JPH0989790A - Defect inspection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a defect inspection apparatus by which the defect of a phase shifter and a light-transmitting foreign body are detected by a method wherein a transmission-type differential interference microscope and a reflection- type differential interference microscope are installed, transmitted light and reflected light are detected and their differential output is obtained. SOLUTION: A beam of light 1 is changed into parallel light by a beam expander 2, it is polarized spatially by an X-Y scanning part 26, it is refracted by a relay lens 7, it is reflected by a semitransparent mirror 3, it is transmitted through a Nomarski prism 13, and two beams of linearly polarized light whose polarization direction is at right angles to each other are formed. They are separated into beams of light at a slight relative angle so as to advance, they are refracted by an objective lens 10, and a laser spot is formed on a binary reticle 8. A beam of light which is reflected by the binary reticle 8 is incident on the lens 10, it is refracted, it is transmitted again through the prism 13, and it is transmitted through a mirror 3 so as to reach a polarization beam splitter 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a defect inspection apparatus, and more particularly to a defect inspection apparatus for inspecting a substrate such as a reticle or a mask used in a lithography process for manufacturing a semiconductor element or a liquid crystal substrate. .

[0002]

2. Description of the Related Art A conventional binary reticle shifter phase difference amount defect inspection apparatus is, for example, SPEI, Proceedings series V.
olume 2254, "Photomask and X-Ray Mask technology,
"A device for measuring the phase amount of a phase shifter as described in p.294-301, in which the phase shifter part to be inspected in the reticle is positioned in the visual field of the optical microscope, and This is a phase shift amount measuring device for a reticle with a phase shifter that measures the phase amount of one sampled point, and thus the conventional device of this kind has only one inspection result for each sampled point. It was unsuitable to inspect all the defects in the reticle, and there was no idea to detect the phase difference amount defect and the foreign substance at the same time.

[0003]

In view of such a situation, the present invention inspects defects of the phase difference amount of the shifter in all the areas in the binary reticle in a short time, and additionally interferes with the exposure of foreign matters and the like. It is an object of the present invention to obtain a reticle defect inspection apparatus which can simultaneously detect contaminants and can be used as a foreign matter inspection apparatus for a reticle without a shifter.

Further, it is possible to obtain a defect inspection apparatus which can be used for detecting a defect of a phase difference amount of a shifter of a ternary reticle (reticle having a phase shifter portion, a light transmitting portion, and a light shielding portion) and a foreign substance attached to the reticle. To aim.

[0005]

To achieve the above object, the present invention provides a defect inspection apparatus for inspecting a reticle having a light shielding portion, a light transmitting portion, and a phase shifter portion for defects.
A laser light source that emits a first light beam, a first objective lens that is arranged along the optical axis that can collect the light beam that is generated in the reflection direction from the reticle, and collects the light beam that is generated in the transmission direction from the reticle. A second objective lens arranged along the optical axis, a half mirror for reflecting the first light beam toward the first objective lens arranged along the optical axis, and a first mirror reflected by the half mirror. Has a ray splitting means for splitting the ray of light into two rays of linear polarization having a first polarization state and a second polarization state and traveling in mutually different directions, and the objective lens has two rays of linear polarization. A part of a light beam that is condensed and forms two beam spots in a first region in a reticle, and is two linearly polarized light beams having a first polarization state and a second polarization state and traveling in mutually different directions. Passes through the objective lens and onto the reticle The light beam is projected, reflected, again incident on the first objective lens, again incident on the light beam separating means, becomes a second light beam having a third polarization state, exits the light beam separating means, passes through the half mirror, and 2 of 1 polarization state and 2nd polarization state
A part of the two linearly polarized light rays traveling in mutually different directions passes through the reticle, enters the second objective lens, enters the light beam combining means, and becomes a third light ray in the fourth polarization state. A first phase difference that is a relative phase difference amount between two linearly polarized light rays of a first polarization state and a second polarization state of the first light ray. One phase difference adjusting means, a first polarization separating means for separating the second light ray into two linearly polarized light rays having a fifth polarization state and a sixth polarization state, and a third light ray A second polarization splitting means for splitting the light into two linearly polarized light rays having a seventh polarization state and an eighth polarization state; and a scanning means for two-dimensionally scanning two beam spots in a first area of the reticle. A first photoelectric conversion element that photoelectrically converts a light beam having a fifth polarization state and outputs a first signal, The sixth light polarization state converting photoelectrically,
A second photoelectric conversion element that outputs a second signal, a third photoelectric conversion element that photoelectrically converts a light beam in a seventh polarization state, and a third photoelectric conversion element that outputs a third signal, and a photoelectric conversion light beam in an eighth polarization state Then, a fourth photoelectric conversion element that outputs a fourth signal, and adjust the intensity ratio of the first signal and the second signal, the fifth signal, the first signal intensity ratio adjusting means to output as a sixth signal, A first signal strength ratio adjusting means for adjusting the strength ratio of the third signal and the fourth signal and outputting the seventh signal and the eighth signal, and a difference between the signal strengths of the fifth signal and the sixth signal. A first difference signal generating means for generating one difference signal; a second difference signal generating means for generating a second difference signal which is a difference in signal strength between the seventh signal and the eighth signal; Third signal strength ratio adjusting means for adjusting the signal strength ratio of the difference signal and the second difference signal to output as a third difference signal and a fourth difference signal, The error signal calculating means for calculating an error signal which is the difference between the third difference signal and the fourth difference signal, and the binarizing means for binarizing the error signal and outputting the binarized signal are provided. The phase difference adjusting means outputs the first difference signal generated at the step between the light shielding part and the phase shifter part and at the step between the light shielding part and the light transmitting part. The first phase difference is adjusted so that the output of the second difference signal and the output of the second difference signal are substantially constant.

