JPH0244365B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention has a function to reduce measurement errors and is suitable for moving equipment such as LSI inspection equipment, processing and inspection of semiconductor products, and other precision machinery that requires high accuracy. It relates to mobile devices.

As an example of this type of conventional moving device, an LSI photomask visual inspection device is shown in FIGS. 1 and 2. Figure 1 is a perspective view with the control mechanism part added.
The figure is a vertical sectional view of a moving device used in the above-mentioned visual inspection device.

An X stage 4 is installed on a stage base 2 via a Y stage 3 to constitute an X/Y stage, and a photomask 1 as an object to be inspected is placed on the X stage 4. The Y stage 3 and the X stage 4 are connected to a Y-axis drive section 5 and an X-axis drive section 6, which are external drive devices, respectively, and can be moved in the Y direction and the X direction, respectively.

The amounts of movement of the X stage 4 and Y stage 3 are measured by an X-axis length measuring device 8 and a Y-axis length measuring device 7, respectively.

On the other hand, means for automatically detecting the pattern of the photomask 1 is configured as follows. An objective lens 9 is provided above the photomask 1, and a pattern sensor 10 is provided on its imaging plane. The output of this pattern sensor 10 is input to a signal comparison circuit 14 via a pattern signal binarization circuit 11. A signal read from the magnetic tape 12 on which circuit pattern design data of the photomask 1 is stored is also input to the signal comparison circuit 14 via the pattern signal binarization circuit 13. Reading of the magnetic tape 12 is carried out according to instructions from the microprocessor 15, and the comparison results in the signal comparison circuit 14 are input to the microprocessor 15.

The Y-axis length measuring device 7 and the X-axis length measuring device 8 are the coordinate length measuring circuit 1.
6, and the coordinate measuring circuit 16 is connected to the microprocessor 15. The microprocessor 15 is also connected to an XY drive control section 17, and can control the X-axis drive section 6 and Y-axis drive section 5 through the XY drive control section 17.

In the above photomask inspection device, the magnetic tape 1
2 stores design data at the time of photomask creation as an image signal, which is converted into a digital image signal of logic levels "0" and "1" by the pattern signal binarization circuit 13. Further, the pattern on the photomask 1 is converted into an image signal by a pattern sensor 10 on an objective lens 9, and converted into a digital image signal of logic levels "0" and "1" by a pattern signal binarization circuit 11.

The digital image signal of the design data read from the magnetic tape 12 and the digital image signal detected from the photomask 1 are compared by the signal comparison circuit 14, and if there is a difference, the microprocessor 1
A signal is sent to 5.

Upon receiving the above signal, the microprocessor 15 determines whether the difference is due to a defect in the circuit pattern of the photomask 1, and if it is a defect in the circuit pattern, it notifies the printer 18 to that effect. This inspection is performed by moving the photomask 1 with respect to the objective lens 9 in the direction of a reciprocating arrow A and sequentially scanning the entire surface.

The microprocessor 15 controls the Y-axis drive section 5 and the X-axis drive section 6 via the XY drive control section 17 in order to move the photomask 1 in the direction of arrow A above. The coordinate measuring circuit 16 measures the inspection position of the photomask 1, and the coordinates of the photomask where a defect is found are outputted to the printer 18 through the microprocessor 15. Further, the coordinate measurement circuit 16 accurately measures the inspection start and end coordinates of the photomask 1 and outputs them to the microprocessor 15. Based on this, the microprocessor 15
Controls the drive of 2.

As explained above, in a device that automatically performs inspection by comparing design data and mask patterns, scanning the stage at a constant speed,
Furthermore, it is particularly important to precisely align the pattern design data and the mask pattern. For this reason, in this type of apparatus, the mechanical precision of the stage used for pattern scanning is increased as much as possible, and inspection is performed while measuring the length with a laser gauge. FIG. 2 shows a cross section of the inspection stage. An XY stage consisting of a stage base 2, a Y stage 3, and an X stage 4 is placed on a base 27, and a θ stage 1 is placed on the XY stage.
9 is placed. The θ stage 19 is used to properly tilt the photomask 1 in the running direction of the XY stage. Further, on the θ stage 19, a plate spring 21 fixed to a spacer 20 and a mask mounting table 23 supported by screws 22 are placed. The photomask 1 is focused on the objective lens 9 by adjusting the screw 22.

A holding table 25 that holds a reflecting mirror 24, which is a target for laser length measurement, is fixed to the X stage 4 of the X-Y stage, and a laser interferometer 26
The distance from the mirror 24 to the mirror 24 is measured. An objective lens 9 above the photomask 1 is supported by a column 29, and a pattern sensor 10 is installed above the objective lens 9.

In the conventional embodiment configured as described above, the laser length measuring device is required to measure the length with a resolution of 0.1 μm or less. The stage of this type of moving device must be constructed to enable highly accurate running, accurate tilting, and accurate focusing. For this reason, a Z stage, a θ stage, a minute drive means, etc. are usually stacked and installed on top of the X/Y stage.

