JPH1022196A - Projection aligner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate displacement due to thermal expansion of a mask caused by irradiating it with illuminating light. SOLUTION: A gas sucking means 22 is provided adjoining a mask 1, and it locally sucks gas near the mask to generate gas flow over the surface of the mask. Thanks to a heat exhausting action (a cooling action) of the gas flow, the mask 1 is cooled to almost an temperature of surrounding gas, thus the temperature thereof is made constant. If a method by which the gas flow is generated over the surface of the mask with the gas sucking means 22 is employed, the gas which cools the mask 1 and therefore becomes high temperature is, from the sucking means, discharged outside of a device as it is. Thereby there is no trouble that a temperature distribution in an exposure device is changed with the gas after mask cooling, and that air fluctuates.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a projection exposure apparatus used in a process of forming a fine circuit pattern of a semiconductor integrated circuit, a liquid crystal display, or the like.

[0002]

2. Description of the Related Art When a semiconductor device or a liquid crystal display device is manufactured by a photolithography process, a pattern image of a photomask or a reticle (hereinafter, referred to as a mask) is formed on a semiconductor wafer or glass coated with a photosensitive agent such as a photoresist. 2. Description of the Related Art A projection exposure apparatus that projects a light on a photosensitive substrate such as a plate via a projection optical system is used. In recent years, as a projection exposure apparatus of this type, a photosensitive substrate is placed on a two-dimensionally movable substrate stage, and the photosensitive substrate is stepped by this substrate stage, and a pattern image of a mask is exposed to the photosensitive substrate. Repeat the operation of exposing each upper shot area sequentially,
A so-called step-and-repeat type exposure apparatus, particularly, a reduction projection type exposure apparatus (stepper) is frequently used.

[0003] For example, a semiconductor element is formed by superposing and exposing a multi-layer circuit pattern on a photosensitive substrate. When the second and subsequent circuit patterns are projected and exposed on the photosensitive substrate, the circuit pattern already formed on the photosensitive substrate is aligned with the mask pattern image, that is, the position between the photosensitive substrate and the mask is adjusted. It is necessary to accurately perform alignment.

In this alignment method, an alignment mark (hereinafter, referred to as a substrate mark) on a photosensitive substrate is illuminated with a light beam having an exposure wavelength to form an image of the substrate mark on a mask pattern surface, and the position of the substrate mark image and the position of the mask are determined. There is a method (hereinafter, referred to as a mask reference method) of directly measuring a positional relationship with an upper alignment mark (hereinafter, referred to as a mask mark) to measure and align a relative positional relationship between a mask and a photosensitive substrate. . However, this method has a problem that a substrate mark portion on a photosensitive substrate and its periphery are exposed to light by exposure light, and is hardly used at present.

An alignment method generally used at present is a method for detecting the position of a substrate mark on a photosensitive substrate with a light beam other than the exposure wavelength, and uses a projection optical system as a part of the substrate mark detection optical system. TTL (through the
A lens type or an off-axis method using a substrate mark detection optical system having an observation field outside the exposure field of the projection optical system. In these systems, the mask and the photosensitive substrate are not directly aligned, but are indirectly adjusted via a reference mark provided in a projection exposure apparatus (generally, on a substrate stage on which the photosensitive substrate is placed). Will do.

More specifically, first, prior to the overlay exposure, the reference mark of the substrate stage is aligned with the position of the projected image of the mask mark on the mask onto the substrate stage.
The position of the substrate stage at that time is measured. Subsequently, the reference mark of the substrate stage is aligned with the substrate mark detection optical system, and at this time, the position of the substrate stage is measured. The difference between these two substrate stage positions is called a baseline amount, and the above measurement sequence is called a baseline measurement.

When a mask pattern image is overlaid and exposed on a shot area of a photosensitive substrate, a substrate mark on the photosensitive substrate is aligned with a substrate mark detection optical system, and the substrate stage is moved from the position of the substrate stage at that time. By moving to a position shifted by the baseline amount and performing exposure,
The circuit pattern already formed on the photosensitive substrate and the image of the mask pattern can be superimposed.

