JPH11176727A - Projection aligner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect with high precision a position in an optical axis direction of a projection optical system on a surface of a substrate, even when wavelengths of aligned lights are substantially reduced and moreover the alignment is carried out in a liquid. SOLUTION: A liquid 7 is supplied to a sidewall 8 so as to satisfy a gap between a lens 4 of a projection optical system which is closest to a wafer W and the wafer W. Ultrasonic waves are emitted from an ultrasonic emission system 5, and the ultrasonic waves reflected by an ultrasonic focusing position SS are received by an ultrasonic reception system 6. Based on a detection signal from the ultrasonic reception system 6, a defocusing amount from a best focusing position in a focusing position SS of ultrasonic waves is acquired. Based on the acquired defocusing amount, a sample ore pedestal 9 is driven in a Z-direction to control a focusing position.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus used in a lithography process for manufacturing, for example, a semiconductor device, a liquid crystal display device, or a thin film magnetic head.

[0002]

2. Description of the Related Art When manufacturing a semiconductor device or the like, an image of a reticle pattern as a photomask is projected on a wafer (or a glass plate or the like) coated with a resist as a substrate through a projection optical system. A projection exposure apparatus of a stepper type or a step-and-scan method for transferring to an area is used.

The resolution of a projection optical system provided in a projection exposure apparatus becomes higher as the exposure wavelength used is shorter and the numerical aperture of the projection optical system is larger. For this reason, with the miniaturization of integrated circuits, the exposure wavelength used in projection exposure apparatuses has become shorter year by year, and the numerical aperture of projection optical systems has also increased. The exposure wavelength that is currently mainstream is 248 nm of KrF excimer laser, but the use of 193 nm of ArF excimer laser of shorter wavelength is also being studied.

[0004] When performing exposure, the depth of focus is as important as the resolution. The resolution R and the depth of focus δ are respectively represented by the following equations. R = k ₁ λ / NA (1) δ = k ₂ λ / NA ² (2) where λ is the exposure wavelength, NA is the numerical aperture of the projection optical system, and k
₁ and k ₂ are process coefficients. To obtain the same resolution, a larger depth of focus can be obtained by using exposure light having a shorter wavelength. However, considering the spectral transmission characteristics of a transmissive optical member (glass material) used for the projection optical system, it is possible to transmit exposure light having a wavelength shorter than 193 nm of an ArF excimer laser and to form a relatively large lens at present. Few uniform glass materials.

[0005]

As described above, it is difficult for a conventional projection exposure apparatus (projection optical system) to use exposure light having a wavelength shorter than 193 nm of an ArF excimer laser. Therefore, an immersion method has been proposed as a method for substantially shortening the exposure wavelength. This means that a wafer is immersed in a predetermined liquid, and the wavelength of the exposure light in the liquid is 1 in air.
/ N times (n is the refractive index of the liquid, usually about 1.2 to 1.6)
Is used to improve the resolution and increase the depth of focus.

By the way, at the time of exposure, the entire exposure range needs to be within the range of the depth of focus of the projection optical system. Therefore, the projection exposure apparatus is provided with a focusing mechanism (autofocus mechanism). In general, a light beam is obliquely incident on the surface of a wafer to be exposed, the reflected light is received by a facing optical system to detect the in-focus state of the wafer surface, and the wafer is moved up and down to focus. It is to drive to a focus position.

A photosensitive film (photoresist) is applied to the surface of the wafer to be exposed, and a pattern is transferred to the photoresist. Therefore, it is desirable to match the photoresist surface with the focal position of the projection optical system,
It is necessary to detect the position of the photoresist surface. In a conventional projection exposure apparatus, a space where a wafer is arranged is filled with air or a gas such as nitrogen. For example, the refractive index of air is 1, and the refractive index of the photoresist applied to the wafer surface is about 1.7. Therefore, the light reflectance at the air-photoresist interface is calculated from the Fresnel equation as follows: Reflectivity = {(1-1.7) / (1 + 1.7)} ² × 100 = 6.7 (%) (3) At the air-photoresist interface, a relatively large amount of light flux for focus detection is reflected. Then, the position of the photoresist surface can be detected.

