JP3047459B2 - Photomask inspection apparatus and photomask inspection method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a photomask inspection apparatus used as an original when transferring a circuit pattern such as a semiconductor, and more particularly, to a phase shifter for changing the phase of transmitted light. The present invention relates to a technique for measuring a phase shift amount in a phase shift photomask in which a shifter film is added to a specific portion.

[Prior Art] A photomask used as a master when a semiconductor circuit is projected and exposed on a wafer and transferred thereon generally has a structure in which a light-shielding pattern made of a metal such as Cr is formed on a glass substrate. .

However, in a photomask having such a structure, when the circuit pattern is miniaturized, there is a problem that a sufficient contrast of a projected image cannot be obtained due to a light diffraction / interference phenomenon. Various phase shift photomasks have been proposed that increase the image contrast by adding a phase shifter film to a specific location to partially change the phase of transmitted light.

In such a phase shift photomask, since it is important to accurately control the phase, it is necessary to inspect the phase shift amount due to the phase shifter film in addition to the presence / absence of a defect in the light shielding pattern. The amount of phase shift has been determined using an ellipsometer or the like that measures the thickness and refractive index of the thin film using multiple reflection between the thin film surface and the interface between the substrate and the thin film.

[Problems to be Solved by the Invention] However, the ellipsometer, which has been conventionally used for inspection of a phase shift photomask, measures the film thickness and the refractive index using reflection at the interface between the substrate and the thin film as described above. Therefore, when the difference in the refractive index between the substrate and the thin film is small, the measurement is very difficult. When the two have the same refractive index, the intensity of the reflected light at the interface becomes zero, so that the measurement becomes impossible.

On the other hand, light sources in photolithography have been shortened in wavelength with the miniaturization of semiconductor circuit patterns, and it is expected that far ultraviolet rays will become the mainstream of light sources in the future. There are few materials having high transmittance to ultraviolet rays, and it is considered that both the phase shifter film and the substrate of the photomask are formed of quartz glass. In this case, the refractive indices of the two become equal, and it is impossible to measure the amount of phase shift using an ellipsometer as described above.

The present invention has been made in view of such a point,
It is an object of the present invention to provide an inspection apparatus for a phase shift photomask capable of accurately measuring a phase shift amount regardless of a refractive index difference between a phase shifter film and a substrate.

Means for Solving the Problems An inspection apparatus according to the present invention has a geometric original pattern on a substrate substantially transparent to a light beam of a predetermined wavelength, and the transparent substrate is provided on at least a part of the original pattern. In an apparatus for inspecting a photomask including a phase member that changes the phase of a light beam that passes through, an illumination optical system that irradiates monochromatic light or quasi-monochromatic light to a pattern to be inspected of the photomask, and from the illumination optical system An inspection optical system that forms an image of the pattern to be inspected by the illumination light beam in a predetermined reference plane, and a light beam that passes through the inspection pattern while the illumination light beam is incident on the photomask at a predetermined incident angle. Of the zero-order diffracted light and one of the ± 1st-order diffracted lights pass through the pupil plane of the inspection optical system almost symmetrically with respect to the optical axis of the inspection optical system. A light beam deflecting means for changing an incident direction of the illumination light beam, and a pattern detecting means arranged at or near the reference plane for photoelectrically detecting an image of the pattern to be inspected by the inspection optical system. .

[Operation] The principle of the present invention will be described with reference to FIG. 1 showing a configuration of an inspection apparatus according to a first embodiment described later.

In the figure, a wavelength-selectable monochromatic light source 1 generates illumination light (light flux L1) having substantially the same wavelength as the wavelength when a phase shift photomask 7 to be inspected is used in an actual photolithography process. Light is relay lens 2,3
Pupil plane of the illumination optical system (photomask 7 to be inspected)
(Fourier transform surface of the pattern surface of FIG. 2) is applied to the spatial filter 4 (light flux L2 in the figure).

Here, the spatial filter 4 corresponds to the light beam deflecting means in the present invention, and has light transmitting portions 4a and 4b, and the other portions are light shielding portions for the illumination light L2. Each of the light transmitting portions 4a and 4b is located at the midpoint between the Fourier transform positions (two places) of the basic period of the line and space pattern (hereinafter, simply referred to as a pattern) formed on the pattern surface of the photomask 7 and the optical axis. , And one of the lights transmitted through the light transmitting portions 4a and 4b is blocked by the shutter 5a or 5b. First
In the example shown in the figure, light passing through the light transmitting portion 4a is blocked by the shutter 5a, and light L3 transmitted through the light transmitting portion 4b is
Is guided to the photomask 7 (light flux L3 in the figure).

