Optical: systems and elements – Single channel simultaneously to or from plural channels
Reexamination Certificate
1999-12-30
2001-09-11
Ben, Loha (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
C359S626000, C359S853000, C356S328000
Reexamination Certificate
active
06288841
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an optical mechanism, and in particular to an optical mechanism for precisely controlling the angle of an incident light beam within a large incident angle range.
2. Description of the Related Art
Currently, an optical measuring apparatus usually needs an optical mechanism system that can specify a single detecting point under any circumstances when measuring a specific position. For example, to prevent design troubles for an ellipsometer during the above-stated measurement, one method is that an incident angle is fixed to perform a multi-wave length measurement, and then the number of unknown quantities is decreased with the cooperation of an appropriate material model. However, this method completely depends on the accuracy of the dispersion formula of the material model, and therefore, it is theoretically inferior to changing the incident angle. It is noted that the principle of changing an incident angle is to measure the intensity or the phase of a reflected light beam by precisely controlling an incident angle or largely changing the incident angle. Then, a signal corresponding to a specific position can be obtained using an inverse mathematical calculation. Nevertheless, it is necessary to have a particular design on the optical mechanism system with a measured point fixed because the angle of the incident light beam is continuously changed.
Basically, the conventional incident angle changeable optical mechanism can be grouped into an arm-rotating type, a single lens focusing type
10
(referring to FIGS.
1
(A) and
1
(B)) and a multi-lens focusing type
20
(referring to FIGS.
2
(A) and
2
(B)) of optical mechanisms. However, these optical mechanisms have several defects, for example, the change of an incident angle is too small, and the spherical phase difference can not be compensated, resulting in more complicated optical mechanisms. Therefore, it is very difficult to find an optical mechanism which can precisely provide a large range of incident angle and make optical paths more closed.
As to the arm-rotating type optical mechanism, measuring a changeable incident angle is performed by using two rotating motors to drive two rotating arms called an incident arm and a reflecting arm, wherein a transmitting terminal is set on the incident arm while a receiving terminal is set on the reflecting arm. However, the optical head of this arm-rotating type optical mechanism must be divided into two parts on function and space because of the existence of the two rotating motors. This will cause a large volume. Meanwhile, it is difficult to increase the accuracy of this optical mechanism, resulting in an expensive cost.
With respect to the single lens focusing type incident angle changeable optical mechanism
10
as shown in FIGS.
1
(A) and
1
(B), it includes a lens
11
, two fixed reflecting prisms
12
,
13
and two moveable reflecting prisms
14
,
15
which can be moved up and down by use of a single axis shift stage. When the reflecting prisms
14
,
15
are moved to the top level of the reflecting prisms
12
,
13
, a corresponding incident angle is approximately 2°. As shown in FIG.
1
(A), when the reflecting prisms
14
,
15
is moved to the bottom level of the reflecting prisms
12
,
13
, a corresponding incident angle is approximately 41°. Since it is difficult to have the numerical aperture (NA) of a single lens more than 1, an incident angle can be hardly over 45°. This results in that the incident angle is only approximately located in the range of 0-45°. That is, an incident angle over 45° can not be provided. Moreover, the single lens focusing type optical mechanism has a problem of spherical phase difference, so it will cause non-unique focuses.
As to the multi-lens focusing type incident angle changeable optical mechanism developed by modifying the single lens focusing type optical mechanism (as shown in FIGS.
2
(A) and
2
(B)), it includes lenses
21
,
22
,
23
, two fixed reflecting prisms
22
,
23
and two moveable reflecting prisms
24
,
25
which can be moved up and down by use of a single axis shift stage. With this multi-lens focusing type incident angle changeable optical mechanism, an incident light beam and a reflected light beam can be still parallel to an original light beam after traveling a specific distance. As shown in FIG.
2
(A), when the reflecting prisms
24
,
25
is moved to the top level of the reflecting prisms
22
,
23
, a corresponding incident angle is approximately 2°. As shown in FIG.
2
(B), when the reflecting prisms
24
,
25
is moved to the bottom level of the reflecting prisms
22
,
23
, a corresponding incident angle is approximately 88°. The multi-lens focusing type incident angle changeable optical mechanism
20
not only can make optical paths more close to each other, but also can have a larger incident angle. However, it is very difficult for the conventional multi-lens focusing type incident angle changeable optical mechanism on design, assembly and calibration. As stated above, the general focusing lenses having a problem of spherical aberration will cause focuses non-unique. Furthermore, with such conventional incident angle changeable optical mechanisms, a fixed point can not be measured through a transparent or translucent dielectric.
SUMMARY OF THE INVENTION
In view of the above, the invention is to provide a series of incident angle changeable optical mechanisms by which space limitation on optical paths can be greatly improved thereby to achieve miniaturization, and a specific point can be measured through a transparent or translucent dielectric.
An optical path overlapping type incident angle changeable optical mechanism according to the invention allows an incident light beam to be incident onto a measured range of a sample within a large incident angle range. This optical mechanism includes
a reflecting prism reflecting the incident light beam to generate a reflected light beam having an angle of 90° with respect to the incident light beam; a concave parabolic cylindric mirror guiding the reflected light beam coming from the reflecting prism to a measured range of a detect-waiting sample to thereby be further reflected to generate a detect-waiting light beam; a concave cylindric mirror used to make the detect-waiting light beam incident onto/reflected by the reflecting prism so as to overlap with the incident light beam; and a light beam splitting means used to separate the detect-waiting light beam from the incident light beam.
A dielectric penetrating/optical path overlapping type incident angle changeable optical mechanism according to the present invention allows an incident light beam to penetrate an observing dielectric having a specific thickness and then incident onto a measured range of a sample within a large incident angle range. This optical mechanism includes a reflecting prism which reflects the incident light beam to generate a reflected light beam having an angle of 90° with respect to the incident light beam; a quasi-concave parabolic cylindric minor used to make the reflected light beam coming from the reflecting prism penetrate the observing dielectric and then incident onto/reflected by a measured range of a detect-waiting sample to thereby generate a detect-waiting light beam; a quasi-concave cylindric mirror used to change the traveling direction of the detect-waiting light beam so as to make the detect-waiting light beam incident onto/reflected by the reflecting prism to thereby overlap with the incident light beam; and a light beam splitting means used to separate the detect-waiting light beam from the incident light beam.
REFERENCES:
patent: 5900981 (1999-05-01), Oren et al.
patent: 5903386 (1999-05-01), Mantravadi et al.
patent: 5969872 (1999-10-01), Oren et al.
patent: 6122107 (2000-09-01), Koch et al.
Chen Shih-Jui
Lee Chih-Kung
Lee Shu-Sheng
Lee Solomon J. H.
Lin Tony C. H.
Ben Loha
Huang Jiawei
National Science Council
Patents J. C.
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