JP3139020B2 - Photomask inspection apparatus and photomask inspection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inspection apparatus for a photomask used as an original when transferring a circuit pattern of a semiconductor or the like. More specifically, a phase member for changing the phase of transmitted light is added to a specific portion. The present invention relates to a technique for measuring a phase change amount in a phase shift photomask.

[0002]

2. Description of the Related Art A photomask used as an original 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, a photomask having such a structure has a problem that when a circuit pattern is miniaturized, a sufficient contrast of a projected image cannot be obtained due to light diffraction and interference phenomena. Various phase-change photomasks have been proposed in which a phase member is added to a specific portion of a bare surface portion to partially change the phase of transmitted light to increase image contrast. For example, Tokiko Sho 6
Japanese Patent Application Laid-Open No. 2-50811 discloses a technique relating to a spatial frequency modulation type photomask.

In such a phase change photomask, since it is important to accurately control the phase, it is necessary to inspect the amount of phase change by a phase member in addition to the presence or absence of a defect in a light shielding pattern. Has determined the amount of phase change 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.

That is, the measurement of the amount of phase change φ by the phase member (mainly made of a SiO ₂ film or the like) is performed by measuring the thickness t of the phase member.
And the refractive index n of the phase member at the exposure wavelength λ when the photomask is used in the actual lithography process, and calculated as Equation (1).

Φ = 2π · (n-1) t / λ (1)

[0007]

However, conventionally,
The ellipsometer used for inspection of the phase change photomask measures the film thickness and refractive index using reflection at the interface between the substrate and the thin film as described above. Is very difficult to measure, and if the refractive indices of the two are equal, the measurement becomes impossible because the intensity of the reflected light at the interface becomes zero.

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

The phase member in the phase shift photomask controls the refractive index n and the thickness d of the phase member so that the phase change φ expressed by the above formula 1 becomes π. The refractive index n changes slightly depending on the conditions for forming the phase member (for example, when forming the phase member, conditions such as temperature, pressure, composition, etc.). There is variation in

For example, assuming that the exposure wavelength is λ = 365 nm and the refractive index of the phase member is n = 1.5, and the error of the phase change is allowed up to 10 °, the error of the thickness d is required to be within ± 20 nm. It is very difficult to control the film thickness within this error range. For this reason, the error of the phase change amount φ (ie,
It is desired to efficiently measure how much φ deviates from π).

However, when the amount of phase change is determined from the thickness and the refractive index of the phase member as in the prior art, the thickness d of the phase member is determined.
In addition, it is necessary to measure the refractive index n, which changes depending on the film forming conditions, each time, and the measurement requires a long time.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and enables accurate measurement of a phase change amount irrespective of a refractive index difference between a phase member and a substrate, and an accurate phase change amount at an exposure wavelength. It is an object of the present invention to provide an inspection apparatus for a phase shift photomask, which can easily and quickly obtain a value.

[0013]

SUMMARY OF THE INVENTION A photomask inspection apparatus according to the present invention has a geometric original pattern on a substrate which is substantially transparent (or reflects a light beam) to a light beam having a predetermined wavelength. In order to achieve the above-described object, a photomask including, at least in a part of a region where an original pattern is formed, a region that changes the phase of a light beam transmitted (or reflected) through the substrate is used as an inspection target. An irradiation optical system for irradiating a monochromatic light or a quasi-monochromatic light to a pattern to be inspected on a mask, and a detecting means for photoelectrically detecting an intensity distribution of light generated on a Fourier transform surface of the pattern to be inspected by the irradiation.

Specifically, the detecting means in the present invention comprises a photoelectric converter for detecting the intensity distribution of light generated on the Fourier transform surface, and a region for changing the phase based on a detection signal output from the photoelectric converter. The irradiation optical system includes a first aperture stop for adjusting the divergence angle of the light beam emitted from the light source, and a second aperture stop for adjusting the irradiation area of the photomask. Preferably, it is provided.

