JPS6141902A - Detecting device for position - Google Patents

Abstract

PURPOSE:To perform accurate position detection even when a distribution having locally different reflection characteristics on a sample surface where a photomark is formed is provided by using the signal of an optical system which is not affected by irregular reflection characteristics between orthogonal oblique incidence type position detection optical systems. CONSTITUTION:Oblique incidence type position detection optical systems each consisting of a projection optical system which consists of a light source 1, condenser lens 2, rectangular aperture stop 3, and projection lens 4 and projects a photomark on the surface of a sample 5 slantingly and a convergence optical system which has an optical axis l2 in the same plane with the optical axis l1 of the projection optical system and converges reflected light from the photomark on a two-dimensional optical position detector 8 are arranged in a couple while planes containing their optical axes cross each other at right angles so that photomarks are superposed one over another on the surface of the sample 5. Then, the output coordinate signal of one two-dimensional optical position detector 8 or 8' is monitored to decide whether the movement of the gravity center of the light quantity of the other detector is caused by movement perpendicular to the surface of the sample 5 or irregularity of reflection characteristics on the surface of the sample 5.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a position detection device for detecting the position t' of a sample surface.

(Background of the Invention) Oblique incidence type position detection devices have been known as position detection devices. This type of device is, for example, provided with a projection optical system that projects the original beam onto the sample surface from an oblique direction, and a gold-plated light receiving optical system that has a companion photoelectric conversion element that receives the reflected light beam from the sample surface. It attempts to detect the position of a sample surface from changes in the position of a reflected light beam on the light receiving surface of a photoelectric conversion element, and is used in devices that automatically set the focal position.

On the other hand, as disclosed in, for example, Japanese Patent Publication No. 56-137101, a charge conversion layer having a predetermined area, a uniform resistance layer having position signal terminals on four sides and laminated on the photoelectric conversion layer, The photoelectric conversion layer is composed of a conductive layer laminated on the opposite side of the resistive layer and has a common terminal, and the photoelectric conversion layer is charged at nine points where light is incident (the center position of the light intensity distribution...hereinafter referred to as the center of gravity position). Occurred on 7t1! When a charge is discharged via the resistive layer and the position signal terminal, it is shunted to the opposing position signal terminal and outputs the center of gravity position of the incident light as coordinate signals V and H based on a rectangular coordinate system based on the difference in charges. Two-dimensional optical position detectors are known.

Therefore, if such a two-dimensional optical position detector is used as the above-mentioned photoelectric conversion element, a nine-coordinate signal corresponding to the barycenter position of the incident light beam can be obtained as a coordinate signal (movement of the sample surface in one direction is caused by light reception). Since the reflected light beam moves in one direction on the surface, if this one direction is made to coincide with one of the coordinate systems on the light receiving surface, it is sufficient to focus only on the coordinate signal V.Of course, in this case, the first-order (The original optical position detector can be used.) A projection optical system that projects an optical mark of a predetermined shape onto the sample surface from an oblique direction, and an optical axis in the same plane as this projection optical system; By providing an optical system that connects the optical mark to the dimensional optical position detector, the coordinate signals v and H of the two-dimensional optical position detector can be easily configured to correspond to the position on the sample surface. can.

However, when such a two-dimensional optical position detector is used as a gold photoelectric conversion element, when the reflection characteristics of the sample surface on which optical marks are formed vary depending on the location and give a nine-dimensional distribution,
The signals V and H no longer correspond to the position of the sample surface.

Therefore, there arises a drawback that accurate position measurement cannot be performed.

(Objective of the Invention) The present invention solves the drawbacks of using a two-dimensional optical position detector as a photoelectric conversion element, and solves the problem of distributing metals in which the reflection characteristics of the sample surface on which optical marks are formed differ depending on the location. It is an object of the present invention to provide a position detection device capable of accurately detecting a position even when the load is given.

