JP2811538B2 - Laser processing equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser processing apparatus,
In particular, the present invention relates to an improvement of an alignment system for controlling the positioning of a work.

[0002]

2. Description of the Related Art Among laser processing apparatuses, particularly, a laser processing apparatus for a minute component such as a semiconductor component is required to have a processing position accuracy of a micron unit. An example of this type of laser processing apparatus will be briefly described with reference to FIG. The laser beam generated by the laser oscillator 40, for example, by KrF is applied to the mask 43 via the first and second mirrors 41 and 42. The laser light that has passed through the mask 43 is turned downward by a dichroic mirror 44 having the function of a half mirror, and is irradiated on a work 46 through a processing lens 45. The work 46 includes a mask 43
Only the area set by the pattern is processed. When the reduction ratio of the processing lens 45 is M, the mask 4
1 / M of the pattern No. 3 is formed.

The work 46 is mounted on a θ stage 47, and the θ stage 47 is provided on an XY stage 48.
As shown in FIG. 5, the θ stage 47 is provided so that the rotation angle θ can be changed in a horizontal state about the center thereof, and the XY stage 48 is in the X-axis direction in the horizontal state where the θ stage 47 is mounted. , Y-axis direction. The workpiece 46 is usually provided with alignment marks 46-1 for alignment at a plurality of locations. The alignment system, which will be described later, positions the workpiece 46 by controlling the driving mechanisms (not shown) of the θ stage 47 and the XY stage 48 while referring to the alignment mark 46-1 to perform position control.

The alignment system includes a processing lens 45.
The observation optical system 50 is disposed on the optical axis of the optical system. The observation optical system 50 includes a two-dimensional CCD,
5. An image signal on the θ stage 47 passing through the dichroic mirror 44 is used as a monitor image as a course image processing device 51.
Send to The coarse image processing device 51 performs image processing on the monitor image to calculate a focus shift, a position shift in the θ direction and the X and Y directions, and sends the calculated position shift to the stage control unit 52.

The stage controller 52 drives the drive mechanism 54 of the upper and lower stages 53 on which the processing lens 45 is mounted based on the transmitted signal indicating the defocus to adjust the vertical position of the upper and lower stages 53. Thereby, the processing lens 45 is focused on the work 46. The stage control unit 52 also drives the respective drive mechanisms of the θ stage 47 and the XY stage 48 based on the signals indicating the positional deviations in the θ direction, X and Y directions,
By performing fine adjustment in the X and Y directions, control is performed so that the work 46 is located at a predetermined position.

[0006]

The work 46
Even if the plate has a thickness of several tens of microns to several hundreds of microns, not only does the thickness vary from work to work, but the same work also varies from part to part. In consideration of such circumstances, a lens having a low NA (numerical aperture, hereinafter abbreviated as NA), that is, a lens having a long depth of focus, is generally used as the processed lens 45. In this case, since the processing lens 45 also serves as the objective lens of the observation optical system 50, it is inevitable that the resolution of the observation optical system 50 deteriorates. This resolution affects the processing position accuracy of the work 46, that is, the processing accuracy.

For example, KrF having a wavelength of 0.248 μm
Let us consider the case of laser light. Processing lens 45
Has a focal depth of ± 50 microns, and the wavelength of the observation light is 0.1 μm.
Assuming 6 microns, depth of focus = ± wavelength / (2 × N
A ² ) and the resolution = (0.6 × wavelength) / NA, the NA of the processing lens 45 is 0.05 ｛= (0.248
/ 2 × 50) ^1/2 、, and the resolution of the observation optical system 50 is 7.2 ｛= 0.6 × 0.6 / 0.05｝ micron.

[0008] This means that the requirement of the processing position accuracy of several tens of microns, which has been required of the conventional laser processing apparatus of this type, can be satisfied. However, recently, there is a case where a processing position accuracy of about 1 micron is required, and the above-mentioned resolution cannot cope with such a request.

