WO2024062563A1

WO2024062563A1 - Lighting optical device and inspection device

Info

Publication number: WO2024062563A1
Application number: PCT/JP2022/035197
Authority: WO
Inventors: 公則田村; 明宏岩松; 俊一松本
Original assignee: 株式会社日立ハイテク
Priority date: 2022-09-21
Filing date: 2022-09-21
Publication date: 2024-03-28

Abstract

In substrate inspection devices, the size of defects and foreign matter which need to be detected has decreased, and use of a high-power deep ultraviolet laser light source to form a beam spot with high precision has increased detection sensitivity. Thus, there is a need to further increase the stability of size and position of a beam spot. Furthermore, it is important that variations in focus position does are not caused when there is a change in ambient temperature during device operation. To this end, provided is a lighting optical system that flexibly changes the beam spot diameter of lighting light in accordance with inspection conditions and stage movement, while also maintaining high-precision focus performance which can handle changes in ambient temperature. More specifically, suppression of variations in focus position is made possible by optimizing the arrangement and materials of an optical element of a transparent optical system constituting a device (see fig. 1).

Description

Illumination optical equipment and inspection equipment

The present invention relates to an illumination optical device and an inspection device.

The illumination optical system and substrate inspection device are used to detect foreign objects on the object to be inspected by irradiating the surface of the object with light and detecting the reflected or scattered light from the object.

In manufacturing lines for semiconductor substrates, thin film substrates, etc., defects present on the surfaces of semiconductor substrates, thin film substrates, etc. are inspected in order to maintain or improve product yield. Inspection for defects can be performed using an inspection device.

Regarding an illumination optical device used in an inspection device, Patent Document 1 addresses the problem of wanting to flexibly change the beam spot diameter in the longitudinal direction according to inspection conditions and stage operation while maintaining the focus of the beam spot. It is disclosed that the beam spot is controlled in the longitudinal direction using a condensing optical system including a cylindrical parabolic mirror and a condensing lens.

International Publication No. 2021/205650

However, the technique described in Patent Document 1 does not take into account beam spot position shift due to environmental temperature changes at all.

Additionally, due to recent technological innovations, the size of defects and foreign objects that need to be detected has become smaller. For this reason, detection sensitivity is increased by forming a beam spot with high precision using a high-output deep ultraviolet laser light source. In order to increase detection sensitivity, there is a need to further improve the stability regarding the size and position of the beam spot. Therefore, highly accurate inspection results cannot be obtained unless the positional shift of the beam spot due to environmental temperature changes is dealt with.

In line with the above-mentioned demand for higher sensitivity in defect detection, higher power output of light sources, shorter wavelengths, and higher stability of beam spot positions, beam It has become necessary to devise ways to improve spot focusing performance.

In view of this situation, the present disclosure provides an illumination optical system and an illumination optical system that flexibly changes the beam spot diameter of illumination light according to inspection conditions and stage operation while maintaining highly accurate focusing performance in response to environmental temperature changes. A board inspection device equipped with the same is provided.

In order to solve the above problems, the present disclosure provides an illumination optical device that expands a luminous flux and focuses it on an object, which includes a light source that emits a luminous flux, and a variable luminous flux diameter unit that enlarges the diameter of the luminous flux from the light source. , a condensing optical system that condenses a beam whose diameter has been expanded onto a target object, the variable beam diameter unit includes at least four lenses, and at least one lens of the variable beam diameter unit satisfies the conditions. Formula (1) is satisfied, at least one lens in the variable beam diameter unit other than the lens that satisfies conditional formula (1) satisfies conditional formula (2), and the condensing optical system has at least two at least two lenses satisfy conditional expression (3), at least one lens of the condensing optical system satisfies conditional expression (1), and at least one lens of the condensing optical system satisfies conditional expression (3). In the illumination optical device, lenses other than the lenses satisfying conditional expression (1) satisfy conditional expression (2).
dn/dt<0...(1)
dn/dt>0...(2)

Here, dn/dt is the temperature coefficient of refractive index, m is the number of lenses included in the condensing optical system, f _i is the focal length of the i-th lens in the condensing optical system, and dn _i /dt is the condensing optical system. The refractive index temperature coefficient of the i-th lens in the system, f is the focal length of the condensing optical system, and MAX_dn _i /dt is the maximum absolute value of the refractive index temperature coefficient of the lens included in the condensing optical system. .