(Summary of the Invention) The present invention has a projection optical system that projects an optical mark of a predetermined shape onto a sample surface from an oblique direction, and an internal pressure optical axis that is coplanar with the optical axis of this projection optical system, and has a light intensity center position. When the sample surface is at a predetermined position, an oblique incidence type position detection optical system consisting of a condensing optical system that collects the reflected light from the sample surface of the optical mark on a two-dimensional optical position detector that outputs a corresponding orthogonal coordinate signal is used. A pair of optical marks including the respective optical axes are arranged perpendicularly to each other so that the optical marks overlap on the sample surface when the two-dimensional optical position detector is on the sample surface. A determination means is provided for monitoring the output coordinate signal of the other two-dimensional position detector to determine whether the movement is due to the movement in the direction perpendicular to the sample surface or the non-uniformity of the reflection characteristics of the sample surface. It is.

(Embodiment) FIG. 1 is a diagram showing the basic configuration of an oblique incidence optical system used in a first embodiment of the present invention. Light from the light source 1 passes through the condenser lens 21 and is irradiated from the back surface of the rectangular aperture diaphragm 3i. The rectangular aperture of the rectangular aperture stop 3 forms an image on the surface of the sample 5 (sample surface) by the projection lens 4 . The sample 5 is placed on a stage (not shown) that moves up and down in the optical axis direction of an observation objective lens 6, and in the state shown in FIG. Assume.

The reflected light from the rectangular aperture formed on the surface of the sample 50 is focused onto the two-dimensional optical position detector 8 by the focusing lens 7, and the rectangular aperture is focused on the detector 8.

And light source 1. Condenser lens 2. Rectangular aperture 3
．． The angle between the optical axis t1 of the first projection optical system formed by the projection lens 4 and the optical axis of the objective lens 60 perpendicular to the surface of the sample 50 is -ψ. The optical axis t of the first condensing optical system formed by
The angle formed between this and the optical axis 4 is ψ1, and the first projection optical system and the first condensing optical system form a first oblique incidence type position detection optical system.

In this example, as shown in the schematic plan view of the principle shown in Fig. US2, the first A second oblique incidence position detection optical system is provided which is formed of the same optical system as the first oblique incidence position detection optical system shown in the figure. That is, the optical axis t1 of the projection optical system and the optical axis t of the second condensing optical system forming the second oblique incidence type position detection optical system are arranged. Note that elements corresponding to the WJ1 projection optical system and the first condensing optical system are indicated with a prime. When the sample 5 is set at the focal position of the objective lens 60, the rectangular aperture images formed on the surface of the sample 5 by both projection optical systems are aligned so as to overlap with each other.

Now, if there is a difference in reflectance of 6V on the surface of the sample 5 where the rectangular aperture 1a30 is formed, specifically, the shaded area in FIG. 2 has a lower reflectance than the other areas, two-dimensional optical position detection Vessel 8
．． The rectangular opening @ on 8' becomes a trap as shown in plan in FIG. That is, in the two-dimensional optical position detector 8, the direction V of the coordinate system is as shown in the figure.

If Ht is constant (the direction of the plane containing the optical axis of the first oblique incidence optical system is 1v, and the direction iH is orthogonal thereto), and the center of the photoelectric conversion surface is t - the origin, the coordinate signals are vA = α, HA =
It becomes O. In other words, since the light intensity falls in the shaded area, it should originally be V, W O, but the center of gravity position Q
This is because A is biased towards the bright direction (positive direction of V). Therefore, when position detection is performed only from the output signal of the two-dimensional optical position detector 8, if the sample is located behind the focal position of the objective lens 6.
It is judged that it is on the side, that is, in the rear bin.

On the other hand, on the two-dimensional optical position detector 8' side, as shown in the figure, the coordinate system V, Hg is determined (direction 1v of the plane included in the optical axis of the second oblique incidence optical system, direction perpendicular to it is H), and the photoelectric If the center of the conversion plane is the origin, the coordinate signals are V1, Q, Hi
= β.

Here, the coordinate signals in the V direction of the two-dimensional optical position detector 8 and the coordinate signals in the H direction of the two-dimensional optical position detector 8' are approximately equal (that is, in the above example, α and β).

