JPH0729812A - Optical system for alignment - Google Patents

Abstract

PURPOSE:To provide an optical system for alignment in which the accuracy and safety of alignment is prevented from lowering due to the heat generated from a laser light source. CONSTITUTION:A laser light source 1 is disposed while being separated spatially from optical components 15, 24, 25... disposed in a chamber 32. The laser light source 11 is connected with the optical components 15, 24, 25 through a single mode optical fiber 41.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alignment optical device used for alignment between objects using an optical phenomenon.

[0002]

2. Description of the Related Art As is well known, recently, attempts have been made to form a circuit pattern of a VLSI by an equal magnification exposure using an X-ray exposure apparatus. In order to perform pattern transfer using such an apparatus, it is necessary to align the mask and the wafer with high precision prior to exposure. In this case, it is necessary to realize overlay accuracy of about ± 0.05 μm in order to form a fine pattern of 0.2 μm.

An apparatus for highly accurately aligning a mask and a wafer arranged to face each other in a plane orthogonal to the facing direction is shown in Japanese Patent Application No. 63-329731 and Japanese Patent Application No. 2-25836. As described above, an optical heterodyne interference type alignment device using a diffraction grating is considered.

FIG. 3 schematically shows a main part of a typical optical heterodyne interference type alignment device. In this alignment device, a diffraction grating 1 is provided on a mask (not shown), and a diffraction grating 2 is provided on a wafer (not shown) so as to face the diffraction grating 1.

Now, it is assumed that the X-axis direction on the Cartesian coordinates shown in the figure is the alignment direction. The diffraction grating 1 is composed of a first grating 3a and a second grating 3b arranged in the Y-axis direction. Similarly, the diffraction grating 2 is also composed of a first grating 4a and a second grating 4b arranged in the Y-axis direction. That is, in this alignment device, the first grating 3a of the diffraction grating 1 and the first grating 4a of the diffraction grating 2 are paired, and the second grating 3b of the diffraction grating 1 and the second grating 4b of the diffraction grating 2 are paired. I have to.

The first grating 3a constituting the diffraction grating 1 is, for example, a checkered pattern provided at a pitch of P _{x in} the X-axis direction, and the second grating 3b is formed as a transparent window. ing. The first grating 4a forming the diffraction grating 2 is formed as a reflecting surface using the surface of the wafer as it is, and the second grating 4b has a checkered pattern at a pitch of P _{x in} the X-axis direction. It has been provided.

[0007] In this alignment device, facing the upper surfaces of the first grating 3a and the second grating 3b constituting the diffraction grating 1 and symmetrically with respect to a plane orthogonal to the alignment direction, specifically, Irradiates two laser beams 5 and 6 having different frequencies f ₁ and f ₂ from the directions of the ± first order of the X-direction pitch of the grating. These laser beams 5 and 6 are divided into two beams emitted from a laser light source by a half mirror or the like as described later, and then modulated to different frequencies f ₁ and f ₂ by _two acousto-optic modulators. It was obtained.

When the laser beams 5 and 6 are thus irradiated, the diffracted interference light I _M reflected and diffracted by the first grating 3a of the diffraction grating 1 is two-dimensionally distributed and emitted from the first grating 3a. At the same time, the interference diffracted light I _{W, which} is transmitted through the second grating 3 b, reflected and diffracted by the second grating 4 b of the diffraction grating 2 and interferes, and again transmitted through the second grating 3 b, is emitted in a two-dimensional distribution.

Therefore, light of a specific order of the interference diffracted light I _M , for example, 0th order in the alignment direction and 1 in the Y-axis direction.
The next light is detected, and a first beat signal having a frequency Δf = | f ₁ −f ₂ | including a phase shift φ _M corresponding to the mask position shift is obtained. On the other hand, the light of a specific order in the interference diffracted light I _W , for example, the 0 th order light in the alignment direction and the 1 st order light in the Y-axis direction is detected, and the phase shift φ _W corresponding to the wafer position shift is included. A second beat signal having a sub-frequency Δf = | f ₁ −f ₂ | is obtained.

In this alignment device, the phase difference between the first beat signal and the second beat signal, that is, | X _M -X _W |
Is calculated, and the positional shift between the mask and the wafer is calculated to obtain. Then, based on this value, the actuator for driving the wafer table is controlled to perform the alignment.