Further features related to the present disclosure will become apparent from the description herein and the accompanying drawings. In addition, aspects of the present disclosure may be realized and realized by means of the elements and combinations of various elements and aspects of the following detailed description and appended claims.
The descriptions herein are merely typical examples and do not limit the scope of claims or applications of the present disclosure in any way.

The technology disclosed herein makes it possible to maintain high-precision focusing performance even when the temperature changes.

FIG. 2 is a diagram illustrating a configuration example of an illumination optical system OP1 according to a first embodiment of the present disclosure. FIG. 2 is a diagram illustrating a schematic internal configuration example of a variable beam diameter unit 4 according to the present disclosure. FIG. 3 is a diagram illustrating a schematic configuration example of a condensing optical system 5 according to the first embodiment. 3 is a diagram showing an example of the configuration of a support structure 6. FIG. 1 is a diagram showing an example of a schematic configuration of a board inspection apparatus 100. FIG. It is a figure showing an example of composition of illumination optical system OP1 concerning a 2nd embodiment. 3 is a diagram showing an example of the arrangement of two

spherical lenses

25c and 25d in the condensing optical system 25. FIG.

Increasing the output of the light source based on the increased sensitivity of defect detection, as well as the heat generated by the motors used to drive high-speed rotation stages and other motors used to adjust the amount of light and the optical axis, may cause damage to the vicinity of the illumination optical system (configuration shown in Figure 1). (near the element) changes frequently. However, it is necessary to maintain highly sensitive defect detection even when the temperature changes, and for this purpose, it is extremely important to maintain the focusing performance of the beam spot formed on the wafer.

Embodiments of the present disclosure propose a technique that makes it possible to maintain focus performance of a beam spot formed on a wafer. Embodiments of the present invention will be described below based on the accompanying drawings.

(1) First embodiment <Configuration example of illumination optical system>
FIG. 1 is a diagram illustrating a configuration example of an illumination optical system OP1 according to a first embodiment of the present disclosure. The illumination optical system OP1 includes a DUV light source (Deep Ultra Violet light source: wavelength range is 200 to 300 nm) 1, an attenuator 2, a mirror 3, a variable beam diameter unit (expander) 4, and a condensing optical system. The illumination optical system OP1 includes a system 5, a support structure 6, and a control section 8 (the control section 8 may be provided outside the illumination optical system OP1).

The DUV light source 1 emits parallel light (which may be called linear light). Note that in FIG. 1, parallel light is schematically shown as a straight line. Further, in this embodiment, the DUV light source 1 is used as a light source, but the present invention is not limited to this, and a light source that emits light of any wavelength can be used.

The support structure 6 can fix a group of elements (the attenuator 2, the mirror 3, the variable beam diameter unit 4, the condensing optical system 5, etc.) for guiding the light from the DUV light source 1 to the inspection object 7. It has a structure. The support structure 6 may be composed of a single fixed member or support member, or may be a mechanical structure made up of a plurality of members combined. For example, the control unit 8 changes the position on the optical axis of the

cylindrical lenses

5a and 5b of the condensing optical system 5 supported by the support structure 6 (moves on the optical axis) in response to an instruction input by the user. can be done.

For example, the light emitted from the DUV light source 1 undergoes light intensity adjustment by the attenuator 2. The light whose quantity has been adjusted is reflected by the mirror 3, its course direction is changed, and it is guided to the beam diameter variable unit 4. The variable beam diameter unit 4 enlarges the beam diameter of the light reflected by the mirror 3 and guides it to the condensing optical system 5 . The condensing optical system 5 condenses the light whose beam diameter has been expanded, and irradiates the condensed light onto the inspection object 7 .

In the illumination optical system OP1 shown in FIG. 1, the internal configuration of the variable beam diameter unit 4 and the internal configuration of the condensing optical system 5 are devised to maintain focus performance even when the temperature changes.

<Example of internal configuration of variable beam diameter unit 4>
FIG. 2 is a diagram showing a schematic internal configuration example of the variable beam diameter unit 4 according to this embodiment. The variable beam diameter unit 4 includes a positive lens group (at least one positive lens) 4a, a negative lens group (at least one negative lens) 4b, and a positive lens group (consisting of two positive lenses) 4c group. (composed of at least four lenses).

