JP2003307465A - Apparatus and method for inspection of grating - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To quickly inspect a specimen containing a fine grating by using a simple inspection apparatus and a simple inspection method without using a transmission electron microscope. <P>SOLUTION: From among diffracted light by the fine grating in the specimen (a mask for an EB aligner), information (a coupling efficiency) measured as a transmittance or a reflectance regarding 0-order diffracted light as direct light is acquired, the information is compared with an analytical result regarding the grating, and a shape of the grating is quantified. As a measuring priciple, the coupling efficiency at the grating which is unequvocally decided by an optical constant of an inspection apparatus, a mask physical property, a mask structure and the shape of the grating is measured, the shape of the grating, a duty especially in a very small grating part and a line width of an isolated line are measured, and a defect is inspected. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inspection apparatus and method using optical means, and relates to a technique for measuring and inspecting a minute grating having a periodic structure below the diffraction limit.

[0002]

2. Description of the Related Art Generally, in the semiconductor manufacturing process,
An optical microscope is well known as a fine pattern inspection means having an optical image formation means. For the limiting resolution “D” in the optical microscope, the light source wavelength is “λ”,
When the numerical aperture of the objective lens is written as “NA” and the optical constant is written as “K ₁ ”, the relational expression of “D = K ₁ · λ / NA” is established.

Therefore, in order to improve the limiting resolution D, the following approach can be considered.

(I) To reduce the optical constant K ₁ (II) To shorten the light source wavelength λ (III) To increase the numerical aperture NA.

Here, regarding the optical constant K ₁ of (I),
In a general optical microscope, the limit of about 0.5 to 0.6, which is the focusing limit of the first-order diffracted light necessary for forming an image, is set. Note that in the lithographic process typified by semiconductor is referred to as super-resolution technique, a phase difference provided to mask the transmitted light, using a technique such as to improve the contrast on the image plane, a K ₁ of about 0.35 It succeeded in making it as small as, and is approaching the physical limit of K ₁ = 0.25. This technique can be applied to a fine pattern inspection apparatus having an optical image forming means, but for example, the phase shift method requires optimization for each sample condition to be measured, and only for a specific pattern. It is valid. For this reason, it is difficult to put it into practical use in an inspection device that requires versatility.

Therefore, in order to improve the limiting resolution, generally, the wavelength of the light source λ is shortened and the NA of the objective lens is increased.

That is, regarding the light source wavelength of the above (II), an inspection apparatus in the deep ultraviolet region of 193 to 266 nm (nanometers) is widely used by making full use of the wavelength conversion technology of an excimer laser, a mercury lamp, and a solid laser. The numerical aperture NA of the objective lens in the optical microscope is 0.95.
It has been put to practical use to a certain degree. In addition, the above (I
Regarding II), although it is possible to increase the NA to 1.0 or more by a technique such as liquid immersion using a refracting liquid, there are serious obstacles to the practical use of the inspection device.

By the way, in recent years, the miniaturization of semiconductor circuit patterns has progressed more rapidly than the speed at which the trend toward higher resolution has progressed, and optical fine pattern inspection is reaching its limit. This is particularly remarkable in the field of low-voltage electron beam exposure apparatus mask inspection, etc., which uses a 1 × mask, which bears the most advanced design rules in the next-generation semiconductor process, and the required resolution is at present. It greatly exceeds the resolution of optical microscopes that can be realized with. Therefore, introduction of a fine grating mask pattern inspection device using a transmission electron microscope using an electron beam is being promoted.

[0009]

However, in the measurement using the transmission electron microscope (transmission electron beam scanning microscope), there are the following problems in terms of manufacturing cost and the like.

That is, in this measuring method, an electron objective lens and an electron projection lens are required to expand the electron beam that has passed through the sample, and a highly sensitive high-speed decay type scintillator and the like are required for visualization of fluorescence. Therefore, it is very expensive. Furthermore, although it surpasses the optical type in terms of resolution, it has problems such as slow processing speed because damage to the resist sample, contamination contamination, and observation in vacuum are required.

Therefore, an object of the present invention is to make it possible to quickly inspect an object to be inspected including a grating by using a simple inspecting apparatus and method without using a transmission electron microscope.

[0012]

In order to solve the above problems, a grating inspection apparatus according to the present invention irradiates a light source having a single wavelength and an observation surface of an object to be inspected with light from the light source. An illumination optical system for, and a detection optical system for detecting the light transmitted through the inspection object or the light reflected by the inspection object among the light from the light source, among the diffracted light by the grating of the inspection object, Measurement processing means for obtaining information measured as the transmittance or the reflectance of the 0th-order diffracted light which is direct light, and quantifying the shape of the grating by comparing the information with the analysis result of the grating. Is provided.

In the grating inspection method according to the present invention, the light from the light source having a single wavelength is applied to the observation surface of the inspection object, and the light transmitted through the inspection object or reflected by the inspection object is reflected. A step of detecting the generated light as an image signal by a detection optical system, and measuring the coupling efficiency as the transmittance or reflectance of the 0th-order diffracted light that is direct light among the diffracted light by the grating of the object to be inspected; In order to compare the measurement result with the analysis result related to the grating, a calculation process is performed on the measurement result or the analysis result, and a step of quantifying the shape of the grating by comparing the two results is provided.

In the present invention, as an optical fine pattern inspection apparatus and method, the inspection object is not a microscopic observation by spatial separation using image formation, but an inspection target is a fine repetitive pattern or a periodic structure (fine grating structure). Limited
By regarding the grating portion as an optical waveguide and knowing the coupling efficiency of the illumination light in the optical waveguide, that is, the transmittance and the reflectance, information on the shape of the grating can be obtained.

According to the present invention, the short-wavelength light source, the high-aperture objective lens, and the high-sensitivity image pickup device, which are required for fine structure observation, are released from the concept of limiting resolution discussed in optical microscopes. It becomes possible to configure the device for observing the micro-grating structure with only relatively easy-to-obtain optical elements, without making the essential requirement, and to perform measurement and inspection without using a transmission electron beam scanning microscope. It can be performed.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is an inspection apparatus for optically inspecting the shape of a grating (diffraction grating) having a fine repeating pattern structure or a periodic structure. And an inspection method, and can be applied to inspection of a mask for an EB (electron beam) exposure apparatus, for example.

That is, in the mask manufacturing process for the EB exposure apparatus, since there is no simple inspection method so far, it is necessary to frequently use a very expensive transmission electron beam scanning microscope. The problem is that the inspection cost accounts for a high proportion of the cost for manufacturing the device mask. Therefore, in the inspection process, by introducing a simple measuring device and promptly detecting a defective portion, it is possible to prevent a defective product from flowing to the next process and reduce the mask manufacturing cost for the EB exposure device. There is a need, and the use of the present invention enables a fundamental solution to the problem.

When the present invention is applied to a mask inspection apparatus for an EB exposure apparatus, the measuring principle is as follows:
By measuring the amount that is uniquely determined by the optical constants of the inspection device, the physical properties of the mask, the mask structure, and the shape of the micrograting (coupling efficiency in the micrograting), the shape of the micrograting, especially the duty of the micrograting, the isolated line It is possible to measure the line width, pinhole diameter, and inspect for defects, thereby providing a simple inspection device.

