JPH10254118A - Method for measuring phase of phase shift mask and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the phase difference of a phase shift film and the uniformity of the phase shift film at high speed. SOLUTION: A DUV(deep ultraviolet) laser beam is made into two-frequency orthogonal linearly polarized light R by a frequency shifter 14. This two- frequency orthogonal linearly polarized light R is separated by every polarized light component by a second polarization beam splitter 23. One of the light beams is transmitted through the entire surface of a photomask 10 and the other is passed through respective mirrors 25, 26 and again these light rays are synthesized again by a third polarization beam splitter 27. The interference light generated at this time is converted to an interference signal Q by a photodetector 29. The phase difference of the phase shift film 2 is determined from the phase difference between this interference signal Q and the reference signal (s).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to inspection of a short-length photomask (reticle) used as a projection master in a lithography process for manufacturing a semiconductor device, and more particularly to a phase shift film of a phase shift mask. The present invention relates to a method and an apparatus for measuring a phase of a phase shift mask for measuring a phase difference.

[0002]

2. Description of the Related Art In a lithography process for manufacturing a semiconductor device, for example, phase shift exposure is performed.
This phase shift exposure is performed by using a phase shift mask in which a phase shift film (shifter) 2 for inverting the phase of light by 180 ° on a glass substrate 1 as shown in FIG. The light intensity becomes zero at the part,
The resolution of the resist can be greatly improved, and the depth of focus can be greatly improved.

The phase shift mask used for such phase shift exposure needs to have a uniform phase difference in the phase shift film 2, and therefore, the thickness of the phase shift film 2 is measured. I have.

The measurement of the film thickness of the phase shift film 2 includes:
For example, an ellipsometer is used. This ellipsometer irradiates the phase shift film 2 with elliptically polarized light from a light source 3 as shown in FIG. 4, and measures the polarization plane with an analyzer 4 so that the reflected light becomes linearly polarized light. At this time,
A polarizer that minimizes the amount of reflected light from the phase shift film 2 and a phase shift film 2 based on an angle set by the analyzer 4
Is to measure the thickness of the film.

However, such film thickness measurement can measure the film thickness of a part of the phase shift film 2 irradiated with linearly polarized light, that is, can measure the absolute value of the phase difference. It takes time to measure that it is formed uniformly over the entire surface.

That is, in the phase shift mask, the phase shift film 2 is formed on the entire surface of the glass substrate 1 before forming the mask pattern. On the other hand, film thickness measurement using an ellipsometer requires, for example, 3 to 5 minutes of measurement time for one point of film thickness measurement.

For this reason, in the film thickness measurement using an ellipsometer, it takes a very long time to measure the film thickness of the phase shift film 2 over the entire surface. Further, as a method of measuring the phase difference of the phase shift mask, there are methods using a shearing interferometer or a Mach-Zehnder interferometer, and these measuring methods are also absolute value measurements of the phase difference. It takes a very long time to measure over the entire surface.

[0008]

As described above, the phase difference measurement of the phase shift mask is a method of measuring the absolute value of the phase difference in any of the methods, and it is necessary to measure the thickness of the phase shift film 2 over the entire surface. Is very time consuming.

Accordingly, an object of the present invention is to provide a phase shift mask phase measuring method which can easily measure the phase difference of a phase shift film. It is another object of the present invention to provide a phase shift mask phase measuring apparatus capable of easily measuring the phase difference of a phase shift film. Another object of the present invention is to provide a phase shift mask phase measuring apparatus capable of measuring the phase difference of the phase shift film and the uniformity of the phase shift film at high speed.

[0010]

According to a first aspect of the present invention, there is provided a phase shift mask phase measuring method for measuring a phase difference of a phase shift film in a phase shift mask for deep ultraviolet light. A first step of separating linearly polarized light for each polarization component and transmitting one through a phase shift mask and passing the other through at least air, and separating the light transmitted through the phase shift mask and the light passed through at least air. A second step of re-combining to obtain interference light;
Measuring the phase difference of the phase shift film from the phase difference between the interference signal corresponding to the interference light obtained in the step and the reference signal corresponding to the two-frequency orthogonal linearly polarized light. Is the way.