However, in the case of a projection exposure apparatus employing the liquid immersion method, the space in which the wafer is arranged is filled with liquid. For example, when the liquid is water, its refractive index is 1.3, and the light reflectance at the water-photoresist interface is calculated from the Fresnel equation as follows. Reflectivity = {(1.3-1.7) / (1.3 + 1.7)} ² × 100 = 1.8 (%) (4) The space between the water-photoresist interface is smaller than that of the air-photoresist interface. And the difference between the refractive index of the photoresist and the photoresist, the reflectance of the light beam for focus detection decreases,
It becomes difficult to accurately detect the position of the photoresist surface.

In view of the foregoing, it is an object of the present invention to provide a projection exposure apparatus capable of shortening the wavelength of exposure light and transferring a finer pattern. Furthermore, even when exposure is performed on a substrate coated with a photosensitive material in a liquid, projection exposure that can detect the position of the surface of the photosensitive material in the optical axis direction of the projection optical system with high accuracy. It is also an object to provide a device.

[0010]

According to the present invention, there is provided a projection exposure apparatus for transferring a pattern image of a mask (R) onto a substrate (W) via a projection optical system (PL).
A liquid immersion device (2, 8) for supplying a predetermined liquid (7) to the surface of the substrate (W), and an ultrasonic wave transmitted to the surface of the substrate (W) via the liquid (7), And an ultrasonic type surface position detecting device (5, 6) for detecting the position of the surface of the projection optical system (PL) in the direction of the optical axis by detecting the ultrasonic wave reflected by the surface. .

According to the projection exposure apparatus of the present invention, the pattern image of the mask (R) is exposed to the surface of the substrate (W) via the liquid (7). The wavelength can be shortened to 1 / n times the wavelength in the middle (n is the refractive index of the liquid (7)). Further, since the position of the surface of the substrate (W) in the optical axis direction is detected with high accuracy by the ultrasonic type surface position detecting device (5, 6), it is difficult to detect the surface position by the optical type surface position detecting device. Even in the liquid (7), the position can be detected with high accuracy.

A photosensitive material (P) is formed on the surface of the substrate (W).
R) is applied, the surface position detecting device (5, 6)
Is a projection optical system (3, 3) on the surface of the photosensitive material (PR).
It is desirable to detect the position 4) in the optical axis direction. In this case, the image plane of the projection optical system (3, 4) is changed to the photosensitive material (P).
R). The liquid (7) is filled so as to fill the space between the tip of the optical element (4) on the substrate (W) side of the projection optical system (PL) and the surface of the substrate (W).
Is desirably supplied. In this case, the wavelength of the exposure light on the surface of the substrate (W) can be shortened to 1 / n times the wavelength of the exposure light in air (n is the refractive index of the liquid (7)). Further, since the lens barrel (3) of the projection optical system (PL) does not come into contact with the liquid (7), there is an advantage that the lens barrel (3) is hardly corroded.

The liquid (7) is water (refractive index 1.
3) or an organic solvent (for example, alcohol (ethanol (refractive index: 1.36), etc.)), seder oil (refractive index: 1.52)
Etc.). In this case, when water is used as the liquid (7), there is an advantage that it can be easily obtained. When an organic solvent is used as the liquid (7), there is an advantage that the lens barrel (3) of the projection optical system (PL) is less likely to corrode. Further, in the case where sedder oil is used as the liquid (7), its refractive index is as large as about 1.5, and the wavelength of the exposure light can be made shorter.

A substrate stage (10) for holding the substrate (W) and positioning the substrate (W) on a plane perpendicular to the optical axis of the projection optical system (PL); It is desirable to include a height control stage (9) for controlling the position of the substrate (W) in the optical axis direction (3, 4) of the projection optical system based on the detection result of (6). in this case,
The surface of the substrate (W) can be adjusted with high accuracy to the image plane of the projection optical system (3, 4).

