JP2018189529A - Permeability measurement method and permeability measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a transmittance measurement method capable of stably measuring a transmittance of an opaque resin film having three-degrees of an overdose.SOLUTION: A transmittance measurement method forms a horizontally shifted interference image on an imaging device by irradiating illumination beams to a monitor pattern. An interference image (21) formed by transmitted beams having transmitted a transparent substrate only and the interference images (22a, 22b) between the transmitted light having transmitted both the transparent substrate and the shielding film are formed by adjusting a horizontally shifted amount of the shearing interferometer. Subsequently, phase modulation for one cycle is performed, and amplitude of the phase modulation of each interference image is measured. In the present invention, the transmittance of the shielding layer can be calculated by calculating the square of a ratio of the amplitude of the phase modulation data of the interference images between the transmitted light transmitting the transparent substrate only and the transmitting light transmitting both of the transparent substrate and the shielding layer. As a result, the transmittance can be stably measured without being affected by disturbance even in the case of the shielding layer having an extremely low transmittance.SELECTED DRAWING: Figure 1

Description

The present invention relates to a transmittance measuring method and a transmittance measuring apparatus for measuring the transmittance of a light shielding film formed on a mask blank or various photomasks.
In particular, the present invention is effective for measuring the transmittance of a light-shielding film having an extremely low transmittance with an OD (Optical Density) of about 2 to 4 (transmittance is around 0.01% to 1%).

  Since the transmittance of the light-shielding film formed on the photomask affects various processes such as an etching process, it is required to be strictly controlled. As a latest photomask, a binary type photomask (Molysil binary OMOG: Opaque MoSi On Glass) using a material film of molybdenum silicon as a main component and a transmittance of about 0.1% as a light shielding film has been put into practical use. . This Morishiri binary mask has excellent resolution, dimensional accuracy, etching performance, cleaning resistance, and the like, and has characteristics effective for various processes. Therefore, if the transmittance measurement of the light shielding film of the Morisiri binary mask can be managed with high accuracy, it is extremely beneficial in the semiconductor device manufacturing process. On the other hand, the problem with this light-shielding film is that the transmittance is about 0.1%, the transmittance is very low, and it is difficult to measure and manage the transmittance. Incidentally, the transmittance of the light shielding film used in the halftone phase shift mask is about 6%, and the transmittance can be measured relatively easily. Therefore, if a measurement method capable of measuring the transmittance of the light shielding film of the Morishiri binary mask with high accuracy is developed, the yield in the device manufacturing process can be further improved. In this specification, a binary type photomask using molybdenum silicon as a main component and a material film having a transmittance of about 0.01% to 0.1% as a light-shielding film is referred to as a “morishiri binary mask”. The light-shielding film used for the mask is referred to as a “morisiri binary light-shielding film”.

Conventionally, a measuring method using a shearing interferometer is known as a method for measuring the transmittance of a light-shielding film of a photomask (see, for example, Patent Document 1). In this measurement method, the phase shift amount and the transmittance are measured using a measurement apparatus that measures the phase shift amount of the phase shift mask as it is. In this conventional transmittance measuring method, a monitor pattern of a light transmitting portion without a light shielding film is formed on a phase shift mask to be inspected, and a light beam emitted from a light source device is projected toward the monitor pattern. The transmitted beam emitted from the phase shift mask enters the Mach-Zehnder interferometer and is converted into two beams that are laterally shifted from each other by a predetermined shearing amount. Two beams in which the transmitted light that has passed through the light transmission part is superimposed by two beams, the transmitted light that has been formed on both sides of the light and transmitted through the light shielding film, and the transmitted light that has passed through the light transmission part are superimposed. The interference image and two interference images formed by superimposing the transmitted lights that are formed on both sides of the interference image and transmitted through the light shielding film are formed. The laterally shifted interference image formed by the two beams is picked up by a CCD camera. Then, phase modulation for one period is performed on the laterally shifted interference image, and the amplitude of the interference image formed by the transmitted light that has passed through the light transmission part and the interference image formed by the transmitted light that has transmitted through the light shielding film The ratio with the amplitude is obtained, and the obtained ratio is output as the transmittance.
JP 2005-83974 A

  In the conventional transmittance measuring method described above, the amplitude of the interference image by the transmitted light that has passed through the light shielding film is used, so the amount of transmitted light incident on the CCD camera is extremely small, and fluctuations in dark noise, external light, etc. There was a problem that was easily affected by the disturbance. In particular, due to the small amount of light incident on the imaging device, measurement errors between measurement devices are likely to occur, and there is a difficulty in measurement accuracy. For this reason, there has been a problem in the quality control of the Morishiri binary mask useful for various processes.

An object of the present invention is to solve the problems described above, the light-shielding film transmittance of about 0.01% to 1%, particularly stable transmittance can be measured the measuring method 及 beauty transmittance transmittance Mori silicon binary shielding film The realization of the measuring device.

