JP2514699B2 - Position shift detection method and position shift detection device using diffraction grating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention uses a diffraction grating as a length measuring standard, and a relative phase between the diffraction gratings by the phase of a beat signal obtained by interfering diffracted light with optical heterodyne. Related to a positional deviation detecting method and a positional deviation detecting device used for measuring the overlay accuracy between patterns formed in an exposure apparatus or the like for manufacturing a semiconductor IC or LSI Is.

[Problems to be solved by conventional techniques and inventions]

Conventionally, as a method for measuring this kind of positional deviation, there is a method of first baking the measurement pattern and measuring the mutual deviation of the patterns with a pattern line width measuring device, and secondly, using a grid having a different pitch. Vernier method of reading the portion of the grid that exactly burns on the integrated circuit, and thirdly, a method of forming a long and narrow resistor and electrode on the integrated circuit and comparing each value of the resistor, Fourth, there is a method in which a diffraction grating is printed on an integrated circuit and the amount of pattern deviation is measured by the phase difference of diffracted light.

However, according to the method using the first pattern line width measuring device, the accuracy of such a device is usually 0.01 μ at most.
There is a problem that only an accuracy of about m can be obtained, and even the second vernier method can only obtain an accuracy of about 0.04 μm. Further, the third resistance measuring method has accuracy, but has a problem that a considerably complicated processing step is required for the measurement.

On the other hand, the fourth method is a method proposed as a simple and inexpensive method in consideration of the above first to third problems. FIG. 4 shows an example of an apparatus for measuring the amount of positional deviation using such a phase difference signal (Japanese Patent Laid-Open No. 62-56).
818).

In the figure, a wafer 2 to be detected is placed on a stage 1.
Is placed. The wafer 2 has been baked and developed twice by the exposure device, and the exposure pattern thus formed on the mask or reticle of the exposure device is overprinted on the surface of the wafer 2. When two exposure patterns are printed on the wafer 2, a diffraction grating MP composed of two sets of diffraction gratings as shown in FIG. 5 showing the printing positions of the exposure patterns is formed. The first diffraction gratings MA1 and MA2 are baked together with the exposure pattern during the first exposure process,
The grid elements are formed at positions separated from each other by a distance d in the y-axis direction and extend in the x-axis direction, and are formed at predetermined intervals in the x-direction.

On the other hand, the second diffraction gratings MB1 and MB2 are similarly formed by the second overlay exposure process at positions separated from each other by a distance d in the y-axis direction and extend in the x-axis direction. And is baked so as to be inserted alternately between the first diffraction gratings MA1 and MA2 in the y-axis direction.

Here, if there is no misalignment between the first diffraction gratings MA1 and MA2 and the second diffraction gratings MB1 and MB2 in the y-axis direction, each grating element of the first diffraction gratings MA1 and MA2 and the second diffraction gratings MA1 and MA2 The diffraction gratings MB1 and MB2 are formed so as to be aligned with the respective grating elements on the same straight line in the x-axis direction. At this time, it can be determined that the first and second exposure patterns are not displaced. On the other hand, if the positions of the first and second exposure patterns deviate from each other by Δy in the y-axis direction, this misregistration causes the diffraction gratings MA1, MA2, and MB.
1 and MB2 appear as positional deviation Δy between corresponding lattice elements.

Therefore, the first-order diffracted light LF1 of the first coherent light LL1 generated by the diffraction grating MP is emitted by irradiating the diffraction grating MP having the configuration shown in FIG. 5 with two coherent light beams LL1 and LL2 having different frequencies. Of the first coherent light LL2 and the reflection direction of the first-order diffracted light LF2 of the second coherent light LL2 are selected to coincide with each other, and the direction is substantially vertical to the surface of the wafer 2.

Here, the two coherent light fluxes LL1 and LL2 having different frequencies are generated by the two ultrasonic modulators 14 and 18. That is, the laser light generated by the laser 11 is incident on the shunt (beam splitter) 13 through the collimator lens systems 12A and 12B. The shunt 13 divides the laser into two and modulates the first laser light by the ultrasonic modulator 14 with a modulation signal S1 (see FIG. 6. The modulation signal S1 is the oscillator 3).
Electrically generated by 4, 37 and the frequency conversion circuit 38. ), The frequency is shifted and modulated by the frequency f1, and then the wafer 2 is bent by the mirrors 15 and 16.
The diffraction grating MP is irradiated with the first coherent light beam LL1.

