JPH0642918A - Aligning method and apparatus - Google Patents

Abstract

PURPOSE:To align a wafer with a mask in a stable manner with high accuracy by combining monochromatic lights of a plurality of different wavelengths on the same optical axis and measuring the phase difference on the basis of signals of the best intensity or S/N ratio. CONSTITUTION:The optical paths of laser lights of the center wavelengths #11, #12, #13 generated form the light sources 1a, 1b, 1c are combined on the same optical axis by mirrors 2a, 2b, 2c, and brought into a polarizing beam splitter 3 via a mirror 4c. The splitter 3 separates the light to components of one plane of polarization and those of the other plane of polarization. The mirrors 4a, 4c guide the separated light to a mask diffraction grating 5 and a wafer diffraction grating 6. The diffracted light is, through a mirror 4d, brought into mirrors 70a, 70b, 70c and detected by detectors 7a, 7b, 7c. A signal processing means 8 compares the intensity or S/N ratio of the signals, selects a good signal, predicts the phase difference of the signals from the gratings 5, 6, thereby aligning the mask 7 with the wafer B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a suitable aligning method applied to an exposure apparatus or a pattern evaluation apparatus for manufacturing a semiconductor IC or LSI, and a aligning apparatus used for carrying out the method.

[0002]

2. Description of the Related Art In the precision position detecting technology for aligners for synchrotron radiation photolithography, photosteppers and the like, an optical heterodyne position detecting method has begun to be put to practical use at the level of a prototype, as in Japanese Patent Laid-Open No. 62-261003. There is.

FIG. 3 shows an outline of the position detecting means utilizing the interference diffracted light shown in the above-mentioned prior art. First, the apparatus configuration is such that the mask A which is the first object and the second object. Each diffraction grating 5 formed on the wafer B as an object
0 and 60, a light source 10 composed of a laser device for generating two frequencies of slightly different orthogonal linearly polarized lights, and a polarization beam splitter 30 described later to adjust the directions of the separated lights to adjust the diffraction gratings 50 and 60. The incident means including the mirrors 41 and 42 for irradiating from the direction having an angle of ± θn (θn satisfies the diffraction formula shown in the following formula 1) with respect to the normal to the lattice plane, and the two polarized light coming from the light source 10 The polarization beam splitter 30 and the diffraction gratings 50 and 60 which are separated and branched in the directions of the mirrors 41 and 42, respectively.
From the optical interference means consisting of polarizing plates 31 and 32 for interfering each diffracted light extracted in the vertical direction from the polarizing plates 31 and 32, and a detector 71 for detecting the beat signal generated by interfering with the polarizing plates 31 and 32, It has a detecting means composed of 72 and a signal processing means 80 for detecting the phase shift of the beat signals detected by the detectors 71 and 72 and displaying the detected phase shift on the phase meter.

[0004]

[Equation 1]

The light emitted from the light source 10 has two frequency components f ₁ and f ₂ and has a polarization beam splitter.
The light having the frequency component of f ₁ and the light having the frequency component of f ₂ are separated by 30 and are incident on the diffraction gratings 50 and 60 by the mirrors 41 and 42 from the ± n-order directions (for example, ± 1st-order directions). Lights f ₁ and f ₂ (shown by broken lines in the figure) diffracted in the vertical direction from the diffraction gratings 50 and 60 pass through the mirror 43 and the prism mirror 44 and become coherent at the respective polarizing plates 31 and 32, and the detector 71, At 72, beat signals are detected respectively. Between the beat signals detected by the detectors 71 and 72, a phase difference proportional to the amount of positional deviation of the diffraction gratings 50 and 60 is generated. By detecting this phase difference with the phase meter of the signal processing means 80, the two diffraction gratings 5
The amount of relative displacement between 0 and 60 will be known.

[0006]

In the position detecting method using monochromatic light including the above-mentioned optical heterodyne system, since the coherence of monochromatic laser light is extremely high, interference with the transparent film such as the shape of the diffraction grating or the resist is caused. Under certain conditions, the signal strength becomes extremely low, and the position detection accuracy deteriorates.

FIG. 4 shows changes in the diffraction efficiency in the 0-dimensional and the 1-dimensional with respect to the grating step h (difference between the highest position and the lowest position in the grating height direction) of the lamellar diffraction grating, and it shows a periodic variation according to the diffraction efficiency. A decrease in signal strength is observed.