Also, the coordinate signals in the H direction of the two-dimensional optical position detector 8 and the coordinate signals in the V direction of the two-dimensional optical position detector 8' are approximately equal (both are set to 0 in the above example). Therefore, if the two-dimensional optical position detector 8
' If no movement of the center of gravity in the H direction is observed, the coordinate signal of the two-dimensional optical position detector 8 in the V direction is due only to the position of the sample and is providing correct positional information. become. On the other hand, if the center of gravity of the two-dimensional optical position detector 8 is not observed to move in the H direction, the coordinate signal in the ■ direction of the two-dimensional optical position detector 8' can be attributed only to the sample position @VC. . Therefore, by mutually monitoring each of the two-dimensional optical position detectors 8, 8', only the correct position signal t
can be discriminated.

Figure @4 shows an embodiment of a circuit that processes coordinate signals obtained from the two-dimensional optical position detectors 8 and 8'.

The coordinate signal VA obtained from the two-dimensional optical position detector 8 is converted into a digital coordinate signal by an analog-to-digital converter (hereinafter referred to as A/D converter) 9, and then sent to one input terminal of the first selector IO. is input. The coordinate signal v1'i from the two-dimensional optical position detector 8' is inputted to the other input terminal of the first selector lO, and the digital signal V≦ converted by the A/D converter 11 is input. The control terminal VC of the first selector 10 receives the coordinate signal H of the two-dimensional optical position detector 8'.
The output terminal of a first window comparator 12 that determines whether or not a is within a predetermined range is connected.

The first window comparator 12 has a voltage "t + vt t" as the upper and lower limit voltages determined by the accuracy of position detection, and the coordinate signal H1 is the window voltage ■I rV!
If there is a difference between the two, the first signal is output, and otherwise, the first and second signals are output. When the first selector 10 receives the first signal as a control signal, it outputs it to the output signal Vi k of the A/D converter 9, and when the second gI signal is input as the control signal, it outputs it to the A/D converter 11. The output signal vIt- is outputted to the output terminal. The output terminal of the first selector 10 is the second selector 1
Connected to one input terminal of 4. The other input terminal of the second selector 14 is grounded. The output terminal of the OR gate 15 is connected to the control terminal of the second selector 14, and the output terminal of the @1 window comparator 12 is connected to one input terminal of the OR gate 15.
The other input terminal is connected to the output terminal of a second window comparator 13 which is compared with the coordinate signal HAt of the two-dimensional light position displacement device 8 minus the window voltage vI +Vt. The second window comparator 13 is the same as the first window comparator 12, and outputs the first signal if the coordinate signal H^ is between the window voltages V, , V, and otherwise outputs the second signal. Output. The second selector 14 outputs the signal from the first selector 10 when the 8gl signal is input to the control terminal, and outputs a ground potential sound when the second signal is input. Either input terminal of OR gate 15 is @1
If it is a signal, the first signal is output, otherwise the second signal is output.
Output a signal. The second signal output from the OR gate 15 is also used as an abnormality warning signal.

Because of this arrangement, if the coordinate signal Ha is between the window voltages 1 and vt and the first signal is generated from the window comparator 12, the selector 10 selects the coordinate signal Va' from the A/D converter 9. Output k. The OR gate 15 is configured such that at least one of the input signals is the first one.
If it is a signal, the signal from the selector 10 is output, and the selector 14 outputs the coordinate signal ``M''. This signal has vt corresponding to the deviation of the stage (not shown) from the in-focus position. Further, if the second signal is generated from the window comparator 12, the selector lO outputs the coordinate signal V1' from the A/D converter 11. In this case, the coordinate signal H^ is the window voltage V.

And■! If the second window comparator 13 is outputting the first signal during this period, the coordinate signal y, 1 is output through the selector 14 (this signal also has a value corresponding to the deviation from the focus position of the stage). ), if the second window comparator 13 outputs the second signal, the selector 14 outputs the full ground potential, while the OR gate 1
The second signal No. 5 is used as an abnormality signal to warn that measurement is not possible.

