2 with a transparent adhesive.

A cross-sectional view of the interference filter 66 is shown in FIG. 7a. As shown in FIG. 7a, the interference filter 66 is made by sequentially forming a silver layer Ag, a silicon dioxide layer SiO ₂ and a silver layer Ag on a glass plate 68 by vacuum evaporation. As shown in the figure, the thickness of the silicon dioxide layer SiO ₂ is varied in a number of steps equal to the number of wavelengths used for detection. Therefore, the thinnest part of the silicon dioxide layer SiO ₂ transmits only the shortest wavelength light, as shown in the graph of FIG. 7b, and as the silicon dioxide film SiO ₂ becomes thicker, the longer wavelength light Transmits only light. The film thicknesses of the silver layer Ag and the silicon dioxide layer SiO ₂ are determined depending on the predetermined wavelength to be used for detection. Each step width W is determined to correspond to the width of each silicon photodiode of the array sensor 56.

FIG. 8 is a perspective view showing the optical sensor of this embodiment. By using such an optical sensor, according to this embodiment, the reflectance of the monitor glass 30 can be detected simultaneously for a large number of wavelengths.

FIG. 9 is an exploded view showing another configuration of the second photodetector. As shown in the figure, seven silicon photodiodes 72 are fixed on a substrate 70, and each silicon photodiode 72 has a corresponding one on the anode side. electrically connected to a lead wire 74,
The cathode side is electrically connected to a common ground lead wire 76. Interference filters 78 having different transmission wavelengths are disposed on the light receiving surface of each silicon photodiode 72, and above the interference filter 78 is a mask plate 80 having a through hole 80a for regulating the beam width incident on each silicon photodiode 72. is located. In this way, the photodetector can also be configured without using an array sensor.

Next, the circuit configuration inside the control box 40 and its operation will be explained using FIG. 10. In FIG. 10, P ₁ , P ₂ , and Pn represent each silicon photodiode that constitutes the array sensor of FIG. 6, and Pr represents a silicon photodiode that constitutes the first photodetector 48 for obtaining a reference signal. A diode whose output is used to compensate for changes in the intensity of the light source. Taking photodiode P ₁ as an example to explain the configuration below, photodiode P ₁ is connected between the inverting and non-inverting input terminals of operational amplifier A ₁ , and the non-inverting input terminal of operational amplifier A ₁ is grounded. There is. A negative feedback resistor _R1 is connected between the output terminal and the inverting input terminal of the operational amplifier _A1 . The output of operational amplifier _A1 is turned on by the microcomputer 42.
−OFF is input to the inverting input terminal of the integrator B ₁ via the switch SA ₁ and the resistor. A memory capacitor C ₁ and a microcomputer 4 are connected between the inverting input terminal and output terminal of the integrator B ₁ .
Switch SB ₁ whose ON-OFF is controlled by SB 2
are connected in parallel, and the non-inverting input terminal is grounded. The output of the integrator B ₁ is input to an A/D converter 84 via a switch S ₁ whose ON/OFF state is controlled by a control circuit 82 controlled by a microcomputer 42 . A/
The output of the D converter 84 is sent to the microcomputer 42.
is input.

Hereinafter, each of the silicon photodiodes _P2 ...Pn and Pr also has the same circuit configuration as _P1 . In the figure, a portion surrounded by a dotted line constitutes a processing circuit 52. Although not shown, the microcomputer 42 also controls the flash emission timing of the light source.

Below, the circuit operation of FIG. 10 will be explained. First, before the light source emits light, the switches SA ₁ , SA ₂ to
SAn, SAr are ON, switches SB ₁ , SB ₂ ~ SBn,
SBr, S ₁ , S ₂ to Sn, and Sr are in an OFF state. In this state, the electronic flash discharge tube serving as the light source emits a flash of light, and the light is guided to the photodiode Pr via the optical fiber 46, and a thin film is deposited via the optical fiber 36 in a vacuum evaporation device. The monitor glass 30 that has been vacuum-deposited is irradiated, and the monitor glass 30
The reflected light is guided through the optical fiber 38 to an array sensor having a large number (n in the figure) of silicon photodiodes P ₁ to Pn, each of which detects only light of a specific wavelength.

