JP2002115053A - Film thickness control method, and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a multi-layered optical film of high performance. SOLUTION: A vaporization source 2 is provided in a vacuum device 1, and a characteristic monitor substrate 3, a film thickness control monitor substrate 4 and a substrate holder 5 for installing a product substrate are also disposed therein. The characteristic monitor comprises the characteristic monitor substrate 3, a light flooding/receiving unit 6, and a measuring unit 7, and the measured value is incorporated in an operation unit 8 and used in deriving a film constant of the film deposited on the monitor. The film thickness control monitor comprises the substrate 6, a light flooding/receiving unit 9 including a monitor exchange mechanism, and a measuring unit 10, and detects the peak of the monochromatic reflectance or transmissivity, and controls the film thickness. By using the film constant obtained by the characteristic monitor, the film is deposited while being re-designed so as to be corresponding to the optical film thickness in the atmosphere successively for each layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for controlling the thickness of an optical multilayer film such as a dichroic film (optical element for color separation) used for a liquid crystal projector or a TV camera.

[0002]

2. Description of the Related Art Conventionally, methods for controlling the thickness of an optical multilayer film include:
An optical film thickness control monitor including a monitor substrate on which a film is formed, a monitor substrate exchange mechanism for exchanging the monitor substrate, a light projecting unit, a control wavelength filter exchanging unit, a light receiving unit, and an intensity measuring unit is used.

However, in recent years, in order to perform film thickness control with higher precision, as shown in Japanese Patent Application Laid-Open No. 7-72307, optical characteristics during film formation of a product itself or a product substitute monitor are measured, and the measurement results are obtained. There has been proposed a method of correcting and controlling the initial target film thickness (or refractive index) of a product so as to directly approach the final target characteristic based on the above. Japanese Patent Application Laid-Open No. 7-72307 discloses an example of a sputtering method. Since the film thickness can be controlled by time control in which the film forming speed is relatively stable, it is effective to obtain a corrected target film thickness. It is considered.

Further, as disclosed in Japanese Patent Application Laid-Open No. 5-255850, a characteristic monitor instead of a product is used in combination with a conventional film thickness control monitor. A method for controlling the film thickness (or the refractive index) has been proposed.

Japanese Patent Application Laid-Open No. 5-255850 discloses an example of a vapor deposition method. In addition to a conventional film thickness control monitor, a fixed characteristic monitor for obtaining lamination characteristics is provided.
Correction and control of the target film thickness achieves improvement and stabilization of product characteristics.

[0006]

However, in particular, in the case of the above-mentioned Japanese Patent Laid-Open No. 5-255850, the initial target film thickness is set according to the characteristic result of the characteristic monitor so as to reduce the error from the target characteristic. It is described that the films are corrected and the films are sequentially formed, but no actual correction method or the like is disclosed. For example, when obtaining the characteristics of an optical multi-layer film such as a dichroic film, it is important to control a film thickness control monitor such as how many layers and which control wavelength are to be used among a plurality of monitor substrates.

Table 1 shows an example of the structure of a vapor-deposited red dichroic film (prism type, incidence angle at the bonding surface of 45 degrees).
The number of layers indicates the layer number from the substrate side, and the odd-numbered layers are Al ₂ O ₃
Layers and even layers indicate TiO ₂ layers. The target Ds is a physical film thickness (nm), and the large 588N is an average refractive index in the atmosphere at a wavelength of 588 nm previously obtained from a single film.
88n is the average refractive index in vacuum at a wavelength of 588 nm. True 588 nD indicates the optical film thickness (nm) in vacuum at a wavelength of 588 nm.

The flat S / M indicates the average film thickness ratio between the characteristic monitor substrate and the film thickness monitor substrate. The film thickness of the characteristic monitor substrate reflects the film thickness on the product, that is, is set so as to have a correlation. It is. The average film thickness ratio S / M is obtained in advance as an average value from the film thickness Dm on the film thickness monitor substrate expected from the control wavelength and the film thickness Ds obtained from the characteristic monitor. A control wavelength is newly determined based on the average thickness ratio S / M.

The monitor number indicates the number of a plurality of monitor substrates to be used for forming each layer. For example, the monitor substrate 1 has the first, third, fifteenth, and seventeenth layers. Used.