A defect inspection apparatus for inspecting a reticle for defects having a light-shielding portion, a light-transmitting portion, and a phase shifter portion, which comprises microscope means capable of independently forming a transmission differential image and a reflection differential image, and a transmission differential image. Photoelectric conversion means for photoelectrically converting the image and the reflected differential image independently to generate a transmitted differential signal and a reflected differential signal; intensity adjusting means for adjusting the relative intensity ratio of the transmitted differential signal and the reflected differential signal; After the relative intensity is adjusted by the adjusting means, an error signal that is the difference between the two signal intensities is calculated, and a determination circuit that determines a defect based on the error signal is provided. And a defect inspection apparatus, wherein a defect is inspected in such a state that an output of a transmission differential signal and an output of a reflection differential signal generated at a step between a light shielding portion and a light transmitting portion are substantially constant.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION First, the principle of the present invention will be described. [Principle] FIG. 4 shows a principle explanatory view of the epi-illumination microscope portion of the present invention. Cartesian coordinates displayed near each optical element (X
1, Y1) to (X5, Y5) are orthogonal to the optical axis AX,
And the same direction. Further, hereinafter, the azimuth with respect to each coordinate axis is simply referred to as the azimuth with respect to the X axis and the Y axis.

A light ray i00 traveling along the optical axis AX0 is transmitted through a rotatable polarizer P, becomes linearly polarized light having a plane of polarization with an azimuth angle φ0 with respect to the X1 axis, passes through a ¼ wavelength plate Q, and has a phase. The light beam i0 is modulated and the half mirror H
It is reflected by W 1 toward the Nomarski prism W2 along the optical axis AX. The Nomarski prism W2 and the objective lens O1 provide the illumination light EO and the illumination light OE that are 2δ sheared on the object plane S (the plane of the X3 and Y3 coordinates). The illumination light EO is linearly polarized light having a polarization plane parallel to the Y3 axis, and the illumination light OE is linearly polarized light having a polarization plane parallel to the X3 axis.

The relative phase difference α between the illumination light EO and the illumination light OE is variable by changing the polarizer angle φ0 (see the equation (2)). The illumination light is reflected toward the objective lens O1 by the object on the object surface S, and the light beam is the objective lens O1.
1. The Nomarski prism W2 again forms one light beam. When the object is a perfect mirror surface with no phase difference, the optical axis of the Nomarski prism W2 is adjusted so that the phase difference given to the illumination light EO and the illumination light OE is an integral multiple of 2π between the object and the Nomarski prism W2. Adjust the position across the AX.

The rays that have been combined again by the Nomarski prism W2 reach the polarization beam splitter PBS1. X of the rays reaching the beam splitter PBS1
The component of the plane of polarization parallel to the azimuth of φ1 = 45 ° with respect to the axis is transmitted and becomes the light ray IT1, and the component of the plane of polarization parallel to the azimuth of φ1 + 90 ° = 135 ° with respect to the X axis is reflected and becomes the ray IR1. Proceed along AX1.

Next, assuming that the influence of the OTF of the lens is not considered, the intensity of the differential interference image by the rays IT1 and IR1 at the step position is obtained. Since the step of the object to be observed is basically a one-dimensional structure, the following analysis is performed one-dimensionally including the optical system. Although the actual optical system is two-dimensional, in the following discussion, one-dimensional assumption is perfectly acceptable.

In the following description, the intensity of the point image on the image plane of the image-type differential interference microscope will be described. However, the image-type differential interference microscope is different in that the depth of focus also differs depending on the differential interference microscope of the laser scanning optical system. If the σ value of the illumination system in the microscope is set appropriately, the same differential interference contrast image can be obtained. Further, since the present invention is a laser scanning microscope that follows the optical system of a differential interference microscope, the amplitude and phase information of the two beams on the object generated by the light beam separating means (for example, Nomarski prism) is the light beam combining means (for example, Since it is stored in one light beam generated by the interference of two light waves in the Nomarski prism, a differential interference contrast image can be obtained by a photoelectric conversion element installed at a position other than the image plane, for example, near the pupil conjugate plane.

Therefore, the photoelectric conversion element of the embodiment of the present invention may be installed at any position after the light beam combining means. One image point obtained by a differential interference microscope corresponds to two object points that are separated from each other by a distance 2δ due to shear. Let these be O (+ δ) and O (-δ), and let the relative phase difference be ψ
Then, it can be shown as the equation (1).

[0014]

[Equation 1]

Assuming that the phase difference added by the differential interference microscope is α1 and α2, the intensities IT1 (α1) and IR1 (α2) of the interference image corresponding to the light rays IT1 and IR1 are C (3), (3), It becomes like Formula (4), and the relationship with the polarizer angle φ0 is shown by Formula (2).

