JPH11327119A - Method and equipment for measuring amount of phase shift for phase shift mask substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately and directly measure the amount of phase shift of a phase shifter layer formed on a transparent substrate in a non-contact and non-destructive manner when the phase shifter layer is formed. SOLUTION: In this method for measuring the amount of phase shift for a phase shift mask substrate wherein the phase difference of transmitted light before and after forming of a phase shifter layer on a transparent substrate at the same position of the transparent substrate, a dummy transparent substrate is mounted on a sample stage of an interferometer, on which a transparent substrate is to be mounted, instead of the transparent substrate while the phase shifter layer is formed on the transparent substrate. Phase variation of the transmitted light through the dummy transparent substrate is detected during formation of the layer, and when a phase of light passing through the transparent substrate after the phase shifter layer is formed on the transparent substrate, the mount of varied phase shift is canceled out by compensating the length of one of optical paths of the interferometer by means of an optical-path-length compensating means 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase shift amount measuring apparatus for a phase shift mask substrate, and more particularly, to a halftone phase shifter among photomasks used as original plates to be projected in a lithography step in manufacturing a semiconductor device. The present invention relates to an apparatus for directly measuring a phase shift amount of a phase shift mask blank before a shift mask is manufactured.

[0002]

2. Description of the Related Art A halftone type phase shift mask is known as one of phase shift masks. The halftone type phase shift mask is manufactured by a process as shown in FIG. 3, for example. First, as shown in FIG. 3A, a high-purity synthetic quartz substrate 21 which has been optically polished and washed well is prepared, and then, as shown in FIG. And the like, the phase shift amount of the light of the used wavelength λ is 18 times smaller than that of the portion where the translucent film 22 is not provided.
The phase shift mask blanks 23 are obtained by forming a film so as to be shifted by 0 ° or an odd multiple thereof. Next, as shown in FIG. 3C, a resist pattern 24 is formed on the blanks 23 by lithography. Next, FIG.
As shown in (d), the semi-transparent film 22 exposed from the resist pattern 24 is exposed to high-frequency plasma to selectively perform dry etching to obtain a desired semi-transparent film pattern 25. Finally, the remaining resist 24 is peeled off, and as shown in FIG. 4E, a halftone type phase shift photomask 26 in which the transmittance of the used wavelength λ of the halftone phase shift unit 25 is 1% to 50%. Is obtained.

When manufacturing such a halftone type phase shift mask 26, the semitransparent film 22 constituting the phase shifter layer is formed so that the phase shift amount is exactly 180 ° (or an odd multiple thereof). is important. Conventionally, there are mainly the following two methods for the measurement.

A) Breakdown inspection: A phase shifter pattern is formed on a halftone type phase shift mask blank by a lift-off method or a photolithography method, and a phase shifter portion and a non-phase shifter portion are formed.
The phase shift amount of the phase shifter and the non-phase shifter is measured by a phase difference measuring device utilizing interference by light having the same wavelength as that used in the stepper exposure.

B) Nondestructive inspection: After measuring the thickness of the phase shifter layer using an optical film thickness meter, the amount of phase shift is determined by calculation from the known refractive index of the phase shifter layer and the measured thickness.

[0006]

In the above conventional method, the shift amount of the halftone phase shift mask blank cannot be directly measured by the nondestructive inspection. Therefore, the halftone type phase shift mask blank is formed until the mask pattern is formed. Inspection of the phase shift amount of the shift mask cannot be performed, and there is a problem that it is difficult to completely avoid initial failure of the phase shift amount.

The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to reduce the amount of phase shift when a phase shifter layer is formed on a transparent substrate in a non-contact / non-destructive manner. It is to provide a method and an apparatus for accurate and direct measurement at the same time.

[0008]

SUMMARY OF THE INVENTION A phase shift amount measuring method for a phase shift mask substrate according to the present invention is characterized in that a phase difference of transmitted light at the same place on a transparent substrate is determined before and after a phase shifter layer is formed on the transparent substrate. In the phase shift amount measuring method for a phase shift mask substrate measured using a light beam interferometer, a dummy transparent substrate is placed on a sample stage of an interferometer on which the transparent substrate is placed while forming a phase shifter layer on the transparent substrate. Instead, when detecting the phase variation of the light passing through the dummy transparent substrate during that time, when measuring the phase of the light passing through the transparent substrate after forming a phase shifter layer on the transparent substrate Further, the method is characterized in that the phase fluctuation is compensated by correcting the optical path length of one optical path of the interferometer.

