JP4178838B2 - Illumination device and microscope illumination device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is applied to a microscope, a semiconductor inspection apparatus, and the like, and relates to an illumination apparatus that switches an illumination state of a surface to be illuminated such as a sample surface or a wafer surface, and a microscope illumination apparatus.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an illumination device, particularly an illumination device applied to a microscope, has a function of changing an illumination state by changing the diameter of an aperture stop or a field stop according to an inspection object.
For example, the microscope can change the incident angle range of illumination light (hereinafter referred to as NA of illumination light) into at least two types. This is because the NA of the illumination light is changed according to the inspection object to maintain the inspection accuracy.
[0003]
A mechanism for that purpose is a linear slider, a turret, or the like that selectively inserts a diaphragm having two types of diameters at an opening position in the lighting device.
In addition, in semiconductor inspection devices (particularly overlay inspection devices) and the like, in particular, when measuring a pattern with a step, if the telecentricity of illumination light is not strictly adjusted, an inspection position error will occur. The aperture stop is fixedly provided in the apparatus so that it cannot be switched.
[0004]
[Problems to be solved by the invention]
By the way, even in a semiconductor inspection apparatus (particularly, overlay inspection apparatus), an observation state such as contrast adjustment is performed by changing the aperture function according to the surface state of a semiconductor wafer as a test object and changing the characteristics of the transfer function of the optical system. There are many requests to adjust the state to a desired state. However, since a semiconductor inspection apparatus (particularly, overlay inspection apparatus) uses an illumination device that strictly requires telecentricity as described above, a switching mechanism (linear slider) for an aperture stop used in the above-described microscope or the like. Etc.), it is necessary to design and manufacture the switching mechanism with high accuracy (aperture / positioning accuracy of the aperture stop), and there is a problem that the apparatus is complicated, large-sized, and expensive.
[0005]
Specifically, if you try to switch the aperture stop using the microscope switching mechanism, the stop position will shift, the aperture stop surface will sag, etc., resulting in a decrease in telecentricity and the shape of the illumination aperture. Asymmetry may occur and desired illumination light may not be obtained. In particular, when the aperture stop diameter is small, the posture greatly changes the state of the illumination light, which is a serious problem.
[0006]
Therefore, an object of the present invention is to provide an illuminating device and a microscope illuminating device capable of easily and accurately switching the illumination state.
[0007]
[Means for Solving the Problems]
The illuminating device of the present invention is arranged so that the first optical path and the second optical path can be switched in order to switch the illumination state of the illuminated surface between the light source and the illuminated surface, and the first optical path is The incident optical path that enters the branch point that branches from the second optical path and the exit optical path that exits from the junction where the first optical path joins the second optical path are on parallel lines that are separated from each other, and A non-movable optical element is disposed in the first optical path formed between the branch point and the junction point, and is removable between the branch point and the optical element, and A switching member for selectively setting the first optical path / the second optical path in accordance with the insertion / removal, and the switching member is composed of a pair of facing parallel reflecting surfaces fixed to each other; The first optical path having a substantially Z shape is formed by reflection on the reflecting surface. It is intended to.
[0009]
Further, the optical element is an aperture or a field stop having a constant diameter .
Further, the optical element may be I Oh pinhole plate.
[0010]
Also, the non-common path between said first optical path of said second optical path, the diaphragm having a wider diameter than the diaphragm may be disposed.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0012]
[First Embodiment]
A first embodiment of the present invention will be described with reference to FIG. 1, FIG. 2, FIG. 3, and FIG.
In the present embodiment, an illumination device mounted on the overlay inspection apparatus will be described.
1 and 3 are configuration diagrams of the illumination device of the present embodiment, and FIG. 2 is a schematic view of an optical path in the illumination device. The difference between FIG. 1 and FIG. 3 is the illumination state.
[0013]
As shown in FIGS. 1 and 3, the illumination device 10 includes a light source 11, a collector lens 12, a filter 13, and relay lenses 14 a and 14 b in this order, and a condenser lens 15 disposed inside the microscope unit 10 ′. Illumination light is supplied to the object, and the object O (wafer) is illuminated through a prism (for illumination light / imaging light branching) 16 and a first objective lens 17 arranged inside the microscope unit 10 ′. To do.
