JPH0365603A - Method of aligning position - Google Patents

Abstract

PURPOSE:To enable highly-precise position alignment of a mask with a projecting lens and with a wafer by forming two first diffraction gratings on a first substance and a second diffraction grating on a second substance. CONSTITUTION:A high-reflection mirror 16 and a half mirror 17 are disposed above a mask 11, and a minus primary diffracted light q1 generated at a first mark 14 is led to a photoelectric detector 18 by the high-reflection mirror 16 through the half mirror 17. A plus primary diffracted light p1 generated at a first mark 13 is led to the photoelectric detector 18 by the half mirror 17. The minus primary diffracted light q1 and the plus primary diffracted light p1 interfere with each other at the half mirror 17 and an interference light e1 is sent to the detector 18. Then, a detection signal of the detector 18 is sent to a signal processing circuit 19. Besides, a high-reflection mirror 20 is provided above a second mark 15, a reflected interference light e2 generated at the second mark 15 is led to a photoelectric detector 21 and a detection signal is sent to a signal processing circuit 22. By this constitution, the mask can be aligned in position with a projecting lens and also with a wafer.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a method for aligning two objects, and particularly to a method for aligning a mask, a wafer, and a projection lens used for pattern transfer. Concerning a preferred alignment method.

(Prior Art) In recent years, with the miniaturization of circuit patterns of semiconductor devices such as LSIs, optical projection exposure apparatuses having high resolution performance have come to be widely used as pattern transfer means. When performing transfer using this equipment, it is necessary to align the mask with high precision with respect to the optical axis of the projection lens and to match the relative position of the mask and wafer with high precision (mamasf alignment) prior to exposure. . °.

By the way, the method for such mask alignment is as follows:
Another optical system different from the projection optical system (of'f'-axis
The wafer is positioned by detecting marks formed in advance on the wafer using a s microscope), and then the wafer is moved with high precision to a predetermined position within the field of view of the projection optical system, and the mask is positioned precisely in advance. of'f'-
axis method, and TTL (T hroug
h T he L ens ) method, where off
The -axis method has the advantage that the time required for alignment is short because the number of alignments is small, and the throughput (processing speed) is high. However, it is necessary to move the aligned wafer by an accurate distance to the position to be transferred, and an absolute length measurement system must also be provided.

For this reason, error factors increase, making it difficult to align with high precision. Therefore, in order to perform alignment with higher precision, a method such as the TTL method that detects marks on the mask and wafer through a projection optical system and performs direct alignment has become popular.

As one of such TTL alignment methods, 2
A method of superimposing two gratings (Reference G,
Dubroeucq, 1980. M.E., W.

RTrutna, J r, 1948.5PI
E etc.). This is the projection lens 1 as shown in Figure 5.
A grating-like mark 4 is formed on the mask 1 and a grating-like mark 5 is formed on the wafer 3 between a mask 2 and a wafer 3 which are arranged opposite to each other. When alignment light is incident in this state, the diffracted light generated by the grating mark 5 is irradiated onto the grating mark 4 through the projection lens 1, and the interference light generated by the grating mark 4 is guided to the photoelectric detector 6. However, the output of this photoelectric detector 6 indicates the overlapping state of each grating-like mark 4.5 as shown in FIG. The signal strength reaches its maximum (or minimum) "-" in state B).Therefore, by providing signal processing (such as vibration type synchronous detection processing) that can detect the maximum value (or minimum value) with high accuracy, high accuracy can be achieved. alignment is possible.

By the way, when performing exposure, when a projection lens is used, distortion occurs in a portion of the transfer pattern corresponding to the periphery of the field of view of the projection lens. Therefore, it is necessary to accurately align the center position of the mask 2 with respect to the optical axis of the projection lens 1 in order to eliminate the overlay error between the first transfer and the second transfer during exposure of the wafer. In addition, since the optical system for exposure is adjusted so that the light is irradiated uniformly around the optical axis of the projection lens, the center position of the mask 2 is adjusted to the projection lens 1 in order to uniformly irradiate the mask 2. It is necessary to accurately align the optical axis of the

However, alignment using the TTL method described above involves aligning the relative positions of the mask 2 and the wafer 3 with high precision, but it is difficult to align the mask 2 with respect to the optical axis of the projection lens 1. ing.

