JPH0914925A - Ultraviolet/visible region optical system - Google Patents

Abstract

PURPOSE: To provide an ultraviolet and visible region optical system which can maintain a proper balance of quantity of light, is less affected by stray light, and can correct aberration. CONSTITUTION: A rear back side mirror 15 of a light source 12 is arranged to increase the quantity of ultraviolet rays from the back. Also, optical elements 44 and 55 are arranged within a light path. The optical element 44 changes its radius of curvature between the front and back, forms a high-reflectively dielectric multilayer film on the front to reflect ultraviolet rays, and reflects transmitted light on the back where a high-reflectivlity metal film is formed. The optical element 55 has a dielectric multilayer film for highly reflecting only ultraviolet light and less reflects visible light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultraviolet / visible optical system, and more particularly to an optical system for a film thickness control meter, for example, an ultraviolet / visible photometric film thickness used for film thickness control of a vacuum film forming apparatus. The present invention relates to an ultraviolet / visible range optical system which can be preferably used in a control meter optical system.

[0002]

2. Description of the Related Art A conventional optical system for a photometric film thickness control meter of a vacuum film forming apparatus is known to have a structure shown in FIG. The configuration is such that the light obtained from the light source 12 is condensed by the lens 13 in order to control the change in the light amount of the monitor glass 11 during film formation,
The light is reflected by the optical element 14 and made incident on the monitor glass 11, and the reflected light from the monitor glass 11 is reflected by the optical element 14 and guided to a photometric system (not shown).
As the optical element 14, as shown in FIG. 3, a high reflectance metal film 31 is vapor-deposited on an optical glass substrate 21, and a dielectric protective film 32 is overcoated thereon. This optical system is effective in the photometry of wavelengths in the visible range where the amount of light from the light source is large and the influence of aberrations due to lenses and optical elements is small. Further, for the light receiving portion of this optical system, wavelength selection is performed using an interference filter having a high transmittance in the visible range.

[0003]

However, in photometry in the ultraviolet to visible wavelength range, the amount of light from the light source decreases in the ultraviolet range, and the spectral characteristics given by this optical element 14 (see FIG. 4) The overall light intensity balance becomes poor. Also, the interference filter in the ultraviolet region cannot be used for photometry because of its low transmittance. Therefore, it is conceivable to perform photometry using a monochromator. However, when a monochromator is used, it becomes more susceptible to stray light due to visible light when selecting the wavelength of ultraviolet light. Furthermore, as the materials for lenses and optical elements, glass that can be used in the ultraviolet region is scarce, so that chromatic aberration cannot be sufficiently corrected. In addition, aberration correction cannot be performed by the optical element 14 that only has surface reflection. Therefore,
When such an optical system is used, it adversely affects the highly accurate film thickness control by photometry in the ultraviolet region, and it becomes difficult to control the film thickness.

As described above, when performing photometry in the ultraviolet to visible range with an optical system using a monochromator, there are few glasses that can be used in the ultraviolet range and the effect of stray light caused by the difference in the balance of light quantity. Therefore, the chromatic aberration cannot be sufficiently corrected, and there are problems due to the stability and the like caused by the durability of the optical element, which makes its use difficult.

Incidentally, such a problem exists not only in the film thickness control meter but also in the optical measuring device for performing measurement using light in a wide band.

The present invention solves the above problems of the prior art. The first object of the present invention is to provide an ultraviolet / visible range optical system capable of maintaining an appropriate light amount balance and less affected by stray light. Especially.

A second object of the present invention is to provide an ultraviolet / visible range optical system capable of correcting aberrations.

[0008]

In order to achieve the above first object, according to the first aspect of the present invention, the ultraviolet region is relatively higher than the visible region in the optical path for guiding the light from the light source. An ultraviolet / visible range optical system is provided which is provided with an optical element for reflecting light.

As the above-mentioned optical element, for example, a reflecting mirror which is arranged behind the light source and which reflects the ultraviolet region with a higher reflection than the visible region can be cited. This optical element can be, for example, a rear surface mirror that selectively reflects ultraviolet light.

