JP6424043B2 - Illumination device, optical inspection device, and optical microscope - Google Patents

Description

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

  For example, an optical inspection apparatus is generally used for inspecting a semiconductor wafer. In an optical inspection apparatus, an illumination light is irradiated to a semiconductor wafer to be inspected, an image obtained by light reflected on the surface of the semiconductor wafer is captured, and the presence or absence of defects or the like is inspected from this image. . Also in an optical microscope, an observation object may be irradiated with illumination light and an image obtained by the transmitted light or reflected light may be captured.

  In the optical inspection apparatus, as a method for increasing the detection sensitivity of defects on a semiconductor wafer, parameters such as the amount of illumination light irradiated on the surface of the semiconductor wafer, the light beam angle distribution, the wavelength, and the polarization direction are adjusted. . Since various circuit patterns exist in semiconductor wafers, there are optimum parameters for each wafer. Among them, there is a circuit pattern in which the detection sensitivity is increased by increasing the light beam angle from the outer periphery in the light beam angle distribution of the illumination light incident on the semiconductor wafer.

  In an illumination device for an optical inspection device, an ultra-high pressure mercury (UV) lamp is used as a light source, and light emitted from the light source is reflected by a reflector and condensed toward a subsequent optical system. However, the light amount distribution of the illumination light irradiated on the semiconductor wafer is non-uniform reflecting the light ray angle of the light incident on the optical system described above. That is, as shown in FIG. 6, the light intensity distribution on the pupil plane of this illumination light has the smallest light quantity at the center due to the shadow of the bulb of the ultrahigh pressure mercury lamp, and the highest light quantity at the position beyond the shadow. The light intensity gradually decreases from the outer periphery toward the outer periphery. FIG. 6 is a graph showing a cross-sectional light amount distribution passing through the center of the pupil plane of the illumination light.

  Therefore, it has been proposed to use a DMD (Digital Micromirror Device) element in which a plurality of fine mirrors whose inclination changes depending on on / off of the drive voltage, and to change the ray angle distribution of illumination light by each mirror. (See Patent Document 1). However, when a DMD element is used, the amount of light is reduced overall due to the low reflectivity of the mirror.

  The amount of illumination light is a parameter required when inspecting all semiconductor patterns. For this reason, it is indispensable to ensure a sufficient amount of light when inspecting a semiconductor wafer. Therefore, when a DMD element is used, it is difficult to secure a sufficient amount of light to increase detection sensitivity.

  On the other hand, it has been proposed to change the light beam angle distribution of illumination light by using optical elements having different transmittances in the concentric direction (see Patent Document 2). However, even when such an optical element is used, the detection sensitivity may be reduced due to the loss of light quantity.

International Publication No. 2005/026843 JP 2007-33790 A

  One of the aspects of the present invention has been proposed in view of such a conventional situation, and is capable of changing the light beam angle distribution of the illumination light while suppressing the loss of the light amount. An object is to provide an illumination apparatus capable of increasing the angle, and an optical inspection apparatus and an optical microscope capable of further improving detection sensitivity by including such an illumination apparatus.

In order to achieve the above object, the present invention provides the following means.
[1] A lighting device according to a first aspect of the present invention includes a light source that emits light, and a multiple reflection element that emits the light from the light incident surface, and after multiple reflection inside thereof, emits the light from the light emission surface. And an optical element that is arranged in an optical path between the light source and the multiple reflection element and changes a light beam angle distribution of the light, and the optical element includes at least two pairs of conical lenses. the between two conical lens while the light passes through, Ri optical path of the light beam between the inner and outer circumferential sides of the pupil plane of the light swapped further wavelength switching mechanism for switching the wavelength of the light And a lens moving mechanism for moving at least one of the two conical lenses in the optical axis direction according to the wavelength of the light switched by the wavelength switching mechanism .

[2] In the illumination device according to [1], the light intensity on the outer peripheral side is relatively higher than the light intensity on the inner peripheral side on the pupil plane of the light before entering the two conical lenses. The light intensity on the outer peripheral side may be relatively higher than the light intensity on the inner peripheral side on the pupil plane of the light after entering the two conical lenses.

[ 3 ] An optical inspection apparatus according to the second aspect of the present invention includes the illumination device according to [1] or [2] .

[ 4 ] An optical microscope according to a third aspect of the present invention includes the illumination device according to [1] or [2] .

