JPH0335107A - Diffraction grating for detecting relative position - Google Patents

Abstract

PURPOSE:To decrease the influence of multiple reflections and to detect positions with high accuracy by providing a reflection type diffraction grating for preventing the multiple reflections in the opaque parts of a transmission type diffraction grating and on the surface opposite to the reflection type diffraction grating. CONSTITUTION:The transmission type diffraction grating 6a has the reflection type diffraction grating 41 for preventing the multiple reflections on the surfaces, opposite to the reflection type diffraction grating 8, of the opaque parts 31a. The multiple reflections which are liable to arise between the opaque parts 31a of the grating 6an the diffraction grating 8 are suppressed by the presence of this grating 41. The influence of the multiple reflections is decreased at the time of detecting the relative positions by a double diffraction grating method. Contribution is thus made to the high-accuracy detection of the positions.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to a diffraction grating for relative position detection.

(Prior Art) As is well known, circuit patterns in VLSIs are formed using an exposure device. That is, a circuit pattern is formed on a mask in advance, and this is transferred onto the wafer using, for example, X-rays.

By the way, in order to transfer such a circuit pattern to a desired area on the wafer, it is necessary to set the relative position between the mask and the wafer with high precision prior to transfer. The double diffraction grating method is known as a typical method for aligning the relative positions of Marsuf and Ueno\, for example in the direction along the opposing surfaces. In this method, for example, a transmission type diffraction grating is provided on the mask and a reflection type diffraction grating is provided on the Ueno\, and monochromatic light is emitted from above the mask.
That is, laser light is irradiated. Then, the laser beam is diffracted in the order of the diffraction grating of the mask, the diffraction grating of the sea urchin/ alignment in the direction along the opposing surface.

FIG. 7 shows a schematic configuration of an alignment device that aligns the mask and the wafer 1 using this method.

In the figure, 1 indicates a wafer table arranged movably in the x and y directions, and 2 indicates a wafer fixed on the wafer table 1. A mask 3 is placed above the wafer 2 and facing the wafer 2. This mask 3 is supported by a stationary part via a holder 4 and an actuator 5 for position adjustment in two directions.

Transmissive diffraction gratings 6 and 7 are provided at predetermined positions on the mask 3, respectively. Further, a reflective diffraction grating 8 is provided on the wafer 2 at a position facing the diffraction grating 6, and a reflective diffraction grating 9 is also provided at a position facing the diffraction grating 7. In these diffraction gratings, diffraction gratings 6 and 8 form one set to form a double diffraction grating, and diffraction gratings 7 and 9 form another set to form a double diffraction grating. There is.

An alignment device 11 is provided above the mask 3 for aligning the mask 3 and the wafer 2 using the two sets of double diffraction gratings described above.

This alignment device 11 is constructed as follows. That is, a laser beam 13 having a wavelength λ outputted from a laser light source 12 is alternately and perpendicularly irradiated onto the diffraction grating 6.7 via the vibrating mirror 14 and the deflection elements 15a and 15b. Note that the vibrating mirror 14 is driven by the output of the oscillator 16. On the other hand, at a position above the mask 3, a diffracted light intensity 11 of a specific order in the diffracted light obtained by diffracting the diffraction grating 6, the diffraction grating 8, and the diffraction grating 6 in this order by irradiating the laser beam 13 and A sensor 17 is arranged to commonly receive the diffracted light intensity (2) of a specific order in the diffracted light obtained by diffracting the diffraction grating 7, the diffraction grating 9, and the diffraction grating 7 in this order, either directly or through a reflecting mirror. There is. The output of the sensor 17 is amplified by an amplifier 18 and then introduced into a synchronous detector 19 driven by using the output of the oscillator 16 as a reference signal, where 11, ! It is separated into two parts. The two signals are then introduced into the signal processing circuit 20. This signal processing circuit 20 is
Δl-11-I2 is calculated, and a signal in the direction of setting ΔI to 0 is given to the motor 22 for controlling the wafer table position via the motor drive circuit 21.