As the optical element, it is possible to use a reflective optical element having a dielectric multilayer film that selectively reflects ultraviolet light highly highly.

Furthermore, a reflective optical element having a first reflection area and a second reflection area can be provided in the optical path.
The reflective optical element may have a structure in which ultraviolet light is reflected by the first reflective area and light transmitted through the first reflective area is reflected by the second reflective area. The reflective optical element has an optical substrate, the first reflective region is provided on the front surface side of the optical substrate, and the second reflective region is provided on the rear surface side of the optical substrate. It is possible to use a structure in which the front surface side and the back surface side have different radii of curvature.

Further, the reflective optical element has a high-reflectance dielectric multilayer film for reflecting ultraviolet light in the first reflection area, and the high-reflectance dielectric multilayer film in the second reflection area. A structure having a high reflectance metal film for reflecting light transmitted through the film can be adopted.

Further, in order to achieve the second object of the present invention, according to the second aspect of the present invention, a first reflection region is provided on the surface side in the optical path for guiding the light from the light source, A first reflective optical element having a structure having a second reflection area on the back surface side, reflecting ultraviolet light on the front surface side, and reflecting light transmitted through the reflection surface on the front surface side on the back surface side; An ultraviolet / visible range optical system is provided in which the first reflective optical element has different curvatures on the front surface side and the back surface side.

In the second aspect, a reflecting mirror disposed behind the light source in the optical path for guiding the light from the light source, for reflecting the ultraviolet region relatively higher than the visible region, and the ultraviolet light selectively. A second reflective optical element having a highly reflective dielectric multilayer film may be further provided.

By using the ultraviolet / visible range optical system of the present invention having the above-described structure, the object to be measured is arranged in the optical path of the ultraviolet / visible range optical system, and the arranged position is the light from the light source. Is guided to the measurement target, and an optical system for an optical measuring device, which is a position where light from the measurement target can be guided to a position to be measured, is obtained.

Further, in the optical system used in the film thickness control meter for controlling the film thickness by measuring the film thickness using the light from the film thickness monitor placed in the film forming apparatus,
By using the visible range optical system, the film thickness monitor is arranged in the optical path of the ultraviolet / visible range optical system, and the position where the film thickness monitor is arranged is such that the light from the light source is guided to the film thickness monitor.
An optical system for a film thickness controller, which is a position where light from the film thickness monitor can be guided to the film thickness controller, can be obtained.

[0017]

According to the present invention, by interposing an optical element that selectively reflects ultraviolet light in the optical path, the amount of ultraviolet light is relatively increased and the amount of ultraviolet light and visible light is balanced. Can be kept moderate. As a result, it is possible to realize an ultraviolet / visible range optical system that is less affected by stray light. In particular, it is possible to reduce the influence of stray light due to visible light, which has been a problem when measuring ultraviolet light with a small light amount.

Further, according to the present invention, it is possible to correct the influence of aberration by forming the reflecting surface of the reflecting optical element into two surfaces, the front surface and the back surface, and changing the radius of curvature of each surface.

Further, according to the present invention, by providing a rear surface mirror or a high-reflectivity dielectric multilayer film on the optical element, the durability of the mirror such as a decrease in the surface adhesive force of the film and a deterioration of the surface due to ultraviolet light. Can be improved.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an optical system according to the first embodiment of the present invention. In FIG. 1, the optical system of the present embodiment includes a light source 12, an optical element 15 disposed behind the light source 12, a condenser lens 13 and an aberration correction optical element 44 sequentially disposed in front of the light source 12. And the optical element 14 and the monitor glass 11 with the optical element 14 and the light amount adjusting optical element 55 interposed therebetween.