Therefore, a photocurrent I ₁ -In proportional to the light intensity of each specific wavelength among the light reflected by the monitor glass flows through each photodiode P ₁ -Pn, and each current is generated by each operational amplifier A ₁ -An. , are converted into voltages V ₁ to Vn proportional to their respective current values. At the same time, a photocurrent Ir corresponding to the emission intensity of the light source flows through the silicon photodiode Pr, and this current is converted into a voltage Vr by the operational amplifier Ar. Each voltage
V ₁ ~Vn, Vr are connected to integrators B ₁ ~Bn, Br via switches SA ₁ ~SAn, SAr, which are in the ON state, respectively.
are applied to each capacitor C ₁ ~ Cn, Cr
Each voltage V ₁ to Vn, Vr is stored in memory. That is, voltages _V1 to Vn and Vr corresponding to the intensity of light received by the photodiodes _P1 to Pn and Pr are stored in the capacitors _C1 to Cn and Cr, respectively.

Next, after the above memory is completed, the control circuit 82 is controlled by a signal from the microcomputer 42.
However, as shown in FIG. 11, the switches S ₁ to Sn, Sr
are turned on sequentially for a certain period of time. As a result, the A/D converter 84 sequentially inputs the voltages V ₁ -Vn, Vr stored in the capacitors C ₁ -Cn, Cr, respectively, and sequentially A/D converts the voltages V ₁ -Vn, Vr. Then, corresponding signals are sequentially sent to the microcomputer 42. That is, the microcomputer 42 sequentially takes in digital signals corresponding to the light intensity received by each of the photodiodes _P1 to Pn and Pr. When all the loading is completed, the microcomputer 42 turns on all the switches SB ₁ to SBn, SBr, and each memory capacitor C ₁ to Cn, Cr
is reset.

The above is a single operation of measuring the intensity of reflected light on the monitor glass in order to monitor the thickness of the thin film vacuum-deposited on the monitor glass. This embodiment is configured to measure the intensity of reflected light from the monitor glass from time to time by repeating the above steps.

The microcomputer 42 calculates the reflectance of the monitor glass during vacuum deposition of a thin film for each specific wavelength based on the reflected light intensity obtained as described above. This calculation will be explained. First, the intensity of reflected light from the monitor glass in vacuum before vacuum deposition of a thin film is measured for each specific wavelength as described above, and is stored in the microcomputer 42.
This is defined as X ₀₁ to X _0o for each specific wavelength. n is the number of specific wavelengths, ie, the number of cells used for measurement in the array sensor. Since this reflected light intensity corresponds to the reflectance of the vapor deposition surface of the monitor glass and its back surface, the reflectance is calculated by correcting the amount of reflection from the back surface. Calculate the refractive index as a monitor glass. When blue plate glass with a refractive index of 1.52 is used as a monitor glass, the reflectance on both the front and back surfaces is 8.01%, and on one side it is 42%, so the i-th specific wavelength (i =
1, 2, ..., n)), the reflectance Ri is Ri (%) = {(A×Xki/Xoi-B) / (A×B×Xki /Xoi+C)}×100. However, A=0.0801 B=0.042 C=0.9156. The microcomputer 42 stores all the momentary reflectances for each wavelength calculated in this way, and uses them to display the display unit 4.
2a, you can simultaneously display the reflectance of each wavelength at a certain point during vacuum deposition in real time, display the temporal change in reflectance at a single specific wavelength, or display both at the same time. It is configured so that it can be done.

As an example, from the air side to the substrate glass side,
The first layer is MgF ₂ with a thickness of λ/4 (λ = 510 mm), the second layer is MgF 2 with a thickness of λ/4 (λ = 510 mm),
The layer is ZrO ₂ with a thickness of λ/2, and the third layer is with a thickness of λ/4.
A case will be described in which cumulative monitoring is performed to monitor the thickness of each film without replacing the monitor glass when a three-layer anti-reflection film made of Al ₂ O ₃ is vacuum-deposited on a photographic lens using the apparatus of this embodiment. . 1st
FIG. 2a shows the display on the display section 42a when the vacuum deposition of the third layer is completed. The vertical axis represents reflectance, and the horizontal axis represents wavelength and time. In the figure, the plots marked with (x) show the reflectance at each wavelength, and the plots marked with (·) show the change in reflectance over time, which is shown by the sixth plot from the left of the mark (x) (wavelength 510 mm). ing. In order to control the thickness of the third layer using the device of this embodiment, the spectral reflectance curve when the third layer has a predetermined thickness is assumed in advance through experiments and calculations, and each Prot (x)
Vapor deposition may be stopped when the curve is located on the curve. Further, as in the conventional case, the vapor deposition may be stopped when the plot marked with (.) shows a peak. Subsequently, FIG. 12b shows a state in which the vacuum evaporation of the second layer is completed, and FIG. 12c shows a state in which the vacuum evaporation of the first layer is completed. As is clear from the (X) plot in Figure 2c, when the first layer deposition is completed, the spectral reflectance characteristics of the entire anti-reflection film are displayed, so the performance of the anti-reflection film as a whole can be evaluated. You can check. Furthermore, according to this embodiment, the spectral reflectance during vacuum deposition can be displayed in real time.