[0015]

The principle of measuring the amount of phase change in the present invention will be described with reference to FIG. Two openings 2a (corresponding to the transparent portion A and the phase member addition portion B of the pattern to be inspected in the embodiment described later) are adjacent to each other in the irradiation area of the vertically irradiated light beam, and one opening It is assumed that the phase of the transmitted light of the (phase member adding portion B) changes by (π + θ) with respect to the transmitted light of the other opening (transparent portion A). Here, θ is an error in the amount of phase change. At this time, the intensity distribution of the Fourier transform image (diffraction image) by the light beam transmitted through the two apertures can be expressed by Expression (2).

[0016]

(Equation 1)

Here, u is the spatial frequency coordinate of the Fourier transform plane. Equation (2) (2a · sin (2π · a · u) / 2π · a · u)
Represents a Fourier transform image of two apertures having a width 2a, and has a minimum point at u = ± 1 / 2a, ± 1 / a, ± 3 / 2a,.
This is an inc function.

In the equation (2), (exp (2πaiu) + exp ((π
+ Θ) i) · exp (-2πaiu)) (hereinafter referred to as Q) is a term that becomes sin (2 πau) when θ = 0 (when there is no error in the amount of phase change). Let u = 0, ± 1 /
2a, ± 1 / a, ± 3 / 2a, ...

The intensity distribution of the Fourier transform image when θ = 0 is represented by a solid line in FIG. 5, and the origin and the minimum point position (the zero point position in FIG. 5) coincide, and appear on both sides of the origin. The peak intensities are equal.

On the other hand, when θ ≠ 0 (when there is an error in the amount of phase change), the Q portion of equation (2) becomes equation (3),
The minimum point is u = θ / 4πa, (± π + θ / 2) (1 / 2πa), (± 2πa
+ θ / 2) (1 / 2πa). The intensity distribution of the Fourier transform image when θ ≠ 0 is represented by a dotted line in FIG. 5, and the minimum point position is shifted from the origin u ₀ of the spatial frequency coordinate by u ₁ , and the two peaks sandwiching the minimum point The intensity of one of the peaks decreases.

Q = exp (θi / 2) · 2i · sin (2πau−θ / 2) (3)

Here, when θ ≠ 0, focusing on the coordinates u _{1 of the} minimum point closest to the origin u ₀ of the spatial frequency coordinates,
u ₁ = θ / 4πa, and u ₁ is proportional to the phase change amount error θ. That is, the phase variation error is determined quantitatively by obtaining the coordinates u ₁ nearest local minimum point to the origin u _0. Note that specifically described in the examples below for how to determine the origin u ₀ as a reference.

Here, the Fourier transform image does not change even if the two apertures irradiated with the light beam are shifted from the optical axis. Therefore, in the present invention, it is not necessary to strictly align the two openings (patterns to be inspected) to be inspected with respect to the optical axis, which is very advantageous when the device is implemented.

When there is a difference between the transmittances of the light beams of the two openings (ie, when the transmittance of the phase member added to one opening is not 100%), the intensity of the minimum point of the Fourier transform image is obtained. Is higher in accordance with the degree of light absorption by the phase member (the minimum point becomes zero if the transmittance of the phase member is 100%), but the spatial frequency coordinate position of the minimum point does not change. Therefore, according to the present invention, even when the light beam is absorbed by the phase member, the amount of phase change can be accurately measured.

As described above, when θ ≠ 0 (when there is an error in the amount of phase change), the minimum point of the Fourier transform image deviates from the origin, and one of two peaks sandwiching the minimum point. Since the height of the peak decreases, the presence or absence of an error in the amount of phase change can be easily checked by measuring the peak height of the Fourier transform image.

[0026]

FIG. 1 is a block diagram of a photomask inspection apparatus according to an embodiment of the present invention. In the figure, a light source 1 is the same as a light source of an exposure apparatus in which a photomask 8 to be inspected is actually used. In this embodiment, a mercury lamp is used. When a laser (for example, a KrF excimer laser) is used as the light source of the exposure apparatus, the laser is used as the light source accordingly.

It is desirable that the wavelength for the measurement is substantially equal to the exposure wavelength, because the phase member has dispersion and the refractive index of the phase member is different at a wavelength different from the exposure wavelength.

