JPH04359421A - Laser processing device - Google Patents

Abstract

PURPOSE:To provide a laser processing device capable of switching over laser light into two optical paths promptly and obtaining an enough quantity of light in either optical path. CONSTITUTION:A laser processing device, which is provided with a pulse oscillation type laser light source 1 and processes by allowing laser light from the light source 1 to enter a target sire 6, has a rotation converter 30 which is rotary-driven. The rotation converter 30 divides incident laser light into either of a plurality of optical paths L1 and L2, depending on its rotary angle positions. This device is provided with an angle position detection means 33 which detects the rotation angle of the rotation angle converter 30 and a trigger means 42 which triggers a laser light source 1 when a detected angle position reaches a specified position of either optical path.

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 that performs processing by entering a laser beam from a pulse oscillation type laser light source into a target area. Examples of this type of laser processing apparatus include an exposure apparatus that prints a pattern on a wafer using laser light, and a laser processing apparatus that performs processing using laser light.

0002

2. Description of the Related Art A reduction projection type sequential movement type exposure apparatus (so-called stepper) using a pulse oscillation type excimer laser as a light source has heretofore been known. This stepper sequentially overlays different patterns on each of multiple layers on the wafer and exposes them to light. Therefore, the overlay accuracy, or alignment accuracy (for example, the minimum resolution line (approximately 1/4 of the width) is required. Naturally, as the minimum circuit pattern becomes smaller, higher alignment accuracy is required.

[0003] Incidentally, in 16M DRAM (16 megabit dynamic random access memory), the minimum pattern size is 0.4 to 0.5 μm, and the required alignment accuracy (average value + 3σ) is 0.10 to 0.
．． However, in a 64M DRAM, the minimum pattern size is 0.3 to 0.4 μm, and the required alignment accuracy (average value + 3σ) is about 0.08 to 0.10 μm. In order to achieve such high alignment accuracy, the alignment method is also off-axis (Off-Ax).
is) method to TTR (Through The Re
(ticle) method. T like this
For example, the TR type alignment sensor is
This method is disclosed in Publication No. 39963, Japanese Utility Model Publication No. 1-21557, and the like.

FIG. 9 is a diagram showing a schematic configuration of a conventional excimer stepper employing such a TTR type alignment sensor. The light source 1 oscillates, for example, a KrF excimer laser with a wavelength of 248 nm, and when projecting and exposing the transfer pattern of the reticle 4 onto the wafer 6, the movable mirror 2 is moved away from the optical path L1 indicated by the thick solid line, and the laser light source 1 The pulsed light is reflected by a beam splitter 3, and the laser light is made incident on a wafer 6 via a reticle 4 and a reduction projection lens 5. The wafer 6 is placed on a two-dimensionally movable wafer stage 7. On the other hand, when performing TTR alignment, move the movable mirror 2 to the laser light source 1 as shown in the figure.
The movable mirror 2 bends the laser beam in the direction of the dotted line along the optical path L2 shown by the thick broken line, and passes the laser beam through the mirror 9 to the beam splitter 10,
11. The laser beam reflected by the beam splitter 10 hits the alignment mark RY on the reticle 4.
1. The beam enters the wafer alignment mark WY1 on the wafer 6 through the reduction projection lens 5, and the beam splitter 1
The laser beam reflected by the wafer 6 is incident on the wafer alignment mark WY2 on the wafer 6 via the alignment mark RY2 on the reticle 4 and the reduction projection lens 5. The reflected light from the wafer alignment mark WY1 passes through the reduction projection lens 5 and the alignment mark RY1 on the reticle 4, passes through the beam splitter 10, and forms an image on the photoelectric detector (such as a CCD array sensor) 12, and forms an image on the wafer alignment mark W.
The reflected light from Y2 passes through the reduction projection lens 5, the alignment mark RY2 on the reticle 4, the beam splitter 11, and forms an image on a photoelectric detector (hereinafter referred to as a TTR sensor) 13. Note that the photoelectric detectors 12 and 13 have their respective light receiving surfaces aligned with the reticle 4 and the wafer 6 by means of a lens system (not shown).
It is arranged so that it is almost conjugate with .

