JPH0115082B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device that performs alignment using two diffraction gratings arranged in parallel, and in particular, an apparatus that is less susceptible to the influence of gap fluctuations between each diffraction grating and has a simplified configuration. This invention relates to an alignment device that has been developed.

Conventionally, this type of alignment device involves vibrating at least one of two diffraction gratings arranged in parallel in the irradiation direction of the coherent light to change the distance between the gratings, or modulating the wavelength of the coherent light. This modulates the phase of the diffracted light, thereby eliminating the influence of fluctuations in the gap between each diffraction grating due to floor vibration, etc.
10080). This device is currently being applied, for example, to alignment between a semiconductor wafer and an IC mask.

However, as semiconductor wafers have become larger in recent years,
The diameter of IC masks is becoming larger. For this reason, if the phase of the diffracted light is modulated by, for example, micro-vibrating the IC mask using the conventional alignment device, it is difficult to vibrate the entire surface of the IC mask uniformly, so the detection location may vary depending on the position. There was a risk that the detected amount of deviation would be biased, leading to a decrease in accuracy.

On the other hand, when applying a method that modulates the wavelength of coherent light to modulate the phase of diffracted light, the above IC
Although it is not affected by the increase in the size of the mask, the laser oscillation device for obtaining coherent light becomes complicated and large, making the device extremely expensive and not suitable for practical use.

The present invention has been made in view of the above circumstances, and its purpose is to always perform stable and highly accurate alignment regardless of the size of the object to be aligned, and to have a simple and inexpensive configuration. The object of the present invention is to provide a positioning device that is suitable for use.

In the present invention, two diffraction gratings arranged in parallel are vertically irradiated with a plurality of coherent lights having different wavelengths, and the difference between the interference intensity in the +n-order direction and the -n-order direction of the diffracted light by each diffraction grating is is detected for each of the above-mentioned coherent lights, the root mean square of each of these interference intensities is determined, and this value is used as the mutual displacement amount of each diffraction grating, that is, the mutual displacement amount of the objects to be aligned. Achieve your purpose.

First, the principle of the present invention will be explained. As shown in FIG. 1, when coherent light 3 is perpendicularly irradiated onto diffraction gratings 1 and 2 which are arranged parallel to each other with an interval d, the following three types of diffracted light are generated. That is, (i) Diffracted light 3a, 3a reflected by the diffraction grating 1 (ii) Diffracted light 3 transmitted through the diffraction grating 1, specularly reflected by the diffraction grating 2, and diffracted by the diffraction grating 1 again
b, 3b (iii) These are the diffracted lights 3c, 3c which are transmitted through the diffraction grating 1 and then reflected and diffracted by the diffraction grating 2. And each of these diffracted lights 3a, 3b, 3
Letting the amplitudes of c be a, b, and c, respectively, the interference intensity I ⁺ n of interference light in the +n-order direction by these diffracted lights 3a, 3b, and 3c is I ⁺ⁿ = a ² + b ² + c ² + 2ab cos4πd /λ +2ac cos (4πd/λ+2πn・ΔX/P) +2bc cos (2πn・ΔX/P) ...(1) On the other hand, the interference intensity of the interference light in the -n order direction is I ^-n
It is known that I ^-n = a ² + b ² + c ² + 2ab cos4πd/λ + 2ac cos (4πd/λ-2πn・ΔX/P) +2bc cos (2πn・ΔX/P) ...(2) There is. However, P is the grating pitch of the diffraction gratings 1 and 2, and ΔX is the amount of deviation between the diffraction gratings 1 and 2.

Also, the difference between these interference strengths I ⁺ⁿ I ^-n is I ^-n −I ⁺ⁿ = 2ac {cos (4πd/λ−2πn・ΔX/P) −cos (4πd/λ+2πn・ΔX/P) } =4ac sin(2πn・ΔX/P) sin(4πd/
λ) ...(3).