Therefore, when the TTL method is used for mask alignment, in order to align the mask 2 with respect to the optical axis of the projection lens 1, it is necessary to provide a positioning means different from the TTL method, such as reticle alignment. In this case, TTL
Since alignment and reticle alignment are completely different optical systems, not only does the entire apparatus become complicated, but also a reference is required for each alignment system, making it easy for errors to occur.

(Problems to be Solved by the Invention) Although it is possible to align the mask and the wafer as described above, it is difficult to align the mask and the projection lens with high precision.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an alignment method that allows highly accurate alignment of a mask and a projection lens, as well as alignment of both a mask and a lens.

[Structure of the Invention] (Means and Effects for Solving the Problems) The present invention provides an alignment method for aligning the mutual positions of a first object and a second object that are arranged to face each other via a projection lens, and a projection lens. At least two first diffraction gratings are formed on the first object, a second diffraction grating is formed on the second object, and each of the first diffraction gratings is irradiated with alignment light of the same wavelength. The interference light of each diffracted light from these first diffraction gratings is detected to obtain positional information of the first object with respect to the projection lens, and at the same time, the transmitted diffracted light of each first diffraction grating is passed through the projection lens to the second object. This alignment method attempts to achieve the above objective by irradiating the diffraction grating and detecting the reflected diffracted light from the second diffraction grating to obtain relative position information between the first object and the second object. .

Further, the present invention is an alignment method that attempts to achieve the above object by modulating the wavelength of at least one of the alignment lights irradiated to each first diffraction grating in addition to the above means.

(Example) Hereinafter, a first example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an alignment apparatus in which this method is applied to a semiconductor exposure apparatus. In the figure, reference numeral 10 denotes a projection lens, and a mask 11 and a wafer 12 are arranged in the optical axis direction of the projection lens 10 so as to sandwich the projection lens 10 therebetween. Note that the projection lens 10 is equipped with an exposure light source (
(not shown). Here, first marks 13, 14 each consisting of a diffraction grating are formed on the mask 11, and second marks 15, also consisting of a diffraction grating, are formed on the wafer 12. Note that the first marks 13 and 14 are, for example, a one-dimensional grid pattern as shown in FIG. 2(a), and the second mark 15 is, for example, as shown in FIG.
The two-dimensional lattice pattern shown in b) or the checkered lattice pattern shown in FIG.

Incidentally, a high reflection mirror 16 and a half mirror 17 are arranged above the mask 11. High reflection mirror 16
is for guiding the first-order diffracted light qt generated at the first mark 14 to the photoelectric detector 18 through the half mirror 17,
Further, the half mirror 17 guides the +1st order diffracted light p1 generated by the first mark 13 to the photoelectric detector 18. Here, the -1st-order diffracted light q1 and the +1st-order diffracted light pl interfere with each other at the half mirror 17, and this interference light el is sent to the photoelectric detector 18. The detection signal of this photoelectric detector 18 is sent to a signal processing circuit 19.

Further, a high reflection mirror 20 is provided above the second mark 15 so that reflected interference light e2 generated at the second mark 15 is guided to a photoelectric detector 21. A detection signal from this photoelectric detector 2 is sent to a signal processing circuit 22.

Furthermore, 23 is a frequency shift mechanism, which has a function of shifting the frequency or wavelength of one of the alignment lights p and q, for example, q. Note that this frequency shift mechanism 23 transmits a frequency signal indicating the shifted frequency to each signal processing circuit 1.
Send out on 9.22.

In addition, each signal processing circuit 9 has a function of the optical hetero gain phase detection method, that is, when the frequency shift mechanism 23 is operating, a frequency signal is input as a reference signal, and the phase of this frequency signal and the signal from the photoelectric detector 18 are input. It has a function of obtaining positional information of the mask 11 with respect to the projection lens 10 by determining the difference between the detection signal and the beat phase. The other signal processing circuit 22 inputs a frequency signal as a reference signal when the frequency shift mechanism 23 is operating, and calculates the difference between the phase of this frequency signal and the phase of the beat of the detection signal from the photoelectric detector 21. It has a function of obtaining relative position information between the mask 11 and the wafer 12 by determining the relative position information of the mask 11 and the wafer 12.