Accordingly, an object of the present invention is to provide a laser processing apparatus which can realize a processing position accuracy of about 1 micron by providing a fine alignment optical system having a high resolution separately from the observation optical system.

[0010]

SUMMARY OF THE INVENTION The present invention is directed to a method for obtaining a monitor image of a work placed on a work stage, which is arranged on an optical axis of a processing lens for performing laser processing on the work. An observation optical system, a course image processing unit for processing a monitor image from the observation optical system to calculate position information necessary for alignment, an upper and lower stage on which the processing lens is mounted based on the position information, and In a laser processing apparatus including a stage control unit that performs focusing and positioning between the processing lens and the work by driving a work stage, an optical axis is provided at a position different from the optical axis of the processing lens. And N larger than the numerical aperture (NA) of the processed lens.
A fine image processing unit for processing a monitor image from the fine alignment optical system to calculate position information necessary for fine alignment, and The unit drives the work stage based on the position information from the course image processing unit, enables the fine alignment optical system to observe the alignment mark added to the work, and further includes the fine image processing unit While driving the upper and lower stages to perform fine focusing and performing alignment with respect to the alignment mark, the work stage is driven by a predetermined distance to position the work in the processing area. It is characterized by.

The processing lens and the fine alignment optical system are respectively mounted on the upper and lower stages with their focal lengths adjusted so as to focus on the same plane.

[0012]

In the laser processing apparatus according to the present invention, the work is first arranged at a position observable by the fine alignment optical system based on the observation result of the observation optical system, and then the fine alignment optical system independent of the observation optical system is provided. Based on this, fine focusing and alignment are performed. In other words, the NA of the fine alignment optical system
Is larger than that of the processed lens, so that the resolution, that is, the detection accuracy is higher than that of the observation optical system.

In particular, in the present invention, since the fine alignment optical system and the processing lens are mounted on the same upper and lower stages, even if the upper and lower stages are changed in posture due to yawing, pitching, rolling and the like accompanying the vertical movement. However, the processing position accuracy does not decrease due to the change in the posture.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a laser processing apparatus according to one embodiment of the present invention will be described. In FIG. 1, the same parts as those in FIG. In this embodiment,
An observation optical system 50 that is arranged on the optical axis of the processing lens 45 and obtains a monitor image in a wide field of view through the processing lens 45 is used as a course alignment optical system including the processing lens 45, and independently of this, The first feature is that a fine alignment optical system 11 is provided separately from the optical axis, and a fine image obtained through the fine alignment optical system 11 is processed by a fine image processing device 12. Since at least one fine alignment optical system 11 only needs to be provided, only one case will be described here. The fine alignment optical system 11 has an N larger than the NA of the processing lens 45.
An objective lens 13 having an A is included, and its field of view is narrower than the field of view of the observation optical system 50.

Then, the objective lens 13 and the processing lens 45
The second feature is that the fine alignment optical system 11 and the processing lens 45 are mounted on one upper and lower stage 14 in a state where the focus points are matched so that they are on the same plane. The upper and lower stages 14 include a driving mechanism 15
Driven by

The fine image processing apparatus 12 performs a fine focusing process using the monitor image obtained by the fine alignment optical system 14, and also performs a work 46
The position shift in the X, Y, and θ directions with respect to the upper alignment mark is calculated and sent to the stage control unit 16. The stage control unit 16 controls each drive mechanism of the drive mechanism 15, the θ stage 47, and the XY stage 48 based on a signal from the course image processing apparatus 51, and also controls each of the drive mechanisms based on a signal from the fan image processing apparatus 12. Control the mechanism.

The operation of the laser processing apparatus will be described below.

When the work 46 is mounted on the θ stage 47, the observation optical system 50 that can detect a wide field of view
The alignment mark on 6 is caught up, and the course image processing device 51 obtains the distance L1 between the alignment mark and the center of the course alignment optical system, that is, the optical axis, from the caught up monitor image.