Therefore, for example, even when two coherent lights with wavelengths λ ₁ and λ ₂ are irradiated, the interference intensity difference I〓 ₁ , I〓 ₂ for each coherent beam is as follows: I〓 ₁ = I〓 ₁ ^{- n} −I〓 ₁ ⁺ⁿ = 4ac sin (2πn・ΔX/P) sin (4πd/λ ₁ )...
(4) I〓 ₂ ＝I〓 ₂ ^-n −I〓 ₂ ⁺ⁿ ＝4ac sin(2πn・ΔX/P) sin(4πd/λ ₂ )……
(5)

In order to obtain the same effect as when modulating the coherent light in a pseudo manner, each of the above interference intensities I〓 ₁ , I〓 ₂
Combine and average. That is, if we calculate the square mean of the above I〓 ₁ and I〓 ₂ , we get becomes. This formula also becomes, using the relationship sin ² θ=1−cos2θ/2, And further, from the relationship cosθ+cos=2cosθ+/2・cosθ−/2 becomes.

Here, if cos {4πd (1/λ ₁ -1/λ ₂ )}≪1, then cos {4πd (1/λ ₁ +1/λ ₂ )} cos {4πd (1/λ ₁ -1/λ ₂ ) }≪1, and the above equation (7) is approximately 1. On the other hand, the relationship cos{4πd(1/λ ₁ -1/λ ₂ )}≪1 is obtained when 4πd(1/λ ₁ -1/λ ₂ )≒(m+1/2)π (m is an integer), that is, , d≒1/4(λ ₁ λ ₂ /λ ₂ −λ ₁ )(m+1/2).

Therefore, the above formula (7) is d≒1/4 (λ ₁ λ ₂ /λ ₂ -λ ₁ ) (m+1/2)...
When (8), I≒4ac sin(2πn・ΔX/P)...(9).

This relationship will be explained in more detail. That is, in Equation (7) above, the term √ is the difference between diffraction gratings 1 and 2.
It represents the change component due to the gap d between the two, and eliminating the influence of the gap d means cos {4πd (1/λ ₁ + 1/λ ₂ )} × cos {4πd (1/λ ₁ − 1/λ ₂ )} is always approximately O, that is, at least one of cos{4πd(1/λ ₁ +1/λ ₂ )} or cos{4πd(1/λ ₁ −1/λ ₂ )} is always approximately O. This means that it should be approximately O.

Now, if we assume that λ ₁ and λ ₂ are set to λ ₁ = 0.4880 μm and λ ₂ = 0.5145 μm, which are typical periods of an argon laser, then the above (7)
Cos {4πd (1/λ ₁ -1/λ ₂ )} in the formula is expressed as shown in Figure 5 a, and cos {4πd (1/λ ₂ +1/λ ₁ )} is expressed as shown in Figure 5 b. It is expressed as shown below. FIG. 5b is an enlarged view of the period shown in FIG. 5a.
As is clear from this figure, the characteristic period (about 5 μm) of cos {4πd (1/λ ₁ - 1/λ ₂ )} is equal to cos {4πd (1/λ 2 )}.
λ ₁ + 1/λ ₂ )} is significantly longer than the characteristic period (approximately 0.12 μm).

On the other hand, semiconductor wafers caused by external vibrations, etc.
According to current technology, variation in the gap between the IC mask and the IC mask can be suppressed to a maximum of about ±0.1 μm. That is, regarding gap fluctuations, it is sufficient to make it possible to ignore even fluctuations within this range of ±0.1 μm.

Therefore, when this condition is applied to the characteristics shown in Fig. 5 above, the maximum variation range of the gap d (±
The amount of change in interference intensity I at 0.1μm) is cos
Although {4πd(1/λ ₁ +1/λ ₂ )} is very large, cos{4πd(1/λ ₁ −1/λ ₂ )} is so small that it can be ignored. For this reason, cos {4πd (1/λ ₁ + 1/λ ₂ )} ×cos {4πd (1/λ ₁ -1/λ ₂ )} in the above equation (7) should always be approximately O. In this case, the initial value of the gap d may be set so that cos{4πd(1/λ ₁ −1/λ ₂ )}≪1. This value corresponds to, for example, d=8.29 μm in the example of FIG. 5 above. With this setting, even if the gap d fluctuates within the range of ±0.1 μm, the amount of change in cos {4πd (1/λ ₁ - 1/λ ₂ )} is small and ≒O is maintained. Therefore, the above cos{4πd (1/λ ₁ +1/λ ₂ )} ×cos {4πd (1/λ ₁ −1/λ ₂ )} also maintains approximately O. As a result, the gap d
It becomes possible to substantially eliminate the influence of fluctuations in the interference intensity I. Therefore, the above equation (9) holds true.

