JPS61206222A - Focalizing device - Google Patents

Abstract

PURPOSE:To simplify the positioning of photoreceiving element at a focalized position by using no mechanical shifting element by a method wherein an array type element is used as a photoreceiving element and luminous flux reflected from a specimen surface is detected and then the focalization is performed by making a comparison between a reference position and a position being detected. CONSTITUTION:A projecting optical path 5 makes arrangement so that light emitted from a light source 6 may be magnified by a collimator lens 7 to be entered into a slit 8 which is provided with at least two or more openings 8a while a lens 9 and a reflector 10 may form images 8b on a wafer 2. On the other hand, reflecting light 11 from the wafer 2 likewise makes arrangement so that another reflector 12 and another lens 13 may form images 8c on a photoreceiving element 14. The output from photoreceiving element 14 temporarily memorizes waveforms by a memory circuit 16 through the intermediary of an A/D converter 15 and then calculates the central position address of each wave form image of the memory circuit 16 by a point of intersection detecting circuit 17. When the focalization is carried out, said detected results calculated by an adder 18 are compared with the results detected by the other memory circuits 2, 19 to drive a driving source 4 by a drive control circuit 21 in terms of the results.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to position detection and alignment of a sample surface, and in particular to a focusing method suitable for position detection and alignment of a reduction lens of a reduction projection exposure apparatus with respect to a sample surface. It is related to the device.

[Background of the invention]

As described in Japanese Patent Application Laid-open No. 56-42205, the conventional device irradiates a light beam obliquely onto the sample surface, focuses the reflected light onto a detection slit in front of a light receiving element, and then detects the detection slit. The method used was to obtain a modulated signal by relatively vibrating light and passing through a skeleton slit, and detect the phase of this signal to detect the focus.

This method can be easily performed by detecting the difference between the detected waveform when the focus is focused and the detected waveform when the focus is deviated from the focused position, but since the formed image and the slit are vibrated relative to each other, A vibrating mirror shall be provided.

Therefore, the detection accuracy deteriorates due to the busyness of the mechanically operating elements.9 Difficulty in aligning the light receiving element at the in-focus position It is possible that the focal position may shift due to changes in the light receiving element over time.

[Purpose of the invention]

An object of the present invention is to solve the above-mentioned problems of the prior art, to eliminate mechanical moving elements in the detection method, to simplify alignment of the light-receiving element at the focal point position, and to reduce changes in the light-receiving element over time. An object of the present invention is to provide a focusing device that enables focus detection and focusing.

[Summary of the invention]

In order to achieve the above object, the present invention uses a focusing device in which a light beam is incident obliquely on a sample surface, the light beam is reflected, and an image is formed on an array type light receiving element. By detecting the position of the light beam at
This enables focus detection and focusing with little temporal change in the light receiving element.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. Figure 1 is a configuration diagram of one embodiment, Figure 2 is a top view of Figure @1,
FIG. 5 shows a signal waveform obtained in this embodiment, FIG. 4 is an enlarged view of FIG. 5, and FIG. 5 and FIG. 6 show an example of signal waveform processing. 1 and 2, the reduction lens 1 is fixed on the top of the wafer 2, and the wafer 2 is placed on the table 3.
The table 5 is installed so as to be movable in the vertical direction by the drive source 4. In the projection optical path 5 , the emitted light from the light emitting source 6 is magnified by a collimator lens 7 and enters a slit 8 . The slit 8 has at least two or more openings 8α (in this embodiment, there are five openings as shown in FIG. 2), and a lens 91 and a reflecting mirror 10 are arranged so as to form an image on the wafer 2.
An image 8b is formed as shown in FIG. The reflected light 11 from the wafer 2 is reflected by a reflecting mirror 12 . The lens 15 connects the light receiving element 14 with the second
They are arranged so as to form an image 8c as shown in the figure. The output of the light receiving element 14 is sent to the memory circuit 16 via the A/D converter 15.
(1 shape is temporarily stored, and the address of the center position of each image of the waveform in the storage circuit 16 is calculated by the intersection detection circuit 17 which detects the position of the image 8C.

In the case of the in-focus position, the result of the adder 18 and the address of each center position are stored in the memory circuit (2) 19.

When performing focusing, the detected result is calculated by an adder 1, and the detected result is calculated by a storage circuit (2) 19 and a comparison circuit 20, and the drive control circuit 21 drives the drive source 4 using the result. Place it in As shown in Figure 1 (
, the calculation and comparison circuits inside the dotted lines can perform similar processing in the combiator 22. In the above configuration, a certain amount of wafers 2 (
Move in steps (approximately 0.5 μm) and perform a trial firing.
Find the location with the best degree of decomposition and fix the table 3. The reflected light 11 from the light projecting optical path 5 is transmitted to the light receiving element 14.
The image is formed on the light receiving element 14 using a COD or a photodiode array sensor, etc. In this embodiment, since five slits 8 are used, an array element in which at least 50 elements are arranged is used. As shown in FIG. 5 (corresponding to the opening 8α of the slit 8, the opening 8α is
4. The waveform 18 of the comb is determined by the brightness and darkness of the light of each element that receives the light.
can be obtained. Focus detection and alignment are performed using the center address of this waveform.

