JP2017129500A - Phase shift measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a phase shift amount measurement device whose structure is simple and temperature stability is excellent.SOLUTION: Disclosed is a device for measuring the phase shift amount of a phase shift mask 15. This device includes: a diffraction grating 7 which generates a plurality of diffraction light on a single optical path reaching from a light source 1 to an imaging device 2 for imaging a double interference image by diffracting linearly polarized light; a Nomarski prism 11 which generates a laterally shifting double image of a pattern of the phase shift mask 15 and interferes diffracted light passing through a pattern part 18 of the phase shift mask 15 and a phase shifter part 19; and moving means 21 for performing slide-movement of the Nomarski prism 11 in the generation direction of the double image.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a phase shift amount measuring apparatus for measuring a phase shift amount of a phase shift mask, and particularly relates to a phase shift amount measuring apparatus having a simple structure and excellent temperature stability.

  A conventional phase shift amount measuring apparatus measures a phase difference of transmitted light at the same location of a transparent substrate before and after forming a phase shifter layer on the transparent substrate using a Mach-Zehnder interferometer. While the phase shifter layer is formed, a dummy transparent substrate is placed instead on the sample stage of the interferometer on which the transparent substrate is placed, and the phase fluctuation of the light transmitted through the dummy transparent substrate in between is detected. When measuring the phase of the light transmitted through the transparent substrate after the phase shifter layer is formed on the transparent substrate, the phase variation is offset by correcting the optical path length with the optical path length correcting means of one optical path of the interferometer. (For example, refer to Patent Document 1).

JP 11-327119 A

  However, in such a conventional phase shift amount measuring apparatus, the Mach-Zehnder interferometer separates the optical path into two and recombines them, and since the structure is complicated, the two optical path lengths are adjusted. There is a problem that the operation is difficult and the optical path length of the two separated optical paths is long, so that the temperature stability is lacking.

  In addition, since interference also occurs due to the optical path difference between the two optical paths including the thickness of the mask body, each time the mask is replaced, the optical path length of the two optical paths is reduced so that interference due to variations in the thickness of the mask body does not occur. Adjustment is required. Therefore, it is not practical in consideration of variations in the thickness of mass-produced masks.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a phase shift amount measuring apparatus that addresses such problems and has a simple structure and excellent temperature stability.

  In order to achieve the above object, a phase shift amount measuring device according to the present invention is a device for measuring a phase shift amount of a phase shift mask, on a single optical path from a light source to an imaging device for capturing a double interference image. In addition, a diffraction grating that diffracts linearly polarized light to generate a plurality of diffracted lights, and a laterally shifted double image of the pattern of the phase shift mask are generated, and the pattern portion and the phase shifter portion of the phase shift mask are passed. A double wedge prism that interferes with the diffracted light; and a moving unit that slides the double wedge prism in the double image generation direction.

  According to the present invention, unlike a conventional structure in which a double wedge prism is disposed on each of two separate optical paths, a simple structure in which one double wedge prism is movably disposed on a single optical path. Can realize sharing interference. Therefore, the manufacturing cost of the device can be reduced. Further, the optical path difference between the two interfering light beams is extremely small because it is determined in the double wedge prism. Therefore, the temperature stability is excellent, and the phase shift amount can be measured with high accuracy. Furthermore, measurement of the phase shift amount and measurement of the transmittance of the phase shifter layer can be performed simultaneously.

It is a front view which shows one Embodiment of the phase shift amount measuring apparatus by this invention. It is explanatory drawing which shows the phase shift mask for to-be-measured, (a) is a top view, (b) is the sectional view on the AA line of (a). It is explanatory drawing shown about the design of a diffraction grating. It is a graph which shows the luminance change of an interference image. It is explanatory drawing explaining the measurement of the phase shift amount by the phase shift amount measuring apparatus by this invention, (a) The example of a measurement of only a phase shift amount is shown, (b) shows the measurement example of a phase shift amount and the transmittance | permeability. . It is a top view explaining the pinhole board used instead of a diffraction grating.

  Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a front view showing an embodiment of a phase shift amount measuring apparatus according to the present invention. This phase shift amount measuring device is for measuring the phase shift amount of the phase shift mask, and the polarizer 3 is arranged on a single optical path from the light source 1 to the two-dimensional image pickup device 2 that takes a double interference image. The first λ / 4 plate 4, the condenser lens 5, the bandpass filter 6, the diffraction grating 7, the illumination lens 8, the sample stage 9, the objective lens 10, the Nomarski prism 11, and the second The λ / 4 plate 12, the analyzer 13, and the imaging lens 14 are provided in this order.