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1A shows a schematic configuration of a projection exposure apparatus according to the present embodiment. In FIG. 1A, an ArF excimer laser light source as an exposure light source,
Wavelength 193 emitted from illumination optical system 1 including optical integrator, field stop, condenser lens, etc.
Exposure light IL composed of ultraviolet pulse light of nm
Illuminate the pattern provided in the The pattern of the reticle R is a wafer coated with a photoresist PR at a predetermined projection magnification β (β is, for example, ４ ，, ５, etc.) via a telecentric projection optical system PL on both sides (or one side on the wafer side). The image is reduced and projected on the exposure area on W. The exposure light IL is a KrF excimer laser light (wavelength 248 n).
m), F ₂ excimer laser light (wavelength 157 nm), i-line of a mercury lamp (wavelength 365 nm), or the like may be used.
Hereinafter, the Z axis is taken in parallel with the optical axis AX of the projection optical system PL,
In the following description, the Y axis is taken along a direction perpendicular to the plane of FIG. 1A in a plane perpendicular to the Z axis, and the X axis is taken along a direction parallel to the plane of FIG.

The reticle R is held on a reticle stage RST. The reticle stage RST has a built-in mechanism capable of finely moving in the X, Y, and rotation directions. The two-dimensional position and rotation angle of reticle stage RST are measured in real time by a laser interferometer (not shown). On the other hand, the wafer W is held on a sample table 9 via a wafer holder (not shown), and the sample table 9 controls the focus position (position in the Z direction) and the tilt angle of the wafer W.
It is fixed on the stage 10. A cylindrical side wall 8 is provided on the sample stage 9, and the inside is filled with a liquid 7. The liquid 7 is supplied into the side wall 8 through the nozzle 2a by the liquid supply / recovery system 2 including a pump or the like before the exposure, and is recovered after the exposure. In the projection exposure apparatus of this example, water (refractive index: 1.3) is used as the liquid 7.
Since the wavelength of light is 1 / 1.3 times that of air in water, the wavelength of exposure light formed by an ArF excimer laser (wavelength: 193 nm) is substantially shortened to about 148 nm.

The lens barrel 3 of the projection optical system PL is made of metal, and in order to prevent corrosion by the liquid 7, the contact portion between the projection optical system PL and the liquid 7 is closest to the wafer W in this example. Only the lens 4 is used. A focus position detection system (hereinafter, referred to as “AF sensors 5 and 6”) including an ultrasonic emission system 5 and an ultrasonic reception system 6 is attached to the side surface of the lens barrel 3 of the projection optical system PL. .

FIG. 1B is an enlarged view of the vicinity of the side wall 8 in FIG. 1A. In FIG. 1B, the transfer of the wafer W onto the sample stage 9 or the sample stage An openable and closable door 8a is provided for use in carrying out from the vehicle 9. Further, the nozzle 2a of the liquid supply and recovery system 2 is configured to be able to be driven up and down during supply and recovery of the liquid.

Referring back to FIG. 1A, the Z stage 10 moves along an XY plane parallel to the image plane of the projection optical system PL.
The XY stage 11 is fixed on a Y stage 11, and is mounted on a base (not shown). The Z stage 10 controls the focus position (position in the Z direction) and the tilt angle of the wafer W to bring the surface of the photoresist PR on the wafer W onto the image plane of the projection optical system PL by an autofocus method and an autoleveling method. The XY stage 11 performs alignment of the wafer W in the X and Y directions. The two-dimensional position and rotation angle of the sample table 9 (wafer W) are measured in real time by the laser interferometer 13 as the position of the movable mirror 12. Control information is sent from the main control system 14 to the wafer stage drive system 15 based on the measurement result, and the operations of the Z stage 10 and the XY stage 11 are controlled. At the time of exposure, each shot area on the wafer W is sequentially shifted to the exposure position. It moves and the pattern of the reticle R is exposed and transferred to each shot area.

Next, the AF sensors 5 and 6 of the projection exposure apparatus of this embodiment will be described. FIG. 2A is an enlarged view of the vicinity of the lower portion of the projection optical system of the present embodiment. In FIG. 2A, the ultrasonic wave emitting system 5 includes an ultrasonic wave generating element 5a and an ultrasonic focusing element 5b. Is provided. A frequency of 50 MHz emitted from an ultrasonic wave generating element 5a composed of a piezoelectric element or the like
The ultrasonic wave of about 200 MHz is focused on the focusing position SS on the surface of the photoresist PR applied to the wafer W by the ultrasonic focusing element 5b, is reflected at the focusing position SS, and enters the ultrasonic receiving system 6. The ultrasonic receiving system 6 includes an ultrasonic receiving element 6a, an ultrasonic focusing element 6b, and a sound insulating plate 6 that can vibrate.
The ultrasonic wave incident on the ultrasonic receiving system 6 is focused by the ultrasonic focusing element 6b, and is incident on the ultrasonic receiving element 6a through the opening of the sound insulating plate 6c. The detection signal of the ultrasonic receiving element 6a is supplied to the main control system 14. An opening for transmitting ultrasonic waves is provided at the center of the sound insulating plate 6c, and the main control system 14 laterally shifts (or vibrates) the sound insulating plate 6c by the sound insulating plate driving mechanism 6d, and the ultrasonic receiving element 6a The position where the detection signal becomes maximum is detected. Or
The detection signal of the ultrasonic receiving element 6a may be synchronously detected with a signal synchronized with the vibration of the sound insulating plate 6c.