By the way, the actual apparatus is as shown in the perspective view of FIG. 3, and each of the alignment lights p and q is a laser output from a HeNe laser oscillation device that outputs light of a wavelength different from the wavelength of the light source for exposure. Light is used. and,
This laser beam is divided into alignment beams p and q by a half mirror or the like and sent to a lens 24 and a condenser lens 2.
5 and is irradiated onto the first marks 13 and 14. The half mirror 17 and the high reflection mirrors 20 and 16 are arranged at positions where they do not block the exposure light.

Next, the operation of the device configured as described above will be described with respect to the case where the frequency shift mechanism 23 does not operate and the case where the frequency shift mechanism 23 operates.

■When the frequency shift mechanism does not operate When the alignment lights p and q of the same wavelength are irradiated to the first marks 13 and 14, respectively, these first marks 13
．． At 14, ±nn next light occurs. Of these, the first
The +1st order diffracted light 1 generated at the mirror 13 is a half mirror.
17, the 11th-order transmitted diffracted light p
2 advances towards the projection lens 10. At the same time, the 1st-order leading light q2 generated at the first mark 14 is reflected by the high-reflection mirror 16 and travels toward the half mirror 17, and the +1st-order transmitted diffracted light q2 is reflected by the projection lens 1.
Proceed towards 0. Here, a phase difference occurs between the +1st-order diffracted leading light i and the 11th-order leading light q1 in the half mirror 17, and this phase difference is caused by the projection lens 10 of the mask 11.
It corresponds to the position relative to. However, the interference light el between the +1st-order diffraction destination beam 1 and the 11st-order destination beam q1 is detected by the photoelectric detector 1.
8, this photoelectric detector 18 outputs a detection signal according to the light intensity of the interference light el. As a result, positional information of the mask 11 with respect to the projection lens 10 can be obtained from this light intensity.

On the other hand, a phase difference occurs between the -1st order transmitted diffraction light p2 and the +1st order transmitted diffraction light q2 depending on the position of the mask 11 and the projection lens 10, and these -1st order transmitted diffraction light p2
The second and +1st-order transmitted diffracted lights q2 are focused by the projection lens 10 and irradiated onto the second mark 15. As a result, each transmitted diffracted light p2. Moiré fringes occur due to the interference of q2, and each transmitted diffracted light p2.
q2 is diffracted by the second mark 15. Of the ±nn order forward lights generated by this diffraction, the 0th order lead light is reflected by the high reflection mirror 20 as reflected interference light e2 and guided to the photoelectric detector 21.

Here, the light intensity of the reflected interference light e2 corresponds to whether the moiré fringes and the second mark 15 match or do not match. Therefore, the detection signal from the photoelectric detector 21 becomes relative position information between the mask 11 and the wafer 12.

As a result, the mask 11 is aligned with the projection lens 1o and the mask 11 and the wafer 12 are aligned based on the position information of the mask 11 with respect to the projection lens 1o and the relative position information of the mask 11 and the wafer 12.

(2) When the frequency shift mechanism is activated In this case, the frequency shift mechanism 23 is placed on the optical path of the alignment photoelectric, and the frequency of the alignment photoelectric is shifted by f. As a result, a difference in frequency f occurs between the +1st-order diffracted light i and the 11th-order diffracted light q1, and a beat of frequency f occurs in the interference light el between these diffracted lights pl and Ql. Here, the phase of this beat represents positional information between the mask 11 and the projection lens 1o. However, the signal processing circuit 19 compares the phase of the beat detected by the photoelectric detector 18 with the phase of the frequency signal from the frequency shift mechanism 23,
From this shift, positional information of the mask 11 with respect to the projection lens 1o is determined.

On the other hand, in the light intensity of the reflected interference light e2 from the second mark 15, a beat of frequency f occurs, similar to the interference light el.

However, the signal processing circuit 22 compares the phase of the beat detected by the photoelectric detector 21 with the phase of the frequency signal from the frequency shift mechanism 23, and obtains relative position information between the mask 11 and the wafer 12 from this shift.

In this way, in the above embodiment, each of the first marks 13 and 14 is irradiated with each of the alignment lights p and q of the same wavelength, and the interference light eL of the diffracted light is detected and the projection lens 10 of the mask 11 is Along with this, the transmitted diffracted light p2. of each first mark 1B, 1.4 is obtained. q2 is irradiated onto the second mark 15, and the mask 1 is detected from the moire fringes.
Since the relative position information between the projection lens 1 and the wafer 12 is determined, the mask 11 can be aligned with the projection lens 10 with high precision, and the mask 11 and the wafer 12 can be aligned with high precision. As a result, even if the same wafer 12 is exposed multiple times, no deviation occurs in the transferred patterns.