[0016]

[Equation 2]

[0017]

(Equation 3)

[0018]

[Equation 4]

The differential output S + is defined by the equation (5). k +
Is a constant indicating the gain of the electric system when the differential output is obtained. Equation (6) is obtained from equations (3) and (4).

[0020]

(Equation 5)

[0021]

(Equation 6)

Since the condition that the differential output S + becomes zero when there is no object is S ₊ = 0, Ψ = 0, a = b, the equation (7) is obtained from the equation (6).

[0023]

(Equation 7)

When the expression (7) is satisfied, the differential output expression (5) becomes a dark field image with zero output when there is no object,
A dark field image can be obtained with respect to the set value α1 of the phase difference of an arbitrary microscope. Further, when 0 < k ₊ < 1, the constant k + can be constituted by an attenuator (attenuator). At this time, from the equation (7), the set value α1 of the phase difference of the microscope is −π / 2 < α1 < π / 2 At this time, the polarizer angle φ1 is 0 < φ1 < π / 2 from the equation (2). In the case of 2 <φ ₁ < π, π / 2 <α1 < 3π / 2, the differential output S− is defined by the equation (8) using the constant k−.

[0025]

(Equation 8)

The constant k-is represented by the equation (9), and within the range represented by the equation (10), this is an attenuator (attenuator).
Can be configured.

[0027]

[Equation 9]

[0028]

(Equation 10)

Equations (6) and (8) can be summarized as (11)
It can be shown as a formula.

[0030]

[Equation 11]

Here, the average phase of the step portion of the object is Ψ _a ,
When the phase difference α1 of the microscope is determined so as to satisfy the expression (12) with a small amount of phase change δ, as shown in the expression (13),
It is possible to maximize the contrast of the minute phase change amount δ from the average phase Ψ _a of the step portion of the phase object. This means that when detecting a defect in the phase shifter portion of a halftone reticle, which is a binary reticle, if the average phase of the step portion of the phase shifter portion, that is, the edge portion is matched with Ψ _a , inspection can be performed with the maximum contrast. .

[0032]

(Equation 12)

[0033]

(Equation 13)

FIG. 5 is an explanatory view of another principle of the present invention, which is an explanatory view of the principle of the microscope portion of the transillumination method. The light rays OE and EO transmitted through the object are the objective lens O2,
The Nomarski prism W1 again forms one light beam. The position of the Nomarski prism W1 is adjusted in the direction crossing the optical axis AX so that the phase difference given to the two light beams between the two Nomarski prisms W1 and W2 becomes α1t and α2t.

Of the rays reaching the beam splitter PBS2, the component of the plane of polarization parallel to the azimuth of φ2 = 45 ° with respect to the X axis is transmitted and becomes a ray IT2, and φ2 + 90 ° = with respect to the X axis.
The component of the plane of polarization parallel to the azimuth of 135 ° is reflected and the light beam IR
2 and proceed along AX2. Phase differences α1 and α2 added by the differential interference microscope and rays IT2 and I
Intensity IT2 (α1), IR2 at the image point corresponding to R2
(Α2) etc. can be discussed in the same way as epi-illumination. The object for transmitted illumination is expressed by the expression (14) corresponding to the expression (1).
The relationship between the phase differences α1t and α2t is expressed by equation (15).
(The following subscript t indicates transmitted illumination.) The intensities IT2 (α1) and IR2 (α2) at this time are (16) and (1
It can be shown by the equation 7).

[0036]

[Equation 14]

[0037]

(Equation 15)

[0038]

(Equation 16)

[0039]

[Equation 17]

The transmitted illumination difference image S + t is (18).

[0041]

(Equation 18)

Here, the condition that the differential output S + t becomes zero when there is no object is S _{+ t} = 0, Ψ _t = 0, a _t = b _t , and from equation (18), equation (19) is changed to obtain.

[0043]

[Equation 19]

When the equation (19) is satisfied, the differential output (1
The expression (8) becomes a dark field image in which the output is zero when there is no object, and a dark field image can be obtained for any phase difference setting value α1t of the microscope. Further, when 0 < k _{+ t} < 1, the constant kt can be configured by an attenuator (attenuator). At this time, the set value α1t of the phase difference of the microscope is −π / 2 < α1t < π / 2 from the equation (19). Further, under other conditions π / 2 <α1t < 3π / 2, the differential output S−t is set to (2
0) is defined as follows.

[0045]

(Equation 20)

The constant k−t is expressed by the equation (21), and (2
The constant k−t can be configured by an attenuator (attenuator) within the range represented by the formula (2).

[0047]

(Equation 21)

[0048]

(Equation 22)

Equations (18) and (20) are summarized in (23)
It is shown as an expression.

[0050]

(Equation 23)

Here, the average phase of the step portion of the object is Ψ
_a t, a minute phase variation .DELTA.t, if so to determine the phase difference α1t microscope so as to satisfy the expression (24), (25) as in equation a minute from the average phase [psi _a t of the stepped portion of the phase object It is possible to maximize the contrast of the phase change amount δt. This is done is examined average phase of [psi _a t Tosureba maximum contrast of the stepped portion of the phase shifter portion when detecting the defect of the phase shifter portion of the half-tone reticle is a binary reticle, for example.

