JPH0569300B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a foreign matter inspection device that detects foreign matter such as dust attached to the surface of a photomask or reticle used in a semiconductor manufacturing process by irradiating a scanning beam.

Note that in this specification, a "reticle" includes a "photomask," and the explanation using a reticle as an example can be similarly applied to a photomask.

[Background of the Invention] Generally, in the IC manufacturing process, a method is adopted in which the exposure pattern of a reticle is transferred onto a semiconductor wafer coated with resist using a projection optical system of a semiconductor printing device (stepper or mask aligner). There is.

When a pattern is transferred from a reticle to a wafer coated with resist using semiconductor printing equipment, if defects such as dust adhere to the reticle surface, the shape of the defect will be printed in addition to the original reticle pattern, resulting in the IC being printed. This causes a decrease in manufacturing yield.

In particular, "steppers" print multiple desired reticle patterns onto wafers using step-and-repeat techniques.
When using this method, one piece of dust on the reticle will be printed onto the entire surface of the wafer.

Therefore, in recent years, it has become essential to accurately detect dust on a reticle. Furthermore, shortening of inspection time is required to improve yield.

[Prior Art] FIG. 7 shows the configuration of a conventional foreign matter inspection device for detecting foreign matter such as dust on a reticle. A laser beam 3 from a laser light source (not shown) irradiates the reticle 1 along a predetermined scanning line via a scanning light source system 2 consisting of a rotating mirror or the like.
When inspecting the top surface (pattern back surface) 1a of the reticle 1, the scanning beam 3 is reflected by mirrors 14 and 15 to irradiate the top surface 1a of the reticle. The reflected and scattered light of the scanning beam 3 is detected by a photodetector 17a via a condensing lens 6a, and any foreign matter is detected. Lower surface of reticle 1 (pattern forming surface) 1
When inspecting b, the position of the mirror 14 is changed to remove it from the optical path of the scanning beam 3, and the scanning optical system 2
The lower surface 1b of the reticle is irradiated with the scanning beam 3 through the mirror 18. 6b is a condensing lens,
17b is a photodetector.

[Problems with the prior art] In such a conventional foreign matter inspection device, in order to inspect the pattern forming surface 1b and the back surface 1a of the reticle, the mirror 14 must be switched and each surface must be inspected separately. It took a lot of time.

[Object of the Invention] The present invention has been made in view of the drawbacks of the prior art described above, and an object of the present invention is to provide a foreign object inspection device that has a simple structure, shortens inspection time, and can obtain highly reliable detection results. do.

[Example] The present invention will be described below based on an example shown in the drawings. In FIG. 1, the reticle 1 is held by a support device (reticle stage), not shown, with the pattern back surface 1a facing upward and the pattern forming surface 1b facing downward. On the upper surface side of the reticle 1, a pattern backside illumination mirror 5 and a pattern backside detection light receiving system 30 are installed. The light receiving system 30 includes a condenser lens 6a, an aperture 7a, an optical fiber 8a, and a light sensor 9a such as a photomultiplier tube or a semiconductor light receiving element. Similarly, on the lower surface side of the reticle 1, a pattern forming surface irradiation mirror 10 and a pattern forming surface detecting light receiving system 31 are arranged. Like the light receiving system 30, the light receiving system 31 includes a condenser lens 6b, an aperture 7b, an optical fiber 8b, and an optical sensor 9b. Reference numeral 2 denotes a scanning optical system, which is composed of a rotating mirror (not shown) and the like. A laser beam from a laser light source (not shown) passes through the scanning optical system 2 and scans the reticle scanning surface as a scanning beam 3 in a direction perpendicular to the drawing. A half mirror 4 is provided on the optical path of the scanning beam 3 from the scanning optical system 2. The scanning beam 3 is divided into two by this half mirror 4, and each mirror 5 and 10 scans the back surface 1a of the reticle 1.
and pattern forming surface 1b are simultaneously irradiated. At this time, the irradiation point P on the back surface 1a and the pattern forming surface 1
The mirrors 5 and 10 and the half mirror 4 are arranged so that the irradiation points Q in b are shifted from each other and irradiate different positions on the reticle 1. The optical path length of each divided scanning beam is determined so that it is focused on each inspection surface, and mirrors 5, 10 and half mirror 4 are set so that the optical path lengths of both divided beams are equal. Placed.