The transmittance measuring method according to the present invention is a transmittance measuring method for measuring the transmittance of a light shielding film of a mask blank or a photomask in which a light shielding film is formed on a transparent substrate using a shearing interferometer,
A step of partially removing the light shielding film from the mask blank or the photomask and forming a monitor pattern in a form in which the surface of the transparent substrate is exposed;
Projecting the illumination beam toward the monitor pattern from the side of the transparent substrate where the light-shielding film is not formed;
Condensing transmitted light emitted from the mask blank or photomask through an objective lens, and sending the collected transmitted light to a shearing interferometer;
Splitting the transmitted light incident on the shearing interferometer into a first transmitted beam propagating through the shearing optical path and a second transmitted beam propagating through the phase modulation optical path;
Adjusting the shearing amount of the shearing interferometer to form a combined beam in which the first transmitted beam propagating in the shearing optical path and the second transmitted beam propagating in the phase modulation optical path partially overlap;
Making the combined beam incident on an imaging device to form an interference image by laterally shifting;
Performing phase modulation for one period on the laterally shifted interference image to obtain phase modulation data indicating a relationship between a phase modulation amount and a luminance value,
The laterally shifted interference image is located on one side of the first interference image and the first interference image formed by the interference of transmitted light transmitted only through the transparent substrate of the mask blank or photomask, and is transparent The second interference image formed by the interference between the transmitted light transmitted only through the substrate and the transmitted light transmitted through both the transparent substrate and the light shielding film, and the other side of the first interference image, only the transparent substrate A third interference image formed by interference between the transmitted light transmitted through the transparent substrate and the transmitted light transmitted through both the transparent substrate and the light shielding film,
The transmittance measurement method further calculates a square of a ratio between the amplitude of the phase modulation data of the first interference image and the amplitude of the phase modulation data of the second interference image and / or the third interference image. Including the step of:

In the present invention, the interference image is formed by the interference between the transmitted light transmitted only through the transparent substrate and the interference between the transmitted light transmitted only through the transparent substrate and the transmitted light transmitted through both the transparent substrate and the light shielding film. The second interference image is used, and the interference image formed by the interference between the transmitted lights that have passed through the light shielding film is not used. Therefore, the amount of light incident on the imaging device is further increased and is affected by disturbance. A difficult transmittance measurement method is realized.
Furthermore, in the transmittance measuring method according to the present invention, the amount of lateral shift in the shearing interferometer is small, so the area occupied by the monitor pattern can be reduced. Further, since the monitor pattern is formed only by removing the light shielding film in a small area, an advantage that it can be formed by a simple lift-off process is achieved.

  The transmittance measuring method according to the present invention is characterized in that the light-shielding film is a morishiri binary light-shielding film having a transmittance of about 0.01% to 0.1%. Since the transmittance measuring method according to the present invention does not use the interference image between the transmitted lights that have passed through the light shielding film, the transmittance of the morishiri binary light shielding film having a transmittance of about 0.1% is stabilized with high accuracy. Can be measured. As a result, it is possible to contribute to quality control of the photomask that is advantageous for various processes such as etching.

The transmittance measuring method according to the present invention shears the transmittance of a mask blank light shielding film in which a transparent binary light shielding film having a transmittance of 0.01% to 0.1% is uniformly formed on a transparent substrate. A transmittance measuring method for measuring using an interferometer,
A step of partially removing the light shielding film from the mask blanks to form a monitor pattern in which the surface of the transparent substrate is exposed;
Projecting an illumination beam toward the monitor pattern from the side of the transparent substrate where the light-shielding film is not formed;
Condensing the transmitted light emitted from the mask blank through the objective lens, and sending the collected transmitted light to the shearing interferometer;
Splitting the transmitted light incident on the shearing interferometer into first and second transmitted beams;
Adjusting the shearing amount of the shearing interferometer to form a combined beam in which the first transmitted beam propagating in the shearing optical path and the second transmitted beam propagating in the phase modulation optical path partially overlap;
Making the combined beam incident on an imaging device to form an interference image by laterally shifting;
Performing phase modulation for one period on the laterally shifted interference image to obtain phase modulation data indicating a relationship between a phase modulation amount and a luminance value,
The laterally shifted interference image includes a first interference image formed by interference between transmitted lights transmitted through only the transparent substrate, and transmitted light positioned on one side of the first interference image and transmitted only through the transparent substrate. And the second interference image formed by interference between the transmitted light transmitted through both the transparent substrate and the light shielding film, and the transmitted light transmitted through only the transparent substrate and transparent, located on the other side of the first interference image A third interference image formed by interference with transmitted light transmitted through both the substrate and the light shielding film,
And a step of calculating a square of a ratio between the amplitude of the phase modulation data of the first interference image and the amplitude of the phase modulation data of the second interference image and / or the third interference image. And

  In the present invention, since the transmittance of the Morishiri binary light-shielding film can be measured with high accuracy, a transmittance measuring method useful for quality control of mask blanks used in the manufacture of the Morishiri binary mask is realized.