FIG. 2 is a cross-sectional view showing an example of a pattern formed on the photomask 7. As shown, on one surface of the substrate of the photomask 7, a light-shielding portion 7c (substrate + light-shielding pattern), a transmission portion (mask naked surface portion) 7a, and a phase shift portion (substrate + phase shifter film) are arranged at a predetermined pitch. 7b is formed and the transmission part
The basic pattern of the light-shielding portion 7c, the light-shielding portion 7c, the phase-shifting portion 7b, and the light-shielding portion 7c is a periodic pattern in which the basic unit is repeated.

Here, the width of the transmission portion 7a is a, the width of the phase shift portion 7b is b, the amplitude transmittance of the transmission portion 7a is 1, and the amplitude transmittance of the phase shift portion 7b is te ^iδ (0 ≦ t ≦ 1). Assuming that the distance (basic cycle of repetition) from one transmission part 7a to the next transmission part 7a is P, the amplitudes of the zero-order diffracted light and the ± first-order diffracted light generated by this pattern, D _O , and D ± 1 are relative to each other. As a value It is represented by

Here, the amount of phase shift [rad] by the phase shifter film is δ.

In FIG. 1, the illumination light L3 that has passed through the transmission part 4b illuminates the photomask 7 with a tilt with respect to the optical axis via the condenser lens 6. The angle between the illumination light L3 and the optical axis is determined by the position of the light transmitting portion 4b of the spatial filter 4 described above. As described above, the light transmitting portion 4b
Is provided at an intermediate point between the optical axis and the Fourier transform position of the basic period of the pattern formed on the photomask 7, the angle between the illumination light L3 and the optical axis is When the light is vertically incident, the angle formed by the optical axis is half of the direction in which the ± 1st-order diffracted light is generated. Therefore, the first
Illumination light reaching the photomask 7 from the transmission part 4b as shown in the figure.
The direction of L3 is a -1/2 order direction when the illumination light is perpendicularly incident on the photomask 7. Assuming that the shutter 5a is open and the upper reaches the photomask 7 from the light transmitting portion 4a, the direction becomes the +1/2 order, contrary to the case shown in FIG.

As shown, when the photomask 7 is illuminated with the illumination light L3 having a tilt in the -1/2 order, the zero-order diffracted light L40 due to the pattern to be inspected travels straight and is generated in the -1/2 direction. The first-order diffracted light L41 is generated in the (−1 / 2 + 1) order = 1/2 order, and the −1st-order diffracted light is generated in the (−1 / 2−1) = − 3/2 order.

Here, since the direction in which the first-order diffracted light is generated is determined by λ / P (λ: the wavelength of the illumination light), if the pattern pitch P is reduced or if the numerical aperture of the inspection optical system 8 is small, ± 1. The light in the secondary direction passes through the inspection optical system 8, and the light in the ± 3/2 direction does not enter the inspection optical system 8. At this time, the zero-order diffracted light L40 and the + 1st-order diffracted light L41 condensed by the inspection optical system 8 reach the light receiving surface of the position detector 10 located at the image plane position of the pattern by the inspection optical system 8, and the two light beams An interference fringe due to the interference of appears.

Assuming that the pattern surface of the photomask 7 and the imaging magnification of the position detector 10 are M, the intensity distribution P of the interference fringes is Can be represented by Here, x is the detection position of the interference fringe in the image plane.

To simplify this, A is a component independent of the position x (DC component), C is a cosine component, and S is a sine component.

Accordingly, as shown in FIG. 3, the interference fringes 11 (shown as the light intensity distribution in the figure) move in the ± x direction (the direction crossing the interference fringes) depending on the values of C and S.

The phase shift φ [rad] of the intensity distribution of the interference fringes is Becomes

Period of light intensity of pattern image (interference fringe) (period of light and dark)
Is the imaging magnification M × the pattern pitch P, so the pattern shift amount Δx is It is.

Thus, the shift amount Δx in the ± x direction of the image (interference fringe)
It can be seen from the above that φ is determined, and therefore the amount of phase shift δ due to the phase shifter film is determined.

Next, a reference (origin) for measuring the pattern shift amount Δx
Explain how to decide. In addition to the above-described measurement in which the light transmitting part 4a of the spatial filter 4 of FIG. 1 is closed by the shutter 5a and the light transmitting part 4b is opened, the light transmitting part 4a is opened, the light transmitting part 4b is closed, and the measurement is performed again. This time, the interference fringes move in the minus direction, and the movement amount is measured as -Δx. Therefore, if the measurement with only the light transmitting portion 4a opened and the measurement with only the light transmitting portion 4b opened are separately performed, and the difference between the image positions in both is obtained,
This is 2Δx. That is, the phase shift amount due to the phase shifter film can be obtained from this value.

Alternatively, the reference point can be obtained by opening both the light transmitting portions 4a and 4b of the spatial filter 4 and performing measurement using light from both light transmitting portions simultaneously.
In this case, the shift amount of the pattern due to the light from the light transmitting part 4a and the shift amount due to the light from the light transmitting part 4b cancel each other, and as a result, the shift amount Δx of the pattern becomes zero. I do.

