JPS63194886A - Device for detecting laser optical axis - Google Patents

Abstract

PURPOSE:To improve the accuracy in detecting an optical axis by providing an eccentric detection means at the beam split position serving as well with the beam waist of a laser main body and arranging an inclination detecting means at the beam split position serving with a beam condensing point. CONSTITUTION:The laser beam position detector D1 as the eccentric detection means composed of a quarter detector is arranged at the position serving with the beam waist 2 of the laser main body 1. The laser beam position detector D2 as an inclination detecting means is then arranged at the position serving with the beam condensing position 4 located between beam expanders 3, 5. When the axis of the laser beam forms an eccentricity, the eccentric amt. is detected with the movement of the beam spot on the detector D1 and for the inclination of the beam the detector D2 performs the detection independently from the detector D1. Consequently the optical axis adjustment on the eccentricity and inclination is extremely facilitated to improve the optical axis detection accuracy.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a laser optical axis adjustment device used for laser optical axis adjustment in micro line width measuring machines, laser processing machines, etc. that require precise optical axis alignment. This invention relates to a detection device.

(Prior Art) Conventionally, in a device that optically measures the line width of a resicle pattern or an exposed wafer pattern in semiconductor manufacturing equipment using a laser beam, a laser beam emitted from a laser body is The sample surface is irradiated as a minute spot through the beam, and accurate alignment of the optical axis is required.

Such optical axis adjustment of the laser beam can be carried out by splitting a part of the laser beam 100 emitted from the laser main body 101 by beam splitters 102a and 102b installed at two locations, as shown in FIG. 5, for example. focus plate 103
a, 103b, and magnifying lenses 104a, 104b.
This allows for visual observation using the magnifying lens 1.
Focus plates 103a and 1 for observation through 04a and 104b
By adjusting the position of the laser main body 101 so that the beam projection @ (beam spot) of 03b is at the same position, the optical axis can be adjusted to a specified optical axis position.

Furthermore, as a device for electrically detecting the optical axis deviation of a laser beam, for example, the device shown in FIG.
-154389).

In FIG. 6, a laser beam 101 from a laser main body 101 is imaged as a beam spot on a sample 110 by an objective lens 108, and a half mirror 102 provided in the middle of the optical path leading to the objective lens 108 focuses the laser beam 100. Partially divided and parallel movement of the optical axis,
That is, a beam spot is applied to an eccentricity detector D1 using a four-part detector that detects eccentricity, and a half mirror 1
A part of the laser beam 100 divided by 02 is further divided by a half mirror 102b, and a beam spot is imaged on a tilt detector D2 using a 4-split detector, which detects the tilt of the optical axis by a detection lens 106. ing.

In the device shown in Fig. 6, when the optical axis of the laser beam is eccentrically moved in parallel, the beam spot hitting the eccentricity detector D1 moves and the received light output changes in accordance with the eccentricity. When the optical axis of the laser beam is tilted, the beam spot focused on the tilt detector D2 moves, and a received light output corresponding to the tilt amount is expected to be obtained.

(Problems to be Solved by the Invention) However, in the optical axis adjustment using the conventional optical monitor shown in Fig. 5, the optical axis adjustment is performed by looking at the deviation between the two laser spots. Therefore, it is difficult to tell whether the relative deviation of the laser spot is due to the eccentricity of the laser body or the inclination of the laser body.
There was a problem in that the adjustment work of the optical axis was delayed.

Furthermore, if the position of the laser beam shifts due to heat or shock during use of the device, there is a limit to visual determination of the shift, so the optical axis shift cannot be detected, and the line width etc. caused by the laser beam There was also the problem that the measurement accuracy was reduced.