  The preferred embodiment of the transmittance measuring method according to the present invention includes the amplitude of the phase modulation data of the first interference image, and the phase modulation data of the second interference image and the third interference image adjacent to the first interference image. Each of the squares of the ratio to the amplitude is calculated, and an average value of the two calculated square values is output as the transmittance of the light shielding film. In the transmittance measuring method according to the present invention, an interference image due to interference between transmitted lights transmitted through only a transparent substrate, transmitted light transmitted only through the transparent substrate on both sides thereof, and transmitted light transmitted through both the transparent substrate and the light shielding film, Thus, two transmittance measurement data can be calculated using two different interference images by performing only one phase modulation operation. Therefore, by obtaining the average of the two transmittance measurement data obtained at the same time, the influence of fluctuation and flare of the optical system is reduced, and more stable measurement can be performed. As a result, it is possible to stably perform measurement with little measurement error even if the transmittance is 0.01% to 0.1% and a very small value of the Morisiri binary light-shielding film.

A transmittance measuring device according to the present invention is a transmittance measuring device for measuring the transmittance of a light shielding film of a mask blank or a photomask in which a light shielding film is formed on a transparent substrate,
A stage for supporting a mask blank or a photomask having a monitor pattern in which the light shielding film is partially removed and the transparent substrate is exposed;
An illumination system that projects an illumination beam toward the monitor pattern from the side where the light shielding film of the transparent substrate is not formed,
An objective lens for condensing transmitted light emitted from the mask blank or photomask;
A shearing interferometer that receives transmitted light collected by an objective lens, a beam splitting element that divides incident transmitted light into first and second transmitted beams, a shearing optical path that shears the first transmitted beam, A phase modulation optical path that performs phase modulation on the second transmitted beam, and a shearing interferometer including a beam combining element that combines the shearing optical path and the transmitted beam that has propagated through the phase modulated optical path;
An imaging device that receives the combined beam emitted from the shearing interferometer;
A signal processing device that processes the output signal from the imaging device and outputs the transmittance of the light shielding film,
On the imaging device, the first interference image formed by the interference of transmitted light that has transmitted only through the transparent substrate of the mask blank or the photomask, and the first interference image are located on one side of the transparent image and are transparent. The second interference image formed by the interference between the transmitted light transmitted only through the substrate and the transmitted light transmitted through both the transparent substrate and the light shielding film, and the other side of the first interference image, only the transparent substrate A laterally shifted interference image including a third interference image formed by the interference between the transmitted light transmitted through and the transmitted light transmitted through both the transparent substrate and the light shielding film,
The signal processing device includes means for calculating a square of a ratio between the amplitude of the phase modulation data of the first interference image and the amplitude of the phase modulation data of the second interference image and / or the third interference image. It is characterized by having.

In the transmittance measuring method according to the present invention, without using an interference image due to interference between transmitted lights transmitted through both the transparent substrate and the light shielding film, the transmitted light transmitted only through the transparent substrate and both the transparent substrate and the light shielding film are transmitted. Since the amplitude of the interference image formed by the interference with the transmitted light is used, the amount of the transmitted light incident on the imaging device is increased, and the transmittance measurement that is not easily affected by the disturbance can be performed. As a result, it is possible to stably and accurately measure the transmittance of the low-transmittance Morishiri binary light-shielding film having a transmittance of about 0.01% to 0.1% used for the Morishimorishiri binary mask. Become.
Further, since the monitor pattern can be formed on the light shielding film in a small area by a simple lift-off process, the monitor pattern can be easily formed and the area occupied by the monitor pattern can be further reduced.
Moreover, since the interference image used for phase shift amount measurement and the interference image used for transmittance measurement are common, both phase shift amount and transmittance can be performed in parallel by one measurement operation. .

It is a diagram which shows an example of the transmittance | permeability measuring apparatus by this invention. It is the top view and sectional drawing which show an example of the monitor pattern by this invention. It is a figure which shows the interference image formed on an imaging device. It is a graph which shows the phase modulation data which show the relationship between the phase modulation amount acquired by the phase modulation for 1 period, and a luminance change. It is a figure which shows typically the relationship between the wave front of the 1st transmitted light which propagated the shearing optical path 6a, and the wave front of the 2nd transmitted light which propagated the phase modulation optical path 6b. It is a figure which shows the luminance change of the 2nd and 3rd interference image by a fringe scan.