When inspecting the surface of a reticle, the scanning optical system 2
The scanning beam 3 from the reticle 1 is divided into two by a half mirror 4, and scans while simultaneously irradiating positions P and Q separated by an appropriate distance on both the back surface 1a and pattern forming surface 1b of the reticle 1. When dust 19 is attached to point P, the scanning beam that irradiates this dust 19 is diffusely reflected and scattered all over the surrounding area, and a part of the scattered light is focused by the condensing lens 6a and passes through the aperture 7.
a, and is guided to an optical sensor 9a by an optical fiber 8a and detected. Aperture 7 of each light receiving system 30, 31
a, 7b are arranged near the condensing positions of the condensing lenses 6a, 6b in each system, so each light receiving system 30,
31 does not receive the reflected and scattered light from the scanning beam irradiating the opposite surface, but only receives the reflected and scattered light from the scanning beam on the side where each system is disposed. Therefore, the scattered light from the dust 19 is not detected by the optical sensor 9b of the light receiving system 31 on the reflective surface.

The function of the apertures 7a and 7b will be further explained using FIG. 2. The scanning beam 3 that illuminates the back surface 1a of the reticle 1 is partially scattered on the reticle surface, and a portion of it is focused by the condenser lens 6a as shown by the solid line, converging near the slit 40 of the aperture 7a, and passing through this slit 40. do. On the other hand, scanning beam 3
The remaining beam that was not scattered passes through the reticle 1 and is reflected and scattered by a pattern (not shown) on the pattern forming surface 1b on the opposite side or by dust, and a part of it is reflected by the condenser lens 6a as shown by the dotted line.
The light is focused by However, this scattered light (dotted line) from the pattern forming surface 1b is focused in a direction away from the slit 40 of the aperture 7a, is blocked by the aperture 7a, and is not detected by the optical sensor 9a. In this way, the optical axis of the scanning beam 3 and the light receiving system 30 are arranged so as to block scattered light other than the reflected and scattered light to be detected.
is placed at a predetermined angle with the optical axis (dotted chain line) of
The focal point of the condenser lens, the size and position of the slit of the diaphragm, etc. are set in advance at appropriate positions. The same applies to the light receiving system 31 on the opposite side. Note that the condenser lenses 6a and 6b are arranged so as to avoid the direction in which non-scattered light is transmitted or reflected by the reticle 1.

FIG. 3 shows the configuration of another embodiment of the present invention. In this embodiment, a beam 3 is divided into two by a half mirror 2.
In this example, both surfaces of the reticle are irradiated perpendicularly by mirrors 5 and 10, respectively. A transparent parallel plane plate 11 is disposed between the half mirror 4 and one of the mirrors 10 in order to equalize the optical distances of the two time-divided beams to each irradiation surface. In addition, the light receiving system is made more compact by focusing the light using gradient index lens arrays 12a and 12b such as Self-Occupling Lens Array (trade name). A cylindrical lens, a bar lens, or the like may be used instead of the self-occurring lens array (trade name). Other configurations, operations, and effects are similar to those of the previous embodiment.

FIG. 4 shows the configuration of yet another embodiment of the present invention. In this embodiment, a half mirror 20 is provided between two mirrors 5 and 13, and the same surface of the reticle 1 (pattern back surface 1a in this example) is scanned with two scanning beams. Half mirror 20 and mirrors 5 and 13 are arranged so that the optical path lengths of the two divided scanning beams are equal. 22 and 23 are light receiving systems, which are provided corresponding to each scanning beam. Light receiving system 22, 2
3 is similar to the structure of the embodiment shown in FIG. 1 or 3.

FIG. 5 shows a modification of the embodiment shown in FIG. In this example, a transparent parallel plane plate 21 is provided as the optical path length correction means for the two divided scanning beams, similar to the embodiment shown in FIG. The rest of the structure is the same as the embodiment shown in FIG.