A positive lens group 4a is arranged on the DUV light source 1 side, and a positive lens group 4c is arranged on the inspection object 7 side. Parallel light enters the variable beam diameter unit 4, and light emitted therefrom is also parallel light. However, the light is emitted with a diameter of the luminous flux that is enlarged relative to the diameter of the incident luminous flux. The variable beam diameter unit 4 is configured such that any or all of the groups constituting it can operate in the optical axis direction, thereby changing the diameter of the emitted beam.

When at least two lenses included in the positive lens group 4c are made of materials having the same sign of refractive index temperature coefficient (dn/dt), the refractive index becomes higher (lower) due to temperature changes, and the light flux diameter variable unit 4 The emitted light beam converges (diverges). However, in order to condense the light generated from the light source 1 onto the wafer (object to be inspected 7), the light beam emitted from the variable beam diameter unit 4 needs to be parallel light.

On the other hand, if at least two lenses included in the positive lens group 4c are made of materials with refractive index temperature coefficients (dn/dt) of opposite signs, when the environmental temperature rises, the refractive index temperature coefficient shown by equation (1) The refractive power of the lens increases, but the refractive power of the lens with the temperature coefficient of refraction expressed by equation (2) weakens, so it is possible to reduce (at least partially cancel out) the defocus change when the temperature rises. can. As a result, even when the environmental temperature changes, the light emitted from the variable beam diameter unit 4 can be made into substantially parallel light.
dn/dt>0... (1)
dn/dt<0... (2)

Synthetic quartz (dn/dt>0) and fluorite (dn/dt<0) can be cited as an example of a combination of materials having refractive index temperature coefficients (dn/dt) of opposite signs. If synthetic quartz (dn/dt > 0) or fluorite (dn/dt < 0) is used as the material of the lens constituting the variable beam diameter unit 4, it is possible to suppress defocusing when the environmental temperature changes based on the above-mentioned theory. be.

In the case of the configuration shown in FIG. 2, for example, the positive lens group 4a and the negative lens group 4b are made of synthetic quartz, and one of the two positive lenses included in the lens group 4c is made of synthetic quartz and the other is made of fluorite. , it becomes possible to suppress the focus fluctuation when the environmental temperature changes as described above. Note that similar effects can be expected when the positive lens group 4a and the negative lens group 4b are made of fluorite, and of the two positive lenses included in the lens group 4c, one is made of quartz and the other is made of fluorite.

<Example of configuration of condensing optical system 5>
FIG. 3 is a diagram showing a schematic configuration example of the condensing optical system 5. As shown in FIG. The condensing optical system 5 includes, in order from the variable beam diameter unit 4 side (light incident side), at least two

cylindrical lenses

5a and 5b, two folding mirrors 5c and 5d, and one cylindrical parabolic mirror 5e. Equipped with. Note that depending on the angle at which the light is irradiated onto the inspection object 7, the

mirrors

5c and 5d may not be essential components.

The parallel light from the variable beam diameter unit 4 is focused onto the inspection object 7 by the

cylindrical lenses

5a and 5b and the cylindrical parabolic mirror 5e. What is condensed by the

cylindrical lenses

5a and 5b is the light flux in the vertical direction of the paper in FIG. The light beam in the depth direction of the paper is focused onto the inspection object 7 by the cylindrical parabolic mirror 5e.

The amount of focus variation (change in focal position) when the temperature changes can be estimated from the product of the lens' refractive power (=reciprocal of focal length) and refractive index temperature coefficient (dn/dt). If the sum of the products of the focal length and the temperature coefficient of refractive index of each lens constituting the optical system is small, the focus fluctuation is also small. Therefore, it is important to satisfy the following formula.

where each character or character expression is
m: number of lenses included in the condensing optical system;
f _i : focal length of the i-th lens of the condensing optical system;
dn _i /dt: refractive index temperature coefficient of the i-th lens of the condensing optical system;
f: focal length of condensing optical system;
MAX_dn _i /dt: maximum absolute value of refractive index temperature coefficient in the lens included in the condensing optical system;
It shows.

The right side of equation (3) indicates the amount of focus variation if the condensing optical system 5 were composed of lenses made of a single material. If the left side of equation (3) is smaller than the right side of equation (3), it means that the optical system is capable of suppressing focus fluctuations due to temperature changes.