  FIG. 1 is a diagram showing an example of a transmittance measuring apparatus according to the present invention. In this example, the transmittance of a light-shielding film of a mask blank used for manufacturing a photomask of morigiri binary (OMOG: Opaque MoSi On Glass) is measured. Of course, the present invention can be used not only for mask blanks but also for measuring the transmittance of light shielding films of various photomasks such as binary masks and phase shift masks. OMOG mask blanks are formed by uniformly forming a morishiri binary shading film having an OD of about 3 to 4 (transmittance: about 0.1% to 0.01%) on a transparent substrate such as quartz glass. ing. In this example, an ArF laser actually used in the exposure apparatus is used as the illumination light source 1. As an illumination light source, a deuterium lamp that generates ultraviolet light having a wavelength of 193.4 nm or a KrF laser that emits ultraviolet light having a wavelength of 248 nm may be used. When measuring the light shielding film of the mask blank for KrF, the transmittance of the light shielding film of the mask blank for KrF can be obtained by converting the wavelength of the data measured using the ArF laser.

  The illumination beam emitted from the illumination light source 1 is condensed by the condenser lens 2 and projected toward the mask blank 3 arranged on the XY stage. The mask blank 3 has a transparent substrate 3a and a light shielding film 3b formed thereon, and projects an illumination beam from the side of the transparent substrate where the light shielding film is not formed. In addition, a monitor pattern is formed on the mask blank, and the monitor pattern is formed by removing a part of the light shielding film by lift-off processing and partially exposing the surface of the transparent substrate. Accordingly, the illumination beam illuminates the monitor pattern, which is an area where the light shielding film is not present, and the surrounding area where the light shielding film is present.

The illumination light incident on the monitor pattern of the mask blank 3 is transmitted through only the transparent substrate 3a and emitted, and the illumination beam incident on the surrounding area is transmitted through both the transparent substrate 3a and the light shielding film 3b. The transmitted light emitted from the mask blank 3 is collected by the objective lens 4 and enters the shearing interferometer (two-beam interferometer) 6 through the relay lens 5. In this example, a Mach-Zender interferometer is used as the shearing interferometer. The Mach-Zehnder interferometer 6 has two optical paths: a shearing optical path 6a that performs lateral shift and a phase modulation optical path 6b that performs phase modulation. As the shearing interferometer, various shearing interference optical systems such as a Nomarski prism can be used.

  The transmitted beam incident on the Mach-Zehnder interferometer 6 is split by the half mirror 7 into first and second transmitted beams. The first transmitted beam (first transmitted light) propagates through the shearing optical path 6 a and enters the first double wedge prism 8. The first double wedge prism 8 functions to introduce a predetermined lateral shift amount between the first transmitted beam and the second transmitted beam. In this example, the first transmitted beam is sheared by 10 μm. . The first transmitted beam emitted from the first double wedge prism enters the half mirror 10 through the total reflection mirror 9.

  The second transmitted beam (second transmitted light) propagating through the phase modulation optical path 6 b enters the half mirror 10 through the total reflection mirror 11 and the second double wedge prism 12. The second double wedge prism 12 has a function of performing phase modulation (fringe scan). One wedge prism 12a is connected to a linear motor 13 and moves in a direction perpendicular to the optical axis to form a second transmitted beam. On the other hand, a continuous phase difference (phase modulation amount) for one period is given.

  The first and second transmitted beams shifted laterally from each other by a predetermined shearing amount are combined by the half mirror 10 to form a combined beam. The combined beam is imaged on the imaging device 15 via the imaging lens 14 and forms an interference image on the imaging device. The imaging device 15 has a plurality of light receiving elements arranged in a two-dimensional array. Incident light incident on each light receiving element is converted into an electric signal, and the electric signal of each light receiving element is sequentially read out, and the amplifier 16 Then, the signal is supplied to the signal processing circuit 17. The signal processing circuit 17 has a fast Fourier transform unit, and the transmittance of the light shielding film 3b is calculated by the fast Fourier transform unit. As will be described later, when the phase shift mask is measured, the phase shift amount can be calculated in parallel with the transmittance measurement.

  FIG. 2 is a diagram illustrating an example of a monitor pattern. 2A is a plan view, and FIG. 2B is a cross-sectional view taken along the line II. A light shielding film 3b is formed on the transparent substrate 3a of the mask blank, and the monitor pattern 3c is formed by partially removing the light shielding film and exposing the surface of the transparent substrate. The monitor pattern 3c is a square pattern of 20 μm × 20 μm. Since the monitor pattern of the present invention is formed only by partially removing the light shielding film as a square pattern of 20 μm × 20 μm, it can be formed by a simple lift-off process.

  FIG. 3 is a diagram for explaining a combined interference image formed on the imaging apparatus by a combined beam, that is, a laterally shifted interference image. FIG. 3A schematically shows an image formed on the imaging device by the second transmitted beam propagating through the phase-modulated optical path, and FIG. 3B shows the first shifted laterally through the shearing optical path. FIG. 3C schematically shows an interference image formed by a combined beam obtained by combining the first transmitted beam and the second transmitted beam. In this example, the monitor pattern has a rectangular shape of 20 μm × 20 μm, and the shearing amount is 10 μm on the imaging device.