On the other hand, in the conventional device shown in FIG. 6, it is planned to independently detect eccentricity due to parallel movement of the optical axis and inclination of the optical axis. Since the beam spot is simply divided by a half mirror and focused on the eccentric detector D1, and the beam spot is imaged on the tilt detector D2, if the laser beam is tilted with respect to the specified optical axis, tilt detection is possible. As the beam spot of the detector D2 shifts from the center position, the beam spot of the eccentric detector D1 also moves slightly from the center position, and the beam spot of the eccentric detector D1 deviates from the center position. Both detection outputs of D2 are obtained, and it is not possible to accurately distinguish between positional deviation due to inclination and positional deviation due to eccentricity. Conversely, even when the optical axis is eccentric due to parallel movement, detection outputs from both detectors D1 and D2 are similarly obtained.

Therefore, when adjusting the optical axis, it is necessary to first correct the inclination of the laser beam and then correct the eccentricity due to parallel movement of the optical axis (the reverse is not possible).

However, it is difficult to adjust only the inclination of the laser body independently, and as the inclination is adjusted, the optical axis also becomes slightly eccentric, and as a result, the eccentricity and inclination adjustment must be adjusted at the same time. However, there still remained the problem that adjustments were complicated.

(Means for Solving the Problems) The present invention was made in view of such conventional problems, and it is possible to individually determine whether the positional deviation of the laser beam is due to eccentricity or inclination of the laser body. It is an object of the present invention to provide a laser optical axis detection device which detects the optical axis and allows precise optical axis adjustment to be performed simply and easily.

In order to achieve this object, in the present invention, the beam spot is imaged by being placed at a beam splitting position that is conjugate with the beam waist of the laser body, and the optical axis position of the beam waist is adjusted from a prescribed optical axis position. There is an eccentricity detection means that outputs a signal according to the eccentricity ω of the beam waist by the movement of the beam spot when the beam is eccentric, and an eccentricity detection means that is placed at a beam splitting position that is conjugate with the focal point of the laser beam to form an image of the beam spot. , a tilt detection means is provided which outputs a signal according to the amount of tilt of the laser beam based on the movement of the beam spot when the laser beam is tilted with respect to a prescribed optical axis.

(Function) According to the configuration of the present invention, when the radar main body is eccentrically shifted in a direction perpendicular to the optical axis,
The beam spot hitting the eccentricity detection means placed at the beam splitting position conjugate to the beam waist of the laser main body moves and outputs a detection signal according to the amount of eccentricity of the beam waist, and the focal point of this divided laser beam is Since the position of the beam spot that hits the tilt detection means placed at the beam splitting position that is conjugate with Eccentricity can be adjusted.

On the other hand, when the laser beam is tilted with respect to the specified optical axis and is displaced, the beam spot that hits the tilt detection means placed at the beam splitting position that is conjugate to the focal point of the laser beam moves. At this time, since the beam spot hitting the eccentricity detection means placed at the beam splitting position conjugate to the beam waste 1 does not move, a detection signal is obtained only from the inclination detection means, and by monitoring this inclination detection signal, the laser beam The tilt can be adjusted.

Of course, even if the laser beam is misaligned due to eccentricity and inclination at the same time during adjustment, the eccentricity and inclination can be monitored at the same time, making the adjustment work for aligning the optical axis extremely easy and greatly improving the adjustment accuracy. can be increased to

In addition, even if the laser beam position shifts due to heat or shock during use after adjustment, the movement of the beam spot can be detected and monitored electrically, so even slight position shifts can be detected accurately. The optical axis can be adjusted in a highly accurate state at all times.

Furthermore, it is possible to servo control the adjustment mechanism of the laser body based on the detection signal of the eccentricity and tilt detection means, and once the initial adjustment of the optical axis is performed, the specified optical axis adjustment state is automatically adjusted from then on. can be maintained.

(Embodiment) FIG. 1 is an explanatory diagram showing an embodiment of the present invention, taking as an example a laser optical system for raster scanning a laser spot on a sample surface.