The light beam emitted from the light source 1 is reflected by an elliptical mirror 2
And is bent by the mirror 3. Then, the light source image 6 is formed on the aperture stop (pinhole plate or slit plate) 5 by the relay lens 4. At least one of the elliptical mirror 2 and the mirror 3 is constituted by a dichroic mirror, and the light beam becomes monochromatic light having the same wavelength as the exposure wavelength. When a dichroic mirror is not used, a wavelength selection element (interference filter or the like) is separately provided between the relay lens 4 and the aperture stop 5, for example.

The aperture stop 5 increases the spatial coherence of the light beam from the light source 1 and increases the contrast of the Fourier transform image to be detected. When a slit plate is used as the aperture stop 5, the longitudinal direction of the slit is made to coincide with the direction of the boundary between the transparent portion and the phase member addition portion of the pattern to be inspected (described later).

The light beam emitted from the aperture stop 5 is converted into a parallel light beam by the lens 7,
With this, the beam diameter is reduced to a predetermined size. The light beam from the variable aperture stop 11 is held on a stage RS that is two-dimensionally moved by a driving unit 16 in a plane orthogonal to the optical axis (the operation of the stage RS will be described later). Illuminate evenly.

The lens 7 is arranged at a position such that the distance from the aperture stop 5 to the lens 7 and the distance from the lens 7 to the photomask 8 are substantially equal to the focal length of the lens 7.

The light beam transmitted through the photomask 8 is incident on a Fourier transform lens 9, which forms a Fourier transform image FP. The distance from the photomask 8 to the Fourier transform lens 9 is substantially equal to the focal length f of the Fourier transform lens, and a photoelectric converter 10 is disposed at the rear focal position of the Fourier transform lens 9. A linear array sensor or the like can be used as the photoelectric converter 10, and it is sufficient that the photoelectric converter 10 be at least a one-dimensional optical sensor, and a photodetector having a scanning slit may be used.

The Fourier transform lens 9 is not always necessary. If the distance from the photomask 8 to the photoelectric converter 10 is sufficiently large with respect to the width of the two openings of the pattern to be inspected, the Fourier transform lens 9 is required. At least, a Fourier transform image FP (far-field image) is formed on the light receiving surface of the photoelectric converter 10.

The Fourier transform image FP from the photoelectric converter 10
Is sent to the signal processing circuit 12, where i-
Processing including V conversion and A / D conversion is performed. The calculating means 13 such as a microcomputer obtains the spatial frequency coordinates of the minimum point of the Fourier transform image FP based on the data stored in advance and the signal from the signal processing circuit 12, and calculates the phase member provided on the pattern to be inspected. Is calculated. The calculated phase change amount is displayed on the display 14.

Here, FIG. 4 is a plan view showing an example of the photomask 8, and in addition to the circuit pattern RP, a test pattern TP (pattern to be inspected) formed in the same manufacturing process.
Is provided. The test pattern TP is, together with the circuit pattern RP, an area P surrounded by a light-shielding body LS such as chrome.
A (here, in particular, an area corresponding to a street line).

FIGS. 2 (a) and 2 (b) and FIGS. 3 (a) and 3 (b) are a plan view and a sectional view showing an example of the test pattern TP in this embodiment. 2, a light-shielding portion 8b made of chrome or the like is formed on a transparent substrate 8a so as to surround a region corresponding to the test pattern TP. Light shielding part 8
The area surrounded by b is divided into two, one of which is a transparent part A (transparent substrate 8a bare surface part) and the other is a phase member addition part B to which the phase member 22 is added. In this embodiment, the transparent portion A
And the area ratio of the phase member addition portion B is approximately 1: 1.

In the example of FIG. 3, in addition to the configuration of the test pattern of FIG. 2, a light shielding portion 8b is provided at the boundary between the transparent portion A and the phase member adding portion B. By doing so, the dark line (corresponding to the minimum point of the intensity distribution) of the Fourier transform image becomes clear, and the detection accuracy is improved.