  Since the monitor pattern is constituted by a rectangular area without the light shielding film in the area of the light shielding film, as shown in FIGS. 3A and 3B, both the transparent substrate and the light shielding film are used as the monitor pattern image. Square bright images 20a and 20b formed by a transmitted beam transmitted through only the transparent substrate are formed in a low-luminance background area formed by the transmitted light transmitted. On the other hand, since a shearing amount of 10 μm is introduced between the first transmitted beam and the second transmitted beam, the images 20a and 20b of the two monitor patterns are relatively displaced by 10 μm. Therefore, as shown in FIG. 3C, as a composite image, in the center of the imaging device, a first interference image 21 formed by interference between transmitted lights transmitted through only a transparent substrate having a width of 10 μm, and its Second and third interference images 22a and 22b each having a width of 10 μm formed by interference between transmitted light formed on both sides and transmitted through both the transparent substrate and the light shielding film and transmitted light transmitted through only the transparent substrate; A background image 23 is formed that is formed around the interference images and is formed by transmitted light that has passed through both the transparent substrate and the light shielding film.

  When performing transmittance measurement and phase difference measurement, the first interference image and the second and third interference images are used. Therefore, the operator specifies three measurement pixel areas while observing the laterally shifted interference image displayed on the monitor. Then, measurement is performed using luminance data output from the specified pixel area.

Next, a method for measuring the transmittance of the light shielding film will be described. The luminance I of the interference light in the two-beam interference method is defined by the following basic formula.
I = A ₁ ² + A ₂ ² + 2√A ₁ × √A ₂ × cosφ
Here, the transmitted light transmitted through the monitor pattern, that is, the luminance value of the first interference image 21 formed by the interference between the transmitted beams transmitted only through the transparent substrate is I1, and the transmitted beam transmitted only through the transparent substrate The luminance values of the second and third interference images 22a and 22b formed by interference with the transmitted beam transmitted through both the transparent substrate and the light shielding film are I2, and the transmitted beams transmitted through both the transparent substrate and the light shielding film are The luminance value of the interference image 23 is I3. Further, the luminance of the transmitted through only the transparent substrate transmitting light is A _QZ, the luminance of the transmitted light both transmitted through the transparent substrate and the light-shielding film and A _S. The luminance of the three interference images is expressed by the following formula.
I1 = A _QZ ² + A _QZ ² + 2√A _QZ × √A _QZ × cos φ
I 2 = A _QZ ² + A _S ² + 2√A _QZ × √A _S × cos φ
I 3 = A _S ² + A _S ² + 2√A _S × √A _S × cos φ

When phase modulation for one period is performed, the factors related to the transmittances of the luminance values I1 to I3 are defined by the terms indicating the amplitudes of the above equations. When the amplitudes of the luminance values I1 to I3 are displayed as Amp1 to Amp3,
Amp1 = 2√A _QZ × √A _QZ
Amp2 = 2√A _QZ × √A _S
Amp3 = 2√A _S × √A _S

Here, the relative transmittance T of the light shielding film based on the transmittance of the transparent substrate (quartz glass region) is defined by the following equation.
T = Amp3 / Amp1
= A _S / A _QZ
The transmittance defined by the above equation is a conventional transmittance measurement.

Further expansion of the above equation can be expressed as follows.
T = A _S / A _QZ
= (√A _S / √A _QZ ) ²
= (Amp2 / Amp1) ²
As indicated by the above equation, the relative transmittance of the light shielding film based on the transmittance of the quartz glass is obtained by the ratio between the luminance amplitude of the first interference image 21 and the luminance amplitude of the interference images 22a or 22b on both sides. be able to. Therefore, the transmittance of the light-shielding film with reference to the transmittance of quartz glass is obtained by phase-modulating the laterally shifted interference image shown in FIG. It can be obtained by obtaining the amplitude of the third interference image 22a or 22b and obtaining the square of the ratio of the obtained amplitude.

FIG. 4 shows the first interference image 21 and the second or third interference when the second wedge prism 12a is moved in the direction orthogonal to the optical axis direction and fringe scanning is performed and phase modulation is performed for one period. It is a graph which shows the phase change data which show the luminance change of the image 22a or 22b, ie, the relationship between a phase modulation amount and a luminance change. The wedge prism 12a is continuously moved in the direction of the optical axis, and a phase difference corresponding to one cycle that continuously changes is introduced into the transmitted beam propagating through the phase modulation optical path. By performing phase modulation for one period, the interference fringe waveforms of the first to third interference images are obtained. Therefore, in the signal processing device, the transmittance of the light shielding film is obtained by dividing the amplitude Amp2 by the amplitude Amp1, and further squaring the divided value. As described above, according to the present invention, the transmittance of the light shielding film can be measured by performing only one phase modulation operation. Furthermore, in the present invention, the interference image between the transmission beams transmitted through both the transparent substrate and the light shielding film is not used, and the interference between the transmission beam transmitted only through the transparent substrate and the transmission beam transmitted through both the transparent substrate and the light shielding film is used. Since an image is used, data of an image area with an increased amount of light incident on the imaging device is used, and transmittance measurement that is not affected by disturbance can be performed.