First, to explain the configuration, 1 is a laser body that emits parallel laser beams, and is installed on a mounting base so as to be adjustable in three-dimensional directions. Reference numeral 1a denotes a spare laser device, which is designed to be switched to when the main laser device 1 becomes unusable. Like the main laser device 1, this spare laser device 1a is also installed on a mounting base so as to be adjustable in three dimensions.

As shown in the figure, the optical path system of the laser beam emitted from the laser main body 1 to the sample surface 18 includes a beam expander 3.5, a beam splitter 6, a beam expander 7.8, a condenser lens 9, and a pair of moving lenses. Beam moving unit 11 equipped with mirror 10, slit 12, parallel plane plate for raster scanning, beam expander 14, half mirror 1
5. An image rotation prism 16 for beam rotation and an objective lens 17 are provided.

On the other hand, a beam expander 3a is provided in the optical path system of the laser beam from the preliminary laser main body 1a.

5b, 22.24 are provided. Further, a switching mirror 32 is disposed following the beam expander 24, and when the main laser device 1 is used, the switching mirror 32 is in the position shown by the solid line, but when the backup laser device 1a is used, the switching mirror 32 is located at the position shown by the solid line. 32 is switched to the position shown by the dotted line so that the laser beam from the preliminary laser device 1a is sent to the optical system after the beam splitter 6.

Regarding the optical system of the laser beam leading to the sample surface 18 shown in FIG. A position detector D1 is arranged, and a four-split detector, for example, is used as the laser beam position detector D1. The laser beam position detector D1, which is placed at a position conjugate with the beam waist 2, is irradiated with the beam divided by the beam splitter 6, that is, the beam that has passed through the beam splitter 6, to form a beam spot. It is forming an image. The beam spot imaged on the laser beam position detector D1 is caused by, for example, an eccentricity in which the laser main body 1 causes axis deviation and moves in parallel in a direction perpendicular to the prescribed optical axis. Since the beam waist 2 is also eccentric due to eccentricity, the beam spot on the laser beam position detector D1, which is placed at a position conjugate with the beam waist 2, moves according to the amount of eccentricity of the beam waist 2.
The amount of eccentricity (the amount of deviation parallel to the direction orthogonal to the optical axis) of the laser main body 1 can be detected from the received light output of the laser beam position detector D1.

On the other hand, a laser beam position detector D2 as a tilt detection means is arranged at a position conjugate to the convergence point 4 of the laser beam emitted from the laser device 1 and located between the beam expanders 3 and 5. be done.

That is, a part of the laser beam is split by a half mirror 15 provided in the middle of the optical system from the laser device 1 to the sample surface 18, and a lens 19 is provided at a position conjugate with the converging point 4 of the laser beam. A laser beam is incident on the laser beam position detector D2 to form a beam spot. The laser beam position detector D2 as the tilt detection means also uses, for example, a four-split detector like Dl.

Even if the optical axis position of the beam waist 2 is on the specified optical axis, the beam spot imaged on the laser beam position detector D2 arranged at a position conjugate to the converging point 4 of the laser beam is When the main body 1 is tilted, the focal point 4 for the laser beam shifts from the prescribed optical axis, and the laser beam position detector D2 shifts according to the shift of the focal point 4.
The upper beam spot also moves, and the inclination of the laser beam can be detected from the detection output of the laser beam position detector D2 as the beam spot moves.

Of course, even if eccentricity occurs that causes a movement of the beam spot on the laser beam position detector D1 as an eccentricity detection means, the position of the laser beam focal point 4 does not change, so the laser beam as an inclination detection means The beam bond on the position detector D2 does not move, and even if the laser beam tilts, which causes the beam spot on the sear beam position detector D2 as a tilt detection means to move, the beam waist 2 does not move. Therefore, the beam spot on the laser beam position detector D1 does not move, and as a result, the eccentricity and inclination of the laser beam can be detected individually by the laser beam position detectors D1 and D2. In addition, the laser beam position detector D1. The conjugate relationship with respect to D2 is similarly established for the laser device 1a of Pre-4AE.