Here, in the pattern to be inspected suitable in the present invention, the area ratio between the transparent portion A and the phase adding portion B does not need to be 1: 1 as described above, and at least two opening portions A,
B only needs to have substantially the same width in the arrangement direction (X direction in FIGS. 2 and 3). This is because even if the lengths in the Y direction in FIGS. 2 and 3 are different, the minimum point (described later) of the Fourier transform image does not change, and the intensity value (peak value) at the maximum point does not change. However, the shape and size of the two openings A and B are not limited as long as the above conditions are satisfied, but are preferably rectangular.

Next, the operation of measuring the amount of phase change using the apparatus of this embodiment will be described. After the photomask 8 to be inspected is held on the stage RS, before the measurement, the stage RS is moved so that the light beam is applied to the region of the photomask 8 where only the transparent portion or only the phase member is added. The optical beam is moved two-dimensionally, and a Fourier transform image when the light beam has no phase difference is detected by the photoelectric converter 10. At this time, it is desirable that the variable aperture stop 11 is driven to set the illumination area on the photomask 8 to have substantially the same shape and size as the transparent section A or the phase member addition section B.

The Fourier transform image when the light beam has no phase difference has a peak at a position corresponding to the origin u ₀ of the spatial frequency coordinate. By detecting this peak position, the origin u ₀ of the spatial frequency coordinate is detected. Can be determined. The peak position can be easily detected by slicing the waveform at a predetermined intensity and taking an intermediate point. The detected peak position (the origin position of the spatial frequency coordinate) is stored in the calculating means 13 as a reference position.

When the reference position is determined in this manner, a transparent substrate without a phase member or another substrate having a phase member formed on the entire surface may be used instead of the photomask 8.

Next, the test pattern T of the photomask 8 is
The driving unit 16 moves the stage RS two-dimensionally so that P enters the irradiation area of the light beam from the lens 7. At this time, the beam diameter of the irradiation light is the test pattern T
It is adjusted by the variable aperture stop 11 according to the size and shape of P.

At this time, the spatial frequency coordinate position of the minimum point of the Fourier transform image can be determined even if the test pattern TP is displaced from the optical axis (in FIG.
Therefore, if the test pattern TP is included in the irradiation area, the alignment of the photomask 8 with respect to the light beam does not have to be performed so strictly.

Also, even if the photomask 8 does not exactly match the rear focal position of the lens 7 and the front focal position of the Fourier transform lens 9 (even if the photomask 8 moves in the direction of arrow Z in FIG. 1). ), Since the spatial frequency coordinate position of the minimum point of the Fourier transform image does not change, it is not necessary to perform the positioning of the photomask 8 in the optical axis direction so strictly.

However, when the photomask 8 is tilted with respect to the optical axis, the optical path length of the phase member 22 changes, resulting in a measurement error of the amount of phase change. Is desirable. Further, when the photomask 8 rotates around the optical axis, a dark line formed on the Fourier transform plane rotates, and a detection error of a minimum point occurs. Therefore, when the stage RS is rotated around the optical axis during the measurement, No.

After the photomask 8 is positioned as described above, the test pattern TP is uniformly irradiated with a light beam, and a Fourier transform image FP (phase of the test pattern TP) formed by the transmitted light of the test pattern TP is formed. If the transmittance of the member 22 is 100%, a Fourier transform image as shown by the dotted line in FIG. 5 described above) is detected by the photoelectric converter 10.

The detection signal of the photoelectric converter 10 is sent to the arithmetic means 13 via the signal processing circuit 12, and the arithmetic means 13 stores the spatial frequency coordinate u of the minimum point closest to the origin u ₀ stored previously. seek _1.

When the phase change amount is (π + θ), as described above, since u ₁ = θ / 4πa, the error θ = 4
πau.

Here, 2a is the width of the transparent portion A and the phase member addition portion B of the test pattern TP, and u is the distance. Therefore, to convert the error θ into a spatial frequency, it is sufficient to add 1 / λf. , Θ ′ = 4πau ₁ / λf
Thus, the phase change amount error θ ′ in the test pattern TP is calculated. λ is the wavelength of the irradiation light, f is the focal length of the Fourier transform lens, and is stored in advance in the calculating means 13. The calculated phase change amount error is displayed on the display 14.

