JPS6167036A - Method and apparatus for compensating projection magnification of projection exposer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method and apparatus for compensating for changes in the projection magnification of a projection exposure apparatus due to variations in environmental conditions.

More specifically, the present invention relates to a method and apparatus for correcting changes in the lateral magnification of a projection optical system in a projection type precision exposure apparatus due to changes in environmental conditions, particularly atmospheric pressure.

Technical Background of the Invention In recent years, as semiconductor devices have become increasingly required to be ultra-fine and highly integrated, extremely high precision is required in the manufacturing and processing of semiconductor devices, especially VLSIs. Therefore, even in projection exposure equipment conventionally used for precision manufacturing of semiconductors, the magnification (usually 11
5 to 1/10) must be extremely accurate. For example, a semiconductor chip with a particularly fine structure requires a dimensional accuracy of 0.1 micron (μ), which for a 14 millimeter (fl) square LSI is 0.1 (μ) ÷ 14 ( m) =; This means that a very high magnification accuracy of 7x 10-' is required.

K to obtain such high magnification accuracy.

Conventionally, close attention has been paid to the settings of the optical system of an exposure apparatus.

However, recently, various experiments using an exposure apparatus have revealed that variations in the apparatus environment have a substantial effect on the pattern reduction (transfer) magnification. This is thought to be because, for example, when the temperature of the equipment environment changes, the lens barrel of the projection optical system thermally expands or contracts, changing the distance between the original plate and the lens, and also because the humidity of the environment changes. In this case, it is thought that this is because the humidity of the air within the projection optical system also changes, causing a change in the relative refractive index of the lens.

For this reason, the environmental temperature etc. are strictly controlled and controlled; for example, the temperature change in a clean room is usually ±0.1°C.
It is suppressed below.

Here, it goes without saying that atmospheric pressure fluctuations should also be taken into consideration as an important environmental factor that substantially affects the refractive index of the air within the projection optical system and, therefore, the reduction magnification of the pattern. For simplicity, the lens of the projection optical system will be replaced with one thin lens as shown in FIG. 1. Also, the distance to the thin lens may be S? The distance from the thin lens to *)'o' of the original plate is s/, and the refractive index of air is n.

The refractive index of the thin lens is nQ, the radius of curvature is r,
r! Then, the focal length ψ, the bonding formula, and the lateral i ratio m are expressed as follows.

s' s +ψ (2) m=
l/ (3)
S However, s = s / n
(4) s'= s'/n
(5), where s and s' are positive in the direction in which the light travels, and therefore, the lateral magnification m is negative in the case of an inverted real image.9 Generally, when the air pressure P changes, the refractive index n of the air also changes. However, the relationship between P and n is given by the following equation.

n 1 =A (T) (n s-1)
(61S However, P is the standard atmospheric pressure, and P s = 760 x mHg = 1015 millibar (mb).' Also, n is the standard refractive index at standard atmospheric pressure, and the wavelength is 435 nm. The coefficient A (T) is a function of the temperature T, and is 1 at the standard temperature (15° C.).

Therefore, if there is no change from the standard temperature, then Thus, the refractive index of air is δ. If S is unchanged, 5Ks will change as is clear from equation (4). Further, at this time, as is clear from equation (1), ψ also changes by 5, but since the exposure apparatus is always in autofocus mode, i' is also determined so as to satisfy equation (2).

From the above, the change in lateral magnification δm is finally given by the following equation.

δ□=n(nro-n)m(1-m)δn(8) Here, between the object (original plate) yo and the image size y,, /, To' = m yo(9) Since there is a relationship, the following equation is obtained from equations (8) and (11).