Furthermore, since the alignment photoelectric signal is shifted by the frequency shift mechanism 23 and the optical hetero gain phase detection method is used in each signal processing circuit 19 and 22 accordingly, it is not affected by changes in the reflectance of the mask 11, etc. .

Next, a second embodiment of the present invention will be described with reference to FIG. Note that the same parts as in FIG. 1 are given the same reference numerals, and detailed explanation thereof will be omitted. The apparatus shown in FIG. 4 scans the alignment photoelectric. That is, the alignment photoelectric is sent to the 71-half mirror 31 through the beam scanning mechanism 30, and this half mirror 3
1, the alignment light is split into two directions, and one of the alignment lights is
is reflected by a high reflection mirror 32 and sent to the first mark 13, and the other alignment photoelectric 2 is sent to the first mark 14. and each first mark 1
Predetermined diffracted lights of the ±nn-th order forward lights generated in step 3.14 are respectively condensed by a condenser lens 33 and irradiated onto a third mark 34 made of a diffraction grating. Then, interference occurs on this third mark 34, and this interference light e
3 is made incident on the photoelectric detector 35. Here, the light intensity of the interference light e3 is determined by the projection lens 10 of the mask 11.
It corresponds to the position relative to. However, photoelectric detector 3
5 detects the light intensity of the interference light e3 and sends the detection signal to the signal processing circuit 36. On the other hand, a signal processing circuit 37 is connected to the photoelectric detection circuit 21, and these signal processing circuits 36
．． A scan synchronization signal from the beam scanning mechanism 30 is input to 37. However, these signal processing circuits 3
6.37 receives the scan synchronization signal and performs alignment photoelectric 1. photoelectric detector 3 in synchronization with the scan of r2.
The detection signal from 5°21 is manually processed. As a result, the mask 11 is aligned with the projection lens 10, and the mask 11 and the wafer 12 are aligned, as in the first embodiment.

In this way, by scanning the alignment light and signal-processing each interference light in synchronization with this scanning, it becomes immune to external influences.

Note that the present invention is not limited to the above-mentioned embodiment, and may be modified without departing from the spirit thereof. For example, although the above embodiment has been applied to the mutual alignment of a mask, wafer, and projection lens, the present invention is not limited thereto and can also be applied to alignment of objects.

[Effects of the Invention] As detailed above, according to the present invention, it is possible to provide an alignment method in which a mask and a projection lens can be aligned with high precision, and also a mask and a wafer can be aligned with high precision.

[Brief explanation of drawings]

1 to 3 are diagrams for explaining a first embodiment of an alignment device to which the alignment method of the present invention is applied,
Figure 1 is a configuration diagram, Figure 2 is a schematic diagram of each mark, Figure 3 is an external view of the actual device, Figure 4 is a configuration diagram of the second embodiment of the present invention, and Figures 5 and 6. FIG. 1 is a diagram for explaining a conventional technique. 10... Projection lens, 11... Mask, 12...
Wafer, 13.14...First mark, 15...Second mark, 16.20...High reflection mirror 17.
...)\-Fumirar 18.21...Photoelectric detector, 1
9.22... Signal processing circuit, 23... Frequency shift mechanism, 30... Beam scanning mechanism, 31... Half mirror 32... High reflection mirror 33... Condensing lens, 34...・Third mark, 35... photoelectric detector,
36.37...Signal processing circuit.

Claims (2)

[Claims] (1) In an alignment method of aligning the projection lens with a first object and a second object that are arranged to face each other via a projection lens, the first object is provided with at least two first diffraction gratings. At the same time, a second diffraction grating is formed on the second object, and each alignment light of the same wavelength is irradiated to these first diffraction gratings to produce interference light of each diffracted light from these first diffraction gratings. is detected to obtain positional information of the first object with respect to the projection lens, and together with this, the transmitted diffraction light of each of the first diffraction gratings is irradiated to the second diffraction grating through the projection lens, and the second diffraction grating is detecting the reflected diffracted light from the diffraction grating of the first object and the second object.
An alignment method characterized by obtaining relative position information with an object. (2) The alignment method according to claim (1), wherein the wavelength of at least one of the alignment lights irradiated onto each first diffraction grating is modulated.