[0008] Since this baseline measurement requires about 1 to 2 minutes, in actual exposure to a photosensitive substrate, a large number of photosensitive substrates are efficiently exposed at a high throughput. Is performed only when the type of the photosensitive substrate to be exposed is changed (that is, when the mask to be exposed is changed), and the alignment of each photosensitive substrate is performed only by the substrate mark detection optical system using the baseline amount. I was

[0009]

As described above, in normal pattern exposure using a projection exposure apparatus, during exposure of a large number of photosensitive substrates of the same type (same process), a mask projected image and No position measurement of the mask itself is performed. That is, the overlay exposure is performed on the assumption that the position of the mask on the mask stage does not move at all. Incidentally, in order to increase the throughput of the exposure apparatus, the energy of the illumination light applied to the mask per unit time is steadily increasing. This is partly because the illuminance itself applied to the mask is increasing, and the mask is irradiated with illumination light by shortening the time not involved in exposure (such as the time for exchanging the photosensitive substrate and the time for aligning the photosensitive substrate). This is because the percentage of time spent is increasing.

As a result, the energy of the illumination light is accumulated in the mask, and the mask thermally expands during the exposure of a large number of photosensitive substrates, so that the position of the mask may be shifted. As a solution to this, when exposing a large number of photosensitive substrates, it is conceivable to correct the mask misalignment by re-measuring the baseline amount for each of several photosensitive substrates, but the time required for the baseline measurement is considered. Only the throughput will be reduced, which is not practical. The present invention has been made in view of such problems of the related art, and has as its object to realize a projection exposure apparatus with higher accuracy and higher throughput by eliminating a positional shift due to thermal expansion of a mask. .

[0011]

According to the present invention, the above object is achieved by generating a gas flow locally on the mask surface and cooling the mask by the gas flow. Here, it is important that the gas flow on the mask surface is generated not by blowing but by suction. That is, the present invention provides a projection exposure apparatus including an illumination optical system for illuminating a mask, a mask stage for holding the mask, and a projection optical system for projecting a pattern formed on the mask onto a photosensitive substrate. Gas suction means is provided, and gas near the mask is locally sucked to form a gas flow on the surface of the mask.

According to the present invention, a gas flow is formed on the surface of the mask held on the mask stage by the gas suction means. The mask is cooled to about the temperature of the surrounding gas by the exhaust heat action (cooling action) of the gas flow, and the temperature is kept constant. Even if the mask is heated by illuminating light by the exposure operation, the heat is exhausted by the gas flowing on the surface of the mask, so that the heat does not remain in the mask itself, and the mask does not rise in temperature or cause thermal expansion. . In order to efficiently generate a gas flow on the mask surface by suction by the gas suction means, it is desirable to provide a wind shield means for blocking the air between the illumination optical system and the mask, at least on the gas suction side.

As a means for generating a gas flow on the mask surface, a method of using a blowing means instead of the gas suction means and blowing gas from the blowing means onto the mask surface is also conceivable.
However, around the mask, high-precision measuring devices that dislike heat and air fluctuations, such as a laser interferometer that detects the position of the mask stage and a mask microscope that detects mask marks, are arranged. If this is done, the gas flow that has taken the heat of the mask and has become high temperature will reach those measuring devices and fluctuate the temperature of the measuring devices or penetrate into the optical path, adversely affecting the measurement accuracy.

On the other hand, when a method of generating a gas flow on the mask surface by local suction by the gas suction means as in the present invention is adopted, the gas which has cooled the mask and has become hot can be directly discharged from the suction means. Since the gas can be discharged out of the apparatus, there is no inconvenience that the gas distribution after the cooling of the mask changes the temperature distribution in the exposure apparatus or generates air fluctuations.

The temperature of the gas (mainly air) in the projection exposure apparatus is generally always kept constant by a temperature controller, and the gas flow formed on the mask surface by the gas suction means is almost constant temperature. Although it is a simple gas flow, the mask temperature can be more accurately maintained at a constant temperature by blowing a constant-temperature gas flow controlled at a predetermined temperature locally to this portion, and the mask can be heated even if exposed to light. There is no risk of thermal expansion. That is, a blowing means for locally blowing a gas whose temperature has been adjusted to a predetermined temperature is provided in the vicinity of the mask, and when the gas suction means and the blowing means are used in combination, the effect of cooling the mask while eliminating the influence on the surroundings is further improved. Can be raised.