In this case, it is desirable that the optical path length of one of the two-beam interferometer is always modulated by one period of the interference fringe.

Further, the phase shift amount measuring apparatus for a phase shift mask substrate according to the present invention is a phase shift mask for measuring a phase difference of transmitted light at the same place on a transparent substrate before and after forming a phase shifter layer on the transparent substrate. In the substrate phase shift amount measuring apparatus, an optical path dividing unit that divides light from the same light source into a measurement optical path and a reference optical path, and a sample stage that is disposed in the measurement optical path and that exchangeably mounts a measurement sample,
Light path combining means for combining the measurement light path and the reference light path; a phase modulation means disposed on one of the measurement light path and the reference light path; and a first modulation means disposed on one of the measurement light path and the reference light path.
An optical path length correcting means, a second optical path length correcting means disposed on one of the measurement optical path and the reference optical path, a means for photoelectrically converting the light that has been interfered by being combined by the optical path combining means, and A control device that receives the detection signal of (a) and controls the phase modulation unit, the first optical path length correction unit, and the second optical path length correction unit; and a storage unit connected to the control device. The apparatus sends a signal for modulating the interference fringes for one cycle to the phase modulation means, and transmits the measurement sample from the transparent substrate before forming the phase shifter layer to the dummy transparent substrate, and also from the dummy transparent substrate after forming the phase shifter layer. When switching to the transparent substrate, a signal for correcting the optical path length difference between the transparent substrate before forming the phase shifter layer and the dummy transparent substrate is sent to the first optical path length correcting means, and the dummy transparent substrate is Penetrate When detecting a phase variation of light and switching the measurement sample from the dummy transparent substrate to the transparent substrate after forming the phase shifter layer, sending an optical path length correction signal corresponding to the phase variation to the second optical path length correcting means. It is characterized by the following.

In this case, the phase modulating means and the second optical path length correcting means can be constituted by the same linearly driven double wedge prism.

Further, the first optical path length correcting means can be constituted by a linearly driven double wedge prism.

Further, the phase modulating means, the first optical path length correcting means, and the second optical path length correcting means can be constituted by the same linear drive double wedge prism.

In the present invention, while forming the phase shifter layer on the transparent substrate, a dummy transparent substrate is placed instead on the sample stage of the interferometer on which the transparent substrate is placed,
The phase variation of the light passing through the dummy transparent substrate during that time is detected, and when measuring the phase of the light passing through the transparent substrate after the phase shifter layer is formed on the transparent substrate, the phase variation is measured by the interferometer. Since the optical path length of the optical path is corrected and canceled, the amount of phase shift can be measured in a non-contact and non-destructive manner with respect to the sample when the phase shifter layer is formed on the substrate. Unlike the indirect guarantee by measuring the film thickness and the refractive index, the phase shift amount can be accurately measured even when the measurement interval before and after the phase shifter layer is formed is long.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The phase shift amount measuring method for a phase shift mask substrate of the present invention is intended to directly measure the phase difference of a halftone type phase shift mask blank in a non-destructive and non-contact manner using an interferometer. Before and after forming the phase shifter layer,
The transmitted light phase of the substrate to be measured is measured at the same location on the same substrate, the results are automatically recorded, and the difference between the two is calculated to determine the phase difference. However, at this time, since it takes a long time to form the phase shifter layer, the time interval for acquiring the measurement data before and after the phase shifter layer is formed is long, and there is a high possibility that an error due to a temperature drift of the interferometer occurs.

According to the present invention, during a period other than the time of sample measurement, a dummy transparent substrate is placed on the sample stage, drift due to temperature or the like is detected from a change in interference fringes, and a change with time of the interference fringes due to drift is always detected. Monitor. Then, the optical path length correction required to cancel the drift component from the signal is performed by negative feedback control. Therefore, even if the measurement interval before and after forming the phase shifter layer is long,
Accurate measurement of the phase shift amount of the phase shifter layer becomes possible.

FIG. 1 shows a schematic configuration of an embodiment of a phase shift amount measuring apparatus for a phase shift mask substrate according to the present invention. In this embodiment, the interferometer for measuring the phase amount between the halftone phase shift mask blanks (before forming the phase shifter layer) and the dummy transparent substrate before and after forming the sample phase shifter layer is as follows. Although a Mach-Zehnder interferometer is used, it is obvious that another interferometer may be used.