[0014]
Note that the microscope unit 10 ′ includes an optical system in which the first objective lens 17, the prism 16, and the second objective lens 19 are arranged in this order from the subject O side, and the subject O formed on the imaging surface I. The image is taken and image data is acquired.
[0015]
At the time of use, the visual field of the microscope unit 10 ′ captures an overlay mark (formed in the semiconductor manufacturing process) on the test object O. The image data of the overlay mark acquired by the microscope 10 ′ is used for the calculation processing of the shift amount between the overlay marks by the computer in the overlay inspection apparatus.
Here, since the overlay mark is formed by patterning a thin film, it has a stepped structure. Each overlay mark is formed on a layer having a different height on the test object O.
[0016]
For this reason, at the time of normal inspection, it is necessary to emphasize the edge of the overlay mark by making the incident angle range of the illumination light smaller than the imaging light beam from the test object O to the imaging surface I.
On the other hand, depending on the test object O, the surface may be rough as a whole, and if the edge is emphasized in that case, the shape of the surface is also emphasized, so that the overlay mark is difficult to detect. .
[0017]
Therefore, in this case, it is necessary to make the incident angle range of the illumination light larger than the imaging light beam from the test object O to the imaging surface I to reduce the edge enhancement effect.
Therefore, in order to make it possible to accurately detect various overlay marks, the illumination device 10 needs to change the NA of the illumination light with respect to the test object O into at least two types.
[0018]
As shown in FIG. 2, the illuminating device 10 includes a first optical path R1 and a second optical path R2 that are branched between the light source 11 and the test object 0 in a switchable manner. The lighting state of the object O is switched.
FIG. 1 shows a state in which the first optical path R1 is set, and FIG. 3 shows a state in which the second optical path R2 is set.
[0019]
As shown in FIGS. 1 and 3, in order to make the NA of illumination light variable, the first optical path R1 and the second optical path R2 branch midway between the relay lenses 14a and 14b.
As shown in FIG. 2, among the non-common optical paths from the branch point Pa to the confluence Pb, the smaller aperture stop AS1 is fixedly arranged on the first optical path R1, and the second optical path An aperture stop AS2 having a larger diameter is fixedly arranged on R2.
[0020]
The diameter of the aperture stop AS1 limits the diameter of the illumination light beam (incident angle range to the test object O) to be small (for example, about 0.6 to 0.8).
The diameter of the aperture stop AS2 is slightly larger than the aperture diameter of the first objective lens 17, and does not actively limit the diameter of the illumination light beam (incident angle range on the test object O), but limits stray light. Only.
[0021]
Here, the optical path length of the first optical path R1 (optical distance consisting of the refractive index of the medium and the geometric distance) and the optical path length of the second optical path R2 are the same.
Further, the aperture stop AS1 and the aperture stop AS2 are both arranged at a position conjugate with the pupil of the first objective lens 17.
Among these, at least the aperture stop AS1 has a small diameter and therefore has a high accuracy required for its alignment, so that it is accurately positioned with respect to the optical axes of the relay lens 14b, the condenser lens 15 and the prism 16.
[0022]
By the way, in this embodiment, the incident optical path to the branch point Pa between the first optical path R1 and the second optical path R2, and the outgoing optical path from the confluence Pb with the second optical path R2 of the first optical path R1 Are on parallel lines separated from each other.
Therefore, at least the mirrors M11 and M12 for setting the first optical path R1 and the mirrors M21 and M22 for setting the second optical path R2 are used in the illumination device 10 (hereinafter referred to as four mirrors). Explain the case where is used.)
[0023]
The mirror M11 is a mirror that should be placed at the branch point Pa, and the mirror M22 is a mirror that should be placed at the junction Pb.
The arrangement position of the aperture stop AS1 is after being deflected twice by the mirror M11 and the mirror M12. The aperture stop AS2 is between the mirror M21 and the mirror M22.
[0024]
In this embodiment, for switching between the first optical path R1 shown in FIG. 1 and the second optical path R2 shown in FIG. 3, the switching member 1 formed by fixing the mirror M11 and the mirror M12 is branched. It is detachably provided between the point Pa and the aperture stop AS1.
In the switching member 1, the mirror M11 to be inserted at the position of the branch point Pb and the mirror M12 that guides the emitted light beam from the mirror M11 to the aperture stop AS1 are fixed facing each other in parallel.
