JP2514699C - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention uses a diffraction grating as a measurement standard, and uses a phase of a beat signal obtained by optically heterodyne-interfering diffracted light to determine a relative distance between diffraction gratings. Detect the amount of displacement,
For example, the present invention relates to a position shift detection method and a position shift detection apparatus used when measuring the overlay accuracy between patterns formed in an exposure apparatus for manufacturing a semiconductor IC or an LSI. [Problems to be Solved by the Related Art] Conventionally, as a method of measuring this kind of misalignment, first, a pattern for measurement is burned and a misalignment between patterns is measured by a pattern line width measuring device. Second, a vernier type in which grids with different pitches are baked on an integrated circuit to read the part of the grid that just overlaps, and thirdly, a thin elongated resistor and an electrode are formed on the integrated circuit by superimposing them. Fourth, there is a method of comparing each value of the resistor, and fourthly, a method of printing a diffraction grating on an integrated circuit and measuring a pattern shift amount based on a phase difference of diffracted light. However, according to the method using the first pattern line width measuring device, usually, the accuracy of such a device can only be obtained at most about 0.01 μm, and also by the second vernier method, 0.04 μm There is a problem that only a degree of accuracy can be obtained. Further, the third resistance measurement method has a problem that, although accuracy is obtained, 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 first to third problems. FIG. 4 shows an example of an apparatus for measuring the amount of displacement using such a phase difference signal (Japanese Patent Publication No. 62-56818). In the figure, a wafer 2 to be detected is placed on a stage 1. The wafer 2 has been baked and developed twice by the exposure apparatus, and thus the exposure pattern formed on the mask or reticle of the exposure apparatus 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.
Is formed. The first diffraction gratings MA1 and MA2 are grating elements that are baked together with the exposure pattern during the first exposure processing, 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 second diffraction gratings MB1 and MB2 are similarly formed at positions separated by a distance d in the y-axis direction and extended in the x-axis direction by the second superposition exposure process. And the first diffraction grating MA1 in the y-axis direction.
And MA2 so as to be inserted alternately. Here, the first diffraction gratings MA1, MA2 and the second diffraction grating MB1 are arranged in the y-axis direction.
, MB2, the respective grating elements of the first diffraction gratings MA1, MA2 and the respective grating elements of the second diffraction gratings MB1, MB2 are formed so as to be aligned on the same straight line in the x-axis direction. At this time, it can be determined that there is no displacement between the first and second exposure patterns. On the other hand, if the positions of the first and second exposure patterns are shifted from each other by .DELTA.y in the y-axis direction, this position shift is caused by the diffraction gratings MA1, MA2 and MB1.
, MB2 as a displacement Δy between the corresponding lattice elements. Therefore, the diffraction grating MP having the configuration shown in FIG. 5 is irradiated with two coherent light beams LL1 and LL2 having different frequencies from each other, and the first-order diffraction light LF1 of the first coherent light LL1 generated by the diffraction grating MP. And the direction of reflection of the first-order diffracted light LF2 of the second coherent light LL2 are selected so as to be substantially perpendicular to the surface of the wafer 2. Here, two coherent light beams having different frequencies from each other, LL1 and LL2, 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 parts, and divides the first laser beam into a modulation signal S1 by the ultrasonic modulator 14 (see FIG. 6. The modulation signal S1 is a transmitter
It is generated electrically by 34, 37 and the frequency conversion circuit 38. ), The frequency is shifted and modulated by the frequency 11, and the beam is irradiated as a first coherent light beam LL 1 onto the diffraction grating MP of the wafer 2 while being bent by the mirrors 15 and 16. Further, the shunt device 13 irradiates the second laser beam to the ultrasonic modulator 18 via the mirror 17 and modulates the signal S2 (see FIG. 6. The modulation signal S2 is a signal obtained by the transmitter 37). After the frequency is shifted by the frequency f2, the mirror 19
, 20 and irradiates the diffraction grating MP of the wafer 2 as a second coherent light beam LL2. Thus, the diffracted lights LF1 and LF2 generated by the diffraction grating MP interfere with each other, pass through the objective lens 3, the diaphragm 4, and further enter the photoelectric conversion element array 6 through the half mirror 5. The half mirror 5 is configured to turn the diffracted light passing through the stop 4 back to the eyepiece 7 to observe interference fringes. The photoelectric conversion element array 6 detects the interference light of the diffracted light with the photoelectric conversion elements DA1, DA2, DB1, and DB2 corresponding to the elements MA1, MA2, MB1, and MB2 of the diffraction grating MP, respectively.
