JPH04127151A - Pattern inspecting device - Google Patents

Abstract

PURPOSE:To accurately align the surface of a sample to be inspected on the focus position of a detection optical system with high frequency responsiveness by providing a counter spring and deviating an area irradiated with 1st light used for a pattern inspection from the area irradiated with 2nd light used for detecting the positional deviation. CONSTITUTION:A device is provided with the counter spring 30 which is connected between the lens barrel 24 and a fixing part 29 and for balancing the weight of the lens barrel 24. And also, the optical system for detection constituted of beam benders 43a,43b and a lens 44a, etc., and the optical system for detection constituted of beam benders 43c, 43d and a lens 44b, etc., are arranged so that they may be slightly deviated form each other at the opposite position symmetrical to the central axis of the lens barrel 24. Then, a load which is put on a driving member 31 can be reduced, the measurement difference in detecting the positional deviation which is caused by optical interference by each other and diffused external light can be reduced by deviating the area irradiated with the position detecting light from the area irradiated with the pattern inspecting light. Thus, the surface of the sample to be inspected can be accurately and automatically aligned on the focus position of the detection optical system with the high frequency responsiveness.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a pattern inspection device used for detecting pattern defects, measuring pattern dimensions, observing patterns, etc. This invention relates to an improvement in a pattern inspection device equipped with a focusing function.

(Prior Art) In the manufacture of ICs, if a master mask or reticle has a defect such as a pattern break, it is impossible to obtain a desired semiconductor element, resulting in a decrease in yield. For this reason, automatic mask defect inspection apparatuses have conventionally been used to automatically inspect pattern defects in master masks, reticles, and the like. In this apparatus, a spot-shaped light is irradiated onto the mask surface, and a table on which the mask is placed is moved in the X-Y direction to inspect the entire surface of the mask for defects. Reducing the size of the detectable defect requires increasing the magnification of the detection optical system, resulting in a shallower depth of focus of the optical system. If the depth of focus of the optical system becomes shallow, the surface to be inspected may deviate from the depth of focus due to mask warping or the like, making it impossible to detect defects. Therefore, for the above-mentioned devices,
An automatic focusing mechanism is added that automatically brings the surface to be inspected into the depth of focus of the detection optics.

FIG. 7 is a schematic configuration diagram showing a conventional pattern defect inspection apparatus equipped with an automatic focusing mechanism. In the figure, 1 is a reticle, and this reticle 1 is movable in the X direction (horizontal direction on the page) and Y direction (front and back direction on the page) on the fixed part 2.
It is placed on table 3. An optical lens barrel 6 including an objective lens 4, a photodetector element 5, etc. is arranged above the reticle 1. This optical lens barrel 6 is fixed to a fixed end via an elastic member 7. Further, the optical lens barrel 6 is connected to a motor 8. Warm 9. It is moved up and down by a drive mechanism consisting of a worm wheel 10, screws 11, and the like. In addition, an air introduction hole 12 is provided at the bottom of the optical barrel 6.
An air micrometer consisting of an outlet hole (nozzle) 13, etc. is provided. This air micrometer sends air onto the reticle 1 from the nozzle 13 and converts the distance from the back pressure.

14 is a light source, and light from this light source 14 is focused by a condenser lens 15 and irradiated onto the upper surface (surface to be inspected) of the reticle 1. Then, the pattern of the reticle 1 is inspected by focusing the light transmitted through the reticle 1 on the light receiving surface of the photodetecting element 5 using the objective lens 4. Therefore, when there is a low frequency vertical movement such as a warp of the reticle 1, this displacement is detected by the air micrometer and the optical mirror @6 is moved up and down by the drive mechanism to prevent the warp or the like of the reticle 1. Automatic focusing follows. Therefore, even if the reticle 1 has low-frequency vertical movement such as warpage, pattern defect inspection can be performed with high accuracy.

By the way, in such a tracking device, as in an LSI, the line width of the pattern becomes extremely narrow and the allowable defect size becomes even smaller, so that the depth of focus of the detection optical system becomes even shallower. As a result, it is necessary to perform automatic focusing by following not only the warpage of the mask but also the running accuracy of the X-Y table on which the mask is placed and the movement, and changes in vertical movement due to vibrations during running. The frequency of these displacements is much higher than the frequency due to warpage of the mask, and it is impossible to track them with the above-mentioned automatic focusing mechanism. For this reason, it has been difficult for conventional devices to accurately inspect defects in patterns with narrow line widths, such as in LSIs.

Therefore, the present inventors first proposed a pattern inspection device equipped with a positional deviation detection mechanism that optically detects the positional deviation between the inspected surface of the sample and the detection optical system (Japanese Patent Application No. 57-460
No. 50). The positional deviation detection mechanism of this device focuses the light beam from the light beam generation source 1 and the optical detection element for detecting the positional deviation on the surface to be inspected of the sample, and makes the light beam incident on the surface to be inspected at a predetermined level. It consists of an optical system that emits light at a corner and forms an image of the reflected light on the light receiving surface of the photodetecting element. By using this optical positional deviation detection mechanism, it becomes possible to correct the positional deviation of the surface to be inspected with high precision and good responsiveness.

However, this type of device has caused the following problems. That is, in the optical positional deviation detection mechanism, accurate positional deviation detection may become difficult due to the influence of light other than the amount of light used for positional deviation detection, especially disturbance light that does not have a negative distribution intensity. . In the above example, the light used for pattern inspection is irradiated at the same position as the light used for positional deviation detection, and the intense light used for pattern inspection is diffusely reflected by the presence or absence of a pattern and by the pattern edges. This may enter the positional deviation detection mechanism, resulting in a measurement error in positional deviation detection. In order to avoid this problem, there is a method in which the wavelengths of the light used for pattern inspection and the light used for positional deviation detection are different, and the sensors are selected accordingly to prevent interference between pattern inspection and positional deviation detection. However, it was far from perfect.

Note that the above-mentioned problem is not limited to detecting defects in patterns, but also applies to various pattern inspection apparatuses that measure or observe the dimensions of patterns.

(Issue 8 to be solved by the invention) As described above, in conventional pattern inspection devices, it is difficult to automatically align the detection surface of the sample with the focal position of the detection optical system with high frequency response, and , it was not possible to inspect defects in patterns with high precision.

This invention was developed in consideration of the above-mentioned problems of the present invention, and it is possible to automatically align the detection surface of the sample with the focal position of the detection optical system with high precision and high frequency response, and to eliminate defects such as minute patterns. It is an object of the present invention to provide a pattern inspection device that can perform inspection with high accuracy.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention irradiates the surface of the sample to be inspected with first light and collects information contained in the transmitted light or reflected light. In a pattern inspection apparatus for inspecting a pattern on a surface to be inspected, an optical lens barrel provided along the optical axis direction of the first light and having a detection means for pattern inspection attached thereto; an elastic member that supports the optical lens barrel movably in the optical axis direction of the first light at a free end; and an elastic member that is connected between the optical lens barrel and the fixed part and balances the weight of the optical lens barrel. a counter spring connected to the optical lens barrel and the fixed part for driving the optical lens barrel to move in the optical axis direction of the first light; Positional deviation in which a second light is irradiated at an incident angle and at a position different from the irradiation area of the first light, and the reflected light is detected to detect a deviation between a desired position and an actual position of the surface to be inspected. It is characterized by comprising a detection mechanism and a control means for controlling the amount of movement of the optical lens barrel by the drive means based on the detection information of the positional deviation detection mechanism.

(Function) The first feature of the structure described above is that a counter spring is provided, and the second feature is that the first light used for pattern inspection and the detection of positional deviation are used. The reason is that the irradiation area with the second light provided is shifted.

By providing the counterspring, which is the first feature of the present invention, it is possible to reduce the load applied to the drive member, thereby allowing the drive member to move the optical lens barrel at high speed. .

In addition, by shifting the irradiation areas of the position detection light and the pattern inspection light, which is the second feature, it is possible to reduce measurement errors in position shift detection due to mutual interference of light, disturbance, etc.

By employing the above image configuration, it becomes possible to automatically align the surface to be inspected of the sample, which is the object of the present invention, with the focal position of the detection optical system with high precision and high frequency response.

(Embodiment) FIG. 1 is a schematic configuration diagram showing a pattern defect inspection apparatus according to an embodiment of the present invention. In the figure, 21 is a reticle (sample), and this reticle 21 is placed on an XY table (not shown) with its surface to be inspected facing down. A light source 22 is arranged above the reticle 2 , and light from the light source 22 is focused through a condenser lens 23 and irradiated onto the reticle 21 . The light transmitted through the reticle 21 is transmitted through objective lenses 25a and 25b provided at the top of the optical barrel 24.
, 25c, an image is formed on the light receiving surface of the pattern inspection photodetector element 26 provided at the lower part of the optical barrel 24. By comparing the pattern information obtained by this photodetecting element 26 with the designed pattern information, the presence or absence of pattern defects is inspected.

The optical lens barrel 24 is fixed to a fixing part 29 via elastic members 27 and 28 arranged to form parallel springs. The elastic members 27 and 28 are provided by perforating desired portions of the disc body axially symmetrically, as shown in the plan view and the cross section taken along arrow A-A in FIGS. 2(a) and 2(b), respectively. This allows the optical barrel 24 to move only in the optical axis direction (vertical direction).

Further, a counterspring 30 and a drive member 31, which are the first feature of the present invention, are connected between the optical barrel 24 and the fixed part 29, respectively. counter spring 3
0 supports the optical lens barrel 24 and balances the weight of this lens barrel 24. The drive member 31 is made of an element having a piezoelectric effect, such as a piezo element made of lead zirconate titanate porcelain, so it expands and contracts when a voltage is applied by the drive circuit 32, thereby causing the optical barrel 24 to move up and down. It is something that can be moved. In addition, 33°34.3 in Figure 1
5.36 connects the elastic members 27 and 28 to the optical lens barrel 24, respectively.
and a fixing member for fixing to the fixing part 29, and the fixing members 33 to 36 are each fixed to the optical lens barrel 24 or the fixing part 29 by bolts (not shown).

Further, a light emitting power source 41 is provided on the left side of the optical barrel 24.
A light emitting element (light beam generation source) 42 driven to emit light by
is installed. The light from this light emitting element 42 is
The beam becomes a focused beam and is irradiated onto the surface of the reticle 21 to be inspected via the beam benders 43a, 43b and the lens 44a.

The reflected light from the inspection surface of the reticle 21 is transmitted to the beam bender 4.
3c, 43d and the lens 44b, the optical barrel 24
The image is formed on the light-receiving surface of a light-receiving element (photo-detecting element for positional deviation detection) 45 attached to the right side of the image. Here, the light from the light emitting element 42 is irradiated onto a position 52 on the surface to be inspected of the sample 21, which is slightly shifted from the irradiation area 51 of the light from the light source 22, as shown in FIG. . Shifting the irradiation area in this way is the second feature of the present invention. That is, a detection optical system consisting of beam benders 43a, 43b, lens 44a, etc., beam bender 43c,
43d and a detection optical system including a lens 44b and the like are arranged slightly shifted from opposing positions symmetrical about the central axis of the lens barrel 24. The irradiation position 52 of the light from the light emitting element 42 is shifted from the irradiation area 51 of the light from the light source 22 in a direction perpendicular to the facing direction of each detection optical system. The light receiving element 45 is composed of, for example, a two-part photodiode, and the surface to be inspected of the sample 21 is located at a desired position, that is, the objective lens 25a.

It is positioned so that a spot of reflected light is imaged at the center when it is at the focal point of the optical system consisting of 25c to 25c, the photodetector 26, and the like.

The two outputs of the light receiving element 45 are supplied to a division circuit 48 via a subtraction circuit 46 and an addition circuit 47, respectively. The output of this divider circuit 48 is determined by the sample 21 regardless of changes in the luminous intensity of the light emitting element 42 or changes in the transmittance or emissivity of optical elements in the optical path. This corresponds to the vertical movement of the surface to be inspected. Then, the output of the division circuit 48, that is, the positional deviation information is transmitted to the drive circuit 32.
The amount of movement of the optical lens barrel 24 is thereby controlled. Note that the vertical positional deviation that occurs due to the difference between the positional deviation detection position and the pattern inspection position is 0.5 when the warpage of the sample 21 is within several [mm].
This value is less than [μm] and can be ignored.

Here, when the surface to be inspected of the sample 21 is at the focal point of the optical system, a spot is imaged at the center of the light receiving element 45 as described above, so the output of the subtraction circuit 46 becomes zero.

Therefore, the output of the divider circuit 48 also becomes zero, and the optical lens barrel 24
is not moved.

On the other hand, if the surface to be inspected of the sample 21 deviates from the focal position of the optical system, for example, if it is displaced downward from the focal position, the spot imaged on the light receiving element 45 will shift downward from the central part. . Therefore, the output of the subtraction circuit 46 becomes positive or negative and is applied to the drive circuit 32 via the division circuit 48. Then, a voltage is applied by the drive circuit 32 in a direction that causes the drive member 31 to extend. As a result, the light source barrel 24 moves upward, and as a result, the positional deviation of the surface to be inspected is corrected. Furthermore, if the surface to be inspected of the sample 21 deviates downward from the focal point position of the optical system, the operation will be reversed to that described above, and the positional deviation will be automatically corrected.

By providing the counterspring, which is the first feature of the present invention, it is possible to reduce the load applied to the drive member, thereby allowing the drive member to move the optical lens barrel at high speed. Ru.

Furthermore, by shifting the irradiation areas of the light for position detection and the light for button inspection, which is the second feature, it is possible to reduce measurement errors in detecting positional deviation due to mutual interference of light, disturbance, etc.

By employing the above image configuration, it becomes possible to automatically align the surface to be inspected of the sample, which is the object of the present invention, with the focal position of the detection optical system with high precision and high frequency response.

In this way, in this apparatus, the reticle 21 is moved with the surface to be inspected of the reticle 21 always aligned with the focal position of the detection optical system.
can be inspected for pattern defects. In this case, a piezo element (minimum displacement of 50 people, response frequency of 5 kHz
Since the optical lens barrel 24 is moved by the elastic deformation of the elastic members 27 and 28, high resolution and high response frequency can be obtained. In reality, the minimum resolution is 0.
1 [μm] and a response frequency of 300 [Hz]. Moreover, since the irradiation position 52 of the light from the light emitting element 42 is slightly shifted from the irradiation area 51 of the light from the light source 22, measurement errors in positional deviation detection occur due to the influence of the light used for pattern inspection. It is possible to reliably eliminate such inconveniences. In addition, since the optical barrel 24 is supported by elastic members 27 and 28 arranged to form parallel springs, the lateral rigidity is high, and the optical barrel 24
Even when the optical lens barrel 24 is moved up and down, there is no problem such as tilting of the optical lens barrel 24. Furthermore, since the weight of the optical lens barrel 24 is supported by the counterspring 30, the load applied to the drive member 31 can be reduced. Further, the light emitting element 42. Since the positional deviation detection mechanism consisting of the light receiving element 45, lenses 44a, 44b, beam benders 43a, . can be made smaller, which has the effect of improving positional deviation detection accuracy.

Note that the present invention is not limited to the embodiments described above. For example, the irradiation position of the light used for positional deviation detection may be shifted along the direction facing the detection optical system, as shown in FIGS. 4 and 5. Furthermore, the irradiation position of the light used for positional deviation detection is not limited to one location, but the irradiation position is set to two locations sandwiching the irradiation area of the light used for the pattern inspection, as shown in FIG. However, the positional shift may be detected by averaging the reflected light from each irradiation position. In this case, it is possible to further reduce the vertical positional deviation due to the difference between the pattern inspection position and the positional deviation detection position. Similarly, the irradiation positions of light used for positional deviation detection can be set to three or more locations.

Further, the configuration of the positional deviation detection mechanism is not necessarily limited to the embodiment, and can be changed as appropriate according to specifications. Furthermore, it goes without saying that the positional deviation correction mechanism can also be changed as appropriate depending on the specifications. In addition to the pattern defect inspection apparatus, the present invention can be applied to various pattern inspection apparatuses used for pattern dimension measurement, pattern observation, and the like. In short, the present invention can be implemented with various modifications without departing from the gist thereof.

[Effects of the Invention] As described in detail above, according to the present invention, it is possible to precisely align the surface to be inspected with the focal position of the detection optical system with high frequency response, thereby eliminating defects in fine patterns. etc. can be inspected with high precision.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing a pattern defect inspection device according to an embodiment of the present invention, and FIGS. 2(a) and 2(b) are a plan view and a cross-sectional view showing the shape of an elastic member used in the above embodiment device. , FIG. 3 is a plan view for explaining the operation of the above embodiment,
4 to 6 are diagrams for explaining modified examples, respectively, and FIG. 7 is a schematic configuration diagram showing a conventional device. 21... Reticle (sample), 22... Light source, 23-...
- Condensing lens, 24... Optical lens barrel, 25a, 25b. 25c...Objective lens, 26...Photodetection element for pattern inspection, 27.28...Elastic member, 29...Fixing part. 30... Counter spring, 31... Drive member. 32... Drive circuit, 42... Light emitting element, 43a, 4
3b. beam bender. 44b...Lens. 5... Light receiving element (light detecting element for detecting positional deviation) irradiation area. 2...Irradiation position.

Claims (3)

[Claims] (1) In a pattern inspection device that irradiates a surface to be inspected of a sample with first light and inspects a pattern on the surface to be inspected based on information contained in the transmitted light or reflected light, a pattern of the surface to be inspected is inspected along the optical axis direction of the first light. an elastic member having one end fixed to a fixed part and supporting the optical barrel movably in the optical axis direction of the first light at its free end; a counter spring connected between the optical barrel and the fixing part to balance the weight of the optical barrel; and a counter spring connected between the optical barrel and the fixing part to balance the weight of the optical barrel. a drive means for moving and driving the first light in the optical axis direction; irradiating the inspection surface with a second light at a predetermined angle of incidence and offset from the irradiation area of the first light; a positional deviation detection mechanism that detects the reflected light to detect a deviation between the desired position and the actual position of the surface to be inspected, and movement of the optical lens barrel by the drive means based on the detection information of the positional deviation detection mechanism. A pattern inspection device comprising: a control means for controlling an amount; and a pattern inspection device. (2) The irradiation area of the second light is outside the irradiation area of the first light and is irradiated in the vicinity of the irradiation area of the first light. The pattern inspection device according to item 1. (3) The optical lens barrel is formed in a cylindrical shape and has a threaded portion on its outer circumferential surface, and is disposed in a hollow portion of a fixing portion provided with a threaded portion on its inner circumferential surface, and the elastic member and one end of the driving means is fixed to the optical barrel by nuts screwed into the outer threaded portion, and the other ends of the elastic member and the driving means are fixed to the optical barrel by nuts screwed into the inner threaded portion. 2. The pattern inspection device according to claim 1, wherein the pattern inspection device is fixed to a fixed portion.