[0025]
According to these mirrors M11 and M12, when the switching member 1 is inserted (see FIG. 1), the first optical path R1 is set to be approximately Z-shaped.
By the way, if it is only for switching, the mirror M12 may be fixed without moving together with the mirror M11.
However, in this embodiment, the mirror M12 is actively moved as the switching member 1 together with the mirror M11.
[0026]
Thus, if they are moved together in a state where they are fixed in parallel in advance, as shown in FIG. 4, even if the entire posture and position of the switching member 1 are slightly shifted (for example, from the state indicated by the dotted line to the state indicated by the solid line). Even if a deviation occurs, the deflection angle at the mirror M11 and the deflection angle at the mirror M12 are in a complex angle relationship, so that the incident angle with respect to the aperture stop AS1 is maintained.
[0027]
At this time, the incident position with respect to the aperture stop AS1 may be shifted in a direction perpendicular to the optical axis. However, regarding the influence of the shift on the emitted light beam of the aperture stop AS1, the light source 11, the collector lens 12, and the relay lens 14a are designed so that the light source image formed at the position of the aperture stop AS1 becomes sufficiently large. If you do, you will be surely compensated.
[0028]
Therefore, the light beam emitted from the aperture stop AS1 (and thus the illumination state of the test object O) is maintained even if a slight deviation occurs in the overall posture and position of the switching member 1.
Of the mirrors M21 and M22 for setting the second optical path R2, the mirror M22 to be arranged at the confluence Pb is unnecessary when the first optical path R1 is set, so that it can be inserted and removed. Preferably it is.
[0029]
Moreover, the mirror 22 is preferably connected (fixed) to the switching member 1 so as to be detached / inserted in conjunction with the insertion / removal of the switching member 1. If connected, an actuator (not shown) for driving the switching member 1 and an actuator for driving the mirror 22 can be used in common, so the cost can be reduced.
As described above, since the diameter of the aperture stop AS2 in the second optical path R2 is larger than the diameter of the aperture stop AS1 in the first optical path R1, the state shown in FIG. 3 (the second optical path R2 is set). The light beam emitted from the aperture stop AS2 at the time is maintained in a desired state even if the position and posture of the mirror M22 are slightly deviated, and the illumination state of the test object O is also maintained in a desired state. Be drunk.
[0030]
Therefore, in the present embodiment, the desired two types of illumination can be accurately set without providing a strong guide mechanism or stage or a fine feed device on the switching member 1 (that is, simple and easy). The lighting state can be switched accurately.)
Note that the switching of the switching member 1 may be performed manually in addition to the actuator. In any case, the switching member 1 is preferably provided with a guide mechanism so that its moving direction and stop position are determined.
[0031]
Further, the moving direction at the time of switching of the switching member 1, the shape of the switching member 1, the guide mechanism, and the like are selected so as not to disturb the first optical path R1 and the second optical path R2. According to FIG. 1 and FIG. 3, the movement direction is represented as the vertical direction of the paper surface, but it goes without saying that the front and back direction of the paper surface may be used.
[0032]
[Second Embodiment]
A second embodiment of the present invention will be described with reference to FIGS.
In the present embodiment, an illumination device mounted on a scanning microscope capable of switching between confocal observation and bright field observation will be described. Here, only differences from the first embodiment will be described.
[0033]
5 and 6 are configuration diagrams of the illumination device of the present embodiment. The difference between FIG. 5 and FIG. 6 is the difference in the illumination state.
As shown in FIGS. 5 and 6, the illumination device 20 includes a light source 21, a collector lens 22, and a filter 23 arranged in this order, and a prism (illumination light / imaging light branching) disposed inside the microscope unit 20 ′. The object O is illuminated through 26 and the first objective lens 27.
[0034]
Note that the microscope unit 20 ′ sequentially arranges the first objective lens 27 and the prism 26 from the object O side, and forms an image of the light beam from the object O on the light receiving surface I of the TDI sensor.
The microscope unit 20 ′ can switch between bright field observation and confocal observation (among these, the confocal observation transmits image data of the test object while sending a stage (not shown) on which the test object O is placed. The whole image data is obtained by acquiring part by part.)
[0035]
In connection with this, in the illuminating device 20, it is necessary to change the illumination area (field of view) of the test object O into at least two types.
Similarly to the illuminating device 10 of the first embodiment, the illuminating device 20 also has a first optical path R1 (see FIG. 5) and a second optical path R2 (see FIG. 6) that branch between the light source 11 and the test object 0. ) To be switchable.