[0052]

(Equation 24)

[0053]

(Equation 25)

When observing a circuit pattern on a defect-free reticle, both the differential outputs S ± and S ± t have values other than zero only at the step portion. Considering defect detection by a simple binarization process, it is desirable to obtain a signal having a minimum value (zero) in every portion including a circuit pattern on a defect-free binary reticle. Here, as an example of the step of the binary reticle, constants at1 and bt for transmitted light are given.
1, Ψt1, and ar1, br1, Ψr1 for the reflected light, and the step is shown by the equation (26). The transparent differential output S ± r1 and the transparent differential output S ± t1 of the corresponding differential outputs are (27),
Equation (28) is obtained. The phase differences α1 and α1t are essentially arbitrary. For example, when mainly detecting a phase shifter defect, (8), (2
It is determined according to the equation 0). The constants k ± and k ± t are determined according to the equations (7), (9), (19), and (21), or the transmission differential output S ± t1 becomes zero when there is no object experimentally. The reflection differential output S ± r1 is determined to be zero when the object is a perfect mirror surface.

The constant j is a constant at1, bt1, Ψt1, a
Based on r1, br1, and Ψr1, the equation (29) is set to zero and calculation is performed. Then, using the value, the error signal E
If the error signal E is generated, it is possible to make the error signal E zero at all steps and flat portions (that is, all portions) of the defect-free portion of the reticle. With such a setting, if the error signal E is binarized at an appropriate slice level, it is possible to detect contaminants such as defects in the phase shift amount of the phase shifter portion and foreign substances at the same time.

Actually constants at1, bt1, Ψt1, ar
Even if 1, br1 and Ψr1 are unknown, the constant j may be experimentally determined so that the error signal E becomes zero in the defect-free portion.

[0057]

(Equation 26)

[0058]

[Equation 27]

[0059]

[Equation 28]

[0060]

(Equation 29)

Next, in the case of a three-valued reticle, there are two types of steps, and there is a step Orcg between the chrome film and the glass portion and a step Orcs between the chrome film and the shifter portion for reflected light (30) and (31). Indicated by. The reflection differential output S ± rcg and the reflection differential output S ± rcs of the corresponding differential outputs are given by the equations (34) and (35). The phase difference α1 is determined so as to satisfy the expression (38). The coefficient k ± is determined according to the equation (7) or the equation (9). At this time, the reflected differential output Srcg and the reflected differential output Srcs show the same intensity value in the step portion, and are zero in the flat portion without the step.

Regarding the transmitted light, there are Otcg of the step between the chrome film and the glass portion and Otcs of the step between the chrome film and the shifter portion, which are represented by the equations (34) and (35). Corresponding differential output transparent differential output Stcg, transparent differential output S
tcs is given by the equations (36) and (37). The phase difference α1t is determined so as to satisfy the expression (39). The coefficient k ± t is (1
It is determined according to the equation (9) or the equation (21). At this time, the transmission differential output S ± tcg and the transmission differential output S ± tcs show the same intensity value in the step portion, and are zero in the flat portion without the step.

The constants k ± and k ± t are (7), (9), (1
9), (21) or experimentally determined so that the transmission differential output becomes zero when there is no object and the reflection differential output becomes zero when the object is a perfect mirror surface. . The constant jp in the equation (40) is a constant arcg, br.
cg, Ψrcg, arcs, brcs, Ψrcs, at
cg, btcg, Ψtcg, atcs, btcs, Ψt
Based on cs, the formula (40) is set to zero and calculated. Then, if the error signal E is generated using that value,
It is possible to make the error signal E zero in every step of the defect-free part of the reticle and in the flat part (that is, all parts). With such a setting, if the error signal E is binarized at an appropriate slice level, it is possible to detect contaminants such as defects in the phase shift amount of the phase shifter portion and foreign substances at the same time.

Actually constants arcg, brcg, Ψrc
g, arcs, brcs, Ψrcs, atcg, btc
Even if g, Ψtcg, atcs, btcs, Ψtcs are unknown, the constant jp may be experimentally determined so that the error signal Ep in the defect-free portion becomes zero.

[0065]

[Equation 30]

[Structure / Operation] FIG. 1 is a view showing the structure of a defect inspection apparatus according to the first embodiment of the present invention. The detailed azimuth of the optical element is as described in the "Principle" section.
Light source 1 is a laser light source and the emitted light is 45
Linear polarization of the plane of polarization in the azimuth direction. This light beam is converted into parallel light by the beam expander 2 and the XY scanning unit 2
Two linearly polarized lights that are spatially deflected by 6, are refracted by the relay lens 7, are reflected by the half mirror 3 along the optical axis AX, pass through the Nomarski prism 13, and have their polarization directions orthogonal to each other, The light beam splits into light rays having a slight relative angle, travels, is refracted by the objective lens 10, and forms a laser spot on the binary reticle 8. One of the two linearly polarized lights is a linearly polarized light having a plane of polarization parallel to the paper surface and the other is a linearly polarized light perpendicular to the paper surface.

On the binary reticle 8, two spots slightly displaced by the action of the Nomarski prism 13 are formed close to each other, and these spots are one-dimensionally scanned on the object 9 by the action of the XY scanning section 26. . The light beam reflected by the binary reticle 8 enters the objective lens 10, is refracted, passes through the Nomarski prism 13 located near the pupil position of the objective lens 10 again, passes through the half mirror 3, and reaches the polarization beam splitter 14. . The light ray passing through the polarization beam splitter 14 becomes a light ray IT1 and becomes a linearly polarized light having an azimuth of 45 ° with respect to the X axis. The light ray reflected by the polarization beam splitter 14 becomes a light ray IR1 and becomes a linearly polarized light having an azimuth of 135 ° on the X axis.