According to a second aspect of the present invention, there is provided a phase shift mask phase measurement apparatus for measuring a phase difference of a phase shift film in a phase shift mask for deep ultraviolet light. And a polarization beam splitter that separates the two-frequency orthogonal linearly polarized light output from the deep ultraviolet light source for each polarization component for transmission through a phase shift mask and at least for passage through air. Interfering means for obtaining an interference signal corresponding to interference light between the light transmitted through the phase shift mask and at least the light passed through the air, and an interference signal obtained by the interference means and a two-frequency orthogonal signal output from the deep ultraviolet light source A phase calculating means for calculating a phase difference of the phase shift film from a phase difference with a reference signal corresponding to linearly polarized light.

In such a phase shift mask phase measuring apparatus, the two-frequency orthogonal linearly polarized light output from the deep ultraviolet light source is transmitted through the phase shift mask and at least through the air by the polarizing beam splitter. The light for transmission through the phase shift mask is transmitted through the phase shift mask, and the light for passing through the air passes through the air.

Thereafter, interference light between the light transmitted through the phase shift mask and the light passed through the air is obtained, and an interference signal corresponding to the interference light and two-frequency orthogonal linearly polarized light output from the deep ultraviolet light source are obtained. The phase difference of the phase shift film is obtained from the phase difference with the corresponding reference signal.

According to a third aspect of the present invention, in the phase shift mask phase measuring apparatus according to the second aspect, a table on which the phase shift mask is mounted, and movement control of the table,
A table controller for transmitting one of the lights separated by the polarization beam splitter through the entire surface of the phase shift mask is added.

With such a phase shift mask phase measuring apparatus, one of the lights polarized and separated by the polarization beam splitter is applied to the entire surface of the phase shift mask by controlling the movement of the table on which the phase shift mask is mounted. To Penetrate.

Therefore, the interference signal corresponding to the interference light between the light transmitted through the entire surface of the phase shift mask and the light passing through the air and the reference signal corresponding to the two-frequency orthogonal linearly polarized light output from the deep ultraviolet light source. The phase difference of the phase shift film over the entire surface of the phase shift mask is determined from the phase difference.

According to a fourth aspect of the present invention, in a phase shift mask phase measuring apparatus for measuring a phase difference of a phase shift film in a phase shift mask for deep ultraviolet light, a laser oscillator for outputting deep ultraviolet laser light, A frequency shifter that outputs the deep ultraviolet laser light output from the oscillator as intensity-modulated two-frequency orthogonal linearly polarized light, and the two-frequency orthogonal linearly polarized light that is output from the frequency shifter is used for transmission through a phase shift mask and in air or A polarizing beam splitter that separates each polarized light component for passing through quartz, and reference optics that allows light passing through air or quartz that has been polarized and separated by the polarizing beam splitter to pass through air or quartz. System, a table on which a phase shift mask is mounted, and movement control of this table, and a polarization beam splitter separates each polarization component. A table controller for transmitting one of the divided lights through the entire surface of the phase shift mask, and a beam splitter for combining the light transmitted through the phase shift mask with the light passed through the air or quartz by the reference optical system to obtain interference light. And a photodetector that converts an interference signal corresponding to the interference light obtained by the beam splitter, and a phase difference between the interference signal output from the photodetector and a reference signal synchronized with an oscillator that drives a frequency shifter. A phase measurement device for a phase shift mask, comprising: a phase calculation means for determining a phase difference over the entire surface of the phase shift film.

In such a phase shift mask phase measuring apparatus, the deep ultraviolet laser light output from the laser oscillator becomes intensity-modulated two-frequency orthogonal linearly polarized light through a frequency shifter. The polarization beam splitter separates the polarized light into light for transmission through the phase shift mask and at least light for passage through the air, of which light for transmission through the phase shift mask is transmitted through the phase shift mask, and light for transmission through the air is air. Pass through.

