JPS5919912A - Immersion distance holding device - Google Patents

Abstract

PURPOSE:To prevent the resolving power of an optical system from decreasing by equipping a control system with a reference device which has flow rate resistance similar to that of the opening part of a detector and a suction path with flow rate resistance similar to that of a suction path for liquid from the detector. CONSTITUTION:An amplification control circuit 10 drives a sample table 8 so that the output of a piezoelectric transducer 9, i.e. pressure in the detector 3 is constant. When the suction pressure of a suction source 11 fluctuates, the detected pressure in the detector 3 also varies to cause malfunction apparently as if an interval (h) were varied. For this purpose, the reference device which has a restrictor 14 with flow rate resistance similar to flow rate resistance depending upon the interval between the detector opening part 19 and a sample 17 and a restrictor 13 similar to a restrictor 12 is coupled with the suction source 11. Consequently, the variation with the pressure difference between the detected pressure and reference pressure is eliminated and the piezoelectric transducer 9 transduces this pressure difference into an electric signal; and the amplification control circuit 10 drives the sample table so that its output value is constant. Therefore, the malfunction of the control system is eliminated and a decrease in the resolving power of the optical system is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an immersion distance maintaining device for positioning and holding a sample in an immersion type optical device, and in particular to an automatic focusing device for an exposure device that projects a pattern onto a sample submerged in liquid. The present invention relates to a distance keeping device suitable for use in conjunction with the present invention.

In an optical device that uses an optical lens to observe or project a pattern, increasing the numerical aperture NA is a known method for improving the resolving power of an objective lens.

As a method for this purpose, it is known to interpose a liquid between the objective lens and the sample in order to increase the refractive index of the medium. An immersion microscope has been commercialized as an optical device using the method described above. Focusing of an immersion microscope on a sample is performed only by visual adjustment, and no means for automatically focusing has been established.

In the case of a microscope, it is difficult to make adjustments visually, but exposure equipment, especially exposure equipment used in the manufacturing process of semiconductor integrated circuits (hereinafter simply referred to as exposure equipment), can automatically adjust the adjustment at high speed and with high precision. Focusing is required.

In addition, existing immersion microscopes have the disadvantage that it is difficult to easily remove the particles attached to the tip of the objective lens, which reduces the resolution of the optical system.

The object of the present invention is to automatically position and hold the sample at its focal position with high precision in an optical device for observing a sample in a liquid or forming a pattern on the sample, and to use an objective lens. It is an object of the present invention to provide a device which makes it possible to easily remove air bubbles attached to the surface of the object.

The inventors of the present application have developed a means for immersing a sample in liquid in order to improve resolution in an exposure apparatus, and have already filed a patent application (Japanese Patent Application No. 56-37977). In addition, a means to improve resolution in detecting patterns on a sample was developed, and a patent application was filed (Japanese Patent Application No. 84784/1984).
has been done. There is a need for a device that automatically focuses the large diameter lens (objective lens) used in these immersion type exposure devices, and the present invention was made to solve this problem.

Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 1 is an explanatory diagram of the configuration of an embodiment of the apparatus of the present invention.

In the figure, 1 is the optical member (objective lens) of the optical device (exposure device), 2 is the lens barrel, B is the detector provided at the lower end of the lens barrel 2, 4 is the liquid suction hole, and 5 is the detection Vessel 6
6 is a liquid for immersion, 7 is a sample, 8 is a sample stage including a driving device, 9 is a piezoelectric transducer that converts the detected pressure into an electrical signal and outputs it, 10 is an amplification control circuit; 11 is a liquid suction source; 12. 13. 14 is a throttle that adjusts the flow rate of the liquid, 15 is a liquid reservoir, 16 is a filter, 17 is a suction source for supplying liquid B, 18 is a filter, 19
is the aperture of the detector 6.

The detector 5 is made to have substantially the same shape as the space formed by the optical path between the objective lens of the exposure apparatus or the optical member 1 and the sample 7, and is connected to the lower end of the lens barrel 2. In addition,
The reason why the structure of the detector 3 is made almost the same as the optical path of the optical system is to improve the response characteristics when controlling the position of the sample stage.