When there is no circuit pattern on the binary reticle 8 that causes a phase difference between the two beams,
The phase difference given to the two rays between the Nomarski prism 13 and the reticle 8 is a round trip, and the ray IT1 is α.
1. The position of the Nomarski prism 13 is adjusted by the actuator 41 in the direction crossing the optical axis AX so that α2 = π + α1 for the light ray IR1. Actuator 41
Are controlled by the computer 20.

The light beam transmitted through the binary reticle 8 passes through the condenser lens 42 and the Nomarski prism 6, is combined into one parallel light beam, and reaches the polarization beam splitter 27. The light ray passing through the polarization beam splitter 27 becomes a light ray IT2 and becomes a linearly polarized light having an azimuth of 45 ° with respect to the X axis. The light beam reflected by the polarization beam splitter 27 becomes a light beam IR2 and becomes a linearly polarized light having an azimuth of 135 ° on the X axis.

Assuming that the azimuth angle of each optical element in FIG. 1 with respect to the X axis about the optical axis AX is positive in the Y axis direction, the wedges of the Nomarski prism 6 and the Nomarski prism 13 are oriented at 0 ° and the polarization beam splitter 14 is used. And the analyzer angle (θ4) of the polarization beam splitter 27 is + 45 °. Note that these are the same as those in FIGS. 2 and 3.

When there is no circuit pattern or the like on the binary reticle 8 that causes a phase difference between the two beams, the two rays are given to the two rays between the two Nomarski prisms 6 and 13. The phase difference is round-trip, α1t for ray IT2 and α2 for ray IR2.
The position of the Nomarski prism 6 is adjusted by the actuator 23 in the direction crossing the optical axis AX so that t = π + α1t. The actuator 23 is controlled by the computer 20.

The light beam IT1 is refracted by the lens 15 and photoelectrically converted by the photoelectric conversion element 17. The photoelectric conversion element 17 outputs the video signal S1 to the differential amplifier 19.
The light ray IR1 is refracted by the lens 16 and photoelectrically converted by the photoelectric conversion element 18. The photoelectric conversion element 18 outputs the video signal S2. Video signal S1 or video signal S2
Is attenuated in signal strength by the attenuator 40 at a rate designated by the computer 20 (multiplied by the constant k ± in the equations (7) and (9)) and input to the differential amplifier 19.

The light ray IT2 is refracted by the lens 29 and photoelectrically converted by the photoelectric conversion element 31. The photoelectric conversion element 31 outputs the video signal S3 to the differential amplifier 32.
The light ray IR2 is refracted by the lens 28 and photoelectrically converted by the photoelectric conversion element 30. The photoelectric conversion element 31 outputs the video signal S4. Video signal S3 or video signal S
4 attenuates the signal strength by the attenuator 39 at a rate designated by the computer 20 ((19), (21)).
It is input to the differential amplifier 32 after being multiplied by the constant k ± t of the equation).

The second differential amplifier 24 is composed of two differential amplifiers 1.
9. After adjusting the gain of the output of the differential amplifier 32 to the ratio specified by the computer 20, (2
After being multiplied by the constant j in the equation (9) or the constant jp in the equation (40), an error signal which is a difference signal between them is output. The second differential amplifier 24 includes two differential amplifiers 19 and three differential amplifiers 3.
The error signal E is output by taking the difference between the two outputs S5 and S6. The output S5 immediately before being input to the second operational amplifier 24,
In S6, the relative gain is adjusted so that the ratio is designated by the computer 20. Relative gain adjustment circuits 50 and 50a adjust the relative signal strengths of the outputs S5 and S6 immediately before being input to the second operational amplifier 24. That is, the relative gain adjusting circuits 50 and 50a multiply at least one of the output S5 and the output S6 by the constant j of the equation (29) or the constant jp of the equation (40) to obtain the relative signal strength of the outputs S5 and S6. Adjust. As described above, the second differential amplifier 24 outputs the output S after the gain adjustment.
An error signal E is output by taking the difference between 5 and S6.

The error signal is input to the signal processing circuit 33 having a window comparator circuit which is a binarizing circuit having two slice levels on the plus side and the minus side. The signal processing circuit 33 outputs the binarization result of the error signal, the intensity value of the error signal, and the like to the synchronizer 34. The two slice levels on the plus side and the minus side of the window comparator circuit of the signal processing circuit 33 are set to a level at which a pseudo defect does not occur due to optical noise or electrical noise. The slice level can be set externally via the interface 22 and the computer 20.

The synchronizing device 34 is used for the XY scanning unit 2 during the inspection.
6 and the XY stage 37 are synchronously controlled. The XY scanning unit 26 is driven via the actuator 25. XY
The stage 37 is driven via an actuator 38. A light beam from the light source 1 is scanned in the X direction by the XY scanning unit 26, and the two-dimensional area on the reticle is inspected by moving the XY stage 37 in the Y direction.
The synchronizing device 34 outputs the binarization result of the error signal and the intensity value of the error signal to the computer 20 in synchronization with the control signals (position signals) of the XY scanning unit 26 and the XY stage 37.