In the semiconductor device process, the process is complicated, and it is practically very difficult to suppress this interference effect, and the alignment accuracy is greatly influenced by the process.

The present invention was devised in view of the above problems of the prior art, and the signal for position detection is affected by the influence of process conditions such as mark shapes such as steps in the diffraction grating and resist film thickness. It is an object of the present invention to provide a very stable and highly accurate alignment method and alignment device that can always obtain good results.

[0010]

Therefore, according to the method of the present invention, the first object provided with the first diffraction grating and the second object provided with the second diffraction grating are arranged to face each other with a constant interval. Let
In the alignment method in which monochromatic light is made incident on these diffraction gratings and the relative positions of both objects are detected using the diffracted light generated from both diffraction gratings, and these are aligned, two or more monochromatic lights having desired wavelengths are detected. The basic feature is that light is combined on the same optical path axis, relative positions of both objects are detected independently for each wavelength, and alignment is performed based on one or more detection signals of them.

In the above-mentioned structure, it is preferable to prepare the first and second diffraction gratings each having a period corresponding to each wavelength corresponding to the difference in each wavelength of the incident light.

A second aspect of the present invention is the configuration of the apparatus according to the first aspect of the present invention, in which the first diffraction grating provided on the first object, the second diffraction grating provided on the second object, the first object, and / Or second
A moving mechanism that moves the object, a light source that generates monochromatic light,
Incident means for making the monochromatic light emitted from the light source incident on each diffraction grating, detection means for detecting the diffracted light extracted from these diffraction gratings, and measuring the phase difference between these detection signals A plurality of the light sources are used in an alignment apparatus having a signal processing control means for outputting a control signal to the moving mechanism based on the phase difference to move the first object and / or the second object to perform the alignment. A plurality of monochromatic lights of different wavelengths are provided, and an optical axis synthesizing means for synthesizing these lights on the same optical path axis is provided, and the first and second diffraction gratings have a period corresponding to each monochromatic light. Further, as the detecting means, those having a structure capable of separately detecting the diffracted light for each wavelength and independently detecting the diffracted light are used. In addition, as the signal processing control means, the intensities or S / N ratios of the detected signals are compared. Best belief It is basically characterized in that as the arrangement for measuring the phase difference based on.

Both of the above two inventions are applied to the optical position detecting technique using monochromatic light.
When it is applied to the configuration of the optical heterodyne system that obtains the phase difference between the beat signal originating in the diffraction grating and the beat signal originating in the second diffraction grating, a detection signal with high signal strength can be obtained, which is effective. In the optical heterodyne system, laser light that emits coherent light of two slightly different frequency components in orthogonal polarization planes, such as transverse Zeeman laser light, is used, and cannot be said to be monochromatic light in an absolute sense. , The two frequency components of the laser light are very similar,
In the sense that the central wavelength is single, it can be said to be monochromatic light as opposed to polychromatic light such as natural light. In other optical heterodyne system,
There is also a configuration in which monochromatic laser light is branched, and one or both of them is slightly shifted in frequency by a frequency shifter such as an acousto-optical element to irradiate them on a diffraction grating. In this case also, the configuration of the above-mentioned 2 invention can be applied. Needless to say.

[0014]

Operation: Laser light having a desired wavelength emitted from a plurality of light sources is used on the same optical path axis, and position deviation information is detected independently by a plurality of diffraction gratings waiting for a cycle corresponding to each wavelength, By selectively using a signal having a strong signal strength or a good S / N ratio to perform the alignment, it is possible to always perform the alignment with high accuracy without being affected by the process.

[0015]

EXAMPLES Specific examples of the present invention will be described below.

FIG. 1 is a schematic view showing the arrangement of an optical heterodyne alignment device according to an embodiment of the second invention used for aligning a mask A and a wafer B in a synchrotron radiation exposure apparatus. Regarding the respective moving mechanisms of the mask A and the wafer B, only the mask stage 9a and the wafer stage 9b are shown, respectively, and other configurations are omitted.