Table 1 Number of layers Target Ds Large Ds 588N True 588n True 588nD Flat S / M Control wavelength Monitor number 1 89 1.63 1.59 141 1.04 487 1 2 95 2.38 2.26 215 1.03 425 2 3 136 1.63 1.59 215 1.04 445 1 4 95 2.38 2.26 214 1.05 429 2 5 85 1.63 1.59 136 1.10 445 3 6 102 2.38 2.26 232 1.04 445 4 7 84 1.63 1.59 134 1.06 470 3 8 101 2.38 2.26 229 1.05 450 4 9 84 1.63 1.59 134 1.02 495 3 10 101 2.38 2.26 229 1.05 451 4 11 79 1.63 1.59 125 1.01 491 3 12 95 2.38 2.26 214 1.05 448 4 13 123 1.63 1.59 196 1.01 548 3 14 84 2.38 2.26 190 1.03 420 2 15 136 1.63 1.59 216 1.00 541 1 16 92 2.38 2.26 208 1.05 420 2 17 103 1.63 1.59 164 0.99 567 1

FIG. 5 shows that the gas pressure at the time of forming the TiO ₂ film is 1 × 10 ^-4 Torr by introducing oxygen based on the conditions shown in Table 1.
The gas pressure during the formation of the r, Al ₂ O ₃ film is 0.8 × 10 ⁻⁴ To
rr is used as a standard gas pressure, and the result of producing a red dichroic film is shown. The Ts design value indicates the design value of the transmittance of the S-polarized light component based on the atmospheric constant, and the Ts vacuum design value is a value obtained by predicting the characteristics in a vacuum from the vacuum average refractive index measured in a vacuum. The measured values of Ts indicate the results of fabrication, and are the characteristic values after joining one week after film formation.

As shown in the transmission characteristics of the S-polarized light component, the half-value wavelength of the target characteristics in the atmosphere (the wavelength at which the transmittance of the S-polarized light component is 50%) does not coincide with the actual half-value wavelength of the air characteristics after film formation. . Half-value wavelength in vacuum at this time (Ts vacuum design value)
Therefore, the shift amount to the half-value wavelength in the atmosphere is about 21 nm.

The reason for the inconsistency is that the refractive index in vacuum is assumed to be the same if the film forming conditions are the same in the case of a single layer and in the case of a multilayer. In the case of, it is considered that the refractive index in the atmosphere is different. That is, an average refractive index of 588 obtained in the atmosphere
When designing and manufacturing using N, there arises a problem that a target characteristic, in particular, a half-value wavelength cannot be obtained.

The characteristics of the film formed on the characteristic monitor substrate are measured to determine the film constant in vacuum (refractive value ns, film thickness Ds).
Is fixed, the film constant is fixed, the film thickness of the next layer and subsequent layers is redesigned in accordance with the target characteristics in vacuum, and the corrected vacuum target optical film thickness (nD) s of the next layer and subsequent layers is determined. Considering the film thickness ratio (= Ds / Dm) of the film-formed layers and the constant of the film-formed layers on the film thickness control monitor substrate, the corrected vacuum target optical film thickness (nD) m of the next layer on the characteristic monitor substrate When the film thickness is controlled by determining the monochromatic control wavelength corresponding to the above, the characteristics close to the target vacuum characteristics can be obtained, but the target characteristics in the atmosphere cannot be obtained.

Further, the mismatch between the design value in the atmosphere and the characteristics of the film formation result, especially the mismatch between the half-value wavelengths, results from the difference between the refractive index used for the design and the refractive index actually formed. In other words, the average refractive index of the single-layer film under the conditions determined as the standard conditions for film formation depends on the standing time after film formation, but in about one week, water is sufficiently taken into the film pores. On the other hand, the refractive index of the film after lamination is a state in which water has not yet been sufficiently taken into the film pores for the same standing time.

An object of the present invention is to solve the above-mentioned problems,
It is an object of the present invention to provide a film thickness control method and an apparatus for accurately obtaining a target atmospheric refractive index characteristic.

[0017]

According to a first aspect of the present invention, there is provided a film thickness control monitor for controlling a film thickness and a characteristic monitor for measuring the reflection or transmission characteristics of a laminated film. In a vacuum apparatus having both, an atmospheric film refractive index (N) is estimated from a film refractive index (n) measured in a vacuum,
The target atmospheric optical film thickness (ND) is determined using the predicted atmospheric film refractive index, and the monochromatic control wavelength for obtaining the vacuum optical film thickness (nD) corresponding to the target atmospheric optical film thickness is determined. This is a film thickness control method characterized in that the film thickness is determined and controlled.