Four beat signals SA1, SA2, SB1, and SB2 (= f1-f2) are generated, and these four beat signals are sent to the displacement detection control circuit 25. FIG. 6 shows a detailed configuration diagram of the displacement detection control circuit 25. Position shift detection control circuit
At 25, the phases of the beat signals SA1, SA2, SB1, and SB2 are changed to PLL circuits 32A,
The frequency Δf (= f) from which the phases are locked at 32B, 32C, and 32D, and the noise is removed.
0) phase outputs SFA, SFB, SFC, SFD are obtained. This phase output SFA,
The phases of SFB, SFC, SFD and the phase of the reference frequency output S0 obtained from the transmitter 34 are compared by phase difference detection circuits 33A, 33B, 33C, 33D, and the phase differences α,
Based on β, γ and δ, the displacement calculating circuit 35 calculates the displacement △ y by the following formula に よ っ て y = (d / (4π)) · ((3β−3γ−α + δ) / 4) (1) Then, the position shift amount 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 using the reference signal generated by the electronic circuit, the fluctuation of the detection optical system, the temperature of the air atmosphere of the optical path system,
It is susceptible to fluctuations such as atmospheric pressure, and the phase difference signal fluctuates, causing an error in the amount of displacement. In the method of eliminating the influence of the inclination between the optical system and the diffraction grating by the above equation (1), in addition to the instability of the four electronic circuit systems for detecting the phase difference, a calculation error due to a difference in circuit characteristics between the four electronic circuit systems is eliminated. There is a problem that it is difficult to detect misalignment with high accuracy because it is easily included. An object of the present invention is to use the first and second diffraction gratings as measurement scales and form a third diffraction grating for measuring the amount of displacement with respect to the diffraction grating in order to eliminate the above-mentioned disadvantages. The first, second, and third diffraction gratings are irradiated with two wavelengths of monochromatic light slightly different in frequency from each other, and diffracted light generated from the diffraction grating is subjected to optical heterodyne interference; And the first, second, and third optical heterodyne interference beat signals are generated from the first, second, and third diffraction gratings, respectively, and the phase difference between the first, second, and third optical heterodyne interference beat signals is changed. By detecting the position shift amount between the first, second, and third diffraction gratings, a position shift detection method using a diffraction grating that is more stable and more accurate than a conventional one. And misalignment detector It is to provide a. [Means for Solving the Problems] The displacement detection method of the present invention uses the first or second diffraction grating fixed or formed on an object as a measurement standard, and the first diffraction grating, The second diffraction grating and the third diffraction grating are arranged in the order of the third diffraction grating so that the first and second diffraction gratings are aligned with each other to form the third diffraction grating. The first, second, and third diffraction gratings are irradiated with two wavelengths of monochromatic light whose frequencies are slightly different from each other,
The first, second, and third diffraction gratings cause optical heterodyne interference of diffracted light, and the first, second, and third diffraction gratings cause first, second, and third heterodyne interference, respectively. Generating a beat signal, detecting a first phase difference between the first and second optical heterodyne interference beat signals and a second phase difference between the second and third optical heterodyne interference beat signals, There is a feature that the relative position shift amount between the diffraction gratings can be detected by performing the difference processing of the first and second phase differences. Further, the position shift detecting device of the present invention includes first and second diffraction gratings fixed or formed on an object, the first diffraction grating, the second diffraction grating, and the third diffraction grating. The first and second diffraction gratings are aligned and fixed or formed so as to be arranged in the order described above. A light source that generates light, and an incidence unit that causes two wavelengths of monochromatic light emitted from the light source to enter the first, second, and third diffraction gratings;
The two-wavelength diffracted light generated from the second and third diffraction gratings is combined, and the first, second, and third optical heterodyne interference beat signals are respectively obtained from the first, second, and third diffraction gratings. Detecting the first phase difference between the first and second optical heterodyne interference beat signals and the second phase difference between the second and third optical heterodyne interference beat signals Then, the difference processing of the first and second phase difference, the first, the second, from the device configuration with a signal processing device that measures the amount of displacement between the third diffraction grating, the second There is a feature that the amount of displacement between the first, second, and third diffraction gratings can be measured. The present invention is directed to a relative displacement between a reference diffraction grating and a measurement diffraction grating, that is, a semiconductor IC or an LSI, based on a difference between a phase difference between the reference diffraction grating and a phase difference between the measurement diffraction gratings.