As described above, in the present invention, the illumination light amount distribution is adjusted on the pupil plane of the illumination optical system or its conjugate plane, and only a light beam obliquely incident on the photomask at a specific direction and angle is used as illumination light. I'm using That is, the luminous flux deflecting means so that the zero-order diffracted light and the + 1st-order or -1st-order diffracted light of the light transmitted through the pattern to be inspected of the photomask pass through the pupil plane of the inspection optical system almost symmetrically with respect to the optical axis. Accordingly, the incident direction of the illumination light beam is changed based on the pitch of the pattern to be inspected or the like, and the illumination light beam is irradiated on the pattern to be inspected at a predetermined incident angle. For this reason, on the light receiving surface of the phase detecting means, an image is formed by two light beams of zero-order diffracted light and + 1st-order or -1st-order diffracted light, and the amount of phase shift is obtained by detecting the shift amount of the interference fringes due to the interference of the two light beams. Can be If the energy transmittance of the phase shifter film = t ² is known, the phase shift amount of the phase shifter film whose transmittance is not 100% can be measured by the apparatus of the present invention.

Further, as is clear from the optical path diagram of FIG. 1, in the inspection apparatus of the present invention, the zero-order diffracted light and the first-order diffracted light by the pattern of the photomask pass through an optical path symmetric with respect to the optical axis. For this reason, the position of the interference fringes does not change due to the wavefront aberration generated due to the displacement (defocus) of the position detecting means from the image plane, the spherical aberration of the inspection optical system, and the like, so that the measurement can be performed with high accuracy.

In the above description, for ease of explanation, an example has been described in which a spatial filter having an opening at a predetermined position is arranged on the pupil plane of the illumination optical system as a light beam deflecting means. The present invention is not limited to the members, and the entire illumination light beam may be focused on a specific position on the pupil plane of the illumination optical system.

[Embodiment] Fig. 1 shows a configuration of an inspection apparatus according to a first embodiment of the present invention.

The inspection apparatus of the present embodiment includes a light source unit 1, an illumination optical system (relay lenses 2, 3, a mirror MR and a condenser lens 6), an inspection optical system 8 and a position detector 10, and the illumination optical system and the inspection optical system 8 They are arranged so that their optical axes coincide on the same axis. The photomask 7 to be inspected is held vertically between the illumination optical system and the inspection optical system 8 with respect to the optical axis.
Are arranged such that the light receiving surface is located near the image forming surface of the inspection optical system 8. The pupil plane of the illumination optical system (photomask 7)
In the vicinity of the Fourier transform plane of the pattern to be inspected, a spatial filter 4 having light transmitting portions 4a and 4b near the position corresponding to 1/2 of the fundamental period when the pattern to be inspected is Fourier transformed is provided. ing. The light transmitting portions 4a and 4b are provided with sliding shutters 5a and 5b, respectively.
Light transmitting portion 4a by the motor MT _1, also open 4b into two joint when, has become possible to open only one side. In the figure,
The light transmitting portion 4a is closed by the shutter 5a.

In such an apparatus, the light beam L1 emitted from the light source unit 1
Is monochromatic light having substantially the same wavelength as the exposure wavelength when the phase shift photomask 7 is actually used in the photolithography process, and reaches the spatial filter 4 via the relay lenses 2, 3 and the mirror MR (FIG. Luminous flux L2). Since the spatial filter 4 blocks the illumination light L2 except for the light transmitting portions 4a and 4b, the light amount distribution on the pupil plane of the illumination optical system is the same as the basic period when the pattern to be inspected is Fourier-transformed. The light amount becomes zero except at the 1/2 corresponding point and its vicinity. In FIG. 1, since the shutter 5a is closed, only the illumination light L2 incident on the light transmitting portion 4b is irradiated onto the photomask 7 by the condenser lens 6.

Here, FIG. 2 is a cross-sectional view of the pattern to be inspected TP formed on the photomask, and as described above, the basic unit of the transmission part 7a, the light shielding part 7c, the phase shift part 7b, and the light shielding part 7c. Are repeated. At this time, if the basic period of the pattern is P (the distance from the transmission portion 7a to the next transmission portion 7a or the distance from the phase shift portion 7b to the phase shift portion 7b), the optical Fourier transform position of the basic period is ± λ / P (λ is the wavelength of the illumination light). Therefore, when inspecting a pattern as shown in FIG.
The light transmitting portions 4a and 4b are within ± 1/2 from the optical axis of the illumination optical system.
-A center point is provided at a point separated by fλ / P (f is the focal length of the condenser lens 6).

