JPH07119569B2 - Optical scanning type position detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention scans an object surface having a predetermined pattern with a light beam, and reflects light such as scattered light or diffracted light from this pattern. It relates to a device for detecting the position of the pattern by detecting.

[Conventional technology]

This type of apparatus is used for measuring a fine pattern formed on a semiconductor wafer and for alignment in an exposure apparatus used in a semiconductor manufacturing process.

The optical scanning mechanism for this purpose is generally composed of a reflecting mirror and a vibrator, or a slit and a rotor in order to have a compact structure.

[Problems to be solved by the invention]

However, due to the driving method of the oscillator and the rotor, non-linear movement and unstable movement peculiar to the oscillator cause fluctuations in the scanning speed of the detection light on the alignment mark, which causes an error for position detection or alignment. There was a fear that it would occur. Specifically, in the method of measuring the scanning time from the reference mark position to the alignment mark position to obtain the deviation amount from the reference mark position, which is generally performed for alignment, the scanning speed of the alignment light is In some cases, fluctuations in the measurement result in measurement errors, and as a result, the alignment accuracy is reduced.

Further, configuring the scanning member to move the scanning light at a constant speed will complicate and upsize the device,
It is also difficult to improve the accuracy of constant velocity. In particular, when a light beam is scanned by the reciprocating motion of an oscillator for vibrating the vibrating mirror, it is ideal to use a sine wave as the drive signal for the oscillator, so the unit time There is a problem that the scanning light movement distance per hit and the rotation angle of the vibrating mirror do not correspond one to one, and as a result, an alignment error is likely to occur.

Therefore, an object of the present invention is to solve these drawbacks and to provide a scanning type optical position detecting device capable of stably detecting an object to be detected regardless of the fluctuation of the speed of the optical scanning member. .

[Means for solving problems]

The present invention is directed to a main optical system for converging a first light beam on an object plane, and a light flux traveling in the optical path of the main optical system for scanning the first light beam on the object plane. It is based on an optical scanning type position detecting device provided with a scanning member having a deflecting reflecting mirror for changing the direction and a photoelectric detecting means for receiving reflected light from the object plane. Then, the deflection reflecting mirror is irradiated with a second light beam different from the first light beam, and the second light beam reflected by the deflection reflecting mirror is received to correspond to the angular position of the deflection reflecting mirror. An angular position detecting means for outputting a detection signal, and a photoelectric signal output from the photoelectric detecting means for scanning the first light beam on the object plane by the deflecting reflecting mirror are detected by the angular position detecting means. Object position detecting means for detecting the position of the object on the basis of the received signal in synchronization with the signal is provided.

[Work]

According to such a configuration of the present invention, since the position of the deflecting reflecting mirror for scanning is sequentially detected by the position detecting means of the deflecting reflecting mirror, even if the vibration and rotation of the deflecting reflecting mirror are not constant, Since the signal of the position detecting means can be measured according to the position of the deflecting mirror, the position of the detected object can be accurately detected. Moreover, since the deflection reflecting mirror itself for scanning the detection light on the object to be detected is irradiated with the light beam through another optical path to detect the position of the deflection reflecting mirror, the deflection reflecting mirror itself Even if there is a change over time or deformation due to heat, etc., there is little risk of lowering the measurement accuracy.

Specifically, the angular position of the deflecting / reflecting mirror is obtained by detecting the amount of movement of the reflected light corresponding to the angular position of the deflecting / reflecting mirror by the position detecting means of the deflecting / reflecting mirror, and the main optical system for alignment is obtained from this position signal. The trigger for counting the signal for detecting the alignment mark in the optical signal from is applied.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to FIG. 1 showing an embodiment of the present invention.

FIG. 1 is a schematic configuration diagram showing a configuration in which an optical scanning type position detection device according to the present invention is adopted in an alignment system of a projection type exposure apparatus.