Since the complex and large structure described above is used, if the target of the length measuring means (reflector 24 in the above example) is installed on the photomask 1, it will be difficult to adjust the tilt or focus of the photomask 1. Adjustment of the length measuring means each time (in the above example, the laser interferometer 26
There is the inconvenience of having to adjust the optical axis of the In order to eliminate these complications, conventionally, the target of the high-precision length measuring means is generally attached to an XY stage, and the displacement of the photomask is detected by measuring the amount of movement of the XY stage. That is, in the example shown in FIG.
The reflecting mirror 24 is fixed through the laser interferometer 26.
It is customary to measure the change in the distance l ₀ between the mirror 24 and the reflector 24.

When using the above configuration, when attempting to detect minute displacements of about 1 μm, errors due to thermal expansion and contraction of the constituent members cannot be ignored. For example, in the apparatus shown in FIG.
Assuming that the X stage 4, holding table 25, etc. are made of a 200 mm square steel plate, a 1° C. change in ambient temperature causes a 2 μm displacement at the center.

If a 2 μm error occurs due to thermal expansion and contraction as described above, the signal comparison circuit 14 will determine that there is a 2 μm defect even if there is no defect in the circuit pattern of the photomask 1. On the other hand, as LSIs become more highly integrated, there is a need to improve defect detection accuracy, and pattern defects of about 1 μm, which were previously acceptable, are no longer tolerated, and defect detection of 0.5 μm or less is now necessary. ing. Under these technical requirements, the thermal expansion/contraction error due to the temperature change cannot be ignored.

In order to solve the above-mentioned problems, an object of the present invention is to enable highly accurate focusing of an object to be measured with respect to an optical system, reduce measurement errors caused by thermal expansion and contraction, and change the horizontal displacement of an object to be measured. It is an object of the present invention to provide a moving device having a function of reducing measurement errors so as to be able to perform ultra-high precision length measurement.

That is, in order to achieve the above object, the present invention has the following features:
An X-Y stage supported movably in two-dimensional directions (horizontal X and Y); A mounting table on which an object is placed, and an optical system that obtains an optical image of the object to be measured (an optical system that observes the optical image formed on the object to perform inspection, etc., or an optical system that forms an optical image on the object to be measured). (optical system for performing processing, etc.) and the mounting table in the X-Y direction in order to focus the object to be measured on the optical system.
A fine movement control means that performs fine movement control (tilt adjustment control, focusing control) in the vertical direction of the stage and fixes it at an arbitrary position, and measures the horizontal displacement of the target provided on the X-Y stage. measuring means for measuring the horizontal displacement of the object to be measured; and when the measuring means measures the horizontal displacement of the object to be measured, the target is fixed horizontally to the mounting table; This moving device has a function of reducing measurement errors, and is characterized in that it is equipped with a connecting means for connecting the target and the mounting table so that the target and the mounting table are connected to each other. In particular, the present invention focuses an object to be measured with respect to an optical system that observes an optical image formed on an object to be measured and performs an inspection, or an optical system that forms an optical image on an object to be measured and processes it. It is clear that the present invention can be applied to processing, inspection, etc. of semiconductor products that require (imaging).

Next, one embodiment of the present invention will be described with reference to FIG. This embodiment is an improvement by applying the present invention to the inspection stage of the conventional LSI photomask visual inspection device shown in FIGS. 1 and 2, and FIG. 3 is a vertical sectional view of the moving device. , is a diagram corresponding to FIG. 2 in the conventional device.

The difference between FIG. 3 (this embodiment) and FIG. 2 (conventional device) is that one end of the plate 28 is fixed to the holder 25 of the reflecting mirror 24, and a vacuum suction part 28a is constructed at the tip of the plate 28. It is connected to the vacuum pump VAC. Reference numeral 31 designates a connecting pipe, 32 a solenoid valve provided in the pipe, and 33 a breather connected to the solenoid valve.

The left end of the plate 28 as shown in the figure is fixed to the reflector holding stand 25, and the right end thereof is fixed to the mask mounting stand (mounting stand).
23. A vacuum chuck 28a is formed at the contact portion, and the vacuum chuck 28a is connected to the vacuum pump by operating the solenoid valve 32.
It is configured so that it can be switched to communicate with VAC or breather 33. At this time, a pressing force is applied to the mask mounting table 23 by the plate spring 21 against the XY stage 4, and the vacuum chuck 28a is
Even if the mask mounting base 23 is sucked with the mask mounting base 2
3 never pops up. That is, plate 2
8 is formed to be more flexible in the vertical direction than the plate spring 21, and the vacuum chuck 28a is formed so as to be in contact with the mask holder 23 within the range of elastic deformation of the plate 28.

When using this device, the vacuum chuck 28a is communicated with the breather 33 to cancel the vacuum suction, and by adjusting the screw 22, the mask mounting table 23 is finely moved vertically around the leaf spring 21 (tilt adjustment). The photomask 1 is tilted and focused while being fixed at an arbitrary position by controlling the photomask 1 (control and focusing control), and when this is completed, the vacuum chuck 28a is communicated with the vacuum pump VAC to attract the mask mounting base 23. As a result, the reflector 24 and the mask mounting table 23, which are the targets of the length measuring means,
and are interconnected via a plate 28. This embodiment is provided with means for connecting the target of the length measuring means and the movable table as described above.