Now, the photo mask 7 is placed on the two-dimensional movable stage RS in a horizontal plane by the motor MT _2, the test pattern TP prior to inspection is set in the illumination area of the illumination light L3. The zero-order diffracted light L40 and the + 1st-order diffracted light L41 of the illumination light L3 due to the pattern TP to be inspected enter the inspection optical system 8, are once focused on the pupil plane, and pass almost symmetrically with respect to the optical axis AX. , And forms an image on the surface of the position detector 10. The position detector 10 measures the position of the image of the pattern to be inspected in the image plane. Since the pattern to be inspected TP is a line-and-space pattern in which transmission parts, light-shielding parts and phase shift parts are arranged at a predetermined pitch, its image shows a sinusoidal intensity distribution. For this reason, the measurement of the position of the image (interference fringe) is easily performed by measuring the coordinates of some points of the peak position of the sinusoidal intensity distribution or some points of the position having a certain specific intensity. . The pattern to be inspected TP
Depending on the pitch, duty ratio, etc., the -1st-order diffracted light or the second-order or higher-order diffracted light from the pattern TP can enter the inspection optical system 8, the vicinity of the pupil plane of the inspection optical system 8 as shown in FIG. It is desirable to arrange a spatial filter 9 capable of selectively extracting zero-order + first-order diffracted light.

Close shutter 5a, shutter 5b
Open and measure the position of the image of the pattern, then the control circuit
50 the shutter 5a open by the motor MT _1, the shutter 5b
Is closed and the same measurement is performed. From the difference 2Δx between the position of the image when only the shutter 5a is opened and the position of the image when only the shutter 5b is opened, the phase shift φ of the intensity distribution of the image is obtained from the above equation (2). ), The phase shift amount δ due to the phase shifter film is obtained.

Alternatively, after performing the measurement with only the shutter 5b open, the measurement may be performed with both the shutters 5a and 5b open. In this case, the difference between the image positions in the two measurements is Δx
In the same manner, the phase shift amount δ can be obtained.

Here, in the present embodiment, as described above, the lateral shift of the pattern image due to the wavefront aberration or the like caused by the defocus hardly occurs, and the depth of focus is wide, so that the best image plane of the inspection optical system 8 can be obtained. On the other hand, it is not necessary to make the position detectors 10 exactly match. When focusing, after opening both the shutters 5a and 5b, the position detector 10 is moved to the optical axis A.
The contrast of the pattern image may be measured while moving up and down along X, and the position where the contrast is highest may be determined as the best focus position (best imaging plane).

Next, FIG. 4 is an optical path diagram showing a configuration of an inspection apparatus according to a second embodiment of the present invention.

In the figure, a light beam L1 generated from a light source 1 emitting monochromatic or quasi-monochromatic light is shaped by relay lenses 2 and 3, and illuminates a transparent flat plate 20 on which a diffraction grating 21 is cut. Diffraction grating 21
It may be formed of a light shielding member such as Cr. Further, it may be formed of a dielectric film giving a phase difference.

Zero-order diffracted light Lc, -1st-order diffracted light La, 1 by diffraction grating 21
The second-order diffracted light Lb is transmitted by the relay lens 22 to a point on the optical axis on the pupil plane (Fourier transform plane) of the illumination optical system (the relay lenses 2 and 3 and the condenser lens 6) and the pattern TP to be inspected.
Are condensed at points corresponding to one half of the fundamental period of.

On the pupil plane of this illumination optical system, shutters 5a, 5b, 5c are provided at positions corresponding to the respective converging points of the -1st order diffracted light, the + 1st order diffracted light, and the 0th order diffracted light by the diffraction grating 21. In this embodiment, the diffraction grating 21, the relay lens 22, and the shutters 5a, 5b, 5c constitute a light beam deflecting unit.

In the present embodiment, since the light flux on the optical axis of the illumination optical system, that is, the zero-order diffracted light Lc is unnecessary, the shutter 5c is always in a light-blocking state, and the shutters 5a and 5b are freely openable and closable. . FIG. 4 shows a state where the shutter 5a on the optical path of the + 1st-order diffracted light La is closed and the shutter 5b on the optical path of the -1st-order diffracted light Lb is opened. Accordingly, in the case of the drawing, only the + 1st-order diffracted light Lb is guided to the photomask 7 by the condenser lens 6 and illuminates the pattern TP to be inspected. At this time, diffracted light of each order is generated by the pattern TP to be inspected. However, since the illumination light L3 illuminates the photomask 7 from the -1/2 order, as in the first embodiment, the zero-order diffracted light L40 Only the first-order diffracted light L41 enters the inspection optical system 8 (the optical axis matches the optical axis of the illumination optical system). And zero-order diffracted light
An image of a pattern formed by two light beams of L40 and first-order diffracted light L41 is formed on the light receiving surface of the position detector 10.