In this embodiment, a mask diffraction grating 5 and a wafer diffraction grating 6 provided on the mask A and the wafer B,
A moving mechanism showing only the mask stage 9a and the wafer stage 9b, light sources 1a, 1b and 1c composed of transverse Zeeman lasers emitting coherent light having slightly different frequencies with their polarization planes orthogonal to each other, and via a mirror 4c. The incident coherent light is separated by the polarization beam splitter 3 which is one of the optical interference means, and the separated light is separated by both diffraction gratings 5.
And diffracted light extracted in the vertical direction are guided horizontally by the mirror 4d, which is made up of mirrors 4a and 4b for irradiating 6 and 6, and they are generated by interfering with another polarizing plate (not shown) which is another optical interference means on the way. Detector that detects the beat signal
7a, 7b, and 7c, and a phase difference between these detection signals is measured and based on the phase difference, a control signal for alignment is output to each moving mechanism of the mask stage 9a and the wafer stage 9b. It has a signal processing control means 8.

In the above structure, the light sources 1a, 1b, 1c are
It emits monochromatic lights having central wavelengths λ ₁ , λ ₂ , and λ ₃ , respectively, and it is preferable that these wavelengths are not close to each other. Then, by the optical axis synthesizing means consisting of the total reflection mirror 2c and the dielectric multilayer mirrors 2a and 2b set for each wavelength, the light of the wavelength λ ₃ is reflected by the total reflection mirror 2c and the wavelengths of λ ₂ and λ ₁ . The light beams have their respective optical paths combined on the same optical path axis by the dielectric multilayer film mirrors 2a and 2b, and the polarization beam splitter is passed through the mirror 4c.
It is supposed to be ejected to 3.

On the other hand, as shown in FIG. 2, the diffraction gratings 5 and 6 provided on the mask A and the wafer B have three diffraction gratings corresponding to the respective wavelengths λ ₁ , λ ₂ and λ ₃ of the _three monochromatic lights. Period P ₁ , P
₂ and P ₃ are formed respectively. That is, according to the diffraction equation of the equation 1, when the wavelength of the laser light of the light source is λi and the incident angle θn, the relation with the period Pi of the diffraction grating is as shown in the following equation 2.

[0020]

[Equation 2]

Assuming that the incident light of this embodiment is incident from the ± 1st order, the following expression 3 is obtained.

[0022]

[Equation 3]

Therefore, for the respective wavelengths λ ₁ , λ ₂ , λ _{3 of the} laser light incident on the same optical path axis, the diffraction gratings of the periods P ₁ , P ₂ , P ₃ corresponding to the respective wavelengths λ ₁ , λ ₂ , λ ₃ are provided on the mask A and the wafer. It will be formed in each of B.

Further, the detecting means is composed of detectors 7a, 7a.
In contrast to b and 7c, the diffracted light extracted on the same optical path axis as shown in FIG. 2 is converted into two dielectric multilayer film mirrors 70a and 7c.
0b and the total reflection mirror 70c are respectively taken out to detect the beat signal, and the detector 7
Since a, 7b, and 7c have sensitivity corresponding to each wavelength region, they can be detected separately for each wavelength separately (that is, the detector 7a has a wavelength λ ₁ ,
The detector 7b detects a wavelength λ _{2 and} the detector 7c detects a wavelength λ ₃ ).

In addition, the signal processing control means 8 monitors the detection signals from the detectors 7a, 7b, 7c, selects the most stable signal (strong signal strength or good S / N ratio), and The circuit configuration for measuring the phase difference between the signals derived from the mask diffraction grating 5 and the wafer diffraction grating 6 is provided above.

The operation of the configuration of this embodiment described above will be described below.