As is clear from this relationship, each diffraction grating 1,
If the distance between the two diffraction gratings (gap) is set to a value corresponding to equation (8) above, even if the distance between each diffraction grating 1 and 2 changes slightly in that state, equation (9) above will hardly change. First, the amount of deviation ΔX between the diffraction gratings 1 and 2
It becomes a function of only.

Therefore, if the alignment device is configured with attention to the above relationship, alignment can be performed that is almost unaffected by fluctuations in the distance d between the diffraction gratings 1 and 2.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a schematic diagram of the alignment device in the same embodiment. In the figure, a semiconductor wafer 13 as an object to be aligned is placed on a movable table 12 that is movable on a base 11. On the peripheral edge of the semiconductor wafer 13, first diffraction gratings 14 are provided, for example, every 90 degrees. The moving table 12 is precisely moved by a table driving device 15 having a pulse motor. On the other hand, above the semiconductor wafer 13, an IC mask 17 is supported by a support stand 16 and is arranged in parallel as an object to be aligned. A second diffraction grating 1 is provided at the periphery of the IC mask 17, facing the first diffraction grating 14.
8 is provided. The grating pitches of the first and second diffraction gratings 14 and 18 are both set to have the same length. Further, the distance (gap) between the first and second diffraction gratings 14 and 18 is set by vertical movement of the support base 16 so as to satisfy the above-mentioned formula (8).

The alignment device of this embodiment applies two laser beams of different wavelengths (λ ₁ =0.488 μm and λ ₂ =0.5145 μm) from, for example, the argon gas laser device 20 to the first and second diffraction gratings 14 and 18. )2
1 and 22 are irradiated vertically. Then, the diffracted lights 23 and 24 in the +n-order direction and the -n-order direction by the respective diffraction gratings 14 and 18 are separated and received by the spectroscopic diffraction gratings 25 and 26 into parts corresponding to the respective laser beams 21 and 22. vessels 27a, 27b and 2
It is detected at 8a and 28b. After that, these light receivers 27a, 27b and 28a, 28
The detection signals of b are respectively transmitted to preamplifiers 29a and 2
After amplification by 9b and 30a, 30b, differential amplifiers 31, 32 subtract signals having the same wavelength from each other. Then, a signal corresponding to the interference intensity difference obtained by each of these differential amplifiers 31 and 32 is introduced into the arithmetic circuit 33, where the root mean square of each of the interference intensity differences is calculated, and this calculated value is used as the above-mentioned. The amount of deviation between the semiconductor wafer 13 and the IC mask 17 is displayed on the display device 34. At the same time, the calculated value of the arithmetic circuit 33 is also led to the table moving device 15. Table moving device 15
is to move the moving table 12 in order to make the above calculated value zero.

With such a configuration, each diffraction grating 14,
When the laser beams 21 and 22 are irradiated onto the diffraction gratings 14 and 18, interference light 2 with an intensity corresponding to the amount of deviation between the diffraction gratings 14 and 18 is generated.
3 and 24 are arranged in the +n-th direction and the -n-th direction, respectively;
The light is detected at 28b and converted into a light reception signal. Each of these received light signals is amplified separately and then introduced into operational amplifiers 31 and 32, where the difference between signals having the same wavelength is determined. This results in
The disturbance light components that have entered the light receivers 27a, 27b and 28a, 28b are canceled out and removed. Then, each of the above difference signals from which the disturbance light component has been removed is
The arithmetic circuit 33 calculates the square mean. As a result, as is clear from equation (9) above, the diffraction grating 1
The influence of the distance d between 4 and 18 is eliminated. Therefore, during alignment, the diffraction grating 1 may be damaged due to floor vibration, etc.
Even if the distance d between 4 and 18 changes, its influence will not appear in the detection result of the amount of positional deviation. The above effects are shown in a graph as shown in Fig. 3.
In other words, the distance between diffraction gratings (gap) d is plotted on the horizontal axis.
, and the output signal of the arithmetic circuit 33, that is, the root mean square value I of each difference signal, is plotted on the vertical axis. When expressed as a value, it is approximately constant. This indicates that the output signal of the arithmetic circuit 33 hardly changes due to the variation in the distance d between the diffraction gratings 14 and 18, as described above. Incidentally, when only one laser beam is used, the detected value (I ^-n -I ⁺ⁿ ) changes greatly due to variations in the gap d, as shown in FIG. 4, and is not usable.