The image focused on the TTR sensor 12 includes a reticle alignment mark RY1 and a wafer alignment mark WY1, and by processing the image signal from the TTR sensor 12, the reticle alignment mark RY1 and the wafer alignment mark RY1 are The amount of positional deviation relative to the alignment mark WY1 can be obtained. Similarly, T
From the image signal from the TR sensor 13, the amount of relative positional deviation between the reticle alignment mark RY2 and the wafer alignment mark WY2 can be obtained.

FIG. 10 is a diagram showing another example of a conventional excimer stepper employing a TTR type alignment sensor. Similar to FIG. 9, the solid line indicates the exposure optical path L1, and the dotted line indicates the alignment optical path L2. In this example, the beam splitter 14 is fixedly installed, and the movable shutter 8 is made removable between the fixed beam splitter 14 and the beam splitter 3, so that the transfer pattern on the reticle 4 is not transferred onto the wafer 6 during alignment. The movable shutter 8 is inserted into the optical path, and after the alignment operation is completed, when the exposure operation begins, the movable shutter 8 is retreated from the optical path, and the transfer pattern on the reticle 4 is projected onto the wafer 6 for exposure. According to this method, even during exposure, the positional deviation information is captured and the positioning operation of the reticle 4 and the wafer 6 is continuously performed, thereby improving the positioning accuracy.

In the above-mentioned two conventional examples, two sets of alignment sensors are used to perform positioning.
In practice, a 3-channel or 4-channel method is used in which alignment is performed using one or two sets of alignment sensors, and the wafer or reticle, or both, are moved so that the amount of deviation is approximately zero. , alignment is performed between the projected image of the reticle pattern and the exposed area (circuit pattern) on the wafer.

[0008]

However, such conventional steppers have the following problems. (1) The wafer is divided into multiple exposure areas where the same transfer pattern on the reticle is exposed, and the movable mirror 2 and movable shutter 8 are inserted into the optical path or withdrawn each time each exposure area is exposed. Therefore, the time required to insert and remove the mirror and shutter cannot be reduced very much, and it takes about 0.5 seconds at the shortest to position the mirror and shutter, and a decrease in throughput is unavoidable. (2) In addition to the problem (1), the stepper shown in FIG. 10 also has the problem that a sufficient amount of alignment light cannot be obtained.

SUMMARY OF THE INVENTION An object of the present invention is to provide a laser processing apparatus that can quickly switch a laser beam into two optical paths and provide a sufficient amount of light for alignment or transfer in either optical path.

0010

[Means for Solving the Problems] The present invention will be explained in conjunction with FIGS. 1 and 3 showing an embodiment. It is applied to a laser processing device that performs processing by entering light into a target region 6. Then, the laser beam that is rotationally driven and incident is routed through a plurality of optical paths L1,
A rotation switch 30 for branching to either of L2, and angular position detection means 3 for detecting the rotation angle of this rotation switch 30.
3 and a trigger means 42 for triggering the laser light source 1 when the detected angular position reaches a predetermined position corresponding to one of the optical paths, the above-mentioned object is achieved.

[0011]

[Function] Rotary switch 30 placed opposite the laser light source 1
and detect its angular position. Rotation switch 30
When the laser light source 1 is triggered by the trigger means 42 when the angular position reaches a predetermined angular position corresponding to one optical path, the laser light from the laser light source 1 travels along one optical path. Further, when the laser light source 1 is triggered by the trigger means 42 when the angular position of the rotary switch 30 reaches a predetermined angular position corresponding to the other optical path, the laser light from the laser light source 1 advances along the other optical path. Therefore, the laser beam can be quickly switched to two optical paths, and a sufficient amount of light can be obtained in either optical path.