In addition, the irradiation angle of the scanning beam to the inspection surface,
The distance between the irradiation positions of the two scanning beams, etc. can be adjusted by changing the position of each optical element such as a half mirror, mirror-parallel plane, etc. Further, the optical path length may be corrected by using a prism instead of the parallel plane plate.
When a prism is used, it is also possible to control the irradiation angle.

FIG. 6 shows yet another embodiment of the invention. In this embodiment, a pellicle 24a is provided on both sides of the reticle 1.
24b shows a foreign matter inspection device for inspecting the surface of a reticle with a pellicle attached thereto. The divided scanning beam inspects the reticle surface (pattern back surface 1a and pattern forming surface 1b), and also receives reflected light from the pellicle surface to inspect the pellicle surface. Therefore, the light receiving system 30 for inspecting the reticle surface,
Light receiving system 32, 3 for other pellicle surface inspection of 31
It is equipped with 3. The configurations of these light receiving systems 32 and 33 are the same as those of the light receiving systems 30 and 31, and include condenser lens arrays 112a and 112b, and an aperture 107.
a, 107b, optical fibers 108a, 108b, and optical sensors 109a, 109b. In this case, the apertures 7a, 107a,
By appropriately forming 7b and 107b, interference of scattered light to be received by adjacent light receiving systems 30, 32 and 31, 33 is suppressed, crosstalk between inspection surfaces is prevented, and foreign matter on each inspection surface is ensured. detected.

[Effects of the Invention] As explained above, by simultaneously irradiating the substrate surface with a plurality of beams with equal optical path lengths,
It is now possible to irradiate each irradiation section with the same irradiation state, suppressing variations in foreign object inspection at each irradiation section, and allowing rapid and accurate foreign object inspection.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is an explanatory diagram of the function of the aperture used in the present invention, Fig. 3 is a block diagram of another embodiment of the present invention, and Fig. 4 is a block diagram of another embodiment of the present invention. FIG. 5 is a configuration diagram of a modification of the embodiment shown in FIG. 4, FIG. 6 is a configuration diagram of yet another embodiment of the present invention, and FIG. 7 is a conventional foreign object inspection device. FIG. 1...Reticle, 2...Scanning optical system, 3...Scanning beam, 4,20...Half mirror, 5,1
0, 13...Mirror, 6a, 6b, 106a, 1
06b...Condensing lens, 7a, 7b, 107a,
107b...Aperture, 9a, 9b, 109a, 10
9b... Optical sensor.

Claims (1)

[Claims] 1. The scanning beam from the scanning optical system is divided into a plurality of scanning beams, and the optical path lengths of the plurality of scanning beams until they are incident on the substrate to be inspected are made equal to each other, so that the plurality of scanning beams are simultaneously applied. A foreign object inspection characterized by having a beam split irradiation means for irradiating the test substrate, and a plurality of light detection means for separately detecting the reflected light from the irradiation part of each scanning beam on the test board. Device. 2. The foreign matter inspection apparatus according to claim 1, wherein the beam division irradiation means divides the scanning beam so as to irradiate both sides of the substrate. 3. The foreign matter inspection apparatus according to claim 1, wherein the beam division irradiation means divides the scanning beam so as to irradiate different positions on the same surface of the substrate. 4. The beam split irradiation means comprises a half mirror and a mirror for reflecting the beam split by the half mirror and irradiating the substrate surface.
Foreign matter inspection device according to any one of the preceding paragraphs. 5. Any one of claims 1 to 4, characterized in that an optical path length correction means for equalizing the optical path length of each scanning beam is provided on the optical path of the divided scanning beams. foreign matter inspection equipment. 6. The foreign matter inspection apparatus according to claim 5, wherein the optical path length correction means comprises a transparent parallel plane plate. 7. The foreign matter inspection apparatus according to claim 5, wherein the optical path length correction means is comprised of a prism. 8. Any one of claims 1 to 7, wherein the light detection means has an aperture means for blocking reflected light from other than the irradiation part to be detected by the light detection means. Foreign matter inspection device according to item 1.