In FIG. 4, the Fourier transform surface of the pattern to be inspected TP provided with the shutters 5a, 5b, 5c is also a Fourier transform surface with respect to the diffraction grating 21.
Is located at a position having an image forming relationship with the photomask 7. Diffraction grating 21
When the imaging magnification of the photomask 7 is N times, the pitch of the diffraction grating 21 may be 2P / N (P is the pitch of the pattern TP to be inspected of the photomask 7).

As in the first embodiment, the phase shift amount is measured by first measuring the position of the image on the position detector 10 in the state of FIG. 4, then closing the shutter 5b and opening the shutter 5a. ,
Again, the position of the image on the imaging plane is measured and the difference 2Δx
Is obtained from the equation.

Next, FIG. 5 is an optical path diagram showing a configuration of an inspection apparatus according to a third embodiment of the present invention.

In the figure, illumination light L1 emitted from a light source 1 emitting monochromatic or quasi-monochromatic light is shaped by relay lenses 2 and 3, and reflected by a movable mirror (vibrating mirror) 30. The movable mirror 30 is rotatable about an axis perpendicular to the plane of the paper, and a motor,
It is rotated by an active member 31 such as a piezo element. At this time, the light beams La and Lb reflected by the movable mirror 30 are shifted in a direction parallel to the plane of the drawing by the rotation of the movable mirror 30. In FIG. 5, the reflected light beam is located at a position Lb on the right side of the optical axis in the figure.
Further, another rotation axis of the movable mirror 30 may be added so that the reflected light beam is shifted in the direction perpendicular to the paper surface by the movable mirror 30 and the active member 31.

The positions of the reflected light beams La and Lb on the Fourier transform surface 33 with respect to the condenser lens 6 of the pattern to be inspected TP are the first positions.
As in the embodiment and the second embodiment, the movable mirror 30 is adjusted so as to be at the midpoint (two places) between the Fourier transform position of the fundamental period of the pattern to be inspected TP and the optical axis. In FIG. 5, the movable mirror 30 is adjusted so that the reflected light flux Lb is converged by the lens 32 at the midpoint between the -1st-order diffracted light corresponding point on the right side of the drawing and the optical axis.

In this state, the photomask 7 is illuminated by the illumination light L3 having a tilt of −1/2 order, and the pattern TP (1
Only the zero-order diffracted light L40 and the + 1st-order diffracted light L41 by the two-dimensional line and space pattern enter the inspection optical system 8 having the same optical axis as the illumination optical system, and the pattern image is formed on the position detector 10. (The zero-order diffracted light passing through the inspection optical system 8 is represented by L50, and the + 1st-order diffracted light is represented by L51).

In such an inspection apparatus, in order to detect the shift amount of the image of the pattern, after detecting the image position of the zero-order diffracted light by L50 and the + 1st-order diffracted light L51, the reflecting mirror 30 is adjusted to adjust the reflected light flux La.
At the other midpoint between the point corresponding to the fundamental period of the pattern on the Fourier transform plane and the optical axis (the point corresponding to the + 1st-order diffracted light and the midpoint of the optical axis), and the position of the interference fringes is measured again. From the difference 2Δx between the two measurements, the phase shift amount δ due to the phase shifter film is obtained.

As in the embodiment shown in FIG. 5, if the entire illumination light is condensed at a specific position on the Fourier transform surface without using a light shielding member as a light beam deflecting means, the loss of the illumination light amount is small, The intensity of the image detected by the position detector 10 increases, and the shift amount of the image can be measured more accurately.

6 and 7 are views showing a configuration of a modification of the inspection apparatus according to the third embodiment. However, the configuration on the photomask 7 side from the Fourier transform plane (pupil plane of the illumination optical system) 33 of the photomask 7 is completely the same as that of the third embodiment shown in FIG. Members having the same functions and functions as those of the third embodiment (FIG. 5) are denoted by the same reference numerals.

In FIG. 6, an illumination light L1 emitted from a light source 1 is transmitted through a relay lens system 2, 3 to a lens system 4 having a positive power.
The light is applied to the lens system 41 having 0 and negative power. The lens systems 40 and 41 are arranged on a plane conjugate with the photomask 7. The sum of the powers of the lens systems 40 and 41 is zero. The lens systems 40, 41 are respectively lens driving members 42,
43 allows the illumination optical system to move in a plane substantially perpendicular to the optical axis AX '. The illumination light beam transmitted through the lens systems 40 and 41 becomes a light beam having a principal ray different from the optical axis AX ′,
The light is condensed into a spot at a position different from the optical axis AX 'on the Fourier transform surface 33 via the lens system 32. The photomask 7 side from the Fourier transform plane 33 is the same as in the third embodiment.

By the way, in FIG. 6, the lens systems 40 and 41 are moved along the optical axis A in the plane of the paper.
It is moved in the opposite direction to X 'and by approximately the same distance. As a result, the illumination light beam transmitted through the lens systems 40 and 41 is tilted by a predetermined angle with respect to the optical axis AX ', and
Incident on. Therefore, if the positions of the lens systems 40 and 41 are adjusted by the lens driving members 42 and 43, the emitted light beam can be directed to an arbitrary direction. The lens driving members 42 and 43 are controlled by the control circuit 50.

In addition, a lens system having a positive power is newly provided on the photomask 7 side from the lens 41, and this lens system is also made movable by a lens driving member, and the lens systems 40 and 41 and a lens having a newly added positive power are further provided. The system may be configured so that the total power of the system becomes zero. Similarly, the lens system 40
Further, a lens system having a negative power may be provided on the light source 1 side, and the total power of the lens systems 40 and 41 and the newly added negative lens system may be zero.

The configuration of the lens system movable with respect to the optical axis AX 'is not limited to only the above combination,
A lens group composed of a plurality of lens elements having a total power of each lens system of zero may be used as long as each lens element is driven to direct an illumination light beam in an arbitrary direction. Further, the lens element to be driven is not limited at all, and may be any lens element capable of directing the illumination light beam in an arbitrary direction.

In FIG. 7, the illumination light emitted from the light source 1 is shown.
After being condensed by the relay lens system 2, L1 is incident on a light transmitting means 45 such as an optical fiber. When the photomask 7 is used as the object plane, the exit end of the light transmitting means 45 is arranged in the pupil plane of the illumination optical system, that is, in the Fourier transform plane 33 of the photomask 7. Further, the emission end face of the light transmitting means 45 is
Thus, the illumination light can be moved in a plane substantially perpendicular to the optical axis AX 'of the illumination optical system, and the illumination light flux can be distributed at an arbitrary position in the Fourier transform plane 33. Therefore, the illumination light beam emitted from the light transmission means 45 is converted into a parallel light beam by the lens system 6 and is irradiated on the photomask 7 at a predetermined incident angle. The photomask 7 side from the Fourier transform surface 33 has the same configuration as in the third embodiment, and the driving member 44 is controlled by the control circuit 50 as in the third embodiment.

In each of the above embodiments, the ratio (so-called σ value) between the numerical aperture of the illumination optical system and the numerical aperture of the inspection optical system 8 is, for example,
It is desirable to set it to about 0.2 or less.

Further, the contrast of the pattern image due to two-beam interference between the zero-order diffracted light and the + 1st-order or -1st-order diffracted light formed on the position detector 10 is highest when the zero-order light and the first-order light have the same intensity. If the strength is significantly different, it will be very low.
Therefore, if the area coverage between the phase shifter film and the mask bare surface in the pattern to be inspected is 1: 1, the zero-order light is canceled out and hardly occurs. Therefore, in order to make the intensity ratio between the zero-order light and the first-order light approximately equal, the area ratio of the pattern to be inspected should be set to about 7: 1 to 7: 2 or 1: 7 to 2: 7. desirable.

Further, the cosine component decreases as the values of a and b are closer to each other in the above equation (1).
= S / c increases. However, a and b
, The amount of zero-order light decreases, and the position detector 10
The pattern image above cannot have sufficient contrast. In order to obtain a sufficient image contrast even under such conditions, a neutral density filter may be arranged near the pupil plane of the inspection optical system 8 so that the intensity of the first-order diffracted light approaches the zero-order light. As a result, the values of a and b in the above equation (1) can be made close to each other, and the change in φ with respect to the change in δ becomes large, so that the phase shift amount can be measured more accurately. At this time, since the phase of the first-order diffracted light can be shifted from that of the zero-order light by passing through the neutral density filter, it is desirable to provide the neutral density filter so that the phase difference between them becomes 2nπ (n is an integer). . As the neutral density filter, for example, a dielectric multilayer film having high reflectance may be used.

In the first embodiment, when the pitch of the pattern to be inspected TP changes, the size and position of the aperture in the spatial filter 4 arranged in the pupil plane of the illumination optical system also change.
For example, it is desirable that several types of spatial filters are prepared in advance in accordance with the Fourier transform pattern of the pattern to be inspected TP, and these are configured to be interchangeably inserted in the pupil plane. Further, a liquid crystal element, an electrochromic element, or the like may be used as the spatial filter 4, and the angle of incidence of the illumination light beam L3 corresponding to the photomask 7 can be easily adjusted according to a change in the pitch of the pattern to be inspected TP. There is. At this time, by adjusting the transmittance of the portion through which the ± primary light passes, the spatial filter 50 can be used.
(FIG. 5) can be provided to the light shielding member.

Here, the photomask to be inspected may be any photomask provided that it has a phase shifter, such as a spatial frequency modulation type, edge enhancement type, or light-shielding effect enhancement type phase shift photomask, or a phase shifter (dielectric film) and a mask. A photomask formed only of the bare surface portion may be used.
In particular, in the case of the edge enhancement type or the light-shielding effect enhancement type, it is desirable to prepare a pattern to be inspected separately from the circuit pattern as in the above embodiment.

In each of the above-described embodiments, the light source 1 may be a laser light source, a combination of an incandescent lamp such as a tungsten lamp with a bandpass filter, or a combination of a bright line lamp such as a mercury lamp with a bandpass filter and an interference filter. May be. The illumination light is monochromatic light or quasi-monochromatic light having substantially the same wavelength as the exposure wavelength when the phase shift photomask to be inspected is used in an actual photolithography process. For example, a phase shift photomask for i-line (365 nm) of a mercury lamp and a g-line (436 nm) of a mercury lamp
When it is necessary to inspect both of the phase shift photomasks, the light source 1 is a combination of a mercury lamp and a bandpass filter, and the bandpass filter is selected according to the type of the phase shift photomask (for i-line and g-line). Should be converted.

Also, when inspecting a phase shift photomask for a KrF laser, a KrF laser light source or a light source that combines a xenon mercury lamp with a band-pass filter in addition to the mercury lamp light source above is provided, and depending on the type of photomask. What is necessary is just to use a light source properly. At this time, it is assumed that each optical member in the embodiment has been aberration-corrected for various wavelengths to be used.

The position detector 10 in each embodiment may be an image sensor such as a CCD, or a combination of an image pickup tube and a signal processing circuit, or a light amount sensor having one or a plurality of transmission slits may generate interference. Relative scanning in the direction perpendicular to the stripes (image of the pattern to be inspected) may be performed, the light amount distribution thereof may be measured, and the position may be measured by a processing circuit. It is preferable that the interval between the plurality of transmission slits is the same as the pitch of the interference fringes. The image forming magnification of the inspection optical system 8 is preferably an enlargement system so that the pattern of the photomask 7 is enlarged and projected on the position detector 10.

In the above description, the illumination light beam L3 for illuminating the photomask 7 is inclined with respect to the optical axis in a plane parallel to the plane of the paper in order to make the drawing easier to see. This is because the pattern to be inspected TP 7 is a pattern arranged in a direction perpendicular to the paper surface as shown in FIG. 2, and when the pattern to be inspected is arranged in another direction, Light flux L3 illuminating photomask 7
Needless to say, there is also a tilt in the direction perpendicular to the paper surface. At this time, in the first and second embodiments, the spatial filter 4, the shutters 5a and 5b, the diffraction
1 patterned transparent flat plate 20 and shutters 5a, 5b
Is rotated with respect to the optical axis, so that a pattern to be inspected having an arbitrary direction can be handled. As described above, in the third embodiment, the movable mirror 30 may be rotated about two rotation axes.

The pattern to be inspected shown in FIG. 2 is one example. For example, according to the configuration shown in FIG. 2, there is no light-shielding portion 7c and only a transmission portion 7a and a phase shift portion 7b. Is also good. Further, the energy transmittance of the phase shift section 7b may be an arbitrary value. However, as shown in the equation (1), the energy transmittance t ² and its square root t (0 ≦ t ≦
1, real number) affects the measurement of the phase shift amount δ of the phase shifter film, so t ² must be known. t ²
May be measured by using a measuring device separately, but a uniform opening pattern and a uniform phase shifter film (energy transmittance = t ² ) pattern are formed on the photomask 7. The inspection apparatus according to the present invention may be used to determine the light amount ratio of two patterns, and t ² may be determined from this value. Even when the illumination light L3 is irradiated on the uniform aperture pattern or the uniform phase shifter film pattern, the positive
Since no first-order diffracted light L41 is generated, only the zero-order diffracted light (transmitted light) L40 reaches the position detector 10. First, a uniform aperture pattern is illuminated with the illumination light L3, and the position detector at that time
Then, the light quantity on the position detector 10 is determined as E0, and then the uniform phase shifter film pattern is illuminated with the illumination light L3 to determine the light quantity on the position detector 10 as E1. From this, t ² = E ₁ / E ₀ is obtained.

The function of calculating t ² = E ₁ / E ₀ may be provided in the position detector 10 or a calculator connected to the position detector 10 by an electric signal may be provided. In addition, by this arithmetic unit,
The calculation for obtaining δ from Δx and t ² may be performed using the expressions (1) and (2).

The inspection pattern may be provided in the photomask 7 as a pattern dedicated to the inspection, or an appropriate pattern may be selected from the circuit patterns in the photomask 7 and used as the pattern to be inspected. Further, the pitch, duty ratio, and the like of the pattern to be inspected TP may be arbitrary. The mechanical member holding the photomask 7 is desirably movable on a plane perpendicular to the optical axis of the inspection optical system and the illumination optical system so that the pattern to be inspected at an arbitrary position in the photomask 7 can be inspected. .

[Effects of the Invention] As described above, in the present invention, the illuminance distribution on the pupil plane of the illumination optical system or its conjugate plane is adjusted, and the photomask is illuminated only by illumination light having a specific angle with respect to the optical axis. Then, the phase shift amount of the phase shifter film is obtained by detecting the shift amount of the interference image of the pattern to be inspected due to the two light beams of the zero-order diffracted light and the + 1st-order light or the -1st-order light. Even if the refractive index of the shifter film is almost the same, the phase shift amount can be measured without any problem. Further, in the present invention, the phase shift amount is obtained by detecting the position shift (shift of the phase of the sine wave) of the interference image composed of a large number of interference fringes, instead of calculating the phase shift amount by the intensity detection as in the related art. Because we measure
The SN ratio is improved, and it is possible to measure the phase shift amount with extremely high accuracy.

[Brief description of the drawings]

FIG. 1 is an optical path diagram showing the configuration of a first embodiment of the present invention, and FIG.
FIG. 3 is a sectional view showing an example of a pattern to be inspected, FIG. 3 is a conceptual diagram showing an intensity distribution of an image of the pattern to be inspected, FIG. 4 is an optical path diagram showing a configuration of a second embodiment of the present invention, and FIG. FIG. 6 is an optical path diagram showing the configuration of the third embodiment of the present invention, and FIGS.
It is a figure showing composition of a modification of an inspection device by an example. [Explanation of Signs of Main Parts] 1 ... Light source 2,3 ... Relay lens 4 ... Spatial filter 5a, 5b, 5c ... Shutter 6 ... Condenser lens 7 ... Photomask 8 ... Inspection optical system 10 ... … Position detector 21 …… Diffraction grating 30… Reflector 31 …… Active element

Claims (9)

(57) [Claims] 1. A substrate having a geometrical original pattern substantially transparent to a light beam having a predetermined wavelength, and at least a part of the original pattern includes a phase for changing a phase of a light beam transmitted through the transparent substrate. In a photomask inspection apparatus for inspecting a photomask provided with a member, an illumination optical system for irradiating a monochromatic light or a quasi-monochromatic light to the pattern to be inspected of the photomask; An inspection optical system that forms an image of the illumination light beam on a photomask at a predetermined angle of incidence, and a zero-order diffracted light beam of light transmitted through the pattern to be inspected. The illumination light with respect to the photomask so that any one of ± first-order diffracted light passes through the pupil plane of the inspection optical system substantially symmetrically with respect to the optical axis of the inspection optical system. A light beam deflecting means for changing an incident direction of light; and a pattern detecting means disposed on or near the reference plane and photoelectrically detecting an image of the pattern to be inspected by the inspection optical system. Inspection equipment. 2. A photodetector for detecting one of the zero-order diffracted light and ± 1st-order diffracted light; a pattern detector based on a detection signal output from the photodetector; 2. The photomask inspection apparatus according to claim 1, further comprising: an operation circuit for calculating a phase shift amount of transmitted light of the phase member provided in the apparatus. 3. The inspection optical system has a spatial filter near the pupil plane for blocking light other than one of the zero-order diffraction light and ± 1st-order diffraction light passing through the pattern to be inspected. The photomask inspection apparatus according to claim 1 or 2, wherein: 4. The inspection optical system according to claim 1, wherein said inspection optical system has a light shielding member capable of reducing at least one of said zero-order diffraction light and + 1st-order or -1st-order diffraction light passing through said pattern to be inspected. Item 4. The photomask inspection apparatus according to any one of Items 1 to 3. 5. The pattern to be inspected is a one-dimensional line and space pattern, and is formed at a part of the original pattern or at a different position in the same manufacturing process as the original pattern. Item 2. The photomask inspection apparatus according to Item 1. 6. The photomask inspection apparatus according to claim 1, wherein said phase member has a predetermined transmittance. 7. A photomask inspection method for inspecting a photomask having a pattern and a phase member provided on at least a part of the pattern and changing the phase of light transmitted through the pattern by an inspection optical system, Irradiating the phase member with light; and any one of the zero-order diffracted light and the ± 1st-order diffracted light transmitted through the phase member is substantially symmetric with respect to the optical axis of the inspection optical system at the pupil plane of the inspection optical system. A method for inspecting a photomask, comprising: passing the light; and detecting an image of the phase portion formed by the inspection optical system. 8. The photomask inspection method according to claim 7, wherein the wavelength of the light is substantially equal to the wavelength of light used in a lithography process using the photomask. 9. The photomask inspection method according to claim 7, wherein the phase member has a predetermined transmittance.