At this time, the light for transmitting the phase shift mask is transmitted through the entire surface of the phase shift mask by controlling the movement of the table on which the phase shift mask is mounted. Thereafter, interference light between the light transmitted through the phase shift mask and the light transmitted through the air is obtained. An interference signal corresponding to the interference light and a reference corresponding to the two-frequency orthogonal linearly polarized light output from the deep ultraviolet light source are obtained. The phase difference of the phase shift film is obtained from the phase difference with the signal.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. According to the phase shift mask phase measuring method of the present invention, two frequency orthogonal linearly polarized light of a single frequency deep ultraviolet laser beam (DUV laser beam: Deep Ultra Violet) is separated for each polarization component, and one of the two components is separated by a phase shift mask. And a second step of recombining light transmitted through the phase shift mask and light transmitted through air or quartz to obtain interference light. And a third step of obtaining the phase difference of the phase shift film from the phase difference between the interference signal corresponding to the interference light obtained in the second step and the reference signal corresponding to the two-frequency orthogonal linearly polarized light. doing. Here, the two-frequency orthogonal linearly polarized light means that two linearly polarized light beams orthogonal to each other are combined and formed, and both linearly polarized light beams have different frequencies. Therefore,
Different information can be transmitted for each linearly polarized light.

FIG. 1 is a block diagram of a phase shift mask phase measuring apparatus according to claims 1 to 4 to which the phase shift mask phase measuring method is applied. The phase shift mask 10
The phase shift film 2 is formed over the entire surface of the glass substrate 1 before the mask pattern is formed.

This phase shift mask 10 is mounted on an XY table 11 which is movable on an XY plane. The XY table 11 is moved and controlled on the XY plane by the drive control of the table controller 12 so that the entire surface of the phase shift mask 10 is irradiated with light.

On the other hand, the laser oscillator 13 has a function of outputting a single-frequency DUV laser beam (wavelength: 248 nm). On the laser beam path of the laser oscillator 13,
A frequency shifter 14 is provided.

A combination of the laser oscillator 13 and the frequency shifter 14 constitutes a heterodyne light source. The frequency shifter 14 has a function of converting the DUV laser light output from the laser oscillator 13 into intensity-modulated two-frequency orthogonal linearly polarized light R (ω, ω + Δω). FIG. 2 is a configuration diagram of the frequency shifter 14. Show.

On the optical axis of the DUV laser light output from the laser oscillator 13, a first polarization beam splitter (P
BS) 15 and the first from the laser oscillator 13
A quarter-wave plate 16 and a fixed mirror 17 are arranged on the opposite side via the polarization beam splitter 15.

A quarter-wave plate 18 and a movable mirror 19 are arranged in one branching direction of the first polarizing beam splitter 15. The movable mirror 19 is provided with a modulation piezoelectric actuator (PZT: piezo element) 20 on the back surface, and is movable along one branch optical axis of the first polarization beam splitter 15.

The piezoelectric actuator 20 includes an amplifier 2
1, a PZT driving oscillator 22 is connected,
It is finely moved in accordance with the sawtooth signal output from the PZT driving oscillator 22.

The PZT driving oscillator 22 outputs a synchronizing signal for the sawtooth signal output operation as a reference signal s. A second polarization beam splitter 23 is arranged on the optical path of the two-frequency orthogonal linearly polarized light R (ω, ω + Δω) output from the frequency shifter 14.

This second polarization beam splitter 23
Two-frequency orthogonal linearly polarized light R output from the frequency shifter 14
Is separated for each polarization component for transmission through the phase shift mask 10 and for transmission through air or quartz.

Of these, the optical path for transmission to the phase shift mask 10 is set in the direction in which the phase shift mask 10 is arranged, and the reference optical system 24 is arranged on the optical path for passage into the air or quartz. Have been.

The reference optical system 24 allows the light separated for each polarization component by the second polarization beam splitter 23 to pass through the air, and includes two mirrors 25 and 26.

The third polarization beam splitter 27 combines the light transmitted through the phase shift mask 10 and the light passed through the air by the reference optical system 24 to obtain interference light. On the interference light output side of the beam splitter 27, a photodetector 29 is disposed via a polarizing plate 28 for adjusting the wavefront.

The photo detector 29 photoelectrically converts interference light and outputs an interference signal Q. For example, a photodiode and a photomultiplier are used. The phase meter 30 has a function of measuring the phase difference of the phase shift film 2 from the phase difference between the interference signal Q output from the photo detector 29 and the reference signal s output from the PZT driving oscillator 22 of the frequency shifter 14. Have.

The computer 31 captures the phase difference of the phase shift film 2 measured by the phase meter 30 and issues the XY table 11 to the table controller 12.
Has the function of calculating the phase difference of the phase shift film 2 over the entire surface of the phase shift mask 10 based on the movement position signal of the phase shift mask 10.