First, the laser beams having the central wavelengths λ ₁ , λ ₂ and λ ₃ emitted from the light sources 1a, 1b and 1c are made the same by the optical axis combining means of the total reflection mirror 2c and the dielectric multilayer film mirrors 2a and 2b. The optical paths are combined on the optical path axis and enter the polarization beam splitter 3 via the mirror 4c. The polarization beam splitter 3 separates each laser light into light of one polarization plane component and light of another polarization plane orthogonal to each other. The mirrors 4a and 4b of the incident means mask the separated laser beams with a mask diffraction grating.
5 and the wafer diffraction grating 6 are made incident from the ± first-order directions. The light diffracted in the vertical direction from the diffraction gratings 5 and 6 is a mirror.
After passing through 4d, the dielectric multilayer film mirrors 70a, 70b and the total reflection mirror 70a are reached, and detected by the detectors 7a, 7b, 7c. On the way, two orthogonal polarization planes of each monochromatic light are superposed on one polarization plane by the polarizing plate or the like (not shown) so that the two frequency components interfere with each other, and three kinds of beat signals are generated. Therefore, the detector 7a selects the beat signal derived from the laser light having the wavelength λ ₁ , the detector 7b selects the beat signal derived from the laser light having the wavelength λ ₂ , and the detector 7c selects the beat signal derived from the laser light having the wavelength λ _3. Will be detected. Then, the signal processing control means 8 compares the signal intensities or S / N ratios of the three beat signals to select one good signal, and selects one from the mask diffraction grating 5 and the wafer diffraction grating 6. Measure the phase difference. The signal processing control means 8 outputs a control signal to the mask stage 9a and the wafer stage 9b on the basis of the positional deviation information between the mask A and the wafer B obtained in this way to align the mask A and the wafer B.

As described above, in the present embodiment, since optical heterodyne detection is performed by using a plurality of monochromatic lights having different wavelengths, signal deterioration due to the interference effect peculiar to monochromatic light can be suppressed, and highly stable and highly accurate alignment is possible. Became possible.

[0029]

According to the position detecting method and apparatus of the present invention described in detail above, the position detecting signal is not influenced by the process conditions such as the mark shape such as the step of the diffraction grating and the resist film thickness, and is always good. It can be obtained in a stable state, and extremely stable and highly accurate alignment can be performed.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the configuration of an embodiment of a second invention device.

FIG. 2 is an explanatory diagram showing a state of installation of a diffraction grating and a diffraction state of laser light in the configuration of this embodiment.

FIG. 3 is a perspective view showing a conventional optical heterodyne position detection configuration.

FIG. 4 is a graph showing the diffraction efficiency of diffracted light due to the difference in the steps of the diffraction grating.

[Explanation of symbols]

1a, 1b, 1c, 10 Light source 2a, 2b Dielectric multilayer mirror 2c Total reflection mirror 3, 30 Polarizing beam splitter 31, 32 Polarizing plate 4a, 4b, 4c, 4d, 40, 41, 42, 43 Mirror 44 Prism mirror 5, 5a, 5b, 5c, 50 Mask diffraction grating 6, 6a, 6b, 6c, 60 Wafer diffraction grating 7a, 7b, 7c, 71, 72 Detector 70a, 70b Dielectric multilayer mirror 70c Total reflection mirror 8 Signal processing control Means 80 Signal processing means 9a, 90 Mask stage 9b, 91 Wafer stage

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01L 21/68 G 8418-4M

Claims (3)

[Claims] 1. A first object provided with a first diffraction grating and a second object provided with a second diffraction grating are arranged so as to face each other with a constant gap, and monochromatic light is applied to these diffraction gratings. In the alignment method in which the relative positions of both objects are detected by using the diffracted light that is incident and is generated from both diffraction gratings, two or more monochromatic lights having a desired wavelength are combined on the same optical path axis in an alignment method for aligning them. Then, the relative position of both objects is detected independently for each wavelength, and the alignment is performed based on one or more detection signals of the two. 2. The alignment method according to claim 1, wherein each of the first and second diffraction gratings has a plurality of periods corresponding to the plurality of monochromatic lights. The alignment method according to claim 1. 3. A first diffraction grating provided on the first object,
A second diffraction grating provided on the second object, a moving mechanism for moving the first object and / or the second object, a light source for generating monochromatic light, and a monochromatic light emitted from the light source, respectively. Incident means for entering the diffraction grating, detection means for detecting the diffracted light extracted from these diffraction gratings, and measuring the phase difference between these detection signals and outputting a control signal to the moving mechanism based on the phase difference Then, in an alignment device having a signal processing control means for moving the first object and / or the second object to perform alignment, a plurality of monochromatic lights of different wavelengths are generated by using a plurality of the light sources, Further, an optical axis synthesizing means for synthesizing these lights on the same optical path axis is provided, and the first and second diffraction gratings are respectively provided with a period corresponding to each monochromatic light, and further the diffracted light as the detecting means. Is separated for each wavelength In addition, the signal processing control means may be configured to measure the phase difference based on the best signal by comparing the intensity or S / N ratio of the detection signal. Characteristic alignment device.