[0036]
However, in the present embodiment, as shown in FIGS. 5 and 6, in order to make the illumination area variable, the first optical path R <b> 1 and the second optical path R <b> 2 branch midway between the prism 26 and the filter 23. Between.
Of the non-common optical paths from the branch point Pa to the confluence Pb, the field stop FS1 having a smaller diameter is fixedly disposed toward the first optical path R1, and the diameter of the field stop FS1 is increased toward the second optical path R2. The larger field stop FS2 is fixedly arranged.
[0037]
The field stop FS1 is a pinhole plate for confocal observation (a plurality of pinholes are formed), and limits the illumination area of the test object O to a part.
The diameter of the field stop FS2 is sufficiently large, and the illumination area of the test object O is set to a size necessary for normal bright field observation.
Further, the optical path length of the first optical path R1 (the optical distance composed of the refractive index of the medium and the geometric distance) and the optical path length of the second optical path R2 are the same.
[0038]
Further, the field stop FS1 and the field stop FS2 are both arranged at a position conjugate with the test object O (and the light receiving surface I). Each pinhole formed in the field stop FS1 corresponds to each light receiving portion of a TDI sensor (not shown) disposed on the light receiving surface I.
Of these, at least the field stop FS1 has a high accuracy required for its alignment, and is therefore accurately positioned with respect to the optical axis of the prism 26.
[0039]
By the way, also in this embodiment, as shown in FIGS. 5 and 6, the incident optical path to the branch point Pa of the first optical path R1 and the second optical path R2 and the second optical path R1 of the second optical path R1. The exit optical path from the junction Pb with the optical path R2 is on parallel lines that are separated from each other.
Therefore, as in the first embodiment, at least the mirrors M11 and M12 for setting the first optical path R1 and the mirrors M21 and M22 for setting the second optical path R2 are used (hereinafter referred to as four mirrors). Explain the case where is used.)
[0040]
The relationship between the mirrors M11, M12, M21, and M22 and the field stop FS1 and the field stop FS2 is the same as the relationship between the mirrors M11, M12, M21, and M22, the aperture stop AS1, and the aperture stop AS2 in the first embodiment. .
[0041]
Also in this embodiment, the mirrors M11 and M12 are fixed so as to be accurately parallel for switching between the first optical path R1 shown in FIG. 5 and the second optical path R2 shown in FIG. A switching member 2 that can be inserted and removed is used.
According to the switching member 2, as with the switching member 1 of the first embodiment, the incident angle with respect to the field stop FS1 is maintained even if a slight shift occurs in the overall posture and position of the switching member 2.
[0042]
Further, there is a possibility that the incident position with respect to the field stop FS1 is shifted in a direction perpendicular to the optical axis, but regarding the influence of the shift on the emitted light beam of the field stop FS1, the light beam incident on the position of the field stop FS1 is sufficient. As long as the light source 21 and the collector lens 22 are designed to be thicker, they can be compensated reliably.
Therefore, the emitted light beam from the field stop FS1 (and thus the illumination state of the test object O) is maintained even if a slight deviation occurs in the overall posture and position of the switching member 2.
[0043]
Further, since the mirror M22 to be arranged at the junction Pb is not necessary when the first optical path R1 is set, it is preferable that the mirror M22 can be inserted and removed, and the switching member 2 is inserted as in the first embodiment. It is preferably connected (fixed) to the switching member 2 so as to be detached / inserted in conjunction with the withdrawal.
Further, as described above, the diameter of the field stop FS2 in the second optical path R2 is larger than the diameter of the field stop FS1 in the first optical path R1, and therefore the state shown in FIG. 6 (the second optical path R2 is set). The light beam emitted from the field stop FS2 at the time of the measurement is maintained in a desired state even if there is a slight deviation in the position and posture of the mirror M22, and the illumination state of the test object O is also maintained in the desired state. Be drunk.
[0044]
Therefore, according to the present embodiment, the illumination state can be easily and accurately switched by the switching member 2 as in the first embodiment.
The switching of the switching member 2 may be performed manually in addition to the actuator. In any case, the switching member 2 is preferably provided with a guide mechanism so that its moving direction and stop position are determined.