  The polarizer 3 extracts linearly polarized light from random light emitted from the light source 1, and is, for example, a polarizing plate that extracts polarized light in the same direction as the transmission axis. Alternatively, a polarization beam splitter may be used. Here, a case where a polarizing plate is used will be described.

  A first λ / 4 plate 4 is disposed downstream of the polarizer 3 in the light traveling direction. The first λ / 4 plate 4 is used to change the linearly polarized light into a circularly polarized state by giving a phase difference of λ / 4 to the polarization plane of incident light. It is provided to remove the birefringence of the transparent substrate 15 (referred to as “sample mask”). The first λ / 4 plate 4 and the second λ / 4 plate 12 described later are not essential components and may be omitted.

  A condenser lens 5 is disposed downstream of the first λ / 4 plate 4 in the light traveling direction. The condenser lens 5 converts the light source light emitted from the light source 1 into parallel light, and is provided with the front focal point matched with the second focal position of an elliptical reflecting mirror (not shown) that reflects the light source light forward. .

  A band pass filter 6 is disposed downstream of the condenser lens 5 in the light traveling direction. This band pass filter 6 selectively transmits light of a specific wavelength, for example, selectively transmits mixed light of g-line (436 nm), h-line (405 nm) and i-line (365 nm). However, it may be one that transmits only one light ray selected from the g-line, h-line, and i-line, and is provided with a filter that transmits each of the light beams in a switchable manner. Also good.

  A diffraction grating 7 is disposed downstream of the bandpass filter 6 in the light traveling direction. The diffraction grating 7 diffracts incident light and separates it into a multi-order diffracted light and emits it. For example, the diffraction grating 7 has a structure in which a plurality of parallel slits are arranged at equal intervals.

  An illumination lens 8 is disposed downstream of the diffraction grating 7 in the light traveling direction. The illumination lens 8 squeezes the multi-order diffracted light emitted from the diffraction grating 7 and irradiates the sample mask 15, and is provided with the front focal point matched with the position of the diffraction grating 7 on the optical axis.

  A sample stage 9 is provided downstream of the illumination lens 8 in the light traveling direction. As shown in FIG. 2, the sample stage 9 includes a sample mask 15 in which, for example, a rectangular pattern portion 18 and a phase shifter portion 19 are formed on a phase shifter layer 17 deposited on a transparent substrate 16 such as quartz. The opening 20 is formed at the center so that light can pass from the bottom to the top in FIG. The mask surface of the sample mask 15 held on the sample stage 9 (the surface on which the phase shifter layer 17 is formed) matches the rear focus of the illumination lens 8. As a result, the multi-order diffracted light emitted from the diffraction grating 7 interferes with the surface of the sample mask 15.

In this case, the shear amount (interference fringe pitch) of the light beam separated by the diffraction grating 7 on the surface of the sample mask 15 is S ₁ , the reinforcing diffraction angle is θ, the focal length of the illumination lens 8 is f, and the wavelength of the illumination light is Assuming that λ and the slit pitch of the diffraction grating 7 are P, the shear amount S ₁ is calculated as follows: S ₁ = f × sin θ (1)
It is expressed. Incidentally, shear amount S ₁ is generally, although determined in accordance with the arrangement pitch of the pattern of the sample mask 15, when the sequence of the pattern is not constant, for example, may be determined on an average value, designer desired to be set Value.

Further, the slit pitch P of the diffraction grating 7 is expressed as follows: P × sin θ = λ (2)
It is expressed.

Therefore, the slit pitch P of the diffraction grating 7 is P = f × λ / S ₁ (3) from the above equations (1) and (2).
It is represented by

Here, for example, when the shear amount S ₁ = 2 μm, f = 50 mm, and λ = 365 nm, the slit pitch P is P = 9.125 mm according to the equation (3). Further, when the shear amount S ₁ = 2 μm, f = 50 mm, and λ = 436 nm, the slit pitch P is P = 10.9 mm according to the equation (3). Thus, even if the slit pitch P of the diffraction grating 7 is formed with a relatively coarse pitch of about 10 mm, interference fringes with high contrast can be generated on the surface of the sample mask 15 at a pitch of about 2 μm.

  An objective lens 10 is disposed facing the sample mask 15 downstream of the sample stage 9 in the light traveling direction. The objective lens 10 collects the light beam that has passed through the sample mask 15 at the pupil position, and cooperates with the imaging lens 14 described later to expand the pattern image of the sample mask 15 onto the imaging surface of the imaging device 2. To form an image.