If the two

cylindrical lenses

5a and 5b are made of the same glass material (same optical glass) and have different signs of power (refractive power), then formula (3) can be satisfied. This makes it possible to realize an optical system with small focus fluctuations. Here, let us assume that the power of the cylindrical lens 5a is positive (convex lens), the power of the cylindrical lens 5b is negative (concave lens), both glass materials are fluorite, and the environmental temperature rises. In this case, the refractive power of the cylindrical lens 5a weakens due to the temperature rise, but the refractive power of the cylindrical lens 5b strengthens, making it possible to cancel (at least partially offset) the overall refractive power fluctuations. As a result, it becomes possible to suppress focus fluctuations on the inspection object 7.

Further, by optimizing the focal length of each lens so that the left side of equation (3) becomes extremely small, it is possible to enhance the effect of suppressing focus fluctuations. Further, it is preferable for aberration correction to arrange two cylindrical lenses with their power surfaces facing each other. For example, during an inspection (while the condensing optical system 5 is in use), the focal length can be optimized by moving the cylindrical lenses 5a and/or 5b on the optical axis. For example, a camera (not shown) acquires an image of the beam spot size on the inspection object (for example, a wafer) 7, and the user confirms it. Then, in response to a user's instruction, the control unit 8 moves the cylindrical lenses 5a and/or 5b on the optical axis, so that the beam spot size can be adjusted as appropriate.

Furthermore, by using a low expansion metal (such as Invar) as a material constituting the support structure 6 that holds the optical elements including the

cylindrical lenses

5a and 5b and the cylindrical parabolic mirror 5e, focus performance during temperature changes is improved. can be further increased.

The focal lengths of the

cylindrical lenses

5a and 5b and the cylindrical parabolic mirror 5e are each optimized so that the light is focused on the inspection object 7. In addition, the

cylindrical lenses

5a and 5b and the cylindrical parabolic mirror 5e have different focal lengths, so that the beam spot diameter on the inspection object 7 is linear (linear: the beam spot shape is such that the major axis is the minor axis). It is constructed so that it can be formed into a very large elliptical shape (compared to the elliptical shape). The linear shape (elliptical shape) is used to increase the throughput by increasing the scanning width when performing beam scanning while rotating or moving the stage (not shown) on which the inspection object 7 (wafer) is placed. This is to do so.

The combined focal length of the

cylindrical lenses

5a and 5b is fA, the focal length of the cylindrical parabolic mirror 5e is fB, the angle of elevation of light beam incidence on the inspection object 7 is θ, the wavelength of the DUV light source 1 is λ, and the condensing optical system 5 is If the diameter of the incident beam (luminous flux) in the longitudinal direction is DA, and the diameter of the beam in the lateral direction is DB, then the beam diameter φA formed in the horizontal direction on the inspection object 7 in FIG. 3 and the beam diameter formed in the depth direction. The relationship between the beam diameter φB and the beam diameter φB is expressed by the following equations (4) and (5).
φA=1.22*fA*λ/(DA*sinθ)... (4)
φB=1.22*fB*λ/(DA*sinθ)... (5)

Therefore, the beam spot diameter and beam aspect ratio are adjusted by adjusting the beam diameter (DA and DB) incident on the condensing optical system 5, the combined focal length of the

cylindrical lenses

5a and 5b, and the focal length of the cylindrical parabolic mirror 5e. It can be seen that control is possible by doing this. Note that in this embodiment, the combined focal length of the

cylindrical lenses

5a and 5b is longer than the focal length of the cylindrical parabolic mirror 5e, so on the inspection object 7, the long axis is in the left-right direction in the plane of the paper, and the long axis is short in the depth direction in the plane of the paper. An axis is formed.

As described above, by moving one or each of the

cylindrical lenses

5a and 5b in the optical axis direction, the focal length corresponding to the longitudinal side of the beam spot can be changed. Therefore, it is possible to control the aspect ratio of the beam spot irradiated onto the inspection object 7. Note that, as described above, the control unit 8 controls the lens drive unit (the lens drive unit itself is not shown) that moves the

cylindrical lenses

5a and 5b in response to instructions input by the user, thereby moving the cylindrical lenses. The position of 5a and/or 5b on the optical axis can be moved.