Further, the shunt device 13 causes the second laser light to enter the ultrasonic modulator 18 via the mirror 17, and a modulation signal S2 (see FIG. 6; the modulation signal S2 is a signal obtained by the oscillator 37). After shift-modulating the frequency by the frequency f2 by
While being bent by the mirrors 19 and 20, the diffraction grating MP of the wafer 2 is irradiated with the second coherent light beam LL2.

Thus, the diffracted lights LF1 and LF2 generated by the diffraction grating MP interfere with each other and pass through the objective lens 3 and the diaphragm 4,
Further, the light enters the photoelectric conversion element array 6 through the half mirror 5. The half mirror 5 is configured to be able to return the diffracted light that has passed through the diaphragm 4 to the eyepiece 7 and observe interference fringes. The photoelectric conversion element array 6 includes each element MA of the diffraction grating MP.
Corresponding to 1, MA2, MB1 and MB2, the interference light of the diffracted light is detected by photoelectric conversion elements DA1, DA2, DB1 and DB2 respectively, and the frequency Δf
Four beat signals SA1, SA2, SB1 and SB2 of (= f1−f2) are generated, and these four beat 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 position shift detection control circuit 25, the beat signals SA1 and SA
The frequency Δf (= f where noise is eliminated by phase-locking the phases of 2, SB1 and SB2 with PLL circuits 32A, 32B, 32C and 32D, respectively.
0) Phase outputs SFA, SFB, SFC, SFD are obtained. This phase output SFA, SFB, SFC, the phase of the SFD and the phase of the reference frequency output S0 obtained from the oscillator 34 phase difference detection circuit 33A, 33B,
33C and 33D, and based on the phase differences α, β, γ, and δ, the positional deviation calculation circuit 35 calculates the positional deviation amount Δy by the following expression Δy = (d / (4π)) · ((3β−3γ− α + δ) / 4)
The calculation is performed according to (1), and the amount of positional deviation 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 obtained by using the reference signal generated by the electronic circuit, the influence of the minute fluctuation of the detection optical system, the temperature of the air atmosphere of the optical path system, the fluctuation of the atmospheric pressure and the like. Therefore, the phase difference signal fluctuates, which causes an error in the position shift amount. Further, in the method of eliminating the influence of the tilt between the optical system and the diffraction grating by the above formula (1), in addition to the instability of the four electronic circuit systems for detecting the phase difference, the calculation error due to the difference in the mutual circuit characteristics is caused. There is a problem in that it is easy to include and it is difficult to detect the positional deviation with high accuracy.

The object of the present invention is to eliminate the above-mentioned drawbacks, firstly,
And the second diffraction grating is used as a measurement standard, and a third diffraction grating for measuring the amount of positional deviation is formed with respect to the diffraction grating, and the first, second, and third diffraction gratings have a frequency Enter monochromatic light of two wavelengths slightly different from each other, and diffracted light generated from the diffraction grating causes optical heterodyne interference,
Generating first, second, and third optical heterodyne interference beat signals from the first, second, and third diffraction gratings, respectively, and generating first, second, and third optical heterodyne interference beat signals. By measuring the amount of positional deviation between the first, second, and third diffraction gratings by detecting the change in the phase difference between the signals, the diffraction that is more stable and more accurate than the conventional one. It is an object of the present invention to provide a positional deviation detection method and a positional deviation detection device using a grid.

[Means for solving the problem]

The position deviation detecting method of the present invention uses the first and second diffraction gratings as a measurement reference scale, forms a third diffraction grating for measuring the position deviation amount with respect to the diffraction grating, and Measuring the amount of misalignment between the first, second, and third diffraction gratings by detecting the resulting phase difference changes between the first, second, and third optical heterodyne interference beat signals. The phase difference between the first and second optical heterodyne interference beat signals is used as a reference value, and the relative difference between the diffraction gratings is determined by the difference between the phase difference between the second and third optical heterodyne interference beat signals. There is a feature that the amount of displacement can be detected.