As shown in FIGS. 4 and 5, a detection method that interpolates the center address to the center address of the waveform 181C is as shown in FIGS. 4 and 5.
A corresponding threshold value 22 is given. - is calculated for the addresses of the elements above and below this threshold value 22.

As shown in FIG. 5, α1 and α are divided in the element output direction at a pitch of 9, and the same division is performed in the element address direction at a pitch of P (10 minutes in this embodiment). The division address in the element address direction is defined as hl, which is a position directly above or intersecting the threshold value 22 with the divided element divided in the element output direction (in this embodiment, it is 5 division ports from α). Similarly, set the address to α1 on the opposite side. −, the center address of waveform 18 x
Find n. xn = h, +(by-hl) 12
becomes. There is also a method shown in FIG. The element address immediately above the threshold value 22 is found, and from this, at least two or more element addresses 'ls't on both sides are found. A linear curve 25 is assumed from this '1s'*. The intersection point (x) between the linear curve 23 and the threshold value 22 is found, and the center address xn of the waveform 18 is found in the same way.This process is performed by the intersection detection circuit 17.

When the wafer 2 deviates from the in-focus position, for example, as shown in FIG. The image is projected at a position shifted from the focal position. At this time, the waveform becomes a waveform 19 as shown in FIG. 5, where the waveform 18 at the focal point position is shifted in parallel.

Similarly, the center addresses x'1 to 21 of waveform 19. However, if the stage 5 is moved so that this deviation is eliminated, focusing is possible. An example of this method is shown below. The center addresses of the winter mountains of the light receiving element 14 at the focal point position, that is, the reference position, are calculated respectively, and the sum is calculated in one day using an adder. In other words, Chihe=he+ro+ro+he+to.

This element address and total number are stored in the memory circuit (2) 1q. The adder 18 calculates the center address at the shifted position in the same way. That is, “t =”s +4
+zl, +2'4+z%. Detected element address.

The comparison circuit 20 compares the total number with the reference value within +9 of the memory circuit (2), and the drive control circuit 21 drives the drive source 4 using the drive control circuit 21 to bring the difference between Focusing at the in-focus point position is possible by moving it closer to the reference position. In this embodiment, the sum of each center is calculated and compared, but the same effect can be obtained by comparing each waveform.

If the focal point position changes for some reason, the stage 5 is fixed at the new focal point position, the element address at the new reference position is detected as described above, and the memory circuit (2) 1
All you have to do is change the contents of 9. It can be set at any position within the detection range of the array element of the light receiving element 14, and the optical system can be adjusted.

No adjustment is necessary.

In this example, an array element is used as a light receiving element.
A similar effect can be obtained by a method in which an image of the slit 8 is received by a camera tube such as a TV camera, and the image is processed using known techniques to detect and align the focal position.

〔Effect of the invention〕

According to the present invention, in the focusing device, an array type element is used as a light receiving element to detect the position of the light beam reflected from the sample surface, and the detected position is compared with the reference position for focusing. Because there are no mechanical moving elements, alignment of the light-receiving element at the focal point position is easy, and there is less deterioration in accuracy due to changes in the light-receiving element over time.Comparing the sum of the addresses of the detected waveforms is peaceful. It is possible to achieve precise positioning, which has the effect of improving detection sensitivity and yield.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of an embodiment of the present invention, Fig. 2 is a view of Fig. 1 seen from above, Fig. 5 is a signal waveform diagram obtained in Fig. 1, and Fig. 4 is a diagram of Fig. 5. The enlarged views of FIGS. 5 and 6 are explanatory diagrams of one embodiment of signal waveform processing. DESCRIPTION OF SYMBOLS 1... Reduction lens, 5... Stage, 4... Drive source 8... Slit, 14... Detection element, 16...
Memory circuit, 17... Intersection detection circuit, 1B... Reference adder, 19... Detection adder, 20... Comparison circuit,
21... Drive control circuit. N..., -〇Fig.

Claims (1)

[Claims] 1. A means for irradiating a light beam onto the sample surface, a means for reflecting the light beam on the sample surface and forming an image on a light-receiving element, a means for freely moving the sample, and using an array-type element for the light-receiving element, means for detecting the position of the reflected light on the element; and means for comparing the detected position on the sample surface with a reference position determined in advance;
A focusing device comprising: a means for giving a command to a means for freely moving the sample based on the comparison result to move the sample to a reference position.