In this case as well, the system consisting of the air blowing system and the suction system is constituted as close as possible by using the air shielding means, and the gas blown by the air blowing means is dissipated in the apparatus as much as possible. It is preferable that the suction is performed by the suction means without performing. By doing so, the mask can be cooled without affecting other parts of the projection exposure apparatus. A mask microscope for detecting a mask mark is provided on the mask. In order to avoid air fluctuations on the optical path of the mask microscope due to the gas flow generated on the mask surface, and to prevent the gas flow from colliding with the mask microscope and generating minute vibration, gas suction means and air blowing means It is preferable that the opening is provided so as to avoid the position of the mask microscope.

According to the present invention, the temperature rise of the mask can be avoided without affecting other parts of the projection exposure apparatus, so that a large number of photosensitive substrates can be continuously connected without performing baseline measurement on the way. Even when exposure is performed, high-accuracy alignment without pattern overlay displacement due to thermal expansion of the mask can always be realized.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view of an example of a projection exposure apparatus according to the present invention, and FIG. 2 is a detailed view around a mask. The mask 1 is uniformly illuminated by the illumination optical system 13, and the pattern drawn on the mask 1 is projected and exposed to a shot area on the photosensitive substrate 4 via the projection optical system 3.
The mask 1 is fixed on a mask stage 2 by vacuum suction, and the photosensitive substrate 4 is fixed on a substrate holder 5 on a substrate stage 6 by vacuum suction. Substrate stage 6
Is movable two-dimensionally in a plane perpendicular to the optical axis of the projection optical system 3 by driving means 25 such as a motor, and the position of the substrate stage 6 is between the movable mirror 7 fixed to the substrate stage 6. Are measured by the laser interferometer 8.

The projection exposure apparatus generally has a large variation in various performances with respect to the environmental temperature.
Is installed in a room and the environmental temperature is a predetermined temperature (for example, 21 ° C.)
Has been maintained. The gas in the chamber 14 is exhausted (intake) from the exhaust opening 17 and sent to the temperature controller 19 via the exhaust duct 18. In the temperature controller 19, the temperature of the sent gas is adjusted to a predetermined temperature, and then,
0, and is sent to the dust filter 15. The gas removed by the dust filter 15 is blown into the chamber 14 through the blow opening 16 and circulated.

When the substrate stage 6 is driven by the driving means 25, each shot area of the photosensitive substrate 4 is sequentially moved directly below the projection optical system 3, and the mask 1 is placed on a pattern already formed in the shot area. Are superposed and exposed. For alignment of the shot area on the photosensitive substrate 1, a TTL detecting optical system 10 to 11 for detecting a substrate mark on the photosensitive substrate 4 via the projection optical system 3 and a separate off-axis detecting system 9 are used. I do. Of course, it goes without saying that the above-described baseline measurement is performed prior to the detection of the substrate mark.

If the substrate stage 6 is moved below the projection optical system 3 in accordance with the output value of the laser interferometer 8 based on the detected position of the alignment mark and the baseline amount in these detection optical systems, the pattern of the mask 1 can be obtained. And the position of the existing pattern formed on the photosensitive substrate 4 almost coincides with a desired relationship. However, in the case of the alignment method other than the “mask reference method” as in this example, if the position of the mask 1 fluctuates after the baseline measurement as described above,
This positional relationship will also fluctuate. In the conventional apparatus, the illumination optical system 13
There was a temperature rise and thermal expansion of the mask 1 itself due to irradiation of illumination light from. Although the mask 1 is vacuum-adsorbed to the mask stage 2, the stress due to the thermal expansion of the mask 1 exceeds the vacuum attraction force, and the mask 1 is slightly shifted, though slightly.