Further, the position shift detection device of the present invention is fixed on an object,
Alternatively, the first and second diffraction gratings formed and the third diffraction grating that is aligned with and fixed to the diffraction grating, or the third diffraction grating that is formed are provided, and the frequencies are slightly different from each other. A light source for generating monochromatic light of two wavelengths, an incidence means for injecting monochromatic light of two wavelengths into the first, second and third diffraction gratings, and the first, second and third diffraction gratings From the diffraction grating to generate first, second, and third optical heterodyne interference beat signals, respectively, and the first generated by the optical synthesis detection means. From the device configuration of the signal processing device that calculates and processes the phase difference signal between the second and third optical heterodyne interference beam signals, measure the amount of positional deviation between the first, second, and third diffraction gratings. There is a feature that can be done.

The present invention is intended to manufacture a semiconductor IC or LSI, which is a relative positional deviation amount between the reference diffraction grating and the measurement diffraction grating due to the difference between the phase difference between the reference diffraction grating and the measurement diffraction grating. The overlay accuracy between the patterns formed in the exposure apparatus or the like is measured. Therefore, in the present invention, since the beat signal serving as the measurement reference is generated by the same optical system as the beam signal for measuring the relative positional deviation amount, a small fluctuation of the detection optical system, the temperature of the air in the optical path system, the atmospheric pressure, etc. The influence of fluctuation can be eliminated, and the relative displacement amount can be detected with high stability and high accuracy.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 3. The same reference numerals as those in FIGS. 4 to 6 denote the same members.

FIG. 1 shows an embodiment of the positional deviation detecting device according to the present invention. In FIG. 1, the laser light emitted from the two-wavelength orthogonal polarization laser light source 40 passes through a mirror 41 and a polarization beam splitter 42 to generate only a horizontal component (p-polarized component) or a vertical component (s-polarized component). It is split into two linearly polarized lights having two different wavelengths. Of these, the p-polarized component is the mirror 43
An elliptical beam 46 is formed by an optical system composed of a cylindrical lens 44 and an objective lens 45 via, and a normal direction perpendicular to the diffraction grating surface (a direction normal to a diffraction grating surface 48 is formed on a diffraction grating 48 formed on a wafer 47 placed on an xy stage 51. It is incident from the direction of the first-order diffraction angle with respect to the z direction). On the other hand, similarly, the s-polarized component becomes an elliptical beam 50 by the optical system including the cylindrical lens 49 and the objective lens 45, and is symmetrical with the elliptical beam 46 with respect to the normal direction (Z direction) perpendicular to the diffraction grating surface. From the direction of the first-order diffraction angle of the diffraction grating 48
Incident on.

As shown in FIG. 2, the diffraction grating 48 is provided by the exposure device.
It is a pattern formed by a single baking and development process.
That is, the wafer 47 is overlaid with two types of exposure patterns formed on the masks or reticles of two exposure apparatuses. When two types of exposure patterns are printed, a diffraction grating composed of three sets of diffraction gratings as shown in FIG. 2 showing the printing positions of the exposure patterns is formed. The first diffraction gratings HD1 and HD2 are grating elements that are baked together with the exposure pattern during the first exposure process, are formed at positions separated from each other by a distance d in the y-axis direction, and extend in the x-axis direction, It is formed at a predetermined interval in the x direction.

On the other hand, the third diffraction grating HD3 is similarly formed at the positions separated from each other by the distance d in the y-axis direction by the second overlay exposure processing, and the first diffraction grating HD1 is formed in the y-axis direction. And the second diffraction grating HD2 are formed at a predetermined interval in the x direction.

Here, in the y-axis direction, if there is no displacement between the first diffraction grating HD1 and the second diffraction grating HD2 and the third diffraction grating HD3, the first and second diffraction gratings HD1 , H
Each grating element of D2 and the grating element of the third diffraction grating HD3 are formed so as to be aligned on the same straight line in the x-axis direction. At this time, if the first and second exposure patterns are not misaligned. You can judge. On the other hand, if the positions of the first and second exposure patterns deviate from each other by Δy in the y-axis direction, this positional deviation is regarded as the positional deviation Δy between the corresponding grating elements of the diffraction gratings HD1, HD2 and HD3. It is designed to appear.

The three diffraction gratings HD1, HD2, and HD3 have two wavelengths for each incident light 4
6 and 50 are arranged in the same elliptical beam spot 52. The diffraction grating pitch d is set to be equal to each other.

