JPH0290006A - Detecting method for positional displacement by diffraction grating and detecting apparatus therefor - Google Patents

Abstract

PURPOSE:To enable the detection of the amount of a positional displacement with high accuracy by generating first to third heterodyne interference beat signals from first to third diffraction gratings and by detecting a change in a phase difference among optical heterodyne interference beat signals. CONSTITUTION:Laser light from a two-wavelength orthogonal polarization laser light source 40 is separated into lights of two wavelengths of horizontal and vertical components by a polarized-beam splitter 42, and these lights are turned to the elliptic beams 46 and 50 through optical systems respectively and fall in the direction (z) on a diffraction grating 48 formed on a wafer 47 set on an xy stage 51. By three sets of diffraction gratings of the diffraction grating 48, three heterodyne interference synthetic diffracted lights 53 to 55 are obtained in the direction (z) respectively from the incident light 46 and 50. These synthetic diffracted lights 53 to 55 are divided in two directions by a half mirror 56, and those in one direction are observed by an eyepiece 70, while those in the other direction are inputted as optical heterodyne interference beat signals HY1 to HY3 to a signal processing unit 69 through photodetectors 66 to 68. Then, a change in a phase difference among the signals HY1 to HY3 is detected and the amount of a positional displacement can be detected from the change in the phase difference.

Description

DETAILED DESCRIPTION OF THE INVENTION C. Industrial Application Field] The present invention uses a diffraction grating as a sub-length standard, and uses the phase of a heat signal obtained by optical heterodyne interference of diffracted light to determine the relative relationship between the diffraction gratings. A positional deviation detection method and a positional deviation detection device used to detect the amount of positional deviation, for example, to measure the alignment accuracy between buttons formed in an exposure apparatus for manufacturing semiconductor ICs and LSIs, and a positional deviation detection device. It is related to.

[Prior art/problems to be solved by the invention] Conventionally, the method of measuring this type of positional deviation is to first burn the measurement button and measure the deviation between the buttons using a button line width measuring device. The second is the vernier method, which prints grids with different pitches on the integrated circuit and reads the exact part of the grid, and the third is the long and narrow resistor on the integrated circuit? I! There is a method of overlapping the pole with °C and comparing the valley value of the resistor, and a fourth method is to print a diffraction grating on an integrated circuit and measure the shift of the batten by the phase difference of the diffracted light. .

However, according to the method using the first batan line width measuring device, the accuracy of that type of device is usually at most 0.01.
There is a problem in that an accuracy of only about 1 jm can be obtained, and even with the second vernier method, an accuracy of only 0.04 um can be obtained. Furthermore, while the third resistance measurement method provides accuracy, it also requires a fairly complex process to perform the measurement.

On the other hand, the fourth method is a method that has been proposed as a simple and inexpensive method, taking into consideration the problems 2-3. Fig. 4 shows an example of a device that measures the amount of positional deviation using such a phase difference signal (published patent in 1982).
-56818).

In the figure, a wafer 2 to be detected is placed on a stage 1. The Ueno\2 has been printed and developed twice by the exposure device, and the exposure button formed on the mask or reticle L of the exposure device is overprinted on the surface of the Ueno\2. When two exposure stamps are printed on the wafer 2, a diffraction grating MI) consisting of two sets of diffraction gratings as shown in FIG. 5 representing the first burnt position of the exposure stamp is formed. first diffraction grating M
AI and M2 are lattice elements that are printed together with the exposure button during the first exposure process, are formed at a distance d from each other in the y-axis direction, and extend in the X-axis direction. They are formed at predetermined intervals.

By multiplying this by χ・1, the second diffraction grating MI31 and MB2
are formed in the same way in the y-axis direction at positions separated by a distance of d.
It consists of i grating elements extending in the X-axis direction and is printed so as to be inserted alternately between the first diffraction gratings MAI and MΔ2 in the y-axis direction.

Here, if there is no positional deviation between the first diffraction gratings MA1, MΔ2 and the second diffraction gratings MBI, MB2 in the y-axis direction, each grating element of the first diffraction gratings MAI, MA2 and the second diffraction grating Diffraction grating MBI, MB2? q grating elements are formed so as to be aligned on the same straight line in the X-axis direction, and in this case, it can be determined that there is no positional shift between the first and second exposure buttons.

On the other hand, if the positions of the first and second exposure buttons are shifted from each other by Δy in the y-axis direction, this positional shift is caused by the diffraction grating MΔ1. The positional deviation between the corresponding grid elements of MA2, MBI, and MI32 is made to appear as Δy.
There is C.