Next, experimental results will be described. The apparatus shown in FIG. 1 was used as a measurement apparatus, a phase shift mask was used as a sample, and the transmittance of a light shielding film functioning as a phase shifter was measured. In the measurement, as a measurement method, a measurement method (conventional measurement method) using the interference image 21 and the interference image 23 (interference image of transmitted light transmitted through both the transparent substrate and the light shielding film) in FIG. The measurement method (the measurement method of the present invention) using the interference image 21 and the interference image 22a (interference image by the transmitted light transmitted through only the transparent substrate and the transmitted light transmitted through both the transparent substrate and the light shielding film) was compared. . The measurement was performed 10 times, and the results of the measured transmittance (%) are as follows.
Conventional measuring method Measuring method according to the present invention
1 0.916064 0.866351
2 0.906921 0.866351
3 0.867061 0.868589
4 0.874908 0.865988
5 0.87298 0.860951
6 0.890207 0.863472
7 0.903267 0.869215
8 0.92609 0.861351
9 0.883823 0.867184
10 0.873302 0.874431
Average 0.891462 0.866473
3 sigma 0.0583353 0.011318

From the above experimental results, it was confirmed that 3 sigma was reduced to about 1/5 in the measurement method according to the present invention compared to the conventional measurement method.

  Next, measurement of the phase shift amount of the phase shift mask using the light shielding film as the phase shifter will be described. As shown in FIG. 3C, in the measurement method according to the present invention, both the transmitted light transmitted only through the transparent substrate and both the transparent substrate and the light shielding film are provided on both sides of the interference image 21 by the transmitted light transmitted through only the transparent substrate. Interference images 22a and 22b are formed by the transmitted light that has passed through. Therefore, by using these two interference images 22a and 22b, the phase shift amount of the light shielding film in the photomask using the light shielding film as a phase shifter can be measured.

FIG. 5 is a diagram schematically showing the relationship between the wavefront of the first transmitted light propagated through the shearing optical path 6a and the wavefront of the second transmitted light propagated through the phase modulation optical path 6b. In FIG. 5, phi ₀ indicates the phase difference defined by the optical path length difference between the first transmission light and the second transmitted light, phi ₁ is first transmitted light and the second in the second interference image 22a A phase difference between the transmitted light, φ ₂ indicates a phase difference between the first transmitted light and the second transmitted light in the third interference image 22b, and φ indicates a monitor pattern corresponding to a phase shifter The amount of phase shift is shown. As shown in FIG. 5, the following expression is established between the phase shift amount φ, the phase differences φ ₁ , φ _2, and φ ₀ based on the relationship between the wavefronts of the two transmitted lights shifted laterally from each other.
φ = φ ₀ −φ ₁
φ = φ ₂ −φ ₀
The phase shift amount φ of the light shielding film is given by the following equation.
φ = (φ ₂ − φ ₁ ) / 2
Therefore, the phase shift amount of the monitor pattern can be obtained from the phase differences φ ₁ and φ ₂ in the second and third interference images included in the laterally shifted interference image.

FIG. 6 shows changes in luminance of the second and third interference images 22a and 22b when the second wedge prism 12a is moved in the direction orthogonal to the optical axis direction and fringe scanning is performed and phase modulation is performed for one period. That is, it is a graph showing phase modulation data indicating the relationship between the phase modulation amount and the luminance value. The wedge prism 12a is moved by one period in the optical axis direction, and a phase difference of 2π is introduced into the transmitted beam propagating through the phase modulation optical path 6b. At this time, the change in the output signal (luminance value) from the light receiving element included in the second interference image 22a is indicated by a solid line, and the change in the output signal (luminance value) from the light receiving element included in the third interference image 22b. Is indicated by a broken line. For example, the phase difference between the peaks of two luminance change curves is the phase difference between the two interference images 22a and 22b. The phase difference Δφ (Δφ = (φ ₂ −φ ₁ ) / 2) between the two interference images is processed by the fast Fourier transform (FFT) means provided in the signal processing device 17 using the phase modulation data. It is calculated by performing. Therefore, the phase shift amount of the light shielding film is obtained by obtaining the phase difference between the two interference images by the fast Fourier transform process. Note that the phase modulation amount at the time of phase modulation can be obtained from the position information of the wedge prism. Or it can also obtain | require from the time relevant to the moving speed of a wedge prism.