The present invention can be widely used for optical inspection of various objects (objects to be inspected) including a grating. In the following, a mask for an EB exposure device is used for the inspection. The configuration of the device will be described.

Before describing the apparatus and method according to the present invention,
The concept introduced as "coupling efficiency" will be described.

The "coupling efficiency" includes the transmission efficiency and the reflection efficiency for quantifying the optical coupling state when the object is irradiated with the illumination light. Specifically, it means transmittance and reflectance, but in general, these terms mean, for example, in the diffraction phenomenon, in addition to 0th-order light, 1
The term "coupling efficiency" is used in this specification as an expression that includes the transmittance and reflectance in the case of only zero-order light, because it is often defined to include higher-order light of the order and higher. . As will be described later, in the present invention,
The information of the coupling efficiency, which is measured as the transmittance or the reflectance of the 0th-order light (direct light) of the observation target, is used, and the imaging phenomenon for the 1st or higher order light is not used in the measurement. Therefore, in the description of the present specification, when it is necessary to indicate the order with respect to the coupling efficiency (particularly, in the case of the 0th order diffracted light), the specific order is specified.

FIG. 1 shows an outline of a configuration example of a grating inspection device 1 as an optical measuring device to which the present invention is applied.

This grating inspection apparatus 1 targets an object to be inspected 100 (EB exposure mask in this example) as an observation target, irradiates one surface of the minute grating on the EB exposure mask with a laser beam, and the minute grating It is an inspection device for inspecting and measuring various information of the minute grating existing on the observation target by measuring the amount of direct light guided to the back side.

The grating inspection device 1 has the following components.・ A light source with a single wavelength, an illumination optical system, and a detection optical system.

Regarding the light source LS, the spectral emission line of a monochromatic laser light source or a discharge lamp (such as a mercury lamp) is narrowed to about 10 nm full width at half maximum by an optical means such as a dichroic mirror and an interference filter. A squeezed light source can be used. In this example, a laser light source 1L that emits a parallel light beam having a predetermined light amount and a beam diameter is used (as an short-wavelength laser, an ArF excimer laser or
YAG quadruple wave laser and the like can be mentioned. ).

The illumination optical system LO is an optical system for irradiating the observation surface of the inspected object 100 with light from the light source LS, and the detection optical system DO is one of the light from the light source LS to be inspected. It is an optical system for detecting the light transmitted through the object 100 or the light reflected by the inspection object.

First, the illumination optical system LO will be described.
The light emitted from the laser light source 1L is split into two by the beam splitter 2, and one of the lights passes through the shutter unit 3 and reaches the scan mirror 6 via the scan (scanning) mirror 4 and the relay optical system 5. . The scan mirrors 4 and 6 form a parallel beam emitted from the laser light source 1L on the lower surface of the inspection object (mask for EB exposure apparatus) 100 (hereinafter, the upper side of FIG. 1 is defined as the upper side of the apparatus). Beam scanning is performed to perform coherent illumination at an arbitrary position in the observation area. In addition, the relay optical system 5 and the relay optical system 7 described later include scan mirrors 4 and 6.
Is an afocal relay optical system for maintaining the surface of the image forming conjugate state.

Between the scan mirror 6 and the mirror RF,
The relay optical system 7 is arranged, and the light whose optical path has been changed by the mirror RF is λ / 2 wavelength plate (half wavelength plate) adjustment unit 8, beam splitter 9, λ / 2 wavelength plate adjustment unit 10 Further, the light passes through the λ / 4 wavelength plate (quarter wavelength plate) adjustment unit 11, passes through the condenser lens 13, and is irradiated to the inspection object 100. That is, the condenser lens 1
3 is provided for imaging on the lower surface of the mask for the EB exposure apparatus.

The pupil 12 is the entrance pupil of the condenser lens 13, and the λ / 2 wavelength plate adjusting unit 8 is used to arbitrarily rotate the polarization state of the laser light emitted in the linear polarization state. , Λ / 2 wave plate (half wave plate) and a mechanism for rotating the wave plate around the optical axis.

One of the light beams split by the beam splitter 9 passes through the imaging lens 21 and reaches the image pickup device 22 for the finder, and the other light beam passes through the λ / 2 wavelength plate adjusting unit 10, λ /. An image is formed by the condenser lens 13 through the four-wave plate adjusting unit 11. That is, the beam splitter 9, the imaging lens 21, and the imaging device 22 are
It constitutes a finder microscope.

With respect to the λ / 2 wavelength plate adjusting unit 10 and the λ / 4 wavelength plate adjusting unit 11, the laser light emitted from the laser light source 1L is formed into a fine grating on the mask for the EB exposure device in an arbitrary polarization state. It is provided for coupling (optical coupling). still,
Each adjustment unit includes a respective wave plate and a mechanism for rotating them around the optical axis.

Next, the detection optical system DO will be described.
The pickup lens 14 is arranged immediately above the inspection object 100. That is, after coupling with the minute grating on the lower surface of the mask for the EB exposure apparatus, the EB
A pickup lens 14 is provided for detecting the laser light guided to the upper surface of the mask for the exposure apparatus, and the light transmitted through the lens 14 has a λ / 4 wavelength plate adjusting unit 16 and a λ / 2. The wave plate adjusting unit 17, the beam splitter 18, and the imaging lens 19 reach the image pickup device 20 for detection (in this example, a configuration for detecting the transmitted light of the inspection object is adopted. .).

The pupil 15 is the exit pupil of the pickup lens 14, and the λ / 4 wavelength plate adjusting unit 16 and
The λ / 2 wavelength plate adjusting unit 17 is provided to adjust the polarization state of the light transmitted through the pickup lens 14, and these are provided in the λ / 2 wavelength plate adjusting unit 10 described above.
Also, it has the same configuration as the λ / 4 wavelength plate adjusting unit 11.

Regarding the illumination optical system for microscopically observing the object to be inspected (the mask for the EB exposure device) from the upper surface with epi-illumination, one of the lights split by the beam splitter 2 is
Shutter unit 23, optical path changing mirrors 24, 2
Rotating diffuser plate 2 for speckle noise removal after 4
5, the Koehler illumination optical system 26, the aperture stop 27, the field stop 28, and the beam splitter 18 via the λ / 2 wavelength plate adjusting unit 29. The λ / 2 wavelength plate adjusting unit 29 has a function of arbitrarily rotating the polarization state of the laser light emitted in the linearly polarized state, and
It is equipped with a two-wave plate and its rotating mechanism.

Although not shown in the figure, the grating inspection apparatus 1 shown in FIG. 1 exclusively uses the means for performing coherent illumination using a laser light source and the means for performing incoherent illumination and partial coherent illumination. It is configured to be able to.

In the grating inspection apparatus 1, the coherent illumination means is used to propagate the coupling light to the mask for the EB exposure apparatus. As described above, the scan mirrors 4 and 6 are used as the scanning mechanism of the coherent illumination light. However, the present invention is not limited to this, and various scanning mechanisms (for example, an acousto-optic device, a polygon mirror, a Nippon disc, etc.) can be used.