In this embodiment, a gas suction means 22 is provided adjacent to the mask 1 for sucking and exhausting gas near the mask 1. The gas suction means 22 is a kind of duct having one end opened near the mask 1 and the other end connected to a gas exhaust duct 18 circulating in the chamber 14, and the exhaust duct 1 generated by the temperature controller 19.
The gas in the space between the mask 1 and the illumination optical system 13 is sucked by the negative pressure inside the mask 8 to generate a gas flow on the surface of the mask 1. Due to the installation of the gas suction means 22, gas at a predetermined temperature circulating in the chamber 14 flows into the space between the illumination optical system 13 and the mask 1, and a gas flow is formed on the surface of the mask 1. . The energy of the illumination light applied to the mask 1 by the illumination optical system 13 is dissipated by this gas flow, and the temperature of the mask 1 itself does not rise. Further, the gas flow that has been heated by absorbing the heat of the mask 1 is discharged into the exhaust duct 18 without being directly discharged into the chamber 14, and is adjusted to a predetermined temperature by the temperature controller 19, and then the air flow opening 16 From the chamber 14. Therefore, the heat of the mask 1 is transferred by gas flow to other places in the chamber 14, for example, the projection optical system 3 and the substrate mark detection optical system 9, and the temperature is increased to deteriorate the imaging characteristics, There is no drift of the position detection value.

As shown in FIG. 2, the suction end near the mask 1 of the gas suction means 22 is designed to efficiently suck only the gas between the mask 1 and the illumination optical system 13, that is, extra gas from another direction. The illumination optical system 1
3 or a wind shield member 22 for shielding the space between the mask stages 2
a, 22b are provided.

In general, mask microscopes 30a and 30b for positioning the mask 1 and performing baseline measurement are provided near the mask stage 2 to which the mask 1 is fixed. Therefore, as shown in FIG. 2A, the opening of the gas suction means 22 is
It is desirable to have a structure that avoids the positions of 0a and 30b. This is because, when the gas flow collides with the mask microscopes 30a and 30b, a minute vibration is generated in the mask microscopes 30a and 30b, and the detection accuracy of the mask microscopes 30a and 30b may be deteriorated. By providing the opening of the gas suction means 22 so as to avoid the positions of the mask microscopes 30a and 30b, a strong gas flow is not generated at the position of the mask microscope, thereby avoiding the generation of vibrations of the mask microscopes 30a and 30b and the mask microscope. It is possible to avoid the occurrence of air fluctuations in the optical paths of 30a and 30b and the deterioration of detection accuracy. Further, the gas suction means can be arranged between the mask 1 and the projection optical system 3 and can perform air cooling from both sides of the mask 1.

According to this embodiment, even when continuously exposing a large number of photosensitive substrates, if the baseline measurement is first performed once, then the mask is displaced due to the thermal expansion of the mask, and the base is shifted. There is no danger that the line volume will go wrong. Therefore, it is not necessary to perform the baseline measurement again, and the frequent baseline measurement does not lower the throughput.

FIG. 3 is a schematic view of another embodiment of the projection exposure apparatus according to the present invention, and FIG. 4 is a detailed view around a mask.
In this embodiment, a blowing means is added so as to face the gas suction means. 3 and 4, the same members as those in FIGS. 1 and 2 are denoted by the same reference numerals, and detailed description will be omitted. In this embodiment, a blowing means 21 for blowing gas at a predetermined temperature to the mask 1 and a gas suction means 2 for sucking and exhausting gas near the mask 1.
2 was added. As described with reference to FIGS. 1 and 2, the gas suction unit 22 blocks the space between the illumination optical system 13 and the mask stage 2 so that the gas in the space between the illumination optical system 13 and the mask 1 can be efficiently sucked. Wind shielding members 22a, 22
b is provided.

The temperature of the blower member 21 is adjusted by the temperature controller 19, a part of the gas removed by the dust filter 15 is guided by a duct, and blown onto the surface of the mask 1 from the side opposite to the gas suction means 22. At this time, the blowing means 21 is, like the gas suction means 22, a mask microscope 30a, 30b.
It is preferable to consider so that a strong air flow is not generated at the position. For this reason, the opening of the blowing means 21 is
As shown in (a), it is desirable that the structure be such that the positions of the mask microscopes 30a and 30b are avoided. With this structure, a strong gas flow collides with the mask microscopes 30a and 30b, causing the mask microscopes 30a and 30b to vibrate minutely or generating air fluctuations in the optical paths thereof, thereby causing the mask microscope 3a and 30b to vibrate.
It is possible to prevent the detection accuracy of 0a and 30b from deteriorating.

