JPH01207603A - Position detecting device - Google Patents

Abstract

PURPOSE:To improve the positioning accuracy without decreasing the throughput nor increasing the pulse oscillation frequency by obtaining correction values by pulses which are obtained by comparing the light quantity values of the respective pulses detected by a 1st detector with a specific set value. CONSTITUTION:The laser beam which is emitted by a laser oscillation device 10 and polarized by a shutter 14 is incident on the detector 104 through a half- mirror 100 and a lens 102. The detector 104 sends out a photoelectric signal corresponding to the quantity of photodetection to an alignment controller 50. Then the light which is transmitted through the shutter 14 reaches the beam splitter 22 through a concave lens 16, a convex lens 18, and a fly-eye integrator lens 20. Then, the light which is deflected is incident on the detector 38, whose photoelectric signal is sent to the alignment controller 50. Dispersion in the quantity of light by the pulses which is detected by the detector 104 is generated centering on a certain constant value, so the deviations of the respective pulses from the constant value are found. The light quantity signal waveform of the detector 48 is corrected according to the result to remove the influence of dispersion in the quantity of light on the pulses.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device for detecting the relative position between a reticle and a wafer in, for example, an exposure apparatus.

[Prior Art] Conventionally, there are various alignment mechanisms in exposure apparatuses. For example, the apparatus shown in FIG. 2 is an example of the configuration of an exposure apparatus that has a 4i17 positioning mechanism that has been proposed in recent years, although it is not yet publicly known.

In the figure, a laser oscillation device 1o that emits pulsed light like excimer laser light has its intensity, pulse interval, etc. controlled by a laser control device 12.

The laser beam emitted from the laser oscillation device 10 is
Light is blocked by a mirror shutter 14 except during exposure, and the mirror shutter 14 operates only during exposure so that exposure can be performed.

Next, the laser beam passes through the concave lens 16'EL and the convex lens 1.
After being expanded to an appropriate diameter by a beam expander consisting of 8 beams, the beam passes through a fly's eye incretor lens 20. After passing through the beam splitter 22, the beam is deflected by a mirror 24 and illuminates the entire surface of the reticle R via a condenser lens 26. Further, the laser beam that has passed through the reticle R projects a pattern image of the reticle R onto the wafer W via the projection lens 28.

On the other hand, the interferometer 30 generates a measurement pulse (up-down pulse) for each unit movement amount (for example, 0.02 μm) of the stage 32, and measures these 81 measurement pulses with an up-down counter or the like, and the measured measurement data is is delivered to the stage control lid 34. Based on the measurement data, the stage control device 34 sends a control signal to the stage drive device 36 while checking the position of the stage 32. The stage drive device 36 moves the stage 32 in the X and Y directions on the rectangular coordinates in a step-and-repeat manner based on commands from the stage control device 34.

By moving the stage 32 as described above and performing exposure while moving the wafer W placed on the stage 32 in a step-and-repeat manner, the pattern on the resicle R is projected onto the wafer W in an array. Can be exposed to light.

When performing exposure using the apparatus configured as above, the first
It is necessary to expose the pattern to be formed in the second step while accurately superimposing it on the same position of the pattern on the wafer W that has been exposed in the step. In this case, a high level of overlay accuracy (alignment accuracy) is required, and for this reason, it is necessary to accurately detect the relative positional relationship between the reticle R and the wafer W.

The following methods are available as methods for performing the above position detection. In other words, a reference point (hereinafter referred to as "fiducial mark") is provided on the stage, first the positional relationship between the reticle and the fiducial mark is measured, and then the positional relationship between the fiducial mark and the wafer is measured. The positional relationship is measured and the relative positional relationship between the reticle and the square is determined from these results. The exposure apparatus shown in FIG. 2 employs the method described above.

The apparatus shown in FIG. 2 is configured to irradiate a fiducial mark provided on the stage with light having the same wavelength as the exposure light from below the stage, causing the fiducial mark to emit light.

Next, to explain this configuration in detail, the laser oscillation device lO
The laser beam emitted from the mirror shutter 14 is deflected by the reflective surface of the mirror shutter 14, and then passed through the concave lens 38 and the convex lens 4.
The laser beam incident on the optical fiber 42 is made to have an appropriate NA (numerical aperture) through the optical fiber 42 and enters the stage 32 through the optical fiber 42 .

Laser beam 1 incident on stage 32, lens 4
4 and a mirror 46, a slit-shaped fiducial mark FM provided on the upper surface of the stage 32 is irradiated.