[0045]
In addition, the moving direction at the time of switching of the switching member 2, the shape of the switching member 2, the guide mechanism, and the like are selected so as not to disturb the first optical path R1 and the second optical path R2. According to FIGS. 5 and 6, the movement direction is represented as the vertical direction of the paper surface, but it goes without saying that the front and back direction of the paper surface may be used.
[Others]
In each of the above embodiments, the two mirrors M11 and M12 are used as the switching member, but a prism having two reflecting surfaces may be used. Since the refractive index of the prism is different even at the same geometric distance as that of air, the optical path length is adjusted so that the optical distance of the second optical path R2 is the same as that of the first optical path R1. Adjustment such as inserting a transparent member (glass or the like) is necessary.
[0046]
In each of the above embodiments, two reflecting surfaces (mirrors M11 and M12) are used as the switching member. However, if the reflecting member is composed of a pair of parallel reflecting surfaces fixed to each other, four or six are used. The number of the first optical path R1 may be made into a plurality of continuous Z-shapes (sawtooth shapes) by using other even number of reflecting surfaces such as. In either case, since the first deflection angle and the last deflection angle are in a complex angle relationship, the same effect as in the above embodiment can be obtained (however, it is preferable to use two sheets because the number of parts is small). Needless to say.)
[0047]
In each of the above embodiments, the case where the optical element that is used for a microscope and is fixedly arranged in the first optical path R1 is a diaphragm has been described. However, an illumination device mounted on an optical device other than a microscope, The present invention is also applicable when the optical element fixed to one optical path R1 is other than the stop.
In each of the above embodiments, the optical element fixedly arranged in the second optical path R2 is a diaphragm having a large diameter. However, any optical element may be used as long as the accuracy required for alignment is low. Needless to say, nothing need be arranged in the second optical path R2.
[0048]
In each of the above embodiments, the mirror M22 that can be inserted into and removed from the junction Pb is used. However, if the loss of the light amount can be ignored, both the first optical path R1 and the second optical path R2 are set. A possible fixed half mirror may be used instead. However, in a general lighting device, a mirror that can be inserted / removed is preferable because it is desired to avoid a loss of light amount as much as possible.
[0049]
【The invention's effect】
As described above, according to the present invention, an illumination device and a microscope illumination device capable of easily and accurately switching the illumination state are realized.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a lighting device according to a first embodiment (when a first optical path R1 is set).
FIG. 2 is a schematic view of an optical path in the illumination device.
FIG. 3 is a configuration diagram of the illumination device according to the first embodiment (when the second optical path R2 is set).
FIG. 4 is a diagram illustrating a relationship between mirrors M11 and M12 and an optical path.
FIG. 5 is a configuration diagram of the illumination device according to the second embodiment (when the first optical path R1 is set).
FIG. 6 is a configuration diagram of the illumination device according to the second embodiment (when the second optical path R2 is set).
[Explanation of symbols]
1, 2, switching member M11, M12, M21, M22 Mirror 10, 20 Illumination device 10 ', 20' Microscope 11, 21 Light source 21, 22 Collector lens 13 Filter 14 Relay lens 15 Condensation lens 16, 26 Prism 17, 27 First Objective lens O Object I Image plane (imaging surface, light receiving surface)
Pa Branch point Pb Junction point

Claims (3)

In order to switch the illumination state of the illuminated surface between the light source and the illuminated surface, the first optical path and the second optical path are arranged to be switchable,
An incident optical path where the first optical path is incident on a branch point branched from the second optical path and an outgoing optical path which is emitted from a confluence where the first optical path merges with the second optical path are separated from each other. On parallel lines,
A non-movable optical element is disposed in the first optical path formed between the branch point and the junction point,
A switching member that is detachable between the branch point and the optical element and that selectively sets the first optical path / second optical path according to the insertion / removal thereof,
The switching member is
Fixed facing a pair of parallel reflecting surfaces each other state, and are not to form the first optical path roughly Z shape by reflection in their reflective surfaces,
The microscope illumination apparatus , wherein the optical element is an aperture or a field stop having a constant diameter . The microscope illumination apparatus according to claim 1 ,
The optical illumination device is a pinhole plate. The microscope illumination apparatus according to claim 1 or 2 ,
A microscope illumination device, wherein a diaphragm having a diameter wider than that of the diaphragm is disposed in a non-common optical path of the second optical path with the first optical path.

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