The reticle R is uniformly illuminated by the light flux from the illumination light source means 50 through the condenser lens 51, and the predetermined pattern on the reticle R is projected and transferred onto the wafer W by the projection lens L. Here, in order to set the positions of the reticle R and the wafer W in a predetermined relationship, a main optical system including alignment optical systems 10 and 20 for detecting the positional relationship between the two is provided. As the optical scanning member 2 for scanning the laser light supplied from the laser light source 1 on the reticle R and the wafer W, a vibrating mirror 2a and a rotor 2b for vibrating the vibrating mirror 2a are provided. The laser light is expanded to a desired beam width by the beam expander 3, shaped into a rectangular beam through the cylindrical lens 4, reflected by the vibrating mirror 2a, and then transmitted through the condenser lens 5 and the semitransparent mirror HM to be an objective. The light passes through the lens 6 and is reflected by the mirror M to reach the reticle R. The laser light is focused on the reticle R as a rectangular beam spot, and the light flux passing through the reticle R reaches the wafer W through the projection objective lens L and a rectangular beam spot is also formed on the wafer W. The light reflected by the wafer W again passes through the projection objective lens L, returns along the original path, passes through the reticle R, and is transmitted through the semitransparent mirror HM.
It is incident on the detector 7 reflected by.

Here, a rectangular beam is formed on the surface of the reticle R and the wafer W by the optical system 10 from the light source 1 to the cylindrical lens 4 and the optical system 20 including the condenser lens 5, the half mirror HM, the objective lens 6 and the mirror M. Is formed and a main optical system for receiving reflected light from the object surface to be detected is formed. The center of vibration of the reflecting surface of the vibrating mirror 2a that constitutes the optical scanning unit 2 is arranged so as to substantially coincide with the pupil position of the main optical system, and the projection objective lens L is on the image side (wafer side) thereof. Wafer W because it is telecentric
The chief ray of the scanning light on the surface always enters perpendicularly to the wafer surface.

The reflection angle of the laser light is continuously changed by the scanning member 2 including the vibrating mirror 2a and the rotor 2b for vibrating the vibrating mirror 2a, whereby the rectangular beam spot of the laser light is formed on the reticle R and the wafer W. To be scanned. During the scan,
Light reflected from the alignment mark M _W on the alignment mark M _R and the wafer W on the reticle R returns along the original can route including diffracted light and scattered light, the detector 7
Then each alignment mark on the wafer W and reticle R
A signal is generated for each reflected light from M _W and M _R. This signal is amplified by the preamplifier 16, converted into a digital signal by the A / D converter 14, and stored in the memory circuit 13.

Signal of the memory circuit 13 is Kaiori by the microprocessor 11 and the computation dedicated processor 12, the alignment marks on the reticle R M _R and the alignment mark M _W on the wafer W
Find the amount of alignment error with. Based on the obtained error amount, the microprocessor 11 sends a signal to the stage driving means 9 to move the stage by a predetermined amount by the stage driving motor 8 and detects the position of the stage by the interferometer 17 to detect the position on the reticle R. an alignment mark M _W on the alignment mark M _R and the wafer W is controlled to be a predetermined positional relationship.

On the other hand, an irradiation optical system 30 for irradiating the second light beam on the same reflecting surface of the vibrating mirror 2a as the deflecting reflecting mirror on an optical path different from the optical path of the alignment beam, and the irradiation optical system.
A condensing optical system 40 for condensing the second light beam supplied from 30 and reflected by the vibrating mirror 2a is provided. Here, the reflection position of the alignment beam and the reflection position of the second light beam are configured to substantially match on the reflection surface of the deflecting mirror. The plane including the optical axis of the irradiation optical system of the second light beam and the optical axis of the condensing optical system for condensing the second light beam is the light of the main optical system on the deflecting reflection mirror 2a. It is configured to coincide with the incident surface of the beam, and this incident surface is configured to be perpendicular to the rotation center of the deflective reflecting mirror 2a. Therefore, the accuracy of detecting the position of the deflection mirror is highest. Then, the vibration position of the vibrating mirror 2a can be detected by the output of the detector 44 which detects the position of the second light beam condensed by this condensing optical system, and this position is on the wafer W surface of the alignment scanning light. One to one
Corresponding to. Specifically, the irradiation optical system 30 has a second laser light source 31 that emits a laser beam having a wavelength different from that of the laser beam used for the main optical system for alignment, and a beam expander 32 that expands the diameter of this light beam. The condensing optical system has a lens 41 that condenses the reflected light from the vibrating mirror 2a, a cylindrical lens 42, a grating 43 for an encoder, and a detector 44. Then, the wavelength of the alignment light beam and the wavelength of the second light beam for detecting the position of the deflecting / reflecting mirror are set to different wavelengths, and further, the wavelength light used for one of the optical systems is different from the sensitivity of the detector used for the other optical system. By setting the wavelength in the low wavelength region, it is possible to reduce noise in detecting the beam spot positions of both beams and perform detection with higher accuracy.