An optical element 15 arranged behind the light source 12
Is a rear surface mirror for increasing the amount of ultraviolet light that is directed toward the front of the light source with respect to the ultraviolet light having a small amount of light emitted from the light source 12. Further, the optical element 55 has a spectral reflectance characteristic shown in FIG. 7, and has a reflection function that functions as a light quantity adjusting optical element that uses a dielectric multilayer film that highly reflects only ultraviolet light and lowly reflects visible light. It's a mirror. Therefore, when the optical element 55 is included in the optical path, the visible region is suppressed in this portion, so that the light amount balance from the ultraviolet region to the visible region in the entire optical system is adjusted.

In this optical system, the light quantity spectrum when a xenon lamp is used as the light source 12 is
This is indicated by the solid line 41 in FIG. As a comparative example, a light intensity spectrum of a xenon lamp measured by using the conventional optical system shown in FIG. 2 is shown by a solid line 42 in FIG. As is clear from the results shown in the figure, according to the present embodiment, the light amount in the ultraviolet light is increased, and the light amount in the visible light is decreased, so that it is possible to maintain a proper light amount balance as the entire optical system. . Therefore, it is understood that the effect of stray light due to visible light is reduced when performing photometry in the ultraviolet region.

The arrangement of the optical elements is not limited to that shown in FIG. For example, as shown in FIGS. 11 and 12, the arrangement of the optical element 55 can be changed. FIG.
Shows an example in which the optical element 55 is replaced with the optical element 14 immediately after the aberration correcting optical element 44. FIG.
Shows an example in which the optical element 55 is replaced with the optical element 14 immediately behind the monitor glass 11. In either case, the light quantity balance between visible light and ultraviolet light can be maintained.

Next, a second embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG.

In this embodiment, the optical element shown in FIG. 5 is used as the optical element 44 in the optical system shown in FIG. The optical element shown in FIG. 5 has different curvatures on the front surface and the back surface,
A high reflectance dielectric multilayer film 23 for the ultraviolet region is deposited on the front surface, and a high reflectance metal film 23 for the visible region is deposited on the back surface. As a result, the optical element 44 has a first reflection region for reflecting ultraviolet light formed on the front surface side, and a light for transmitting visible light, for example, visible light, transmitted through the first reflection region on the back surface side. A second reflective area is formed. This makes it possible to correct each geometrical optical aberration. That is, according to the present embodiment, it is understood that the aberration correction, which cannot be performed conventionally, can be performed.

Next, the effect of aberration correction according to the embodiment of the present invention will be described with reference to FIG.

FIG. 9 is a layout diagram when the effect of aberration in the optical system of the present invention is calculated. Regarding the radius of curvature of the optical element in this example, the optical element 15 has r1 = 40, r2 = −40, and the center thickness is 10, and the optical element 44 has r1 = −30.
0, r2 = 300, and the center thickness was 16. The optical path length from the light source 12 to the surface of the monitor glass 11 is 30 from the light source 12 to the optical element 11, and the optical element 11 to the optical element 44.
Is 100, and the distance from the optical element 44 to the surface of the monitor glass is 280.7. Further, the refractive index of the glass material for visible light and ultraviolet light was n = 1.5 for visible light and n = 1.53 for ultraviolet light. Here, when the paraxial back focus of the visible light and the ultraviolet light when the visible light and the ultraviolet light are reflected only on the surface of the optical element 44 using the conventional optical element 14 is calculated,
33.476 mm for visible light, 280.7 for ultraviolet light
It becomes 6 mm, which shows that there is an influence of aberration. When visible light is reflected on the front surface and ultraviolet light is reflected on the rear surface using the optical element 44 in this example, the visible light is 280.72 mm and the ultraviolet light is 280.76 mm, and aberration correction is performed. I understand.

Next, application examples of the optical system of the present invention will be described.
This will be described with reference to FIG.