In this formula (10), if n = 1, then formula (7) is obtained.Furthermore, if n = 1.5, δP δy,' = 0.00084 y,' (1-m) -Q
It becomes 3s. When the reduction magnification is 115 times, since it is an inverted image, m=-0,2, and the LSI chip size Yo'=10 (am) tδ! ', = 20 (m
b) then δy,''':, 0.2 (μ) (14. The values of these variations δr, δy, / have been confirmed in experiments using actual exposure equipment. This 0.2 Although errors on the order of microns (μ) appear extremely small, they cannot be ignored in recent exposure apparatuses that require so-called sub-micron accuracy, and correction is absolutely necessary.

OBJECTS OF THE INVENTION Accordingly, an object of the present invention is to compensate for fluctuations in the projection (reduction) magnification of a transfer pattern caused by changes in the environmental conditions of a projection exposure apparatus, particularly changes in atmospheric pressure, thereby enabling high-precision no-turn transfer. An object of the present invention is to provide a projection exposure method and apparatus for the same.

SUMMARY OF THE INVENTION 1' In order to achieve the above object, according to the method according to the present invention, the environmental conditions (particularly atmospheric pressure) of the projection exposure apparatus are first measured and detected, and the internal pressure of the projection optical system is adjusted according to the detected value. pressure,
Therefore, the optical distance from the original plate such as a reticle to the projection lens is controlled by changing the refractive index of the gas within the projection optical system.

Further, the device according to the present invention includes a device for detecting changes in environmental conditions such as atmospheric pressure as described above, a device for adjusting the pressure within the projection optical system, and a device for adjusting the pressure within the projection optical system according to the detected value. The characteristic component is a device that controls the above-mentioned pressure adjustment device so as to change the pressure adjustment device. This is what makes it possible.

DESCRIPTION OF A PREFERRED EMBODIMENT Next, FIG. 2 shows the overall structure of a projection exposure apparatus which is a preferred embodiment of the present invention. As shown in the figure, the exposure apparatus main body 1 includes a light source 2, an illumination optical system 4 including a condenser lens 6, a support table 6 on which a reticle 5 having a transfer pattern is placed, and a projection lens 7 including a projection lens 7. The lens barrel 9 includes an optical system 8 and is attached to a fixed arm 12. Further, an optical system 16 for setting the focus and alignment (plane position) of the projected image is also installed in the exposure machine main body 1.

Furthermore, the projection optical system 8 described above has a pressure adjustment chamber (hereinafter simply referred to as a "chamber") 10 defined by partition walls 11a and 11b made of a material such as glass, which is connected to the projection lens 7 and the original plate 5. It is set in between. Then, the projection magnification of the projection optical system 80 is corrected by changing the pressure of the air in the chamber, and therefore the refractive index.

On the XY table 15 arranged under the exposure machine main body 1,
A semiconductor wafer 14 is placed on the tower. The transferred pattern on the original plate 5 is reduced in size by the projection optical system 8 and imaged onto the semiconductor wafer 14 .

In addition, a barometer 17 is installed near the exposure machine main body 1,
Usually, it detects the atmospheric pressure inside the clean room. In this example, we used a barometer because we are concerned with compensating for fluctuations in projection magnification caused by fluctuations in barometric pressure.However, if the influence of fluctuations in temperature and humidity is also a problem, a thermometer may be used. It is also possible to install a temperature sensor (temperature sensor) and a hygrometer.

On the other hand, a pressure gauge 12 is installed inside the chamber 10,
Detect the air pressure inside the chamber. Then, detection signals are sent from the barometer 17 and the pressure gauge 12 to the control section 18. As will be explained in detail later, correlation information between the atmospheric pressure or the air pressure in the clean room and the reduction rate is input and stored in advance into the control unit 18, and the control unit 18 controls the pressure in the chamber based on the above detection signal. Calculate the correction amount.

As a result of the calculation, if it is necessary to pressurize the air in the chamber 10, the control unit 18 controls the direction switching valve (6-port valve) 2.
1 to control the chamber 1 as shown in FIG.
0 and the compressor 19, and sends a drive signal to the compressor 19.