In the incoherent illumination or the partial coherent illumination, since a certain area is illuminated at once, the influence of interference with the diffracted light from the peripheral pattern is detected when the coupling efficiency described later is detected. Therefore, it is necessary to add a restriction by the field of view. Incoherent illumination or partially coherent illumination means can be used as the coupling light propagation means by providing a field diaphragm with a mechanism that prevents interference with surrounding patterns by matching the field of view to a minute grating area. You can use it.

The image information detected by the image pickup device 20 of the detection optical system D0 is sent to the measurement processing means 30 and processed. The measurement processing means 30 uses an information processing means such as a computer to perform image processing, optical measurement,
The analysis process is performed, and the process necessary for inspecting the grating shape is performed based on the information about the 0th-order diffracted light that is direct light among the diffracted light by the grating of the inspection object 100. Specifically, in order to quantify the grating shape by acquiring the information of the coupling efficiency measured as the transmittance or the reflectance of the 0th-order diffracted light and comparing the information with the analysis result of the grating. Is performed (the measurement principle and processing will be described in detail later), and the result is sent to the output processing unit 40 to perform a judgment display and the like of the inspection result, but before that, it is the inspected object. , EB exposure apparatus mask will be described with reference to the schematic diagram shown in FIG.

A minute grating portion (or a grating area) 101 having a finite area is formed on the mask for the EB exposure apparatus. As shown separately on the right side of FIG. The rectangular region 202 where the grating exists, and the waveguides 203 that form the individual gratings (that is, the waveguides 203 are optical paths, and one of them is extracted and shown in the figure, The grating 201 is formed by a group of a large number of waveguides arranged at a predetermined interval.
Are formed. ).

The reason is that the illumination light applied to the mask so as to guide the light through the grating portion 101 is
After being collected by the pickup lens 14, the imaging device 2
However, regarding the image signal obtained by the image pickup device 20, the diffraction image generated in the rectangular region 202 where the grating exists (hereinafter, simply referred to as “region 202”) and the waveguide 203 are detected. This is because it is affected by the generated mode light.

The influence of the diffracted image generated in the region 202 depends on the form of the illumination optical system, that is, the NA of the condenser lens and the coherence factor of the illumination such as critical illumination or Koehler illumination.

As described above, the fact that the actual grating portion (101) is formed in the finite area and the influence of the diffraction image at the edge portion (edge) of the finite area exists, and further, for each grating, Waveguide mode light according to a deterministic equation determined by the shape, the numerical aperture of the illumination optical system, the spectral characteristics of the micro-grating, the film thickness, etc. is also observed (these influences are caused by the imaging device 20). It is reflected in the acquired image information.).

FIG. 3 is a schematic view schematically showing the condenser lens 13 and the pickup lens 14 of the mask, mainly the grating portion 101. The Z direction in the drawing is the optical axis direction. The X direction perpendicular to this is the grating formation direction (although not shown, the Y direction is perpendicular to the plane of the drawing and is perpendicular to the X and Z directions). is there.).

The laser light transmitted through the condenser lens 13 is
The lower surface of the grating portion 101 is illuminated so as to be at the beam waist position, and the wavefront at that position is propagated to the grating portion 101 in a parallel wave state.

When monochromatic light having an arbitrary wavelength is irradiated onto a mask pattern surface having such a minute grating, the diffraction angle at each order, which is diffracted by the grating, can be calculated by the linear expression of the grating pitch and the light source wavelength. Although it can be easily obtained with, the diffraction efficiency in an arbitrary order, that is, the coupling efficiency is given by solving the Maxwell equation.

Diffracted light that can be observed in a far field (far distance) as propagating light is observed as propagating light to the front and the rear (the direction toward the image pickup device 20 is defined as the front in FIG. 1). On the other hand, an evanescent wave is generated in the grating, and the evanescent wave is near
Only observed in the Field (short distance). Therefore, to correctly calculate the coupling efficiency of the grating, it is necessary to solve the Maxwell equation including the evanescent light.

4 and 5 show the grating portion 10
It is a conceptual explanatory view at the time of irradiating a parallel wave with respect to 1.

FIG. 4 shows the case where the grating pitch "d" is larger than the light source wavelength λ (d> λ). In addition to 0th-order diffracted light (direct light), + 1st-order, -1st-order, etc. diffracted light appears. .

On the other hand, FIG. 5 shows the case where d is smaller than λ (d <λ), and the 0th-order light and the evanescent wave propagating in the grating (in the figure, the left and right directions are shown respectively). This is indicated by the arrow pointing to the right).

By the way, in the grating inspection apparatus according to the present invention, as a main observation target, a sample having a periodic structure below the optical image formation limit, that is, a minute amount such that diffracted light of the first order or higher is not generated as propagating light. Since the target is the grating, the diffracted light that is observed is the 0th-order diffracted light (that is, direct light that is transmitted or reflected).

As will be described later, regarding the coupling efficiency, the light source wavelength, the irradiation NA, the condensing NA, the physical properties such as the permittivity ε and the permeability μ of the sample substance, the grating pitch, the grating duty, the sample such as the film thickness and the hierarchical structure. It is uniquely determined from the structure. Therefore, it is possible to measure the coupling efficiency and further solve the Maxwell equation from known information about the sample, and compare the obtained value with the observation result (image information obtained by the imaging device 20). . That is, regarding the 0th-order diffracted light, by comparing the observed value (or the observed value) with the analysis result of the Maxwell equation obtained from known information about the sample, the optical imaging limit is exceeded, that is, the spatial separation is It is possible to realize measurement and inspection of a fine pattern having an impossible periodic structure.

The measurement principle of the above-described grating inspection device 1 will be described in detail below.

First, regarding the laser light source 1L, in consideration of the resolving power of the detection optical system DO, for example, a YAG quadruple wave laser having a wavelength of 266 nanometers, an argon ion laser double wave having a wavelength of 244 nanometers, etc. However, the light source wavelength required for the laser light source should be determined depending on the physical properties of the material to be observed, that is, the mask for the EB exposure apparatus. That is, EB
Regarding the coupling efficiency of coupling by the fine grating on the mask for the exposure apparatus and the coupling efficiency for guiding in the mask for the EB exposure apparatus, the numerical aperture of the condenser lens 13, the coherence factor of illumination, E
This is because not only the shape of the minute grating on the mask for the B exposure apparatus but also the material physical properties of the mask, in particular, the spectral characteristics (dielectric constant ε, magnetic permeability μ) of the material are greatly influenced.

In the grating inspection apparatus 1, the non-grating portion of the mask for the EB exposure apparatus (the portion existing between the adjacent waveguides 203) is determined by the light source wavelength of the laser light source 1L, the material and the thickness of the minute grating mask. ) Transmittance is assumed to be silicon (Si) that can be diverted from the semiconductor manufacturing process as the mask material in order to avoid becoming noise for optical detection (coupling efficiency detection) of the grating part. is doing. Therefore, as shown in FIG. 6, it is preferable that the laser light source 1L has a wavelength range in which the light source wavelength of the laser light source 1L does not pass through the mask for the EB exposure device having a predetermined thickness, that is, a light source wavelength of 400 nanometers or less.

FIG. 6 exemplifies the wavelength dependence of the transmittance of a light beam that is vertically incident on the non-grating part. The horizontal axis represents wavelength (unit: nm) and the vertical axis represents transmission. The rate (percentage) is taken.