In such an alignment device, the frequency f
System and interference diffracted light I for obtaining the laser beams 5 and 6 of ₁ and f ₂ and irradiating them to the upper surface of the diffraction grating 1 under the above conditions
A system that detects _M and I _W and converts them into electric signals is required.

These systems are constructed as shown in FIG. That is, reference numeral 11 in the drawing denotes a laser light source.
The laser beam having strong coherence emitted from the laser light source 11 is divided into a first optical path and a second optical path by the beam splitter 12. The divided luminous fluxes are converted into acousto-optic modulators 13 and 14
Are modulated to slightly different frequencies f ₁ and f ₂ , respectively, and these are irradiated through the folding mirror 15 toward the diffraction grating 1 provided on the mask 16 in the above relationship.

Of the diffracted light generated by the irradiation of the light beams of frequencies f ₁ and f ₂ , the diffracted light of the 0th order in the alignment direction and the 1st order diffracted light I _M (0, 0) in the direction orthogonal to the alignment direction. 1),
The light of I _W (0,1) is received by the sensors 22 and 23 as detection light, and two beat signals are obtained. The mask 16 and the wafer 18 are aligned using the two beat signals as positional information. In FIG. 4, reference numeral 24 denotes a mirror, and 2
Reference numeral 5 indicates a lens.

By the way, such an alignment apparatus is provided with an X
The line exposure apparatus is usually provided as shown in FIG. That is, the beryllium wall 3 is made to face the mask 16.
1 and a chamber 32 in which the beryllium wall 31 and the mask 16 are closed so as to form a part of the chamber wall, and the laser light source 1 shown in FIG.
1 and acousto-optic modulators 13 and 14, and an optical component system such as a folding mirror 15. Then, in order to reduce the attenuation of X-rays between the beryllium wall 31 and the mask 16, the inside of the chamber 32 is kept in a vacuum atmosphere or a helium gas atmosphere. Further, in order to discharge the heat generated by the laser light source 11 to the outside of the chamber 32, the laser tube 3
3 is provided with a refrigerant passage 34, and a refrigerant is allowed to flow through the refrigerant passage 34 through a pipe 35. The beryllium wall 31 is for holding the vacuum of the X-ray guide path 36, and the SOR is provided through the beryllium wall 31.
The X-ray 37 generated by the above is irradiated.

However, the alignment device constructed as described above, particularly the alignment optical device including the laser light source and the optical component system in which a plurality of optical components are combined, has the following problems.

That is, when the laser tube 33 is in an oscillating state, the laser tube 33 generates heat. Most of this heat is carried out of the chamber 32 by the refrigerant flowing through the refrigerant passage 34 through the pipe 35. However, not all the heat generated can be carried out of the chamber 32. Therefore, the density of air around the laser light source 11 changes, and natural convection occurs in the chamber 32. When such natural convection occurs, the spatial density distribution of air around the optical components arranged in the chamber 32 changes with time, and as a result, the refractive index distribution of light changes with time. Due to this, the optical path length L of the light fluctuates. In the optical heterodyne interference type alignment device, the phase of light has an important meaning. When the wavelength of light is λ, the phase depends on (2π · L / λ). When it fluctuates, the phase also fluctuates. In addition, it is difficult to cool the laser tube 33 to a uniform temperature via the coolant passage 34, and as a result, the optical axis position also fluctuates. Due to these reasons, as shown in FIG. 6, there is a problem that the alignment signal is not stable forever and desired alignment accuracy cannot be obtained.

[0017]

As described above, the conventional alignment optical device has a problem in that the alignment signal is structurally changed. Therefore, an object of the present invention is to provide an alignment optical device capable of solving the above-mentioned problems.

[0018]

To achieve the above object, in the alignment optical device according to the present invention, the laser light source and the optical component system are spatially separated from each other, and the laser light source and the optical component system are provided. The optical component system is connected by an optical fiber. When the optical fiber is incorporated in the optical heterodyne interference type alignment device, a single mode optical fiber is used.

[0019]

Since the laser light source and the optical component system are spatially separated from each other, the heat generated by the laser light source does not affect the placement field of the optical component system. Therefore,
The optical path length of the optical component system does not fluctuate, and the phase of light can be stabilized. Also, since the laser tube of the laser light source can be cooled uniformly in the atmosphere,
Variations in the optical axis position can also be prevented, and alignment detection accuracy and stability can be significantly improved.