Three diffraction gratings HD1, HD2, HD3 due to incident light 46, 50
From each of the three diffracted lights of the first-order diffracted lights of two wavelengths in the Z direction, that is, the incident light 46 by the first diffraction grating HD1
Optical heterodyne interference combined diffracted light 53 of the first-order diffracted light and the minus first-order diffracted light of the incident light 50, and optical heterodyne interference combined diffracted light 54 similarly obtained in the Z direction from the second diffraction grating HD2.
And optical heterodyne or interference-formed diffracted light 55 which is also obtained in the Z direction from the third diffraction grating HD3. The three combined lights 53, 54, 55 are divided and exposed in two directions by the half mirror 56, and one of them is separated by the prism-shaped mirrors 57, 58, 59, and the condensing lenses 60, 61, 62, and the polarized light, respectively. Board 6
It is detected by the photodetectors 66 and 68 via 3, 64 and 65, and is input to the signal processing control unit 69 as optical heterodyne interference beat signals HY1, HY2 and HY3. The other one divided by the half mirror 56 is configured so that the diffracted light can be observed by the eyepiece 70.

In the signal processing control unit 69, the first and second diffraction gratings HD1 and H
Optical heterodyne interference beat signals HY1 and HY2 obtained from D2
About HY1, the phase difference ΔφO of HY2 and the optical heterodyne interference beat signal HY3 obtained from the third diffraction grating HD3
And HY2, the phase difference Δφ corresponding to the positional deviation amount Δy between the diffraction gratings HD1, HD2 and HD3 is calculated from the phase difference ΔφY of HY3 with respect to HY2 by the following formula.

Δφ = ΔφY−ΔφO = 2π · 2 · Δy / d (2) where Δφ0 is the displacement detection optical system and the diffraction grating HD
It is the phase difference caused by the rotational shift of the xy plane from 1, HD2, and HD3. That is, the misregistration detection optical system originally has the reference diffraction gratings 71, 72, 73 formed so that the respective grating elements are arranged on the same straight line as shown in FIG. Adjusting the direction so that it is parallel to the x-axis, and the major axis direction of the two overlapping elliptical beams of the optical system being the reference line of the optical system, the reference line of the optical system and the grating element of the diffraction grating The center line of is set to match. Therefore, if the direction of the grating element of the diffraction grating is set parallel to the x-axis, then ΔφO = 0 in the above equation (2). Further, as shown in FIG. 3B, when the direction of the grating element of the diffraction grating is deviated from the direction of the x-axis, the directions of the grating element of the diffraction grating are completely coincident with each other and are aligned on a straight line. A phase difference ΔφO is also generated between HY1 and HY2 between the first diffraction grating HD1 and the second diffraction grating HD2 which are lined up. Therefore, for the optical heterodyne interference beat signals HY3 and HY2, it is necessary to subtract the error ΔφO caused by the rotation deviation from the phase difference ΔφY of HY3 with respect to HY2. The signal processing control unit 69 can easily find Δy from the above equation (2) and display the value.

In the above embodiment, the two-wavelength orthogonal polarization laser light source is used as the two-wavelength monochromatic light source, but the same is true even if light generated using an acousto-optic device such as a Bragg cell is used as the two-wavelength monochromatic light. The effect of can be obtained. In this case, the dual wavelength monochromatic light source can be made compact by combining the acoustooptic device and the semiconductor laser. Furthermore, by using an optical fiber such as a polarization-preserving optical fiber for the incident optical system of the two-wavelength laser light, the movement amount detection optical system main body and the two-wavelength monochromatic light source are separated, and the technology of connecting both with an optical fiber is applied. By doing so, the position detection optical system can be made more compact.

Also, an example has been described in which the direction of the incident light to the diffraction grating and the direction of the diffracted light from the diffraction grating are included in the yz plane that is perpendicular to the diffraction grating surface, but the direction of the incident light to the diffraction grating and the diffraction grating As for the direction of the diffracted light from, the optical heterodyne interference beat signal is detected by optically combining the diffracted light of two wavelengths, that is, the oblique incidence and the oblique emission, which are not included in the yz plane perpendicular to the diffraction grating surface. Can also obtain the same effect.

Furthermore, as the diffraction grating in the present invention, either an absorption type diffraction grating or a phase type diffraction grating may be used,
In addition to the binary diffraction grating, various diffraction gratings such as a sinusoidal diffraction grating and a phrase diffraction grating can be used, and a reflection type diffraction grating can be used as the diffraction grating in addition to the transmission type.

