JPS63199419A - Projection exposure device - Google Patents

Abstract

PURPOSE:To predict, detect and correct the variation of image formation characteristics due to a temperature rise in a projection optical system with high precision by a simple means, and to stabilize image forming characteristics with high accuracy by automatically controlling a focusing mechanism on the basis of an output measuring the pressure change of a closed space formed between optical elements in an optical system. CONSTITUTION:A lighting means 2 irradiating the pattern of an original plate 1, a projection optical system 3 projecting the irradiated pattern onto a body to be exposed 4, a focusing mechanism 8 for conforming the image surface of the projection optical system 3 and a photosensitive surface on the body to be exposed 4, a closed space formed between optical elements in the projection optical system 3, a pressure- change measuring means 20 measuring the pressure change of the closed space, and a control means 22 automatically controlling the focusing mechanism 8 on the basis of an output from the pressure-change measuring means 20 are provided. When the pressure of the closed space in a projection lens 3 rises due to a temperature rise by exposure beams, a thin-film 19 is spread. The quantity of the spread is detected by the electrostatic capacity sensor 20 and the pressure change is acquired, and the CPU 22 drives the piezo-element 8 through a piezo-driver 26 on the basis of the pressure change.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a projection exposure apparatus that can maintain optical characteristics such as an imaging position and magnification with high precision.

[Prior art] In recent years, reduction projection exposure equipment (hereinafter referred to as steppers) has been introduced to many VLSI production sites and has brought great results, but one of its important performances is improved overlay matching accuracy. It will be done.

Among the factors that affect this matching accuracy, the magnification and focus error of the projection optical system are important. Super LSI
The size of the patterns used for this purpose is becoming increasingly finer year by year, and as a result, it is desired to further reduce these errors and further improve matching accuracy.

Currently, by adjusting the magnification and focus of the projection optical system when installing the apparatus, the magnification error can be ignored. However, this type of exposure apparatus uses exposure light with strong energy to transfer the circuit pattern onto the photoresist on the wafer, which increases the ambient temperature within the projection lens. Therefore, as the lens temperature and lens atmosphere temperature rise, changes in the index of the lens, changes in the surface, etc. appear, and as a result, the optical characteristics (magnification error and focus change) of the projection lens are affected. Therefore, conventionally when using such a projection lens, a means has been used to detect the ambient temperature and predict and correct changes in imaging performance.

[Problems to be Solved by the Invention] However, according to such a means, it is not possible to sufficiently cope with the above-mentioned changes in the imaging characteristics caused by the increase in the lens and lens atmosphere temperature.

In order to solve this problem, it is possible to insert a temperature sensor directly into the projection lens from the lens barrel, but since the sensor cannot be installed within the effective optical path, the actual temperature rise cannot be ascertained, and the sensor must be made smaller. There are problems such as insufficient temperature sensitivity due to the need to

Another option is to attach a pressure gauge to the lens barrel and measure pressure changes due to temperature changes inside the sealed projection lens, but a normal gauge would be unable to track minute pressure fluctuations inside the projection lens. is the current situation.

In addition, as an example of a patent application, an application (Japanese Patent Laid-Open No. 60-7935
No. 7 and Japanese Unexamined Patent Publication No. 60-79358). However, with this method, there are problems such as an increase in the size of the apparatus, instability of imaging characteristics due to fluctuations in the circulating gas, and an inability to follow the rapid startup of the projection optical system at the start of exposure.

In view of these problems, it is an object of the present invention to improve the imaging characteristics caused by the temperature rise in the projection optical system by using a simple means that does not involve increasing the size of the device, such as installing a temperature controller, in a projection exposure apparatus. The objective is to predict, detect, and correct changes with high precision to stabilize imaging characteristics with high precision.

[Means and effects for solving the problems] In order to achieve the above object, the present invention provides a projection exposure apparatus having a focus control means, in which at least a part of the space between the optical elements of the projection optical system is a closed space, and the exposure light is Temperature changes within the projection optical system due to energy accumulation, etc. are interpreted as changes in the pressure within the sealed space, and imaging characteristics such as focus changes and imaging position changes due to temperature changes within the projection optical system are determined from this pressure change. By predicting changes in the image quality and correcting the focus mechanism based on this, a uniform imaging state is always maintained.

The pressure change can be measured, for example, by forming a part of the boundary between the closed space and the outside with a thin film that is sensitive to pressure differences, and measuring the pressure change in the closed space as the amount of displacement of the thin film.
Detection is possible by converting this amount of displacement into pressure.