In this case, the computer 31 determines the phase change of the phase shift film 2 when the light passes through the air in the reference optical system 24, and passes the light through the quartz in the reference optical system 24. In this case, the absolute value of the phase difference due to the phase shift film 2 is obtained.

Next, the operation of the device configured as described above will be described. Single frequency DU from laser oscillator 13
When the V laser light is output, the DUV laser light enters the first polarization beam splitter 15 of the frequency shifter 14, and is separated and polarized by the polarization beam splitter 15 into two polarized lights ω and ω + Δω orthogonal to each other. 1 /
The light passes through the four-wavelength plates 16 and 18 and reaches the fixed mirror 17 and the movable mirror 19 and is folded.

The lights ω and ω + Δω turned back by the fixed mirror 17 and the movable mirror 19 respectively pass through the quarter-wave plates 16 and 18 again and enter the first polarizing beam splitter 15, where Recombined and emitted.

At this time, since the movable mirror 19 is finely moved in accordance with the sawtooth signal output from the PZT driving oscillator 22, the first polarization beam splitter 15 outputs a two-frequency quadrature orthogonally modulated in a sawtooth shape. It is emitted as linearly polarized light (beat signal) R (ω, ω + Δω).

The two-frequency orthogonal linearly polarized light R (ω, ω + Δ
ω) is separated by the second polarizing beam splitter 23 for each polarization component for transmission through the phase shift mask 10 and for transmission through air or quartz.

Since the optical path for transmission to the phase shift mask 10 is set in the direction in which the phase shift mask 10 is arranged, this light is transmitted through the phase shift mask 10 and travels through the third polarization beam. The light enters the splitter 27.

At this time, since the computer 31 issues a movement position signal of the XY table 11 to the table controller 12, the XY table 11 applies the second polarization to the entire surface of the phase shift mask 10 placed thereon. It moves so that the light polarized and separated by the beam splitter 23 is transmitted.

Accordingly, the second polarization beam splitter 23
The light separated for each polarization component is scanned over the entire surface of the phase shift mask 10 and enters the third polarization beam splitter 27.

At the same time, the other light separated for each polarization component by the second polarization beam splitter 23 passes through the mirrors 25 and 26 of the reference optical system 24 in the air and is transmitted to the third polarization beam splitter 27. Incident.

In the third polarization beam splitter 27, the light transmitted through the phase shift mask 10 and the reference optical system 2
4 and the light that has passed through the air is incident,
These lights are combined to generate interference light.

The interference light is applied to a polarizing plate 28 for adjusting the wavefront.
And enters the photodetector 29. The photodetector 29 photoelectrically converts the incident interference light into an interference signal Q.
Is output. This interference signal Q has a phase shift mask 1
The phase difference information by the 0 phase shift film 2 is included.

Therefore, the phase meter 30 is connected to the photo detector 29
, A reference signal s output from the PZT driving oscillator 22 of the frequency shifter 14, and a phase difference of the phase shift film 2 based on a phase difference between the interference signal Q and the reference signal s. Is measured.

The computer 31 captures the phase difference of the phase shift film 2 measured by the phase meter 30 and issues the XY table 11 to the table controller 12.
The phase difference of the phase shift film 2 over the entire surface of the phase shift mask 10 is obtained based on the moving position signal of the above.

In this case, if light passes through the air in the reference optical system 24, the computer 31 obtains a phase change of the phase shift film 2. Further, if the light passes through the quartz in the reference optical system 24, the computer 31 obtains the absolute value of the phase difference by the phase shift film 2.

As described above, in one embodiment,
The DUV laser light is linearly polarized in two orthogonal frequencies and separated for each polarization component, and one of the lights is transmitted through the entire surface of the phase shift mask 10 and the other is passed through air or quartz, and these lights are combined again. The phase shift film 2 is obtained from the phase difference between the interference signal Q corresponding to the interference light and the reference signal s.
, The phase difference of the phase shift film 2 can be easily measured, the uniformity of the phase shift film 2 can be measured with high accuracy, and the phase difference and the phase shift film 2 can be measured at high speed.