Here, as will be described later, the pulse generating circuit 18 of the position detecting means of the deflecting reflecting mirror generates trigger pulses for alignment corresponding to the scanning position of the second light beam, and the reticle is counted by counting the trigger pulses. It is possible to detect the positional relationship between the position of the upper alignment mark and the alignment mark on the wafer.

That is, the positional relationship between the alignment mark M _W on Arai meth mark M _R and the wafer W on the reticle R is the detection light emanating when the scanning light beam has scanned the alignment marks is converted into electrical signals by the detector 7, Further A /
A signal emitted corresponding to each alignment mark is converted into a digital signal in synchronism with the number of pulses from the pulse generation circuit counted by the counter circuit 15 using the D converter 14, and stored in the memory circuit 13. In other words, the light scanned by the scanning member 2 is the alignment mark on the reticle R.
The M _R and the wafer W alignment mark M _W on while moving from the scanning start position to the scanning end position, the positional relationship therebetween is detected stored by a pulse (position pulse) signal generated at fixed intervals.

Light receiving optical system 40 for detecting the position of the deflecting mirror as a scanning member
The position signal detected by the detector 44 is converted into an electric signal, and the pulse generation circuit 18 generates a trigger pulse at a constant distance on the detector 44 based on the analog signal. This trigger pulse is input to the scanner drive circuit 19 and the counter circuit 15 that control the rotation of the rotor 2b. The counter circuit 15 calculates and records the relative relationship between the angular position of the vibrating mirror 2a and the position of the scanning light from the position information from the pulse generation circuit 18 and the stage position information from the stage drive circuit 9, and records it in the memory. The address signal of the circuit 13 and the trigger pulse of the A / D converter 14 are generated.

By the way, of the main optical system for alignment, the vibrating mirror 2a
The optical system 20 from the reticle R to the reticle R is configured to be optically similar to the position detecting condensing optical system 40 of the vibrating mirror 2a. That is, the distance traveled by the scanning light beam on the reticle with respect to the reflection of the vibrating mirror 2a and the distance traveled by the second light beam for detecting the position of the vibrating mirror 2a on the light receiving surface of the position detecting detector 44 of the deflecting reflecting mirror. And are configured in a proportional relationship with a predetermined scaling ratio. Specifically, the second
The distortion aberration amount of the condensing optical system for condensing the beam is configured to be substantially equal to the distortion aberration amount on the surface of the main optical system facing the detected object. Therefore, the movement amounts of the alignment scanning light beam and the position detecting second light beam of the vibrating mirror 2a are maintained in a one-to-one correspondence relationship. Therefore, even when the scanning light 1 cannot scan the reticle R and the wafer W at a constant speed, alignment is performed with the trigger pulse according to the position of the scanning beam as a reference, so that the position coordinate is always correct. An alignment signal can be obtained.