The computer 20 generates a map showing the position of the defect in the reticle and the intensity of the error signal at the defect position, and displays it on the display unit 21. The computer 20 controls the actuators 23, 41, 25, and 38, and can finely adjust the Nomarski prism 6 and the Nomarski prism 13 described above. The phase difference amount of the microscope and the attenuator 3 before the inspection is started.
It is possible to automatically set up gains of 9 and 40 and constants j and jp. This setup uses a defect-free reticle or a defect-free reticle.

The constants j and jp are selected according to the type of reticle. If the reticle is a binary reticle (chrome conventional reticle, halftone reticle), the former is used, and the phase difference α1 and α1t of the microscope are optimized by the equations (13) and (25), especially the detection sensitivity of the phase shifter defect. Is optional unless If the reticle is a ternary reticle (such as a Levenson type reticle in which a phase shifter and a light-shielding film are mixed), the latter is used, and the microscope phase differences α1 and α1t are (38),
In order to satisfy the expression (39), that is, both the differential output of the epi-illumination and the differential output of the reflective illumination are constant values in two cases of the step of the light shielding film and the phase shifter and the step of the light shielding film and the light transmitting portion. To be

Therefore, there are a plurality of inspection modes in this embodiment including two kinds of inspection modes when the inspection object is a binary reticle and when the inspection object is a ternary reticle. In other inspection modes, for example, the inspection target is a binary reticle, and the detection sensitivity of defects in the phase shifter portion is (13), (2
There are cases where optimization is performed according to the equation (5). It goes without saying that there is an error output in each of such a plurality of inspection modes. In addition, the phase difference of the microscope before the inspection and the attenuator 3
Automatic setup of gains of 9 and 40 and constants j and jp is also performed according to each inspection mode.

The external operator uses the interface 2
Input the type of reticle to be inspected (binary reticle, ternary reticle, etc.), inspection mode, inspection sensitivity, inspection area, execution of initial setting of the apparatus, execution of inspection, etc. to the computer 20 via 2. To do. FIG. 2 is a diagram showing the device configuration of the second embodiment of the present invention. In the second embodiment, the Nomarski prism (6, 13) in the first embodiment is replaced with a prism having a polarization beam splitter surface. Since other configurations are the same, only the portion of the prism having the polarization beam splitter surface will be described. For convenience of explanation, it is assumed that the Nomarski prism 13 and the actuator 41 in the apparatus of FIG. 1 are replaced with the apparatus of FIG. 2 (reflection mirror M3, prism 81, actuator 83).

In FIG. 2, the light beam from the light source 1 is reflected by the half mirror 3 and enters the reflecting mirror M3 in FIG. The light beam reflected by the mirror M3 enters the prism 81. The prism 81 is composed of two reflection planes M1 and M2 and a polarization beam splitter plane PBS1. These planes are perpendicular to the plane of the paper. Polarization beam splitter plane PB
S1 transmits linearly polarized light having a plane of polarization parallel to the paper surface and reflects vertically polarized linearly polarized light. The reflection plane M1 and the polarization beam splitter plane PBS1 are parallel to each other, and the reflection plane M2
And the polarization beam splitter plane PBS1 is at an angle (for example, several degrees) from parallel. The prism 81 can be rotated about an axis of rotation 82 by an actuator 83, and can also be moved by the actuator 83 in a direction parallel to the paper surface and parallel to the polarization beam splitter plane PBS1. The actuator 83 is also controlled by the computer 20.

The prism 81 has exactly the same function as a Nomarski prism. That is, the incident light beams are polarized planes orthogonal to each other and have a slight angle (separation angle).
Split into two rays. The two light rays enter the reticle 8 through the objective lens 10 and form two spots on the reticle 8 that are slightly displaced. The two light rays are reflected by the reticle 8 and go back to the original optical path to become one light ray again and go out of the prism 81.

When the prism 81 is rotated about the rotary shaft 80 by the actuator 83, the shear amount can be changed. Further, the phase difference between the two light rays can be adjusted by moving the light beam in a direction parallel to the plane of the drawing and parallel to the polarization beam splitter plane PBS1 (direction orthogonal to the optical axis of the lens 10). If the reflecting mirror M3 is rotated by the actuator 84 about the rotation axis 80 in accordance with the rotation of the prism 81 so that the reflecting mirror M3 is always parallel to the PBS1, the movement of one light beam is reduced.
Only the other ray can move. The actuators 83 and 84 are also controlled by the computer 20.
In this way, the prism 81 can adjust the shear amount (shift amount on the reticle 8) and the initial phase difference amount, and can be handled in the same manner as a Nomarski prism. Therefore, the configuration and functions other than the light beam splitting means are the same as those in the first to second embodiments, and there is no problem at all. Similarly, the Nomarski prism 6 and the actuator 23 can be replaced with the device (reflection mirror M3, prism 81, actuators 83, 84) shown in FIG.

FIG. 3 is a diagram showing a device configuration of a third embodiment of the present invention. The third embodiment is a modification of the second embodiment. The difference from the second embodiment lies in the light beam separating means (or the light beam combining means). For the sake of convenience of explanation, the Nomarski prism 13 and the actuator 41 in the apparatus of FIG. 1 are replaced by the apparatus of FIG. 3 (reflection mirrors M1, M2, M) for convenience of explanation.
3, the polarization beam splitters PBS1 and PBS2, and the actuator 90) will be replaced.