[0020]

Embodiments will be described below with reference to the drawings. FIG. 1 shows a schematic view in which an alignment optical device according to an embodiment of the present invention is incorporated into a positioning device in an X-ray exposure apparatus.

This alignment device is of the optical heterodyne interference type, and its principle is the same as that shown in FIGS. Therefore, the same parts as those in FIG. 5 are designated by the same reference numerals.

This alignment apparatus differs from the conventional one shown in FIG. 5 in that the laser light source 11 is arranged in the atmosphere outside the chamber 32, and the laser beam emitted from the laser light source 11 is a single mode optical. The purpose is to guide it to the optical component system arranged in the chamber 32 through the fiber 41.

That is, the laser tube 33 of the laser light source 11
Are placed in the atmosphere to allow natural cooling. Then, the laser beam emitted from the laser tube 33 is incident on one end side of the optical fiber 41 via the lens 42. The other end of the optical fiber 41 is connected to the chamber 3
It is located in the chamber 32 in such a manner as to penetrate the second vessel wall in an airtight manner. A lens 43 is provided at the tip end portion thereof so as to face the mirror 24 located at the light incident end of the optical component system arranged in the chamber 32. That is, the laser beam emitted from the laser tube 33 enters the optical component system arranged in the chamber 32 through the lens 42, the optical fiber 41, and the lens 43 in this order. In this example as well, the chamber 32
The inside is kept in a vacuum atmosphere or a helium gas atmosphere.

As described above, since the laser light source 11 and the optical component system are spatially separated from each other, the laser light source 1
The heat generated in 1 does not affect the placement field of the optical component system. Therefore, the optical path length of the optical component system does not fluctuate, and the phase of light can be stabilized. Further, since the laser tube 33 of the laser light source 11 can be cooled uniformly in the atmosphere, it is possible to prevent the fluctuation of the optical axis position and improve the alignment detection accuracy and stability.

According to the experiment, as shown in FIG. 2, it was confirmed that the alignment signal did not fluctuate. In addition,
The invention is not limited to the embodiments described above. That is, the above-described embodiment is an example in which the present invention is applied to the alignment optical device incorporated in the alignment device of the X-ray exposure apparatus, but is also applied to the alignment optical device incorporated in the alignment device of the optical exposure device. Of course you can.

[0026]

As described above, according to the present invention,
It is possible to eliminate a decrease in alignment accuracy and a decrease in stability due to heat generated by the laser light source.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example in which an alignment optical device according to an embodiment of the present invention is incorporated in a positioning device of an X-ray exposure apparatus.

FIG. 2 is a characteristic diagram showing experimental results of the alignment device.

FIG. 3 is a schematic diagram of a main part of an optical heterodyne interferometric alignment device.

FIG. 4 is a schematic diagram showing a configuration of an optical system in the alignment device.

FIG. 5 is a schematic diagram showing a conventional example in which the alignment device is incorporated in an X-ray exposure device.

FIG. 6 is a characteristic diagram showing an experimental result of the conventional alignment device.

[Explanation of symbols]

1, 2 ... Diffraction grating 3a, 4a ... First grating 3b, 4b ... Second grating 5,6 ... Laser beam 11 ... Laser light source 12 ... Half mirror 13, 14 ... Acousto-optic modulator 15 ... Folding mirror 16 ... Mask 18 ... Wafer 22,23 ... Sensor 24 ... Mirror 25 ... Lens 31 ... Beryllium wall 32 ... Chamber 33 ... Laser tube 36 ... X-ray guide path 37 ... X-ray 41 ... Optical fiber 42,43 ... Lens

Claims (3)

[Claims] 1. An alignment optical device comprising a laser light source and an optical component system including a plurality of optical components, which is used for alignment between objects utilizing an optical phenomenon, wherein the laser light source and the optical component system are provided. Are spatially separated from each other, and the laser light source and the optical component system are connected by an optical fiber. 2. The alignment optical apparatus according to claim 1, wherein the optical fiber is of a single mode. 3. The alignment optical apparatus according to claim 1, wherein the optical component system constitutes a phase measurement system of an optical heterodyne interference optical system.