The method of detecting the coordinate values u ₀ and u ₁ of the minimum points in the signal processing circuit 12 is not limited to a method of slicing a signal waveform with a predetermined voltage value and finding the middle point thereof. Any method (any conventional method) may be used.

Circuit pattern RP and test pattern TP
Are formed in the same process, and the phase change amounts of both patterns can be regarded as being equal. By measuring the phase change amount error of the test pattern TP as described above, the phase change amount error of the circuit pattern RP is obtained. You can know.

In the example of FIG. 4, only one test pattern TP is provided at the approximate center of the photomask 8. However, if the test pattern TP is provided at each position of the photomask 8 and a phase change amount error is obtained, respectively. And the error distribution in the photomask 8 can be known. Needless to say, a part of the circuit pattern RP may be used as the pattern to be inspected without providing the test pattern TP.

In the above description, in order to determine the reference position prior to the measurement of the amount of phase change, the light beam is applied to only the transparent portion or only the phase member added portion, and the peak of the Fourier transform image is obtained. Although the position (minimum point) is detected and used as the origin of the spatial frequency coordinates, the reference position can also be determined by a method as shown in FIG.

First, as shown in FIG. 6 (a), in a state where the phase member adding portion B is located on the left side of the paper and the transparent portion A is located on the right side (the transparent portion A may be on the left and the phase member adding portion B may be on the right. Needless to say), irradiate the test pattern TP with a light beam,
A Fourier transform image due to transmitted light is detected.

Next, as shown in FIG. 6B, the positions of the transparent portion A and the phase member adding portion B are exchanged with respect to the boundary line, the light beam is again irradiated on the test pattern TP, and the Fourier transform by the transmitted light is performed. Detect the image.

The Fourier transform images in the cases of FIGS. 6 (a) and 6 (b) are respectively FP _a and FP _{b in} FIG. 6 (c), and the minimum point of the Fourier transform image FP _a is at the origin. shifted by u ₁ to the right side against, minimum point of the Fourier transform image FP _b are shifted by u ₁ to the left side with respect to the origin. Thus, the difference in minimum point position of the Fourier transform image FP _a and FP _b is 2u _1, and the midpoint of the minimum point position of the Fourier transform image FP _a and FP _b is the origin u ₀ of the spatial frequency coordinates.

As described above, the Fourier transform image does not change even if the test pattern TP deviates from the optical axis.
In the measurement in (a) and the measurement in FIG. 6 (b), it is not necessary to strictly align the positions of the boundaries between the transparent portion A and the phase member addition portion B so as to match. However, the measurement in FIG.
During the measurement in (b), the stage RS holding the photomask 8 must not be rotated around the optical axis. FIG.
The test patterns shown in each of (a) and (b) may be formed on the same mask or may be formed on different masks.

Here, FIGS. 8 and 9 show graphs obtained by calculating a Fourier transform image when the test pattern of FIG. 2 is used. FIG. 8 shows that the transmittance of the phase member 22 is 100%.
FP _{0 to} FP ₉ in the figure are the intensity distributions of the Fourier transform image when the phase change amount error θ is 0 °, 20 °, 40 °, 60 °,.

As shown in the figure, as the error of the amount of phase change increases, the spatial frequency coordinate of the minimum point (zero point) changes from the coordinate origin 0 (that is, u ₀ ) to u _9. The distance between the minimum point and the origin is large.
Also, as the value of the phase change amount error θ increases, the height of the higher peak (peak on the left side of the paper) of the two peaks sandwiching the minimum point becomes higher, and the lower peak (peak on the right side of the paper) ) Is lower (the display of the graph is normalized, so that the height of the higher peak is constant). Therefore, by measuring the peak height of the Fourier transform image (the difference between the heights of the two peaks), it is possible to easily know the approximate error of the phase change amount.

[0060] Figure 9 shows the case the transmittance of the phase member 22 is 25%, drawing FP ₁₀ ~FP ₁₃ each phase variation error θ is 0 °, 20 °, 40 ° , if the 60 ° 5 is an intensity distribution of the Fourier transform image of FIG. When light is absorbed by the phase member 22, the intensity of the minimum point between the two peaks does not become zero, but the spatial frequency coordinate position of each minimum point is the same as in FIG. It can be seen that the absorption of light at the point does not affect the measurement of the amount of phase change.

