JPS6193625A - Pattern detector - Google Patents

Abstract

PURPOSE:To make it possible to perform high-speed, automatic control of the amount of projected light, by forming a part, which detects the amount of reflected light from a body, on light receiving surfaces of a photoelectric detector so that the part is separated from a part for detecting a light signal from a pattern, and simultaneously detecting the amount of light in a pattern detecting region and a detected pattern signal. CONSTITUTION:The distribution of scattered light, which is observed at the position of a photodetector 18 of an alignment mark is extended in the direction perpendicular to the extending direction of a pattern. Meanwhile, the scattered light from a material having an irregular shape such as dust spreads uniformly. Light receiving surfaces 18b, 18d, 18f and 18h detect the scattered light caused by the difference in steps in the mark pattern. Light receiving surfaces 18a, 18c, 18e and 18g detect only the scattered light from the dust and the like, which spreads uniformly. Based on the difference, only the signal component, from which the effect of the dust and the like is removed, can be taken out. The amount of the projected light is controlled by said signal at the light receiving surface, which detects non-scattered light.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field 1 of the Invention] The present invention relates to a position B in which a photoelectric converter is used to detect an optical signal from a pattern drawn on an object to be detected such as a mask or a wafer, and particularly relates to the above-mentioned method. IIJB the amount of light irradiated to the detected object
The present invention relates to a pattern detection device capable of obtaining a pattern detection signal of an appropriate level.

[Background of the Invention] This type of pattern detection device is used in a mask or wafer position detection device or a mask or wafer defect inspection device in a semiconductor printing device or the like.

゛Conventionally, signal detection 1i1 aimed at position detection by pattern in position detection IIm! Special application as 1984-4
No. 745-59-4747, patent application No. 59-5635-5
A photodetector using a photoelectric detector as disclosed in No. 9-5637 is known. In such IUT, it is necessary to optimize the output of the photoelectric detector to some extent in order to accurately judge the pattern, and for this purpose, it is necessary to control the gain of the amplifier that amplifies the output of the photoelectric detector, or It has been difficult to control the amount of light irradiated onto the object to be detected.

Some devices have already been proposed to optimize this output, but in these devices, the light amount detector for controlling the detection output also doubles as a pattern detection detector, or Detectors were installed independently regardless of the area. However, since the former functions as a pattern detector as well as a light intensity detector, for example, if there is no target pattern in the light irradiation area, the light intensity may not be detected, or the detected light intensity value may be inaccurate. In order to measure the amount of light, it is necessary to process the detected output to determine the amount of light. In addition, in the latter case, the amount of detected light does not necessarily match the amount of light in the pattern detection area, and as a result, the output output from the detector is either too much or too little, making it impossible to obtain an optimal signal, making it difficult to detect position by pattern, etc. There were some inconveniences in which this was not possible.

[Object of the Invention] The present invention has been made for the purpose of eliminating the drawbacks of the above-mentioned conventional example, and the amount of light in the pattern detection area can be adjusted by using a complicated processing circuit and redundant pattern detection f! 41ii! This compact design allows simultaneous detection of the pattern detection signal and high-speed automatic control of the amount of light irradiated in the pattern detection area without adding an external independent detector and without impairing the characteristics of pattern detection. The present invention aims to provide pattern detection H!t that can be realized at low cost.

[Description of Embodiments] The present invention will be described in detail below with reference to the drawings. FIG. 1 is a principle diagram of a signal detection system of an automatic mask and wafer alignment apparatus to which pattern detection II according to an embodiment of the present invention is applied. 1 is a laser light source, 2 is a condensing lens, 3 is a rotating polygon mirror, 4 is a relay lens, 5 is a beam splitter for splitting the light into 22 or less visual optical systems, 6 is a field lens, 7 is 14 Beam splitter for splitting the light into the following photoelectric detection optical system, 8 is a relay lens, 9
19 to 21 are beam splitters for guiding light from illumination optical systems for visual observation, 10 is a feed for the objective lens 11, 12 is a mask, and 13 is a wafer.

Here, the conjugate relationship of the laser beam itself is as follows. That is, the laser beam is focused at the position 30 by the -H focusing lens 2. The spot diameter of the laser beam at the position 30 is determined by the diameter of the incident laser beam and the focal length fz of the condenser lens 2.

Assuming that the laser beam is uniformly distributed within the radius,
The diameter d of the laser spot is expressed as (1-2,44λ・f2/D).The laser beam diverging from the position 30 is reflected by the rotating polygon &!t3, passes through the relay lens 4, and enters the -H field. It is connected to a point 32 near the lens 6.

