JPS6165433A - Inspecting device for object position of objective lens - Google Patents

Abstract

PURPOSE:To prevent the detecting accuracy from being affected by a sample, by detecting the electrostatic capacitance between the electrode made to coat the surface of the objective lens that is closest to the object and the electrode formed on the surface of the mirror cylinder of the objective lens which is closer to the object. CONSTITUTION:From an oscillating circuit 12, a high frequency is impressed across the connection point of capacitors C2 and C3 and the connection point of capacitors C1 and an electrode 9. When the relative position of an object 3 and the objective lens 6 varies, the capacitance of an electrostatic capacitor C0 between the electrodes 8 and 9 varies, and high frequency is outputted from the bridge under amplitude modulation. Unbalanced voltages are taken out by passing modulated waves, outputted from a detecting circuit 13 and the bridge 11, through a low-pass filter. A DC amplifier 14 amplifies this unbalanced voltage and drives an indicator 15. The indicator 15 the position of the object 3.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention J The present invention relates to a device for detecting the position of a target object with respect to an objective lens. The present invention relates to an object position detection device for an objective lens suitable as a detection system for detection and automatic focusing.

[Cargo Storage of the Invention] Conventionally, as this type of device, optical detection means, detection means using an air sensor, and the like have been proposed. In the former optical detection means, as shown in FIG. 5, light from a light source 1 is focused on a sample 3 through a first optical system 2, and reflected light from the sample 3 is focused on a sample 3. 4, the light is received by the light receiving element 5, and the position of the main optical system (objective lens) 6 is detected from the incident position of the reflected light on the light receiving element 5. However, with this method, if the reflectance of the sample 3 is low, the detection error may become large or detection may not be possible. Furthermore, as shown in FIG. 6, there is a drawback that detection errors occur even when the sample is tilted. That is, in FIG. 6, the position of the main optical system 6 on the optical axis of the sample 3 shown by the thick line is the same as that shown by the thin line, but if it is tilted as shown by the thick line, the second The incident position of the reflected light (two-dot chain line) on the optical system 4 shifts upward, and the position of the sample 3 is detected as being above the thin line.

In order to deal with this, a method has been put into practical use in which multiple air sensors 7 are arranged around the main optical system 6 and the relative position of the objective lens and the object is detected from the values of each sensor, as shown in Figure 7. has been done. However, this method has the disadvantage that the response speed is slow due to the characteristics of the air sensor. Furthermore, since such an air sensor can only be placed around the main optical system 6, as the aperture of the main optical system 6 becomes larger, the relative spacing between the sensors 7 also becomes wider, and the relative distance M between the sensors 7 and 7 on the sample 3 increases. There are drawbacks such as the inability to detect irregularities in small areas.

[Object of the Invention] In view of the problems in the conventional example described above, the object of the present invention is to
It is an object of the present invention to provide an object position detection device for an objective lens whose detection accuracy is not easily affected by the reflectance of a sample and the inclination and unevenness of the surface and which is capable of detecting the object position at high speed. A second object of the present invention is to provide an apparatus capable of detecting inclinations and irregularities on the surface of a sample.

[Explanation of Examples l Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 shows the configuration of an objective lens portion to which Noah's object position detection device is applied (an embodiment of the present invention (appendix 1)).

In the figure, 3 is a sample (target object), 61 is an objective lens as a main optical system, 8 is a first electrode, and 9 is a second electrode. Further, 61 is a lens barrel of the objective lens 6, and 62 is a lens located closest to the object 3 constituting the optical system of the objective lens 6.

The first electrode 8 is a transparent and conductive thin film that is attached to the lens 62.
It is formed by coating.

This first electrode 8 preferably has as little optical loss as possible, and can be made of, for example, a metal (aluminum or the like) coating material that is commonly used as an antireflection coating for lenses. In addition, when applying such an anti-reflection metal coating to the object side surface of the lens 62, it is necessary to insulate the metal coating from the lens barrel 61 by, for example, removing the portion around the metal coating that contacts the lens barrel 61. Accordingly, it can be used as the first electrode of the present invention.

