JPH10254124A - Method for inspecting phase shift mask and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the phase difference of phase shifters in a short time by illuminating a phase shift mask with light of a prescribed wavelength, interfering this light with reference light to generate interference fringes and calculating the phase quantity of the phase shifters from the phase information of the phase shifter parts and non-phase shifter parts of these interference fringes. SOLUTION: The light emitted from a light source 1 having coherence is split to the reference light and the object light by a beam splitter 2. The object light is cast to the phase shift mask 5 and forms a phase shift mask image on a sensor 15 by an objective lens 7 and an image forming lens 13. On the other hand, the reference light is magnified by a mirror 3, a variable angle mirror 10 and lenses 11, 12 to a size which interferes with the object light on the sensor 15 which is two-dimensional CCDs and is cast as parallel luminous fluxes. The object light and the reference light are interfered on the sensor 15 and the interference fringe images are obtd. by an image processing section 16. The phase shift quantity is found with a phase calculation section 17 by using the images obtd. in this image processing section 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting a phase shift mask used for manufacturing a highly integrated circuit such as ULSI, and more particularly, to a method for accurately measuring a phase difference of a phase shifter of the phase shift mask. The present invention relates to an inspection method and an inspection method.

[0002]

2. Description of the Related Art A semiconductor integrated circuit is formed by applying a resist on a non-processed substrate such as a silicon wafer, exposing a desired pattern by a projection exposure apparatus such as a stepper, and repeating development, etching, film formation and the like. Manufactured.

A mask called a mask used in an exposure process for forming a pattern in the semiconductor integrated circuit tends to be required to be more and more accurate as the performance and integration of a semiconductor integrated circuit are increased. For example, a dimensional deviation in a five-fold mask for a 64M DRAM requires a dimensional accuracy of 0.07 μm (3σ).

Further, a device pattern formed by using these masks is 0.35 μm in a 64 MDRAM.
In addition, miniaturization is required with the increase in the degree of integration, and various exposure methods have been studied and proposed in order to meet such a requirement.

[0005] However, the device pattern of 64MDRAM and thereafter has a limit of the optical resolution in the conventional exposure method using a mask. To overcome this limit, for example, Japanese Patent Application Laid-Open No. 58-173744, Japanese Patent Publication No. As disclosed in Japanese Patent No. 59296 and the like, a mask based on a new concept called a phase shift mask has been proposed. The phase shift mask is a technique for improving the resolution and contrast of a projected image by manipulating the phase of light transmitted through the mask.

Next, a projection system using a phase shift mask will be described. FIG. 9 is an explanatory diagram showing the principle of the phase shift. 10A and 10B show a conventional method, in which FIG.
(B) shows the amplitude of light on the mask, (c) shows the amplitude of light on the wafer, and (d) shows the light intensity on the wafer.

In the conventional method, as shown in FIG.
A light shielding film 7 made of chromium or the like on a substrate 70 made of glass or the like.
1 is formed, and a light transmitting portion of a predetermined pattern is formed. As shown in FIG. 9A, the phase shift mask is a phase shifter 72 which is a transmission film for inverting the phase (a phase difference of 180 °) to one of the adjacent light transmission portions on the mask.
Is provided. Therefore, in the conventional method, the amplitude of the light on the mask becomes in-phase as shown in FIG. 10B, and the amplitude of the light on the wafer also becomes in-phase as shown in FIG. 10C. While the pattern on the wafer cannot be separated as shown in FIG. 10 (d), when the phase shift is used, the light transmitted therethrough causes the adjacent patterns to be separated from each other as shown in FIG. 9 (b). Since the phases are opposite to each other, the light intensity becomes zero at the boundary between the patterns, and adjacent patterns can be clearly separated as shown in FIG. 9D.
As described above, when the phase shifter is used, a pattern that cannot be separated conventionally can be separated, and the resolution can be improved.

Another method is a halftone phase shift mask. FIG. 11 shows the principle of this halftone phase shift mask. Conventionally, the light-shielding portion is formed of a 100% light-shielding film, but the halftone phase mask is formed of a halftone light-shielding film having a transmittance of several percent. A phase shift made of a transmission film for inverting the phase (180 ° phase difference) is provided above or below the halftone light-shielding film. Therefore, the amplitude of the light on the mask is as shown in FIG. 11B in the conventional method, and is distributed so as to spread out from the opening of the mask to the outside. As a result, as shown in FIG. The upper light intensity distribution does not have a shape corresponding to the mask pattern, but has a distribution in which the skirt spreads outward from the mask opening. On the contrary,
In the halftone phase shift mask, light leaked from the halftone light-shielding film 73 is given a phase difference by the phase shift layer 74, and as shown in FIG. Since the amplitude is as shown in FIG. 11C, the light amplitude becomes zero at the boundary between the patterns as shown in FIG. 11C, and the spread of the light intensity distribution can be suppressed. When a halftone phase shift mask is used in this manner, a pattern that could not be resolved conventionally can be resolved, and the resolution can be improved.