Therefore, in the diffraction grating MP having the configuration shown in FIG.
The reflection direction of the first order light LFI of the first coherent light LL1 generated by the diffraction grating MP and the first order light LF of the second coherent light LL2
The reflection direction of the wafer 2 is selected to coincide with the direction of reflection of the wafer 2, and the direction is selected to be approximately perpendicular to the surface 1 of the wafer 2.

Here, two coherent beams of light with different frequencies,
L L and LL2 are two ultrasound modulators 14.1
Generated by 8. That is, the laser tip generated by the laser 11 is collimated with the collimator lens system 12A, 1
The beam passes through 2B and enters a beam splitter 13. The shunt i3 divides the laser beam into two and modulates the first laser beam with the ultrasonic modulator 14 as a signal 31 (see FIG. 6).

The modulation signal Sl is electrically generated by the oscillator 34,378L and the frequency conversion circuit 38. ), the frequency is shift-modulated by the frequency f1, and then the mirror +5.
Diffraction grating MPJ of wafer 2 is bent by 16
Second, it is irradiated as a first coherent light beam L1,1.

Further, the shunt device 13 inputs the second laser beam into the ultrasonic modulator 18 via the mirror 17, and inputs the modulated signal S2 (sixth
See diagram. Modulated signal S2 is a signal obtained by transmitter 37. ), the second coherent light beam L is transmitted onto the diffraction grating MP of the Ueno 12 while being bent by the mirror 19.20.
Light q4 as L2.

(The diffracted light LFI generated by the diffraction grating MP
and LF2 interfere with each other and pass through the objective lens 3, the aperture 4, and further) -- the charge conversion element array 6 through the humeror 5.
incident on . The nof mirror 5 is configured to return the diffracted light that has passed through the aperture 4 to the eyepiece 7 so that interference fringes can be observed. The photoelectric conversion element row 6 converts the interference light of the diffracted light into photoelectric conversion elements DAI, DΔ2, and DΔ2 corresponding to the respective elements MAl, MA2, MBI, and MB2 of the diffraction grating MP.
Four heat signals S A, l, SA2.5I31, S with frequency Δf (=llf2) detected by DBI and DB2
B2 is generated, and these four heat signals are sent to the positional deviation detection control circuit 25.

FIG. 6 shows a detailed configuration diagram of the positional deviation detection control circuit 25. In the positional deviation detection control circuit 25, the heat signal SAl,
The phases of SA2, SBI, and SB2 are changed to PLL direction paths 32A and 3.
Phase output SFA%S of frequency Δf (-10) with phase locking and noise removed at 2B, 32G, and 32D, respectively
FB, SFC,.

Get SFD. This phase output SFA, 5FBSSFC,
The phase of the SFD and the phase of the reference frequency output SO obtained from the oscillator 34 are detected by phase difference detection circuits 33A, 33B, 33.
C133D, and the positional deviation calculation circuit 35 calculates the positional deviation amount Δy based on the phase differences α, β, γ, and δ, respectively.
is calculated by the following equation 3 (%), and the misaligned jet is displayed on the display device 36. Here, d represents the pitch of the diffraction grating MP.

However, in the fourth method, since the phase difference is determined using a reference signal generated by an electronic circuit, the effects of minute fluctuations in the detection optical system and fluctuations in the temperature and atmospheric pressure of the air atmosphere in the optical path system may be affected. The phase difference signal fluctuates, which causes an error in the amount of positional deviation.

In addition, in the method of eliminating the influence of the inclination between the optical system and the diffraction grating using equation (1) above, in addition to the instability of the four electronic circuit systems that detect the phase difference, calculation errors due to differences in the circuit characteristics between the four electronic circuit systems are eliminated. This poses a problem in that it is difficult to detect positional deviations with high accuracy.

SUMMARY OF THE INVENTION In order to eliminate the above-mentioned drawbacks, an object of the present invention is to use a first and second diffraction grating as a measurement standard, and form a second diffraction grating for measuring the amount of positional deviation with respect to the diffraction grating. , applying monochromatic light of two wavelengths whose frequencies are slightly different from each other to the first, second, and third diffraction gratings;
The diffracted light generated from the diffraction grating is subjected to optical heterodyne interference to generate first, second and third optical heterodyne interference heat signals from the first, second and third diffraction gratings, respectively. By measuring the positional deviation between the first, second, and third diffraction gratings by detecting the phase difference change between the second and third heterodyne interference heat signals, Rather, it is an object of the present invention to provide a positional deviation detection method and a positional deviation detection device using a diffraction grating that are highly stable and highly accurate.