FIG. 10 is a block diagram showing an example in which the optical system of the present invention is incorporated in a film thickness controller of a vacuum film forming apparatus. In this embodiment, the wavelength of the optical reflection intensity of the film forming substance formed on the monitor glass 11 installed in the vacuum film forming apparatus 60 is selected by the monochromator 61, and the film thickness is set by the controller 62. It is a mechanism to control. In the example shown in FIG. 10, the optical system shown in FIG. 1 is applied. The incidence of light on the monitor glass 11 and the emission of light from the monitor glass 11 are performed through a window 60b provided in a part of the vacuum container 60a of the vacuum film forming apparatus 60. For the description of the optical system, refer to the description of the first embodiment.

According to the embodiments described above, the present invention is
The rear-view mirror disposed behind the light source selectively reflects the ultraviolet light forward, thereby increasing the amount of ultraviolet light traveling forward. In addition, by using an optical element that uses a dielectric multilayer film that only highly reflects ultraviolet light and lowly reflects visible light, the ultraviolet light is relatively increased, and the light amount balance of the entire optical system is adjusted. Keep the light intensity balance with and moderate. As a result, it is possible to reduce the influence of stray light due to visible light when the ultraviolet light is measured by the monochromator.

Further, a high reflectance dielectric multilayer film is formed on the surface of the reflective optical element to reflect ultraviolet light, and the transmitted light is reflected on the back surface on which the high reflectance metal film is formed.
By using the reflecting surface as the front surface and the back surface and changing the radius of curvature between the front surface and the back surface, it becomes possible to correct the aberration generated in the optical system.

Further, by providing a rear-view mirror or a high-reflectivity dielectric multilayer film on the optical element, the durability of the mirror such as a decrease in the surface adhesive force of the film and surface deterioration due to ultraviolet light is improved, and long-term use is achieved. The stability at the time of can be ensured. Therefore, the photometric film thickness control can be stably performed. That is, there is an effect that it can be used stably for a long period of time after being turned on.

In the above-mentioned embodiment, the aberration is reduced by increasing the radius of curvature of the lens arranged for focusing on the monitor glass. As the radius of curvature of the lens increases, the focal length increases, so by adding a reflective optical element and increasing the optical path length,
Absorbing.

As described above, according to the present invention, it has become possible to control the photometric film thickness in the ultraviolet region, which has heretofore been impossible.
Since the film thickness control method can be performed with an optical film thickness at a wavelength in the ultraviolet region, it is possible to form a thin film for the ultraviolet region with high precision.

[0036]

According to the present invention, the light amount of ultraviolet light can be relatively increased and the light amount balance between ultraviolet light and visible light can be appropriately maintained. Further, according to the present invention, it is possible to correct the influence of aberration by forming the reflecting surface of the reflecting optical element into two surfaces, the front surface and the back surface, and changing the radius of curvature of each surface.

[Brief description of the drawings]

FIG. 1 is an optical path diagram showing a configuration of an optical system in a first embodiment of the present invention.

FIG. 2 is an optical path diagram showing a configuration of a conventional optical system.

FIG. 3 is a sectional view of an optical element used in a conventional optical system.

FIG. 4 is a graph showing a spectral reflectance characteristic of a conventional optical element.

FIG. 5 is a sectional view of an optical element used in the second embodiment of the present invention.

FIG. 6 is a graph showing the spectral reflectance characteristics of the optical element according to the second embodiment of the present invention.

FIG. 7 is a graph showing spectral reflectance characteristics of the optical element according to the first embodiment of the present invention.

FIG. 8 is a graph showing a comparison between the light amount of the xenon lamp according to the first embodiment of the present invention and the light amount of the xenon lamp according to the conventional example.

FIG. 9 is an explanatory diagram showing an effect of aberration in the present invention.

FIG. 10 is an explanatory view showing a state in which the present invention is incorporated in a film thickness controller of a vacuum film forming apparatus.

FIG. 11 is an optical path diagram showing an example in which the arrangement of optical elements is changed in the optical system of the present invention.

FIG. 12 is an optical path diagram showing an example in which the arrangement of the optical element 55 of the optical system of the present invention is changed.