  In the present invention, the phase modulation data of the three interference images can be acquired simultaneously by performing only one fringe scan, so that it is possible to simultaneously measure both the transmittance and the phase modulation amount of the light shielding film. .

  The present invention is not limited to the above-described embodiments, and various modifications and changes can be made. For example, in the above-described embodiment, the transmittance is output by calculating the square of the ratio between the amplitude of the phase modulation data of the first interference image and the amplitude of the phase modulation data of the second or third interference image. It is also possible to calculate the square of the ratio between the amplitude of the phase modulation data of the first interference image and the amplitude of the phase modulation data of both the second and third interference images and output the transmittance. In this case, since the transmittances of two parts having different measurement parts are respectively measured, it is also possible to obtain an average value of the two transmitted transmittance values and output the obtained average value as the transmittance. . By using the average value of the transmittance of the two parts, the influence of fluctuation and flare of the optical system is reduced, and more accurate measurement can be performed. In this case, the signal processing apparatus includes: a first amplitude ratio calculating unit that calculates a square of a ratio between the amplitude of the phase modulation data of the first interference image and the amplitude of the phase modulation data of the second interference image; Second amplitude ratio calculation means for calculating the square of the ratio of the amplitude of the phase modulation data of the first interference image and the amplitude of the phase modulation data of the third interference image, and calculation of the first and second amplitude ratios Means for obtaining an average value of output signals from the means, and outputting the obtained average value as the transmittance of the light shielding film.

  Further, in the above-described embodiment, the two-dimensional imaging device is used as the light detection unit, and the first to third interference images are formed on the two-dimensional imaging device. It is also possible to detect the brightness of the interference light that forms the first to third interference images with each photomultiplier tube using a double tube.

  Furthermore, when reading the charge of each light receiving element of the imaging device, it is also possible to sequentially read out charges for a plurality of pixels such as 2 × 2 by using a binning function. The transmittance of the Morishiri binary light-shielding film is about 0.01% to 0.1%, and the amount of light incident on the light receiving element is extremely small. Therefore, more stable measurement can be performed by using the binning function.

DESCRIPTION OF SYMBOLS 1 Light source 2 Condensing lens 3 Mask blanks 4 Objective lens 5 Relay lens 6 Shearing interferometer 7, 10 Half mirror 8, 12 Double wedge prism 9, 11 Total reflection mirror 13 Linear motor 14 Imaging lens 15 Two-dimensional imaging device 16 Amplifier 17 Signal processor 20a, 20b Monitor pattern image 21 First interference image 22a Second interference image 22b Third interference image

Claims (10)