[0012] In the section of means and effects for solving the above-mentioned problems that explains the structure of the present invention, figures of embodiments are used to make the present invention easier to understand. It is not limited to.

[0013]

[Embodiment] An embodiment of the present invention will be explained with reference to FIGS. 1 to 4. FIG. 1 shows the overall schematic structure of an excimer stepper similar to that in FIG. 9, and the same parts as in FIG. 9 are given the same reference numerals. The difference from the conventional example shown in FIG. 9 is that a rotary switch 30 is installed in the optical path between the excimer laser 1 and the beam splitter 3 instead of the beam splitter 2. The rotation switch 30 includes four rotary blades 31 as shown in FIG. 2, a motor 32 that rotationally drives the rotary blades 31, and a rotary encoder 33 that detects the angular position of the rotary blades 31. As can be seen from FIG. 2, the four rotating blades 31 are arranged at equal intervals, and each blade 31 is provided with a reflecting mirror 31a. When the reflective mirror 31a faces the laser light source 1, the laser light travels along the alignment optical path L2, and when the laser light source 1 faces between the rotary blades 31, the laser light travels along the exposure optical path L1. Note that reference numeral 15 in FIG. 1 is an optical axis correction optical system, which can be provided when optical axis deviation of the alignment optical path L2 becomes a problem.

FIG. 3 shows how the excimer laser 1 is connected to the rotary switch 30.
This shows a circuit that triggers in synchronization with the rotational angular position of. The stepper control system 41 commands the rotational speed of the rotary encoder 33 and the angular position at which the excimer laser 1 is to be triggered. 42 is a comparator, which compares the count value (not shown) of a counter (not shown) built in the rotary encoder 33
1) and the trigger angle command value output from the stepper control system 41, and when they match, a trigger signal is output to the excimer laser 1. The count value from the rotary encoder 33 is also input to the stepper control system 41.

During alignment and exposure operations of the excimer stepper configured as described above, the trigger timings of the rotation switch 30 and the excimer laser 1 are controlled as follows. The following explanation will be made with reference to FIGS. 2, 4, and 5, but the position in FIG. 2(a) is the 0 degree position of the rotary switch 30,
The position shown in FIG. 2(b) is assumed to be a 45 degree position. Further, FIG. 4 is a time chart during the alignment operation, and FIG. 5 is a time chart during the exposure operation, in which the horizontal axis represents time and the vertical axis represents the rotation angle of the rotary blade 31 (count value of rotary encoder output). The trigger signal indicated by a broken line in FIG. 4 indicates a case where laser light is used for alignment, and the trigger signal indicated by a solid line in FIG. 5 indicates a case where laser light is used for exposure.

During alignment operation, first the comparator 42
Set it to "0 degrees". When the rotary encoder 33 outputs a rotation angle position of 0 degrees at the same time as the rotation switch 30 starts rotating, a trigger signal TA1 is output. Thereafter, the stepper control system 41 resets the angle command value to 90 degrees and sets the comparator 42 to "90 degrees." As a result, when the output count value of the rotary encoder 33 reaches 90 degrees, the trigger signal T is output from the comparator 42.
A2 is output. By repeating the same operation thereafter, TA3, TA4, . . . are output every time 180 degrees, 270 degrees, . . . are detected. Therefore, the excimer laser 1 is triggered at the timing shown in the time chart of FIG. The images of WY1 and WY2 are sent to the TTR sensor 12.
, 13.

The oscillation frequency of the laser and the rotation speed of the rotation switch 30 are determined as follows. When the maximum repetition oscillation frequency of the laser is 400 pulses/second, in order to perform the alignment operation at the maximum repetition oscillation frequency, it is sufficient to rotate the rotary blade 31 once with 4 pulses, and the rotation command speed from the stepper control system 41 is 6000rpm (400/4
= 100 revolutions/second). In addition, if you want to lower the oscillation frequency while keeping the rotation speed of the rotation switch 30 at 6000 rpm for alignment operation reasons, the angle command signal can be changed to
If set to 0 degrees and 180 degrees, the oscillation frequency will be halved.
The oscillation frequency can be reduced to 1 by setting only "0 degrees".
/4 can be set. Further, by setting the speed command value from the stepper control system 41 to an arbitrary value, the excimer laser 1 can be oscillated at an arbitrary oscillation frequency.

