Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Reexamination Certificate
2001-12-11
2003-09-09
Evans, F. L. (Department: 2877)
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
C356S328000, C356S124000
Reexamination Certificate
active
06618141
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a device for measuring the spectral reflectance of surface reflection light in mirrors, filters, lenses and the like, employed in optical devices. The invention furthermore relates to a process for measuring the spectral reflectance.
2. Description of Related Art
In an optical device, such as an exposure device, a light irradiation device, optical elements are employed such as reflectors, various filters, or lenses. These optical elements often require that the spectral reflectance be measured. The expression “spectral reflectance” is defined as the reflectance factor of light of a certain wavelength. For example, in a mirror fabricated, with a vacuum evaporated film on its surface, to reflect light of only a certain wavelength, as well as a lens or a filter having an anti-reflection film, it is often necessary to measure the spectral reflectance to confirm that the optical properties of the vacuum evaporated film formed or the antireflection film correspond with the computed values for the optical properties.
A conventional device used to measure the reflectance factor of the reflection surface of a mirror, lens, or filter, is shown in Japanese utility model application JP 55-21088.
FIG. 6
is a schematic cross section of the arrangement of the JP 55-21088 device for measurement of the reflectance factor. This device for measuring the reflectance factor includes a cage-like body
71
, a light source part
72
, and a light receiving part
73
. The lateral cross section of the cage-like body
71
is pentagonal and the cage-like body
71
has an angled top plate
75
and a bottom plate
77
in which a light transmission opening
76
is formed.
One of the oblique walls of the angled top plate
75
is provided with the light source part
72
, while the other oblique wall is provided with the light receiving part
73
. The angle of the uppermost part of the angled top plate
75
is defined by the size of the crossing angle at which the optical axis La of the light source part
72
and the optical axis Lb of the light receiving part
73
cross one another on the surface S of the measuring object M. Leg
78
, which is one of several legs, projects from the bottom plate
77
and adjoins the surface S.
The crossing angle between the optical axis La of the light source part
72
and the optical axis Lb of the light receiving part
73
is fixed according to the angle of incidence of the light incident on the surface S. For example, in the situation in which the surface S of the reflection surface of a mirror is used to reflect incident light with an angle of incidence of 30 degrees, it is necessary to measure the reflectance factor in the situation in which the light is incident with an angle of incidence of 30 degrees on the surface S. The crossing angle between the optical axis La and the optical axis Lb is therefore 60 degrees in the vicinity of the surface S.
The reflectance factor of a reflection surface is generally the ratio of the change of the reflectance factor to the difference of the angle of incidence which becomes greater as the angle of incidence of the light becomes greater. The above described crossing angle in a device for measuring the reflectance factor is normally fixed in the range from 0 degrees to 120 degrees for the following reasons:
Many practical reflectors are used with an angle of incidence of the light in the range from 30 to 60 degrees.
To determine the characteristic of the antireflection film of a lens or filter, a measurement is taken in the state in which the angle of incidence is 0 degrees.
In the light source part
72
there are a light source lamp
81
and a diffuser
83
. The light source lamp
81
is a small halogen lamp. In the light receiving part
73
there are a lens
84
on which the light reflected by the surface S is incident and a light receiving apparatus
85
which consists of a photoelectric cell.
In this device for measuring the reflectance factor, the light from the light source lamp
81
of the light source part
72
is scattered by means of the diffuser
83
and then the light is emitted forward with an irradiance which is uniform in all directions and is emitted via the light transmission opening
76
of the bottom plate
77
of the cage-shaped body
71
onto the surface S. The light reflected by the surface S is incident again via the light transmission opening
76
on the light receiving part
73
and is projected via the lens
84
onto the light receiving surface of the light receiving apparatus
85
. Based upon the radiance of the above described reflection light, the reflectance factor of the surface S is determined.
In the light receiving part
73
a state is implemented in which over the entire range of the solid angle, which is viewed from the light receiving surface of the light receiving apparatus
85
via the lens
84
, there is the image of the diffuser
83
broadened with a uniform irradiance. The amount of the light received by the light receiving apparatus
85
is therefore independent of the shape of the measuring object, but is proportional only to the reflectance factor of the surface S.
When the reflectance factor is measured by the above described device, it is necessary to obtain a reference which is characteristic of this device for measuring the reflectance factor. Then using this reference, the reflectance factor is determined in the manner described below.
Determination of the reference is done before measuring the reflectance factor of the measuring object or after the measurement task. Specifically, a standard mirror with a known reflectance factor is used to determine the reference. Specifically, light is emitted onto the reflection surface of the standard mirror by means of the device of
FIG. 6
which will measure the reflectance factor and the irradiance of the reflection light. In this manner, a reference is determined for device for measuring the reflectance factor of measuring object.
The reflectance factor of the surface S can be obtained by the same computation employed to compute the quotient (a/b) and the spectral reflectance &agr; of the above described standard mirror. That is, for the surface S, the quotient (a/b) is obtained by dividing the value a which is the irradiance of the reflection light obtained with respect to the surface S of the actual measuring object, by the value b which is the irradiance of the reflection light from the standard mirror (reference).
For example, in the case in which the value a of the irradiance of the reflection light measured with respect to the surface S is 7 mW/cm
2
, and in which the value b of the irradiance of the reflection light is 10 mW/cm
2
which was obtained from the standard mirror with a spectral reflectance &agr; of 80%, the reflectance factor of the surface S is computed as follows:
(7/10)×80(%)=56(%)
In the above described device for measuring the reflectance factor the disadvantages are the following:
(1) With respect to the measurement wavelength, when the reflectance factor is measured, it is necessary for the measurement light emitted onto the surface of the measuring object to have the same wavelength as the light which optically treats the above described measuring object for the actual application.
For example, in the situation in which the reflectance factor of an optical element such as a mirror used in a UV exposure device is measured, the desired result cannot be obtained when the reflectance factor of the UV light, with the same wavelength as the UV light which is intended to optically treat the optical element, is not measured. The wavelength of the light for treatment of the optical element can be different depending on the intended use of the optical device. For example, the light can be over a certain UV wavelength range or, alternatively, in a device for exposing a circuit pattern, the light can be a strictly predetermined wavelength of 365 nm which corresponds to the wavelength at which the resist has sensitivity.
It is therefore n
Kameda Hiroyuki
Moroishi Kotaro
Shinbori Masashi
Evans F. L.
Geisel Kara
Nixon & Peabody LLP
Safran David S.
Ushiodenki Kabushiki Kaisha
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