FIG. 2B is an enlarged view of the vicinity of the focusing position SS of the ultrasonic wave on the surface of the photoresist PR.
In (b), a photoresist PR for photosensitivity is applied on the wafer W. Position SS on photoresist PR surface by conventional optical oblique incidence AF sensor
Is detected, the refractive index of the liquid 7 and that of the photoresist PR are substantially the same, and the reflectance becomes extremely low.
7, the detected position SS ′ is not located on the surface of the photoresist PR, and the surface of the substrate of the wafer W is aligned with the image plane of the projection optical system PL. . Since the ultrasonic waves from the AF sensors 5 and 6 of this example travel along the path 16 and are reflected on the surface of the photoresist PR, the position SS on the surface of the photoresist PR is accurately detected, and the surface of the photoresist PR is accurately detected. Can be focused on the image plane.

The position in the Z direction of the surface of the photoresist PR is calculated from the lateral shift amount of the focused position of the ultrasonic wave on the ultrasonic receiving element 6a according to the same principle as that of the conventional optical oblique incidence type AF sensor. Is detected. That is, if the wafer W is shifted downward (-Z direction) in FIG. 2B, the focus position on the ultrasonic receiving element 6a in FIG. If it shifts upward in the middle, the ultrasonic receiving element 6
Since the focus position on a is shifted downward, the amount of change in the focus position on the surface of the photoresist PR can be obtained from this lateral shift amount. Therefore, the best focus position may be determined in advance by a test print or the like, and at that time, the center of the opening (or the center of vibration) of the sound insulating plate 6c may be aligned with the center of the focused position of the ultrasonic wave.

FIG. 3 shows a relationship between a focus signal D obtained by synchronously detecting a detection signal from the ultrasonic receiving system 6 and a focus position Z on the surface of the photoresist PR as an example. In the main control system 14, the detection signal from the ultrasonic receiver 6a is synchronously rectified by the drive signal of the sound insulating plate 6c, so that the focus position S of the ultrasonic wave on the surface of the photoresist PR.
In response to S, a focus signal D that changes substantially proportionally to the focus position Z within a predetermined range is generated. In this example, the focus signal D corresponding to the ultrasonic focus position SS
Is adjusted so that it becomes 0 when the focusing position SS coincides with the image plane (best focus position) of the projection optical system PL, and the main control system 14 defocuses from the focus signal D. The amount (deviation amount) can be obtained. When the focus position of the wafer W is upward, the Z stage 10 (wafer W) is moved downward,
Conversely, when the focus position is below, the Z stage 10 (wafer W) is moved upward to perform exposure.

Although water (refractive index: 1.3) is used as the liquid 7 in this embodiment, an organic solvent (eg, alcohol, cedar oil, etc.) can be used as the liquid 7. In this case, there is an advantage that the lens barrel 3 of the projection optical system PL is hardly corroded. In addition, when a sedar oil (refractive index: 1.5) is used, the refractive index is as large as 1.5, and the exposure light can be substantially shortened in wavelength.

The focus position is detected by
A sound insulation plate having a plurality of openings is arranged in the ultrasonic emission system 5,
Each of the focus positions at a plurality of points on the photoresist surface may be detected. Alternatively, a sound insulating plate having a large opening may be arranged in the ultrasonic emission system 5 and the sound insulating plate having a plurality of openings may be detected by an ultrasonic wave. It may be arranged in the receiving system 6 to similarly detect each focus position at a plurality of points.