On the other hand, when it is necessary to reduce the pressure of the air inside the chamber 10, the control unit 18 controls the directional control valve 2 to switch the connection with the chamber 10 to the vacuum pump 20, as shown in FIG.
1 and drives the vacuum bonder 20. after that,
The control unit 18 sends a control signal to open the solenoid valve 24. In this embodiment, between the directional control valve 21 and the chamber 10,
In addition to a solenoid valve 24 for preventing backflow of air, an air reservoir 22 for gradually changing the pressure and an air filter 25 for dehumidification are provided.

Whether or not the desired air pressure is obtained as a result of pressurization or depressurization of the air in the chamber 10 is confirmed by the control unit 18 based on the pressure detection signal from the pressure gauge 12, and whether further pressurization or depressurization is necessary. If there is, the control unit 18 controls the directional control valve 21 and the compressor 19 or vacuum cylinder 120.
A drive signal is sent to Furthermore, when a desired air pressure is obtained within the chamber 10, the control section 18 also sends a control signal to close the electromagnetic valve 24.

Next, we will explain how the amount of air pressure in the chamber that should be increased or decreased to compensate for the reduction factor, which varies depending on variations in atmospheric pressure (or the air pressure in the clean room), is determined. do.

FIG. 4 shows an enlarged view of the chamber 100, and the chamber 10 is defined by two parallel flat glass plates 11a and 11b having a thickness of a. However, for the sake of simplicity, it is assumed that the outer surface of the partition wall 11b of the chamber 10 is almost in contact with the lens surface of the projection lens (thin lens) 7.

The air pressure within this chamber 10 can be freely adjusted as described above.

Furthermore, K, the distance from the original plate y0 to the projection lens surface! , the thickness of the air layer in the chamber 10 is d, the refractive index of the atmosphere (or the air in the clean room) is n, the refractive index of the glass plate on the side wall of the chamber is ng, and the refractive index of the air in the chamber is nI
+ If the refractive index of the projection lens 7 is 00, the optical path length (converted distance) 7 from the original plate to the lens surface is given by the following equation.

Here, from the above equations (1) to (5), the equations for determining the reduction magnification m' of this projection optical system are r, rl. The refractive index of the atmosphere (or the air in a clean room) is δ. When changing the refractive index of the air in the chamber δ
. , if we adjust the magnification m' to 5 to keep it constant by varying it, then δ. It is known that δ1 and δ1 should satisfy the following relational expression.

Since the relationship between the air pressure P and the refractive index n is given by equation (7), we can convert equation (10) to the change in atmospheric pressure (or air pressure in the clean room) δP, I and the correction of the reduction magnification m'. The change in air pressure in the chamber required for δP,.

When inserted into the relational expression, it becomes as follows.

Furthermore, it can be considered that n ''; 1.01 nI''t 1.0, which is from the a divine ceremony.

Here, as a specific numerical value in this example, 1 = 5
00 (III), d=250 (!IIE), a
=25 (m).

Substituting n □ = 1.5 t n g = 1.5 into equation 12, δn, = -4,667δn
(The relational expression 2chin is obtained. Similarly to obtaining the α9 equation, from equation (7), the Kan equation and the 00 equation can be converted to atmospheric pressure (
When the relationship between the change δB in the air pressure in the clean room (or the air pressure in the clean room) and the change δP in the air pressure in the chamber necessary for correcting the reduction magnification m', the following equations are obtained.

Therefore, for example, if δP=10 (mb), the air pressure in the chamber needs to be reduced by 46.67 mm IJ par (mb). Such a relational expression for correcting the air pressure in the chamber is stored in advance as a program in the storage device in the control unit 20, and is based on changes in the atmospheric pressure (or the air pressure in the clean room) sent from the barometer 17. Based on the amount, a correction value for the air pressure in the channel 10 is calculated as described above.