  As described above, according to one aspect of the present invention, it is possible to change the light beam angle distribution of the illumination light while suppressing the loss of the light amount, and particularly to the illumination device capable of increasing the light beam angle from the outer periphery, and By providing such an illumination device, it is possible to provide an optical inspection device and an optical microscope capable of further improving detection sensitivity.

It is a schematic diagram which shows schematic structure of the illuminating device and optical inspection apparatus which concern on one Embodiment of this invention. It is a top view which shows the structure of the optical element with which the illuminating device shown in FIG. 1 is provided. It is a side view which shows the structural example of the light-diffusion element with which the illuminating device shown in FIG. 1 is provided. It is a graph which shows the cross-sectional light quantity distribution which passes along the center of the pupil plane of illumination light at the time of using the optical element shown in FIG. (A) is a top view which shows the optical arrangement in the long wavelength of the optical element shown in FIG. 1, (B) is a top view which shows the optical arrangement in the short wavelength of the optical element shown in FIG. It is a graph which shows the cross-sectional light quantity distribution which passes along the center of the pupil plane of illumination light.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
In the following description, in order to make each component easy to see, the scale of the dimension may be changed depending on the component in the drawings.

(First embodiment)
First, as an embodiment of the present invention, for example, an illumination device 1 and an optical inspection device 100 shown in FIG. 1 will be described. FIG. 1 is a schematic diagram illustrating a schematic configuration of the illumination device 1 and the optical inspection device 100.

  As shown in FIG. 1, the optical inspection apparatus 100 inspects, for example, the presence or absence of defects in a semiconductor wafer (hereinafter simply referred to as a wafer) W to be inspected. Specifically, the optical inspection apparatus 100 includes a light source 2, an optical element 3, a multiple reflection element 4, a light diffusion element 5, a relay optical system 6, an optical path conversion element 7, and a condensing optical system 8. The imaging optical system 9 and the imaging device 10 are roughly provided.

  Among these, the light source 2, the optical element 3, the multiple reflection element 4, the light diffusion element 5, the relay optical system 6, the optical path conversion element 7, and the condensing optical system 8 include the first optical axis AX1. Above, they are arranged side by side. On the other hand, the optical path conversion element 7, the imaging optical system 9, and the imaging device 10 are sequentially arranged side by side on the second optical axis AX2 orthogonal to the first optical axis AX1.

  The illumination device 1 includes a light source 2, an optical element 3, a multiple reflection element 4, a light diffusion element 5, a relay optical system 6, and a condensing optical system 8. The illumination optical system to irradiate is comprised.

  The light source 2 is an ultra high pressure mercury (UV) lamp. A reflector 11 is disposed around the light source 2. The reflector 11 has an inner reflection surface 11a formed so that its cross-sectional shape draws an elliptical line, and the inner reflection surface 11a reflects the light La emitted from the light source 2 so as to be described later. The light Lb is condensed toward the light incident surface 4a.

  For the light source 2, for example, an LED lamp can be used in addition to the above-described ultrahigh pressure mercury lamp. In order to improve detection sensitivity, a point light source having a small light emitting point such as LPP (Laser Produced Plasma) or LDLS (Laser Driven Light Source) may be used as the light source 2. That is, the type of the light source 2 is not particularly limited, and an optimal light source can be appropriately selected and used according to the inspection object.

  The optical element 3 changes the ray angle distribution of the light Lb from the light source 2 toward the multiple reflection element 4. Specifically, the optical element 3 in the present embodiment has a configuration as shown in FIG. FIG. 2 is a plan view showing the configuration of the optical element 3.

  The optical element 3 shown in FIG. 2 includes two conical lenses 21 and 22 and two convex lenses 23 and 24. The two conical lenses 21 and 22 are aligned in the optical axis direction (on the first optical axis AX1) with the surfaces 21b and 22b opposite to the surfaces 21a and 22a on which the tops of the conical lenses are formed facing each other. Has been placed. The two convex lenses 23 and 24 are arranged side by side in the optical axis direction (on the first optical axis AX1) so as to face the surfaces 21a and 22a on which the apexes of the conical lenses 21 and 22 are formed. The arrangement of the two conical lenses 21 and 22 is not limited to the arrangement described above. For example, the two conical lenses 21 and 22 are arranged in a state where the surfaces 21a and 22a on which the tops are formed face each other, or the tops of the two conical lenses 21 and 22 are formed. It is also possible to arrange the surfaces 21a and 22a in the same direction.