  A Nomarski prism 11 is disposed downstream of the objective lens 10 in the light traveling direction. The Nomarski prism 11 generates a laterally shifted double image of the pattern of the sample mask 15 and causes the diffracted light (circularly polarized light) transmitted through the pattern portion 18 and the phase shifter portion 19 of the sample mask 15 to interfere with each other. This is a double wedge prism in which two birefringent crystals are bonded to each other with their crystal axes shifted from each other, and the prism focal point position is made to coincide with the pupil position of the objective lens 10.

  Specifically, the Nomarski prism 11 integrates the circularly polarized light transmitted through the pattern portion 18 of the sample mask 15 and the circularly polarized light transmitted through the phase shifter portion 19. In this case, there is a phase difference between the circularly polarized light transmitted through the pattern unit 18 and the circularly polarized light transmitted through the phase shifter unit 19 depending on the thickness of the phase shifter layer 17 of the phase shifter unit 19 and the refractive index. Occurs. Therefore, the integrated polarized light produces an interference image having a contrast of light and dark based on the phase difference.

In this case, it is preferable that the Nomarski prism 11 is displaced laterally with respect to the optical axis and tilted in the double image generation direction so that a uniform interference image is formed over the entire light exit end face. Note that the lateral shift amount (shear amount S ₂ ) of the double image generated by the Nomarski prism 11 is obtained based on the separation angle of the two polarized lights by the Nomarski prism 11 and the focal length of the objective lens. Therefore, the Nomarski prism 11, the separation angle is produced to a desired shear amount angle S ₂ is obtained.

  More specifically, the Nomarski prism 11 is moved in parallel with the light incident end face or the light exit end face of the Nomarski prism 11 in the double image generation direction by a moving means 21 including, for example, a motor and a ball screw. It is possible. Therefore, when the Nomarski prism 11 is moved by the moving means 21 as described above, the optical path length in the Nomarski prism 11 changes, and a sinusoidal phase modulation occurs in the interference image appearing on the light exit end face. In this case, the phase modulation amount can be obtained from position information of the moved Nomarski prism 11. Alternatively, if the Nomarski prism 11 is moved at a constant speed, it can be obtained from the moving time. Further, the luminance value of the phase modulation can be obtained from the luminance information of the pixel corresponding to the interference image formed on the imaging device 2.

  A second λ / 4 plate 12 is provided downstream of the Nomarski prism 11 in the light traveling direction. The second λ / 4 plate 12 is for returning circularly polarized light to linearly polarized light, and has the same function as the first λ / 4 plate 4.

  An analyzer 13 is provided downstream of the second λ / 4 plate 12 in the light traveling direction. The analyzer 13 is for extracting linearly polarized light having a specific polarization, and is a polarizing plate or a polarizing beam splitter. Here, a case where a polarizing plate is used will be described. In this case, the polarizing plate is arranged so that the transmission axis is orthogonal to the transmission axis of the polarizing plate of the polarizer 3. Thereby, the linearly polarized light transmitted through the polarizing plate of the analyzer 13 has a vibration direction orthogonal to the vibration direction of the linearly polarized light transmitted through the polarizer 3.

  An imaging lens 14 is provided downstream of the analyzer 13 in the light traveling direction. The imaging lens 14 is a condenser lens that cooperates with the objective lens 10 to enlarge and form a pattern image of the sample mask 15 on the imaging surface of the imaging device 2. In this case, the pattern image of the sample mask 15 is separated into two when the image light passes through the Nomarski prism 11 and is shifted laterally. Therefore, the pattern image formed on the imaging surface of the imaging device 2 is horizontal. It becomes a double image shifted to. In addition, since the light beam used for measurement is ultraviolet light such as g-line, h-line, or i-line, an ultraviolet camera is used as the imaging device 2.

Next, the operation of the phase shift amount measuring apparatus configured as described above will be described.
Here, for example, as the sample mask 15, a rectangular pattern portion 18 and a phase shifter outside thereof are formed on a phase shifter layer 17 such as a semitransparent film deposited on a transparent substrate 16 such as quartz as shown in FIG. The case where the phase shift mask formed with the portion 19 is used will be described.

  Random light ultraviolet rays emitted from the light source 1 enter the polarizer 3. Then, the linearly polarized light that is polarized in a specific direction is extracted from the polarizer 3. This linearly polarized light is converted into circularly polarized light by the downstream first λ / 4 plate 4.

  The circularly polarized light is converted into parallel light by the condenser lens 5 further downstream, and then a light beam having a wavelength selected by the bandpass filter 6 enters the diffraction grating 7.