Furthermore, in the above-described embodiment, the diffraction grating having the grating elements arranged in parallel to the x-axis direction is used, but a similar diffraction grating is formed in the y-axis direction perpendicular to the x-axis. , X, y, the optical system can be set in the two directions of x and y so that the positional deviation amounts Δx and Δy in the two directions of x, y can be detected. In this case, in addition to the diffraction grating of the above-mentioned embodiment, a checkered diffraction grating can be used for both the x and y directions.

〔The invention's effect〕

As described in detail above, according to the present invention, the first and second diffraction grating pairs serving as the reference are provided, and the third diffraction grating for measuring the positional deviation amount is set, and the frequency is set to these diffraction gratings. The phase difference between the optical heterodyne interference beam signals obtained from the first and second diffraction grating pairs, which are the reference from the three optical heterodyne interference lights generated from these diffraction gratings by injecting monochromatic lights of slightly different two wavelengths. Is used as a reference value, and by detecting the relative positional deviation amount between the diffraction gratings based on the difference between the phase difference between the second and third optical heterodyne interference beat signals, minute fluctuations in the detection optical system and air in the optical path system are detected. The influence of fluctuations in temperature, atmospheric pressure, etc. can be eliminated, and the relative positional deviation amount can be detected with high stability and high accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram of a positional deviation detecting device shown as an embodiment of the present invention, FIG. 2 is a diagram showing a detailed structure of the diffraction grating 48 of FIG. 1, and FIGS. 3 (a) and 3 (b) are Another diagram showing the detailed configuration of the diffraction grating 48 of FIG. 1, FIG. 4 is a configuration diagram of a conventional positional deviation detecting device, FIG. 5 is a diagram showing the detailed configuration of the diffraction grating MP of FIG. 4, and FIG. The figure is a block diagram showing a detailed configuration of the positional deviation detection control circuit 25 of FIG. 40 …… 2-wavelength orthogonal polarization laser light source, 41,43 …… Mirror, 42 …… Polarization beam splitter, 44,49 …… Cylinder lens, 45 …… Objective lens, 46,50 …… Elliptical incident beam, 47… … Wafer, 48 …… Diffraction grating, 51 …… xy stage, 52 …… Elliptical beam spot, 53,54,55 …… Optical heterodyne interference synthetic diffracted light, 56 …… Half mirror, 57,58,59
...... Prism mirror, 60,61,62 …… Condensing lens, 63,6
4,65 …… Polarizer, 66,67,68 …… Photodetector, 69 …… Signal processing control unit, 70 …… Ocular, 71,72,73 …… Reference diffraction grating.

Continuation of the front page (56) Reference JP-A-63-172904 (JP, A) JP-A-61-215905 (JP, A) JP-A-62-58628 (JP, A) JP-B-3-17212 (JP , B2) JP 62-27730 (JP, B2) JP Hei 2-63288 (JP, B2) JP Hei 7-49926 (JP, B2) JP Hei 6-60808 (JP, B2) JP 7-99325 (JP, B2) JP 6-63739 (JP, B2) JP 7-104131 (JP, B2)

Claims (2)

(57) [Claims] 1. A first diffraction grating and a second diffraction grating fixed or formed on an object are used as a measuring standard, and a third diffraction grating is formed by aligning with the diffraction grating. The first, second, and third diffraction gratings are made to enter monochromatic light of two wavelengths whose frequencies are slightly different from each other, and diffracted light generated from the diffraction gratings is caused to undergo optical heterodyne interference. First, second, and third heterodyne interference beat signals are generated from the third and third diffraction gratings, respectively, and a phase difference change between these first, second, and third optical heterodyne interference beat signals is detected. By
A positional deviation detection method using a diffraction grating, wherein the positional deviation amount between the first, second and third diffraction gratings is measured. 2. A first diffraction grating and a second diffraction grating fixed or formed on an object, and a third diffraction grating fixed or formed by aligning with the diffraction grating, and a frequency. Light sources for generating monochromatic light of two wavelengths slightly different from each other, an incidence means for causing monochromatic light of two wavelengths emitted from the light source to enter the first, second, and third diffraction gratings, and And a photosynthesis detecting means for synthesizing two wavelengths of diffracted lights generated from the first, second, and third diffraction gratings, and generating first, second, and third optical heterodyne interference beat signals from the diffraction gratings, respectively. , A position between the first, second, and third diffraction gratings by performing a calculation process of a phase difference signal between the first, second, and third optical heterodyne interference beat signals generated by the photosynthesis detection means. And a signal processing device for measuring the amount of deviation Positional deviation detecting apparatus according grating characterized by comprising.