Next, a graph obtained by calculating the intensity distribution of the Fourier transform image when the ratio (W _A : W _B ) of the width of the test pattern TP in the arrangement direction of the transparent portion A and the phase member addition portion B is changed. Are shown in FIGS. For simplicity, the transmittance of the phase member 22 is set to 100%, and the phase change amount error θ
0 °, 10 °, 20 °, 30 °.

FIG. 10 shows a case where W _A : W _B = 1: 1, and a minimum point (zero point) clearly appears as in FIG.

FIG. 11 shows the case where W _A : W _B = 1: 2. Even when the transmittance is 100%, the minimum point does not become the zero point. However, the minimum points are clearly shown, and the spatial coordinate position of each minimum point is the same as in FIG. 10, so that the amount of phase change can be measured.

FIG. 12 shows the case where W _A : W _B = 1: 3. The intensity at the minimum point further increases as compared with the case of FIG.
Although the interval between the two peaks is narrow, the minimum point can be detected, so that the amount of phase change can be measured.

FIG. 13 shows the case where W _A : W _B = 1: 4. In this case, it is difficult to detect the minimum point (especially, when the error of the amount of phase change is large, there is almost no peak on one side. (It approaches a single peak), and it is impossible to measure the error of the phase change amount.

FIG. 14 shows the case where W _A : W _B = 1: 0.5, where the width of the two peaks is widened, but the minimum point clearly appears, so that there is no problem in measuring the amount of phase change. .

As can be seen from FIGS. 10 to 14 described above, the width of the transparent portion A and the phase member addition portion B of the pattern to be inspected in the present invention is not necessarily required to be 1: 1 as in the embodiment. If the ratio (W _A : W _B ) is approximately 1: 3 to 3: 1, the error in the amount of phase change can be measured from the position of the minimum point of the Fourier transform image.

FIG. 17 shows a Fourier transform image (phase change error θ = 0 °, 10 °, 20 °, and 10 °) when W _A : W _B = 1: 1 and the transmittance of the phase member 22 is 10%. 30 °). When the transmittance of the phase member 22 decreases, the amount of light from the phase member addition section B decreases, and the peak of the minimum point increases. However, in the case of FIG. 17, the detection of the minimum point is sufficiently possible. Phase member 2 used for photomask 8
Since the transmittance of No. 2 is usually not considered to be extremely small, it can be said that the present invention can detect the amount of phase change regardless of the transmittance.

Next, the intensity distribution of the Fourier transform image when there are three or more apertures in the illumination area is shown in FIGS.
(a). FIG. 15 (a) shows a transparent portion A, a phase member addition portion B, and a transparent portion A within the irradiation area as shown in FIG. 15 (b).
Where three apertures (the width of each aperture in the arrangement direction are equal) are arranged, and a small peak appears at the origin position of the spatial frequency coordinate, and the positions of the minimum points on both sides correspond to the error in the amount of phase change. Therefore, it is difficult to measure the amount of phase change from the Fourier transform image.

FIG. 16A shows four openings (a transparent portion A, a phase member addition portion B, a transparent portion A, and a phase member addition portion B) in the irradiation area as shown in FIG. 16B. (Equal apertures in the arrangement direction of the apertures are arranged), and the Fourier transform image becomes more complicated, and it is difficult to measure the amount of phase change from the Fourier transform image.

Therefore, when a pattern in which the transparent portions A and the phase member adding portions B are alternately used is used as the pattern to be inspected, the beam diameter is adjusted by the variable aperture stop 11 shown in FIG. It is necessary to make only the phase member addition portion B enter the irradiation area.

As described above, as the pattern to be inspected in the present invention, a test pattern in which the adjacent transparent portion A and phase member adding portion B are surrounded by the light shielding portion 8b as shown in the examples of FIGS. Is preferred. The lengths in the direction parallel to the boundary between the transparent portion A and the phase member addition portion B need not be particularly equal.