Conventionally, the phase amount of a phase shifter is determined by measuring the refractive index of a transparent thin film material used for the phase shifter in advance using an ellipsometer or the like, and then measuring the step of the phase shifter pattern formed on the phase shift mask by a contact type. Alternatively, it has been determined by measuring with a non-contact type surface profile measuring device.

[0010]

However, in the phase difference measuring method as described above, it is necessary to measure two kinds of physical quantities, the refractive index and the thickness, when measuring the exact phase difference. In a fine pattern like a pattern, this 2
Measurement of various types of physical quantities on a mask is extremely difficult due to the small measurement area and cannot be realized.

In the actual measurement, the refractive index of the transparent thin film material used for the phase shift is previously measured by an ellipsometer or the like using a dummy mask, and the measured value does not change at all the measured points of all the measured samples. Under the assumption, the phase difference is guaranteed by the measured value of the film thickness of the phase shifter, and lacks strictness.

When the phase difference is assured by measuring the thickness of the phase shifter, if the measuring method is a contact type surface shape measuring device, the contact needle is often used, and the phase shifter pattern may be damaged during the measurement. High and not preferred.

When the phase difference is assured by measuring the phase shifter film thickness, the measuring time of the surface profile measuring apparatus is several seconds to several tens of seconds per measuring point regardless of whether the measuring method is a contact type or a non-contact type. Time is required, and the efficiency is extremely low.

An object of the present invention is to provide a phase shift mask of a phase shift mask which can be easily and without any damage at all, in a short time and directly at the same wavelength as that actually used.
An object of the present invention is to provide a method and a system for inspecting a phase shift mask that accurately measure.

[0015]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for controlling a phase shifter having a partially transparent or halftone phase shifter pattern between a phase shifter arrangement part and a phase shifter non-arrangement part. In the method for inspecting the phase difference, a phase shift mask is illuminated with light having a predetermined wavelength, and this light and the reference light are tilted to interfere with each other to generate interference fringes. The phase amount of the phase shifter is calculated from the phase information of the shifter unit.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory view of a phase shift mask inspection apparatus according to a first embodiment of the present invention. The inspection apparatus includes a light source 1, a beam splitter 2 for dividing light emitted from the light source 1 into object light and reference light, a mirror 3 for changing an angle of the reference light, a stage 4 of a phase shift mask 5, a controller 6 for the stage 4, An objective lens 7, a reference light shutter 8 and its controller 9, a mirror 10 for changing the angle of the reference light and its controller 14, lenses 11 and 12 for enlarging this light,
A lens 13 for imaging light transmitted through the objective lens, a sensor 15 at a position where the object light and the reference light interfere with each other in conjugate with the phase shift mask 5, an image processing unit 16 for processing an image obtained from the sensor 15, an image processing A phase amount calculator 17 for calculating a phase amount from the data obtained from the unit 16; a command unit 18 for issuing a command to the phase shift mask measurement point, an angle between the object light and the reference light, and a command to turn the shutter on and off. .

The operation will be described below. Light emitted from the coherent light source 1 is split by the beam splitter 2 into reference light and object light. The object light is irradiated on the phase shift mask, and the sensor 1 is
5, a phase shift mask image is formed. On the other hand, the reference light is reflected by mirrors 3 and 10 and lenses 11 and 12,
The light is magnified to a size that interferes with the object light on the sensor 15 that is a dimensional CCD, and is illuminated as a parallel light flux. The object light and the reference light interfere with each other on the sensor 15, and if a line and space is used as a pattern, an interference fringe image shown in FIG. The image processing unit 16 uses the obtained image to calculate the phase shift amount in the phase amount calculation unit 17. The signal of the non-phase shifter section 50 taken along the line AA ′ of the image obtained by the image processing section 16 becomes a sine wave as shown by a solid line 54 in FIG. The signal on the BB ′ section of the phase shifter section 52 adjacent to the chrome pattern section 51 becomes a sine wave as shown by a broken line 55 in FIG. The phase difference between these two signals is obtained by 2π × d / L, which is the difference between the phase amount of the non-phase shifter in the AA ′ section and the phase shifter in the BB ′ section. The phase shift amount of the phase shifter in the section BB is measured with reference to the non-phase shifter in the section. In the line and space pattern as shown in FIG. 2, the phase shifters are arranged in the order of 0, π, 0, π.
If the phase shift amount of the phase shifter in the BB 'cross section with respect to the average signal of the signals in the 0 and 50' cross sections is measured, the accuracy of the phase measurement can be improved. In this way, the distribution of the phase shifter in one image is obtained based on the non-phase shifter at the position where the phase difference is 0. This data can determine the distribution of all phase shifters. Based on the distribution result, it is possible to determine whether the phase shifter distribution is within an allowable value or not, and to perform a quality inspection of the phase shift mask. Also, if the interference fringe signal obtained in the cross section is subjected to FFT as shown in FIG. 4 and the phase of the frequency determined by the interference fringe pitch is obtained, this becomes the phase information of the interference fringe signal. The interference fringe signal and the interference fringe signal on the BB 'cross section are each subjected to FFT, and the phase shift amount of the phase shifter can be obtained from the difference between the phases of the frequencies determined by the interference fringe pitch. Further, when the frequency component determined from the interference fringe pitch is shifted so as to coincide with the position of frequency 0 and inverse FFT is performed, the local phase relative to the design value 60 of the CC ′ section of the phase shifter unit 52 shown in FIG. The distribution 61 can be obtained.