The second electrode 9 is arranged on the lens barrel 61 at a position closest to the object 3. For example, if the lens barrel 61 is made of a conductive material such as metal, the 1 ft Film AIG can be used as the second electrode. Furthermore, an upper pole made of a curved material may be attached to the surface of the lens barrel 61 that is close to the object 3. For example, if the second electrode is made of a printed wiring board, even if the lens barrel 61 is conductive, the electric current will be 1fi9.
can be insulated from the lens barrel 61.

FIG. 2 shows another embodiment of the detector portion of the invention. In the figure, the objective lens 6 is shown as a part of the objective lens 6.
The lens 6 closest to the target object 3 among the lenses constituting the
A parallel plane glass 63 is installed between the parallel plane glass 63 and the object 3, and the surface of the object 31tll of this parallel plane glass 63 is coated with a conductive thin film such as aluminum with low optical loss as the first electrode 8.

FIG. 3 is a bottom view showing still another embodiment of the detector portion of the present invention. The detector shown in the figure is different from the detector shown in FIG. 2 in that the second electrode 9 formed on the lens barrel 61 is divided into three parts. As a result, three capacitors are constructed between the first electrode 8 and the electrode 9 of the container 2 using the first electrode 8 as a common electrode, and if the capacitance or capacitance change of each capacitor is measured, it is possible to It is possible to detect the inclination and unevenness of 3.

FIG. 4 shows an example of the overall configuration of an object position detection device for an objective lens according to the present invention. The device comprises a detector, namely a first electrode 8 and a second electrode 9, as well as an object 3 and both electrodes 8.9.
The capacitance of a capacitor Go formed by a substance (such as air) interposed between the object 3 and the object 3 is measured, and the object position of the objective lens 6 is detected based on this capacitance or a change in capacitance. In the figure, 11 is an impedance bridge composed of capacitors C1, C2, C3 and CO, 12 is an oscillation circuit, 13 is a detection circuit, 14 is a DC amplifier, and 15 is the position of object 3 or the deviation from the standard position. The indicator 16 is a power source.

The detection circuit 13 is a detection circuit (not shown) that detects a modulated component from a modulated wave modulated by the capacitance or a change in capacitance of the capacitor Go using the high frequency voltage generated from the oscillator 12 as a carrier wave. It consists of a filter circuit (not shown) that cuts undesired frequency components such as the carrier wave from the output signal of this detection circuit, and connects the connection point between capacitors C1 and C2 of impedance bridge 11 and the connection point between capacitor C3 and first electrode 8. Detects the unbalanced voltage that occurs between the connection points.

Next, the operation of the apparatus shown in the figure will be explained.

In this device, an oscillation circuit 12 generates a high frequency with a stable frequency, and this is applied between the connection point between the capacitors C2 and C3 of the impedance bridge 11 and the connection point between the capacitor C1 and the second electrode 9. therefore,
When the relative position between the object 3 and the objective lens 6 changes, the electrode 8
and the capacitance of the configured capacitor CO changes,
The high frequency applied to the bridge 11 from the oscillation circuit 12 is
This high frequency wave is amplitude modulated (AM) as a carrier wave and output from the bridge 11. Detection circuit 13
The modulated wave input from this bridge 11 is passed through the above-mentioned detection circuit and a low-pass filter for removing the carrier wave to extract its modulation component, that is, an unbalanced voltage, and the DC amplifier 14 amplifies this unbalanced voltage. do,
The indicator 15 is driven. Thereby, the indicator 15 displays the position of the target object 3. Here, if the capacitance of the capacitor C1 is adjusted so that the impedance bridge 11 is balanced with the object 3 set in the in-focus position in advance, the indicator 15 will display the deviation of the object 3 from the in-focus position. I will do it.

Note that the capacitor Co composed of the electrodes 8 and 9
If it is used as a variable space element that contributes to the excavation of the oscillation circuit 12, the output from the excavation circuit 12 will be frequency modulated, but in this case, an FM detection circuit should be used as the detection circuit 13. For example, the capacitance or capacitance change of capacitor CO can be detected.