The circularly polarized light incident on the diffraction grating 7 is separated into multi-order diffracted light by a plurality of slits, exits the diffraction grating 7, and then is narrowed down by the illumination lens 8 to illuminate the sample mask 15 from the back surface. The multi-order diffracted light (circularly polarized light) interferes with the surface of the sample mask 15 (the surface on which the phase shifter layer 17 is formed). A part of the interference light passes through the pattern portion 18 of the sample mask 15, and the other interference light passes through the phase shifter portion 19. As described with reference to FIG. 3, the pitch of the interference fringes (shear amount S ₁ ) is the slit pitch P of the diffraction grating 7, the focal length f of the illumination lens 8, the wavelength λ of the light beam of the illumination light, and the above formula (3 ).

  The multi-order diffracted lights transmitted through the pattern portion 18 and the phase shifter portion 19 of the sample mask 15 are condensed at the pupil position of the objective lens 10 and then dispersed again and enter the Nomarski prism 11. The Nomarski prism 11 has an action of integrating two polarized lights having vibration planes orthogonal to each other into one polarized light. Therefore, each of the two multi-order diffracted lights (the multi-order diffracted lights transmitted through the pattern unit 18 and the phase shifter unit 19) dispersed and incident on the Nomarski prism 11 is again converted into one polarized light (circularly polarized light) by the Nomarski prism 11. The integrated Nomarski prism 11 is emitted. As described above, the multi-order diffracted light transmitted through the pattern unit 18 and the phase shifter unit 19 is integrated into one polarized light by the Nomarski prism 11, thereby generating a plurality of interference fringes on the light exit end face of the Nomarski prism 11. become.

  The circularly polarized light of the plurality of multi-order diffracted lights integrated by the Nomarski prism 11 is returned to linearly polarized light by the second λ / 4 plate 12 and then enters the analyzer 13. The analyzer 13 is arranged so that the transmission axis is orthogonal to the transmission axis of the polarizer 3. Therefore, of the linearly polarized light, polarized linearly polarized light that vibrates in the same direction as the transmission axis of the analyzer 13 is transmitted through the analyzer 13 and collected on the imaging surface of the imaging device 2 by the imaging lens 14 at the subsequent stage. Lighted.

  Thereby, on the imaging surface of the imaging device 2, the pattern image of the sample mask 15 is separated into two images (interference images) shifted laterally (for example, shifted in the X direction in FIG. 2) by the action of the Nomarski prism 11. Enlarged image is formed with In each image, the phase difference between the two images appears as a luminance change.

Here, when the moving means 21 is driven and the Nomarski prism 11 is slid in the double image generation direction to cause phase modulation in the interference image of the double image, the two interference images are shown in FIG. Such a luminance change appears. In the figure, L ₀ indicates a luminance change at a position corresponding to the transparent substrate, L ₁ indicates a luminance change at one interference image position of two interference images, and L ₂ indicates the other interference image of the two interference images. The change in luminance at the position is shown, and each is normalized and represented by the value of the midpoint of the amplitude. In the figure, Φ ₁ indicates the phase difference of the luminance change L ₁ , and Φ ₂ indicates the phase difference of the luminance change L ₂ . Therefore, the phase shift amount δ of the sample mask 15 can be obtained by calculating δ = (Φ ₂ −Φ ₁ ) / 2 by calculating the phase difference (Φ ₂ −Φ ₁ ) of both interference images. . This calculation can be performed in the imaging device 2 or a signal processing device provided separately. In FIG. 4, the amplitude of each luminance change graph is proportional to the transmittance.

Hereinafter, the measurement method of the phase shift amount of the sample mask 15 and the measurement method of the transmittance of the phase shifter layer 17 will be described in detail.
For example, the width of shear amount S ₂ of the sample mask 15 having a rectangular pattern portions 18 of W is observing it through Nomarski prism 11 W, the image pickup apparatus 2, as shown in FIG. 5 (a) As a result of the operation of the Nomarski prism 11, a double image appears laterally shifted. In this case, the interference image of the pattern image 22A shown by the solid line in the figure corresponds to the interference images showing luminance change L ₂ in FIG. 4, the interference image of the pattern image 22B indicated by a broken line, the interference indicating a luminance change in L ₁ Corresponds to the image. Therefore, when the luminance information of the pixel at the position corresponding to each interference image of the imaging device 2 is acquired while moving the Nomarski prism 11 in the double image generation direction, the sine waveforms of the luminance changes L ₁ and L ₂ in FIG. Is obtained.

Therefore, the phase shift amount δ of the sample mask 15 is calculated by calculating the phase difference (Φ ₂ −Φ ₁ ) between the peaks of the sinusoidal waveforms of the luminance changes L ₁ and L ₂ , thereby obtaining δ = (Φ ₂ −Φ ₁ ). / 2 can be calculated. In this case, the luminance change L _{0 at the} position corresponding to the transparent substrate shown in FIG. 4 cannot be obtained. Therefore, the transmittance of the phase shifter layer 17 with respect to the transparent substrate cannot be measured.