Next, the configuration for generating the trigger pulse at a constant interval for alignment corresponding to the scanning position of the scanning light beam by the pulse generating circuit 18 of the deflecting / reflecting mirror position detecting means will be described. First, as shown in the optical sectional view of FIG. 2 and the schematic perspective view of FIG. 3, in the converging optical system 40 for detecting the position of the deflecting / reflecting mirror, the position of the deflecting / reflecting mirror 2a indicated by the broken line in the figure is detected. The second light beam is condensed by the lens 41 which is condensed after being reflected by the deflecting reflecting mirror 2a, and is a cylindrical lens.
The beam is condensed by 42 as a beam shape that extends in a direction perpendicular to the incident surface (sheet surface of the drawing) of the deflecting mirror. Here, as shown in FIG. 2, in the condensing optical system 40, a condensing lens
Since the focal point of 41 is arranged so as to coincide with the rotation center of the deflecting reflecting mirror 2a, the condensing optical system is formed telecentric on the exit side (detector 44 side) thereof. This corresponds to the fact that the objective lens 6 in the optical system 20 of the main optical system for position detection is telecentric on the reticle R side, and when each beam spot is defocused by such a configuration. In addition, the moving distance of the light beam of the main optical system on the reticle R and the moving distance of the second light beam for detecting the position of the deflecting mirror on the detector 44 have a one-to-one correspondence, and are stable. High accuracy is maintained.

The second light beam expanded by the cylindrical lens 42 is incident on the grating plate 43 arranged in front of the detector 44, and the light passing therethrough reaches the detector 44. The grating plate 43 has four transmission gratings that are 90 ° out of phase with each other.
43a, 43b, 43c, 43d are arranged in parallel. Therefore, the intensities of the light beams passing through the respective gratings change in a sine wave shape with a phase difference of 90 °, and the detector 44 outputs four sine wave signals with a phase difference of 90 ° corresponding to the position of the second light beam. Occur. One cycle of this sine wave corresponds to one cycle of the grating.

FIGS. 4A, 4B, and 4C show scanning states of the second light beam on the position detecting grating plate 43 of the deflecting reflecting mirror 2a described above,
FIG. 5 shows a state of scanning of a position detection light beam on a reticle R as an object to be detected which is performed in the same manner, and FIG. 5 is emitted by scanning a second light beam on a grating plate as shown in FIG. 4B. FIG. 6 is a waveform diagram showing a relationship between a signal and a signal emitted by scanning a light beam on the reticle R as shown in FIG. 4C. As shown in FIG. 4C, the spot B _{2S of} the second light beam B ₂ for position detection of the deflecting reflector 2a is caused by the vibration of the deflecting reflector 2a.
Scan on the four gratings 43a, 43b, 43c, 43d as shown in FIG. 4B,
At this time, on the reticle R, the spot B _1S of the light beam B ₁ for position detection on the reticle surface is aligned with the alignment marks M _R1 , M _R2 on the reticle R and the image of the alignment mark on the wafer projected on the reticle surface. Scan M _W.

As shown in Fig. 4B, the expanded light spot of the second light beam B ₂
When the B _{2 S} scans on the grid plate, four grids 43a, 43b, 43c, 4
The output waveforms from the detector corresponding to the light passing through 3d are a, b, c and d in FIG. 5, respectively. The pulse generation circuit 18 divides one cycle of the sine wave into a plurality of m pieces like a so-called encoder circuit based on these four signals,
A divided pulse having a constant period as shown in FIG.

On the other hand, as shown in FIG. 4C, when the extended light spot B _{1s of} the position detection light beam B ₁ scans the reticle surface, one edge M _R1 and the other edge M _R2 of the alignment mark on the reticle are scanned. when, detector 7 as f in Fig. 5 by receiving scattered light from each edge, and a signal S _R2 corresponding to the signal S _R1 and the other edge M _R2 corresponding to one edge M _R1 Occurs. Further, when scanning the image M _W of the wafer alignment mark projected on the reticle surface,
The scanning beam also scans the wafer through the projection lens L, and the scattered diffracted light from the alignment mark on the wafer reaches the detector 7, and the signal S _W as shown in FIG.
Emit.