Next, during the exposure operation of the excimer stepper, that is, when transferring the transfer pattern on the reticle 4 to the wafer 6, the rotation switch 30 and the excimer laser 1 are operated as follows.
control the trigger timing. The time chart in FIG. 5 is for the exposure operation, and the comparator 42 is initially
is set, the rotation switch 30 rotates 45 degrees, and when the rotational angular position from the rotary encoder 33 outputs 45 degrees, the trigger signal TE1 is output. Thereafter, the stepper control system 41 resets the angle command value to 135 degrees and sets the comparator 42 to "135 degrees." As a result, when the output count value of the rotary encoder 33 reaches 135 degrees, the comparator 42 outputs the trigger signal TE2. By repeating the same operation thereafter, 225
, 315 degrees, . . . , the comparator 42 outputs trigger signals TE3, TE4, . Therefore, the excimer laser 1 is triggered at a timing as shown in the time chart of FIG. 5, and the laser light passes between the rotary blades 31 and travels along the exposure optical path L1 to print the transfer pattern on the reticle 4 onto the wafer 6. As described above, by sequentially updating the angular position set in the comparator 42 during each of the alignment operation and the exposure operation, the exposure operation can be started immediately after the alignment operation is completed, and one exposure area on the wafer can be processing time can be reduced.

Next, alignment is also performed during exposure, that is,
Reticle marks RY1, RY2 and wafer mark WY1,
Time charts for detecting the amount of positional deviation from WY2 are shown in FIGS. 6 and 7. FIG. 6 shows a case where the exposure optical path L1 and the alignment optical path L2 are switched for each pulse.
When the maximum repetition frequency of the laser is 400 pulses/second, the rotation speed of the rotation switch 30 may be set to 12,000 rpm.

The time chart in FIG. 7 is for the case where there is one pulse in the alignment optical path for every two pulses in the exposure optical path, and in order to oscillate the laser at 400 pulses/second, the interval between TE1 and TE2, that is, the period, must be adjusted to the maximum repetition frequency. The rotation switching device 30 should be set to correspond to the period of 600
It is sufficient to rotate at 0 rpm. Here, the control in FIGS. 6 and 7 can be performed by sequentially setting the trigger angles in the comparators 42 using the stepper control system 41 and controlling the speed of the rotation switching device 30 in the same manner as described above. As a result, even during the exposure operation, the alignment sensor can detect the amount of relative positional deviation between the reticle marks RY1, RY2 and the wafer marks WY1, WY2. This has the advantage that there is no decrease in

FIG. 8 is a diagram showing a sequence in which exposure areas on a wafer are actually sequentially exposed using a stepper. Here, the period represented by stepping 1 is a period during which the wafer is moved from the previous exposure area to the next exposure area, and for example, a focusing operation using an AF sensor and a leveling sensor disclosed in Japanese Patent Laid-Open No. 113706/1983. and leveling operation (operation for making the best image forming plane of the projection lens 5 substantially coincide with the surface of the exposure area) are executed during this period. When stepping 1 is completed, the stepper control system 41 detects the angular position of the rotation switch 30, and then
The angular position where 0 forms the alignment optical path L2 is set in the comparator 42 as the angle command value. In Figure 8, “270
"degree" is set. When the rotary switch 30 reaches the angular position of 270 degrees, the comparator 42 outputs the trigger signal TA1 to the excimer laser 1.
emits light. At this time, the laser beam emitted from the excimer laser 1 is reflected by the reflection mirror 31a of the rotary switch 30 and travels along the alignment optical path L2, and the wafer alignment marks WY1, WY2 and the reticle alignment marks RY1, RY2 are aligned with the TTR sensor 12. , 13.