Furthermore, the light passes through the relay lens 8 and the objective lens 11 and is imaged at 34 positions corresponding to the mask and wafer surfaces. Therefore, 30.32° 34 in FIG. 1 are conjugate to each other. The diameter φ of the spot 34 that actually scans the mask and wafer surface is determined by the imaging magnification from 30 to 34.
When it is, it is shown as φaXd. To change the scanning spot diameter, d can be changed by changing the beam diameter of the laser beam or the focal length of the lens 2 (1!). This can be realized by changing III f z. Also, if you just want to enlarge the scanning spot, use the condenser lens 2.
This can also be achieved by intentionally moving the position of and defocusing the laser beam at the position of 30. Generally, it is desirable that the diameter of the scanning spot can be selected appropriately depending on the target pattern line width, but the system shown in FIG. 111 can easily cope with changes in the spot diameter. The laser beam focused at the position 34 scans the mask and wafer surfaces as the rotating polygon mirror 3 rotates.

In addition to the conjugate relationship of the scanning beam on the actual object plane as explained above, the image formation relationship of the pupil of the optical system shown in FIG. 1 is also important. The pupil of the objective lens 11 is indicated by 10, and the point 33 on the optical axis, which is the center point of 10, is a rotating polygon! The reflection point 31 of [3 is conjugate with each other. That is, the arrangement shown in FIG. 1 is equivalent to placing a rotating polygon mirror exactly at the position 1110 in terms of the incidence of the laser beam onto the objective lens.

A telecentric objective lens is used when observing reflective objects such as wafers. The objective lens 11 in FIG. 1 is arranged in a telecentric manner, that is, the pupil 10 that determines the light beam passing through the optical system is placed at the front focal position of the objective lens 11. Figure 2 shows this situation. The center 33 of the pupil position Hio, which is also the front focus of the objective lens 11, is conjugate with the laser reflection position [31 of the rotating polygon mirror 3, as described above, so it acts as if a scanning beam were generated from there.

The principal ray, which is the center line of the scanning beam, passes through the front focal point 33 of the objective lens, so after passing through the objective lens 11 it becomes parallel to the optical axis and enters the mask and wafer perpendicularly. If the area hit by the scanning beam is flat, the incident light will be reflected and return to position 33 again. On the other hand, if there is a pattern where the scanning beam hits, the light will be scattered at the edges of the pattern boundaries and will not return to its original state.

In other words, the scattered light is captured by the objective lens 11 and returned to 11
10, it no longer passes through the center 33 of the pupil, but instead passes toward the edge of the pupil. This simply means that scattered light and non-scattered light are spatially separated on land, and Figure 2 shows this separation. That is, when the scanning beam scans the object surface from left to right, for example, the light is not scattered and is reflected back to the pupil 10 until it hits the patterned portion 35. pattern 3
5, the light is scattered and passes through an optical path as shown by the dotted line, and does not return to its original position above the pupil 1o. The area occupied by the non-scattered light at the pupil 1o is the same as the effective diameter of the scanning laser beam. In order to capture scattered light effectively, the effective diameter of this non-scattered light is usually set sufficiently small compared to the diameter of the pupil, and the ratio of this diameter is usually in the range of 0.1 to 0.7. It is preferable to take

Returning to FIG. 1 again, consider the photoelectric detection optical system that separates from the beam splinter 7 and reaches the photodetector 18. In the figure, reference numeral 14 denotes a lens for forming an image of the objective lens 11, and reference numeral 15 denotes a filter that transmits light for photoelectric detection but substantially cuts other wavelengths, such as wavelengths used in the viewing optical system. The position of the photodetector 18 is where an image 1110 is formed by the pupil imaging lens 14. Therefore 11
0. The photodetectors 18 are in a conjugate relationship with each other. In this photoelectric detection system, the light receiving surfaces of the seven photodetectors are arranged so that the output appears only when the scanning spot hits the edge of the pattern. Therefore, the output is 1 in time! As you can see, when the scanning beam hits the edge, a pulse-like signal is generated. If this pattern is a signal from the 7 linement marks on the mask and wafer,
From this signal, the relative positional deviation between the mask and the wafer can be detected. Auto 7 alignment is performed by moving the relative positions of the mask and wafer using a drive system (not shown) so as to correct the detected amount of deviation.