When the apparatus of this embodiment is operated as described above, there is no risk of deviating the optical axis for laser length measurement, and
X stage 4, θ stage 19, mask mounting stand 2
3 and the holding base 25 expand in the direction of arrow B due to thermal expansion, this error is absorbed between the θ stage 19 and the mask mounting base 23, and the reflecting mirror 2
4 is moved together with the mask mounting table 23, so no length measurement error occurs.

If fluid pressure is used as the means for connecting the target of the length measuring means and the moving table as in this embodiment, control is easy and suitable for automation.

FIG. 4 shows an embodiment different from the above. In this embodiment, a minute displacement device 3 in the vertical direction is mounted on the X stage 4.
The mask mounting table 23 is supported by a plate spring 21 that can be bent in the vertical direction between it and a spacer 20 attached to the X stage 4 to absorb horizontal errors caused by thermal expansion and contraction. Equipped with
The present invention is applied to a movable table having a structure in which the above-mentioned minute displacement device 30 is constantly expanded and contracted during operation to correct the focus.One end of the plate 28 (the right end in the figure) is fixed to the mask mounting table 23, A little more than half of the free end side is formed thin so that the flexible portion 2
8b is configured. And the reflector holding stand 25
A vacuum chuck 25a is provided protrudingly from the top to attract the flexible portion 28b. By imparting spring elasticity to the connecting member in this way, the flexible portion 28b
By bending, it is possible to absorb minute vertical displacements of the mask mounting table 23 and prevent the adverse effects of thermal expansion without interfering with the operation of the minute displacement device 30.

The above explanation is about the structure and operation effect for preventing the adverse effects of thermal expansion in only one direction, but if two sets of the above-mentioned structures are installed perpendicularly in the horizontal plane, thermal expansion and contraction in each direction in the horizontal plane can be compensated. This can reduce length measurement errors.

FIG. 5 is a plan view of the embodiment shown in FIG.
One end of the plate 28 is fixed to the upper side and the left side of the figure, respectively, and the flexible portion 2 is formed on the free end side of the plate 28.
8a are respectively opposed to the vacuum chucks 25a. With this configuration, thermal expansion and contraction in the vertical direction in this figure, thermal expansion and contraction in the horizontal direction,
In addition, length measurement errors due to thermal expansion and contraction in each direction, which is a combination of the thermal expansion and contraction in the two directions, are reduced, making highly accurate length measurement possible.

As explained above, according to the present invention, an apparatus for inspecting an optical image formed on a workpiece by observing an optical image formed on the workpiece by an optical system, or a device for performing processing, etc. by forming an optical image on a workpiece using an optical system. In the device that performs
It enables highly accurate focusing of the object to be measured with respect to the optical system, and significantly reduces horizontal displacement errors due to thermal expansion, contraction, etc., making it possible to measure the horizontal displacement of the object with ultra-high precision. It has excellent practical effects.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an example of a conventional LSI photomask inspection machine, and FIG. 2 is a vertical sectional view of a moving device used in the above inspection machine. FIG. 3 is a vertical sectional view of an embodiment of the moving device of the present invention, FIG. 4 is a vertical sectional view of an embodiment different from the above, and FIG. 5 is a plan view of the same. 1...Photomask, 3...Y stage, 4...
X stage, 19... θ stage, 20... Spacer, 21... Leaf spring, 22... Screw, 23...
Mask mounting stand, 24...Reflector, 25...Reflector holding stand, 25a...Vacuum chuck, 26...Laser interferometer, 28...Plate, 28a...Vacuum suction part, 28b...Flexible part, 29...Column, 30
...Minute movement device, 31...Connection pipe, 32...
solenoid valve.

Claims (1)

[Claims] 1. An X-Y stage supported movably in two-dimensional horizontal X and Y directions, and an X-Y stage supported to absorb errors in the horizontal direction with respect to the X-Y stage, and A mounting table on which an object to be measured is placed, an optical system for obtaining an optical image of the object to be measured, and a mounting table for focusing the object to be measured with respect to the optical system.
A fine movement control means for finely controlling the vertical movement of the Y stage and fixing it at an arbitrary position; and a fine movement control means for controlling the vertical movement of the Y stage and fixing it at an arbitrary position; a measuring means for measuring a displacement in a direction; and a measuring means for measuring a displacement in a horizontal direction of the object to be measured; A moving device having a function of reducing measurement errors, characterized in that it is provided with a connecting means for connecting. 2. A moving device having a function of reducing measurement errors as set forth in claim 1, wherein the connecting means is configured to be connected by fluid pressure. 3. A moving device having a function of reducing measurement errors as set forth in claim 1 or 2, characterized in that the connecting means includes a flexible member so as to be further displaceable in the vertical direction. .