In this embodiment, instead of the Nomarski prism, two reflection mirrors M1 and M2 and two polarization beam splitters PBS1 and PBS2 constitute a light beam separating means (or a light beam combining means). PBS1 and PBS2
Polarization beam splitter plane and reflection mirrors M1 and M2
Is parallel to the polarizing beam splitter planes of PBS1 and PBS2 and the reflecting plane of the mirror M1. The mirror M2 can be rotated by an actuator 90 about a rotation axis 91 perpendicular to the sheet. The actuator 90 can also move the whole or a part of these optical systems (for example, only the mirror) in parallel in the X direction.

Polarizing beam splitters PBS1 and PBS2
Transmits linearly polarized light having a plane of polarization parallel to the plane of paper and transmits linearly polarized light having a plane of polarization perpendicular to the plane of paper. Therefore, the illumination light reflected by the mirror M3 is polarized and separated by the PBS1, split into the light rays OE and EO whose polarization directions are orthogonal to each other, and reflected toward the reflection mirrors M1 and M2, respectively. The light ray OE passes through the polarization beam splitter PBS2, the light ray EO is reflected, and travels toward the objective lens 10. The light ray EO is emitted from the PBS 2 in a different direction with respect to the light ray OE by tilting the reflection mirror M2 around the rotation axis 91 by a slight angle. Therefore, the shear amount 2δ after passing through the objective lens can be arbitrarily adjusted. Further, by moving the reflecting mirror M2 in the X direction by the actuator 90, the OE light beam OE
And the initial phase difference amount of the light beam EO can be adjusted.

In this way, the two polarization beam splitters and the two plane mirrors can be used as substitutes for the Nomarski prism, and the same functions can be achieved. Similarly, the Nomarski prism 6 and the actuator 23 can also be replaced with the device of FIG. 3 (reflection mirrors M1, M2, M3, polarization beam splitters PBS1, PBS2, actuator 90).

In the above-mentioned embodiment, the phase difference adjusting mechanism is constituted by a mechanism for moving the Nomarski prism in and out of the optical axis in a direction crossing the optical axis. However, it is close to the polarizer and the polarizer which can rotate about the optical axis AX0 (or AX) as the rotation axis. It can also be achieved by configuring with the provided quarter-wave plate. Polarizer and 1/4 wave plate are used as light source 1 and reticle 8
It is possible to adjust the phase difference between the two light beams separated by the Nomarski prism in the same manner as moving the Nomarski prism by rotating the polarizer provided between the Nomarski prism and the Nomarski prism.

It is also possible to provide a visual observation system and observe the defect based on the defect detection result to observe whether it is a foreign substance or a phase shifter defect. Further, in each of the above-described embodiments, when the light beam separating means (Nomarski prism or the like) can be installed in the vicinity of the pupil of the objective lens, it is preferable that the two straight line changes make a slight angle, and in other places, they are separated in parallel. Any device can be used. The installation location may be appropriately selected according to the optical design of the optical system such as the objective lens and the light beam separating means used.

Further, in the above embodiment, the reticle and the light source 1 are used.
The relative scanning with respect to the ray from the light source may be performed by moving at least one of the reticle stage 37 and the ray from the light source 1 two-dimensionally.

[0091]

As described above, according to the present invention, a conventional reticle having a circuit pattern using a chrome light-shielding film,
It is possible to satisfactorily perform a defect inspection of a phase shifter reticle such as a halftone reticle or a Levenson type in which a circuit pattern is drawn only by the phase shifter made of a light-transmissive thin film. Further, it is possible to provide an inspection apparatus capable of inspecting both the abnormal phase shift amount of the phase shifter portion and the presence / absence of foreign matter adhered to the light transmissive phase object.

[Brief description of drawings]

FIG. 1 is a diagram showing a device configuration of a first embodiment of the present invention.

FIG. 2 is a diagram showing a device configuration of a second embodiment of the present invention.

FIG. 3 is a diagram showing a device configuration of a third embodiment of the present invention.

FIG. 4 is an explanatory view of the principle of the present invention.

FIG. 5 is an explanatory diagram of the principle of the present invention.

[Explanation of symbols]

 1 ─ Light source 6, 13 ─ Nomarski prism 17, 18, 30, 31 ─ Photoelectric conversion element 19, 32 ─ Differential amplifier 24 ─ Second differential amplifier 50, 50a ─ Relative gain adjustment circuit

Claims (12)