Next, the function of the optical system that sends the laser beam from the laser device 1 to the sample surface 18 will be explained as follows.

First, a moving unit 11 equipped with a pair of moving mirrors 10 is movable in the direction of the arrow, and a laser spot is scanned on the sample surface 18 by reading the movement of the moving mirror 10 by the moving unit 11 with an interferometer or the like. be able to.

A slit 12 provided following the movable mirror 10 is arranged at a position conjugate with the sample surface 18, so that the irradiation area of the laser spot on the sample surface 18 can be limited by the slit 12.

The parallel plane plate 13 provided following the slit 12 can rotate in the direction of the arrow, and this rotation causes the movable mirror to
It is also possible to move the laser beam in a direction perpendicular to the scanning direction of the laser beam by zero. Therefore, movement 1t
By combining the scanning of the laser beam by 10 and the scanning of the laser beam by rotation of the parallel plane plate 13, it is possible to perform raster scanning of the laser beam on the sample surface 18.

A half mirror 15 provided subsequent to the beam expander 14 splits the laser beam into a laser beam position detector D2 serving as an inclination detection means, and at the same time serves to guide the reflected beam reflected from the sample surface 18 to the signal detection section 20. Also serves as

Further, a beam rotation mechanism 16 provided subsequent to the half mirror 15 is known as an image rotator and can rotate the beam spot formed on the sample surface 18 as a transmitted image of the slit 12.

FIG. 2 shows a four-part detector used as the laser beam position detectors Di and D2 provided in the laser beam optical system of FIG. 1.

This 4-split detector has a light-receiving surface A and B divided into 4 parts.
, D, C, and from each light receiving surface A-D, light receiving currents Ia, Ib, I according to the light receiving area of the imaged beam spot are generated.
c, Id is obtained.

Here, the beam spot position detection output imaged on the light-receiving surface of the 4-split detector in FIG. 2 is expressed as X.

When trying to obtain data in the Y direction, or in the X'' and Y' directions shifted by 45 degrees, the light-receiving surface A as shown in Table 1 below is required.
It is sufficient to calculate the differential of the light reception output of −D.

Here, in order to iD the beam spot position information in the X direction and Y direction using the differential light reception output of mode 2 shown in Table 1 above, for example, a 4-split detector as shown in the embodiment of FIG. A monitor device based on the above may be used.

In the monitor device shown in FIG. 3, reference numeral 40 is a four-part detector, and since the four-part detector 40 has four light-receiving surfaces A to D as shown in FIG.
The received light output from D is transmitted to IV converters 42a to 42, respectively.
d is converted into a voltage signal, and the X-direction position detection signal shown in mode 2 of Table 1 is calculated by adders 44a, 44b and subtracter 48a. Additionally, the adder 46a
.

46b and subtractor 48b, mode 2 of Table 1 above is selected.
The position detection signal in the Y direction shown in is calculated.

The position detection signals in the X and Y directions obtained by the subtracters 48a and 48b are amplified by amplifiers 50a and 50b, respectively, and
X and Y on each of the meter 52a and Y meter 52b
Display the direction position detection signal.

FIG. 4 is a characteristic graph showing the position detection voltage with respect to the beam position in the X or Y direction obtained from the subtractor 48a or 48b in FIG. By performing differential calculation of the outputs, the position detection voltage becomes OV at the center of the 4-minute υl detector, that is, at the position where the light beams are aligned so that the light receiving areas of the beam spots for the four light receiving surfaces A to D are equal. When the position of this beam spot with respect to the center of the four-part detector moves in the X direction or the Y direction, a change in the position detection voltage resulting in an S curve as shown in the characteristic graph of FIG. 4 is obtained.