The motor 22 operates according to the applied voltage and positions the wafer table 1 in a state of ΔI-0.

In order to achieve alignment in this manner, the diffraction gratings 6.8 and 7.9 provided in pairs on the mask 3 and the wafer 2 are usually formed as shown in FIG. There is. That is, the diffraction grating 6 (7) has an opaque portion 31 which is a striped pattern formed at a predetermined pitch with a resist on the lower surface of the mask 3, and a combination of this opaque portion 31 and a transparent mask component. They are combined to form a transparent type. Further, the diffraction grating 7 (8) is connected to the wafer 2
The protrusions 32 are, for example, a stripe-like pattern formed with a resist at a predetermined pitch on the upper surface, and the protrusions 32 and the wafer constituent material are combined to form a reflective type.

but? However, when a double diffraction grating having the above-mentioned configuration is used, multiple reflections usually occur between the mask and the wafer, that is, between the diffraction gratings forming a pair.

That is, as shown by the two-dot chain line in FIG.
9), and a part of it travels toward the lower surface of the opaque portion 31. Light incident on the lower surface of the opaque portion 31 is reflected by this lower surface toward the diffraction grating 8 (9) side. 8th
In the diffraction grating 6 (7) having the configuration shown in the figure, the light is reflected from the opaque portion 31 toward the diffraction grating 8 (9). Between the n-th order Fourier coefficient f of the reflectance of this reflection diffraction grating and the order n, n
f = 1s1n(1/2)nπ) in the region where is 1 or more
/ (nπ) holds true. To illustrate this in a diagram,
As shown in Fig. 9, the zeroth order is fo-+0.5, and the ±1st order is f-+0.318. Such reflected diffraction light is reflected again by the diffraction grating 8 (9), and a portion of the reflected diffraction light is transmitted through the diffraction grating 6 (7) and diffracted, and enters the sensor 17. For this reason, multiple reflection diffraction light components, especially low-order diffraction light components, are superimposed on the detected diffraction light, which makes it extremely difficult to accurately detect the point where ΔI crosses zero. It was difficult to perform alignment.

(Problems to be Solved by the Invention) As mentioned above, even when trying to detect the relative position of two objects using the double diffraction grating method using a diffraction grating with a conventional structure, the influence of multiple reflections occurring between the diffraction gratings Due to this, there was a problem in which highly accurate position detection could not be performed.

Therefore, an object of the present invention is to provide a relative position detection diffraction grating in which the diffraction grating itself has a function of suppressing multiple reflections.

[Structure of the invention] (Means for solving the problem) In order to solve the above problem, in one embodiment of the present invention, the first
A relative position detection diffraction grating comprising a transmission diffraction grating and a reflection diffraction grating, which are provided in opposing relation to each of the objects, in order to detect the relative position between the object and the second object using the double diffraction grating method. In this method, a reflection type diffraction grating for preventing multiple reflections is provided in an opaque portion of the transmission type diffraction grating and on a surface facing the reflection type diffraction grating.

Specifically, the reflective diffraction grating for preventing multiple reflections is divided into steps of approximately (1m+1)λ/4, where λ is the wavelength of monochromatic light irradiated during relative position detection and m is an arbitrary integer. The opaque portion has two types of reflective surfaces, and the width of one of the reflective surfaces is approximately 1/2 of the width of the opaque portion.

Further, in another embodiment of the present invention, a reflection type diffraction grating for preventing multiple reflections is provided on a surface of the reflection type diffraction grating that faces the transmission type diffraction grating.

The reflective diffraction grating for preventing multiple reflections in this example is partitioned by steps of approximately (2m+1)λ/4, where λ is the wavelength of the monochromatic light irradiated during relative position detection, and m is an arbitrary integer. It is formed into two types of stepped reflective surface structures.

(Function) In one example, the reflection grating for preventing multiple reflections having the above structure is provided in the opaque part of the transmission grating, so the presence of the reflection grating for preventing multiple reflections prevents the transmission grating from forming. Multiple reflections that tend to occur between the opaque portion and the reflective diffraction grating are suppressed.