Is a method for measuring the overlay accuracy between patterns formed in an exposure apparatus or the like for manufacturing the device. 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 displacement, the fluctuation of the detection optical system, the temperature of the air in the optical path system, the atmospheric pressure, etc. The influence of the fluctuation can be removed, and the relative displacement can be detected with high stability and high accuracy. Embodiment An embodiment of the present invention will be described below with reference to FIGS. The same reference numerals as those in FIGS. 4 to 6 denote the same members. FIG. 1 shows an embodiment of a position shift detecting apparatus 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 by a polarizing beam splitter 42 to a horizontal component (p-polarized component),
Alternatively, the light is separated into two wavelengths of linearly polarized light having only a vertical component (s-polarized component) and slightly different frequencies. The p-polarized light component is converted into an elliptical beam 46 by an optical system including a cylindrical lens 44 and an objective lens 45 via a mirror 43, and is diffracted by a diffraction grating 48 formed on a wafer 47 installed on an xy stage 51. The light enters from the direction of the primary diffraction angle with respect to the normal direction (z direction) perpendicular to the lattice plane. On the other hand, the s-polarized light component is similarly converted into an elliptical beam 50 by the optical system including the cylindrical lens 49 and the objective lens 45.
Then, the light enters the diffraction grating 48 from the direction of the primary diffraction angle symmetrical to the elliptical beam 46 with respect to the normal direction (z direction) perpendicular to the diffraction grating surface. As shown in FIG. 2, the diffraction grating 48 is a pattern formed by two printing and developing processes by an exposure device. That is, two types of exposure patterns formed on masks or reticles of two exposure apparatuses are overprinted on the wafer 47. When two types of exposure patterns are printed, a diffraction grating composed of three sets of diffraction gratings as shown in FIG. 2 representing the printing positions of the exposure patterns is formed. First diffraction grating HD
Reference numerals 1 and 2 denote lattice elements which are printed together with the exposure pattern during the first exposure processing, are formed at positions separated from each other by a distance d in the y-axis direction, and extend in the x-axis direction. Is formed. On the other hand, the third diffraction grating HD3 is similarly formed at a position apart from each other by the distance d in the y-axis direction by the second overlapping exposure process, and the first diffraction grating HD1 and the second diffraction grating HD3 are formed. The diffraction grating HD2 is formed at a predetermined interval in the x direction. Here, in the y-axis direction, the first diffraction grating HD1 and the second diffraction grating HD
If there is no displacement between the second diffraction grating HD3 and the third diffraction grating HD3, each of the first and second diffraction gratings HD1 and HD2 and the third diffraction grating HD3 will have an x-axis. The exposure patterns are formed so as to be aligned on the same straight line in the direction. At this time, it can be determined that the first and second exposure patterns have no positional deviation. On the other hand, if the positions of the first and second exposure patterns are displaced from each other by y in the y-axis direction, this displacement will cause a displacement between the corresponding grating elements of the diffraction gratings HD1, HD2, and HD3. It is made to appear as y. The three diffraction gratings HD1, HD2, HD3 are arranged in the same elliptical beam spot 52 of each of the incident lights 46, 50 of two wavelengths. The diffraction grating pitches d are set equal to each other. By the incident light 46, 50, the three diffraction gratings HD1, HD2, HD3
Synthetic diffraction light of three -1st-order diffraction lights of two wavelengths in the direction, that is, the first diffraction grating HD1
Optical heterodyne interference combined diffracted light 53 of the -1st-order diffracted light of the incident light 46 and the -1st-order diffracted light of the incident light 50, and the optical heterodyne interference combined diffracted light similarly obtained in the Z direction from the second diffraction grating HD2 54 and an optical heterodyne interference combined diffracted light 55 similarly obtained in the Z direction from the third diffraction grating HD3. The three combined lights 53, 54, 55 are
After being split and exposed in two directions by a half mirror 56, one is separated by prism mirrors 57, 58, 59, and condensed lenses 60, 61, 62, polarizing plates 63, 64, 65 respectively.
