JPH02153583A - Wavelength stabilization control device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a narrow band (wavelength selective) excimer laser used as a light source for lithography (LSI pattern exposure) in semiconductor manufacturing processes. The present invention relates to a wavelength stabilization control device for an oscillation device.

In particular, it has the advantage of being able to accurately determine the diameter of light interference fringes (fringes) by using multiple linear image sensors arranged two-dimensionally, making it easy to correct misalignment of the optical axis. The present invention relates to a wavelength stabilization control device for a laser oscillation device.

[Prior Art] The configuration of a conventional example will be described with reference to FIGS. 4 and 5. FIG. 4 shows, for example, r IEEE J internal
Quantum E 1electricsJQE-14
(1978), page 17, and FIG. 5 is a plan view showing an image sensor (7) of the conventional wavelength stabilization control device.

In FIG. 4, the conventional wavelength stabilization control device includes a beam splitter (3) provided on the optical axis of the laser beam output from the laser oscillation device (1), and a beam splitter (3) installed on the optical axis of the laser beam output from the laser oscillation device (1). A scattering plate (
4), a Fabry-Perot etalon (5) provided on the exit side of this scattering plate (4), a convex lens (6) provided on the exit side of this Fabry-Perot etalon (5), and this convex lens (6). an image sensor (7) provided on the transmission side of the image sensor (7), an image processing section (8) connected to the image sensor (7), and an input side connected to the image processing section (8) and a Fabry-Perot etalon (2). ) and a servo mechanism (9) whose output side is connected to the servo mechanism (9).

Note that the laser oscillation device (1) is a laser oscillator (1a)
and a total reflection mirror (1b) and a partial reflection mirror (output mirror) placed on both sides of this laser oscillator (1a) (
lc), a laser oscillator (1a), and a partially reflecting mirror (l
c), for example, a Fabry-Perot etalon (2).

In FIG. 5, the image sensor (7) is composed of a linear image sensor (7□) which is a one-dimensional image sensor. This linear image sensor (71) is arranged so that the long side direction is along the X-axis direction.

Next, the operation of the above-mentioned conventional example will be explained with reference to FIGS. 5 and 6. FIG. 6 is a waveform diagram showing the intensity distribution of interference fringes obtained by a conventional wavelength stabilization control device.

The wavelength of the laser beam output from the laser oscillation device (1) can be selected by changing the length of the optical resonator, that is, by changing the gap of the Fabry-Perot etalon (2), which is a wavelength selection element. can.

First, a part of the laser beam output from the laser oscillation device (1) is taken out by the beam splitter (3), scattered by the scattering plate (4), and separated by the Fabry-Perot etalon (5).

The condition for the center wavelength λm of light that can pass through this Fabry-Perot etalon (5) is λm = (2n d
cos θm＞/m −... ■(tatashi, n: refractive index within the gap of Fabry-Perot etalon (2), d
: Gap of Fabry-Perot etalon (2), θIll
: Incident angle to Fabry-Perot etalon (2), II
: any integer).

Only light with a wavelength that satisfies the above condition (2) will generate concentric interference fringes on a plane perpendicular to the optical axis. The interference fringes are condensed by a convex lens (6) and placed on the image sensor (
7) Be guided upwards.

As shown by the solid line in FIG. 6, the intensity distribution of interference fringes is obtained by the arithmetic processing of the image processing section (8).

The diameter Dm of one of the interference fringes is Dm=2fθ... ■ (where f: distance between the convex lens (6) and the image sensor (7), θm=areaos(mλm/2 n d)
).

Therefore, as shown by the dotted lines in FIGS. 5 and 6, if the optical axis of the interference fringes, that is, the center wavelength λ ring shifts, the required diameter will change from Dm to Da'(Dm'
<Da), and an accurate diameter Dm cannot be determined.

A signal representing this diameter DI11 is fed back to the servo machine 1 (9), and the length of the optical resonator, that is, the gap of the Fabry-Perot etalon (2), is controlled and adjusted by the servo machine 1 (9). In other words, from Equation 0, when the wavelength λ of the laser beam is long, the diameter DIIl of the interference fringe becomes small, and when the wavelength λ ring is short, the diameter D- becomes large. A one-dimensional linear image sensor is used for control using phase detection.

[Problems to be Solved by the Invention] In the conventional wavelength stabilization control device as described above, a one-dimensional image sensor is used as an image sensor.
There was a problem in that the image sensor had to be adjusted so as to be placed accurately on the optical axis of the interference fringes.

Furthermore, even if the optical axes of the image sensor and the interference fringes are misaligned due to heat, vibration, etc., there is a problem that correction cannot be made.

This invention was made in order to solve the above-mentioned problems, and it becomes easy to adjust the imaging device so that it is placed on the optical axis of the interference fringes, so that the optical axis of the imaging device and the interference fringes are misaligned. The object of the present invention is to obtain a wavelength stabilization control device capable of correcting.

[Means for Solving the Problems] A wavelength stabilization control device according to the present invention includes the following means.

(i) Optical means for scattering a part of the laser beam, separating it into spectra, and condensing the beam.

(ii) An imaging device that two-dimensionally images the interference fringes of the focused light.

(ii) An image processing unit that calculates the position of the interference fringe by processing the two-dimensionally captured image of the interference fringe.

(iv) a servo mechanism that controls a wavelength selection element that selects the wavelength of the laser beam based on the determined position of the interference fringes;

[Operation] In the present invention, the interference fringes of the focused light are two-dimensionally imaged by the imaging device.

Subsequently, the image processing section performs arithmetic processing on the two-dimensionally captured interference fringe image to determine the position of the interference fringe.

Then, a wavelength selection element that selects the wavelength of the laser beam is controlled by the servo mechanism based on the position of the interference fringes determined above.