Further, in other examples as well, the presence of the reflection type diffraction grating for preventing multiple reflections suppresses multiple reflections that are likely to occur between the opaque portion of the transmission type diffraction grating and the reflection type diffraction grating.

(Example) Examples will be described below with reference to the drawings.

FIG. 1 shows a relative position detection diffraction grating according to an embodiment of the present invention. In this figure, the same parts as in FIG. 8 are indicated by the same reference numerals. Therefore, detailed explanation of the overlapping parts will be omitted.

The difference between the relative position detection diffraction grating according to this embodiment and the conventional one is that the transmission type diffraction grating 6 provided on the mask 3
It has the structure of a (7g).

That is, the transmission type diffraction grating 6a (7a) is provided with a reflection type diffraction grating 41 for preventing multiple reflections on the surface of the opaque portion 31a facing the reflection type diffraction grating 8 (9).

As shown in an enlarged view in FIG. 2, the reflection type diffraction grating 41 for preventing multiple reflection is located at the center of the lower surface of the opaque portion 31a in the figure.
The bottom surface of the groove 42, which has a depth of approximately 1/4 of the wavelength λ of the laser beam 13 and a width of approximately 1/2 of the width p of the opaque portion, is used as one reflective surface 43, and the so-called side wall of the groove 42 The end face is used as the other reflective surface 44, and it is configured by a combination of the two incident surfaces 43 and 44. That is, the reflection type diffraction grating 41 for preventing multiple reflections has the following formula, where λ is the wavelength of monochromatic light irradiated during relative position detection, and m is an arbitrary integer.
It has two types of reflective surfaces 43 and 44 separated by a step of approximately (2m+1)λ/4, and one reflective surface 43 (44).
It is formed into a stepped reflective surface structure whose width is approximately 1/2 of the width of the opaque portion 31a.

With the combination of the transmission type diffraction grating 6a (7a) and the reflection type diffraction grating 8 (9) having such a structure, the opaque portion 3
It has been found that the relationship expressed by the following equation (1) holds between the n-th order Fourier coefficient f of the reflectance of the reflection diffraction grating from 1a and the order n.

f , −[5inl(1/2)nyr l−2sl
n((1/4)n yr l]/, (nπ> ・
...(1) This is illustrated in Figure 3. As you can see from this figure, in the 0th order, fo”0, and in the ±1st order, f ,, -
-0,132. When this characteristic is compared with the characteristic of the conventional one shown in FIG. 8, the values are significantly smaller in the 0th order and the ±1st order. However, on the contrary, it becomes larger for secondary and higher orders. However, when the relative position is detected by detecting diffracted light with the sensor 17, the reflected diffracted light that affects the detected diffracted light is 0th-order and ±1st-order diffracted light, and higher-order such as 2nd and 3rd orders. Reflected and diffracted light has almost no effect. Therefore, as mentioned above, fo-0 in 0th order and f in ±1st order
With the characteristic of -10.132, the reflected diffraction light component superimposed on the detected diffraction light can be made extremely small, and as a result, the relative alignment accuracy can be improved.

Note that the present invention is not limited to the above embodiments.

That is, in the above embodiment, the cross-sectional shape of the groove 42 is a rectangular groove, but as shown in FIG. Even if the groove 42b has a half-groove structure in which the side wall is eliminated, the same effect as in the embodiment described above can be obtained as long as the above-mentioned conditions are satisfied.

FIG. 6 shows the main part of a relative position detection diffraction grating according to still another embodiment of the present invention.

In the relative position detection diffraction grating according to this embodiment, a reflection type diffraction grating 41c for preventing multiple reflections is provided on the diffraction grating 8a (9g) provided on the wafer 2 side. This reflection type diffraction grating 41c for preventing multiple reflection has a diffraction grating 8a (9a
) and a wafer constituent material.