According to the present invention, unlike the method of forcibly lowering the temperature rise of the projection optical system and its atmosphere using a temperature controller, the change in imaging performance due to the rise in temperature is controlled based on the pressure change. Since it is a prediction and correction method, there is no need for a temperature controller or the like to lower the ambient temperature of the optical element, and the installation space for the device does not change at all.

[Example] Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 shows a projection exposure apparatus according to an embodiment of the present invention.

In the figure, 1 is a reticle, 2 is an illumination device necessary for transferring the pattern of the reticle 1, 3 is a projection lens (optical system) having a plurality of optical elements (lenses), and 4 is a projection lens that 5 is a chuck that vacuum-chucks the wafer 4, and 6 is an XYθZ stage that can move the wafer 4 up and down, in the θ and XY directions.

The projection optical system 3 is composed of a plurality of optical elements L1 to L5 arranged at predetermined air intervals. 7 is a lens holder for fixing the optical element L1, 8 is a piezo element necessary for vertically driving the optical element L1, 9 is a sensor for detecting the vertical position of the lens holder 7 with respect to the projection lens 3, 10° 12, 14. 16 is the air interval between each optical element L1 to L5, 11.13.15.17 is each air interval 10
．． 12, 14. Ventilation holes necessary to ventilate 16,
18 is a constant temperature chamber for keeping the ambient temperature of the projection lens 3, wafer 4, XYθZ stage 6, etc. constant; 19 is a thin film attached to a part of the lens barrel so as to seal the inside of the lens barrel; 20 is a constant temperature chamber; A capacitance sensor detects the amount of deformation of the thin film 1 that is deformed due to a pressure change accompanying a temperature rise inside the projection lens 3, 21 is a vent leading to the thin film 1, 22 is a CP
U, 23 is a temperature monitor, 24 is a hot air fan, 25 is a pressure monitor, and 26 is a piezo driver.

In this configuration, the wafer 4 to be exposed is placed on the chuck 5
It is vacuum-adsorbed by the XYθ2 stage 6 and transported to the best focus position and the best exposure position. During exposure, in order to stabilize the temperature environment around the projection lens 3 and the XYθZ stage 6, the CPU 22 always reads temperature fluctuations with the temperature monitor 23 and sends a command value to the hot air fan 24 to set the temperature to the optimum temperature. In addition, in response to fluctuations in atmospheric pressure, the pressure monitor 25 detects the pressure in the outside world (atmospheric pressure), and if there is a fluctuation, the piezo element 8 is driven via the piezo driver 26 to move the optical element L1 up and down to form an optimal image. Make it a characteristic. With all of them on standby, reticle 1
The pattern formed above is imaged and projected onto the wafer 4 via the projection lens 3 by exposure light from the illumination device 2. At this time, ventilation holes other than ventilation hole 21! 1.13.15.1
7 is sealed, and the ventilation hole 21 is connected to the thin film 19.

FIG. 2 is an explanatory diagram of a portion of the optical system 3 that detects the pressure within the closed space.

When the pressure in the sealed space inside the projection lens 3 increases as the temperature rises due to the exposure light, the thin film 19 is expanded as shown in the figure. The capacitance sensor 20 detects this amount of expansion (amount of change).
By detecting this and converting it to pressure, the pressure change in the closed space can be determined.

Next, a method for correcting the projection magnification and imaging plane position by determining the amount of change in the projection magnification and the imaging plane position based on this pressure change will be described.

The projection magnification M and the imaging plane position F of the optical system 3 are functions of the following factors.

M=f (P,,T,,Ta,P,,X)...
(1) )-=g (Pa, Ta, Te, Pe, X)...
・(2) Pa: Atmospheric pressure around the projection lens 3, T, ・Ambient temperature around the projection lens 3, To = Temperature inside the projection lens 3, P8 Two-stage type. The internal pressure of the lens 3,
ΔTa, ΔT8. Assuming ΔPa and ΔX, when the amount of change in projection magnification ΔM and the amount of change in imaging plane position ΔF are sufficiently small, the terms higher than the second order can be ignored, ΔM-A, Δpa+ A2 ΔTa+A3 Δpa+ A4
Δ7. +A5ΔX...(3) ΔF-B, ΔPa+B2ΔTa+B3ΔP, +B4Δ
T, + B5ΔX (4) A, ~A5. at to B5: Constants determined experimentally or theoretically. In addition, the pressure pH in (the sealed chamber of) the projection lens 3
If we consider that its volume ■6 is constant, then it can be expressed as follows.

P,=h (T,,V.)...(5)Δpa=c
, ΔTa...(6) C1: Constant obtained from experiment or theory This ΔPa is also proportional to the amount of change ΔS in the thin film 19, and ΔS
Since K is the atmospheric pressure minus the internal pressure of the projection lens 3, it can be expressed as a proportionality constant K as follows.