The laser beam that has passed through the fiducial mark FM illuminates the reticle mark RM provided on the reticle R via the projection lens 28, and forms a projected image of the fiducial mark FM on the reticle R. . The light transmitted through the reticle R reaches the beam splitter 22 via the condenser lens 26 and the mirror 24, is deflected here, and enters the detector 48 arranged conjugately with the pupil plane of the projection lens 28. The detector 48 sends a photoelectric signal '8 corresponding to the received light to the alignment control device 50.

In the above configuration, the stage 32 is moved 13 times so that the projected image FMa of the fiducial mark FM scans the reticle mark RM on the reticle R as shown in FIG. By performing laser oscillation in synchronization with the optical pulse and measuring the change in the amount of light at this time, a waveform as shown in FIG. 3(b) can be obtained. The flyment control device 50 determines the center position XR of the waveform corresponding to the position where the projected image FMa of the fiducial mark FM and the reticle mark RM almost completely overlap.
From this, the relative position between the reticle R and the stage 32 is calculated. Based on this result, the reticle R and wafer W are relatively aligned. In addition, the system control casing 52
controls a series of these position detection devices.

[Problems to be Solved by the Invention] In the conventional technology as described above, when there is variation in the amount of light emitted from the light source for each pulse, the influence of this variation is reflected on the reticle. This appeared in the light quantity signal waveform when scanning the mark, and it was difficult to draw a smooth waveform.

That is, if there is variation in the amount of light for each pulse oscillation emitted by the laser oscillation device as shown in FIG. 4(a), the light amount signal waveform when scanning the reticle mark is as shown in FIG. 4(b). As such, variations occur in response to variations in pulse oscillation, causing a significant decrease in alignment accuracy.

Conventionally, in order to prevent a decrease in accuracy due to such variations in laser oscillation, the above-mentioned scanning method was used. The accuracy was improved by performing Jl several times and taking the average. However, if the above-mentioned scanning is performed multiple times, the throughput decreases and the efficiency deteriorates accordingly. Further, when an excimer laser or the like is used as a pulse laser, an increase in the number of oscillations is not preferable because it shortens the life of the laser (deterioration of the laser medium).

As described above, conventional devices have had problems due to variations in laser oscillation. The present invention has been made in view of the above problems, and it is an object of the present invention to provide a position detection device that improves alignment accuracy without reducing throughput or increasing the number of pulse oscillations.

[Means for Solving the Problems] In order to achieve the above object, a position detection device according to the present invention includes a beam irradiation means for irradiating a pulsed light beam onto an object having a mark for position detection, and a a first photoelectric detection means that receives the light beam emitted from the irradiation means and outputs a photoelectric signal according to the amount of light for each pulse; (2) a position measuring means that outputs positional information according to the position of the relative scan; and (2) a photoelectric signal that receives optical information generated from the mark by the scanning and responds to a change in the amount of light in the scanning direction. a second photoelectric detection means that outputs a pulse of the light beam based on the difference between a predetermined light amount value of the light beam emitted from the beam irradiation means and the light amount of each pulse detected by the first photoelectric detection means; and a correction means for correcting the photoelectric signal value of the second charging detection means according to the calculated variation for each pulse; The position of the mark is detected based on the mark.

[Function] In the present invention, the first photoelectric detection means is the beam irradiation means! A second photoelectric detection means receives the emitted light beam and outputs a photoelectric signal according to the amount of light for each pulse, and a second photoelectric detection means receives optical information generated from the mark by the scanning and changes the amount of light in the scanning direction. The correction means compares the light amount value of each pulse detected by the first photoelectric detection means with a predetermined light amount value and determines the light amount value of each pulse according to the predetermined light amount value. A correction value for each pulse is determined by calculating the variation with respect to ffi i, H, the photoelectric signal of the second photoelectric detection means is corrected using the correction value, and a signal waveform based on the corrected photoelectric signal value is determined. demand. This waveform is 9! when each pulse has the predetermined light amount value. ), the signal waveform is almost the same as that of the signal waveform, and it is possible to eliminate the distortion caused by the variation among the pulses.

Therefore, by using the corrected waveform, position detection can be performed with high accuracy without increasing the number of pulse oscillations.

[Embodiment FIG. 1 is a block diagram showing an embodiment of the present invention. In this embodiment, a half mirror 100, a lens 102, and a detector 104, which constitute a light receiving section that receives a laser beam emitted from a laser oscillation device 1O, are added to the configuration of the conventional device shown in FIG. . The rest of the structure is almost the same as the conventional device, and the same reference numerals as in FIG. 2 indicate the same parts.