According to a second aspect of the present invention, there is provided a vacuum apparatus having both a film thickness control monitor for controlling the film thickness and a characteristic monitor for measuring the reflection or transmission characteristics of the laminated film, wherein the film is formed during film formation. The thickness of the monitor substrate for film thickness control is controlled by the monochromatic control wavelength of the monitor for thickness control. The film constants (refractive index ns, film thickness Ds) are obtained, and the film constants are converted into the film constants (refractive index Ns, film thickness Ds) in the atmosphere, and the film thicknesses of the next and subsequent layers are fixed by fixing the predicted constants. Is redesigned according to the target characteristics in the atmosphere, the corrected target optical thickness (ND) s of the next layer or the subsequent layer is determined, and the film thickness ratio (= Ds / Dm) of the already formed layer and the film thickness are determined. In consideration of the constants of the already formed layers on the control monitor substrate, the modified vacuum target optics of the next layer on the monitor substrate Decide monochromatic control wavelength corresponding to the thickness (nD) m is a film thickness control method and performing film thickness control.

According to a third aspect of the present invention, there is provided the first or second aspect.
A film forming apparatus characterized in that the film thickness is controlled using the film thickness controlling method described above.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail based on the illustrated embodiment. FIG. 1 shows a configuration diagram of a film thickness control device according to the first embodiment. An evaporation source 2 is provided at a lower portion in a vacuum device 1, and a characteristic monitor substrate 3 and a film are provided above the evaporation source 2. A thickness control monitor board 4 and an umbrella-shaped board holder 5 on which a product board is placed are arranged.

The light beam from the light emitting / receiving unit 6 can be sent / received to / from the characteristic monitor board 3.
Is connected to the calculation unit 8 via the measurement unit 7. on the other hand,
A light beam from the light emitting / receiving unit 9 can be sent / received to / from the film thickness control monitor substrate 4, and the light emitting / receiving unit 9 is connected to the calculation unit 8 via the measuring unit 10. Although not shown, the characteristic monitor substrate 3 and the
A mechanism for replacing the film thickness control monitor substrate 4 and shielding the evaporation material from the evaporation source 2 is built in.

In the characteristic monitor composed of the characteristic monitor substrate 3 and the like, the measured values are taken into the arithmetic unit 8 and the film constants (refractive index ns, film thickness) in vacuum formed on the characteristic monitor substrate 3 are formed. Ds). Using this film constant, it is possible to redesign to obtain target characteristics during film formation.

The film thickness control monitor composed of the film thickness control substrate 4 or the like usually detects the designed monochromatic reflectance or transmittance peak on the film thickness control monitor substrate 4 and controls the film thickness by knowing the film formation value. .

As shown in FIG. 5, conventionally, the target characteristic was obtained by repeating trial and error of adjusting the half-wavelength by changing the control wavelength. However, if the film constant (refractive index N, film thickness D) in the air after lamination can be predicted from the film constant in vacuum (refractive index n, film thickness D) obtained by the characteristic monitor, the film constant (N , D) can be used as the design values in the atmosphere to reduce errors from the production values. Further, even if the film formation conditions fluctuate with respect to the design values in the atmosphere, if the correction is performed based on the obtained film constants in the atmosphere, characteristics close to the design values in the atmosphere should be obtained.

That is, in a vacuum apparatus having both a film thickness control monitor for controlling the film thickness and a characteristic monitor for measuring the reflection or transmission characteristics of the laminated film, the monochromatic control of the film thickness control monitor during film formation. The film thickness of the film thickness control monitor substrate 4 is controlled by the wavelength, and after film formation, the film characteristics formed on the characteristic monitor substrate 3 are measured to obtain film constants (ns, Ds) in vacuum. To the film constants in the atmosphere (Ns, Ds), fix the film constants and redesign the film thickness of the next and subsequent layers according to the target characteristics in the atmosphere, and correct the corrected atmospheric target of the next or subsequent layers. The optical film thickness (ND) s is determined, and the film thickness ratio (= Ds /
Dm) and the constant of the film-formed layer on the film thickness control monitor substrate 4 are taken into consideration, and the monochromatic control wavelength corresponding to the corrected vacuum target optical film thickness (nD) m of the next layer on the monitor substrate 4 is determined. It is important to control the thickness.

As means for estimating the film constants (N, D) in the atmosphere after lamination from the film constants (n, D) in vacuum, empirical values obtained from actual atmospheric lamination characteristics are used. . Alternatively, there is a method of applying a film density equation (Lorentz).

According to this method, an alternate layer red dichroic film of TiO ₂ / Al ₂ O ₃ was formed on the BK7 prism, and one week later, it was bonded to the other prism and evaluated. Ti
The gas pressure at the time of forming the O ₂ film is 1 × 10 ⁻⁴ T by introducing oxygen.
orr, the gas pressure during the formation of the Al ₂ O ₃ film is 0.8 × 10 ⁻⁴
Torr, which was the standard gas pressure.