In the case of a substrate inspection device that detects foreign objects by manipulating a single inspection object, if the beam spot diameter in the longitudinal direction is made larger, the number of scans required is reduced, and the entire surface of the inspection object can be inspected in a shorter time. On the other hand, the positional accuracy of the foreign object is deteriorated. Therefore, it is desirable to be able to change the beam spot diameter in the longitudinal direction in one illumination optical system according to the material of the inspection object, the size of the inspection object, the inspection speed, etc.
The configuration shown in FIG. 3 makes it possible to realize an illumination optical system OP1 that controls the aspect ratio of the beam spot and suppresses focus deviations caused by changes in the environmental temperature.

<Example of configuration of support structure 6>
FIG. 4 is a diagram showing a configuration example of the support structure 6. As shown in FIG. The support structure 6 can be configured by, for example, a base 6a and element support members 6b_1 to 6b_4. The support structure 6 may be configured by fixing a plurality of elements on the same base 6a, or may be configured by a plurality of bases.
Further, the element supporting members 6b_1 to 6b_4 may be formed of a single member, or may be a mechanical structure formed by combining a plurality of members.

<Example of configuration of board inspection device>
FIG. 5 is a diagram showing a schematic configuration example of the board inspection apparatus 100. Although the substrate inspection apparatus 100 shown in FIG. 5 is equipped with the illumination optical system OP1 according to the first embodiment, it may be equipped with an illumination optical system OP2 according to the second embodiment described later.

The substrate inspection apparatus 100 includes an illumination optical system OP1, a stage 111 on which the inspection object 7 is placed, a light receiving lens 112, a light receiving element 113, and an analysis unit 114.

In the board inspection apparatus 100, the inspection object 7 is fixed on a stage 111. This stage 111 is rotatable around a rotation axis in the vertical direction in the plane of FIG. 5, and can also be translated in a direction perpendicular to the rotation axis (for example, in the horizontal direction in the plane of FIG. 5). In this configuration example, it is assumed that the longitudinal direction of the linear beam spot formed by the illumination optical system OP1 also coincides with this.

Further, the inspection object 7 has a disk shape (for example, a wafer), and can be rotated and translated in parallel by the stage 111. This makes it possible to irradiate the entire surface of the disk (inspection object 7) with light.

The light-receiving lens 112 condenses a portion of the diffusely reflected light that is generated when a defect or foreign object on the inspection object 7 is hit by light. The light receiving element 113 converts the light collected by the light receiving lens 112 into an electrical signal. Analysis unit 114 receives the electrical signal from light receiving element 113 and analyzes it. The analysis unit 114 also outputs the analysis result as a test result, for example, on a display screen of a display device (not shown). For this purpose, the analysis unit 114 may include a computer.

In this way, the board inspection apparatus 100 inspects the inspection object 7 (foreign object inspection, defect inspection). Here, as described above, the beam outputted by the illumination optical system OP1 is highly accurately focused in a linear manner, so that inspection can be performed with higher accuracy.

In addition to the signal analysis function, the analysis unit 114 may also have a function of appropriately arranging optical elements (for example, a condensing optical system or a variable beam diameter unit) placed on the optical path (the control unit in FIG. (It may also have the functions of 8). This function may be performed in response to user input of the board inspection apparatus 100, or may be performed automatically by the analysis unit 114. When the analysis unit 114 automatically controls the arrangement of optical elements, the optical elements may be selected so that the electrical signal obtained by the light receiving element 113 is in the optimal state for the target inspection. good. Although FIG. 5 shows one light receiving lens 112 and one light receiving element 113, a plurality of either or both of these may be provided.

(2) Second embodiment <Configuration example of illumination optical system>
FIG. 6 is a diagram showing a configuration example of the illumination optical system OP1 according to the second embodiment. In the illumination optical system OP2 according to the second embodiment, in the illumination optical system OP1 according to the first embodiment, the condensing optical system 5 is composed of an axially symmetrical spherical lens instead of a cylindrical lens.

In other words, in the first embodiment, the light is focused to the left and right of the page by the

cylindrical lenses

5a and 5b, and to the depth of the page by the cylindrical parabolic mirror 5e. Also, the aspect ratio of the beam spot is controlled by providing a difference in focal length between the

cylindrical lenses

5a and 5b and the cylindrical parabolic mirror 5e.