[Means to solve the problem]

The positional deviation detection method of the present invention uses the first and second diffraction gratings as measurement standards, forms a third diffraction grating for measuring the amount of positional deviation with respect to the diffraction gratings, and uses the first and second diffraction gratings as measurement standards. Measure the misalignment between the first, second, and third gratings by detecting the phase difference change between the first, second, and third optical heterodyne interference heat signals respectively resulting from the The diffraction grating is characterized by using the phase difference between the first and second optical heterodyne interference heat signals as a reference value, and the phase difference between the second and third optical heterodyne interference heat signals. It has the feature of being able to detect relative positional misalignment jets between the two.

Further, the positional deviation detection device of the present invention includes first and second diffraction gratings fixed or formed on an object, and a third diffraction grating fixed or formed in alignment with the diffraction grating. a light source that generates monochromatic light of two wavelengths whose frequencies are slightly different from each other; and an input means that makes the monochromatic light of two wavelengths enter the first, second, and third diffraction gratings. A7I No. 1-1 The two lengths of diffracted light generated from the second and third diffraction gratings are synthesized, and the first, second, and third light heterotine interference heat signals are generated from the diffraction gratings, respectively. From the device configuration of a photosynthesis detection means to generate and a signal processing device that calculates and processes a phase difference signal between the first, second, and third pre-heterodyne interference heat signals generated by the photosynthesis detection means, the first ,second,
It also has the feature of being able to measure the amount of positional deviation between the third diffraction grating.

In the present invention, the relative positional deviation m between the reference diffraction grating and the measurement diffraction grating is determined by the difference between the phase difference between the reference diffraction grating and the phase difference between the measurement diffraction grating. The purpose of this test is to measure the overlay accuracy between battens formed in an exposure device or the like. Therefore, in the present invention, since the heat signal serving as the measurement standard is generated by the same optical system as the heat signal used to measure the amount of relative positional deviation,
The effects of minute fluctuations in the detection optical system and fluctuations in air temperature, atmospheric pressure, etc. in the optical path system can be removed, and the amount of relative positional deviation can be detected with high stability and accuracy.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to FIGS. 1 to 3. Note that the same reference numerals as in FIGS. 4 to 6 indicate the same members.

FIG. 1 shows an embodiment of a positional deviation detection device according to the present invention. In FIG. 1, a laser beam emitted from a two-wavelength orthogonally polarized laser light source 40 is transmitted through a mirror 41 and a polarizing beam splitter 42 into a horizontal component (p-polarized component) or a vertical component (s-polarized component), respectively. Linearly polarized light with slightly different frequencies 2
The light is separated into different wavelengths. Of these, the p-polarized light component passes through a mirror 43 and becomes an elliptical beam 46 by an optical system consisting of a cylindrical lens 44 and an objective lens 45, and is transmitted to a diffraction grating 46 formed on a wafer 47 placed on an Xy stage 51F.
8 is incident from the direction of the first-order diffraction angle with respect to the normal direction (7, direction) perpendicular to the diffraction grating surface. On the other hand, the S (a light component) is similarly turned into an elliptical beam 50 by an optical system consisting of a cylindrical lens 49 and a λI object lens 15, and is elliptical in the normal direction (Z direction) perpendicular to the diffraction grating surface. The light enters the diffraction grating 48 from the direction of the first-order diffraction angle that is symmetrical to the beam 46 .

As shown in FIG. 2, the diffraction grating 48 is
This is a baton formed by multiple printing and development processes.

That is, on the wafer 47, two types of exposure buttons formed on masks or reticles of two exposure apparatuses are printed in an overlapping manner. When two types of exposure button are printed, the printing of the exposure button is 3 as shown in Fig. 2 which shows the position.
A diffraction grating consisting of a set of diffraction gratings is formed. The first diffraction gratings HDI and HD2 are grating elements that are printed together with the exposure button during the first exposure process, are formed at a distance d apart from each other in the y-axis direction, and extend in the X-axis direction, They are formed at predetermined intervals in the X direction.

On the other hand, the third diffraction grating HD 3 is similarly formed at a distance of 111d from each other in the y-axis direction by the second overlapping exposure process, and the third diffraction grating HD 3 is formed at a distance of 111d from each other in the y-axis direction. For HDI and second diffraction grating HD2,
They are formed at predetermined intervals in the X direction.