The XY stage 48 is controlled by the stage controller 16 so that the distance L1 between the center of the coarse alignment optical system and the center of the fine alignment optical system 11 is set so that the alignment mark is within the field of view of the fine alignment optical system 11. It is driven by the added amount. Note that the distance L2 is a fixed value and is obtained in advance.

When the alignment mark enters the field of view of the fine alignment optical system 11, the fine image processing device 12 processes the monitor image and issues a command for driving the upper and lower stages 15 so that the light intensity contrast of the alignment mark is maximized. Is output to the stage control unit 16.
This means that high-precision focusing has been performed by the objective lens 13 having an NA larger than the NA of the processing lens 45.

When the fine image processing apparatus 12 completes focusing on the alignment mark, the fine image processing apparatus 12 obtains the distance between the alignment mark and the center of the fine alignment optical system 11 in each of the X, Y, and θ directions.
XY stage 48 necessary to make these distances 0
Is output to the stage control unit 16 as a command.

The above operation is repeated until the distance between the alignment mark and the center of the fine alignment optical system 11 falls within the allowable range of detection accuracy (for example, 1 micron).

[0023] When the distance falls within the allowable range of the detection accuracy, the distance (L2 + delta _XY) by XY stage 48 by being driven back to the original position, the workpiece 46 is returned to the processing region by the processing lens 45 Then, laser processing is started. Incidentally, delta _XY is the distance between the processing pattern and the alignment mark (positional relationship).

Referring to FIG. 2, the principle of calculating distances in the X, Y, and θ directions by the fine alignment optical system 11 will be described. In addition. FIG. 2 shows a case where two fine alignment optical systems 11A and 11B are used. In this case, in the fine alignment optical system 11A, the center C1 and one alignment mark 46-1 are used.
And the distances X1 and Y1 in the X and Y directions between
In the fine alignment optical system 11B, the center C2
Then, a distance Y2 in the Y direction between the position and another alignment mark 46-2 is calculated. It goes without saying that these are performed simultaneously. The distance in the X direction is X
= X1, and the distance in the Y direction is Y = (Y
1 + Y2) / 2, and the distance in the θ direction is θ
= (Y1-Y2) / L. Here, L is the distance between the centers of the two fine alignment optical systems 11A and 11B.

When there is one fine alignment optical system, first, one alignment mark 46-
Then, the distances X1 and Y1 are calculated for 1 and then the fine alignment optical system is moved to
The distance Y2 is calculated for 6-2. Then, the distances in the X, Y, and θ directions are calculated in the same manner as described above.

Further, when there are three fine alignment optical systems, the distances X1, Y1, and Y2 are calculated for each of the three alignment marks.

Here, the effect of the first feature of the present invention will be described. The processing lens 45 has an NA of 0.05, the laser beam wavelength is 0.248 microns, the observation optical system 50 has an alignment light wavelength of 0.6 microns, and the objective lens 13
Assuming that the NA of the laser beam is 0.3 and the wavelength of the alignment light is 0.6 micron, the resolution of the processing lens 45 is 3 microns, the focal depth is ± 50 microns, the resolution of the coarse alignment optical system is 7 microns, and the focal depth is ± 120 microns. Since the resolution of the alignment optical system 11 is 1 micron and the depth of focus is ± 3 microns, a higher resolution than that of the observation optical system 50 can be obtained, so that subsequent alignment can be performed with high detection accuracy.