These series of signal systems are processed by the configuration of each circuit as described above with reference to FIG. That is, between the signals S _R1 and S _R2 from the reticle alignment mark shown in FIG. 5 in f, the position of the signal S _W from the wafer alignment mark, such as FIG. 5 g, the H _1, H ₂ second It can be detected by the number of pulses from the pulse generating circuit 18 as shown in FIG. Then, as shown in FIG. 4C, the number of pulses is the reticle alignment mark on the reticle surface.
It corresponds to the positional relationship between M _R1 and M _R2 and the image M _W of the wafer alignment mark. Therefore, for example, the microprocessor 11 drives the stage S so that the wafer alignment mark image M _W is positioned between the two alignment marks M _R1 and M _R2 , that is, H ₁ = H _2. Is completed.

Here, each grating of the grating plate in the position detecting means of the deflecting reflecting mirror 2a has n periods in the scanning region of the second light beam, and the number of divisions of the sine wave in the pulse generating circuit is m, and on the reticle surface. The minimum unit x that can be measured on the reticle surface is given by x = 1 / nm, and the minimum unit y that can be measured on the wafer surface is the reduction ratio β of the projection lens L. Then, y = l / β nm. For example, if l = 400 μm, n = 200, m = 20, β = 5, then y = 0.02 μm, and alignment with sufficient accuracy for practical use is possible. Further, it is possible to further improve the accuracy by decreasing the grating interval of the grating plate 43 to increase the frequency n in the predetermined scanning width and increasing the number of divisions m of the sine wave to increase the number of pulses. .

In the above embodiment, in the condensing optical system 40 for detecting the position of the deflecting reflecting mirror 2a, the expanded light beam spot B _2S is formed by using the cylindrical lens 42 for simultaneously scanning the four gratings. As shown in the perspective view of FIG. 6, a diffraction grating plate 45 can be used instead of the cylindrical lens. In this case, the direction of the grating groove of the diffraction grating plate 45 coincides with the rotation direction of the deflecting mirror, and it is desirable that the diffraction grating uniformly emits ± 1st order and ± 2nd order diffracted light. The four diffracted lights may be guided to the four grating plates, respectively.

Further, in the above embodiment, the detector 44 is arranged immediately after the grating plate 43 to receive the light passing through the grating plate as it is, but the grating plate 43 passes between the grating plate 43 and the detector 44. By arranging the cylindrical lens for condensing the light, the detector can be made compact. FIG. 7 is a perspective view showing an example of such a configuration, and a cylindrical lens 46 having a positive refracting power is arranged behind the grating plate 43. The generatrix of the cylindrical lens 46 is the extension direction of the extended second light beam,
That is, the four transmissive gratings 43a, 43b, 43c, 43d are arranged in a deflected manner. Then, at the focal position of the cylindrical lens, parallel to the generatrix of the cylindrical lens,
A detector section 44 'having four detectors 44a, 44b, 44c, 44d arranged vertically is arranged. With such a configuration, the second light beam B _2s for scanning the grating plate 43
7 moves from the position shown by the solid line in FIG. 7 to the position shown by the broken line, but the position of the second light beam B _{2F on} the detector part 44 ′ does not change, and the detector part 44 ′ can be made into a small shape. You can do it. In this case, each detector 44
By reducing the light receiving area at a, 44b, 44c, 44d,
The detector response is improved and high-speed scanning can be supported, and the light receiving position can be kept constant regardless of the position of the scanning beam spot, so sensitivity unevenness on the light receiving surface of the detector can be prevented, resulting in higher performance. Can be expected to improve.

In the above-described embodiment, four gratings having mutually different 90 ° phases are arranged in parallel in order to generate a pulse from the position detecting means of the deflecting reflecting mirror 2a. However, the present invention is not limited to this and two gratings are arranged. Alternatively, a configuration with one grid is also possible. Further, in the above embodiment, the vibrating mirror is used as the deflecting reflecting mirror for scanning the light beam, but the present invention is not limited to this, and it is also possible to use a mirror rotating in a fixed direction or a so-called polygon mirror. not.