Therefore, the uniformity of the phase shift film 2 over the entire surface of the phase shift mask 10 can be inspected based on the measurement result of the phase difference of the phase shift film 2 and the uniformity of the phase shift film 2.

[0051]

As described above, according to the first aspect of the present invention, it is possible to provide a phase shift mask phase measuring method capable of easily measuring the phase difference of the phase shift film. Further, according to the second aspect of the present invention, it is possible to provide a phase shift mask phase measuring apparatus capable of easily measuring the phase difference of the phase shift film. Further, according to the third and fourth aspects of the present invention, it is possible to provide a phase shift mask phase measuring apparatus capable of measuring the phase difference of the phase shift film and the uniformity of the phase shift film at a high speed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of a phase measurement device for a phase shift mask according to the present invention.

FIG. 2 is a configuration diagram of a frequency shifter.

FIG. 3 is a configuration diagram of a phase shift mask.

FIG. 4 is a schematic configuration diagram of an ellipsometer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Glass substrate, 2 ... Phase shift film, 10 ... Phase shift mask, 11 ... XY table, 12 ... Table controller, 13 ... Laser oscillator, 14 ... Frequency shifter, 22 ... PZT drive oscillator, 23 ... Second polarization Beam splitter, 24: reference optical system, 27: third polarizing beam splitter, 29: photodetector, 30: phase meter, 31: computer.

Claims (4)

[Claims] In a phase shift mask phase measuring method for measuring a phase difference of a phase shift film in a phase shift mask for deep ultraviolet light, two-frequency orthogonal linearly polarized light of deep ultraviolet light is separated for each polarization component. A first step of transmitting light through the phase shift mask and passing the other through at least air, and recombining light transmitted through the phase shift mask and at least light passed through the air to obtain interference light A second step, and a third step of obtaining a phase difference of the phase shift film from a phase difference between an interference signal corresponding to the interference light obtained in the second step and a reference signal corresponding to the two-frequency orthogonal linearly polarized light. And a step of measuring the phase of the phase shift mask. 2. A phase measuring apparatus for a phase shift mask for measuring a phase difference of a phase shift film in a phase shift mask for deep ultraviolet light, wherein the deep ultraviolet light outputs intensity-modulated two-frequency orthogonal linearly polarized light of deep ultraviolet light. A light source and two-frequency orthogonal linearly polarized light output from the deep ultraviolet light source,
A polarization beam splitter that separates each of the polarization components for transmission through the phase shift mask and at least for passage through the air, and interference light between the light transmitted through the phase shift mask and at least the light transmitted through the air. An interfering means for obtaining a corresponding interference signal; and a phase difference between the interference signal obtained by the interfering means and a reference signal corresponding to two-frequency orthogonal linearly polarized light output from the deep ultraviolet light source. And a phase calculating means for calculating the phase. 3. A table on which the phase shift mask is mounted, a table controller for controlling the movement of the table, and transmitting one light polarized and separated by the polarization beam splitter to the entire surface of the phase shift mask; 3. The phase shift mask phase measuring apparatus according to claim 2, wherein 4. A phase measuring device for a phase shift mask for measuring a phase difference of a phase shift film in a phase shift mask for deep ultraviolet light, comprising: a laser oscillator for outputting a deep ultraviolet laser beam; A frequency shifter that outputs deep ultraviolet laser light as intensity-modulated two-frequency orthogonal linearly polarized light; and a two-frequency orthogonal linearly polarized light that is output from the frequency shifter is transmitted through the phase shift mask and into air or quartz. A polarizing beam splitter that separates each polarization component for passing light, a reference optical system that passes light for passing in air or quartz, which is polarized and separated by the polarizing beam splitter, in air or quartz, A table on which a phase shift mask is mounted, and movement control of the table, and separation for each polarization component by the polarization beam splitter. A table controller for transmitting one of the light beams transmitted to the entire surface of the phase shift mask, and combining the light beam transmitted through the phase shift mask and the light beam passed through the air or quartz by the reference optical system to generate interference light. A beam splitter to be obtained, a photodetector that converts the interference signal according to the interference light obtained by the beam splitter, and a reference signal synchronized with an oscillator that drives the frequency shifter and the interference signal output from the photodetector. A phase calculating means for calculating a phase difference on the entire surface of the phase shift film from the phase difference.