Table 2 shows the target conditions in the first embodiment. The large 588N is the refractive index in the atmosphere estimated from the true 588n value under the standard gas pressure condition. And the target atmospheric design value (true 588n
D) is determined. This target atmospheric design value (true 588 nD)
In order to obtain the characteristics described above, the control wavelength for each monitor is determined using a known average film thickness ratio (flat S / M), and a film is formed.

Table 2 Number of layers Target Ds Large 588N True 588n True 588nD Flat S / M Control wavelength Monitor number 1 96 1.63 1.59 152 1.04 522 1 2 98 2.33 2.26 222 1.03 436 2 3 135 1.63 1.59 215 1.04 445 1 4 96 2.33 2.26 218 1.05 440 2 5 87 1.63 1.59 137 1.10 455 3 6 104 2.33 2.26 235 1.04 450 4 7 86 1.63 1.59 136 1.06 481 3 8 103 2.33 2.26 232 1.05 456 4 9 86 1.63 1.59 136 1.02 504 3 10 103 2.33 2.26 233 1.05 457 4 11 80 1.63 1.59 127 1.01 503 3 12 96 2.33 2.26 218 1.05 452 4 13 123 1.63 1.59 195 1.01 529 3 14 85 2.33 2.26 193 1.03 437 2 15 136 1.63 1.59 216 1.00 514 1 16 94 2.33 2.26 214 1.05 441 2 17 106 1.63 1.59 168 0.99 562 1

FIG. 2 shows the results of the film formation in the first embodiment. The Ts design value indicates the design value of the transmittance of the S-polarized light component in the atmosphere, and the Ts measured value which is the measured value one week later. Has a good agreement with this. The film constants (n, Ds) in vacuum obtained by the characteristic monitor are also in good agreement with the true 588n in Table 2, and the half-wavelength in vacuum (predicted value of Ts vacuum) is changed from the half-wavelength in vacuum to the half-wavelength in air. The movement amount is about 20 nm.

Table 3 shows target conditions in the second embodiment, in which a red dichroic film is formed as in the first embodiment. However, the gas pressure conditions were 1.4 × 10 ⁻⁴ Torr when the TiO ₂ film was formed and 1 × 1 when the Al ₂ O ₃ was formed.
0 ^-4 Torr. This is based on the assumption that the degree of vacuum of the vapor deposition apparatus changes over time (change in partial pressure, deterioration of the measurement gauge, etc.).

Table 3 Number of Layers Target Ds Modified Ds True 588n True 588nD Flat S / M Control Wavelength Monitor Number 1 96 97 1.56 152 1.04 522 1 2 98 101 2.20 222 1.03 436 2 3 135 137 1.56 214 1.04 458 1 4 96 100 2.20 220 1.05 439 2 5 87 89 1.56 139 1.10 456 3 6 104 107 2.20 235 1.04 450 4 7 86 88 1.56 138 1.06 482 3 8 103 105 2.20 231 1.05 455 4 9 86 88 1.56 138 1.02 509 3 10 103 106 2.20 233 1.05 458 4 11 80 83 1.56 130 1.01 506 3 12 96 99 2.20 218 1.05 453 4 13 123 124 1.56 194 1.01 558 3 14 85 88 2.20 194 1.03 429 2 15 136 137 1.56 214 1.00 550 1 16 94 99 2.20 218 1.05 430 2 17 106 109 1.56 170 0.99 578 1

The target Ds in Table 3 is the same as in the first embodiment. However, since the gas pressure is different, the refractive index obtained in a vacuum is also different. From this refractive index, the refractive index in the atmosphere is estimated, and the subsequent layers are obtained so that the characteristics close to the target characteristics in the first embodiment can be obtained. In order to obtain this film thickness, the control wavelength for each monitor is determined using a known average film thickness ratio (flat S / M) to form a film.

FIG. 3 shows the result of fabricating a red dichroic film based on the conditions in Table 3, and the Ts design value is the first.
This is the same as the embodiment. The measured values of Ts are the results of fabrication, and are the characteristics after bonding one week after film formation. Although the gas pressure conditions are different, the measured Ts value agrees well with the Ts design value. At this time, the amount of movement from the half-wavelength in vacuum (Ts vacuum expected value) to the half-wavelength in the atmosphere is about 24 nm.
It is.