  In the optical element 3, while the light Lb passes between the two conical lenses 21 and 22, the optical path of the light beam is switched between the inner peripheral side and the outer peripheral side of the pupil plane of the light Lb. That is, the optical path of the light beam passing through the inner peripheral side of the conical lens 21 in the light beam constituting the light Lb is switched to the outer peripheral side (see the two-dot chain line in FIG. 2). On the other hand, the optical path of the light beam passing through the outer peripheral side of the conical lens 21 is switched to the inner peripheral side (see the broken line in FIG. 2). Moreover, the convex lenses 23 and 24 condense the light Lb that passes at each position.

  The optical element 3 is not limited to the above-described configuration, and may be any configuration that includes at least two paired conical lenses 21 and 22, and depends on the optical design between the light source 2 and the multiple reflection element 4. The convex lenses 23 and 24 can be omitted, or another convex lens or concave lens can be added.

  As shown in FIG. 1, the multiple reflection element 4 is composed of a rod integrator, and has a light incident surface 4a at one end in the longitudinal direction and a light exit surface 4b at the other end in the longitudinal direction. The multiple reflection element 4 causes the light Lc that has passed through the optical element 3 to be incident from the light incident surface 4a, undergoes multiple reflection inside, and then emits the light Ld from the light emitting surface 4b.

  The light diffusing element 5 diffuses the light Ld emitted from the light emitting surface 4 b of the multiple reflecting element 4. Specifically, the light diffusing element 5 has a structure in which a fine concavo-convex pattern 5b is formed on one surface of a substrate 5a as shown in FIG. 3, for example. The light diffusing element 5 is arranged with the surface on which the concave / convex pattern 5 b is formed facing the side opposite to the multiple reflection element 4. Thereby, the light diffusing element 5 emits the light Le diffused by the concavo-convex pattern 5b. The light diffusing element 5 can also be arranged with the surface on which the concave / convex pattern 5 b is formed facing the multiple reflection element 4.

  As shown in FIG. 1, the relay optical system 6 includes a first relay lens 12 and a second relay lens 13, and adjusts the size of the light Lf according to the size of the irradiation surface of the wafer W. .

  The optical path conversion element 7 is composed of a dichroic mirror, and transmits light Lf directed toward the wafer W, while reflecting light Lg reflected back from the wafer W described later toward the imaging device 10.

  The condensing optical system 8 includes a condenser lens 14 and an objective lens 15, and irradiates the condensed light (illumination light L) onto the surface of the wafer W. As a result, the light Lg reflected from the surface of the wafer W passes through the objective lens 15 and the condenser lens 14, enters the optical path conversion element 7, and is reflected toward the imaging optical system 9.

  The imaging optical system 9 includes a condenser lens 16 and an imaging lens 17. The imaging device 10 captures the light Lh reflected by the optical path conversion element 7 in accordance with the size of the imaging surface of the imaging device 10. Form an image on the surface.

  The imaging device 10 is configured by a digital camera using an imaging element such as a CCD or CMOS. The imaging device 10 captures an image obtained by the light Lg reflected from the surface of the wafer W. In the optical inspection apparatus 100, it is possible to inspect the presence or absence of defects on the wafer W from this image.

  In the illumination device 1 of the present embodiment, the light angle distribution of the light Lb from the light source 2 toward the multiple reflection element 4 is changed by the optical element 3 described above. Thereby, the light ray angle from the outer periphery can be increased in the light ray angle distribution of the illumination light L incident on the wafer W while suppressing the loss of the light amount.

  Specifically, in the optical element 32, the light quantity distribution on the pupil plane of the light Lb before entering the two conical lenses 21 and 22 (position A shown in FIG. 2) is shown in FIG. FIG. 4B shows the light quantity distribution on the pupil plane of the light Lc after entering the two conical lenses 21 and 22 (position B shown in FIG. 2).

  As shown in FIG. 4A, the light intensity distribution on the pupil plane of the light Lb before entering the two conical lenses 21 and 22 is relatively lower on the outer peripheral side than on the inner peripheral side. It has become. On the other hand, as shown in FIG. 4B, the light quantity distribution on the pupil plane of the light Lc after being incident on the two conical lenses 21 and 22 has a light intensity on the outer peripheral side rather than a light intensity on the outer peripheral side. Is relatively high.

  In the illumination device 1 of the present embodiment, the optical element 3 described above can increase the light beam angle from the outer periphery in the light beam angle distribution of the illumination light L incident on the wafer W while suppressing the loss of the light amount. Thereby, the optimal illumination light can be obtained for the circuit pattern whose detection sensitivity is increased by such illumination light.