[Explanation of symbols]

11 ... Monitor glass, 12 ... Light source, 13 ... Condensing lens,
14 ... Optical element, 15 ... Optical element (rear surface mirror), 21 ... Substrate, 22 ... High reflectance dielectric multilayer film for ultraviolet region, 23 ... High reflectance metal film for visible region, 31 ... High reflectance metal for visible region Membrane, 3
2 ... Dielectric protective film, 41 ... Xenon lamp light quantity in optical system of the present invention, 42 ... Xenon lamp light quantity in conventional optical system, 44 ... Aberration correction optical element, 55 ... Light quantity adjusting optical element, 60 ... Vacuum film forming apparatus, 61 ... Monochromator, 62 ... Control meter.

Front page continuation (72) Inventor Noriaki Okada 3 2-3 Marunouchi, Chiyoda-ku, Tokyo Nikon Corporation (72) Inventor Takeshi Tsuda 3 2-3 Marunouchi, Chiyoda-ku, Tokyo Nikon Corporation

Claims (11)

[Claims] 1. An ultraviolet / visible range optical system, wherein an optical element for relatively reflecting the ultraviolet range from the visible range is provided in an optical path for guiding light from a light source. 2. The ultraviolet / visible range optical system according to claim 1, wherein, as the optical element, a reflecting mirror arranged behind the light source and reflecting the ultraviolet range relatively higher than the visible range is arranged. . 3. The ultraviolet / visible region optical system according to claim 2, wherein the optical element is a rear surface mirror that selectively reflects ultraviolet light. 4. The ultraviolet / visible range optical system according to claim 1, further comprising a reflective optical element having a dielectric multilayer film that selectively highly reflects ultraviolet light as the optical element. 5. The reflection optical element according to claim 1, further comprising a reflection optical element having a first reflection area and a second reflection area in an optical path, wherein the reflection optical element has a first reflection area. An ultraviolet / visible optical system having a structure that reflects ultraviolet light in a region and reflects light that has passed through the first reflective region in the second reflective region. 6. The reflective optical element according to claim 5, wherein the reflective optical element has an optical substrate, and the first optical element is provided on a front surface side of the optical substrate.
Is provided, the second reflection area is provided on the back surface side, and the front surface side and the back surface side of the optical substrate are configured with different radii of curvature. system. 7. The reflective optical element according to claim 6, wherein the reflective optical element has a high-reflectivity dielectric multilayer film for reflecting ultraviolet light in the first reflective region, and the high reflective dielectric multilayer film in the second reflective region. An ultraviolet / visible optical system having a high-reflectance metal film for reflecting light transmitted through a reflectance dielectric multilayer film. 8. An optical path for guiding light from a light source has a first reflection area on the front surface side, a second reflection area on the back surface side, and reflects ultraviolet light on the front surface side, and the back surface side. And a first reflective optical element having a structure for reflecting light transmitted through a reflective surface on the front surface side, wherein the first reflective optical element has different curvatures on the front surface side and the rear surface side. Ultraviolet / visible optical system. 9. A reflecting mirror, which is disposed behind the light source in the optical path for guiding the light from the light source, and which reflects the ultraviolet region relatively higher than the visible region, and a dielectric multilayer which selectively and highly reflects the ultraviolet light. Second with membrane
The ultraviolet / visible range optical system further comprising: 10. The ultraviolet / visible range optical system according to claim 9, wherein a measurement target is arranged in an optical path of the ultraviolet / visible range optical system, and at a position where the measurement target is light from a light source. An optical system for an optical measuring device, characterized in that the light from the measurement target is guided to the position where it can be guided to a position to be measured. 11. An optical system used in a film thickness controller for controlling film thickness by measuring film thickness using light from a film thickness monitor placed in a film forming apparatus. Equipped with an ultraviolet / visible optical system,
The film thickness monitor is arranged in the optical path of the visible region optical system, and the position where the film thickness monitor is arranged can be such that the light from the light source is guided to the film thickness monitor and the light from the film thickness monitor is guided to the film thickness controller. An optical system for a film thickness control meter, which is a position.