Therefore, a monitor circuit as shown in FIG. 3 is combined with a laser beam position detector D1 using the four-part detector shown in FIG. By setting D2, the eccentricity and inclination of the laser main body 1 can be monitored using, for example, the X meter 52a and the Y meter 52b.

Next, the optical axis adjustment of the laser beam according to the above-described embodiment of the present invention will be explained.

First, the laser device 1 is installed at the completion stage of the sample scanning device using a laser beam as shown in FIG. The imaging position of the beam spot with respect to the laser beam position detectors D1 and D2 using a four-division detector is adjusted.

From the received light output of the laser beam position detector D1 as the eccentricity detecting means, the monitoring device shown in FIG.
Depending on the position of the beam spot at that time, the position detection voltage in the X direction and Y direction according to the S curve shown in Figure 4 is
Since it is displayed on the meters 52a and 52b, the imaging position of the beam spot with respect to the laser beam position detector D1 is adjusted so that the position detection voltage is near the zero point on the S curve in FIG. 4.

Next, regarding the laser beam position detector D2 as the inclination detection means, the position of the movable mirror 10 by the moving unit 11 is set to the lens center of the condensing lens 9, and the beam spot at that time is set at the laser beam position. The position of the laser beam position detector D2 is adjusted so as to be at the center of the four-part detector that constitutes the detector D2. Beaten,
Regarding the laser beam position detector D2, as well as the laser beam position detector D1 described above, by looking at the displays on the X meter 52a and Y meter 52b of the monitor device shown in FIG. Roughly adjust the position detection voltage so that it falls within the position detection voltage near the zero point.

In this way, the laser beam position detector D1. After the rough adjustment for focusing the laser spot of D2 on the center position, the laser beam position detector D1. Make fine adjustments while looking at the four meter displays provided on each monitor device of D2, and complete the adjustment when the range is within the optically acceptable range indicated by the arrow in the S curve in Figure 4.
Laser beam position detector D1. Fix each of D2 in the adjustment position.

Next, regarding the spare laser device @1a, since the position adjustment of the laser beam position detector D1.02 according to the adjustment of the specified optical axis state of the main laser device 1 has been completed, 32 as shown by the broken line to direct the laser beam from the preliminary laser device 1a toward the sample surface 18. At this time, the position detection voltage in the X and/or Y directions is monitored by the laser beam position detector D1. If it has been obtained, since the spare laser device 1a is eccentric from the specified optical axis, the eccentricity of the spare laser device 1a is adjusted so that the detected voltage being monitored becomes zero voltage, while the laser beam If the position detection voltage in the X and/or Y directions is obtained on the monitor display of the position detector D2, the monitor voltage is set to zero since the preliminary laser device 1a is tilted with respect to the specified optical axis. By adjusting the inclination as shown, the optical axis of the preliminary laser device 1a can be aligned.

Furthermore, if the main laser device @1 is replaced while the device is in use, the monitor voltage of the laser beam position detector D1 can be By performing eccentricity adjustment and tilt adjustment based on the monitor voltage of the laser beam position detector, the replaced laser device @1 can be easily aligned to the specified optical axis position.

Furthermore, in the present invention, the adjustment mechanism of the laser device 1 includes three
By providing an axial servo adjustment mechanism, it is possible to automatically maintain the optical axis adjustment state.

That is, the amplifiers 50a, 5 of the monitor device shown in FIG.
The A/D converter 54a receives position detection signals in the X and Y directions due to eccentricity, for example, obtained by Qb.

54b for digital conversion and servo control CPU60a
, 60b and further comparator 56a.

56b compares and discriminates the optical axis adjustment area shown in FIG.
D converters 54a, 54b and comparators 56a, 56
By feedback-controlling the servo adjustment mechanism in the three-axis directions of the laser device 1 based on the position n detection information based on b, for example, even if the position of the laser beam is shifted due to heat or impact during use, Servo control can be performed to automatically maintain the optical III adjustment position.