Effects of the Invention As described above, according to the present invention, environmental conditions such as atmospheric pressure are detected by a detection device installed in or near the projection exposure machine body, and the reduction magnification is corrected in response to changes in the environment. This can be done by controlling the gas pressure within the projection optical system, and can achieve highly accurate pattern transfer, as well as by controlling the distance from the original plate of the projection optical system to the projection lens by other mechanical or electrical methods. By changing , it is also possible to change the optical path length and correct the projection magnification. For example, it is conceivable to drive the support base 6 of the original plate 5 in the vertical direction by a distance corresponding to changes in environmental conditions using a motor, a piezoelectric element, or the like. However, compared to these methods in which the projection optical system device itself is mechanically and physically driven, the method and device of the present invention reduce the damage of the projection optical system device itself. This has the advantage of being less likely to occur, and the optical distance can be easily adjusted.

Although the present invention has been specifically explained based on one embodiment, for example, the specific configuration of the air pressure adjustment mechanism in the chamber may be slightly modified, and a blower may be used instead of a compressor. etc. can also be used. In addition, in the above-mentioned embodiment, the case where the atmospheric pressure inside the chamber is corrected when the environmental conditions such as temperature and humidity are constant and the atmospheric pressure fluctuates was explained, but based on the correlation information obtained through experiments, It is also possible to correct minute changes in the reduction magnification due to changes in temperature or humidity by controlling the pressure inside the chamber.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the projection optical system for explaining the relationship between changes in air pressure in the projection optical system of a projection exposure apparatus and changes in the reduction magnification of pattern transfer. FIG. 3 is an enlarged view of the directional control valve device when the compressor and vacuum pump are switched in the embodiment shown in FIG. 2; The figure is an enlarged view of the projection optical system in the projection exposure apparatus of the embodiment shown in FIG. 2. In addition, in the drawing, 1: g Light machine main body 4: Illumination optical system 5: Original plate 7: Projection lens 82 Projection optical system 9: Lens barrel 10: Pressure adjustment chamber 11a, 11b Glass side wall 12: Pressure gauge 142 Semiconductor wafer 7117
Two barometers 18 Two control parts 19: Compressor 20: Vacuum pump 21°: Directional switching valve (5 people in addition)

Claims (3)

[Claims] (1) Detect changes in atmospheric pressure as an environmental condition of the projection exposure apparatus, calculate a correction value for the gas pressure in the projection optical system of the projection exposure apparatus according to this detected value, and calculate the correction value for the gas pressure in the projection optical system of the projection exposure apparatus based on the correction value. A method of compensating for fluctuations in projection magnification of the projection optical system due to fluctuations in the environmental conditions by controlling the pressure of a gas within the projection optical system to change its refractive index. (2) A pressure adjustment chamber that is provided in the projection optical system of the projection exposure apparatus body and can change the pressure of the gas inside, a drive mechanism that changes the pressure of the gas in the pressure adjustment chamber, and environmental conditions of the projection exposure apparatus. a detection device for detecting the atmospheric pressure as a pressure; a control device that controls the
An apparatus for compensating for changes in projection magnification of the projection optical system due to changes in the environmental conditions by changing the relative refractive index of gas in the pressure adjustment chamber. (3) The pressure adjustment chamber has a constant thickness (d) in the optical axis direction.
and two partition walls having a constant thickness (a) in the optical axis direction for confining the gas layer, and the atmospheric pressure as the environmental condition changes by a certain value (δP). Then, the correction value (δP) for the pressure of the gas layer is determined by the optical axis distance (l) between the thick plate and the projection lens, the relative refractive index (n_0) of the projection lens, and the gas in the environment before the change. From the relative refractive index (n) and the relative refractive index (N_1) of the gas layer, the relational expression δP_1=n_1^2/d{-[n_0]/[n^2(
n_0-n)]l+[n_0n-n^2]/[n^2n
_1(n_0-n)]d+[2a(n_0ng-n^2
]/[n^2ng(n_0-n)]} δP. The projection magnification compensating device according to claim 2, wherein