A transmittance measurement method for measuring the transmittance of a light shielding film of a mask blank or a photomask in which a light shielding film is formed on a transparent substrate using a shearing interferometer,
A step of partially removing the light shielding film from the mask blank or the photomask and forming a monitor pattern in a form in which the transparent substrate is exposed;
Projecting an illumination beam toward the monitor pattern from the side of the transparent substrate where the light-shielding film is not formed;
Condensing transmitted light emitted from the mask blank or photomask through an objective lens, and sending the collected transmitted light to a shearing interferometer;
Splitting the transmitted light incident on the shearing interferometer into first and second transmitted beams;
Adjusting the shearing amount of the shearing interferometer to form a combined beam in which the first transmitted beam propagating in the shearing optical path and the second transmitted beam propagating in the phase modulation optical path partially overlap;
Making the combined beam incident on an imaging device to form an interference image by laterally shifting;
Performing phase modulation for one period on the laterally shifted interference image to obtain phase modulation data indicating a relationship between a phase modulation amount and a luminance value,
The laterally shifted interference image is located on one side of the first interference image and the first interference image formed by the interference of transmitted light transmitted only through the transparent substrate of the mask blank or photomask, and is transparent The second interference image formed by the interference between the transmitted light transmitted only through the substrate and the transmitted light transmitted through both the transparent substrate and the light shielding film, and the other side of the first interference image, only the transparent substrate A third interference image formed by interference between the transmitted light transmitted through the transparent substrate and the transmitted light transmitted through both the transparent substrate and the light shielding film,
The transmittance measurement method further calculates a square of a ratio between the amplitude of the phase modulation data of the first interference image and the amplitude of the phase modulation data of the second interference image and / or the third interference image. A transmittance measurement method comprising the step of:   2. The transmittance measuring method according to claim 1, wherein the light shielding film is a Morisiri binary light shielding film having a transmittance of about 0.01% to 0.1%. Measure the transmittance of the Mori blank binary shading film of mask blanks with the transmittance of 0.01% to 0.1% uniformly on the transparent substrate using a shearing interferometer A transmittance measuring method,
A step of partially removing the light-shielding film from the mask blanks to form a monitor pattern with the transparent substrate exposed;
Projecting the illumination beam emitted from the ArF laser used in the exposure apparatus toward the monitor pattern from the side where the light shielding film of the transparent substrate is not formed;
Condensing the transmitted light emitted from the mask blank through the objective lens, and sending the collected transmitted light to the shearing interferometer;
Splitting the transmitted light incident on the shearing interferometer into first and second transmitted beams;
Adjusting the shearing amount of the shearing interferometer to form a combined beam in which the first transmitted beam propagating in the shearing optical path and the second transmitted beam propagating in the phase modulation optical path partially overlap;
Making the combined beam incident on an imaging device to form an interference image by laterally shifting;
Performing phase modulation for one period on the laterally shifted interference image to obtain phase modulation data indicating a relationship between a phase modulation amount and a luminance value,
The laterally shifted interference image includes a first interference image formed by interference between transmitted lights transmitted through only the transparent substrate, and transmitted light positioned on one side of the first interference image and transmitted only through the transparent substrate. And the second interference image formed by interference between the transmitted light transmitted through both the transparent substrate and the light shielding film, and the transmitted light transmitted through only the transparent substrate and transparent, located on the other side of the first interference image A third interference image formed by interference with transmitted light transmitted through both the substrate and the light shielding film,
And a step of calculating a square of a ratio between the amplitude of the phase modulation data of the first interference image and the amplitude of the phase modulation data of the second interference image and / or the third interference image. A transmittance measuring method.   4. The transmittance measurement method according to claim 1, wherein a ratio between an amplitude of the phase modulation data of the first interference image and an amplitude of the phase modulation data of the second interference image or the third interference image. Is output as the transmittance of the light-shielding film.   4. The transmittance measurement method according to claim 1, wherein the amplitude of the phase modulation data of the first interference image, the second interference image adjacent to the first interference image, and the third interference image are determined. A transmittance measurement method characterized by calculating a square of a ratio to the amplitude of phase modulation data, respectively, and outputting an average value of the calculated two square values as the transmittance of the light shielding film.   6. The transmittance measurement method according to claim 1, wherein the imaging device is configured by a CCD imaging device having a plurality of light receiving elements arranged in a two-dimensional array. Transmittance measurement method.   7. The transmittance measuring method according to claim 6, wherein the CCD image pickup device has a binning function, and reads out charges accumulated in each light receiving device for a plurality of pixels.   8. The transmittance measuring method according to claim 1, wherein a Mach-Zehnder interferometer is used as the shearing interferometer, and an ArF laser used in an exposure apparatus is used as an illumination light source for generating the illumination beam. A transmittance measuring method characterized by the above. A transmittance measuring device for measuring the transmittance of a light shielding film of a mask blank or a photomask in which a light shielding film is formed on a transparent substrate,
A stage for supporting a mask blank or a photomask having a monitor pattern in which the light shielding film is partially removed and the transparent substrate is exposed;
An illumination system that projects an illumination beam toward the monitor pattern from the side where the light shielding film of the transparent substrate is not formed,
An objective lens for condensing transmitted light emitted from the mask blank or photomask;
A shearing interferometer that receives transmitted light collected by an objective lens, a beam splitting element that divides incident transmitted light into first and second transmitted beams, a shearing optical path that shears the first transmitted beam, A phase modulation optical path that performs phase modulation on the second transmitted beam, and a shearing interferometer including a beam combining element that combines the shearing optical path and the transmitted beam that has propagated through the phase modulated optical path to emit a combined beam;
An imaging device that receives the combined beam emitted from the shearing interferometer;
A signal processing device that processes the output signal from the imaging device and outputs the transmittance of the light shielding film,
On the imaging device, the first interference image formed by the interference of transmitted light that has transmitted only through the transparent substrate of the mask blank or the photomask, and the first interference image are located on one side of the transparent image and are transparent. The second interference image formed by the interference between the transmitted light transmitted only through the substrate and the transmitted light transmitted through both the transparent substrate and the light shielding film, and the other side of the first interference image, only the transparent substrate A laterally shifted interference image including a third interference image formed by the interference between the transmitted light transmitted through and the transmitted light transmitted through both the transparent substrate and the light shielding film,
The signal processing device includes means for calculating a square of a ratio between the amplitude of the phase modulation data of the first interference image and the amplitude of the phase modulation data of the second interference image and / or the third interference image. A transmittance measuring device characterized by comprising: The transmittance measuring apparatus according to claim 9, wherein the signal processing device calculates a square of a ratio between an amplitude of the phase modulation data of the first interference image and an amplitude of the phase modulation data of the second interference image. First amplitude ratio calculating means, and second amplitude ratio calculating means for calculating the square of the ratio between the amplitude of the phase modulation data of the first interference image and the amplitude of the phase modulation data of the third interference image; And a means for obtaining an average value of output signals from the first and second amplitude ratio calculating means, and outputting the obtained average value as the transmittance of the light shielding film. .

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