Therefore, according to the apparatus of this embodiment, even if the reflection characteristics of the surface of the specimen on which the rectangular aperture image is generated are partially different,
What is the effect of the above-mentioned non-uniform reflection characteristics in the orthogonal oblique incidence position detection optical system? Since the signal sound from the optical system that does not receive the signal is used, highly accurate position detection is possible.

Since the obtained signal corresponding to the deviation from the nine in-focus position also indicates the direction t of the deviation, the selector 14 is used in the drive circuit of the motor that controls the vertical movement of the stage (not shown).
Autofocus can be achieved by inputting the output signal of

Of course, the output signal t of the selector 14 is displayed, and the displayed value is O.
The stage may be manually driven so as to achieve this. Furthermore, the position of the sample 5 in the optical axis direction of the objective lens 60 may be displayed.

In the state shown in Fig. 2, l(s+β), but in this case, the center of gravity moves outside the allowable range, and β is the voltage V,
It is not between V. Therefore, the selector 10 has V11'=
0 is output, and the selector 14 outputs Hm;0, so V++' = Of from the selector 10. Therefore,
It can be seen that the surface of the sample 50 is in the focused position.

In the above embodiments, a rectangular aperture diaphragm was used, but the shape of the diaphragm aperture is not limited to rectangular, and may be circular or other shapes. The absolute values of the angles that the condensing optical system makes with the normal to the sample surface do not have to be equal. However, if the sample surface is close to a mirror surface, they must be equal.

Furthermore, as in the above embodiment, one of the coordinates of the two-dimensional optical position detector corresponds to the moving direction of the sample surface, which has the advantage of simplifying signal processing. It doesn't mean that the purpose cannot be achieved unless it is related, but is it something to do in the correction calculation? You can do the same thing if you are willing.

In addition, when the sample surface is at the focal position of the objective lens 6,
It is not necessarily necessary that the dimensional optical position detector and the sample surface be conjugated, and the object of the present invention can be achieved by performing all electrical coordinate position corrections in either case.

In addition, in the case of a measurement surface having a pattern formed with regularity in orthogonal directions, such as a wafer, a surface including the optical axes of a pair of oblique illumination optical systems in each direction of the pattern? If they are configured so that they match, the direction of the non-uniformity of the reflection characteristics will often match the direction of the pattern, so there is a probability that it will not be measurable. Can be made smaller.

(Effects of the Invention) As described above, according to the present invention, only correct position information can be obtained even if there is unevenness on the reflecting surface. This method is effective for various types of equipment that require continuous movement and setting of the sample surface at a constant height.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the basic configuration of the oblique incidence optical system used in the first embodiment of the present invention, FIG. 2 is a plan view schematically showing the principle of the first embodiment of the present invention, and FIG. The figure is an electrical block diagram for processing the coordinate signals obtained from the two-dimensional optical position detector of FIG. 2. (Explanation of symbols of main parts) 1・1'...Light source, 2/2'...Condenser lens. 3, 3'... Rectangular aperture diaphragm, 4, 4',... Projection lens. 5...Sample, 7.7'...Condensing lens, 8.8'.
...Two-dimensional optical position detector, 10/14...Selector,
12/13...Window comparator, 15...Or gate.

Claims (1)

[Claims] a projection optical system that projects an optical mark of a predetermined shape onto a sample surface from an oblique direction; and an optical axis that is in the same plane as the optical axis of the projection optical system, and outputs an orthogonal coordinate signal that corresponds to the position of the center of gravity of the light amount. A condensing optical system that condenses the reflected light from the sample surface of the optical mark onto a two-dimensional optical position detector, and an oblique incidence position detection optical system that A pair of optical marks are arranged with their optical axes perpendicular to each other so that they overlap on the sample surface, and the light intensity center position of one of the two-dimensional optical position detectors moves in a direction perpendicular to the sample surface. 2. A position detecting device comprising a determining means for monitoring the output coordinate signal of the other of the two-dimensional optical position detectors to determine whether the change is due to movement of the sample surface or non-uniformity of reflection characteristics of the sample surface.