In FIG. 1, reference numeral 1 denotes a light source, 2 denotes a lens, 3 denotes a beam splitter for splitting an optical path, 4 denotes a sample stage, 5 denotes a measurement sample, and a transparent substrate (21 in FIG. 3) before forming a phase shifter layer. Phase shifter layer (2 in FIG. 3)
2) One of the halftone phase shift mask blanks (23 in FIG. 3) after formation and the dummy transparent substrate, 6 is a mirror, 7 is a double wedge prism for correcting an optical path length when switching the measurement sample 5, and 8 is a double wedge prism. A linear motor for driving the wedge prism 7, a compensator 9 for compensating for an optical path difference between the measurement optical path and the reference optical path, a mirror 10, a double wedge prism 11 for modulation and drift correction, 12
Is a linear motor for driving the double wedge prism 11;
Reference numeral 3 denotes an optical path synthesizing beam splitter, 14 denotes a photodetection photomultiplier, 15 denotes a control device, and 16 denotes a memory.

The monochromatic light from the light source 1 is converted into a parallel light by a lens 2 and split into a measuring light (transmitted light) and a reference light (reflected light) by an optical path splitting beam splitter 3. The light passes through the measurement sample 5 placed and adjusted at the predetermined position above, is reflected by the mirror 6, and reaches the beam splitter for optical path synthesis via the double wedge prism 7 for correcting the optical path length. On the other hand, the reference light reflected by the beam splitter 3 for splitting the optical path
The light is reflected at 0 and reaches the beam splitter for optical path synthesis via the double wedge prism 11 for modulation and drift correction, where it is combined with the measurement light and interferes according to the optical path difference between the optical path of the measurement light and the optical path of the reference light. Then, the interference fringes are photoelectrically converted by the photodetector 14 and the detection signal is input to the controller 15.

The control device 15 transfers the measurement sample 5 from the transparent substrate before forming the phase shifter layer to the dummy transparent substrate.
In addition, every time the dummy transparent substrate is switched to the halftone type phase shift mask blank after the phase shifter layer is formed, a double-sided optical path length difference between the transparent substrate before the phase shifter layer is formed and the dummy transparent substrate is corrected. The wedge prism 7 drive signal is output to the linear motor 8, and the interference fringes detected by the photodetection photomultiplier 14 are modulated to the linear motor 12 for one cycle (one wavelength in the optical path difference: 360 ° in phase). A signal in which a signal for performing the modulation and a signal for correcting the base line of the modulation (the center position of the modulation) are output as a drive signal. Further, the control device 15 stores the phase signal of the interference fringe detected by the photodetection photomultiplier 14.

The phase shift amount measuring process of the phase shift amount measuring apparatus for a phase shift mask substrate having such a configuration will be described with reference to FIG. First, as shown in FIG.
The transparent substrate before the phase shifter layer is formed is placed on the sample stage 4 of FIG. 1, and the position of the sample stage 4 is adjusted in the X-Y direction orthogonal to the optical axis, and the predetermined position of the transparent substrate is adjusted. Position on the axis. In this state, a modulation signal is sent from the control device 15 to the linear motor 12 to reciprocate the double wedge prism 11 as shown by double arrows in FIG. 1 to phase-modulate the optical path length of the reference optical path by one wavelength. In this state, the signal detected from the photodetection photomultiplier 14 has a one-cycle sin curve as shown in FIG. In this state, the position of the optical path length correcting double wedge prism 7 is a, and the center position of the modulation and drift correcting double wedge prism 11 is c.

Next, in order to form a phase shifter layer as shown in FIG. 3B, the transparent substrate before the phase shifter layer is formed at the position shown in FIG.
Instead, a dummy transparent substrate is placed on the sample stage 4, a drive signal is sent from the control device 15 to the linear motor 8, and the double wedge prism 7 is reciprocated as indicated by the double arrow in FIG. A modulation signal is sent from the device 15 to the linear motor 12, and the optical path length of the reference light path is phase-modulated by one wavelength, as in the case of FIG. In this state, the signal detected from the photodetection photomultiplier 14 is shown in FIG.
As shown in FIG. 2B, the double wedge prism 7 for correcting the optical path length has the same phase as the detection signal shown in FIG.
Adjust the position of. The position is set to b. In this state, the center position of the modulation and drift correction double wedge prism 11 remains at c.