If the amount of air blown by the air blowing means 21 is too large,
The gas heated by removing the heat of the mask 1 drifts in the chamber 14 to increase the temperature of other members of the apparatus, or forms a lump in the optical path of the projection optical system 3 and the detection optical systems 8, 9, and 10. To cause deterioration of the image forming characteristic and decrease measurement accuracy. Therefore, it is preferable that the amount of air blown by the air blowing means 21 is set to an amount corresponding to the amount of suction by the gas suction means 22. The shape of the air outlet of the air blowing means 21 and the air inlet or the air shielding means 22 of the gas suction means 22
The arrangement of a and 22b is also preferably designed so that the gas flow blown from the blowing means 21 to the surface of the mask 1 can be sucked by the gas suction means 22 as much as possible.
By doing so, the blowing means 21 and the gas suction means 22 can constitute a substantially closed system, and the temperature rise of the mask 1 can be prevented without affecting other parts in the chamber 14.

In the example shown in FIG. 4, the installation location of the wind shielding means 22a and 22b is limited to only one side of the mask 1, that is, the side where the gas suction means 22 is arranged, so that the mask 1 can be easily replaced. ing. However, for example, by providing an opening / closing mechanism by a hinge or the like, or a detaching mechanism, etc., and by providing a mechanism capable of retreating from the mask transport path at the time of mask replacement, the mask adjacent to the side where the gas suction means 22 is arranged is provided. It is also possible to arrange the wind shielding means on the other two sides of one. In this way, when the mask 1 is covered with the wind shield means on three sides and the gas is blown on the mask surface by the blower means 21 from the remaining side opposite to the gas suction means 22, the heat of the mask 1 is more efficiently removed. Thus, all of the gas used for heat removal can be directly led to the exhaust duct 18.

Also in the present embodiment, a pair of the blowing means 21 and the gas suction means may be further provided between the mask 1 and the projection optical system 3 to perform air cooling from both sides of the mask 1.
In the above description, the negative pressure of the exhaust duct 18 is used as the negative pressure source of the gas suction means 22, and the temperature controller 19 for adjusting the temperature in the chamber 14 as the air source of the air blowing means 21.
Was used. However, the negative pressure source of the gas suction means 22 and the air supply source of the air blowing means 21 may be provided separately from the temperature control device of the chamber 14. Air is generally used as the gas blown from the blower 21 to the mask 1. For example, in a projection exposure apparatus using a vacuum ultraviolet light source, the chamber 14 is filled with helium gas instead of air. In this case, helium gas or the like is used as the gas blown to the mask 1.

[0031]

According to the present invention, since the gas suction means is provided adjacent to the mask to generate a gas flow on the mask surface and air-cool the mask during exposure, the mask is exposed to illumination light during exposure. There is no temperature rise or thermal expansion of the mask. Therefore, high-accuracy overlay exposure can be performed by baseline measurement once before the start of exposure. Further, the gas heated by the heat of the mask does not reach other parts of the apparatus, and does not adversely affect the gas.

[Brief description of the drawings]

FIG. 1 is a schematic view of an example of a projection exposure apparatus according to the present invention.

2A and 2B are detailed views around the mask of FIG. 1, wherein FIG. 2A is a plan view and FIG.

FIG. 3 is a schematic view of another example of the projection exposure apparatus according to the present invention.

4A and 4B are detailed views around the mask of FIG. 3, wherein FIG. 4A is a plan view and FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Mask, 2 ... Mask stage, 3 ... Projection optical system, 4
... photosensitive substrate, 5 ... substrate holder, 6 ... substrate stage, 7 ...
Moving mirror, 8 laser interferometer, 9 off-axis detection system, 10, 11 TTL detection optical system, 12 photosensitive substrate,
13: illumination optical system, 14: chamber, 15: dust filter, 16: ventilation opening, 17: exhaust opening, 18:
Exhaust duct, 19: temperature controller, 20: air duct, 21 ...
Blowing means, 22: gas suction means, 22a, 22b: wind shielding means, 30a, 30b: mask microscope

Claims (2)

[Claims] 1. A projection exposure apparatus comprising: an illumination optical system for illuminating a mask; a mask stage for holding the mask; and a projection optical system for projecting a pattern formed on the mask onto a photosensitive substrate. A projection exposure apparatus, wherein a gas suction means is provided adjacently, and a gas flow is formed on a surface of the mask by locally sucking gas near the mask. 2. The projection exposure apparatus according to claim 1, further comprising: a blower for locally blowing a gas whose temperature has been adjusted to a predetermined temperature near the mask.