The objective lens used in normal exposure equipment has an aperture diameter of 3
[ ] mmφ or more, the imaging area is large, 15 mmφ or more,
The truncated cone-shaped space formed by these two diameters becomes the optical path and occupies a considerable volume. By minimizing this volume, response characteristics are improved.

The sample 7 is fixed on a sample stage 8 that is movable in the direction of the optical axis of the optical system, and the surface of the sample 7 coated with a photosensitive material is covered with an immersion liquid 6.

For the structure of the sample stage 8, a known moving means movable in the optical axis direction can be used.

A suction hole 4 is provided in the upper corner of the detector 3 and is connected by a tube to a suction source 11 via a flow resistance element 12 . When the suction source 11 is activated here, a negative pressure is created inside the detector B, and the liquid 6 flows in through the opening 19 of the detector. The inflowing liquid is passed through the suction source 11 and the filter 16.
The liquid is sent to the liquid reservoir 15 through the. Suction source 11 with constant pressure
When activated, the pressure inside the detector B changes depending on the size of the distance 1] between the detector 6 and the sample 7. For example, the smaller the distance 11, the larger the absolute value of the negative pressure value within the detector 5. Conversely, as the distance 11 increases, the absolute value of the negative pressure value decreases. In this way, the pressure inside the detector 6 is commensurate with the interval 1]. The detector 6 is provided with a pressure detection hole 5 and is connected to a piezoelectric transducer 9 via a tube. The piezoelectric transducer 9 converts pressure into an electrical signal and is connected to a drive system attached to the sample stage 8 via an amplification control circuit 10. The amplification control circuit 10 drives the sample stage 8 so that the output of the piezoelectric transducer 9 is constant, that is, the pressure within the detector 3 (that is, the gap h) is constant.

On the other hand, if the suction pressure of the suction source 11 fluctuates, the detected pressure within the detector 6 also fluctuates, resulting in malfunction as if the apparent interval has changed. In order to eliminate such pressure fluctuations of the suction source, a reference device is provided in the control system of this embodiment. The reference device includes a diaphragm 14 and a diaphragm 16 that have a flow resistance equivalent to that formed by the distance between the detector opening 19 and the sample 7 and a diaphragm 16 that is equivalent to the diaphragm 12, and is connected to the suction source 11. ing. One end of the throttle 14 has its aperture 11 immersed in the liquid in the liquid reservoir 15, and the pressure between the other end of the throttle 14 and the throttle 16 is measured by a pipe as a reference pressure by a piezoelectric transducer 9.
connected to. The other end of the diaphragm 13 is connected to the suction source 11. Since the reference device and detector have the same suction source,
Since the pressure fluctuations of the suction source 11 are equally transmitted, there is no fluctuation due to the pressure difference between the detection pressure and the reference pressure. In this case, the piezoelectric transducer 9 electrically converts the pressure difference between the detected pressure and the reference pressure. Further, the amplification control circuit 10 controls the sample stage 8 so that the output value from the piezoelectric transducer 9, that is, the above-mentioned pressure difference, is constant.
to drive and control.

If a method is adopted in which the pressure difference between the detected pressure and the reference pressure is controlled to be zero, it becomes easy to correct the drift of the amplification control circuit 10. That is, it is sufficient to correct the circuit so that the output of the amplification control circuit 10 becomes zero when the suction source 11 is not operated.

If a constant voltage can be applied to the trench amplification control circuit 10 by an external circuit, an arbitrary offset can be given to the position of the sample stage.

Details of the above two types of circuits are described in, for example, U.S. Pat.

An appropriate amount of the liquid 6 on the sample 7 is supplied from the liquid reservoir 15 through a suitable suction source 17 and filter 18, so that the tip of the detector 2 is immersed therein.

In the apparatus of the present invention configured and operated as described above,
Automatic focusing is possible by setting the interval only once so that the sample surface is at the focal point position of the optical system of the immersion exposure apparatus.