During the formation of the phase shifter layer, an optical path difference fluctuation (drift) may occur between the measurement optical path and the reference optical path of the interferometer of FIG. 1 due to temperature fluctuation or the like. When there is such a drift, the signal detected from the photodetection photomultiplier 14 is, as shown in FIG.
A phase difference occurs in the signal of (b). When there is a phase difference between the detection signal in FIG. 2C and the signal in FIG. 2B stored in the memory 16, the control device 15 applies a negative feedback to the modulation signal sent to the linear motor 12. By changing the baseline, the phase difference is eliminated as shown in FIG. In this state, the center position of the modulation and drift correction double wedge prism 11 is assumed to be c + Δc. In this state, the position of the optical path length correcting double wedge prism 7 remains at b.

Since the phase shifter layer is formed on the transparent substrate used in FIG. 2A during drift correction using such a dummy transparent substrate, the dummy transparent substrate on the sample stage 4 is formed. Is replaced with a halftone type phase shift mask blank after the phase shifter layer is formed, and the position of the sample stage 4 is adjusted and positioned.
At the same time, the control device 15 sends a drive signal to the linear motor 8 to return the position of the double wedge prism 7 for correcting the optical path length to the original position a where the stored position was stored.
The center line of the modulation and drift correction double wedge prism 11 is assumed to be c + Δc, while the baseline of the modulation signal to be sent to 2 remains the value after drift correction. In this state, the signal detected from the photodetection photomultiplier 14 is obtained by correcting the drift of the interferometer due to the temperature and the like while forming the phase shifter layer.
As shown in FIG. 2, there is a phase difference with respect to the signal detected in the state of FIG. 2A before the phase shifter layer is formed on the transparent substrate. The control device 15 stores the stored FIG.
The phase difference between the signal of FIG. 2E and the signal of FIG. 2E is detected. This phase difference is based on the thickness of the formed phase shifter layer. When the monochromatic light from the light source 1 is equal to the used wavelength of the manufactured halftone phase shift mask, it is shown in FIG. Thus, the target phase shifter layer is 180 ° (or an odd multiple thereof) shifted from the phase in the state of FIG. 2A (FIG. 2E).
FIG. ), Its phase difference 180 °
If the value is larger or smaller than ± (allowable amount), it is determined to be defective. When the monochromatic light from the light source 1 is different from the working wavelength of the manufactured halftone phase shift mask, the target phase difference is as follows: the working wavelength is λ, the measurement wavelength is λ _u , and the working wavelength is λ. When the refractive index of the phase shifter layer N, the refractive index of the phase shifter layer in the measurement wavelength lambda _u and _{N u, 180 ° × {(} N-1) / (N u -1)} × (λ u
/ Λ), and if the detected phase difference is larger or smaller than this value ± (allowable amount), it is determined to be defective.

Although the method and apparatus for measuring the amount of phase shift for a phase shift mask substrate according to the present invention have been described based on the embodiments, the present invention is not limited to these embodiments and can be variously modified. For example, the optical path length changing means for modulation and for drift correction may be provided separately, or
The single wedge prism 7 for optical path length correction and the double wedge prism 11 for modulation and drift correction when switching the measurement sample may be used.
In addition, other types of two-beam interferometers other than the Mach-Zehnder interferometer can be used as the interferometer to be used. Further, the phase shift mask blank for measuring the amount of phase shift is not limited to a halftone type phase shift mask blank, but can be applied to other types of phase shift mask blanks.

[0026]

As is apparent from the above description, according to the method and apparatus for measuring the amount of phase shift for the phase shift mask substrate of the present invention, the transparent substrate is placed during the formation of the phase shifter layer on the transparent substrate. Instead, a dummy transparent substrate is placed on the sample stage of the interferometer, and the phase variation of light passing through the dummy transparent substrate is detected between the dummy transparent substrate and the dummy substrate is transmitted through the transparent substrate after the phase shifter layer is formed on the transparent substrate. When measuring the phase of light, the phase fluctuation is compensated by correcting the optical path length of one optical path of the interferometer, so that when the phase shifter layer is formed on the substrate, the
The amount of phase shift can be measured nondestructively. Unlike the indirect guarantee by measuring the film thickness and the refractive index, the phase shift amount can be accurately measured even when the measurement interval before and after the phase shifter layer is formed is long.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an embodiment of a phase shift amount measuring apparatus for a phase shift mask substrate according to the present invention.