As described above, according to the alignment device of this embodiment, by using two laser beams with different wavelengths and simply finding the root mean square value of each interference intensity obtained thereby, it is possible to eliminate the adverse effects caused by vibrations of the floor surface, etc. The amount of positional deviation can be calculated easily and accurately without any problems. As a result, semiconductor wafer 13 and IC mask 1
7 can be accurately and quickly aligned. Further, since there is no need to modulate the laser beam itself as in the conventional case, the structure of the laser device does not become complicated or large, and as a result, a device with a simple structure and low cost can be provided.
Furthermore, in this embodiment, there is no need to vibrate the diffraction grating, so even if the semiconductor wafer 13 and the IC
Even if the mask 17 is large, stable and highly accurate positioning can be performed.

Note that the present invention is not limited to the above embodiments. For example, the wavelength of laser light is λ ₁ =
In addition to using 0.488 μm and λ ₂ =0.5145 μm, other wavelengths may be used. Further, the number of laser beams may be three or more instead of two. In this case, each interference intensity difference is calculated by 2 as I=√〓 ₁ ² +〓 ₂ ² +〓 ₃ ² +...
Just take the average value. In addition, the type of coherent light, the configuration of the arithmetic circuit, etc. can be modified in various ways without departing from the gist of the present invention.

As detailed above, a plurality of coherent beams having different wavelengths are vertically irradiated onto a diffraction grating, and the difference between the interference intensity in the +n-order direction and the interference intensity in the -n-order direction of the diffracted light by the diffraction grating is determined by According to the present invention, each interference light is detected individually, the square mean of these interference intensities is calculated, and this value is used as the amount of positional deviation of the object to be aligned. It is possible to provide a positioning device which can perform positioning with high stability and accuracy, and which is simple in configuration and inexpensive.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram used to explain the principle of the present invention, FIG. 2 is a schematic diagram of the alignment device in an embodiment of the present invention, and FIGS. 3 and 4 are used to explain the operation of the device. FIG. 5 is a characteristic diagram used to explain the principle of the present invention. 1, 2, 14, 18... Diffraction grating, 3... Coherent light, 3a, 3b, 3c... Diffracted light, 12... Moving table, 13... Semiconductor wafer, 15... Table moving device, 17... IC mask, 20... Laser device, 2
1, 22... Laser light, 23, 24... Diffracted light, 2
5, 26... Diffraction grating for spectroscopy, 27a, 27b, 2
8a, 28b...light receiver, 29a, 29b, 30
a, 30b... preamplifier, 31, 32... operational amplifier, 33... operational circuit, 34... display device.

Claims (1)

[Claims] 1. In an alignment device in which first and second diffraction gratings of the same grating pitch are provided on objects to be aligned that are arranged parallel to each other, and the objects to be aligned are aligned with each other, a light source that perpendicularly irradiates a plurality of coherent light beams having different wavelengths onto the first and second diffraction gratings arranged therein, and an interference intensity in the +n-order direction and an interference in the -n-order direction of the diffracted light by each of the diffraction gratings. means for detecting the difference in intensity for each of the coherent beams; and means for obtaining the square mean of the interference intensity differences obtained by the means and obtaining the amount of deviation between the objects to be aligned from this value. A positioning device characterized by comprising: