JPS61213814A - Projection exposure device - Google Patents

Abstract

PURPOSE:To compensate the reduction rate and a focus position with a high precision by providing a refractometer which measures the refractive index of an environmental gas on or near a projection exposure device and providing a control system which compensates the projection magnification and the focus position on the basis of the measured value of this refractometer. CONSTITUTION:In a refractometer 24, and laser light projected to a beam splitter 27 through a transparent window 30 is separated by the beam splitter 27, and separated rays of light are interfered with each other after passing a reference optical path 31 and a measuring optical path 32 respectively. The intensity of light at this time is detected by a photodetector 29 to measure the refractive index of the air in a barrel 5; and if the measured refractive index is different from a preliminarily set value, a control part 40 controls a flow rate control valve on the basis of the measured value of the refractive index to supply each gas to the barrel 5. A variation of the refractive index to be compensated is obtained because the variation of the reduction rate and that of the focus position are related to the variation of the refractive index, and a gas composition is calculated, and the inside of the barrel 5 is adjusted to its gas environment to set the refractive index to a required value. Thus, the practical refractive index of a focusing lens 6 is compensated to a fixed value.

Description

[Detailed Description of the Invention] [Technical Field] The present invention detects changes in the refractive index of the environmental gas in which a projection exposure apparatus is installed, corrects the projection optical system, and sets an appropriate projection magnification and focal position. This invention relates to a projection exposure apparatus that makes it possible.

[Background technology]

In projection exposure equipment used in the photolithography process, which is one of the manufacturing processes for semiconductor devices, the reduction ratio of the projection optical system becomes larger and larger as the pattern to be transferred becomes smaller. This will have a big impact on the pattern.

One of the fluctuations in the reduction ratio is the influence of the refractive index of the atmosphere, represented by air, and the refractive index of the air changes due to changes in the temperature, humidity, and atmospheric pressure of the air, which causes fluctuations in the reduction ratio in the projection optical system. will occur.

For this reason, the applicant first detected the temperature, humidity, and atmospheric pressure of the air, and corrected the distance between a part of the projection optical system, for example, the reticle and the lens, in order to correct the fluctuations in the reduction ratio. They have proposed countermeasures such as correction or supplying various gases into the lens barrel of the projection optical system to maintain a constant gas refractive index within the lens barrel (Japanese Patent Application No. 11831/1983).

However, as mentioned above, this method calculates the refractive index of the air at that time from the measured values of the air's temperature, humidity, and atmospheric pressure.
Since the projection optical system is controlled based on this calculated value, even if an error occurs in any one of the measured values, this will directly become an error in the refractive index. Furthermore, if errors occur in each measurement value, there is a concern that the errors will increase in a superimposed manner, which poses a problem in correcting the projection optical system with high precision.

[Purpose of the invention]

The purpose of the present invention is to directly detect the refractive index of environmental gases such as air and correct the reduction ratio and focal position of the projection optical system based on this, thereby improving the It is an object of the present invention to provide a projection exposure apparatus that can perform highly accurate correction without errors and that can perform projection exposure at an appropriate reduction ratio and focal position.

The above and other objects and novel features of the present invention include:
It will become clear from the description of this specification and the accompanying drawings.

[Summary of the invention]

A brief overview of typical inventions disclosed in this application is as follows.

That is, a refractometer is provided in or near the projection exposure apparatus to measure the refractive index of the environmental gas, and the actual projection magnification of the projection optical system of the projection exposure apparatus is determined based on the measured value of this refractometer. By providing a control system that corrects the focal position, errors in measuring the refractive index of the environmental gas can be reduced as much as possible, and thereby the reduction ratio and the focal position can be corrected with high precision.

A refractometer consists of a reference optical path placed under conditions of a known refractive index, a measurement optical path placed under conditions of ambient gas, and a photodetector that detects the light intensity due to the interference of light passing through both optical paths. The refractive index of the environmental gas at that time can be directly measured.

〔Example〕

FIG. 1 shows an embodiment in which the present invention is applied to a reduction type projection exposure apparatus, in which light from a mercury lamp 1 is reflected by a reflecting mirror 2 and then condensed by a condenser lens 3 to illuminate a particle 4.

An image of the reticle 4 is formed on the surface of the wafer 7 by an imaging lens 6 disposed in a lens barrel 5 below the reticle 4, and the reticle pattern is transferred onto the wafer 7. Wafer 7 is placed on XY table 8.
2 is placed on the table 9.

The lens barrel 5 is composed of an upper barrel 5a that is approximately in the shape of an inverted truncated cone and a cylindrical upper barrel 5b below the imaging lens 6.
Its upper end is integrated with the lower surface of the holder 10 that supports the reticle 4, and its lower end is integrated with the upper peripheral edge of the imaging lens 6, thereby isolating the inside from the outside air. Further, the upper end of the upper cylinder 5b is integrated with the lower end of the imaging lens 6, and the lower end is opened for transmission of projection light. The upper cylinder 5a has two
holes 11 and 12 are opened, and one hole 13 is formed in the upper cylinder 5b.
A tube 14 is connected to holes 11 and 13, while hole 12 is left open. This tube 1
Branch tubes 15, 16, 17 are connected to 4, and a carbon dioxide gas source 21, a nitrogen gas source 22, and an oxygen gas source 23 are connected to each via flow rate control valves 18, 19, and 20.

A control unit 40 is connected to the flow rate control valves 18, 19, and 20, and the flow rate of each gas is controlled based on a signal from a refractometer, which will be described later, and a mixed gas of these can be supplied into the lens barrel 6. can. Note that these control units 40. Each gas source 21
．． 22, 23. Flow control pulp 18. 19. 20.
The tube 14 etc., and the holes 11, 12, 13 of the lens barrel 5
The control system is constructed by the following.

On the other hand, inside the upper cylinder 5a, a refractometer 24 is attached to the inner wall of the cylinder. As shown in detail in FIG. 2, this refractometer 24 includes a reference optical path 31 and a measurement optical path 32 arranged at right angles to each other, and a photodetector element 29. Reference optical path 3
1 is a transparent glass tube 25 having a reflecting mirror 26 at one end and a beam splitter 27 at the other end to keep the inside in a vacuum state.
It is made up of. Furthermore, the measurement optical path 32 includes a reflecting mirror 28 arranged at the same distance from the beam splitter 27 as the transparent glass tube 25 . The beam splitter 27 is arranged to face the photodetecting element 29, and is configured so that a laser beam from a laser light source (not shown) is projected through a transparent window 30 formed in a part of the upper tube 5a. ing.

With this configuration, a portion of the laser light projected onto the beam splitter 27 is reflected by the beam splitter 27, passes through the transparent glass cylinder 25, is reflected by the reflecting mirror 26, and then passes through the transparent glass cylinder 25 again and returns to the beam splitter 27. reach.

The other part passes through the beam splitter 27, is reflected by the reflecting mirror 28, and is returned to the beam splitter 27. Here, both reflected lights interfere, and the light intensity is detected by the photodetector element 29.

Therefore, the relative optical path length of the measurement optical path 32 with respect to the reference optical path 31 can be determined based on the characteristics of the light intensity with respect to the laser beam wavelength and the distance of each optical path 31, 32, and from this, the refractive index in the measurement optical path 32, That is, the refractive index of the air or gas environment inside the lens barrel 5 can be measured.

According to the projection exposure apparatus having the above configuration, the reticle 4 can be illuminated with light from the mercury lamp 1, and the reticle pattern can be projected onto the wafer 7 using the imaging lens 6, which is the same as before. Detailed explanation will be omitted.

On the other hand, in the refractometer 24, the laser light projected onto the beam splitter 27 through the transparent window 30 is separated by the beam splitter 27 and interfered after passing through the reference optical path 31 and the measurement optical path 32, respectively. By detecting the intensity with the photodetector element 29, the refractive index of the air within the lens barrel 5 can be measured. When this measured refractive index differs from a preset value, it means that the relative refractive index of the imaging lens 6 inside the lens barrel 5 changes, causing a shift in the reduction magnification and focal position. are doing.

Therefore, based on the measured value of this refractive index, the controller 4
0, the flow rate control valves 18, 19, 20 are controlled to flow each gas from the respective branch tubes 15, 16, 17 to tube 1.
4 into the lens barrel 5. In the lens barrel 5, each gas is supplied to the upper barrel 5a and the upper barrel 5b through holes 11 and 13, respectively.

Here, the refractive index change of air is 1 atm, standard atmospheric composition, 2
Near 0°C, refractive index change (ppm) = 0°93δT - 0°36δ2
+0001δ8+δ holds true.

However, δ7 = temperature change (°C).

δ2 = atmospheric pressure change (mmHg) δ = relative humidity (%) δ = refractive index change due to air composition (ppm), and this δ is carbon dioxide gas (100%) = 158 pp
m.

Nitrogen gas (100%) = 5ppm.

Oxygen gas (100%) --20 ppm.

Furthermore, the amount of change in reduction rate is: amount of change in reduction rate (PPa) = 2.5 X refractive index change it
(PPM) relationship. Also, focal position change amount (μm) #0.5 X refractive index change amount (
PPM).

Therefore, the amount of refractive index change to be corrected is determined from the measured refractive index at that time, and the gas composition suitable for correction is calculated from this amount and the above-mentioned relational expression, and based on this, the control unit 4
0 controls the flow rate control valve 18° 19.20 to form a mixed gas, and supplies this into the lens barrel 5, thereby adjusting the interior of the lens barrel 5 to the gas environment and adjusting the refractive index to the required value. Can be set to . From this, the effective refractive index of the imaging lens 6 can be corrected to a constant value, and by making this refractive index constant, the reduction ratio and focal position can also be kept constant, achieving highly accurate pattern projection. can.

Note that the gas supplied to the upper tube 5a of the lens barrel 5 is discharged through the hole 12, and the gas supplied to the upper tube 5b is discharged from the lower opening, so that the inside of each tube is maintained at a constant pressure.

〔effect〕

(1) Since a refractometer that measures the refractive index of the environmental gas is placed within or near the projection optical system, it is possible to directly measure the refractive index of this environmental gas and improve the accuracy of the measured value. This makes it possible to maintain the substantial refractive index of the optical system constant, control the reduction ratio and focal position of the optical system constant, and achieve highly accurate projection exposure.

(2) The refractometer has a reference optical path and a measurement optical path, and is configured to measure the refractive index by utilizing the interference of the light that passes through each of these, so it can be easily installed in an optical system. It is possible to accurately measure the refractive index in the vicinity of the optical system.

(3) Based on the measured refractive index, the control system can mix and supply various gases into the optical system and control the environmental gas within the optical system to have a predetermined refractive index.
The above-mentioned reduction ratio and constant focal position can be controlled with good responsiveness, and particularly high-speed projection exposure can be followed.

Although the invention made by the present inventor has been specifically explained above based on examples, it is understood that the present invention is not limited to the above-mentioned examples and can be modified in various ways without departing from the gist thereof. Nor.

For example, in a refractometer, a reflecting mirror on either the reference optical path or the measuring optical path can be moved along the optical path, and the refractive index can be determined by the change in interference when the reflecting mirror is moved. Further, the optical paths may be arranged in parallel, and the reference optical path may be constructed using a light-transmitting member such as glass or transparent liquid if the refractive index is known. Furthermore, the gas used may be air, helium, or the like instead of nitrogen gas or oxygen gas. In this case, it goes without saying that the numerical values in the above-mentioned relational expression will be different.

[Application field]

In the above explanation, the invention made by the present inventor was mainly applied to a reduction type projection exposure apparatus, which is the field of application that formed the background of the invention, but the invention is not limited to this, and the invention is not limited to this. It can be applied to all devices that project and expose patterns.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram of an embodiment of the present invention, and FIG. 2 is a configuration diagram of a refractometer. DESCRIPTION OF SYMBOLS 1... Mercury lamp, 4... Reticle, 5... Lens barrel, 5a... Upper tube, 5b... Upper tube, 6... Imaging lens, 7... Wafer, 11, 12.13...hole, 14
...Tube, 1B, 19.20...Flow rate control valve, 21...Carbon dioxide gas source, 22...Nitrogen gas source, 23...Oxygen gas source, 24...Refractometer, 26
．． 28...Reflecting mirror, 29...Photodetection element, 31...
- Reference optical path, 32... Measurement optical path, 40... Control unit. Figure 1

Claims (1)

[Claims] 1. A refractometer for measuring the refractive index of an environmental gas is provided in or near the projection exposure apparatus, and the projection optical system of the projection exposure apparatus is adjusted based on the measured value of the refractometer. A projection exposure apparatus characterized by being provided with a control system for correcting the actual projection magnification and focal position. 2. The control system is configured to supply gas into the lens barrel of the projection optical system, adjusts the composition of the gas based on the measured refractive index of the environmental gas, and maintains a constant refraction within the lens barrel. 2. A projection exposure apparatus according to claim 1, wherein the projection exposure apparatus can be maintained at a constant speed. 3. A refractometer has a reference optical path placed under conditions of a known refractive index, a measurement optical path placed under conditions of environmental gas, and a light beam that detects the light intensity due to the interference of the light passing through both optical paths. 2. A projection exposure apparatus according to claim 1, further comprising a detection element, and calculating the refractive index of an environmental gas from the characteristics of the light intensity of both optical paths.