In order to measure both the phase shift amount of the sample mask 15 and the transmittance of the phase shifter layer 17, as the Nomarski prism 11, the shear amount S ₂ is S ₂ <W (for example, S _{2) with} respect to the width W of the pattern portion 18. = W / 2) is preferably used. When the sample mask 15 is observed through such a Nomarski prism 11, a double image having a lateral shift amount of W / 2, for example, as shown in FIG. In this case, the left half of the interference image of the pattern image 22A shown by the solid line in FIG. 5 (b) corresponds to the interference images showing luminance change L ₂ in FIG. 4, the pattern image 22A shown by the solid line in FIG. 5 (b) the right half of the interference image (or left half of the interference image of the pattern image 22B indicated by a broken line) corresponds to the interference images showing changes in luminance L ₀ in FIG. 4, the pattern image 22B indicated by a broken line in FIG. 5 (b) right half of the interference image corresponds to the interference images showing luminance change L ₁ in FIG. 4. Therefore, when the luminance information of the pixel at the position corresponding to each interference image of the imaging device 2 is acquired while moving the Nomarski prism 11 in the double image generation direction, the luminance changes L ₀ , L ₁ , L ₂ in FIG. The sine waveform is obtained.

Therefore, the phase shift amount δ of the sample mask 15 is calculated by calculating the phase difference (Φ ₂ −Φ ₁ ) between the peaks of the sinusoidal waveforms of the luminance changes L ₁ and L ₂ , thereby obtaining δ = (Φ ₂ −Φ ₁ ). / 2 can be calculated. Further, as described above, since the amplitude of each luminance change is proportional to the transmittance, for example, the transmittance of the phase shifter layer 17 with respect to the transmittance of the transparent substrate can be obtained by comparing the amplitude of each luminance change. . For example, when the amplitude of the luminance change L ₀ is A ₀ and the amplitudes of the luminance changes L ₁ and L ₂ are A ₁ , the relative transmittance T can be obtained by calculating T = A ₁ / A ₀ .

  In the above embodiment, the case of measuring the phase shift amount in the X direction in FIG. 2 of the sample mask 15 has been described, but the present invention is not limited to this. For example, in order to enable measurement of the phase shift amounts in both the X and Y directions in FIG. 2, it is preferable to include a rotating means that integrally rotates the diffraction grating 7 and the Nomarski prism 11 about 90 degrees around the optical axis. Alternatively, the Nomarski prism 11 may be arranged at a position shifted by 90 degrees about the optical axis, and the diffraction grating 7 may be rotated by 90 degrees. Alternatively, instead of the diffraction grating 7, a pinhole plate 24 having a plurality of pinholes 23 as shown in FIG. 6 in a matrix may be used. Furthermore, in the above embodiment, the sample stage 9 may be configured to be rotatable by 90 degrees.

DESCRIPTION OF SYMBOLS 1 ... Light source 2 ... Imaging device 4 ... 1st (lambda) / 4 board 6 ... Band pass filter 7 ... Diffraction grating 11 ... Nomarski prism (double wedge prism)
12: Second λ / 4 plate 15: Sample mask (phase shift mask)
21 ... Moving means

Claims (5)

An apparatus for measuring a phase shift amount of a phase shift mask,
On a single optical path from the light source to the imaging device that captures the double interference image,
A diffraction grating that diffracts linearly polarized light to generate a plurality of diffracted lights;
A double wedge prism that generates a laterally shifted double image of the pattern of the phase shift mask and interferes the diffracted light that has passed through the pattern portion and the phase shifter portion of the phase shift mask;
Moving means for slidingly moving the double wedge prism in the double image generation direction;
A phase shift amount measuring apparatus comprising:   2. The phase shift amount measuring apparatus according to claim 1, wherein a λ / 4 plate is disposed on the upstream side of the diffraction grating in the light traveling direction and on the downstream side of the double wedge prism in the light traveling direction.   3. The phase shift according to claim 1, wherein a band-pass filter that transmits at least one of g-line, h-line, and i-line is disposed upstream of the diffraction grating in the light traveling direction. Quantity measuring device.   The phase shift amount measuring apparatus according to any one of claims 1 to 3, further comprising a rotating unit that integrally rotates the diffraction grating and the double wedge prism about an optical axis.   The phase shift amount measuring apparatus according to claim 1, wherein the double wedge prism is a Nomarski prism.