In the above description, the case where the irradiation light is transmitted through the photomask 8 has been described. However, the same measurement can be performed for a reflection type photomask. FIG. 7 shows a configuration example in the case of measuring the amount of phase change of a reflective photomask. The configuration on the light source side with respect to the aperture stop 5 is the same as in FIG. 1, and a variable field stop may be provided between the lens 9 and the photomask 18.

In FIG. 7, a light beam emitted from an aperture stop (pinhole plate or slit plate) 5 is a half mirror 1.
Then, the light is reflected by the lens 5 and irradiates the reflective photomask 18 via the lens 9. The reflection substrate 18a is provided with a reflection portion (a reflection substrate 18a bare surface portion) A 'and a phase member addition portion B' to which a reflection type phase member 22a is added, and the light beams are A 'and B', respectively. And returns to the lens 9 through the same optical path.

The light beam transmitted through the lens 9 is transmitted through the half mirror 15 and forms a Fourier transform image FP on the light receiving surface 10a of the photoelectric converter. Also in this case, the Fourier transform image FP
The position of the minimum point changes in accordance with the phase change amount error of the phase member 22a, so that the phase change amount can be measured by detecting the spatial frequency coordinates of the minimum point.

[0076]

As described above, according to the present invention, it is possible to easily and accurately measure an accurate phase change amount (film thickness) in a region where a phase is changed without measuring a film thickness or a refractive index. .

Further, even if there is almost no difference in the refractive index difference between the substrate of the photomask and the phase member, there is no problem in measuring the amount of phase change.

Further, even if the pattern to be inspected on the photomask is displaced from the optical axis, the position of the minimum point of the Fourier transform image does not change. Very advantageous on the above.
Further, even when the irradiation light is absorbed by the phase member, the position of the minimum point of the Fourier transform image does not change, so that the amount of phase change can be obtained with high accuracy regardless of the transmittance of the phase member.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a photomask inspection apparatus according to an embodiment of the present invention.

2A is a plan view showing an example of a test pattern used in the present invention, and FIG. 2B is a cross-sectional view.

3A is a plan view showing an example of a test pattern used in the present invention, and FIG. 3B is a cross-sectional view.

FIG. 4 is a plan view illustrating an example of a photomask.

FIG. 5 is a conceptual diagram showing an intensity distribution of a Fourier transform image.

FIGS. 6 (a), (b), and (c) are conceptual diagrams for explaining how to determine the origin of spatial frequency coordinates.

FIG. 7 is a configuration diagram illustrating an example of an apparatus for measuring a phase change amount of a reflection type photomask.

FIG. 8 is a graph showing an intensity distribution of a Fourier transform image obtained by calculation.

FIG. 9 is a graph showing an intensity distribution of a Fourier transform image obtained by calculation.

FIG. 10 is a graph showing an intensity distribution of a Fourier transform image obtained by calculation.

FIG. 11 is a graph showing an intensity distribution of a Fourier transform image obtained by calculation.

FIG. 12 is a graph showing an intensity distribution of a Fourier transform image obtained by calculation.

FIG. 13 is a graph showing an intensity distribution of a Fourier transform image obtained by calculation.

FIG. 14 is a graph showing an intensity distribution of a Fourier transform image obtained by calculation.

15A is a graph showing an intensity distribution of a Fourier transform image obtained by calculation, and FIG. 15B is a plan view of a pattern to be inspected.

16A is a graph showing an intensity distribution of a Fourier transform image obtained by calculation, and FIG. 16B is a plan view of a pattern to be inspected.

FIG. 17 is a graph showing an intensity distribution of a Fourier transform image obtained by calculation.

[Description of Signs of Main Parts]

 DESCRIPTION OF SYMBOLS 1 Light source 2 Elliptical mirror 5 Aperture stop 8 Photomask 8a Transparent substrate 8b Shielding part 9 Fourier transform lens 10 Photoelectric converter 11 Variable aperture stop 12 Signal processing circuit 13 Computing means 16 Driving means 22 Phase member

Continuation of front page (56) References JP-A-2-210250 (JP, A) JP-A-63-268245 (JP, A) JP-A-59-65428 (JP, A) JP-A-58-158921 (JP) JP-A-56-133830 (JP, A) JP-A-4-177111 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03F 1/00-1/16