Effects As described above, the present invention irradiates light from a light source onto an optical thin film in a vacuum evaporation apparatus, and receives reflected light from the optical thin film by a photoelectric conversion detection section for reflected light photometry. In a film thickness monitoring device for obtaining information regarding the film thickness of an optical thin film, the photoelectric conversion detection unit for reflected light photometry is placed apart from the vacuum evaporation device, and an electronic flash discharge tube is used as the light source,
The reflected light from the optical thin film is guided to the reflected light photometry photoelectric conversion detection section using a first optical fiber disposed close to the optical thin film with one end facing the optical thin film, and the light is further emitted from the electronic flash discharge tube. The emitted light is directly guided to a photoelectric conversion detection unit for light source photometry disposed away from the electronic flash discharge tube using a second optical fiber without passing through the optical thin film, and the intensity of the light source light is determined by the output thereof. It is characterized by being configured to compensate for
With this configuration, it is possible to prevent electrical noise and vibration noise of the vacuum evaporation device from having a negative effect on photoelectric conversion detection, and to obtain a stable signal that corresponds only to the reflectance of the optical thin film. However, it is not necessary to precisely adjust the position of the half mirror or monitor glass as in conventional devices, making adjustment of the optical system extremely easy.Furthermore, in order to prevent the above-mentioned noise, a photoelectric conversion detection section for reflected light metering is installed. Since an electronic flash discharge tube with a strong emission intensity is used as a light source even when placed far away from the light source, sufficient light intensity can be detected. Since the electronic flash discharge tube and the photoelectric conversion detection section for light source photometry are separated from each other, and an optical fiber is used for the optical path between them, the electrical Noise is not detected by the detection section.

Furthermore, if the configuration is such that the light emitted from the light source is guided to the optical thin film by the third optical fiber as in the embodiment, the optical thin film for vertically incident light can be formed as well as the conventional device without using a collimating lens. The reflected light of the optical system can be photometered, and the optical system itself and its adjustment become easier.

Furthermore, if the tips of the first and third optical fibers are combined into one as in the embodiment, the position adjustment can be further simplified.

Furthermore, as in the embodiment, if the photoelectric conversion detection section for reflected light photometry is configured to simultaneously receive reflected light from the optical thin film for a number of specific wavelengths that are different from each other, the spectral reflectance of the optical thin film can be detected in real time. The film thickness can be controlled based on this spectral reflectance.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a conventional example, Fig. 2 is a schematic diagram of an embodiment of the device of the present invention, Fig. 3 is a schematic diagram showing its optical and electrical configuration, and Fig. 4 is a diagram showing the tip of the optical fiber. A diagram showing the positional relationship with the monitor glass, FIGS. 5a, b, and c are diagrams showing modified examples of the optical fiber, FIG. 6 is a sectional view showing the configuration of the photodetector, and FIGS. 7a and b are A cross-sectional view and a graph showing the interference filter, FIG. 8 is a perspective view of the photodetector, FIG. 9 is an exploded perspective view showing another embodiment of the photodetector, and FIG. 10 is an electrical circuit diagram of this embodiment. The circuit diagram shown in Fig. 11 shows the switches S ₁ to Sn, Sr.
Time chart showing ON-OFF, Figure 12a,
b and c are diagrams showing the display on the display unit. 24, 26, 28, 32...vacuum deposition device, 3
8...First optical fiber, 44...Light source, 46...Second optical fiber, 48
...Photoelectric conversion detection section for light source photometry, 50...Photoelectric conversion detection section for reflected light photometry.

Claims (1)

[Scope of Claims] 1. A film thickness monitoring device for monitoring the deposition state of an optical thin film deposited on a monitor glass in a vacuum evaporation device, comprising: a light source; and a light source that directs the light of the light source to the back surface of the monitor glass surface on which the optical thin film is deposited. Vapor deposition is performed using an irradiation means that irradiates from the side, a light receiving means that simultaneously receives only the light of a large number of specific wavelengths that are different from each other among the light reflected from the monitor glass, and the output of the light receiving means before vapor deposition is performed. A storage means for storing the intensity of reflected light from the monitor glass in a state where the light is not exposed is stored for each of a number of specific wavelengths, an output of the light receiving means during vapor deposition, a value stored in the storage means, and a reflectance of the monitor glass itself. A film thickness monitoring device comprising: calculation means for calculating the reflectance of only the surface on which a thin film is deposited for each specific wavelength; and display means for displaying the calculation results of the calculation means.