Here, if there is no positional deviation between the first diffraction grating HDl, the second diffraction grating HD2, and the third diffraction grating HD3 in the y-axis direction, the eleventh and second diffraction gratings i (D I, HD 2 grating elements and the third diffraction grating I (D 3 grating element) are formed four times on the same straight line in the X-axis direction. It can be determined that there is no positional deviation in the first and second exposure slams.On the other hand, if the positions of the first and second exposure taps deviate from each other by Δy in the y-axis direction, this positional deviation is caused by the diffraction grating HD l. , it appears as a positional deviation Δy between corresponding grid elements of HD2 and HD3.

The three diffraction gratings MDI, HD2, HD3 are arranged in the same elliptical beam spot 52 for each of the two wavelengths of incident light 46.50. Furthermore, the diffraction grating pitches d are set equal to each other.

Person Q, I light 46.50, three diffraction gratings HDl,
[(Synthesized diffracted light of three two-wavelength first-order diffracted lights in the Z direction from D2 and HD3, that is, the first diffraction grating HD
An optical heterodyne interference synthesis diffraction light 53 of the 1st-order diffracted light of the incident light 46 due to 1 and the 1st-order diffracted light of the incident light 50;
Optical heterodyne interference composite diffracted light 54 similarly obtained in the Z direction from the second diffraction grating fl D 2 and optical heterodyne interference composite diffracted light 55 similarly obtained in the Z direction from the third diffraction grating HD 3 are obtained. . Three combined lights 53.5
4.55 is divided into two directions by a half mirror 56, and one side is separated by a prismatic mirror 57, 58, 59, and condensing lenses 60.6I, 62, 62,
Optical heterodyne interference heat signals HYI, HY2 are detected by photodetectors 66.68 through polarizing plates 63, 64, 65.
, HY3 are input to the signal processing control unit 69. The other half divided by the half mirror 56 is the eyepiece 7.
0 so that diffracted light can be observed.

In the signal processing control section 69, the first and second diffraction gratings HDI
, optical heterodyne interference heat signal H obtained from HD2
Regarding YI and HY2, phase difference Δ of HY2 with respect to HYI
φ0 and the third diffraction grating! - Regarding the optical heterodyne interference heat signals HY3 and HY2 obtained from ID3)
The phase difference Δφ corresponding to the positional deviation claw Δy between the diffraction grating HI) l and HD 2 and HD 3 is obtained from the following equation.

Δφ=ΔφY−Δφ〇−2π・2・Δy/d (2) Here, ΔφO is the positional deviation detection optical system and the diffraction grating HDI, HD
This is the phase difference caused by the rotational shift in the xy plane between HD 2 and HD 3. In other words, the positional deviation detection optical system is originally
The reference diffraction gratings 7I, 72, 73, which are formed so that the grating elements are aligned on the same straight line as shown in Figure (a), are set on the xy stage so that the direction of the grating elements is parallel to the X axis. The reference line of the optical system is set to match the center line of the grating element of the diffraction grating when the long axis direction of the two overlapping incident elliptical beams of the optical system is used as the reference line of the optical system. It is assumed that there is Therefore,
If the direction of the grating elements of the diffraction grating is set parallel to the X-axis, ΔφO−0 is obtained in the above equation (2). In addition, as shown in Figure 3(b), if the direction of the grating elements of the diffraction grating is shifted from the direction of the There is also a phase difference Δφ between HYl and HY2 between the first diffraction grating HDI and the second diffraction grating HD2 that are lined up.
yields 0. Therefore, the optical heterodyne interference heat signal H
For Y3 and 11Y2, (i(Y 3
It is necessary to subtract the error amount Δφ0 caused by the rotational deviation from the phase difference ΔφY. The signal processing control unit 69 performs the above (2)
) It is easy to obtain Δy from the equation and display the value in a display book.

In the above example, a two-wavelength orthogonally polarized laser light source was used as the two-wavelength monochromatic light source, but the same could be done using light generated using an acousto-optic device such as a Bragg cell as the two-wavelength monochromatic light. effect can be obtained.

In this case, by combining an acousto-optic element and a semiconductor laser, it is possible to make the two-wavelength medium chromatic light source compact.

Furthermore, it is possible to separate the main body of the movable claw detection optical system and the 2-wavelength i4i chromatic light source by using an optical fiber such as a polarization-maintaining optical fiber in the input optical system for the 2-wavelength laser beam, and to couple the two with the optical fiber. By applying this technology, it is possible to further downsize the position detection optical system.