  As described above, the optical inspection apparatus 100 according to the present embodiment includes the illumination apparatus 1 described above, so that it is possible to further improve the detection sensitivity while suppressing the loss of the light amount. Is possible.

  Further, the illumination device 1 of the present embodiment may have a configuration including a wavelength switching mechanism that switches the wavelength of the illumination light L. Although not shown in the figure, for example, a wavelength filter that converts the wavelength of the illumination light L is disposed in any of the optical paths of the illumination device 1. Thereby, the wavelength of the illumination light L can be switched. Moreover, in the illuminating device 1, it is possible to arrange | position the several wavelength filter from which a wavelength differs interchangeably.

  In the illumination device 1, the optical path of the light beam changes due to the chromatic aberration of the lens due to the difference in the wavelength of the illumination light L. For this reason, for example, even if the light beam angle distribution is optimized by the optical element 3 on the long wavelength side, the light path of the light beam changes on the short wavelength side and deviates from the optimum range of the light beam angle distribution.

Therefore, the illumination device 1 is configured to include the lens moving mechanism 30 in addition to the wavelength switching mechanism described above, as shown in FIGS. Lens moving mechanism 30, depending on the wavelength of the illumination light L is switched by the wavelength switching exchange mechanism (in this embodiment, conical lens 22 and convex lens 24) two of the at least one conical lens of the conical lens 21, 22 It is moved in the optical axis direction (direction along the first optical axis AX1).

Here, FIG. 5A is a plan view showing an optical arrangement of the optical element 3 at a long wavelength, and FIG. 5B is a plan view showing an optical arrangement of the optical element 3 at a short wavelength. .
In the illuminating device 1, as shown in FIGS. 5A and 5B, the conical lens 22 and the convex lens 24 are moved in the optical axis direction by the lens moving mechanism 30, so that the optimum according to the wavelength of the illumination light L is obtained. It is possible to obtain a ray angle distribution.

In addition, this invention is not necessarily limited to the thing of the said embodiment, A various change can be added in the range which does not deviate from the meaning of this invention.
For example, in the above-described embodiment, the case where the optical inspection apparatus 100 including the illumination apparatus 1 performs the inspection of the wafer W is exemplified. However, any inspection apparatus that can be inspected by the optical inspection apparatus 100 may be used. It is not limited.

  In addition to the optical inspection apparatus 100, the illumination apparatus 1 can be applied to an optical microscope that irradiates an observation target with illumination light L and captures an image obtained by the transmitted light or reflected light. In the optical microscope provided with such an illuminating device 1, the detection sensitivity can be further improved while suppressing the loss of light quantity, so that observation with high resolution becomes possible.

  DESCRIPTION OF SYMBOLS 1 ... Illuminating device 2 ... Light source 3 ... Optical element 4 ... Multiple reflection element 5 ... Light diffusing element 6 ... Relay optical system 7 ... Optical path conversion element 8 ... Condensing optical system 9 ... Imaging optical system 10 ... Imaging apparatus 11 ... Reflector DESCRIPTION OF SYMBOLS 12 ... 1st relay lens 13 ... 2nd relay lens 14 ... Condenser lens 15 ... Objective lens 16 ... Condensing lens 17 ... Imaging lens 21, 22 ... Conical lens 23, 24 ... Convex lens 30 ... Lens moving mechanism 100 ... Optical inspection device W ... Semiconductor wafer L ... Illumination light

Claims (4)

A light source that emits light;
The light is incident from the light incident surface, and after multiple reflection inside, a multiple reflection element that emits from the light exit surface; and
An optical element that is disposed in an optical path between the light source and the multiple reflection element and changes a light ray angle distribution of the light, and
The optical element includes at least two pairs of conical lenses,
Wherein between the two conical lens while the light passes through, Ri optical path of the light rays swapped between the inner and outer circumferential sides of the pupil plane of the light,
A wavelength switching mechanism for switching the wavelength of the light;
An illumination device comprising: a lens moving mechanism that moves at least one of the two conical lenses in an optical axis direction according to a wavelength of light switched by the wavelength switching mechanism . In the pupil plane of the light before entering the two conical lenses, the light intensity on the outer peripheral side is relatively lower than the light intensity on the inner peripheral side,
2. The illumination device according to claim 1, wherein the light intensity on the outer peripheral side is relatively higher than the light intensity on the inner peripheral side in the pupil plane of the light after entering the two conical lenses. . Optical inspection apparatus characterized by comprising a lighting device according to claim 1 or 2. Optical microscope, characterized in that it comprises a lighting device according to claim 1 or 2.

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