JP4174529B2 - Illumination device and pattern inspection device - Google Patents

Description

The present invention uses a coherent light source, lighting equipment for irradiating light to the illumination target such as a reticle,及 beauty, to a pattern inspection apparatus having a lighting device.

  In Koehler illumination, a configuration is generally adopted in which a light beam is divided by an optical integrator and these are superimposed on an irradiation target surface by a condenser lens. When a light source with high coherency such as a laser is used as a light source of such an illumination optical system, interference fringes are generated due to superposition of wavefronts on the surface of the irradiation target, and there is a problem that uniform illumination cannot be realized. For the purpose of reducing such interference fringes, the light emitted from the light source is divided into a plurality of regions, a detour optical path is formed by a mirror in each optical path, and after giving an optical path difference of more than a coherent distance, An optical system that reduces coherency by combining them has already been proposed (see Patent Document 1). Further, an optical system that realizes a similar bypass optical path with a high refractive index material has also been proposed (see Patent Document 2).

However, in order to increase the coherency reduction effect, it is necessary to increase the number of light beam divisions. However, when only a mirror is used, angle and alignment operations become difficult and productivity may be reduced. In the case of using only a high refractive index material, it is necessary to make the length long in order to give an optical path difference. In the case of an ultraviolet light source, light quantity loss or damage to the high refractive index material is likely to occur.
JP-A-11-344683 JP 2005-337851 A

(1) An object of the present invention is to enable uniform illumination using coherent light.
(2) Or this invention exists in reducing the interference by coherent light.
(3) Alternatively, an object of the present invention is to increase the number of split light beams of coherent light with a simple configuration.
(4) Alternatively, the present invention is to provide an apparatus that can be easily adjusted in an illumination apparatus or a pattern inspection apparatus using coherent light.

(1) The present invention includes a first dividing unit for dividing into a plurality by reflecting the light beam of coherent light, a plurality of first bypass optical path having an optical path difference greater than the coherence length to each other, a plurality in the first divided section Each of the divided light fluxes passes through each first bypass optical path, and is disposed in a part of at least one first bypass optical path, and causes an optical path difference that is equal to or greater than a coherent distance with other parts that are not disposed . An illumination apparatus includes an optical path difference forming material and a first combining unit that integrates a plurality of light beams that have passed through a plurality of first bypass optical paths, and irradiates the illumination target with the integrated light beams.
(2) In the pattern inspection apparatus for inspecting a mask pattern, the present invention provides a light source that outputs a light beam of coherent light, a first dividing unit that divides the light beam into a plurality of pieces by reflection,
In each of at least one first bypass optical path, each of a plurality of first bypass optical paths having optical path differences equal to or greater than a coherent distance and a light beam divided into a plurality by the first splitting unit passes through each first bypass optical path. An optical path difference-forming material that generates an optical path difference that is greater than or equal to a coherent distance with another part that is not disposed, and a plurality of light beams that have passed through the plurality of first bypass optical paths are integrated. A pattern inspection comprising: 1 composition unit; a mask having a pattern irradiated with an integrated light beam; a sensor that receives a pattern image; and a comparison unit that compares an image received by the sensor with a reference image In the device.

  Hereinafter, an illumination device, an illumination method, and a pattern inspection device according to an embodiment of the present invention will be described.

(Lighting device)
The illumination device is a device that irradiates light to an illumination object such as a reticle. The illumination device is used in, for example, a pattern inspection device that inspects a pattern of an inspection object such as a reticle, and an exposure device that forms a pattern on a semiconductor wafer or liquid crystal glass.

  FIG. 1 shows a block diagram of the illumination device 10. The illuminating device 10 includes a laser light source 12, a first optical system 16, a first dividing unit 18, a plurality of first bypass optical paths 20, an optical path difference forming material 22 disposed in the first bypass optical path 20, a first combining unit 24, A second optical system 26 is provided, and the illumination object 28 is irradiated with light. The laser light source 12 outputs a light beam 14 of coherent light. The first optical system 16 is an optical system that processes the light beam 14 output from the laser light source 12. For example, the first optical system 16 includes a collimator lens and expands the light beam 14. The first dividing unit 18 divides the light beam 14 into a plurality of light beams. The plurality of first bypass optical paths 20 cause an optical path difference (L) that is equal to or greater than the coherence distance (l) when light passes through each optical path. In the first bypass optical path 20, the optical path difference forming material 22 is disposed in a part of the optical path. An optical path difference (L) equal to or greater than the coherence distance is generated between the optical path where the optical path difference forming material 22 is arranged and the optical path where the optical path difference forming material 22 is not arranged. The first combining unit 24 is integrated with a plurality of light fluxes that have passed through the first bypass optical path 20, partially passed through the optical path difference forming material 22, and generated an optical path difference (L) that is equal to or greater than the coherence distance in a state before splitting. The combined light beam 140 is created. The second optical system 26 irradiates the illumination object 28 with light having an optical path difference (L) that is equal to or greater than the coherence distance, and is composed of, for example, an integrator or a condenser lens. The integrator mixes the synthesized light beam 140 using a fly-eye lens or the like. The condenser lens collects the mixed light and irradiates the illumination object 28 as an illumination light beam. In this way, the light beam of the coherence light can be divided, the coherency (coherence) can be reduced, mixed, and superimposed on the irradiation object surface.

  FIG. 2 shows a light beam 14 of coherence light, a first dividing unit 18, a plurality of first bypass optical paths 20, a first combining unit 24, a combined light beam 140, and the like. FIG. 2A shows a schematic diagram of the side surface of the first detour optical path 20. FIG. 2B shows a schematic cross-sectional view of the combined light beam 140 when the optical path is viewed from the right direction of FIG. The light beam 14 is split into first bypass optical paths 20a and 20b by the first splitting unit 18. The first bypass optical path 20b includes mirrors 30a and 30b that adjust the optical path length. For this reason, the first bypass optical path 20b has a longer optical path than the first bypass optical path 20a, and the optical path difference from the first bypass optical path 20a is longer than the coherent distance. Due to the arrangement of the mirrors 30a and 30b in FIG. 2, the first bypass optical path 20b has an optical path difference (2L) that is at least twice the coherence distance compared to the first bypass optical path 20a. The first dividing unit 18 may be any member as long as it is a member that can divide a light beam into a plurality of parts. For example, a mirror can be used. The end of the mirror is arranged in the middle of the light beam 14, and a part of the light beam 14 passes through the first bypass optical path 20a without being reflected, and the other light beam 14 passes through the first bypass optical path 20b.

  The optical path difference forming material 22 is disposed in a part of at least one of the first bypass optical paths 20a and 20b. In FIG. 2, the optical path difference forming members 22a and 22b are arranged in both the first bypass optical paths 20a and 20b. The optical path difference forming material 22 only needs to have an optical path difference (L) that is greater than or equal to the coherent distance between the optical path disposed in the first bypass optical path 20 and the optical path that is not disposed. As the optical path difference forming material 22, for example, if the first bypass optical path 20 is a space having a small refractive index such as vacuum or air, a transparent material having a large refractive index such as a quartz plate can be used. In that case, the shorter the optical path difference forming material 22 can be used as the refractive index increases.

  The plurality of light beams that have passed through the first bypass optical paths 20 a and 20 b are integrated by the first combining unit 24 to become a combined light beam 140. The cross section of the combined light beam 140 has divided regions 150a to 150d. The divided region 150a indicates a light beam that passes through the first bypass optical path 20a and does not pass through the optical path difference forming member 22a. Therefore, the light flux in the divided region 150a passes through the shortest optical path. The divided region 150b shows the light beam that has passed through the first bypass optical path 20a and has passed through the optical path difference forming member 22a. Therefore, the light flux in the divided region 150a propagates an extra optical path difference (L) longer than the coherence distance compared to the light flux in the divided region 150a by the amount that has passed through the optical path difference forming member 22a. The divided region 150c indicates a light beam that passes through the second bypass optical path 20b and does not pass through the optical path difference forming member 22b. Therefore, the light flux in the divided region 150c propagates an extra optical path difference (2L) that is at least twice the coherence distance compared to the light flux in the divided region 150a. The divided region 150d indicates a light beam that has passed through the second bypass optical path 20b and has passed through the optical path difference forming member 22b. Therefore, the light beam in the divided region 150d propagates an extra optical path difference (3L) longer than the coherence distance as compared with the light flux in the divided region 150a by the amount that has passed through the optical path difference forming material 22b. As described above, since the light beams in the optical path division regions 150a to 150d pass through optical paths having an optical path difference equal to or greater than the coherent distance, mutual interference is reduced. In addition, the 1st synthetic | combination part 24 should just be what can integrate a some light beam, for example, can use a mirror.

  In FIG. 2, the first bypass optical paths 20a and 20b are optical paths of a space by mirrors, and the optical path difference can be arbitrarily set by adjusting the angles and positions of the mirrors. Further, the optical path difference forming members 22a and 22b can easily set the optical path difference depending on the distance through which light passes and the refractive index. By combining these, adjustment of the number, position, and angle of the mirrors can be reduced, and a large number of divided regions 150a to 150d can be created with a simple configuration. In this way, the number of beam splits can be easily increased, the number of mirrors used can be reduced, the angle and alignment work is facilitated, and the amount of high refractive index material used can be reduced. Loss and damage to the high refractive index material can be reduced. Moreover, the light quantity of each light beam of the division | segmentation area | region 150a-150d can be equalized by changing the arrangement | positioning method of 1st division | segmentation part 20a, 20b and optical path difference forming material 22a, 22b. Thereby, the coherence of coherent light can be reduced more favorably.

(Lighting device with second bypass optical path)
3 and 4 show an example of the lighting device 10 that includes the second dividing unit 32, the second detour light path 34, and the second combining unit 38 in the lighting device 10 of FIGS. 1 and 2. FIG. 4A shows schematic side views of the side surfaces of the first bypass optical path 20 and the second bypass optical path 34. FIG. 4B shows a schematic cross-sectional view of the combined light beam 140 and the combined light beam 142 when the optical path is viewed from the right direction of FIG.

  In FIG. 4, the second dividing unit 32 divides the combined light beam 140 in a direction different from the dividing direction by the first dividing unit 18. That is, the second dividing unit 32 shows a state in which the light beam 140 is rotated at a predetermined rotation angle with respect to the first dividing unit 18 as a rotation axis. The predetermined rotation angle is, for example, 90 degrees. In this case, the first bypass optical path 20b in FIG. 4A is orthogonal to the second bypass optical path 34b. The cross section of the combined light beam 142 in FIG. 4B shows a state rotated 90 degrees to the left with respect to the combined light beam 140.

  The second dividing unit 32 in FIG. 4 divides the combined light beam 140 into a plurality of light beam dividing means such as a mirror. The divided light flux passes through the second bypass optical paths 34a and 34b. The second bypass optical path 34b includes mirrors 30c and 30d. The light beam passing through the second bypass optical path 34b is reflected by the mirrors 30c and 30d and reaches the second combining unit 38. By adjusting the arrangement of the mirrors 30c and 30d, the optical path difference between the second bypass optical paths 34a and 34b can be arbitrarily set. In FIG. 4, the optical path difference is 4L. In the second combining unit 38, the light beams that have passed through the second detour optical paths 34a and 34b are integrated to create a combined light beam 142. In this way, by setting the optical path difference between the second detour optical paths 34a and 34b to 4L, the divided areas 150a to 150d of the combined light beam 140 become the divided areas 152a to 152h of the combined light beam 142, and the divided area is doubled. Can be increased. The divided region 152b of the combined light beam 142 has an optical path difference (L) that is greater than or equal to the coherent distance (l) with respect to the divided region 152a. Similarly, the divided regions 152c to 152h have an optical path difference (2L to 7L) that is equal to or greater than the coherence distance with respect to the divided region 152a. Thus, the light beam 14 of coherent light has a large number of divided regions with low coherence, and the coherence can be reduced as a whole. Although not shown, if the optical path difference forming material 22 is arranged in the second bypass optical paths 34a and 34b in the same manner as the first bypass optical paths 20a and 20b, more divided regions can be created.

  FIG. 5 shows the second dividing units 32a, 32b, and 32c, the second bypass optical paths 34a, 34b, 34c, and 34d, and the second combining units 38a, 38b, and 38c. The light beam 140 is split into two light beams that pass through the second bypass optical path 34a and the second bypass optical paths 34b to 34d by the second splitting unit 32a. The second dividing unit 32b divides the light into two light beams that pass through the second bypass optical path 34b and the second bypass optical paths 34c to 34d. The second dividing unit 32c divides the light into two light beams that pass through the second bypass optical path 34c and the second bypass optical path 34d. The second detour optical path 34d includes mirrors 30c and 30d, and guides the light beam to the second combining unit 38c. The second combining unit 38c combines the light fluxes of the second bypass optical paths 34c and 34d. The second combining unit 38b combines the light fluxes of the second detour optical paths 34c and 34d and the light flux of the second detour optical path 34b. The second combining unit 38a combines the light fluxes of the second bypass optical paths 34b to 34d and the light flux of the second bypass optical path 34a. In this way, the light beam divided by the second splitting unit 32 is integrally combined by the second combining unit 38 to form a combined light beam 144. The second dividing unit 32 and the second combining unit 38 may be any one as long as they divide and combine the light beams. For example, a mirror can be used. The optical path difference between the second detour optical paths 34a, 34b, 34c, and 34d can be arbitrarily set by adjusting the arrangement of the mirrors and the angle. In FIG. 5, each optical path difference is 4L.

  In FIG. 5B, a light beam 144 is a diagram obtained by rotating the light beam 140 90 degrees to the left. The four divided regions 150a to 150d obtained by the first bypass optical path 20 in FIG. 5 become 16 divided regions 154a to 154p by the second bypass optical path 34. The optical paths through which the light fluxes of the divided areas have passed become optical path differences (L), and the optical paths of the divided areas 154a to 154p have optical path differences (L to 15L) with respect to the divided areas 154a.

FIG. 6 shows an increase in the number of bypass optical paths from two to four in the first bypass optical path 20 of the illumination device 10 of FIG. The first dividing unit 18 includes dividing units 18a to 18c, and the plurality of first bypass optical paths 20 includes four first bypass optical paths 20a to 20d, and the first combining unit 24 combines the combining units 24a to 24d. I have. Each optical path difference of the first bypass optical paths 20a to 20d can be set to an arbitrary value by the arrangement of the first dividing unit 18, the mirrors 30a and 30b, and the first combining unit 24. In FIG. 6, the optical path difference is 2L. . Optical path difference forming materials 22a to 22d are disposed in the first bypass optical paths 20a to 20d, respectively. The combined light beam 146 is divided into eight divided regions 156a to 156h. The optical paths of the divided areas 156b to 156h are optical path differences (L to 7L) with respect to the divided area 156a. The second detour optical path 34 in FIG. 6 further divides the combined light beam 146 into four parts, resulting in 32 divided regions 158a to 158z, 158z1,. The optical path through which the luminous flux of each divided region has passed becomes an optical path difference (L), and the optical path of the divided region has an optical path difference (L to 31L) with respect to the divided region 158a.

(Lighting method)
FIG. 7 shows a method of irradiating the illumination object 28 with illumination light. A laser light source 12 outputs a light beam 14 of coherent light. The light beam 14 is magnified by the first optical system 16. The expanded light beam 14 is divided into a plurality of divided regions by the dividing unit 18 (first dividing step S10). The plurality of divided light beams pass through a first bypass optical path having an optical path difference (L) that is equal to or greater than the coherence distance (l), thereby reducing the coherence (first bypass step S11). In the first detour step S11, the divided light beams pass through the optical path where the optical path difference forming material 22 is disposed and the optical path where the optical path difference forming material 22 is not disposed, and the mutual coherence is further weakened (first optical path difference forming step S111). ). The plurality of light beams that have passed through the optical path having an optical path difference equal to or greater than the coherence distance are combined by the first combining unit 24 to become an integrated combined light beam (first combining step S12). In the case of the illuminating device 10 of FIG. 1, the combined light flux is mixed and superimposed through the second optical system 36 and is irradiated onto the illumination object 28 as illumination light.

  In the case of the illuminating device 10 of FIG. 3, the combined light flux is again divided into a plurality of parts (second division step S13). In the second dividing step S13, the combined light beam 140 is divided in a direction different from the dividing direction in the first dividing step. In other words, the second division step S13 rotates at a predetermined rotation angle with the combined light beam 140 as the rotation axis with respect to the first division step. The predetermined rotation angle is, for example, 90 degrees. The plurality of light beams divided in the second division step S13 pass through an optical path having an optical path difference equal to or greater than the coherence distance (second detour step S14). In the second detour step S14, the divided light beams pass through the optical path where the optical path difference forming material 22 is disposed and the optical path where the optical path difference forming member 22 is not disposed as necessary, and the mutual coherence is further weakened (second). Optical path difference forming step S141). In the second optical path difference forming step S141, an optical path difference L that is longer than the coherence distance can be given. The plurality of light beams that have passed through the optical path having an optical path difference equal to or greater than the coherence distance are combined by the second combining unit 38 to become an integrated combined light beam (second combining step S15). The combined luminous flux is mixed through the second optical system 26, superimposed, and irradiated onto the illumination object 28. By taking each step (S10 to S15) as described above, the coherent light can be changed to illumination light with low coherence.

(Pattern inspection device)
FIG. 8 shows a pattern inspection apparatus 50 including the illumination device 10. The pattern inspection apparatus 50 inspects a pattern defect of an inspection object having a mask pattern such as a reticle. The pattern inspection apparatus 50 includes a comparison unit 66 that compares the illumination device 10, the mask 52, the objective optical system 54, the sensor 56, the pattern image 58 with the reference image 64, and detects a defect. The mask 52 is mounted on a mounting table such as an XYθ table that can be moved and is the irradiation object 28 of the illumination device 10. The objective optical system 54 is an enlargement optical system that projects a mask pattern onto the light receiving area of the sensor 56. The sensor 56 receives a mask pattern such as a photodiode array or a CCD camera and electrically acquires a pattern image. The pattern image 58 is stored in the memory. The reference image 64 is created as an image similar to the pattern image 58 by developing the CAD data 60 by the data developing unit 62. Alternatively, as the reference image 64, the pattern image 58 can be used as a reference. The pattern inspection apparatus 50 includes a control system device such as a computer and an optical image acquisition device. The control system device controls the optical image acquisition device to acquire a pattern image, creates a reference image 64, stores it in a memory, compares the pattern image 58 with the reference image 64 by the comparison unit 66, and Defects can be detected.

Block diagram of lighting device Optical path diagram of illumination device and sectional view of luminous flux Block diagram of lighting apparatus having second bypass optical path Optical path diagram and cross-sectional view of luminous flux of lighting device having second detour optical path Optical path diagram and sectional view of luminous flux of another illumination device having the second bypass optical path Optical path diagram and sectional view of luminous flux of another illumination device having the second bypass optical path Flow chart of the method of irradiating illumination objects with irradiation light Block diagram of pattern inspection equipment

Explanation of symbols

10 .. Illumination device 12 .. Laser light source 14. Coherent light beam 140 to 148. Composite light beam 150 to 158. Combined light beam splitting region 16... First optical system 18. 1 detour optical path 22 .. optical path difference forming material 24 .. first synthesis unit 26 .. second optical system 28 .. illumination object 30 .. mirror 32 .. second division unit 34 .. second detour optical path 36. · Second optical path difference forming material 38 · · second synthesis unit 50 · · pattern inspection device 52 · · mask 54 · · objective optical system 56 · · sensor 58 · · pattern image 60 · · CAD data 62 · · data development unit 64..Reference image 66..Comparison part

Claims (4)

A first dividing unit that divides a light beam of coherent light into a plurality of pieces by reflection;
A plurality of first bypass optical path having an optical path difference greater than the coherence length to each other,
Each of the light beams divided into a plurality by the first dividing unit passes through each first detour optical path, and is disposed in a part in at least one first detour optical path, and a coherent distance with other parts not arranged. An optical path difference forming material that causes the above optical path difference;
A first combining unit that integrates a plurality of light beams that have passed through the plurality of first bypass optical paths,
An illumination device that irradiates an illumination object with an integrated light beam. The lighting device according to claim 1.
A second splitting unit that splits the luminous flux integrated in the first combining unit into a plurality of parts;
A plurality of second bypass optical path having an optical path difference greater than the coherence length to each other,
A second combining unit that integrates the light flux that has passed through the second bypass optical path,
The first dividing unit bends a part of the light beam of the coherent light in one direction to form a part of the first bypass optical path, and the second dividing unit converts a part of the light beam integrated by the first combining unit. Illuminating the object to be illuminated with the light beam integrated by the second synthesis unit by bending in a direction different from one direction of the light beam bent by the first splitting unit to form a part of the second bypass optical path apparatus. The lighting device according to claim 1.
An illumination device comprising an optical integrator and a condenser lens arranged in an optical path in front of an illumination object. In a pattern inspection apparatus for inspecting a mask pattern,
A light source that outputs a light beam of coherent light;
A first dividing unit that divides the luminous flux into a plurality of parts by reflection;
A plurality of first bypass optical path having an optical path difference greater than the coherence length to each other,
Each of the light beams divided into a plurality by the first dividing unit passes through each first detour optical path, and is disposed in a part in at least one first detour optical path, and a coherent distance with other parts not arranged. An optical path difference forming material that causes the above optical path difference;
A first combining unit that integrates a plurality of light beams that have passed through a plurality of first bypass optical paths;
A mask having a pattern irradiated with an integrated light beam;
A sensor for receiving a pattern image;
A pattern inspection apparatus comprising: a comparison unit that compares an image received by a sensor with a reference image.

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