As shown in the graph, it can be seen that the transmittance gradually increases from around the wavelength of 400 nm.

Generally, a short-wavelength light source is preferable for observing a fine pattern, but it is assumed that silicon, which is expected to be widely used in the future, as a mask material for an EB exposure apparatus. As a result of the simulation shown in FIG. 7, the YAG quadruple wave laser having a light source wavelength of 266 nm has a larger number of 0 than the ArF excimer laser having a light source wavelength of 193 nm.
It is known to guide second-order diffracted light.

Since the above-mentioned grating inspection device 1 measures the amount of transmitted light, when the transmittance of the non-grating part in the mask sample of the minute grating is high (that is, the sample itself is a substance having a low magnetic permeability with respect to the light of the light source wavelength). In some cases), because it is difficult to obtain the modulation with the guided light of the grating part and it is difficult to secure the measurement accuracy, the non-grating part of the sample blocks the source light or the range of low transmittance as the light source wavelength. The light source wavelength of is used.

FIG. 7 shows the transmittance for each light source wavelength (that is, the transmittance of the 0th-order diffracted light emitted forward) under a certain condition for a minute grating with an infinite period, and the horizontal axis shows the grating. Pitch (unit: μm) is taken, and the vertical axis shows the coupling efficiency (in this case, the transmittance of the 0th-order diffracted light, which is shown as a percentage), showing the influence of the difference in the light source wavelength.

The graph curve "g (λ)" is the wavelength λ
(Nm) represents the characteristic, and λ = 193, 24
8, 266, 355 nm are illustrated.

For example, in the case of λ = 193 nm, the coupling efficiency is low in the range where the grating pitch (spacing) is small, and the transmittance increases from around 0.09 μm, whereas in the case of λ = 266 nm. , The coupling efficiency is relatively high over a wide range (where λ =
At 248 nm and 355 nm, the coupling efficiency is slightly lower than when λ = 266 nm. ).

As described above, it is desirable to determine the required light source wavelength according to the physical properties of the object to be observed and the shape of the minute grating such as the aperture diameter and the thickness. Specifically, in the grating inspection apparatus 1 shown in this example, when silicon is assumed as the material of the mask for the EB exposure apparatus,
A 266-nanometer YAG quadruple wave laser, which is shown to be optimum from the results shown in FIGS. 6 and 7, is used. Further, in this example, the non-grating portion of the mask for the EB exposure apparatus selects a wavelength that is non-transparent to the wavelength of the laser light source 1L, but this is to increase the detection sensitivity. Therefore, the non-grating portion of the mask for the EB exposure device may be transparent to the wavelength of the laser light source 1L. Furthermore, it is also possible to use other light source wavelengths as the ultraviolet light source of 400 nm or less, although there is a difference in detection sensitivity.

FIG. 8 shows the coupling efficiency of transmitted light when the grating thickness, the grating pitch, the light source wavelength, and the illumination conditions are fixed and the grating duty is used as a variable, that is, the forward 0th-order diffracted light, for a minute grating with an infinite period. The results of the analysis are shown. still,
In this figure, the horizontal axis represents the grating duty (percentage), and the vertical axis represents the transmission coupling efficiency (transmittance of the 0th-order diffracted light, which is shown in percentage), showing the relationship between the two.

The graph curve "gg (λ)" (λ
= 193, 248, 266, 355 nm) respectively indicate the difference in the light source wavelength. Regarding the selection of the wavelength,
This is the same as the case of FIG. 7. The “grating duty” corresponds to a percentage of the width occupied by the grating within one pitch, and, for example, when the stripe pattern of the grating is represented by high or low contrast (or light and dark), Is a value obtained by dividing the width of the high transmission portion by the width of one cycle and multiplying it by 100, and expressing it as a percentage.

As is clear from FIG. 8, when the grating thickness, grating pitch, light source wavelength, and illumination conditions are fixed, the grating duty is uniquely determined. Generally, in a minute grating shape represented by a semiconductor exposure mask, the unevenness of the grating pitch (unevenness) and the fluctuation of the grating thickness are sufficiently smaller than the unevenness (unevenness) of the grating duty in the manufacturing process. Is well known, and the grating thickness and the grating pitch can be approximated to be constant in the same process. By utilizing this feature, the grating inspection device 1 according to the present invention can quantify the grating duty for a minute grating having a repetitive pattern or periodicity equal to or less than the optical resolution, while using an optical detecting means. .

Regarding each graph curve gg (λ),
In both cases, the coupling efficiency tends to increase as the grating duty increases, but it can be seen that the coupling efficiency is high especially in the case of the curve gg (266 nm).

Further, the minute grating which is the object of the present invention is not limited to the repetitive pattern, and, for example, isolated lines, contact holes, etc.
If there is periodicity in the interval with the peripheral pattern, it is possible to derive the coupling efficiency. Therefore,
The inspection target is not limited to the mask pattern for the exposure apparatus and may be an actual wiring pattern or the like.

Next, in the above-mentioned grating inspection apparatus 1, the grating portion 1 on the mask for the EB exposure apparatus
A description will be given of how the laser light emitted to 01 is coupled to the pickup lens 14.

The laser light emitted from the laser light source 1L is converged and condensed on the lower surface of the grating portion 101 as described above. In order to obtain the coupling efficiency in the portion 101, as shown in FIG. 2, it is necessary to consider the influence of the grating 201 in the finite area, the rectangular area 202, and the individual waveguides 203, which is rather complicated. .

Therefore, first, a method of analyzing coupling efficiency in a grating having an infinite periodic structure will be described.

The laser light converged and condensed in the grating having the infinite period structure has the optical field characteristic of Gaussian distribution. A plane wave expansion is performed for each incident angle of this light to obtain an angular spectrum distribution. By expanding the plane wave, the coupling to the minute grating can be treated as a plane wave, and the electromagnetic field analysis method using the RCW method can be used for the coupling efficiency in the grating. This method is based on Maxwell (Maxwel
l) One of the methods to solve equations exactly,
"s Coupled-Wave Analysis" method, which is one of the analytical methods for exactly obtaining the diffraction efficiency of an arbitrary order of a plane wave incident on a grating. The analysis method used in the present invention is not limited to the RCW method, and an approximation method that poses no practical problems may be used.

In the entrance aperture, the coupling efficiency of coupling each plane wave to the minute grating, that is,
It suffices to calculate the complex amplitude transmittance and the complex amplitude reflectance and add all the plane wave components.

In recent years, the approximate convergence of the grating theory has rapidly increased due to the development of the RCW method and the like, and the electromagnetic field analysis method of the grating in an infinite period has been almost established. According to the RCW method, the electromagnetic field is divided into TE mode and TM mode, and the forward complex transmittance T and the backward complex reflectance R at an arbitrary order are solved for each. In addition, in the state where the TE wave and the TM wave are correlated with each other, that is, in the state of circularly polarized light or the like, the phase term may be added to solve. Also, regarding the phase matching state between the phases,
Among the wave number vectors, wave number vector components in the grating direction are matched in each order.