In carrying out the present invention, the liquid is sucked through the opening 19 of the detector B. This is an extremely effective measure for removing air bubbles adhering to the inside of the detector 6 and the lower part of the optical member 1. Replace the suction source 11 with a supply source,
Although the method of ejecting liquid from the detector can also detect a pressure commensurate with the gap 1], it is preferable to use a suction source to remove air bubbles generated in the detector. Therefore, when the optical member is located above as in the embodiment, ie, when the structure is such that bubbles generated in the liquid are trapped, suction is required to remove the disturbance of the optical path caused by the bubbles.

In this embodiment, the diameter of the opening 19 of the detector is 6 mmφ9.
When the gap h is 250 μm, using H2O as the liquid, the detection pressure is -1200 mm Aq (gauge pressure), and the flow rate is 0.
．． At 6 e/min, a sample position detection sensitivity of 2.5 mm Aq 7 μm was obtained. It is recognized that when this detection sensitivity is present, it is possible to automatically position and hold the sample with an accuracy of approximately ±0.1 μm.

It should be noted that the data values shown in the above embodiments are merely examples, and can easily be changed as appropriate depending on the viscosity of the liquid, the optical path dimension of the objective lens, etc.

Furthermore, since the device of the present invention can circulate the immersion liquid, it is also possible to filter the immersion liquid, adjust the temperature, and switch between two or more types of liquids.

It goes without saying that the apparatus of the present invention can be widely applied not only to exposure apparatuses, but also to apparatuses that require highly accurate positioning and maintenance in liquid.

As explained above, according to the apparatus of the present invention, in an immersion type optical apparatus, it is possible to automatically position and hold the sample at a predetermined focal point position of the optical system with high precision. Furthermore, since air bubbles adhering to the objective lens can be easily removed, it is possible to prevent a decrease in the resolution of the optical system.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the configuration of an embodiment of the apparatus of the present invention. 1. Optical ablation (interchangeable) lens 2. Lens barrel 3. Detector 4. Liquid suction hole 5. Pressure detection hole 6. Immersion liquid
7.Sample 8..Sample stage 9..Piezoelectric transducer 10.Amplification control circuit 11..Suction source 12.13.14..Aperture 15..Liquid reservoir 16..Filter 1
7...Liquid supply suction source 18...Filter
19...Detector opening Patent attorney Junnosuke Nakamura No. 1 Figure 280 Higashi-Koigakubo-chome, Kokubunji City, Hitachi, Ltd. Central Research Laboratory 0 Inventor: Tsuneo Terasawa, 280 Higashi-Koigakubo-chome, Kokubunji City, Hitachi, Ltd. Chuo Inside the research institute

Claims (2)

[Claims] (1) Liquid immersion for positioning and holding the sample at the focal point of the optical system in an optical device for observing the sample in liquid or projecting an image onto a sample in liquid. The distance maintaining device includes a detector having approximately the same shape as the optical path between the optical system member and the sample at the lower end of the lens barrel of the optical system, and a suction source located closer to the opening of the detector. A detection system is provided with a suction system route or a supply route for sucking or supplying liquid by a supply source, and the pressure inside the detector is adjusted according to the distance between the detector and the sample. A liquid immersion distance holding device comprising a piezoelectric transducer that detects and outputs an electric signal, and a movement control mechanism that positions and holds a sample at a focused position using the direction of the piezoelectric transducer. . (2) The detection system has a flow resistance equivalent to that of the opening of the detector, and has a suction system path for liquid from the detector or a flow resistance similar to that of the supply system path. The movement control mechanism includes an amplification control circuit that inputs the output of the pressure transducer, and the reference device and the detector are connected to the same suction source. and the movement control mechanism is driven and controlled so that the pressure difference between the reference pressure in the reference device and the detected pressure in the detector remains at a constant value. Liquid immersion distance maintaining device (b)
^11 The amplification control circuit has a configuration in which a predetermined voltage can be applied from an external circuit, and the added voltage drives the movement control mechanism so that the sample can be set at a desired position. A liquid immersion distance maintaining device according to claim 2.