FIG. 2 is a diagram for explaining a phase shift amount measuring process of the measuring apparatus of FIG. 1;

FIG. 3 is a diagram illustrating an example of a manufacturing process of a halftone type phase shift mask.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Light source 2 ... Lens 3 ... Beam splitter for optical path division 4 ... Sample stage 5 ... Measurement sample 6 ... Mirror 7 ... Double wedge prism for optical path length correction 8 ... Linear motor for driving double wedge prism 9 ... Compensator for optical path difference compensation 10 ... Mirror 11 ... Double wedge prism for modulation and drift correction 12 ... Linear motor for driving double wedge prism 13 ... Beam splitter 14 for optical path synthesis 14 ... Photomar for photodetection 15 ... Control device 16 ... Memory 21 ... High purity synthetic quartz substrate 22 ... Semi-transparent film 23 ... Phase shift mask blanks 24 ... Resist pattern 25 ... Semi-transparent film pattern (halftone phase shift part) 26 ... Halftone type phase shift photomask

Claims (6)

[Claims] 1. A method for measuring a phase shift amount for a phase shift mask substrate, wherein a phase difference of transmitted light at the same portion of the transparent substrate is measured using a two-beam interferometer before and after a phase shifter layer is formed on the transparent substrate. During the formation of the phase shifter layer on the transparent substrate, a dummy transparent substrate is placed instead on a sample stage of an interferometer on which the transparent substrate is placed, and light transmitted through the dummy transparent substrate in the meantime. When detecting the phase fluctuation, when measuring the phase of light transmitted through the transparent substrate after forming a phase shifter layer on the transparent substrate,
A phase shift amount measuring method for a phase shift mask substrate, wherein the phase fluctuation is compensated by correcting the optical path length of one optical path of the interferometer. 2. The phase shift amount measuring method for a phase shift mask substrate according to claim 1, wherein the optical path length of one of the two light beam interferometers is constantly modulated by one period of the interference fringes. 3. A phase shift amount measuring apparatus for a phase shift mask substrate for measuring a phase difference of transmitted light at the same place on a transparent substrate before and after forming a phase shifter layer on the transparent substrate. Optical path splitting means for splitting a measurement optical path and a reference optical path, a sample stage arranged in the measurement optical path and exchangeably mounting a measurement sample, an optical path synthesizing means for synthesizing the measurement optical path and the reference optical path, and a measurement optical path and a reference A phase modulation unit disposed on one of the optical paths, a first optical path length correction unit disposed on one of the measurement optical path and the reference optical path, and a second optical path length correction unit disposed on one of the measurement optical path and the reference optical path. 2, an optical path length correcting means, a means for photoelectrically converting the light that has been interfered by being combined by the optical path combining means, and a detection signal from the photoelectric conversion, and the phase modulation means, the first optical path length correcting means, No. A control device for controlling the optical path length correction means, and a storage means connected to the control device,
The control device sends a signal for modulating the interference fringes for one cycle to the phase modulation means, the measurement sample from the transparent substrate before forming the phase shifter layer to the dummy transparent substrate, and from the dummy transparent substrate to the phase shifter layer When switching to the transparent substrate after the formation, a signal for correcting the optical path length difference between the transparent substrate before the phase shifter layer is formed and the dummy transparent substrate is sent to the first optical path length correction unit, and the dummy transparent substrate is transmitted. When a phase variation of light transmitted through the substrate is detected and the measurement sample is switched from the dummy transparent substrate to the transparent substrate after the phase shifter layer is formed, the optical path length correction signal corresponding to the phase variation is subjected to the second optical path length correction. A phase shift amount measuring apparatus for a phase shift mask substrate, which is sent to a means. 4. The phase shift amount measuring apparatus for a phase shift mask substrate according to claim 3, wherein said phase modulating means and said second optical path length correcting means comprise the same linear drive double wedge prism. 5. The phase shift amount measuring apparatus for a phase shift mask substrate according to claim 3, wherein said first optical path length correcting means comprises a double wedge prism driven linearly. 6. The phase shifter according to claim 3, wherein said phase modulator, said first optical path length corrector, and said second optical path length corrector comprise the same linear drive double wedge prism. Phase shift amount measuring device for mask substrate.