Further, when the reference light is blocked by the shutter 8 in response to a signal from the command section 18, a phase shift mask image without interference fringes is formed on the sensor 15, and the phase is compared by comparing this image with the design data. Pattern inspection of the shift mask can also be performed.

In this manner, the inspection of the entire surface of the mask can be performed by sequentially performing the inspection of the phase shift amount and the pattern by image processing.

Further, if the above-mentioned phase is measured using light of two different wavelengths as a light source, a phase difference at an arbitrary wavelength can be obtained by using this.

FIG. 6 shows an embodiment in which the light from the light source 1 of the embodiment is divided into two by a fiber. By using the fiber, the space for guiding the reference light can be reduced.

FIG. 7 shows the configuration of an inspection apparatus when two lights having slightly different frequencies are used by the AO modulator according to the second embodiment. The light emitted from the light source 1 is converted by the AO modulator into light having a first wavelength λ and a second wavelength λ ′ slightly different from the first wavelength λ. This light is combined by the mirror 27 and the beam splitter 28, and is applied to the phase shift mask 5 via the mirror 29 and the lens 31. Phase shift mask 5
Is transmitted by the objective lens 7 and the imaging lens 13
Photoelectric conversion element 3 via beam splitters 31 and 37
A phase shift mask image is formed on the pinholes 38 and 38 'on the entire surfaces 9 and 39'. The light passing through the pinhole is detected as a beat signal by the photoelectric conversion elements 39 and 39 '. From these two beat signals, the command section 3 is obtained from the phase shift mask image data formed on the observation camera 32.
6, the photoelectric conversion element unit 40 is finely moved so that one detects only the light from the non-phase shift unit, and the other is slightly moved to detect the light only from the phase shift unit. , The beat signals of the non-phase shift unit and the phase shift unit are obtained. These two beat signals are output to the phase measurement unit 3
4 to determine the respective phases. From the phases of the two beat signals, a phase difference is obtained by the phase difference measuring section 35.
From this phase difference, that is, the phase amount of the phase shift with respect to the non-phase shift can be obtained.

FIG. 8 shows an embodiment in which a portion for detecting a reference beat signal corresponding to a beat signal in a non-phase shift portion is provided at a position where the phase shift mask is not irradiated. According to this embodiment, the photoelectric conversion element unit for detecting the reference beat signal can be fixed.

[0024]

According to the present invention, it is possible to obtain the interference fringes necessary for obtaining the phase difference without using any movable parts, so that the shift amount of the phase shift mask can be measured with high accuracy.

[Brief description of the drawings]

FIG. 1 is a block diagram of a phase shift mask inspection apparatus according to the present invention.

FIG. 2 is an explanatory diagram of an example of an image obtained on a sensor.

FIG. 3 is an explanatory diagram of a signal of a cross section of an image obtained on a sensor.

FIG. 4 shows an FFT of a cross-sectional signal of an image obtained on a sensor.
Explanatory drawing of the example at the time of doing.

FIG. 5 shows an FFT of a cross-sectional signal of an image obtained on a sensor.
Explanatory drawing of an example in which a phase difference distribution is obtained by performing inverse FFT after that.

FIG. 6 is an explanatory diagram of a phase shift mask inspection device when light is split into two using an optical fiber.

FIG. 7 is an explanatory view of a phase shift mask inspection apparatus according to a second embodiment of the present invention.

FIG. 8 is an explanatory diagram of a phase shift mask inspection apparatus when a reference unit according to a second embodiment of the present invention is separately provided.

FIG. 9 is an explanatory diagram showing pattern contrast when a phase shift mask is used.

FIG. 10 is an explanatory diagram showing a pattern contrast when a conventional mask is used.

FIG. 11 is an explanatory diagram showing a pattern contrast when a halftone phase shift mask is used.