Next, the stepper control system 41 causes the rotary switch 30 to set the angle "36" at which the next alignment optical path L2 is formed.
0 degrees" is set in the comparator 42. The rotation switch 30 is
When the angular position reaches 0 degrees (360 degrees), the comparator 42 outputs a trigger signal TA2, and the excimer laser 1 emits laser light. At this time, wafer alignment marks WY1 and WY2 are also placed on the TTR sensors 12 and 13 in the same manner.
and reticle alignment marks RY1, RY2 are imaged. Similarly, trigger signals TA3 and TA4 are output at angles of "90 degrees" and "180 degrees", the laser beam travels along the alignment optical path L2, and alignment signal processing is executed.

In the embodiment shown in FIG. 8, alignment signal processing is performed using four laser pulses, and the signals are taken in and processed within the period of alignment 1, and the respective exposure areas of the reticle 4 and the wafer 2 are aligned. The amount of deviation is required. Then, in the next alignment 2 period, the obtained reticle 4
The amount of relative positional deviation between the exposure area on the wafer 6 and the exposure area on the wafer 6 is corrected. This correction work is performed by moving the reticle 4, the wafer 6, or both. Normally, this alignment is performed with respect to the three axes X, Y, and θ in a plane perpendicular to the optical axis, but in addition to these three axes, there are It may also correct distortion, trapezoidal distortion, etc. These corrections are made by moving the reticle, wafer, or optical member (for example, at least one lens element constituting the projection lens 5) in the optical axis direction (Z) or in the tilt direction (Zθ1, Zθ2) of a plane perpendicular to the optical axis. It is done.

When the alignment 2 operation is completed, the stepper shifts to the exposure operation. When the exposure operation starts, the stepper control system 41 detects the angular position of the rotation switch 30, and sets the angular position at which the rotation switch 30 forms the next exposure optical path L1 to the comparator 42 as an angle command signal. In FIG. 8, "135 degrees" is set. Rotation switch 30 is 135
When the angular position is reached, the comparator 42 outputs a trigger signal TE1 to the excimer laser 1, which causes the excimer laser 1 to emit light. At this time, the laser beam emitted from the excimer laser 1 passes between the blades of the rotary switch 30 and travels along the exposure optical path L1 to print the transfer pattern of the reticle 4 onto the exposure area on the wafer 6.

Next, the stepper control system 41 sets in the comparator 42 the angle "225 degrees" at which the rotation switch 30 forms the next exposure optical path L1. When the rotation switch 30 reaches the angular position of "225 degrees", the comparator 42 outputs a trigger signal TE2.
is output, and the excimer laser 1 emits laser light. At this time as well, the transfer pattern of the reticle 4 is printed onto the exposure area on the wafer in the same manner. Similarly, the angle “3”
Trigger signals TE3 and TE4 at the 15 degree and 45 degree positions
is output, the laser light travels along the exposure optical path L1, and exposure processing is executed.

In the embodiment shown in FIG. 8, the exposure is completed with four laser pulses. Normally, in this exposure operation, it is important to bring the actual exposure amount close to the appropriate exposure amount determined by the sensitivity of the resist that is the member to be exposed, and this determines the exposure amount control accuracy. The following methods are known to achieve desired exposure control accuracy, but the present invention is not limited to these methods, and any method can be adopted. Also, other methods may be used.

(1) "Pulse number method" which lowers the energy of the laser pulse and exposes with a large number of pulses (2) "Correct exposure method" which finely adjusts the energy of the last pulse or several pulses (3) "High voltage control method" that adjusts the pulse energy by changing the applied voltage (or charging voltage) to the laser light source every one pulse or every few pulses (4) The amount of light installed between the laser and the reticle every one pulse or every few pulses "Pulse energy adjustment method" that adjusts pulse energy with a control element

Further, in FIG. 8, when the exposure operation is completed, the stepper moves to the next operation step, Stepping 2. Step 2 is an operation in which a stage for loading a wafer moves to the next exposure area. In this way, stepping 1, alignment 1, alignment 2,
By repeating the exposure operation, each exposure area on the wafer is sequentially exposed.