[Example] Two examples, namely a first example and a second example, will be described.

First, the configuration of the first embodiment will be explained with reference to FIGS. 1 and 2. FIG. 1 is a block diagram showing a first embodiment of the present invention, which is completely the same as the conventional device described above except for the image sensor (7^).

Further, FIG. 2 shows an image sensor (7) of the first embodiment of the present invention.
^) is a plan view showing.

In FIG. 1, the first embodiment of the present invention consists of the same components as those of the conventional device described above, and an image sensor (7^) provided on the transmission side of the convex lens (6). .

Here, the optical means of the present invention includes a beam splitter (
3), scattering plate 4), and Fabry-Perot etalon (5)
) and a convex lens (6).

In FIG. 2, the image sensor (7^) is composed of three linear image sensors (7a), (7b), and (7c). These linear image sensors (7a),
(7b) and (7c) are the distance (f) from the convex lens (6).
) are arranged in a plane perpendicular to the optical axis, and the linear image sensor (7a) is arranged with its long side along the y-axis direction, and the linear image sensors (7b) and (7C) are arranged with their long sides along the y-axis direction. The directions are arranged along the =x-axis and +X-axis directions, respectively.

Next, the operation of the first embodiment described above will be explained with reference to FIG.

As shown in Fig. 2, the peak positions of the light intensity produced by one interference fringe on the three linear image sensors (7a), (7b) and (7C) are A (0, y+>, B (X2,
0>, C(X3,0), the center of this interference fringe (a
, b) is (a, b) = ((x2+xs)/2. (y
+'+xzx+)/2y+1, and the diameter is o = I ((xz'+y12)(xi"+y+"))
/y.

Therefore, even if the center of the circle of interference fringes is not on the x-axis, its diameter can be accurately determined.

The servo machine f11 (9) controls the Fabry-Perot etalon (2) by comparing the above-mentioned diameter with an initially set value.

The first embodiment of the present invention described above uses three linear image sensors (7a), (7b), and (7c) arranged two-dimensionally, so even if the optical axis is shifted, interference fringes will not be generated. Since the center and diameter can be determined, the wavelength can be stably controlled over a long period of time.

In addition, since optical axis deviation and surface blur can be corrected, linear image sensors () a), (7 b) and (7
Mounting c) has a wider tolerance for accuracy, facilitates machining, and allows parts to be processed at lower cost.

Second, the configuration and operation of the second embodiment of the present invention will be explained with reference to FIG. FIG. 3 is a plan view showing an image sensor (7B) according to a second embodiment of the invention.

The second embodiment of the present invention includes an image sensor (7B) instead of the image sensor (7^) in the first embodiment described above.

In FIG. 3, the image sensor (7B) includes six linear image sensors (7d), (7e), (7f), (7g).
, (7h) and (71). These linear image sensors (7d), (7e), (7r),
(7g), (7h), and (71) are arranged in a plane separated by a distance (f) from the convex lens (6), and the linear image sensor (7d) is arranged so that the long side direction is along the +x axis direction. and other linear image sensors (7e), (7f
), (7g), (7h), and (71) are arranged every 60 degrees in the same plane with the linear image sensor (7d) as the base point.

Therefore, if six data points between the positions of the interference fringes can be obtained, optical axis deviation and surface wobbling can be corrected even when the sensor surface is not perpendicular to the optical axis.

In the first and second embodiments described above, it is also possible to issue a warning regarding the optical axis position on the condition that the position of the interference fringes is within a predetermined radius (r).

Further, in the above embodiment, a plurality of one-dimensional linear image sensors are arranged to constitute a two-dimensional image sensor, but for example, C
It goes without saying that the intended purpose can be achieved even if a two-dimensional imaging device such as a CD is used.

[Effects of the Invention] As explained above, the present invention includes an optical means that scatters a part of laser light, separates it, and focuses it, and an imaging device that two-dimensionally images the interference fringes of the focused light. an image processing unit that calculates the position of the interference fringe by processing the two-dimensionally captured interference fringe image; and a wavelength that selects the wavelength of the laser beam based on the determined position of the interference fringe. Since it is equipped with a servo mechanism that controls the selection element, it is easy to adjust the image sensor to be placed on the optical axis of the interference fringes, and it is possible to correct misalignment between the optical axis of the image sensor and the interference fringes. It has the effect of being able to do it.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of the present invention, and FIG.
The figure is a plan view showing an image sensor according to a first embodiment of the invention, and FIG. 3 is a plan view showing an image sensor according to a second embodiment of the invention.
FIG. 4 is a block diagram showing a conventional wavelength stabilization control device.
FIG. 5 is a plan view showing an image sensor of a conventional wavelength stabilization control device, and FIG. 6 is a waveform diagram showing the intensity distribution of interference fringes obtained by a conventional wavelength stabilization control device. (1)... Laser oscillation device, (2)... Fabry-Perot etalon (wavelength selection element), (3... (4... 5... 6... 7Δ... 8...・ 9 ... In addition, is shown. Beam splitter scattering plate, Fabry-Perot etalon, convex lens, image sensor, image processing section, servo mechanism. In each figure, the same reference numerals are the same or equivalent parts: - Mi, Two
Yu 12) Source 3 Figure Not 5 Figure Dm < Dm Interpretation G'' Box/Seal

Claims (1)

[Claims] An optical means that scatters a part of the laser beam, separates it, and focuses it, an image sensor that two-dimensionally images the interference fringes of the focused light, and calculates an image of the two-dimensionally imaged interference fringes. A wavelength characterized by comprising: an image processing unit that processes the interference fringe to determine the position of the interference fringe; and a servo mechanism that controls a wavelength selection element that selects the wavelength of the laser beam based on the determined position of the interference fringe. Stabilization control device.