JPH10289874A - Aligner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aligner which is able to efficiently cool a reticle. SOLUTION: An aligner comprises an air outlet 102a which extends along the direction of the movement of a reticle R, a heat exchanger 102 for blowing temperature-controlled air toward the reticle R and a control unit 104 for controlling the heat exchanger 102 so as to blow air in a condition where the reticle R is positioned at the farthest from a projection optic system PL. Hence, the reticle R can be cooled with the temperature-controlled air whenever the reticle R is synchronously moved, thereby suppressing thermal expansion of the reticle R to a minimum. Further, since the temperature-controlled air is blown toward the reticle R when the reticle R is positioned farthest from the projection optic system PL, the projection optic system PL is prevented, to the utmost, from being affected by the temperature-controlled air.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mask pattern formed on a photosensitive substrate in a photolithography process in a manufacturing process of, for example, a semiconductor device, an image pickup device (such as a CCD), a liquid crystal display device, or a thin film magnetic head. The present invention relates to an exposure apparatus that performs exposure.

[0002]

2. Description of the Related Art For example, in a photolithography process (a process of forming a resist image of a mask pattern on a substrate) for manufacturing a semiconductor device or the like, a reticle pattern as a mask is exposed to a photoresist through a projection optical system. A projection exposure apparatus (stepper or the like) that exposes light onto a substrate (or a wafer or the like) coated with is used.

In a general projection exposure apparatus, a pattern drawn on a reticle is 1/5 to 1 by a projection optical system.
, And is exposed and transferred onto a substrate. that time,
The stage on which the reticle and the substrate are mounted is precisely positioned by a laser interferometer in a direction perpendicular to the optical axis, and the height is also determined in the direction of the optical axis using an AF sensor.

Further, the amount of deviation from the surface perpendicular to the optical axis on the surface of the substrate is detected by a leveling sensor to correct the inclination of the substrate. Further, the relative position between the substrate and the reticle is precisely positioned by the alignment sensor.

The reason why the position and orientation of the reticle and the substrate are accurately measured by using various sensors in the projection exposure apparatus is that the drawing pattern of the reticle to be exposed and transferred to the substrate is extremely fine. That is, in recent years, the integration degree of ULSI has been further increased, and it is required to form a pattern having a line width of, for example, 0.35 μm or less on a wafer.

Therefore, in order to perform the positioning of the reticle and the substrate with extremely high precision, the requirements for the positioning accuracy of the substrate stage and the reticle stage have become extremely strict.
Further, in order to obtain a high resolution, the numerical aperture of the projection optical system increases, the depth of focus becomes shallow, and the demands on the accuracy of AF and leveling are becoming more severe. Similarly, the allowable range of the alignment error with respect to the relative position between the reticle and the wafer is extremely limited.

[0007]

By the way, the reticle is
Intense exposure light continues to be emitted until a large number of substrates have been exposed. The pattern to be transferred to the substrate formed on the reticle is usually chrome-coated, but its reflectivity is about 10%, and the remaining exposure light is absorbed by the reticle and converted into heat. It will be. Further, a pellicle for protection is provided on the pattern forming surface of the reticle,
Therefore, the reticle is more difficult to cool. In a normal exposure operation, the temperature rise on the reticle surface is 2
To 3 ° C.

Here, since the coefficient of thermal expansion of the material of the reticle, for example, quartz, is extremely small, 0.5 to 1 ppm / ° C., the temperature rise of 2 to 3 ° C. only elongates at most about 3 ppm. The thermal expansion of the precision optical device used as a lens hardly causes a problem.

However, in an exposure apparatus that achieves positioning between a reticle and a substrate by optically superposing an index on the reticle and an index on the substrate, extremely precise alignment is required as described above. Therefore, even a reticle of about 3 ppm may be problematic. That is, while the exposure of a large amount of the substrate is continued, the index on the reticle moves due to the expansion of the reticle, and there is a possibility that the baseline used as a reference for alignment may fluctuate. Further, the thermal expansion of the reticle may directly affect the projection magnification error of the pattern.

On the other hand, even if an attempt is made to cool the reticle, an illumination system or the like is generally arranged immediately above the projection optical system in the exposure apparatus, so that a space for arranging the cooling apparatus is secured near the projection optical system. There is also the problem that it cannot be done.

The present invention has been made to solve these problems, and has as its object to provide an exposure apparatus capable of efficiently cooling a reticle.

[0012]

In order to achieve the above object, according to the present invention, a mask (R) is provided to a projection optical system for exposing and transferring a pattern on a mask (R) onto a substrate (W). ) And the substrate (W) are moved in synchronization with each other. The exposure apparatus has discharge ports (102a, 202a, 202b) and discharges a temperature-adjusted gas to the mask (R). 202) and a discharge device (102, 20) such that gas is discharged near the position where the mask (R) is farthest from the projection optical system (PL).
A control system (104, 204) for controlling (2).

According to the exposure apparatus of the present invention, the discharge port (1
02a, 202a, and 202b) and a discharge device (102, 202) for discharging a gas whose temperature has been adjusted to the mask (R), and a position where the mask (R) is farthest from the projection optical system (PL). Since a control system (104, 204) for controlling the discharge device (102, 202) so as to discharge gas is provided in the vicinity, the temperature is adjusted each time the mask (R) is synchronously moved. The mask (R) can be cooled by gas, and the thermal expansion of the mask (R) can be suppressed as much as possible. The gas whose temperature has been adjusted is discharged to the mask (R) in a state where it is farthest from the projection optical system. Can be minimized.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings. The projection exposure apparatus shown in FIG. 1 is an example of a scanning type excimer stepper that performs exposure while scanning a reticle and a photosensitive substrate in synchronization with an illumination area on the reticle. As shown in FIG. 1, the stepper is generally installed in a constant temperature chamber 1. In the constant temperature chamber 1, temperature control with higher accuracy than in a normal clean room is performed. For example, the temperature control of the clean room is in the range of ± 2 to 3 ° C., whereas in the constant temperature chamber 1, the temperature control is ± 0. It is kept within 1 ° C.

The illustrated excimer stepper is a down-flow type stepper, and an air outlet 2 is provided on the ceiling of a chamber 1 for temperature control, and from the outlet 2 as shown by an arrow in the figure. An airflow whose temperature is controlled moves toward the chamber floor along the optical axis of the projection exposure system PL. A HEPA (or ULPA) filter and a chemical filter for preventing foreign matter (dust), sulfate ions, ammonium ions, and the like floating in the clean room from flowing into the chamber 1, especially the exposure apparatus body including the projection optical system. Is located near the air inlet or outlet 2 of the chamber 1.

The scanning projection exposure apparatus shown in FIG.
A light source, which is an excimer laser such as rF, and an illumination optical system (only 3 is indicated by 3), a reticle stage RST that moves the reticle R in the scanning direction, a projection optical system PL, a wafer stage WST that moves the wafer W, and a position of the wafer It mainly comprises an alignment system (14 to 18) for alignment. The illumination optical system includes a fly-eye lens, a condenser lens, and the like, and finally illuminates the reticle R via the condenser lens 3. The illumination optical system illuminates a reticle R, which is a mask on which a circuit pattern or the like is drawn, with substantially uniform illuminance and a predetermined solid angle with illumination light from a light source. A light source (not shown) is generally arranged outside the chamber 1,
The illumination light is led to the illumination optical system 3 using a mirror or the like (not shown).

The reticle stage RST includes a projection optical system P
It is installed on the optical axis AX of L and between the projection optical system PL and the condenser lens 3 and is driven by a reticle driving unit (not shown) composed of a linear motor or the like in the scanning direction (Y direction:
(A direction perpendicular to the paper surface) at a predetermined scanning speed. The reticle stage RST moves with a stroke such that the entire pattern area of the reticle R crosses at least the optical axis AX of the projection optical system. Reticle stage RST
Is provided with a movable mirror 5 for reflecting the laser beam from the interferometer 6 at the end in the X and Y directions, and the reticle stage R
The XY position of ST is, for example, 0.6 n
It is measured in m units. The measurement result by the interferometer 6 is sent to the stage control system 20, and the reticle stage RST
Is performed with high accuracy. Reticle stage RS
On the T, a reticle holder RH is installed.
Is set on the reticle holder RH. Reticle R is
The reticle is held by suction on a reticle holder RH by a vacuum chuck (not shown).

Further, above the reticle stage RST, a reticle alignment microscope 4 facing the optical axis AX is mounted. The relative positions of a reference mark (not shown) formed on the reticle R and a reference mark 13 on the wafer stage 8 are observed by the two sets of microscopes 4.
The relationship between the reticle R and the wafer stage is accurately measured, and both are positioned.

The reticle R is illuminated on the reticle stage RST in a rectangular (slit-shaped) illumination area whose longitudinal direction is in the direction (X direction) perpendicular to the scanning direction (Y direction) of the reticle R. This illumination area is defined by a field stop (not shown) disposed above the reticle stage and at or near a plane conjugate with the reticle R.

The illumination light passing through the reticle R enters the projection optical system PL, and a circuit pattern image of the reticle R is formed on the wafer W by the projection optical system PL. Projection optical system PL
, A plurality of lens elements are accommodated such that the optical axis AX is a common optical axis. The projection optical system PL is provided with a flange 24 at the outer peripheral portion and at the center in the optical axis direction, and is fixed to the gantry 23 of the exposure apparatus main body by the flange portion 24.

The projection magnification of the pattern image of the reticle R projected on the wafer is determined by the magnification and arrangement of the lens elements. A reticle pattern in a slit-shaped illumination area (center substantially coincides with optical axis AX) on reticle R is projected onto wafer W via projection optical system PL.
Since the wafer W has an inverted image relationship with the reticle R via the projection optical system PL, when the reticle R is scanned at a speed Vr in the −Y direction (or + Y direction) during exposure, the wafer W is moved in the direction of the speed Vr. Scanning is performed at a speed Vw in synchronization with the reticle R in the + Y direction (or -Y direction) opposite to the above, and the entire pattern of the reticle R is sequentially exposed on the entire shot area on the wafer W. The scanning speed ratio (Vr / Vw) depends on the projection optical system P
It is determined by the reduction ratio of L.

Wafer W is vacuum-sucked on a wafer holder (not shown) held on wafer stage WST. Wafer stage WST is configured to be movable not only in the above-described scanning direction (Y direction) but also in a direction (X direction) perpendicular to the scanning direction so that a plurality of shot areas on wafer W can be scanned and exposed. And the wafer W
The operation of scanning each upper shot area and the operation of moving to the exposure start position of the next shot area are repeated. Wafer stage WST is driven by a wafer stage drive unit (not shown) such as a motor. The moving speed of wafer stage WST is adjusted according to the ratio Vr / Vw, and moves in synchronization with reticle stage RST. A movable mirror 8 is fixed to an end of wafer stage WST, and a laser beam from interferometer 9 is reflected by movable mirror 8, and reflected light is detected by interferometer 9 so that wafer stage WST is
Is constantly monitored in the XY plane. The reflected light from the movable mirror 8 is detected by the interferometer 9 with a resolution of, for example, about 0.6 nm. The interferometer 9 and the interferometer 6 of the reticle stage RST are mounted on a gantry 23 to prevent relative vibration with other components of the apparatus such as the projection optical system PL.
It is installed above.

The projection exposure apparatus has a function of exposing a new pattern with high accuracy on a pattern already formed on the wafer W by exposure. In order to perform this function, the projection exposure apparatus has a function (wafer alignment system) for detecting the position of the alignment mark on the wafer W and determining the position for performing the overlay exposure. In this example, a projection optical system P is used as the wafer alignment system.
An optical alignment system (14 to 18) provided separately from L is provided. As the light source 13 of the wafer alignment system, a laser, a halogen lamp, or the like is used.

Next, the reticle cooling device of the exposure apparatus according to the embodiment of the present invention will be described in detail below. FIG. 2 is a perspective view of the reticle cooling device 100 according to the first embodiment of the present invention. FIG.
In FIG. 1, the projection optical system PL shown in FIG.
And only the reticle R is extracted, and the rest of the configuration is omitted. The reticle R reciprocates in the Y direction from above the projection optical system PL according to the scanning of the exposure device.

In FIG. 2, a cooling device 100 is arranged adjacent to the reticle R that has reached the end of the reciprocating path (ie, the position furthest away from the projection optical system PL). The cooling device 100 includes an intake fan 101, a heat exchanger 102 as a discharge device, a temperature detector 103, and a control device 104 as a control system electrically connected to these. The intake fan 101 is provided in the chamber 1
It functions to draw in the air inside (FIG. 1) and send it to the heat exchanger 102. The heat exchanger 102 functions to cool the supplied air to a predetermined temperature inside.
Further, the heat exchanger 102 has an outlet 102 as a discharge port which is formed to be elongated along the direction of movement of the reticle and faces the lower surface of the reticle R on which a pattern is drawn.
a, and the cooled air is supplied to the outlet 102
a to the reticle R. The temperature detector 103 has a high field of view, such as a thermoviewer, and can measure the temperature of the entire reticle R by infrared detection.

With the reticle R in between, the outlet 102a
An exhaust device 105 is provided in opposition to. The exhaust device 105 has an exhaust port 105a facing the outlet 102a and having an opening area larger than that. Further, the exhaust device 105 is provided with an exhaust fan 106 facing the exhaust port 105a, and exhausts air sucked from the exhaust port 105a by the exhaust fan 106 to the outside of the chamber 1 via a pipe (not shown). It has become.

The operation of the cooling device 100 according to the present embodiment will be described. The reticle R has a chrome pattern drawn on the lower surface, and such a portion mainly serves as a heat source. At the beginning of the exposure, the reticle R is almost equal to the ambient temperature, and although the intake fan 101 is operating,
The heat exchanger 102 has not exchanged heat yet, so that the outlet 1
The temperature of the air blown from 02a is equal to the ambient temperature.

While the exposure is continued, the control device 104 recognizes via the temperature detector 103 that the chrome pattern is gradually heated by the exposure light and the surface temperature of the reticle R rises to a predetermined temperature. The control device 10
4 starts the reticle cooling operation as follows.

First, the controller 104 inputs a signal relating to the scanning of the reticle R from a controller (not shown) of the exposure apparatus, and obtains a timing at which the reticle R starts to reach a position facing the outlet 102a.

When it is determined that the reticle R has reached such a position, the control device 104 starts heat exchange of the heat exchanger 102 and blows air cooled to a predetermined temperature into the outlet 102.
a, so that the lower surface of the reticle R is cooled. In the present embodiment, when the reticle R returns from the end of the reciprocating movement path, the operation of the intake fan 101 is stopped, but unless the other parts are affected, the intake fan 101 The operation may be continued so that the cooling air always blows out from the outlet 102a.

The outlet 102a has a lateral dimension exceeding the length of the reticle R of 20 cm, so that the entire surface can be cooled without moving the reticle R. In addition, a temperature sensor (not shown) is disposed near the outlet 102a.
The temperature of the air passing through a is detected and output to the control device 104.

The controller 104, based on the information from the temperature sensor and the information from the temperature detector 103, reduces the temperature of the blown air when the temperature of the reticle R is determined to be significant. Next, the heat exchange efficiency of the heat exchanger 102 is controlled.

The control device 104 further includes a temperature detector 103
For example, when it is determined that the temperature of the reticle R has risen significantly based on the information from, the rotation of the intake fan 101 can be controlled so as to increase the flow rate of the blown air.

The outlet 102a is connected to the projection optical system P
L, the air blown out from the outlet 102a by a shielding plate (not shown),
It does not flow above the projection optical system PL. This is because, if air having a temperature different from the ambient temperature is allowed to flow above the projection optical system PL, the refractive index of the space will change, causing a focus blur or the like, which may adversely affect the exposure.

According to the cooling device 100, since the surface temperature of the reticle R is adjusted to ± 0.1 ° C.,
Thermal expansion of the reticle is suppressed, thereby enabling ultra-precise exposure.

Next, a reticle cooling device according to a second embodiment of the present invention will be described in detail below. FIG. 3 is a perspective view of a reticle cooling device 200 according to a second embodiment of the present invention. In FIG. 3, the exhaust device is further omitted for easy understanding. Note that the temperature detector 103 and the intake fan 101 are common to those in the first embodiment, and a description thereof will be omitted.

The difference between the second embodiment shown in FIG. 3 and the first embodiment shown in FIG. 2 lies in the configuration of the heat exchanger 202 as a discharge device. In the first embodiment, an example is shown in which the reticle R is not provided with a foreign matter adhesion preventing film. However, a foreign matter adhesion preventing film (pellicle) is provided so that foreign matter does not adhere to the reticle (particularly, the chrome pattern).
Frame (pellicle frame) may be provided. Even when gas is blown onto the reticle surface on which the pellicle frame is provided, air cannot be cooled because the pellicle frame and the reticle form a sealed space, and the air flow is only disturbed. Therefore,
There is also a need to be able to select whether to direct the cooling air to any side of the reticle. The second embodiment satisfies such a demand.

In FIG. 3, the heat exchanger 202 has upper outlets 202 as discharge outlets having the same opening shape.
a and a lower outlet 202b. The upper outlet 202a faces the upper surface of the reticle R, while the lower outlet 202b faces the lower surface of the reticle R.

An upper valve 202c as a valve for opening and closing the air flow path is provided inside the upper outlet 202a. The upper valve 202c is driven by an actuator 202e as a driving device connected thereto. Has become. On the other hand, inside the lower outlet 202b, a lower valve 202d as a valve for opening and closing the air flow path is provided.
The lower valve 202d is driven by an actuator 202f as a driving device connected thereto. The flow paths from the two valves 202c and 202d to the two outlets 202a and 202b are independent from each other.

The operation of the cooling device 200 according to this embodiment will be described. The reticle R has one of an upper surface (light source side) and a lower surface (projection lens side) (for example, upper surface).
Is provided with a pellicle frame. In such a case, the user inputs reticle information indicating that the pellicle frame is arranged on the upper surface of the reticle R to the control device 204 in advance.

Based on the reticle information, the control device 2
04 controls the actuators 202e and 202f to close the upper valve 202c and open the lower valve 202d. As a result, the cooling air is blown out only from the lower blow-out port 202b, so that the lower surface of the reticle R can be effectively cooled.

On the other hand, when the user previously inputs reticle information indicating that the pellicle frame is arranged on any surface (for example, the lower surface) of reticle R to control device 204, the above case is reversed. The upper valve 20
Since 2c is opened and the lower valve 202d is closed, the cooling air is blown out only from the upper outlet 202a. Note that other cooling operations are common to those of the first embodiment, and a description thereof will be omitted.

By adding a pellicle frame detector or a pellicle presence / absence bar code information reader provided on the reticle, the control device 204 can automatically operate even if the user does not input the reticle information. By controlling the actuators 202e and 202f, the required surface of the reticle can be cooled. Further, if desired, it is possible to control to open both valves 202c and 202d.

[0044]

As described above, according to the exposure apparatus of the present invention, according to the exposure apparatus of the present invention, the thermal expansion of the mask can be suppressed as much as possible. Further, since the gas whose temperature has been adjusted is discharged to the mask at a position apart from the projection optical system, the influence of the gas whose temperature has been adjusted on the projection optical system is minimized. Can be

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a scanning excimer stepper that exposes a reticle and a photosensitive substrate while scanning the reticle in synchronization with an illumination area on the reticle.

FIG. 2 is a perspective view of a reticle cooling device according to a first embodiment of the present invention.

FIG. 3 is a perspective view of a reticle cooling device according to a second embodiment of the present invention.

[Explanation of symbols]

 R: Reticle W: Wafer RH: Reticle holder PL: Projection optical system RST: Reticle stage WST: Wafer stage 1: Chamber 3: Condenser lens 5: Moving mirror 6, 8 Interferometer 101 Intake fan 102, 202 Heat exchanger 102a, 202a, 202b Outlet 202c, 202d Valve 103 Temperature detector 104 , 204 Control device 105 Exhaust device

Claims (7)

[Claims] An exposure apparatus for synchronously moving said mask and said substrate with respect to a projection optical system for exposing and transferring a pattern on a mask onto a substrate, comprising: an ejection port; A discharge device that discharges a gas whose temperature has been adjusted, and a control system that controls the discharge device so that the gas is discharged near the position where the mask is farthest from the projection optical system. Exposure apparatus characterized by the above-mentioned. 2. The exposure apparatus according to claim 1, wherein the control system controls the discharge device so as to discharge the adjusted gas intermittently according to the movement of the mask. . 3. A detector for measuring a temperature of the mask,
2. The exposure apparatus according to claim 1, further comprising: a control device for adjusting a temperature of gas discharged from the discharge device based on a temperature measured by the detector. 4. A detector for measuring a temperature of the mask,
2. The exposure apparatus according to claim 1, further comprising: a control device for adjusting a flow rate of gas discharged from the discharge device based on a temperature measured by the detector. 5. The discharge device has a plurality of discharge ports for discharging the adjusted gas, wherein the openable and closable valve is disposed in correspondence with each of the discharge ports, and according to a type of the mask. 2. The exposure apparatus according to claim 1, further comprising a driving device for independently opening and closing the valve. 6. The driving device further comprises a discriminator for judging the presence or absence of a foreign matter adhesion preventing mechanism to be provided on the mask, and the control system controls the ejection device based on a discrimination result. An exposure apparatus according to claim 5. 7. The exposure apparatus according to claim 1, wherein an exhaust port is provided at a position opposite to the discharge port with the mask interposed therebetween.