And the optical heterodyne interference beat signals HY1 and HY2
, HY3 to the signal processing controller 69. The other one split by the half mirror 56 is configured so that diffracted light can be observed by the eyepiece 70. In the signal processing control unit 69, the phase difference Δφ0 of HY2 with respect to HY1 with respect to the optical heterodyne interference beat signals HY1 and HY2 obtained from the first and second diffraction gratings HD1 and HD2, and the light obtained from the third diffraction grating HD3. For the heterodyne interference beat signals HY3 and HY2, the phase difference Δφ corresponding to the amount of displacement Δy between the diffraction gratings HD1, HD2 and HD3 is obtained from the following equation from the phase difference ΔY of HY3 with respect to HY2. Δφ = ΔφY−Δφ0 = 2π · 2 · Δy / d (2) where Δφ0 is the position deviation detection optical system and the diffraction gratings HD1, HD2, and HD3.
And a phase difference caused by a rotational displacement of the xy plane with the above. In other words, the positional deviation detection optical system originally includes the reference diffraction gratings 71, 72, 73 formed such that the grating elements are arranged on the same straight line as shown in FIG. The direction is set and adjusted so as to be parallel to the x-axis. When the major axis direction of two overlapping elliptical beams of the optical system is set as the reference line of the optical system, the reference line of the optical system and the grating element of the diffraction grating are used. It is assumed that the center line is set to match. Therefore, if the direction of the grating element of the diffraction grating is set parallel to the x-axis, the above (2)
△ φ0 = 0 in the equation. Further, as shown in FIG. 3 (b), when the direction of the grating element of the diffraction grating is shifted with respect to the direction of the x-axis, the directions of the grating element of the diffraction grating completely match, and are aligned on a straight line. A phase difference Δφ0 is generated between HY1 and HY2 also between the first diffraction grating HD1 and the second diffraction grating HD2 which are arranged. Therefore, for the optical heterodyne interference beat signals HY3 and HY2, HY2
It is necessary to subtract the error Δφ0 caused by the rotational deviation from the phase difference ΔφY of 3. The signal processing control unit 69 can easily obtain Δy from the above equation (2) and display the value, etc. In the above embodiment, a two-wavelength orthogonally polarized laser light source is used as the two-wavelength monochromatic light source. However, the same applies when using light generated using an acousto-optic device such as a Bragg cell as the two-wavelength monochromatic light. The effect of can be obtained. In this case, the two-wavelength monochromatic light source can be made compact by combining the acousto-optic element and the semiconductor laser. Furthermore, using an optical fiber such as a polarization-maintaining optical fiber for the incident optical system of the two-wavelength laser light, a technique is used in which the movement amount detection optical system body and the two-wavelength monochromatic light source are separated, and the two are coupled by an optical fiber. By doing so, it is possible to make the position detecting optical system more compact. Also, an example has been described in which the direction of the incident light on the diffraction grating and the direction of the diffracted light from the diffraction grating are included in the yz plane perpendicular to the plane of the diffraction grating. The optical heterodyne interference beat signal is detected by optically combining two wavelengths of diffracted light of oblique incidence and oblique emission not included in the yz plane perpendicular to the diffraction grating surface as the direction of the diffracted light from Can obtain the same effect. Furthermore, as the diffraction grating in the present invention, any of an absorption type diffraction grating and a phase type diffraction grating may be used, and various diffraction gratings such as a sinusoidal diffraction grating and a phrase diffraction grating are not limited to the binary diffraction grating. It is possible to use, and it is also possible to use a reflection type diffraction grating in addition to a transmission type diffraction grating. Furthermore, in the above-described embodiment, a grating element in which the grating elements are arranged in parallel to the x-axis direction is used as the diffraction grating, but a similar diffraction grating is also formed in the y-axis direction perpendicular to the x-axis. , X, y, it is also possible to set the optical system in the two directions x, y so that the amount of