The analysis result of the coupling efficiency in the infinite period grating obtained by the electromagnetic field analysis can be expressed as a complex amplitude distribution on the upper surface of the infinite period grating, and this complex amplitude distribution corresponds to the low pass filter corresponding to the aperture of the pickup lens 14. After passing through, the Fourier transform is performed, that is, the intensity distribution of the Fraunhofer diffraction image on the pupil plane is obtained, and then the inverse Fourier transform is performed to obtain an image intensity equivalent to the image intensity on the imaging device 20 with respect to the grating part. Will be obtained.

Regarding the inspection method according to the present invention, the basic processing procedure is summarized as itemized as follows. (1) In the step (2) of calculating the coupling efficiency of the diffracted light of arbitrary order in the minute grating by analysis, in the step (3) of performing the arithmetic processing for comparing the analysis result with the measurement result (2) A step of comparing the obtained result with the measurement result.

First, in (1), as described with reference to FIG. 8, the light source wavelength, the optical constants, the physical properties and shape characteristics of the grating material, the grating period, the grating region,
When the thickness of the grating is known, the fact that the coupling efficiency of the 0th-order diffracted light is uniquely determined for each grating duty is used. That is, the diffracted light coupling efficiency of an arbitrary order in the minute grating can be calculated by RCW
Law or FDTD (Finite Difference Time Domai
n) Analysis method such as method, or approximate analysis by scalar analysis.

In (2), based on the complex amplitude distribution at the interface of the above-mentioned detection optical system DO of the grating obtained by this analysis, the detection optical system is calculated by a calculation method using a transfer function equivalent to the detection optical system. Obtain the intensity distribution equivalent to the image signal obtained by the system DO.

In (3), the result of (2) is compared with the measurement value of the grating inspection apparatus 1 to quantify the grating duty of the object to be inspected.

By the way, the above-mentioned grating inspection device 1
In the above, the mask for the EB exposure apparatus, which is the inspection object, is a pattern having a finite area as described above.

Therefore, in order to obtain the exact solution of the coupling efficiency, it is necessary to solve the Maxwell equation exactly, as described above, which requires a very large amount of calculation.
Particularly, in a grating analysis having a finite area, a huge amount of calculation is required according to the method known at the present time (however, if the analysis of the grating portion 101 can be performed in a finite structure, a finite area as described below is used). It is not necessary to calculate U2 and U3 related to the frequency response component corresponding to the diffraction image and the waveguide mode light component due to the edge portion of.

Therefore, in the above-described grating inspection apparatus 1 according to the present invention, with respect to the grating portion 101 on the mask for the EB exposure apparatus, as shown in FIG. 2, each element of the grating 201, the rectangular region 202 and the waveguide 203 ( (Composition region), calculate the frequency response in the detection optical system from the complex amplitude distribution of the grating interface obtained by analysis for each region, and perform convolution on the pupil plane. Is devised so that it can be simply compared with the inspection result.

The grating portion 1 having a finite area
Regarding No. 01, the image signal obtained by the image pickup apparatus 20 has an unclear lateral stripe as shown in FIG. 9 when it is displayed as an image, and shows a distribution with shading (as the coupling efficiency. It represents the unevenness of the transmittance.). This is due to the influence of the diffraction image generated in the region 202 and the mode light generated in the waveguide 203 as described above.

The influence of the diffracted image generated in the region 202 depends on the coherence factor of the illumination, and the influence of the mode light generated on the waveguide 203 particularly depends on the shape of the waveguide 203, the spectral characteristics, and the wavelength of the light source. , The numerical aperture of the waveguide and the surface roughness in the waveguide.
In general, the FDTD method is widely used for the waveguide analysis because of the validity of the processing speed and the approximate value, and this method is also used in this example.

In the grating inspection apparatus 1, the grating portion 101 is processed by the following processing.
The influence of the diffraction image generated in the region 202 and the influence of the mode light generated in the waveguide 203 are removed, and the grating 2
The coupling efficiency for only the part 01 is calculated.

(1) Obtaining the Fraunhofer image on the Fourier plane of the pickup lens 14 by the grating 201 (2) Obtaining the Fraunhofer image on the Fourier plane of the pickup lens 14 by the area 202 (3) Waveguide Obtaining the Fraunhofer image intensity distribution on the pupil plane of the mode light generated at 203 (4) Processing so that the analysis result and the measurement result by the imaging device 20 can be compared.

First, in (1), the grating 201
In order to obtain the coupling efficiency in, the complex transmittance and the complex reflectance at an arbitrary diffraction order are obtained for each plane wave using the above-mentioned electromagnetic field analysis method, and from this, the interface of the grating 201 on the focusing optical system side (in this example, , Condenser lens 14
Since the light is emitted from the lower side of FIG. 1, it corresponds to the upper surface of the mask. ) To obtain the complex amplitude distribution. The Fraunhofer image on the Fourier plane of the pickup lens 14 is obtained from the complex amplitude distribution at the interface on the side of the condensing optical system, and this is designated as "U1".

Next, in (2), the Fraunhofer image on the Fourier plane of the pickup lens 14 by the area 202 is obtained, and this is designated as "U2". Incidentally, when the U2 is obtained, the electromagnetic field analysis is suitable in consideration of the polarization dependence, but approximately, a scalar analysis method may be used.

In the above (3), the Fraunhofer image intensity distribution on the pupil plane of the mode light generated in the waveguide 203 is obtained and designated as "U3". As mentioned above, this U3
Regarding the above, the analysis method by the FDTD method is widely known, and the approximation by the FDTD method is also used in this example.

FIG. 10 is a conceptual diagram showing an image of an image on the Fourier plane for each element of the grating portion 101. The direction indicated by the thick arrow indicates the direction of the irradiation light, "Sf" indicates the Fourier plane (pickup lens 14), and "So" indicates the inverse Fourier plane (observation image plane in the image pickup device 20). ing.

Also, "f (X)" (X = 101,201,202,203)
Represents the complex amplitude distribution on the back side of each element,
(X) ”(X = 101, 201, 202, 203) represents the Fourier transform for each element. For example, the value of X indicates the sign of each element, F (201) is the above U1, and F (202) is the above U2.
In addition, when F (203) corresponds to U3 and the convolution (convolution operation) is represented by the symbol “*”, “F (101) = F (201) * F (202) *
The relationship of "F (203)" is established. That is, the influences of the respective elements (regions) denoted by reference numerals 201 to 203 are combined, and F
It will be reflected in (101).

"F ^-1 (101)" represents the inverse Fourier transform of the grating portion 101,
An observation image on the inverse Fourier plane is obtained by the imaging device 20 (see FIG. 9 for an image display example).

Regarding the observation image on the inverse Fourier plane,
Since it cannot be compared with the analysis results obtained in (1) to (3) as it is, it is necessary to perform processing in (4) so that both can be compared.

For that purpose, for example, there is a configuration mode in which the result obtained by performing the necessary arithmetic processing on the observed image is compared with the analysis result.

Regarding the image observed by the image pickup device 20,
The image signal (inspection result) is Fourier-transformed to obtain the intensity distribution on the Fourier surface of the pickup lens 14, and the influence of the diffraction image generated in the region 202 due to the deconvolution in U2 and U3 described above and the waveguide 203 After removing the influence of the mode light, an inverse Fourier transform is performed to obtain a corrected inspection result (hereinafter referred to as “correction inspection result”), and the coupling efficiency of only the grating 201 in the grating portion 101 is calculated. It is possible to perform a simple comparison between the result and the analysis result (analysis solution of infinite periodic structure).

FIG. 11 is an explanatory diagram of a processing form in the measurement processing means 30. In FIG. 11, a portion actually performed by software processing is schematically shown as a block element for convenience of explanation.

The image signal “G” acquired by the image pickup device 20 is sent to the Fourier transform processing section 31 and then to the deconvolution processing section 32.

Analysis unit (or model analysis processing unit) 33
Is responsible for the processing of the above (1) to (3), and information necessary for analysis based on the design specifications of the grating unit can be input, set or selected from the input / operation unit 34. You can do it. Analysis unit 3
3 performs the above U1, U2, and U3 calculation processing, and U2,
The data related to U3 is sent to the deconvolution processing unit 32, and the data related to U1 is sent to the comparison unit 35.

In the deconvolution processing unit 32, based on the data relating to U2 and U3 from the analysis unit 33, the frequency response component corresponding to the diffraction image generated at the edge of the finite area 202 and the above-mentioned waveguide mode light component are obtained. The corresponding frequency response component is removed by deconvolution in the pupil space,
The result is sent to the comparison unit 35.

In the comparison unit 35, the results sent from the deconvolution processing unit 32 and the analysis unit 33 are compared as they are or after undergoing a Fourier transform to determine whether the difference between them is within an allowable range. . Then, the judgment result is displayed on a display device (not shown) or an alarm or the like is issued, or permission or denial when transferring the inspection object to the next step, stop of use, etc. are controlled. For example, if the grating is manufactured as designed, it is determined that the difference between the inspection result and the analysis result is within the allowable error range, and that effect (inspection passed) or error is notified by a display or the like. When the difference between the inspection result and the analysis result is significant, the fact (inspection failure) or error is notified by a display or the like.

As described above, in order to simply compare the analysis result with the inspection result of the minute grating having the finite area, information on the coupling efficiency of only the grating (201) is extracted from the minute grating having the finite area. There is a need to. The Fourier transform processing unit 31 and the deconvolution processing unit 32 have extraction means 36 for that purpose.
This makes it possible to extract the coupling efficiency of only the grating based on the image signal G.

The above (1) to (3) may be obtained by the above (4), so that the order of them does not matter.

In the processing example described above, the correction inspection result, that is, the measurement result is processed and the result is compared with the corresponding analysis result. However, the present invention is not limited to this method and, for example, the analysis result is corrected. There is a mode in which the result of the comparison is compared with the measurement result. That is, after the above U2 and U3 are convoluted by convolution with the image intensity distribution on the pupil plane obtained from the analysis result, Fourier analysis is performed to obtain a corrected analysis result (correction analysis result), A method that allows this to be simply compared with the measurement result (inspection result) may be used.

The processing procedure therefor is summarized as follows.

(1) A frequency response component (U2) corresponding to the grating portion 101 having a finite region and a frequency response component (U3) corresponding to the waveguide mode light component of the grating are added to the Fourier transform image of the analysis result. It is added by convolution in the pupil space. (2) By performing an inverse Fourier transform on the result obtained in (1) (because the image by the imaging device 20 corresponds to the relationship of the Fourier transform with respect to the result in (1)),
It is converted so that it can be compared with the measurement result, that is, the two have an equal relationship. (3) The correction analysis result obtained in (2) is compared with the measurement result.

As to the correction analysis result and the image information obtained by the image pickup device, it is difficult for human eyes to judge the correction analysis result and the image information obtained by the image pickup device as they are, as shown in FIG. By processing, only the components that are purely dependent on the grating are extracted and displayed on an image display device to be visualized, and the results can be visually confirmed while comparing the analysis results with the measurement results, and various types such as displaying the grating duty can be displayed. It can be implemented in the form.

In the grating inspection, it is preferable to use a transmission electron microscope as an auxiliary in order to confirm the consistency of the reference method by the electromagnetic field analysis and to perform the interpolation with the actual data. This is because a lookup table (reference table) is created for each sample condition, or data comparison and reference are performed using a measurement value of a TEM (Transmission Electron Microscope) having a higher resolution as a reference value. Although the present invention does not work on the assumption that a transmission electron microscope is used, there is no problem in providing the inspection device with an additional function in order to improve measurement accuracy.

Further, although the processing described above is performed as signal processing (or information processing) in the measurement processing means 30, a part of it may be realized by optical means. For example, the pickup lens 1 described above
4. By using the Fourier transform lens as the imaging lens 19, an optical filter or an electrical filter (low-pass filter) for observing the information of the Fourier plane, that is, the frequency spectrum, and extracting only the DC (direct current) component from it Filter or bandpass filter). As a result, the area 2
The frequency response component generated in 02 and the frequency response component generated in each waveguide 203 can be removed. That is, in the process described in detail above, in short, since only the DC component of the frequency response image of the grating portion 101 is extracted, a Fourier transform lens is provided in the detection optical system to optically extract the DC component. Alternatively, use of a filter for electrically extracting is effective for speeding up processing, reducing processing load of image information, and the like.

Further, regarding the waveguide mode light,
For example, when a plurality of monochromatic wavelength light sources, vertical multimode laser light sources, or white light sources are used to cancel the waveguide mode light due to the mutual wavelengths, the influence of the waveguide mode light can be eliminated (the mode light is generated). do not do.).
However, in this case, in the calculation processing by the above-mentioned analysis method, it is necessary to analyze the entire wavelength range of the light source and add the results.

Alternatively, the numerical aperture of the condenser lens 13 is set to "N
A1 ”and the numerical aperture of the pickup lens 14 is“ NA ”.
2 ”between these and the light source wavelength“ λ ”and the interval L (cycle) between the modes of the waveguide mode light,“ λ / (NA
By selecting the combination of numerical apertures so that the condition of 1 + NA2)> L ”is satisfied, the fundamental wave information generated by the mode light can be removed (the resolution of the waveguide mode light can be avoided). . Then, it is possible to shorten the time required for processing such as electromagnetic field analysis.

By the way, the above-mentioned grating inspection device 1
With respect to the polarization state of the laser light incident on the grating unit 101, the arbitrary polarization angle in the linear polarization state, the circular polarization state and the arbitrary elliptical polarization state can be adjusted. This is because the electromagnetic wave characteristics that the transmission efficiency (or the transmittance) of the polarization component orthogonal to the grating direction is higher than the transmission efficiency of the polarization component in the grating direction are used. In this example, when observing the grating portion 101, λ /
By rotating each wavelength plate by a predetermined angle in the two-wave plate adjusting unit 10 and the λ / 4 wavelength plate adjusting unit 11, the polarization direction of the incident linearly polarized light is changed to the grating direction of the grating unit 101. On the other hand, the measurement accuracy is improved by rotating it within a range of 0 ° to 90 ° so that the measurement can be performed in a circularly polarized light incident state. As described above, by providing the polarization optical element (including the half-wave plate and the quarter-wave plate, etc.) for adjusting the polarization state in the illumination optical system and the adjusting mechanism thereof, the optimum illumination can be obtained. The condition (polarization state) can be realized.

Furthermore, in the detection optical system DO, the image signal obtained by the image pickup device 20 includes the influence of the phase and polarization error of the optical system such as wavefront aberration and birefringence inherent in the optical system. , In order to analyze including them, a pupil filter function having a phase filter function and a polarization filter function corresponding to the aberration of the optical system and birefringence is set in the pupil space, and the analysis process is performed using the function. It is preferable to carry out.

That is, the transmitted wavefront aberration and the birefringence amount of the detection optical system are individually measured, and the pickup lens 1
In the pupil plane of No. 4, the measured transmitted wavefront aberration of the pickup lens 14 is provided as a phase error function and a polarization error function, thereby eliminating the error of the optical system included in the image information detected by the imaging device 20. You can

The pupil filter function may be provided as optical filter means, electrical filter means, or realized by software processing on a computer (complexization). Should be selected in consideration of the degree, processing time, cost, etc.).

In the method described above, since there is no particular limitation on the period of the grating portion 101, the detection optical system DO is configured so as to detect only the 0th-order diffracted light so that all the gratings can be detected. It is obvious that the application of is possible.

When the observation using the above-mentioned grating inspection apparatus 1 and the fine dimension observation within the resolution limit using the conventional optical microscope are compared, in the former case, the apparatus parameter, that is, the laser light source 1L While using the light source wavelength, the numerical apertures of the condenser lens 13 and the pickup lens 14, the coherence factor of the illumination, the known physical property information about the sample small grating, the information of the grating region and the grating pitch, and the information of the grating thickness, It is an obvious difference that the shape related to the grating duty can be quantified from the coupling efficiency of the direct light observed in the detection optical system DO (that is, until now, the imaging phenomenon for the diffracted light of the first order or higher) From the viewpoint of resolution, it is not possible to leave the device configuration sticking to Only approach results in would naturally faced to the limit.).

The method described above can be used for various applications such as a mask inspection for optical semiconductor exposure typified by a scanning stepper and a reflective mask for semiconductor exposure using soft X-rays. The following application forms can be given.

In the etching step used in the semiconductor exposure mask manufacturing process, the grating inspection apparatus 1 is installed or additionally arranged in the etching apparatus so as to be used as an in-line monitor of etching conditions.・ In the mask cleaning process, in which the surface of the semiconductor exposure mask is oxidized by ozone, and then foreign matter attached to the mask is cleaned by etching with a strong acid, the height of the grating and the state of deformation in the width direction due to the cleaning. A mode in which the grating inspection device 1 is used to monitor the. A mode in which the grating inspection apparatus 1 is installed or additionally arranged in the semiconductor exposure apparatus, and the fine grating shape is monitored when the exposure mask is carried in.

As described above in detail, regarding the coupling efficiency in the grating portion 101,
The physical properties of the mask for the EB exposure apparatus and the optical constants of the condenser lens 13 and the pickup lens 14 are known, and the grating period, pattern length, and pattern width of the grating portion 101 should be quoted from the design data. Can be found at. Therefore, if the film structure (structure in the thickness direction) can be measured by another process or the like, the only parameter required to determine the coupling efficiency is the duty of the grating portion 101. After correcting one or both of the measurement result and the analysis result so that they can be compared at an equal level, the grating portion 101 can be obtained from the comparison result.
Can be quantified or inspected (pass / fail judgment, etc.). For example, if the characteristics shown in FIG. 8 are obtained from the analysis result and the measurement, the data of the coupling efficiency (in this case, the transmittance of the 0th order diffracted light) with the grating duty as a variable for each light source wavelength. In the form of a table (a reference table is created in advance), and after that, when the measurement data of the coupling efficiency is obtained from the image information obtained by the detection optical system DO, the data is converted into a table. The saved data can be referred to and compared easily. That is, since the grating duty of the grating portion 101 is given as a design value, table data referred to by designating that value (comparison reference value is shown).
Then, if the difference between the coupling efficiency measurement data and the measured data is within the allowable range, it is determined that the inspection has passed, and if the difference deviates from the allowable range, it is determined that the inspection has failed.
Of course, it is also possible to make a judgment according to a logic such as a majority decision based on a plurality of inspections. Further, within the allowable range, the upper limit or the lower limit is set in advance, and the upper limit is set according to the conditions. Various embodiments such as a form in which the lower limit is dynamically changed are possible.

In the above description, for easy understanding,
The transmission coupling efficiency, that is, the configuration form and method for detecting the direct light transmittance has been described in detail as an example, but the present invention is not limited to this, and the reflected diffracted light may be used for the above-described measurement. Of course, there is no change in the basic principle.

However, in the mask manufacturing process for the EB exposure apparatus, it is necessary to frequently use a very expensive transmission electron beam scanning microscope because there is no simple inspection method so far, and as a result, Although the inspection cost, which accounts for the manufacturing cost of the mask for the EB exposure apparatus, has been a problem, the grating inspection apparatus 1 can be introduced as a simple measuring apparatus, whereby the defective portion of the mask can be promptly confirmed. It is possible to detect and reduce the manufacturing cost of the mask for the EB exposure apparatus.

[0121]

As is apparent from the above description, according to the inventions of claims 1 and 10, the 0th order diffracted light, which is direct light, among the diffracted light by (the grating of) the object to be inspected. It is possible to quantify the shape of the grating based on the comparison with the analysis result of the grating by measuring the information of the transmittance or the reflectance related to, and to limit the resolution limit associated with the observation of spatial separation by imaging. I do not receive it. Then, without using the transmission electron microscope, the measurement and the shape inspection can be quickly performed on the inspection object including the grating by using a simple inspection method.

According to the second, third and twelfth aspects of the invention, the influence of the diffraction image and the waveguide mode light at the edge portion of the finite region is eliminated for the grating portion having the finite region. , It is possible to easily compare the measurement result with the analysis result.

According to the invention of claim 4, an optical filter is used for the Fourier transform and an optical or electrical filter is used for extracting the direct current component, thereby reducing the load of the measurement processing, and also processing. The time can be shortened.

According to the fifth aspect of the invention, since the limited illumination can be performed on the grating portion of the object to be inspected, it is difficult to be influenced by the diffracted light from the peripheral area, and it is not necessary to limit the visual field.

According to the invention of claim 6, it is possible to prevent the generation of the waveguide mode light related to the grating.

According to the seventh and fifteenth aspects of the present invention, it is possible to prevent the resolution of the waveguide mode light related to the grating by defining the condition for the grating not satisfying the diffraction condition.

According to the eighth aspect of the invention, the polarization state in the illumination optical system can be adjusted so that an appropriate illumination condition can be obtained for the grating of the object to be inspected.

According to the invention of claim 9, by applying to the inspection of the semiconductor exposure mask, it is effective in reducing the inspection cost and the inspection time.

According to the eleventh aspect of the present invention, since the measurement result of the coupling efficiency and the analysis result can be compared using the grating duty as a variable, the grating duty can be quantified.

According to the twelfth and thirteenth aspects of the present invention, the processing load can be reduced by partially simplifying the calculation processing.

According to the fourteenth aspect of the present invention, the reliability of the inspection determination can be improved by obtaining the accurate analysis result.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a grating inspection device according to the present invention.

FIG. 2 is a schematic view of a mask for an EB exposure apparatus which is an inspection object.

FIG. 3 is a schematic view showing a grating portion of an object to be inspected, a condenser lens and a pickup lens.

FIG. 4 is an explanatory diagram of diffracted light when the grating pitch is longer than the light source wavelength.

FIG. 5 is an explanatory diagram of zero-order diffracted light and evanescent waves when the grating pitch is shorter than the light source wavelength.

FIG. 6 is a graph showing, as an example, the wavelength dependence of the transmittance of a light beam that is vertically incident on the non-grating part.

FIG. 7 is a graph diagram comparing the coupling efficiencies of the grating portion for each light source wavelength.

FIG. 8 is a graph illustrating the coupling efficiency of 0th-order diffracted light when the grating duty is used as a parameter.

FIG. 9 is a diagram showing an example of an image detected by an image pickup device which constitutes a detection optical system.

FIG. 10 is a conceptual diagram for explaining a relationship between each element forming a grating portion and each image.

FIG. 11 is an explanatory diagram of a processing form in the measurement processing means.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Grating inspection device, LS ... Light source, LO ... Illumination optical system, DO ... Detection optical system, 13 ... Condensing lens, 14 ... Pickup lens, 30 ... Measurement processing means, 100 ... Inspected object, 101 ... Grating part

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yutaka Imai             6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Soni             -Inside the corporation F term (reference) 2G086 EE12                 2H049 AA03 AA07 AA31

Claims (15)

[Claims] 1. A light source having a single wavelength and an object to be inspected for optically inspecting a shape of the grating for an object to be inspected including a grating having a fine repeating pattern structure or a periodic structure. An illumination optical system for irradiating the observation surface of the object with light from the light source, and a detection optical system for detecting the light transmitted from the object to be inspected or the light reflected by the object to be inspected from the light from the light source. A grating inspection apparatus provided with the above-mentioned information, which is obtained by measuring information as a transmittance or a reflectance of a 0th-order diffracted light which is direct light among the diffracted light by the grating of the object to be inspected. A grating inspection device characterized by being provided with measurement processing means for quantifying the shape of the grating by comparing it with the analysis result of the grating. . 2. The grating inspection apparatus according to claim 1, wherein, for the grating portion having a finite area in the inspection object, a diffraction image at an edge portion of the finite area and an influence of waveguide mode light are removed. In addition, a means for extracting information relating to the coupling efficiency of purely the grating,
A grating inspection apparatus comprising the measurement processing means. 3. The grating inspection apparatus according to claim 2, wherein the measurement processing means Fourier transforms the image signal obtained by the detection optical system and then responds to the diffraction image generated at the edge portion of the finite area. The frequency response component and the frequency response component corresponding to the waveguide mode light component of the grating are removed by deconvolution in the pupil space to obtain the corrected measurement result, and the measurement result is analyzed with the corresponding analysis result. A grating inspection device characterized by comparison. 4. The grating inspection apparatus according to claim 3, wherein a Fourier transform lens is provided in the detection optical system and the detection optical system is provided in order to extract only the DC component of the frequency response image related to the grating portion. An optical or electrical filter for transmitting only a DC component of an image signal obtained by the above method is provided. 5. The grating inspection apparatus according to claim 1, wherein the light source having a single wavelength is a laser light source having monochromaticity or a light source obtained by narrowing a spectral emission line of a discharge lamp to a full width at half maximum of about 10 nm. A grating inspection device using an excimer laser. 6. The grating inspection apparatus according to claim 2, wherein a plurality of monochromatic wavelength light sources, longitudinal multimode laser light sources or white light sources are used to cancel the waveguide mode light due to mutual wavelengths. Inspection device. 7. The grating inspection apparatus according to claim 2, wherein the period of the waveguide mode light is “L”, the light source wavelength is “λ”, and the numerical aperture of the condenser lens that constitutes the illumination optical system is “L”. NA1 ", and the numerical aperture of the pickup lens constituting the detection optical system is referred to as" NA2 "," λ / (NA
1 + NA2)> L ”is established. 8. The grating inspection apparatus according to claim 1, further comprising a polarization optical element and an adjusting mechanism for adjusting the polarization state of the illumination optical system. 9. The grating inspection apparatus according to claim 1, wherein the object to be inspected is a semiconductor exposure mask. 10. An object to be inspected including a grating having a fine repeating pattern structure or a periodic structure, in order to optically inspect the shape of the grating, light from a light source having a single wavelength is used. A grating inspection method for irradiating an observation surface of an inspection object and detecting light transmitted through the inspection object or reflected by the inspection object as an image signal by a detection optical system, Of the diffracted light from the grating, the step of measuring the coupling efficiency as the transmittance or reflectance of the 0th-order diffracted light which is direct light, and the measurement result of the above step are compared to the analysis result of the grating. A step of performing a calculation process on the result or analysis result and quantifying the shape of the grating by comparing both results Grating inspection method, characterized by that example. 11. The grating inspection method according to claim 10, wherein the light source wavelength and the optical constants, the physical properties and characteristics of the grating material are known, and the grating duty is set as a variable to determine the diffracted light in an arbitrary order in the grating. From the step of obtaining the ring efficiency by analysis and the complex amplitude distribution at the interface of the grating on the side of the detection optical system obtained from the above analysis, the detection optical system is calculated by using a transfer function equivalent to the detection optical system. A grating inspection method comprising: a step of obtaining an intensity distribution equivalent to the image signal obtained by a system; and a step of comparing a result of the intensity distribution and a measurement result by the detection optical system. 12. The grating inspection method according to claim 11, further comprising a step of obtaining a coupling efficiency of diffracted light with an arbitrary order by analyzing the grating with an infinite period, and the analysis result and a grating having a finite region. In order to compare the measurement results of the parts, as a step of extracting the information of the coupling efficiency by the grating only from the grating part, after the Fourier transform of the image signal, the diffraction image generated at the edge part of the finite area And a frequency response component corresponding to the waveguide mode light component of the grating are removed by deconvolution in the pupil space, and then inverse Fourier transform is performed. 13. The grating inspecting method according to claim 11, wherein the Fourier transform image of the analysis result corresponds to a frequency response component corresponding to a grating portion having the finite region and a waveguide mode light component of the grating. A grating inspection method comprising the step of adding the frequency response component by convolution in the pupil space and then performing an inverse Fourier transform. 14. The grating inspection method according to claim 11, including the influence of the phase error and polarization error of the optical system such as wavefront aberration and birefringence inherent in the optical system included in the image signal from the detection optical system. In order to analyze, a pupil filter function having a phase filter function and a polarization filter function corresponding to the aberration and birefringence of the optical system is set in the pupil space, and the analysis process is performed using the function. Method. 15. The grating inspection method according to claim 12, wherein a period of the waveguide mode light is “L”, a light source wavelength is “λ”, and a numerical aperture of a condenser lens that constitutes the illumination optical system is “L”. NA1 ", and the numerical aperture of the pickup lens constituting the detection optical system is referred to as" NA2 "," λ / (NA
1 + NA2)> L ”, so that the information of the fundamental wave generated by the waveguide mode light is removed.