Table 4 shows a comparative example, which is the same as the conventional example.
A red dichroic film was prepared. However, gas pressure conditions
Is TiO_Two1.4 × 10 at the time of film formation^-FourTorr, A
l_TwoO _Three1 × 10 at the time of film formation^-FourTorr. Obedience
In the previous example, the vacuum film was converted from the atmospheric design value.
Determine the control wavelength to obtain the thickness (588 nD)
However, in this comparative example, the vacuum setup of FIG.
Redesigned with the measured value as the target, and corrected the film thickness as in the second embodiment.
(Correction Ds) is determined, and each monitor is used to obtain this film thickness.
Using a known average film thickness ratio (flat S / M)
The film is determined and determined.

Table 4 Target value in vacuum Layer number Target Ds Corrected Ds True 588n True 588nD Flat S / M Control wavelength Monitor number 1 89 90 1.56 141 1.04 487 1 2 95 98 2.20 216 1.03 425 2 3 136 135 1.56 211 1.04 440 1 4 95 98 2.20 216 1.05 431 2 5 85 88 1.56 138 1.10 450 3 6 102 106 2.20 232 1.04 446 4 7 84 87 1.56 136 1.06 477 3 8 101 104 2.20 229 1.05 451 4 9 84 87 1.56 136 1.02 501 3 10 101 104 2.20 229 1.05 452 4 11 79 84 1.56 131 1.01 502 3 12 95 100 2.20 221 1.05 451 4 13 123 114 1.56 178 1.01 543 3 14 84 93 2.20 206 1.03 429 2 15 136 133 1.56 208 1.00 531 1 16 92 98 2.20 216 1.05 430 2 17 103 81 1.56 127 0.99 530 1

FIG. 4 shows the results of a comparative example manufactured based on Table 4, where the predicted value of Ts vacuum is in good agreement with the designed value of Ts vacuum. Value) to the half-value wavelength in the atmosphere is about 25 nm
It is. In addition, because the gas pressure was changed, the obtained measured value happened to be close to the Ts design value of the first comparative example. Indicates that the characteristics are not stable due to changes in the film forming conditions.

[0038]

As described above, the method and the apparatus for controlling the film thickness according to the present invention stably produce a high-performance optical multilayer film such as a dichroic film in which the characteristics in the atmosphere match the target value well. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a configuration of a film thickness control device.

FIG. 2 shows S-polarized light transmittance characteristics in the first embodiment.

FIG. 3 shows S-polarized light transmittance characteristics in a second embodiment.

FIG. 4 shows S-polarized light transmittance characteristics in a comparative example.

FIG. 5 shows S-polarized light transmittance characteristics in a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vacuum apparatus 2 Evaporation source 3 Characteristic monitor board 4 Film thickness control monitor board 5 Substrate holder 6 Light emitting / receiving section 7, 10 Measurement section 8 Calculation section 9 Light emitting / receiving section

Claims (3)

[Claims] In a vacuum apparatus having both a film thickness control monitor for controlling the film thickness and a characteristic monitor for measuring the reflection or transmission characteristics of the laminated film, the film refractive index (n) measured in a vacuum is used to determine the atmospheric pressure. Estimate the median film refractive index (N), determine the target atmospheric optical film thickness (ND) using the predicted atmospheric film film refractive index, and determine the optical film thickness in vacuum corresponding to the target atmospheric optical film thickness A film thickness control method comprising determining a monochromatic control wavelength for obtaining (nD) and performing film thickness control. 2. In a vacuum apparatus having both a film thickness control monitor for controlling the film thickness and a characteristic monitor for measuring the reflection or transmission characteristics of the laminated film, monochromatic control of the film thickness control monitor is performed during film formation. The film thickness of the monitor substrate for film thickness control is controlled by the wavelength, and after the film is formed, the characteristics of the film formed on the characteristic monitor substrate of the characteristic monitor are measured in a vacuum, and the film constants (refractive index ns, Film thickness Ds) is obtained, and the film constant is estimated and converted into a film constant (refractive index Ns, film thickness Ds) in the atmosphere. Redesigned, and the corrected atmospheric target optical film thickness (N
D) After determining s, taking into account the film thickness ratio (= Ds / Dm) of the already formed layers and the constant of the already formed layers on the monitor substrate for film thickness control, the modified vacuum of the next layer on the monitor substrate is adjusted. A film thickness control method characterized in that a film thickness is controlled by determining a monochromatic control wavelength corresponding to a target optical film thickness (nD) m. 3. A film forming apparatus, wherein the film thickness is controlled by using the film thickness controlling method according to claim 1.