On the other hand, as shown in FIG. 6, the illumination optical system OP2 according to the second embodiment includes a DUV light source (Deep Ultra Violet light source) 21, an attenuator 22, a mirror 23, and an anamorphic prism 28. , a variable beam diameter unit (expander) 24, a condensing optical system 25, a support structure 26, and a control section 29 (the control section 29 may be provided outside the illumination optical system OP2). Be prepared. In the second embodiment, in the condensing optical system 25, instead of the

cylindrical lenses

5a and 5b according to the first embodiment, axially symmetrical

spherical lenses

25c and 25d are responsible for image formation in the left-right direction and the depth direction in the drawing. ing. Further, an anamorphic prism 28 is provided on the optical path to control the aspect ratio of the beam spot.

The condensing optical system 25 includes, in order when viewed from the DUV light source 21 side, two

mirrors

25a and 25b and two

spherical lenses

25c and 25d. Even when the condensing optical system 25 is configured with an axially symmetrical spherical lens, it is possible to suppress out of focus due to changes in environmental temperature by satisfying the condition shown in equation (3) above.

FIG. 7 is a diagram showing an example of the arrangement of the two

spherical lenses

25c and 25d in the condensing optical system 25. In the condensing optical system 25, when one of the two

spherical lenses

25c and 25d is made of synthetic quartz and the other is made of fluorite, the condition shown in equation (3) can be satisfied. Therefore, similarly to the first embodiment, it is possible to realize a condensing optical system 25 that suppresses focus fluctuations. If we assume that the spherical lens 25c is made of synthetic quartz and the spherical lens 25d is made of fluorite, and the environmental temperature rises, the refractive power of 5c will become stronger but the refractive power of 5d will weaken as the temperature rises, resulting in an overall change in refractive power. It becomes possible to cancel (or at least partially offset) As a result, it becomes possible to suppress focus fluctuations on the inspection object 7.

The circular light beam from the DUV light source 21 becomes elliptical after passing through the anamorphic prism 28. In the example shown in FIG. 6, it is assumed that the longitudinal direction of the elliptical beam emitted from the anamorphic prism 28 corresponds to the depth direction of the paper, and the lateral direction corresponds to the left-right direction of the paper. The pupil diameter D of the beam before entering the condensing optical system 25 is smaller in the horizontal direction (DB) of the drawing than in the depth direction (DA) of the drawing. Since the beam diameters φA and φB on the inspection object 27 are as shown in equations (4) and (5) above, a linear (elliptical) beam spot is formed on the inspection object 27. Here, the length of the beam spot corresponds to the horizontal direction of the paper, and the short length of the beam spot corresponds to the depth direction of the paper.

Further, in the variable beam diameter unit 24 disposed downstream of the anamorphic prism 28, an internal optical element moves in the optical axis direction under the control of the control unit 29 (a lens drive unit (not shown) is controlled by the control unit 29). (by moving an optical element in response to a signal), it is possible to change the size of the elliptical beam.

Furthermore, the focus can be varied by optimizing the focal length of each of the

spherical lenses

25c and 25d so that the left side of equation (3) becomes extremely small (so as to cancel out the difference in the temperature coefficient of refraction between synthetic quartz and fluorite). It is possible to enhance the suppressive effect. Here, the condensing optical system 25 has two lenses, but the number of lenses is not limited as long as it satisfies equation (3).

(3) Others (i) Conditions regarding the distance between lenses in the condensing optical system In the condensing

optical system

5 or 25, the distance between two lenses (DR: the distance between

cylindrical lenses

5a and 5b, or the distance between

spherical lenses

25c and 25d) ) is the distance between the optical elements that is the widest among the optical element intervals included in the condensing optical system 5 or 25 (in the condensing optical system 5, the distance between the cylindrical lens 5a and the cylindrical parabolic mirror 5e). When DR_max is set, focus fluctuation can be suppressed more efficiently by setting DR to less than 1/10 of DR_max (DR<DR_max/10).

(ii) Conditions regarding the focal length of the lens in the variable beam diameter unit 4 and the condensing

optical system

5 or 25 The lenses included in the variable beam diameter unit 4 and the condensing

optical system

5 or 25 are determined by the above equations (1) and (2). ), the lens may be configured to further satisfy equation (6).
|f_max|-|f_min|<50mm... (6)

Here, f_max indicates the focal length of the lens with the longest focal length among the target lenses, and f_min indicates the focal length of the lens with the shortest focal length among the target lenses.