In addition, we have explained an example in which the direction of the incident light to the diffraction grating and the direction of the diffracted light from the diffraction grating include the yz plane perpendicular to the diffraction grating plane. As the direction of the diffracted light from the grating, the diffracted light of two wavelengths, which are obliquely incident 44 and obliquely out, which are not included in the yz plane perpendicular to the diffraction grating plane, are optically combined to detect an optical heterodyne interference heat signal. The same effect can be obtained even if

Furthermore, as the diffraction grating in the present invention, either an absorption type diffraction grating or a phase 'X2@ diffraction grating may be used.
It is possible to use various types of diffraction m+ such as a phrase diffraction grating, and it is also possible to use an anti-qJ type diffraction grating in addition to a transmission type diffraction grating.

Furthermore, in the above embodiment, a diffraction grating in which the grating elements are arranged parallel to the y-axis direction is used, but a similar diffraction grating can also be formed in the y-axis direction perpendicular to the y-axis. It is also possible to set the optical system in two directions of x and y so that positional deviation lightning ΔX and Δy in two directions of , x and y can be detected.

In this case, in addition to the diffraction grating used in the above embodiment, a checkered diffraction grating may be used for both x and y directions.

〔Effect of the invention〕

As explained in detail in Section 2, according to the present invention, a pair of first and second diffraction gratings are provided as a reference, and a third diffraction grating for positional deviation @ measurement is set, and these diffraction gratings are Two wavelengths of rBt color light with slightly different frequencies are incident, and from the three optical heterodyne interference lights generated from these diffraction gratings, the optical heterodyne interference heat signals obtained from the first and first diffraction grating pairs, which serve as a reference. The phase difference between the second and third optical heterodyne interference heat signals is used as a reference value, and the relative positional deviation between the diffraction gratings is detected based on the difference between the phase difference between the second and third optical heterodyne interference heat signals. It is possible to eliminate the influence of fluctuations in the temperature, atmospheric pressure, etc. of the air in the system, and it is possible to detect the amount of relative positional deviation with high stability and accuracy.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a positional deviation detection device shown in one embodiment of the present invention, FIG. 2 is a diagram showing the detailed configuration of the diffraction grating 18 in FIG. 1, and FIG. b) is another diagram showing the detailed configuration of the diffraction grating 48 in FIG. 1, FIG. 4 is a configuration diagram of a conventional positional deviation detection device, and FIG. 5 is a diagram showing the diffraction grating MP in FIG. 4.
FIG. 6 is a block diagram showing the detailed configuration of the positional deviation detection control circuit 25 of FIG. 4. Figure 2 40...2 wavelengths orthogonal (1!Unit laser light source 1.11.4
3...Mirror, 42...Polarizing beam splitter-54
4゜49...Cylindrical lens, 45...χ・1 object lens,
46, 50... Elliptical incident beam, 47... Wafer, 48... Diffraction grating, 51... XY stage, 52
... Elliptical beam spot, 53.54.55 ... Optical heterodyne interference combined diffraction light, 56 ... Half mirror
157,58°59...Prismatic mirror, 60.6
1.62... Condensing lens, 63.64.65... Polarizing plate, 66.67.68... Photodetector, 69... Signal processing control unit, 70... Eyepiece, 71 .72.73・
・Reference diffraction grating. Figure 3'0) η Button diagram

Claims (2)

[Claims] (1) Using the first and second diffraction gratings fixed or formed on the object as measurement standards, align with the diffraction gratings to form a third diffraction grating, and one,
Monochromatic light of two wavelengths whose frequencies are slightly different from each other is made incident on the second and third diffraction gratings, and the diffracted light generated from the diffraction gratings is caused to undergo optical heterodyne interference. by generating first, second, and third optical heterodyne interference heat signals from the diffraction grating, respectively, and detecting a phase difference change between these first, second, and third optical heterodyne interference heat signals; first,
A method for detecting positional deviation using a diffraction grating, the method comprising measuring the amount of positional deviation between second and third diffraction gratings. (2) The first and second diffraction gratings fixed or formed on the object, and the third diffraction grating fixed or formed aligned with the diffraction grating, have frequencies that are different from each other. a light source that generates monochromatic light with two slightly different wavelengths; an input means that causes the monochromatic light of the two wavelengths emitted from the light source to enter the first, second, and third diffraction gratings;
photosynthesis detection means for combining two wavelengths of diffracted light generated from second and third diffraction gratings and generating first, second, and third optical heterodyne interference heat signals from the diffraction gratings; and photosynthesis detection means; calculating and processing a phase difference signal between the first, second, and third optical heterodyne interference heat signals generated by the means to determine the amount of positional shift between the first, second, and third diffraction gratings; 1. A positional deviation detection device using a diffraction grating, comprising a signal processing device for measurement.