As explained above, when the present invention is applied to an excimer stepper, the alignment optical path L2 and the exposure optical path L1 can be switched by the rotary switch 30, and a conventional beam splitter or movable shutter can be inserted into and removed from the optical path. This eliminates the need for additional operations, reduces the time required for optical path switching, and prevents throughput from decreasing. Furthermore, the entire amount of laser light can be guided to the alignment optical path L2, allowing accurate alignment. Note that the mark detection method in the TTR type alignment sensor may be any method including an image processing method. Furthermore, the alignment method to which the present invention can be applied is not limited to the TTR method, but one in which the exposure position and the alignment position are the same, in other words, the exposure operation is started immediately after the alignment operation is completed without moving the wafer or reticle. If the configuration allows this, for example, TTL (Through
h The Lans) method may also be used.

Although the excimer stepper has been described in detail above, the present invention can also be applied to the following various laser processing apparatuses. (1) Laser processing machine that cuts workpieces such as plastics and metals with a laser (2) Laser markers that engrave characters and marks on workpieces such as plastics and metals (3) Silicon oxide etc. on semiconductor substrates (4) A resist removal device (5) A dye laser (which irradiates a dye with a pulsed laser and extracts light with a wavelength specific to the dye) Dye Laser) Therefore, the optical path branched by the rotary switch is the exposure optical path,
Not only the alignment optical path, but also the two unique to the various devices mentioned above.
The optical path is as follows.

Further, the rotary switch may be installed anywhere, for example, it may be housed integrally within the laser light source.

In the configuration of the above embodiment, the rotary encoder 33 constitutes the angle detection means, and the comparator 42 constitutes the trigger means.

[0033]

As explained in detail above, according to the present invention, a plurality of optical paths such as an alignment optical path and an exposure optical path are switched by a rotary switch, so that the conventional beam splitter, movable shutter, etc. There is no need for a member that moves linearly to be inserted into and removed from the optical path to switch the optical path, and the time required for switching the optical path can be shortened, reducing the throughput and reducing the laser processing time. Furthermore, a sufficient amount of laser light can be used in any optical path, allowing more accurate processing.

[Brief explanation of drawings]

[Fig. 1] Overall configuration diagram of an excimer stepper to which the present invention is applied

[Figure 2] Front view of the rotary blade of the rotary switch in Figure 1

[Figure 3]
A block diagram showing the trigger signal generation circuit of the excimer laser in Figure 1.

[Figure 4] Time chart of the angular position of the rotating blade and the trigger signal

[Figure 5] Time chart of the angular position of the rotating blade and the trigger signal

[Figure 6] Time chart of the angular position of the rotating blade and the trigger signal

[Figure 7] Time chart of the angular position of the rotating blade and the trigger signal

[Figure 8] Time chart of the angular position of the rotating blade and the trigger signal

[Figure 9] Diagram showing a conventional example of excimer stepper

[Figure 10]
Diagram showing a conventional example of an excimer stepper

[Explanation of symbols]

1 Excimer laser 3, 10, 11 Beam splitter 4 Reticle 5. Reduction projection lens 6 Wafer 7. Moving stage 9 Mirror 12,13 TTR sensor 30 Rotation switch 31 Rotating blade 31a Reflection mirror 32 Motor 33 Rotary encoder 41 Stepper control system 42 Comparator

Claims (1)

[Claims] Claims: 1. A laser processing apparatus that is equipped with a pulse oscillation type laser light source and performs treatment by inputting laser light from the laser light source to a target area, which is rotationally driven and directs the incident laser light to its rotational angular position. a rotary switch for branching into one of a plurality of optical paths according to the rotational speed; angular position detection means for detecting the rotation angle of the rotary switch; a trigger means for triggering the laser light source when the laser light source is reached.