(4) Summary (i) The illumination optical device according to this embodiment includes a variable beam diameter unit (expander) 4 or 24 and a condensing

optical system

5 or 25. In the variable beam diameter unit, at least one lens is configured to satisfy dn/dt<0 (conditional expression (1)), and at least one other lens is configured to satisfy dn/dt>0 (conditional expression (2)). be done. At least two lenses in the condensing optical system are configured to satisfy conditional expression (3). Furthermore, at least one lens in the condensing optical system is configured to satisfy conditional expression (1), and at least one other lens is configured to satisfy conditional expression (2).

Here, dn/dt is the temperature coefficient of refractive index, m is the number of lenses included in the condensing optical system, f _i is the focal length of the i-th lens in the condensing optical system, and dn _i /dt is the condensing optical system. The refractive index temperature coefficient of the i-th lens in the system, f is the focal length of the condensing optical system, and MAX_dn _i /dt is the maximum absolute value of the refractive index temperature coefficient of the lens included in the condensing optical system. . By configuring the illumination optical device in this manner, it is possible to maintain the focusing performance of the illumination light with high precision even if there is a change in the environmental temperature. Note that in the illumination optical device, a DUV light source that emits linear light and has a wavelength range of 200 nm to 300 nm can be used. Using linear light makes it easier to control the aspect ratio of the beam spot of the light irradiated onto the inspection target. Furthermore, by using beam spots with different aspect ratios, it is possible to increase the throughput when inspecting an object to be inspected.

(ii) If DR is the interval between two lenses included in the condensing optical system, and DR_max is the interval between the optical elements that is the widest among the optical element intervals included in the condensing optical system, then the condensing

optical system

5 or 25 is It is preferable to configure so that DR<DR_max/10 is satisfied. By doing so, it becomes possible to flexibly change the beam spot diameter on the object to be inspected according to the inspection conditions and stage operation.

(iii) The two lenses included in the condensing optical system 5 according to the first embodiment are cylindrical lenses arranged with their power directions facing each other. The two lenses included in the condensing optical system 25 according to the second embodiment are spherical lenses arranged with their power directions facing each other. By doing so, it becomes possible to flexibly change the beam spot diameter on the object to be inspected according to the inspection conditions and stage operation.

(iv) If f_max is the focal length of the lens with the longest focal length among the lenses, and f_max is the focal length of the lens with the shortest focal length among the lenses, then the variable beam diameter unit 4 or 24 and the condensing

optical system

5 or 25 and which satisfies the above dn/dt<0 (conditional expression (1)) and dn/dt>0 (conditional expression (2)) satisfies |f_max|-|f_min|<50mm It can be configured as follows. By doing so, it becomes possible to flexibly change the beam spot diameter on the object to be inspected according to the inspection conditions and stage operation.

(v) The illumination optical device according to the second embodiment includes a control section 29 that moves at least one lens included in the variable beam diameter unit 24 in the optical axis direction. The control unit 29 controls the beam diameter by expanding or reducing the diameter of the beam by moving at least one lens of the variable beam diameter unit 24 in the optical axis direction. By doing so, it becomes possible to flexibly adjust the beam spot diameter.

(vi) The support structure 6 holds at least the variable beam diameter unit 4 or 24 and the condensing

optical system

5 or 25. The support structure can be constructed from a low expansion metal. By providing the support structure 6, each optical element can be stably arranged in the illumination optical device, so that highly accurate focus control can be achieved without being affected by external factors other than environmental temperature changes. Can be done. Further, by configuring the support structure 6 using a low expansion metal, focusing performance during temperature changes can be further improved.

(vii) The illumination optical device according to the first embodiment variably controls the focal length of the condensing optical system 5 by moving the optical elements of the condensing optical system 5 on the optical axis, so that the object is irradiated. The controller 8 includes a control unit 8 that adjusts the aspect ratio of the beam spot (provided that the configuration requirement (i) above is provided). As a result, it is possible to realize an illumination optical system that controls the aspect ratio of the beam spot on the object to be inspected and suppresses defocusing when the environmental temperature changes.

(viii) In the second embodiment, an optical element (anamorphic prism 28) that changes the aspect ratio of the beam spot irradiated onto the inspection object is provided. This makes it possible to easily generate a linear (elliptical) beam.

(ix) The illumination optical device according to this embodiment can be applied to a substrate inspection device. As a result, focus control can be performed with high precision without being affected by environmental temperature changes, so that inspection of the substrate (object to be inspected) can be performed with high precision.