In addition, although the above embodiment took as an example the monitoring of the position detection signal by the calculation of mode 2 in the clothes-1, the position detection in the X and Y directions in mode 1, and furthermore the mode The optical axis adjustment may be performed by similarly monitoring the X'' and Y' force direction position detection shown in 3.

Further, in the above embodiment, a 4-split detector was used as the laser beam position detectors Di and D2, but in addition to the 4-split detector, a two-dimensional position sensor that outputs an analog signal proportional to the position of the beam spot may be used. Image carrying elements can be used.

Furthermore, the laser beam position detectors DI, D used in the present invention
2 can be used not only for detecting the positional deviation of the laser beam, but also as a power monitor of the laser device by adding up the output of each light receiving section, for example, when a 4-split detector is used.

Furthermore, since the laser beam position detector D2 as the tilt detection means is conjugate with the sample surface 18 and the slit 12, if the detection signal obtained from the laser beam position detector D2 is used, the laser beam can be raster scanned. It is also possible to perform an initial ΔΩ determination of the movable mirror 1O and the parallel plane plate 13 for this purpose.

(Effects of the Invention) As explained above, according to the present invention, it is possible to independently detect the eccentricity and inclination of the laser beam, which are caused by positional deviation of the laser main body or optical system, deviation of the laser beam due to temperature, etc. Therefore, the adjustment for aligning the optical axes of the laser main body and the optical member becomes extremely easy, and the optical axes can be aligned with high precision.

In addition, even if the optical axis shifts due to heat or mechanical shock while using the laser device, the optical axis shift can be detected and monitored electrically, so even the slightest positional shift can be detected accurately. This allows the optical axis to be readjusted at all times, ensuring highly accurate optical axis adjustment.

Furthermore, it is possible to perform servo control of the adjustment mechanism of the laser main body based on the detection signal of the eccentricity and tilt position @ curvature detection means.
Once the initial ttll adjustment of the optical axis is performed, the specified optical axis adjustment state can be automatically increased by 1 thereafter.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention, and FIG. 2 is a laser beam position detector Di used in the embodiment of FIG.
Explanatory diagram of the 4-split detector used as D2, 3rd
The figure is a block diagram showing an embodiment of a monitor device that detects a positional deviation detection signal based on the way the light is received and output from a 4-split detector. Figure 4 shows the position of the beam spot obtained by the monitor device in Figure 3. A characteristic diagram showing the detected voltage, FIG. 5.6, is an explanatory diagram showing a conventional example. 1: Laser device (main) 1a: Laser device (spare) 2.2a: Beam waist 3, 5.7.8.9.14.22.24: Beam expander 4.4a: Focus point 6: Beam splitter 10: Movable mirror 11: Movable unit 12 Nislit 13: Flat plane mirror 15: Half mirror 16: Beam rotation mechanism (beam low cheater) 17: Objective lens 18: Sample surface 19: Condensing lens 20: Signal detection unit 25: Switching mirror Dl: Laser beam position detector (eccentricity detection means) D2
:Laser beam position detector (tilt detection means) 40:4
Divided detectors 42a to 42d: I-V converters 44a, 44b
, 46a, 46b: Adders 43a, 48b: Subtractors 50a, 50b: Amplifier 52a: Figure 4 U whistle a diagram

Claims (1)

[Claims] In a laser device that irradiates a laser beam emitted from a laser body onto a sample surface through an optical system, a beam spot is formed by being arranged at a beam splitting position that is conjugate with the beam waist of the laser body. an eccentricity detection means for outputting a signal corresponding to the amount of eccentricity of the beam waist by movement of a beam spot when the optical axis position of the beam waist is eccentric from a prescribed optical axis position; The laser beam is placed at a beam splitting position that is conjugate with the focused point of the laser beam, and the beam spot is imaged, and the tilt of the laser beam is What is claimed is: 1. A laser optical axis detection device, comprising: inclination detection means for outputting a signal according to the amount of inclination.