〔The invention's effect〕

In the configuration of the present invention as described above, since the position of the scanning light beam on the object surface to be detected and the position of the second light beam for detecting the position of the deflecting reflecting mirror are optically equivalent positions, By detecting the position on the object surface to be detected based on the position information of the deflecting mirror by the two light beams, the scanning light beam can be moved to a predetermined position regardless of the scanning state of the position detection light beam and due to the fluctuation of the scanning member. Even when the state is different from the movement mode, it is possible to always perform stable and highly accurate object position detection and measurement.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing the overall configuration of an embodiment of the present invention,
FIG. 2 is an optical configuration diagram showing a state of light beam scanning by the deflecting / reflecting mirror, FIG. 3 is an optical perspective view showing the configuration of a focusing optical system for detecting the position of the deflecting / reflecting mirror, and FIG. FIG. 4B is an optical path diagram showing how the two light beams are scanned by the mirror, and FIG. 4B is a plan view showing how the second light beam is scanned on the grating plate in the focusing optical system for position detection of the deflecting mirror. FIG. 4C is a plan view showing the scanning state of the detection light beam on the reticle surface, FIG. 5 is a waveform diagram of various signals in the embodiment of the present invention, and FIG. 6 is a focusing for detecting the position of the deflecting mirror. FIG. 7 is a perspective view showing a structure using a diffraction grating in the optical system, and FIG. 7 shows a structure in which a cylindrical lens having a positive refracting power is arranged behind the grating plate in the condensing optical system for detecting the position of the deflecting reflecting mirror. It is a perspective view shown. [Explanation of symbols of main parts] 10,20 ...... Main optical system 2a ...... Deflecting reflection mirror (2 ...... scanning member) 2b ...... Rotator (2 ...... scanning member) 30 ...... Irradiation optical system 40 ...... Focusing optics

Claims (7)

[Claims] 1. A main optical system for converging a first light beam on an object plane, and a main optical system arranged in an optical path of the main optical system for scanning the first light beam on the object plane. In an optical scanning type position detecting device comprising a scanning member having a deflecting reflecting mirror for changing the traveling direction of a light beam, and a photoelectric detecting means for receiving reflected light from the object surface, the deflecting reflecting mirror is provided with A second light beam different from the first light beam is emitted, the second light beam reflected by the deflecting reflector is received, and a detection signal corresponding to the angular position of the deflecting reflector is output. Angular position detecting means; detection of photoelectric signals output from the photoelectric detecting means, which are output from the angular position detecting means in accordance with the scanning of the first light beam on the object plane by the deflecting mirror. Captured in synchronization with the signal, The optical-scanning position detecting device characterized by comprising an object position detection means for detecting a position of the object based on the signal. 2. The second light beam is reflected at substantially the same position on the same reflecting surface as the reflecting surface of the first light beam in the deflecting mirror. An optical scanning type position detection device according to claim 1. 3. The angular position detection means includes an irradiation optical system for irradiating the deflecting reflecting mirror with the second light beam through an optical path different from the optical path of the main optical system, and the deflecting reflecting mirror. The condensing optical system for condensing the condensed second light beam, and a photoelectric detector for detecting the position of the condensed second light beam. Or second
An optical scanning type position detection device described in the paragraph. 4. A plane including the optical axis of the irradiation optical system and the optical axis of the condensing optical system substantially coincides with the incident surface of the first optical beam of the main optical system on the deflective mirror. The optical scanning position detecting device according to claim 3, wherein the optical scanning position detecting device is configured as follows. 5. A distortion aberration amount of the condensing optical system is set to a value substantially equal to a distortion aberration amount of the main optical system on the object plane. Or the optical scanning type position detection device according to the fourth item. 6. The condensing optical system includes a condensing lens arranged so that a focal point substantially coincides with a rotation center of the deflective reflecting member, as claimed in any one of claims 3 to 5. An optical scanning type position detection device described in the paragraph. 7. The optical scanning type position according to claim 1, wherein the second light beam has a wavelength range different from that of the first light beam. Detection device.