1, 21

DUV light sources

2, 22

Attenuators

3, 23 Mirrors 4, 24 Luminous flux diameter variable unit 4a Positive lens group 4b Negative lens group 4c

Positive lens group

5, 25 Condensing

optical system

5a,

5b Cylindrical lens

5c, 5d, 25a, 25b Mirror 5e Cylindrical

parabolic mirror

6, 26 Support structure 6a Base 6b_1 Element support member 1
6b_2 Element support member 2
6b_3 Element support member 3
6b_4 Element support member 4
7, 27 Inspection object 8, 29

Control unit

25c, 25d Spherical lens 28 Anamorphic prism 100 Board inspection device 111 Stage 112 Light receiving lens 113 Light receiving element 114 Analysis unit

Claims

An illumination optical device that expands a luminous flux and focuses it on an object,
a light source that emits the luminous flux;
a variable beam diameter unit that expands the diameter of the beam from the light source;
a condensing optical system that condenses a luminous flux with an expanded diameter onto the object,
The variable beam diameter unit includes at least four lenses,
At least one lens of the variable beam diameter unit satisfies conditional expression (1),
At least one lens in the variable beam diameter unit other than the lens that satisfies conditional expression (1) satisfies conditional expression (2),
The condensing optical system includes at least two lenses,
At least two lenses in the condensing optical system satisfy conditional expression (3),
At least one lens of the condensing optical system satisfies conditional expression (1),
In the illumination optical device, at least one lens in the condensing optical system other than the lens satisfying conditional expression (1) satisfies conditional expression (2).
dn/dt<0...(1)
dn/dt>0...(2)

Here, dn/dt is the temperature coefficient of refractive index, m is the number of lenses included in the condensing optical system, f i is the focal length of the i-th lens of the condensing optical system, and dn i /dt is the The refractive index temperature coefficient of the i-th lens of the condensing optical system, f is the focal length of the condensing optical system, MAX_dn i /dt is the maximum absolute value of the refractive index temperature coefficient of the lens included in the condensing optical system, each represents.
In claim 1,
The illumination optical device, wherein the light source is a light source that emits linear light.
In claim 1,
The condensing optical system is an illumination optical device that satisfies conditional expression (4).
DR<DR_max/10...(4)
Here, DR represents the interval between two lenses included in the condensing optical system, and DR_max represents the widest interval between the optical elements included in the condensing optical system.
In claim 1,
In the illumination optical device, the two lenses included in the condensing optical system are cylindrical lenses arranged with their power directions facing each other.
In claim 1,
An illumination optical device in which the lens included in the variable beam diameter unit and the condensing optical system and satisfying conditional expressions (1) and (2) further satisfies conditional expression (5).
|f_max|-|f_min|<50mm...(5)
Here, f_max represents the focal length of the lens with the longest focal length among the applicable lenses, and f_max represents the focal length of the lens with the shortest focal length among the applicable lenses.
In claim 1,
The light source is an illumination optical device that emits light in a wavelength range of 200 to 300 nm.
In claim 1,
An illumination optical device, wherein at least one lens satisfying the conditional expression (1) and at least one lens satisfying the conditional expression (2) included in the variable beam diameter unit are made of the same glass material.
In claim 1, further:
comprising a control unit that moves at least one lens included in the variable beam diameter unit in the optical axis direction,
The illumination optical device is configured such that the control unit controls the beam diameter by changing the diameter of the luminous flux by moving at least one lens included in the variable luminous flux diameter unit in the optical axis direction.
In claim 1, further:
comprising a support structure that holds at least the variable beam diameter unit and the condensing optical system;
The illumination optical device, wherein the support structure is made of a low expansion metal.
In claim 1, further:
A control unit that variably controls the focal length of the focusing optical system by moving an optical element of the focusing optical system on the optical axis and adjusts the aspect ratio of the beam spot irradiated onto the object. , illumination optical equipment.
In claim 1, further:
An illumination optical device comprising an optical element that changes the aspect ratio of a beam spot irradiated onto the object.
An illumination optical device according to claim 1;
a light receiving lens that collects a part of the diffusely reflected light generated when the light from the illumination optical device hits the target object;
a light-receiving element that converts the light focused by the light-receiving lens into an electrical signal;
an analysis unit that analyzes the electrical signal;
an output unit that outputs an analysis result by the analysis unit;
An inspection device comprising: