JPH07192990A - Aligner - Google Patents

Abstract

PURPOSE:To obtain high alignment accuracy of a semiconductor aligner which requires high alignment accuracy by a method wherein a magnification change and a focal-position change caused by the change in surroundings are corrected always and kept constant. CONSTITUTION:By using control means 5, 13 which change the oscillation wavelength of a laser 1 of an exposure light source and which form a slight difference, with reference to atmospheric pressure, in a pressure inside a projection lens 6, a magnification change and a focus change which are caused due to a change in the surroundings of the projection lens 6 are corrected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus for transferring a pattern on a reticle onto a wafer via a projection optical system.

[0002]

2. Description of the Related Art In recent years, semiconductors have become smaller and smaller,
In a 64-mega DRAM LSI, a design rule of a line width of 0.35 μm is desired, and it is inevitable that a further finer design rule will be required in the photolithography technology in the future.

Furthermore, the overlay accuracy is 5 of the design rule.
High precision of about 1/3 to 1/3 is required.

Generally, the resolution R is the numerical aperture N.V. of the projection lens. A. And the exposure wavelength λ are used to express the following relationship (Equation 1).

[0005]

[Equation 1]

Similarly, the depth of focus DOF is expressed by the following (Equation 2).

[0007]

[Equation 2]

In order to improve the resolving power from (Equation 1), it is necessary to shorten the exposure wavelength and increase the numerical aperture of the projection lens. On the contrary, as can be seen from (Equation 2), the depth of focus is increased. Becomes shorter.

Therefore, when exposure is performed using a light source with a short exposure wavelength, not only the wafer height position is detected with high accuracy, but also the focus position of the projection lens is affected. Is large, it is necessary to correct this.

Further, if the temperature, the humidity and the atmospheric pressure change, the refractive index of air also changes, and the image forming performance of the projection lens, especially the focus position and the image forming magnification change.

Therefore, in order to obtain a high overlay accuracy, it is indispensable not only to provide a highly accurate wafer position detecting means, but also to take measures against a variation in the imaging magnification of the projection lens caused by a change in the environment. It is a matter.

This is described in, for example, Japanese Patent Application Laid-Open No. 62-69617.
As described in Japanese Patent Laid-Open Publication No. JP-A-2003-264, there is known a method in which a projection lens is divided into a plurality of air chambers and the pressure of the air chambers is controlled to control magnification variation and focus variation (first conventional example). .

This example will be described below with reference to FIG. In FIG. 2, 101 is a projection lens, 102 is a constant pressure control system, 103 is a pressure offset setting unit, 104 is an exposure light source system, 105 is a wafer stage, H is a pressure-controlled air chamber for magnification adjustment, and N is a focus. Air chambers G1 to G5 whose pressure is controlled for adjustment are typical lens elements.

In this example, in order to correct the magnification variation and focus variation caused by atmospheric pressure variation, the pressure is controlled in the closed air chamber without the projection lens to change the refractive index and the correction is performed.

Specifically, the pressures P1 and P2 are applied to the air chamber H for magnification adjustment and the air chamber N for focus position adjustment so as to correct the normal fluctuation range of atmospheric pressure, respectively.

At this time, appropriate pressure is applied to the air chambers A and B so that the stress applied to each lens element is always in one direction.

As described above, when each lens element is made to receive only the pressure in a constant direction at all times, it becomes unnecessary to strongly hold the lens in the direction different from the direction in which the pressure acts, so that unnecessary distortion is caused in the lens. Is less likely to give more stability.

It is also generally known that the wavelength of the exposure light is changed to change the imaging magnification.

For example, as described in Japanese Patent Publication No. 5-54687, when the numerical values of the projection lens are different from the design values and a desired imaging magnification cannot be obtained, a magnification error fine adjustment means for manufacturing the apparatus. The technique used as is generally known (second conventional example).

This utilizes the fact that the refractive index of the glass member constituting the projection lens slightly changes depending on the incident wavelength.

That is, by changing the image forming magnification by slightly changing the wavelength, it becomes easy to adjust the magnification, which is very difficult to perform by mechanical adjustment.

[0022]

However, in the first conventional example as described above, since the projection lens is provided with four air chambers, the pressure control device becomes complicated.

Further, since the air chambers having a constant volume are set to different pressures in accordance with the change in atmospheric pressure, the air chambers change in volume and the temperature of the air chambers changes.

Therefore, the projection lens has a temperature distribution in the optical axis direction. In particular, the pressure in the air chambers A and B is
Since it is set to a constant value outside the range of atmospheric pressure that can occur on a daily basis, the pressure difference from the standard atmospheric pressure of each air chamber becomes large,
A temperature distribution is also likely to occur, and the lens element G1 on the boundary surface of the air chamber
Etc. will be greatly stressed.

Further, when the pressure value of each air chamber is changed by the above correction, the temperature of the air chamber changes as a result,
It takes a certain time for the projection lens temperature to reach a steady state.

In the standard state, the temperature of the air chamber is T1, the pressure is P1, the volume is V, and the pressure is P to correct the atmospheric pressure fluctuation.
If you change it to 2, this is a constant volume change, so
The following (Equation 3) is established.

[0027]

[Equation 3]

From this (Equation 3), when the reference temperature is set to 23 ° C. and the pressure inside the projection lens 101 changes by 1%, the air chamber temperature changes by 0.2 ° C., which is the temperature distribution of the projection lens. Becomes a non-negligible value, which lowers the imaging performance.

When controlling this with a temperature regulator, a plurality of temperature control devices are required because the temperature distribution is not uniform.

As described above, in the first conventional example, there are problems that stress is generated in each lens element and it is difficult to obtain a uniform temperature distribution.

Further, in the second conventional example in which the exposure wavelength is changed to adjust the magnification, it is used as a fine adjustment means for the magnification in the manufacture of the apparatus, and the continuous fluctuation of the magnification caused by the environmental change when the apparatus is used and No specific consideration is given to the focus variation.

Further, when only one correcting means for changing only the laser wavelength is provided, a specific examination of the focus remaining amount is as shown in (Table 1) below.

[0033]

[Table 1]

When the correction is made only by the change of the laser wavelength, the focus cannot be completely corrected.

Since the depth of focus is short in a high NA projection lens compatible with 64 mega DRAM, this focus residual error cannot be ignored.

In view of the above problems, the present invention changes the magnification and focus of the projection optical system caused by environmental changes during use of the apparatus by changing the wavelength of the laser serving as the light source and setting the atmospheric pressure in the projection optical system. By using two control means for providing a slight differential pressure to the projection lens, two control means for changing the imaging magnification and the focus are used for the projection lens, thereby changing the imaging magnification and the focus for the projection lens. An object of the present invention is to provide an exposure apparatus capable of correcting two fluctuations at the same time.

[0037]

According to the present invention, a laser light source which is an exposure light source and has a variable oscillation wavelength, wavelength control means for setting the oscillation wavelength of the laser light source to a desired wavelength, and a mask pattern by the laser light source. An illumination optical system for illuminating a mask having: a projection optical system for forming an image of the mask pattern on a wafer; a pressure control unit for setting a pressure in the projection lens to a desired pressure; and an inside and outside of the projection optical system. A detection means for detecting pressure and / or temperature; and a calculation means for calculating a necessary change amount of the pressure in the projection optical system and the oscillation wavelength of the laser light source based on the result obtained from the detection means. , The wavelength control means sets the oscillation wavelength of the laser light source to a desired wavelength according to the required change amount, and the pressure control means sets the pressure in the projection lens to a desired pressure. That is an exposure apparatus.

Here, the wavelength control means and the pressure control means set the oscillation wavelength of the laser light source to a desired wavelength so as to correct fluctuations in the imaging magnification and focus position of the projection lens due to environmental changes during use. And set the pressure in the projection lens to the desired pressure.

The pressure control means is set so that the pressure inside the projection lens is substantially uniform and has a small relative difference with respect to the pressure outside the projection lens.

Further, the pressure control means may set the pressure in the projection lens to a desired pressure while causing the gas to flow in the projection lens at a constant flow rate.

[0041]

With the above-described structure, the present invention corrects fluctuations in the imaging magnification and focus of the projection optical system caused by environmental changes during use of the apparatus.

[0042]

Embodiments of the present invention will be described below with reference to FIG.

FIG. 1 is a block diagram of the exposure apparatus of the present invention. In FIG. 1, reference numeral 1 denotes a tunable laser which is a light source,
Reference numeral 2 is an illumination optical system, 3 is a mask, 4 is a pressure detector for detecting the pressure inside and outside the projection lens, and 5 is a gas flow capable of controlling the pressure inside the projection lens to obtain an arbitrary pressure difference from the atmospheric pressure. Is a projection lens, 6 is a projection lens, 10 is a central processing unit that controls each control unit according to the environment, 11 is a wafer, and 13 is a wavelength control unit that controls the wavelength of the laser.

The operation of the above arrangement will be described below. First, the pressure detector 4 detects the pressure inside and outside the projection lens 6, and confirms the amount of environmental change from the reference state.

Based on the output result of the pressure detector 4, the wavelength of the laser 1 and the pressure inside the projection lens 6 are calculated by the calculator 10 in order to correct the magnification variation and the focus variation caused by the environmental change. , The result is the wavelength control device 1
3 and the pressure control device 5.

The calculation method in this case will be described. Assuming that the pressure change amount from the reference pressure is Δpre, the imaging magnification variation ΔM and the focus variation ΔF that occur in the projection lens 6 are generally represented by the following (Equation 4) and (Equation 5).

[0047]

[Equation 4]

[0048]

[Equation 5]

However, k ₁ and k ₂ are constants. Further, assuming that the wavelength difference of the laser 1 from the reference state is Δλ and the pressure difference inside and outside the projection lens 6 is ΔP, Δλ and ΔP are ΔM and Δ
Since they act on F independently, they are expressed by the following (Equation 6) and (Equation 7).

Here, a slight pressure difference provided in the projection lens is applied to the entire projection lens 6.

[0051]

[Equation 6]

[0052]

[Equation 7]

However, k _{3 to} k ₅ are constants. Now, when the change amount from the reference atmospheric pressure is Δpre, it is assumed that the laser wavelength is changed by Δλ and the pressure in the projection lens is changed by ΔP from the reference value in order to correct the image forming magnification change amount ΔM and the focus change amount ΔF, respectively. , ΔM, ΔF are the sums of the sides of (Equation 4) and (Equation 6), (Equation 5) and (Equation 7), and are expressed as (Equation 8) and (Equation 9) below.

[0054]

[Equation 8]

[0055]

[Equation 9]

Therefore, in order to make the image-forming magnification change amount ΔM and the focus change amount ΔF zero, respectively, the left side of (Equation 8) and (Equation 9) may be set to zero and solved for Δpre.

That is, ΔP and Δλ are given by
0) and (Equation 11).

[0058]

[Equation 10]

[0059]

[Equation 11]

As described above, ΔP and Δλ may be calculated from (Equation 10) and (Equation 11) according to the environmental change from the reference state, and the wavelength control device 2 and the pressure control device may be instructed.

The control pressure correction amount ΔP and the laser wavelength correction amount Δλ for making the magnification variation and the focus variation zero when the atmospheric pressure is 953 and 1043 mbar are as follows (Table 2).

[0062]

[Table 2]

Therefore, by changing the pressure inside the projection lens 6 and the emission wavelength of the wavelength tunable laser 1 by the wavelength control device 13 and the pressure control device 5, the focus remaining amount can be effectively reduced to 0 (that is, for the first time). Magnification error is also 0)
Can be

In this case, since a very slight pressure is not applied to the inside and the outside of the projection lens 6, the possibility that the lens element is distorted is extremely small.

Further, since a pressure difference is applied to the entire projection lens, the specific lens element is not easily distorted and the temperature distribution does not occur.

Then, the wavelength control device 2 and the pressure control device perform the actual exposure after setting the wavelength and the pressure to predetermined values, respectively.

The pressure control device 2 controls the pressure while allowing the gas in the projection lens 6 to flow at a constant flow rate.

As described above, according to the present invention, it is possible to constantly keep the magnification variation and the focus variation of the projection optical system caused by the environmental change when the apparatus is used, and it is possible to obtain a high overlay accuracy.

Although the pressure inside and outside the projection lens 6 is detected in the above embodiment, the temperature may be detected, or both the pressure and the temperature may be detected.

[0070]

As described above, according to the present invention, by using the two control means for correcting the laser wavelength and correcting the pressure in the projection lens, the fluctuations in magnification and focus of the projection optical system caused by environmental changes during use of the apparatus can be prevented. A high overlay accuracy can be obtained by correcting the two variations at the same time. Furthermore, since the pressure difference with the atmospheric pressure applied to the entire projection lens is small, the lens element is not easily distorted. Since the differential pressure is applied to the entire projection lens, naturally no particular lens element is distorted and no temperature distribution occurs in the projection lens.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an exposure apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional exposure apparatus

[Explanation of symbols]

 1 Laser 2 Illumination Optical System 3 Mask 4 Detector 5 Pressure Control Device 6 Projection Lens 10 Operator 11 Wafer 13 Wavelength Control Device 101 Projection Lens 102 Constant Pressure Control System 103 Pressure Offset Setting System 104 Light Source System 105 Wafer Stage

Front Page Continuation (72) Inventor Keiichiro Yamanaka 3-10-1 Higashisanda, Tama-ku, Kawasaki City, Kanagawa Prefecture Matsushita Giken Co., Ltd.

Claims (4)

[Claims] 1. A laser light source that is an exposure light source and has a variable oscillation wavelength, a wavelength control unit that sets the oscillation wavelength of the laser light source to a desired wavelength, and an illumination optics that illuminates a mask having a mask pattern by the laser light source. System, a projection optical system for forming an image of the mask pattern on a wafer, pressure control means for setting the pressure in the projection lens to a desired pressure, and pressure and / or temperature inside and outside the projection optical system. Detecting means, and a calculating means for calculating a necessary change amount of the pressure in the projection optical system and the oscillation wavelength of the laser light source based on the result obtained from the detecting means, depending on the necessary change amount An exposure apparatus in which the wavelength control unit sets the oscillation wavelength of the laser light source to a desired wavelength, and the pressure control unit sets the pressure in the projection lens to a desired pressure. 2. The wavelength control means and the pressure control means set the oscillation wavelength of the laser light source to a desired wavelength so as to correct fluctuations in the imaging magnification and focus position of the projection lens due to environmental changes during use. The exposure apparatus according to claim 1, wherein the pressure in the projection lens is set to a desired pressure. 3. The pressure control means is set so that the pressure inside the projection lens is substantially uniform and has a small relative difference with respect to the pressure outside the projection lens.
Or the exposure apparatus according to 2. 4. The exposure apparatus according to claim 1, wherein the pressure control means sets the pressure in the projection lens to a desired pressure while causing a gas to flow in the projection lens at a constant flow rate.