Next, the effect of the second feature of the present invention will be described. Consider the case where the objective lens 13 in the fine alignment optical system is mounted on a stage different from the course alignment optical system with reference to FIG. FIG. 3A shows a stage 2 on which an objective lens 13 is mounted.
The case where 0 is at a certain height is shown. When this type of stage moves in the vertical direction, it is inevitable that the stage slightly tilts (usually about several tens of seconds) due to yawing, pitching, rolling, and the like. FIG. 3B shows this state in an exaggerated manner. Assuming that the distance between the fixed position of the stage 20 and the workpiece 46 is 100 mm and the inclination is 10 mm.
(Seconds), the detection position of the fine alignment optical system, that is, the reference position is shifted from the detection position when there is no inclination, and the shift amount ΔL is 100 × 1
0 ³ (micron) × tan (10 ″) = 5 (micron)
Becomes

As described above, even if the fine alignment optical system using the objective lens 13 having a large NA is employed to obtain the detection accuracy of about 1 micron, the reference position is shifted when the fine alignment optical system is moved for focusing. If the displacement is 5 microns, there is no point in employing the fine alignment optical system.

On the other hand, since the fine alignment optical system and the processing lens 45 are mounted on one upper and lower stage 14 as shown in FIG. 1, the upper and lower stages 14 are assumed to be about 10 (seconds) at the time of focusing. Even if they are tilted, both the objective lens 13 and the processing lens 45 are tilted by the same angle in the same direction. In this case, even if the alignment reference position by the fine alignment optical system is shifted by 5 μm, the processing position by the processing lens 45 is also shifted by 5 μm in the same direction. Therefore, the alignment caused by the movement of the upper and lower stages 14 for focusing. The shift of the reference position only shifts the processing region as a whole, and does not cause a decrease in detection accuracy, in other words, an error in processing position accuracy.

[0031]

As described above, in the laser processing apparatus according to the present invention, apart from the observation optical system coaxial with the optical axis of the processing lens, a fine alignment optical system having a larger NA than the processing lens is provided. In addition, since the fine alignment optical system and the processing lens are mounted on the same upper and lower stages, a detection accuracy of about 1 micron can be obtained, and the processing can be performed with a sufficiently high processing position accuracy as compared with the conventional example.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a laser processing apparatus according to one embodiment of the present invention.

FIG. 2 is a diagram for explaining the principle of performing alignment using two fine alignment optical systems.

FIG. 3 is a diagram for explaining a drawback in a case where the fine alignment optical system is mounted on a stage different from a stage for a processing lens in order to facilitate understanding of the features of the present invention.

FIG. 4 is a diagram showing a schematic configuration of a conventional laser processing apparatus.

FIG. 5 is a view of the work and its peripheral portion shown in FIG. 3 as viewed from above.

[Explanation of symbols]

 Reference Signs List 11 Fine alignment optical system 13 Objective lens 14, 20, 53 Vertical stage 15, 54 Driving mechanism 43 Mask 44 Diclock mirror 45 Work lens 46 Work 46-1, 46-2 Alignment mark 47 θ stage 48 XY stage

Claims (2)

(57) [Claims] 1. An observation optical system which is disposed on an optical axis of a processing lens for performing laser processing on a work placed on a work stage and obtains a monitor image of the work, and the observation optical system. A course image processing unit for processing monitor images from the system to calculate position information necessary for alignment, and driving the work stage and the upper and lower stages equipped with the processing lens based on the position information. In a laser processing apparatus including a processing lens and a stage control unit for performing focusing and positioning between the workpiece, an optical axis is provided at a position different from the optical axis of the processing lens, and the NA of the processing lens is A fine alignment optical system having a larger NA (numerical aperture, hereinafter referred to as NA) is mounted on the upper and lower stages, and the fine alignment optical system is A fine image processing unit for processing the monitor image from and calculating position information necessary for fine alignment, wherein the stage control unit controls the work stage based on the position information from the course image processing unit. The fine mark optical system drives the fine alignment optical system so that the alignment mark attached to the work can be observed. Further, the fine image processing unit drives the upper and lower stages to perform fine focusing, and aligns with the alignment mark. Performing the step (b), driving the work stage by a predetermined distance to position the work in a processing area. 2. The laser processing apparatus according to claim 1, wherein the processing lens and the fine alignment optical system are respectively mounted on the upper and lower stages with a focal length adjusted so as to focus on the same plane. Characteristic laser processing equipment.