[Application Example 1 of the Invention In the above-described embodiments, the present invention is described as an object position detection device for an objective lens.
In particular, it is more effective when used as a measuring device for autofocusing a main lens for printing in a reduction projection exposure apparatus used as a semiconductor manufacturing device. In this case, the output voltage is set to 0 by adjusting the capacitance (6) of the barrier pull capacitance C1 of the impedance bridge 11 at the optimal bin position of the lens, and if the focus shifts for some reason, the output will be 0.1. : By automatically controlling the lens 6 or the object 3 so that the following occurs, exposure can always be performed at the optimum focus position.

Furthermore, if the upper pole of the lens barrel is divided into a plurality of parts and a detection device as described above is constructed for each part, it becomes possible to measure the tendency of the object based on the output from each sensor.

[Effects of the Invention] As described above, according to the present invention, the electrodes are formed on the glass surface closest to the target object among the glass surfaces constituting the objective lens, and on the surface of the lens barrel that is close to the object, respectively. Since the distance to the target object is measured by the capacitance of a capacitor made up of these electrodes and the material intervening between the target object, the detection accuracy is dependent on the reflectance of the sample and the slope and unevenness of the surface. not easily influenced by Furthermore, the detection speed is faster than when using an air sensor or the like.

Furthermore, since a part of the optical element of the main optical system is used as a part of the detector, there is an advantage that the stability of the detection system is improved and the cost can be reduced. Furthermore, by configuring a plurality of capacitors in which one electrode is divided into a plurality of parts and the other electrode is used as a common electrode, it is also possible to detect the inclination or unevenness of the surface of the target object.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view showing a schematic configuration of an objective lens portion to which the present invention is applied; FIG. 2 is a vertical cross-sectional view of an objective lens portion according to another embodiment of the present invention; FIG. A bottom view of an objective lens portion according to still another embodiment of the present invention, FIG. 4 is a block diagram showing the overall configuration of an embodiment of an object position detection device for an objective lens of the present invention, and FIG. FIG. 6 is a diagram for explaining the operation of the mechanism shown in FIG. 5. FIG. 7 is a schematic diagram of the air sensor type focus detection mechanism. 3... Sample (target object), 6... Objective lens, 61
... Lens barrel, 62 ... Lens closest to the target object, 6
3... Parallel plane glass, 8... First electrode, 9 second electrode, 12... Oscillation circuit, 13... Detection circuit,
14...DC amplifier,...indicator.

Claims (1)

[Claims] 1. A device for detecting the position of a target object with respect to an objective lens, which comprises a conductive thin film coated on the surface closest to the target object among the glass surfaces constituting the optical system of the objective lens. A first electrode, a second electrode formed on a surface of the lens barrel of the objective lens close to the target object, and means for measuring capacitance between the first and second electrodes. An object position detection device for an objective lens, characterized in that the position of the target object with respect to the objective lens is detected based on this capacitance. 2. The object position detection device for an objective lens according to claim 1, wherein the glass surface closest to the target object is the lens surface of the objective lens closest to the target object. 3. A parallel plane glass is incorporated as part of the optical system of the objective lens between the lens closest to the target object of the objective lens and the target object, and an optical An object position detection device for an objective lens according to claim 1, characterized in that the first electrode is coated with a conductive thin film with low loss. 4. The object position detection device for an objective lens according to any one of claims 1 to 3, wherein the second electrode is divided into a plurality of parts. 5. The means for measuring the capacitance between the first and second electrodes includes an oscillator that applies a high frequency voltage between the first and second electrodes, and a capacitance between the first and second electrodes. 5. The object position detection device for an objective lens according to claim 1, further comprising a detection circuit for detecting a change in capacitance. 6. A modulated device in which the detection circuit modulates the electrostatic capacitance between the first and second electrodes or a change in electrostatic capacitance using the high frequency voltage applied between the first and second electrodes as a carrier wave. a detection circuit that detects a modulation component from a wave; a filter circuit that cuts an undesired frequency component from the output signal of the detection circuit; a DC amplifier that amplifies the output signal of the filter circuit; 6. The objective lens object position detection device according to claim 5, further comprising an indicator that displays the position of the target object. 7. The object position detection device for an objective lens according to any one of claims 1 to 6, characterized in that a third electrode is provided on the outer periphery of the first and second electrodes.