FIG. 12 is an explanatory diagram of a measurement example of a local distribution of a phase shifter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Light source, 2 ... Beam splitter, 3 ... Mirror, 4 ... Phase shifter mask stage, 5 ... Phase shifter mask, 6 ... Phase shifter mask stage controller, 7 ... Objective lens, 8 ... Shutter, 9 ... Shutter controller, 10 ... Angle Variable mirror 11, 12, Lens 13 Image forming lens 14, Angle variable mirror controller 15, Sensor 16, Image processing unit 17, Phase amount calculation unit 18, Command unit

Claims (14)

[Claims] In a phase shift mask having a phase shifter pattern, coherent light is branched, one light is irradiated to the phase shift mask, and transmitted light from the phase shift mask is transmitted by an imaging lens. A phase shift mask image is formed at a position conjugate with the phase shift mask, and the other light is illuminated at an angle at a position conjugate with the phase shift mask at an angle to cause interference, and a plurality of points having different phase differences of the phase shifter. A phase shifter phase amount is measured from the phase difference of the interference fringe signal to determine the quality of the phase shift mask. 2. A means for branching coherent light, a means for irradiating a phase shift mask having a phase shifter pattern with one light, and a light transmitted from the phase shift mask by an imaging lens. A means for forming an image of the phase shift mask at a position conjugate with the phase shift mask, a means for illuminating the other light at an angle at a position conjugate with the phase shift mask, and an interference fringe signal at the position. Means for detecting, and means for measuring the phase amount of the phase shifter from the phase difference between the interference fringe signals at multiple points where the phase difference of the phase shifter is different,
An apparatus for inspecting a phase shift mask, comprising means for judging the quality of a phase shift mask from the detected phase amount. 3. A phase shift mask having a phase shifter pattern, wherein coherent light is branched, one of the lights is irradiated on the phase shift mask, and transmitted light from the phase shift mask is passed through an imaging lens. A phase shift mask image is formed at a position conjugate with the phase shift mask, and the other light is illuminated at an angle at a position conjugate with the phase shift mask at an angle to cause interference, and a plurality of points having different phase differences of the phase shifter. Measuring the phase shifter phase amount from the phase difference between the interference fringe signals. 4. A means for branching coherent light, a means for irradiating one light to a phase shift mask having a phase shifter pattern, and a light transmitted from the phase shift mask by an imaging lens. A means for forming an image of the phase shift mask at a position conjugate with the phase shift mask, a means for illuminating the other light at an angle at a position conjugate with the phase shift mask, and an interference fringe signal at the position. An apparatus for measuring a phase shift mask, comprising: means for detecting; and means for measuring the phase amount of a phase shifter from the phase difference between interference fringe signals at a plurality of points where the phase shifter has a different phase difference. 5. The phase shift mask inspection method according to claim 1, wherein an average phase amount of the phase shifter is measured from the interference fringe signal. 6. A phase shift mask inspection method according to claim 1, wherein a local phase shift of said phase shifter is measured from said interference fringe signal. 7. A phase shift mask inspection apparatus according to claim 2, further comprising means for measuring an average phase shifter phase amount from said interference fringe signal. 8. A phase shift mask inspection apparatus according to claim 2, further comprising means for measuring a local phase shift of said phase shifter from said interference fringe signal. 9. The phase shift mask measuring method according to claim 1, wherein the average phase amount of the phase shifter is measured from the interference fringe signal. 10. A phase shift mask measuring method according to claim 1, wherein a local phase shifter phase amount is measured from the interference fringe signal. 11. A phase shift mask measuring apparatus according to claim 2, further comprising means for measuring an average phase shifter phase amount from said interference fringe signal. 12. A phase shift mask measuring apparatus according to claim 2, further comprising means for measuring a local phase shifter phase amount from said interference fringe signal. 13. A mask having a phase shifter pattern, wherein light having a coherent light and light having a slightly different wavelength from the light are combined and irradiated onto the mask, and transmitted light from the mask is conjugated with the mask. A phase shifter that photoelectrically converts light at a plurality of points having different phase differences of a phase shifter, measures a phase shifter phase amount from a phase difference of the photoelectrically converted signal, and determines whether a phase shift mask is good or not. Mask inspection method. 14. A method according to claim 13, wherein the light having a coherent light and the light having a slightly different wavelength from the light are combined and then divided into two, and one of the two is irradiated on the mask, and the transmitted light from the mask is transmitted through the mask. The phase shifter unit photoelectrically converts the light of the phase shifter unit at a position conjugate with the other, photoelectrically converts the other light, measures the phase amount of the phase shifter from the phase difference of the photoelectrically converted signal, and determines the quality of the phase shift mask Inspection method for shift mask.