That is, as shown in the figure, the difference in level between the protrusion 32a and the flat part 33 of the constituent material of the wafer 2 is detected by approximately 1/4 of the wavelength of the laser beam 13, that is, by detecting the relative position. When the wavelength of monochromatic light that is irradiated at the same time is λ, and m is an arbitrary integer, there is a step of approximately (21◆l)λ/2, and two types of reflective surfaces (projections 32a and The flat portion 33) constitutes a reflection type diffraction grating 41c for preventing multiple reflections.

Even with such a configuration, the diffraction grating 8a on the wafer 2 side
The 0th order of the nth Fourier coefficient f of the reflectance in (9a) can be set to zero, that is, fo''O, and the same operation and effect as in the previous embodiment can be obtained.

Further, in the case of this embodiment, the diffraction grating 8a (9a) having the same pitch as the conventional one can be used, and only the steps need to be set to the above value, so that the formation of the diffraction grating can be facilitated.

Note that the diffraction grating according to the present invention can be used not only for position detection in a direction along the opposing surfaces of a mask and a wafer, but also for detecting a gap between a mask and a wafer.

Further, its use is not limited to detecting the relative position between a mask and a wafer, but can also be used for various types of relative position detection. Furthermore, the pattern shapes of both diffraction gratings are not limited to striped shapes.

C Effects of the Invention As described above, according to the present invention, the diffraction grating itself has the function of suppressing multiple reflections, so multiple reflections can be prevented when relative positions are detected using the double diffraction grating method. This can reduce the influence and contribute to highly accurate position detection.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a relative position detection diffraction grating according to an embodiment of the present invention, FIG. 2 is a cross-sectional view partially showing a transmission type diffraction grating in the same diffraction grating, and FIG. Figures 4 and 5 are cross-sectional views showing locally modified examples of transmission type diffraction gratings, and Figure 6 is another embodiment of the present invention. 7 is a cross-sectional view showing a locally extracted reflection type diffraction grating in the relative position detection diffraction grating according to FIG.
FIG. 8 is a sectional view of a conventional position detection diffraction grating, and FIG. 9 is a diagram showing the reflection characteristics of a transmission type diffraction grating in the same diffraction grating. 2... Wafer, 3... Mask, 6 a s 7 a
... Transmission type diffraction grating, 8.8a, 9,9a... Reflection type diffraction grating, 11... Alignment device, 31a... Opaque portion, 32.32 a = - protrusion, 41.41a −
41bs41c...Reflection type diffraction grating for preventing multiple reflections,
42, alb...groove, 43. 44... Reflective surface.

Claims (4)

[Claims] (1) In order to detect the relative positions of the first object and the second object by the double diffraction grating method, a relative consisting of a transmission diffraction grating and a reflection diffraction grating is provided in a facing relation to each of the above objects. In the position detection diffraction grating, the transmission type diffraction grating is provided with a reflection type diffraction grating for preventing multiple reflections on its opaque portion and on a surface facing the reflection type diffraction grating. Diffraction grating for use. (2) The reflective diffraction grating for preventing multiple reflections is partitioned by steps of approximately (2m+1)λ/4, where λ is the wavelength of the monochromatic light irradiated during relative position detection, and m is an arbitrary integer. 2. The reflective surface according to claim 1, wherein the reflective surface has two types of reflective surfaces, and the width of one of the reflective surfaces is approximately 1/2 of the width of the opaque portion. Diffraction grating for relative position detection. (3) In order to detect the relative positions of the first object and the second object by the double diffraction grating method, a relative member consisting of a transmission diffraction grating and a reflection diffraction grating is provided in a facing relation to each of the above objects. A diffraction grating for position detection, characterized in that the reflection type diffraction grating includes a reflection type diffraction grating for preventing multiple reflections on a surface facing the transmission type diffraction grating. (4) The reflective diffraction grating for preventing multiple reflections is partitioned by steps of approximately (2m+1)λ/4, where λ is the wavelength of the monochromatic light irradiated during relative position detection, and m is an arbitrary integer. 4. The relative position detection diffraction grating according to claim 3, wherein the diffraction grating is formed in two types of stepped reflective surface structures.