[Claims] 1. A defect inspection device for inspecting a defect of a reticle having a light shielding part, a light transmitting part, and a phase shifter part, wherein a laser light source for emitting a first light beam and a laser beam emitted from the reticle in a reflection direction. A first objective lens arranged along an optical axis capable of collecting a light beam; a second objective lens arranged along an optical axis capable of collecting a light beam generated in the transmission direction from the reticle; A half mirror that reflects one light beam toward the first objective lens that is arranged along the optical axis, and a first light beam that is reflected by the half mirror has a first polarization state and a second polarization state. And a light beam splitting device for splitting into two linearly polarized light beams traveling in mutually different directions, the objective lens condensing the two linearly polarized light beams,
The two beam spots forming the two beam spots in the first region in the reticle, and the two linearly polarized light beams of the first polarization state and the second polarization state, which travel in different directions, are partially The light beam passes through the objective lens, collides with the reticle, is reflected, enters the first objective lens again, and then enters the light beam splitting means again to become a second light beam having a third polarization state. A part of a ray of light which is emitted from the means, is transmitted through the half mirror, and is two linearly polarized lights having the first polarization state and the second polarization state and traveling in different directions, is transmitted through the reticle, The second light beam enters the objective lens, then enters the light beam combining means, becomes a third light beam having a fourth polarization state, and exits from the light beam combining means. The relative phase of two linearly polarized rays of different polarization states A first phase difference adjusting means for adjusting a first phase difference which is an amount, and separating the second light ray into two linearly polarized light rays having a fifth polarization state and a sixth polarization state, One polarization splitting means; a second polarization splitting means for splitting the third light ray into two linearly polarized light rays having a seventh polarization state and an eighth polarization state; and a first polarization splitting means in the reticle. Scanning means for two-dimensionally scanning the two beam spots in a region of, a first photoelectric conversion element that photoelectrically converts the light beam in the fifth polarization state and outputs a first signal, and the sixth polarization Photoelectric conversion of the light beam of the state, a second photoelectric conversion element that outputs a second signal, and photoelectric conversion of the light beam of the seventh polarization state, a third photoelectric conversion element that outputs a third signal, the Photoelectric conversion of a light beam of the eighth polarization state, a fourth photoelectric conversion element for outputting a fourth signal, Adjust the intensity ratio of the first signal and the second signal, the fifth signal,
A first signal intensity ratio adjusting means for outputting as a sixth signal, adjusting the intensity ratio of the third signal and the fourth signal, a seventh signal,
A first signal strength ratio adjusting means for outputting as an eighth signal, a fifth difference signal, and a first difference signal generating means for generating a first difference signal which is a difference in signal strength of the sixth signal, and A second difference signal generating means for generating a second difference signal which is a difference in signal strength between the seventh signal and the eighth signal, and a signal of the first difference signal and the second difference signal Third signal strength ratio adjusting means for adjusting the intensity ratio and outputting as a third difference signal and a fourth difference signal, and calculating an error signal which is the difference between the third difference signal and the fourth difference signal. Error signal calculating means, and binarizing means for binarizing the error signal and outputting the binarized signal, and determining means for determining that there is a defect based on the binarized signal of the error signal. Comprising, the phase difference adjusting means, the step between the light shielding portion and the phase shifter portion, and the light shielding portion and the light transmitting portion As the output of the first difference signal and an output of said second difference signal is substantially constant resulting in a difference, defect inspection apparatus characterized by adjusting the first phase difference. 2. The defect inspection apparatus according to claim 1, wherein either one or both of the light beam separating means and the light beam combining means is a birefringent prism. 3. The defect inspection apparatus according to claim 1, wherein the first phase difference adjusting means is a combination of a quarter-wave plate and a polarizer which can rotate about an optical axis. 4. The first phase difference adjusting means is capable of adjusting the phase difference by moving one or both of the light beam separating means and the light beam combining means in a direction transverse to the optical axis. The defect inspection apparatus according to claim 1. 5. The defect inspection apparatus according to claim 1, wherein the first polarization separation means is a polarization beam splitter. 6. The defect inspection apparatus according to claim 1, wherein the second polarization separation means is a polarization beam splitter. 7. The first light ray is linearly polarized light, and the plane of polarization is relative to the plane of polarized light of the linearly polarized light in the first polarization state.
The defect inspection apparatus according to claim 1, wherein the defect inspection apparatus forms an angle of 45 °. 8. The fifth polarization state is linear polarization,
The reticle inspection apparatus according to claim 1, wherein an angle of 45 ° is formed with respect to the plane of polarization of the linearly polarized light in the first polarization state. 9. The sixth polarization state is linearly polarized light,
The defect inspection apparatus according to claim 1, wherein an angle of 45 ° is formed with respect to the polarization plane of the linearly polarized light in the second polarization state. 10. The seventh polarization state is linearly polarized light, and is 45 with respect to the plane of polarization of the linearly polarized light of the first polarization state.
The defect inspection apparatus according to claim 1, wherein the defect inspection apparatus forms an angle of °. 11. The eighth polarization state is linearly polarized light and is 45 with respect to the plane of polarization of the linearly polarized light of the second polarization state.
The defect inspection apparatus according to claim 1, wherein the defect inspection apparatus forms an angle of °. 12. A defect inspection apparatus for inspecting defects of a reticle having a light-shielding portion, a light-transmitting portion, and a phase shifter portion, comprising microscope means capable of independently forming a transmission differential image and a reflection differential image, and the transmission means. Photoelectric conversion means for independently photoelectrically converting a differential image and a reflected differential image to generate a transmitted differential signal and a reflected differential signal, and an intensity adjusting means capable of adjusting a relative intensity ratio of the transmitted differential signal and the reflected differential signal. And, after adjusting the relative intensity by the intensity adjusting means, calculating an error signal that is a difference between the two signal intensities and determining a defect based on the error signal. And the inspection of the defect in a state where the output of the transmission differential signal and the output of the reflection differential signal generated at the step of the phase shifter section and the step of the light shielding section and the light transmitting section are substantially constant. thing Defect inspection apparatus according to claim.