ΔPa=to ΔS=K (P, -P, )−・・・(7
) Furthermore, from formula (δ), (7), ΔT, = K (P, -P-)/C+ ...... (
8), and the amount of temperature change ΔT inside the projection lens 3 can be determined from the atmospheric pressure P8 around the projection lens 3 and the internal pressure pH of the projection lens 3. Therefore, in order to keep ΔM=O, ΔX−1(8, ΔP, 10
82ΔTll+ A3ΔPa+ A4ΔT−)/As
m-(111, Δ Pa ten A2ΔTll+(8s +
A4) K P a-(8.+A4/C+) KpH
)/Eight.

・・・・・・(9) Since it is sufficient, the piezo element 8 is driven and the optical element L
It is sufficient to differentiate the distance from 1 to L2 by this Δχ.

Also, at this time, ΔF is expressed by equation (4), equation (8), (9)
From ΔF−(Bl−BSAI/A5)Δpa+ (B
2-1t5A2/Δ5)ΔTa” (B3”B4/C+
-As8s/As-AJs/A5) ['a-(B3”B
4+85A3"B5A4/AgC+')KpH...
(10) Therefore, it is sufficient to move the wafer 4 up and down by this ΔF using the XYθZ stage 6.

By the above method, it is possible to correct changes in projection magnification and changes in focus caused by pressure changes and temperature changes around the projection optical system 3 during exposure, and pressure changes (temperature changes) inside the projection lens due to absorption of exposure light energy. .

[Modification of Embodiment] FIG. 3 shows a method of detecting pressure using the piezoresistive effect of a semiconductor instead of the capacitance sensor 20. Pressure measurement using this method utilizes the fact that the sensor chip built into the piezoresistive pressure 5W27 changes its resistance (strain resistance) in response to pressure changes in the closed space of the projection lens 3. Compared to , it is difficult to measure by proxy.
The pressure 5W27 itself also has advantages such as being very compact.

Further, in the above description, air is used as the gas in the closed space of the projection lens 3, but nitrogen, helium, or the like may be used instead.

[Effects of the Invention] As explained above, according to the present invention, the effects of absorption of exposure light energy on optical properties such as projection magnification and image plane position can be easily reduced by small and simple means. It also predicts and detects with high precision and corrects and corrects the imaging characteristics with high precision.
can be maintained.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an optical system according to an embodiment of the present invention, FIG. 2 is a block diagram showing an optical system pressure detector of the apparatus shown in FIG. 1, and FIG. FIG. 7 is a block diagram showing pressure detection means according to a modification of the embodiment. 1 reticle, 2: illumination device, 3: projection lens, 4: wafer, 5: chuck, 6: XYθZ stage, 7: lens holder, 8. Piezo element, 9: Eddy current detector, 10, 12.14. lli: air interval, 11, 13.
15.17: Ventilation hole, 18: Chamber, 19: Thin film, 20: Capacitance sensor, 21: Thin film vent hole, 22: C
PU, 23: Temperature monitor, 24: Hot air fan, 25: Pressure monitor, 26: Piezo driver, 27: Piezo resistance pressure S
W. Patent Applicant Canon Co., Ltd. Agent Patent Attorney Tatsuo Ito Agent Patent Attorney Tetsuya Ito Figure 3

Claims (1)

[Scope of Claims] 1. Illumination means for irradiating the pattern on the original plate; a projection optical system for projecting the pattern irradiated by the illumination means onto the object to be exposed; a focus mechanism for adjusting imaging characteristics when the pattern is imaged on a photosensitive surface of an object; a closed space provided at at least one location between the optical elements of the projection optical system; A projection exposure apparatus comprising: a pressure change measuring means for measuring a pressure change; and a control means for automatically controlling the focus mechanism based on the output of the pressure change measuring means. 2. The projection exposure apparatus according to claim 1, wherein the focus mechanism includes means for moving the optical element and means for moving the object to be exposed. 3. Claim 1, wherein the pressure change measuring means includes a thin film provided as part of the boundary between the closed space and the outside, and means for measuring the amount of displacement of the thin film.
Projection exposure apparatus described in Section 1. 4. The projection exposure apparatus according to claim 1, wherein the pressure change measuring means includes a piezoresistive pressure switch whose resistance changes according to pressure changes in the closed space. 5. The projection exposure apparatus according to claim 1, wherein the gas existing in the closed space is air, nitrogen, or helium. 6. The control means calculates the temperature change of the projection optical system based on the output of the pressure change measurement means and controls the focus mechanism to maintain predetermined imaging characteristics. The projection exposure apparatus according to item 1.