displacement Δx, Δy in the two directions, x, y, can be detected. In this case, a diffraction grating having a checkered pattern may be used in two directions of x and y in addition to the diffraction grating as in the above embodiment. [Effects of the Invention] As described above in detail, according to the present invention, the first and second diffraction grating pairs serving as references are provided, and further, the third diffraction grating for measuring the amount of displacement is set. Optical heterodyne interference beam signals obtained from first and second pairs of diffraction gratings, in which two wavelengths of monochromatic light having slightly different frequencies are incident on the diffraction grating and three optical heterodyne interference lights generated from these diffraction gratings are used as references. With the phase difference between the reference value and the difference between the phase difference between the second and third optical heterodyne interference beat signals, by detecting the relative displacement between the diffraction gratings, the minute fluctuation of the detection optical system, The effects of fluctuations in the temperature, pressure, etc. of the air in the optical path system can be removed, and the relative displacement can be detected with high stability and high accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a position shift detecting device shown as an embodiment of the present invention, FIG. 2 is a diagram showing a detailed configuration of a diffraction grating 48 of FIG. 1, and FIG. a) and (b) are other views showing the detailed configuration of the diffraction grating 48 in FIG. 1, FIG. 4 is a configuration diagram of a conventional displacement detection device, and FIG. 5 is a detail of the diffraction grating MP in FIG. FIG. 6 is a block diagram showing a detailed configuration of the position shift detection control circuit 25 of FIG. 40: two-wavelength orthogonally polarized laser light source, 41, 43: mirror, 42: polarizing beam splitter, 44, 49: cylindrical 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, 64, 65… Polarizer, 66, 67, 68… Light detection Device, 69: signal processing control unit, 70: eyepiece, 71, 72, 73: reference diffraction grating.

Claims (1)

Claims: (1) The first diffraction grating, the second diffraction grating, and the third diffraction grating fixed or formed on an object are used as measurement reference scales. The first, second and third diffraction gratings are aligned with respect to the first and second diffraction gratings so as to be arranged in the order of the diffraction gratings. On the diffraction grating, monochromatic light of two wavelengths whose frequencies are slightly different from each other is made incident, and the first, second, and third diffraction gratings cause light heterodyne interference of the diffracted light, and the first, second, and First, second, and third heterodyne interference beat signals are generated from a third diffraction grating, respectively, and a first phase difference between the first and second optical heterodyne interference beat signals and the second and And the second phase difference between the three optical heterodyne interference beat signals. Detecting and performing a difference process between the first and second phase differences to measure the amount of misalignment between the first, second, and third diffraction gratings. Detection method. (2) First and second diffraction gratings fixed or formed on an object, and arranged in the order of the first diffraction grating, the second diffraction grating, and the third diffraction grating, The first and second diffraction gratings are aligned and fixed or formed, or the third diffraction grating, and a light source that generates monochromatic light of two wavelengths whose frequencies are slightly different from each other, Incident means for causing the monochromatic light of two wavelengths emitted from the light source to enter the first, second, and third diffraction gratings; and a diffraction of two wavelengths generated from the first, second, and third diffraction gratings. Combining the light, the first, second, and first, second, and third from the diffraction grating, respectively, photosynthesis detection means for generating a third optical heterodyne interference beat signal, the first and second, A first phase difference between the optical heterodyne interference beat signal and the second and third Detecting a second phase difference between the optical heterodyne interference beat signals and performing a difference process between the first and second phase differences to obtain a displacement between the first, second, and third diffraction gratings. And a signal processing device for measuring the quantity.