In the configuration shown in FIG. 1, a laser beam emitted from a laser oscillation device 10) and deflected by a shutter 14 is partially split by reflection by a half mirror +00. The laser beam reflected by the half mirror 100 passes through the lens 10.
2 to the detector 104. The detector 104 sends a photoelectric signal corresponding to the amount of light received to the alignment control device 50.

As mentioned above, since there is usually variation in the amount of light for each pulse of the laser beam emitted from the laser oscillation device 10, the amount of light detected by the detector 104 is as shown in FIG. 4(a).
The light amount signal waveform of the detector 48 becomes as shown in FIG. 4(b).

The above-mentioned variation in the amount of light for each pulse occurs around a certain constant value, so by finding the deviation from this constant value for each pulse and correcting the light amount signal waveform of the detector 48 based on this result, The influence of variations in the amount of pulsed light can be removed.

Next, the method of this correction will be explained. First, a constant value that serves as a reference for pulse dispersion is determined. This constant value may be the initial setting value when performing pulse oscillation, but
Generally, prior to position detection, a predetermined number of laser oscillations are performed, and the average value of the light intensity of each pulse at this time is taken, and this value is set as the reference value SE.

For example, when pulse oscillation is performed N times as shown in FIG. 4(a), if the light intensity of the n-th pulse is En, the ratio to the reference value SE determined in advance as described above is E. /SE becomes. On the other hand, the light amount corresponding to the n-th pulse in the light amount signal waveform shown in FIG. 4(b) is P.

Then, Po shows a variation proportional to the variation in the pulse. That is, the amount of light P. is E with respect to the value when the light intensity of the output laser pulse is the reference value SE. /SE times the value. From now on, En/S
P the reciprocal SE/Eo of E. By multiplying by , it is corrected to a light amount value corresponding to the case where the light amount of the output pulse laser is the reference value SE.

Therefore, (S E/E l ) and (S E/E2
'),...

(SE/En), ・, each value obtained by multiplying (SE/EN) (P, ・SE/E1)
, (P2 ・SE/E2), ..., (Po ・SE/
If the light intensity signal waveform is obtained from Eo), -, (PN-, SE/EN), this waveform will be as shown by the broken line in Fig. 4(b), and the light intensity of the output pulse laser is constant at the reference value SE. A waveform corresponding to the waveform corresponding to the case is obtained. By using this waveform, it is possible to eliminate the influence of variations in the amount of light from pulse to pulse of the output pulsed laser, resulting in improved position detection accuracy.

In this example, a method was used in which the reticle was illuminated from a light emitting slit provided on the stage, but the method is not limited to this, and any device that synchronizes pulse oscillation with relative movement to the object to be observed may be used. , which can be applied to any device. Therefore, it goes without saying that pulsed light for alignment may be illuminated from above the reticle, or alignment marks on the wafer may be observed using pulsed light illumination.

[Effects of the Invention] As explained above, even when there is variation in the amount of pulsed light emitted from the light source, the present invention can efficiently detect the position without being affected by the variation. This has the effect of improving throughput and extending the life of a laser such as an excimer laser.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a block diagram showing an example of a conventional device, and Fig. 3 (a) shows a fiducial mark tit! An explanatory diagram showing how the two images scan the reticle mark, FIG. 3(b) is a waveform diagram of the light amount signal obtained by scanning, FIG. 4(a) is a diagram of the light amount distribution for each output laser pulse, and FIG. Figure (b) is a light quantity signal waveform diagram obtained by scanning with the output laser pulse of (a). [Description of symbols of main parts] 10... Laser oscillation device 12... Laser control device 14... Shutter 30... Interferometer 32... Stage 34... Stage control device 36... Stage Drive device 42...Optical fiber 48.104...Detector 50...Alignment control device 52...System control device R...Reticle RM...Reticle mark W...Wafer. Agent Patent Attorney Tadashi Sato Figure 1, 3'4 Figure 2 variant

Claims (1)

[Claims] a beam irradiation means for irradiating a pulsed light beam onto an object having a mark for position detection; one photoelectric detection means; a scanning means for relatively scanning the object and the light beam so that the light beam crosses the mark; a position measuring means for outputting position information according to the position of the relative scan; a second photoelectric detection means that receives optical information generated from the mark by the scanning and outputs a photoelectric signal according to a change in the light amount in the scanning direction; a predetermined light amount value of the light beam emitted from the beam irradiation means; The pulse-by-pulse variation of the light beam is calculated by comparing the amount of light for each pulse detected by the first photoelectric detection means, and the photoelectric power of the second photoelectric detection means is calculated according to the calculated pulse-by-pulse variation. A position detection device comprising: a correction means for correcting a signal value; and detecting the position of the mark based on the corrected photoelectric signal value and the position information.