Claims (13)

(57) [Claims] 1. A substrate which is substantially transparent to a light beam of a predetermined wavelength and has a geometric original pattern, and at least a part of a region where the original pattern is formed has a phase of a light beam transmitted through the substrate. A photomask having a region to be changed is inspected, and an irradiation optical system that irradiates a monochromatic light or a quasi-monochromatic light to a pattern to be inspected of the photomask, A photomask inspection apparatus, comprising: a detection unit for detecting an intensity distribution. 2. A substrate that reflects a light beam of a predetermined wavelength has a geometric original pattern, and the phase of the light beam that reflects the substrate is changed in at least a part of a region where the original pattern is formed. An irradiation optical system that irradiates a photomask having a region with a monochromatic light or a quasi-monochromatic light to a pattern to be inspected of the photomask, and an intensity distribution of light generated on a Fourier transform surface of the pattern to be inspected by the irradiation. A photomask inspection apparatus, comprising: a detection unit configured to detect a photomask. 3. The photoelectric conversion device according to claim 1, wherein the detection unit detects an intensity distribution of light generated on the Fourier transform surface, and detects a phase of an area in which the phase is changed based on a detection signal output from the photoelectric converter. The photomask inspection apparatus according to claim 1, further comprising an arithmetic circuit that calculates a change amount. 4. The pattern to be inspected is arranged in a region of a bare surface portion composed of a transparent portion or a reflection portion, and in the vicinity of the region of the bare surface portion, and adjusts a phase of the light beam transmitted or reflected through the bare surface portion. 3. The photomask inspection apparatus according to claim 1, further comprising: a region to be changed, wherein the width of the bare surface region and the region of changing the phase in the arrangement direction are substantially equal. 5. The illumination optical system includes a first aperture stop for adjusting a divergence angle of a light beam emitted from a light source, and a second aperture stop for adjusting an irradiation area of the photomask. The photomask inspection apparatus according to claim 1 or 2, wherein 6. The photomask inspection apparatus according to claim 1, wherein a wavelength of the light beam applied to the photomask is substantially equal to an exposure wavelength in an exposure step using the photomask. 7. The arithmetic circuit according to claim 3, wherein a spatial frequency coordinate of a minimum point in an intensity distribution of light generated on the Fourier transform surface is detected based on a detection signal from the photoelectric detector. 3. The photomask inspection device according to 1. 8. A photomask inspection method comprising: a pattern region; and a region provided in at least a part of the pattern region and changing a phase of a beam transmitted through the pattern region. Irradiating the pattern to be inspected with light, detecting the spatial frequency coordinates of the minimum point of the Fourier transform image of the pattern to be inspected formed by the irradiation, and based on the spatial frequency coordinates of the minimum point. Obtaining a phase change amount of a region in which a phase is changed. 9. A method for inspecting a photomask comprising: a pattern region; and a region provided in at least a part of the pattern region and changing a phase of a beam reflected by the pattern region, wherein: Irradiating the pattern to be inspected with light, detecting the spatial frequency coordinates of the minimum point of the Fourier transform image of the pattern to be inspected formed by the irradiation, and based on the spatial frequency coordinates of the minimum point. Obtaining a phase change amount of a region in which the phase is changed. 10. The photomask inspection method according to claim 8, wherein the phase changing region absorbs a part of the light. 11. A method for inspecting a photomask comprising a pattern region and a region provided in at least a part of the pattern region and changing the phase of a beam transmitted through the pattern region, wherein the region for changing the phase is Irradiating a pattern to be inspected with light, and detecting an intensity distribution of light generated on the Fourier transform surface of the pattern to be inspected by the irradiation. 12. A photomask inspection method comprising: a pattern region; and a region provided in at least a part of the pattern region and for changing a phase of a beam reflecting the pattern region, wherein the region for changing the phase is Irradiating a pattern to be inspected with light, and detecting an intensity distribution of light generated on the Fourier transform surface of the pattern to be inspected by the irradiation. 13. The photomask inspection method according to claim 11, further comprising a step of obtaining a phase change amount of a region where the phase is changed based on the intensity distribution.