In the above embodiment, the focus position on the photoresist surface of the wafer is detected using ultrasonic waves. However, a leveling sensor for detecting the inclination angle of the photoresist surface using ultrasonic waves may be used. Good. In this leveling sensor, an ultrasonic wave which travels substantially parallel to the surface of the wafer may be irradiated to detect the sound collection position of the reflected ultrasonic wave.

It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that various configurations can be adopted without departing from the gist of the present invention.

[0028]

According to the projection exposure apparatus of the present invention, since the pattern image of the mask is exposed on the surface of the substrate via the liquid, the wavelength of the exposure light on the substrate surface is substantially changed to the wavelength of the liquid having the wavelength in air. The wavelength can be shortened to a reciprocal multiple of the refractive index.
In addition, since the ultrasonic surface position detection device detects the position of the substrate surface in the optical axis direction, the position can be detected with high accuracy even in a liquid where the surface position detection is difficult with the optical surface position detection device. Can be detected.

When the surface position detecting device detects the position of the surface of the photosensitive material in the direction of the optical axis of the projection optical system, the surface of the photosensitive material is detected with respect to the image plane of the projection optical system based on the detected information. Surface can be adjusted with high precision. When the liquid is supplied so as to fill the space between the tip of the optical element on the substrate side of the projection optical system and the surface of the substrate, the exposure light is 1 / n times as large as in air (n is the liquid). (Refractive index) can be shortened, and since the lens barrel of the projection optical system does not come into contact with the liquid, there is an advantage that the lens barrel of the projection optical system is hardly corroded.

Further, when the liquid is water, there is an advantage that the liquid can be easily obtained. When the liquid is an organic solvent (for example, alcohol or cedar oil), there is an advantage that the lens barrel of the projection optical system is hardly corroded. Further, in the case where cedar oil is used as the liquid, its refractive index is 1.5, which is larger than that of water (refractive index: 1.3) or the like, so that the exposure light can be made shorter in wavelength.

Further, a substrate stage for holding the substrate and positioning the substrate on a plane perpendicular to the optical axis of the projection optical system, and an optical axis of the projection optical system for the substrate based on the detection result of the surface position detecting device. When a height control stage for controlling the position in the direction is provided, the image plane of the projection optical system can be adjusted to the exposure position on the substrate surface.

[Brief description of the drawings]

FIG. 1A is a schematic configuration diagram illustrating a projection exposure apparatus according to an embodiment of the present invention, and FIG. 1B is an enlarged view illustrating the vicinity of a side wall 8 in FIG.

2A is a partially enlarged view showing a configuration of a lower portion of the projection exposure apparatus in FIG. 1A, and FIG. 2B is an enlarged view of a portion B in FIG. 2A.

FIG. 3 is a diagram showing a relationship between a focus position Z on a photoresist surface on a wafer W and a focus signal D;

[Explanation of symbols]

 W Wafer R Reticle PL Projection optical system 1 Illumination optical system 2 Liquid supply / recovery system 3 Lens tube 4 Lens 5 Ultrasonic emission system 6 Ultrasonic reception system 7 Liquid 8 Side wall 9 Sample stage 10 Z stage 14 Main control system 15 Wafer stage drive system

Claims (5)

[Claims] 1. A projection exposure apparatus for transferring a mask pattern onto a substrate via a projection optical system, comprising: a liquid immersion device for supplying a predetermined liquid to the surface of the substrate; An ultrasonic type surface position detecting device for transmitting an ultrasonic wave and detecting a position of the surface of the projection optical system in the optical axis direction by detecting an ultrasonic wave reflected by the surface. Characteristic projection exposure apparatus. 2. The method according to claim 1, wherein when the photosensitive material is applied to the surface of the substrate, the surface position detecting device detects a position of the surface of the photosensitive material in an optical axis direction of the projection optical system. The projection exposure apparatus according to claim 1, wherein 3. The liquid supply device according to claim 1, wherein the liquid is supplied so as to fill a space between a front end portion of the optical element on the substrate side of the projection optical system and a surface of the substrate. Projection exposure equipment. 4. The projection exposure apparatus according to claim 1, wherein the liquid is water or an organic solvent. 5. A substrate stage for holding the substrate and positioning the substrate on a plane perpendicular to the optical axis of the projection optical system, and the projection optics of the substrate based on a detection result of the surface position detection device. The projection exposure apparatus according to claim 1, further comprising a height control stage that controls a position of the system in an optical axis direction.