In FIG. 1, illumination systems 19 to 21 and observation systems 22 and below are provided for visual observation. 19 in the figure is a light source for illumination,
20 is a condenser lens which functions to form a light source edge above the pupil 10 of the objective lens 11. Reference numeral 21 denotes a filter having the function of cutting light in a wavelength range to which the photoresist is sensitive. On the other hand, 22 is an erector that rotates the image in the normal direction, and 23 is a filter that cuts the laser wavelength and transmits the wavelength for visual observation.
24 is an eyepiece lens.

On the other hand, an example of a mark suitable for laser spot scanning can be found in, for example, Japanese Patent Application No. 52-5502 entitled "Optical Device". This mark is a rectangular mark shown in FIG. 3 that can detect deviations in X and y with respect to line scanning in one direction. FIG. 3(a) shows a pattern for a mask (or wafer), (b) a pattern for an i, t wafer (or mask), and FIG. 3(C) shows a state when both are subjected to 7-line alignment. Note that the dotted line in Figure (C) is the locus of the scanning laser beam.

If a photoelectric detection system that detects scattered light happens to have a substance that scatters light, such as dust, in the area to be photoelectrically detected, it will pick up the scattered light from this dust as a signal. Dust may be attached to the wafer or inside the scanning optical system, so it must always be taken into consideration.

Detection light from other than the horizontal pattern is a so-called false signal, which is not only undesirable but also causes malfunctions.

For this reason, there is a method of dividing the light-receiving surface of the photodetector in order to remove unwanted detection light from other than the pattern such as the above-mentioned dust. In order to explain the method of dividing the light-receiving surface of the photodetector, consider the distribution of light observed at the seven photodetectors 18 of the photoelectric detection section in FIG. 1. In the explanation so far, scattered light has been understood as a phenomenon of scattering from pattern edges', but in other words, this is nothing but a partial diffraction phenomenon. Therefore, light is scattered in a direction that depends on the directionality of the pattern. In the case of the alignment mark shown in FIG. 3, the distribution of scattered light that is emitted at the position of the photodetector 18, so-called diffraction pattern, is shown in FIG. 4(a).

The fact that the scattered light extends in a direction perpendicular to the direction in which the pattern extends is easily explained by the theory of normal diffraction phenomena. On the other hand, scattered light from an irregularly shaped substance such as a dust collar does not show any particular directionality at the detector 18 and spreads uniformly.

The situation is shown in FIG. 4(b). Figure 4(a).

In both (b), the black dot in the center is the part due to non-scattered light,
The other shaded areas indicate areas where light is spreading. The outer circle indicates the effective diameter of the optical system.

The method of dividing the photodetector utilizes the difference in scattering from the patterned portion and the non-patterned portion at the photodetector position. The light receiving surface of this photodetector is divided into a pattern detection (diffracted light) light receiving surface and a scattered light receiving surface.

The problem with such a photoelectric detection method is that the current amount of light must be detected in order to control the amount of light irradiated onto the object to be detected in order to obtain an optimal detection output.

In other words, since the photodetector 18 is divided to detect scattered light, it cannot detect the amount of light if there is no scattered light, and even if it could, it would not faithfully reflect the reflectance of the detected object. Not there.

In general, the reflection state of the wafer surface varies greatly depending on the type of wafer and processing conditions, so it is not possible to obtain an output that maintains a sufficient S/ simply by controlling the gain of the 7-wavelength amplifier after the photoelectric detector. This is because the signal output to the photoelectric detector falls below the noise level generated by the detector due to insufficient amount of light incident on the photoelectric detector. To avoid this, increase the amount of light irradiated to the wafer and It is essential to increase the size of the optical signal.

If we look again at the distribution of the light observed at the photodetector 18, we can see that the light that returns along the optical path from which the irradiated light came is 1! at the center of the optical system! It can be seen that the amount depends on the reflectance of the object to be detected. Therefore, by adding a divided portion of the photodetector to the center and controlling the irradiation light amount based on the light amount detected there, reliable light amount control becomes possible. Incidentally, the light that is U* at the center, that is, the non-scattered light, is hereinafter referred to as zero-order light.

In the present invention, the light-receiving surface of the photodetector 18 is divided, a zero-order light-receiving surface is provided in addition to the pattern-detection light-receiving surface and the scattered light-receiving surface, and the amount of irradiated light is controlled by the amount of light detected on the zero-order light-receiving surface. is a feature.

FIG. 5 is a schematic top view showing an embodiment of such a photodetector. The 18 photodetectors have light receiving surfaces 18a and 18b that are divided on the same substrate and configured so that signals can be taken out independently.

18c, 18d, 18e, 18f, 1
Tail from 8g, 18h, 18i. Light receiving surfaces 18b, 18d, 18f, 18h l;t
This is a light-receiving surface that detects the scattered light, that is, the diffracted light, due to the step difference in the v-mark pattern.The signal extracted from this is called a mark signal.This mark signal includes the mark pattern diffracted light shown in FIG. It includes a signal due to uniformly spreading scattered light from the dust or particulate pattern shown in FIG. 3(b). Also, 18a.

Reference numerals 18c, 18e, and 18g are light-receiving surfaces on which only the uniformly spread scattered light caused by dust and the like shown in FIG. 4(b) is detected, and the signals extracted from these surfaces are called noise signals. Incidentally, the signal due to scattered light from dust or the like in the mark signal has approximately the same amount as the noise signal and is synchronized with the noise signal. Therefore, by subtracting the noise signal from the mark signal, only the signal due to the mark pattern diffracted light from which the influence of dust and the like has been removed can be extracted.

On the other hand, 181 is a light receiving surface for detecting 0th order light, and the signal extracted from this is called a 0th order optical signal. In the present invention, this O
The amount of irradiation light is controlled by the next optical signal.

Note that this rectangular photodetector 18 can be manufactured using a solar cell or the like.

Next, a signal processing system according to an embodiment of the present invention will be explained. FIG. 6 is a signal diagram for explaining the signal processing. Here, for the convenience of the following explanation, the light receiving surface 181),
The sum of the signals from i8d, 18r, and 18h, that is, the one where the mark signal is output is called the A channel.
The sum of the signals from the light receiving surfaces 18a, 18c, 18e, and IQ, that is, the side from which the noise signal is output is called the B channel. FIG. 6(a) shows the positional relationship when the patterns on the mask and wafer are scanned.

In this figure, the dashed line indicates the laser scanning light, and the dust 4
The arrangement is exactly the same as in FIG. 3(C) except that 2 is on the scanning line. FIG. 6(b) shows the output of the A channel, and FIG. 6(C) shows the output of the B channel. The A channel is a detection channel for "pattern + dust" and the B channel is a detection channel for "dust", so the output is straight as shown in the figure.

FIGS. 6(d) to 6(f) show the three bad states of the signal that has passed through the differential amplifier that performs the operation (A-8).

(d) is when the A-channel garbage signal and B-channel garbage signal cancel each other out just fine, (e) is when the A-channel garbage signal is thicker, and (f) is the case where the B-channel garbage signal is cancelled. This is a case where the problem is too large to be completely canceled. Which of (d) to (d) will be determined depends on a number of factors, such as the characteristics of dust scattering, the magnification applied to one or both signals during differential amplification, and the sensitivity difference of photodetectors. I can't decide.

However, compared to the output of (b) which simply cuts only the non-scattered light, the signals l) to (f) which are the signals after passing through the differential amplifier
suppresses noise and increases the pattern S/N ratio.

In FIG. 6, (g) shows an O-order optical signal. In the absence of pattern scattering, this output reflects the reflectance of the detected object. By increasing the light intensity of the laser irradiation system to 1ill II using this O-order optical signal, the optimum light ω can be obtained, and a mark signal at an optimum level can be obtained as the output of the photoelectric detector.

・ Figure 7 is the same as Figure 6 (g) (0th order light receiving surface 1
81, (a) shows the output when the light amount is excessive, (b) shows the output when the light amount is insufficient, and (c) shows the output when the optimal first-out control is performed.

FIG. 8 shows a specific example of the pattern detection circuit of the present invention. In the same figure, the light emitted from the laser 1 is reflected by the mask 12 and the wafer 13, and is split from the original optical path by the beam splitter 7. ! & enters the detector 18. The output signal from the photoelectric detector 18 is an O-order optical signal detected by the O-order light receiving surface 18i, which is sent to the light amount detection amplifier 45, and a mark signal receiving surface 18b, 1ad, 18f.

A sum signal of the mark signals detected at 1811 is input to the detector amplifier 46. Then, this O-th optical signal is given to the light amount control circuit 44 via the amplifier 45, and the light it! l
A regulator 43 adjusts the amount of light transmitted from the laser 1 according to the output of the light amount control circuit 44, so that the amount of light irradiated onto the mask 12 and the wafer 13 is 1 m. This results in
Mark signal receiving surfaces 18b, 18d, 18f,
At 18h, mark signals at the optimum level due to the optimum light amount are detected, and the sum of the mark signals is appropriately amplified by the detector amplifier 46 and sent to a signal processing circuit (not shown).

[Application Examples of the Invention] Note that the present invention is not limited to the above-described embodiments, and can be implemented with appropriate modifications. For example, instead of a photodetector having light-receiving surfaces divided on the same plane as in the above embodiment, a mirror that tilts the light beam in a different direction may be attached to each light-receiving surface, and a configuration may be adopted in which light is received by multiple dedicated detectors. Of course, it is possible to transform the device so that it receives light on substantially the same surface. Or 18b, 1g (1, 18f) of the light receiving surfaces of the 7 Otodetectors in Fig.
, 18h.

It is also possible to use a photodetector with only a 18i light receiving surface.

Furthermore, in the above embodiment, an example was explained in which the present invention was applied to a position detection device for aligning a mask and a wafer. It can be applied to all conventional signal processing, such as mask defect inspection.

C. Effects of the Invention] As described above, according to the present invention, the amount of light in the pattern detection area can be detected simultaneously with pattern detection and on the same plane. Therefore, it is possible to control the irradiation light amount at an appropriate level with high reliability without reducing the throughput of the equipment to which the present invention is applied, such as semiconductor manufacturing equipment, half-half inspection equipment, or mask inspection equipment. A pattern detection signal can be output. Further, the detection control circuit for this purpose is simple and does not require any special detector space outside the pattern detection area.

[Brief explanation of the drawing]

Fig. 1 shows the principle of the signal detection system of a mask and wafer automatic alignment device to which a pattern detection device according to an embodiment of the present invention is applied; the second factor is a diagram showing the action of a telecentric objective lens; Fig. 3 is a diagram showing an example of a mark used in the automatic alignment device shown in Figure 1, Figures 4 (a) and (b) are diagrams showing the light receiving area of a diffraction pattern from a mark and dust, respectively, and Figure 5 is a diagram showing an example of a mark used in the automatic alignment device shown in Figure 1. FIG. 6 is a diagram showing a photodetector according to an embodiment of the invention; FIG. 6 is a diagram showing a photoelectric detection signal according to an embodiment of the invention; FIG. 7 is a diagram showing an output signal from the zero-order light receiving surface of the photodetector in FIG. 5. and FIG. 8 are diagrams showing a specific example of the pattern detection circuit of the present invention. , 1... Laser light source, 2.4.6.8.14.20.
22゜24...Lens, 3...Rotating polygon mirror, 5,7
．． 9...Beam splitter, 10...Objective lens 1
1 pupil, 11...objective lens, 12...mask, 1
3...Wafer, 15.21.23...Filter, 1
8... Photodetector, 18b, 18d. 18f, 18h...Pattern detection light receiving surface, 18i
... 0th order light receiving surface, 1 ... Light source for illumination, 35 ...
- Pattern depression, 42... Dust, 43... Light amount adjuster, 44... Light amount control circuit, 45... Light amount detection amplifier, 46... Detector amplifier.

Claims (1)

[Scope of Claims] 1. In a pattern detection device that irradiates light onto an object to be detected and detects an optical signal from a pattern formed on the object using a photoelectric detector, the light-receiving surface of the photoelectric detector A portion for detecting the amount of reflected light from the detection area of the object is formed separately from a portion for detecting the optical signal from the pattern, and the amount of irradiated light is controlled based on the detection signal in the light amount detection portion. A pattern detection device characterized by: 2. The pattern detection device according to claim 1, wherein the optical signal from the pattern is diffracted light in the pattern, and the light for detecting the amount of light is non-scattered light in the detection area. 3. The light-receiving surface of the photoelectric detector is arranged on the object to be detected at a focal plane for parallel light rays or at a position conjugate with the focal plane, and the light amount detection portion is formed in the center of the light-receiving surface. 3. The pattern detection device according to claim 2, wherein the optical signal detection portion is formed in a radial band shape in a portion other than the central portion of the light receiving surface. 4. At least one of the optical signal detection section and the light amount detection section is composed of a mirror disposed at a predetermined location on the light receiving surface and a photoelectric element disposed outside the light receiving surface and receiving reflected light from the mirror. A pattern detection device according to any one of claims 1 to 3.