JPH07104458A - Transmission factor measuring method and device - Google Patents

Abstract

PURPOSE:To provide a measuring method and a measuring device for a transmission factor in a translucent zone, regarding a such member as a half-tone type phase shift photomask having both of a translucent zone for fine phase shift and a transparent zone. CONSTITUTION:Two beams having the prescribed coherent wavelength of equal amplitude and phase are respectively transmitted through a fine translucent zone and a transparent zone in the vicinity thereof and, then, made to interfere with each other. Thereafter, coherent light available therefrom is adjusted, thereby obtaining a maximum value Imax and a minimum value Imin for the intensity of the coherent light. Then, a light transmission factor in the translucent zone is expressed as an intensity ratio, using a transmission factor in the transparent zone as reference, based upon both of the maximum and minimum values.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to measurement of transmittance in a minute area, and particularly, in a photomask used as a projection original plate in a lithographic process for manufacturing a semiconductor element, a phase difference The present invention relates to an apparatus for measuring the relative transmittance of a half-tone type phase shift photomask having a transmittance-controlled phase shift pattern to a transparent region of a semi-shielded region.

[0002]

2. Description of the Related Art In recent years, with the high integration of semiconductor integrated circuits, further miniaturization has been required for reticles used in the fabrication of these circuits. Currently 1
The line width of a device pattern transferred from a 5 × reticle for a 6M DRAM is as fine as 0.6 μm.
In the case of a 64M DRAM device pattern, 0.
The resolution of a line width of 35 μm is required, and the conventional optical exposure method using a stepper has reached the limit. Therefore, the resolution of the device pattern transferred from the reticle in light exposure can be improved, and attention has been paid to a phase shift photomask of a system that can be used in the current stepper. The phase shift photomask is disclosed in JP-A-58-17344 and JP-B-62.
Although the basic idea and principle have already been described in No. 59296, the merit of continuing the existing optical exposure system as it is is reviewed, and development of various types of phase shift photomasks is actively studied. It's starting to happen. A halftone type phase shift photomask as shown in FIG. 2 is one of them. The halftone type has recently attracted attention because of its simple manufacturing method, and details are described in JP-A-4-136854 and the like. In the case of this halftone type phase shift photomask, it is necessary to control the phase difference with respect to the transparent region for the light of a predetermined wavelength used for transfer for the semitransparent region that also serves as the shifter portion and the semi-shielding portion. Moreover, it is necessary to control the light transmittance. For this reason, in the case of the halftone type phase shift photomask, it has become necessary to directly and accurately measure the phase difference and the transmittance with respect to the transparent region in the fine micron-order pattern portion. . In order to meet the demand, there is Japanese Patent Application No. 4-278737 of the present inventor's application for the phase difference measurement for a transparent region in a fine micron-order pattern portion, but for the measurement of the transmittance, At present, there is no one that can meet this demand. In particular, recently, with the demand for high dimensional accuracy of the photomask, the plate thickness of the photomask has become large, which makes further miniaturization in the transmittance measurement difficult. Conventionally, in a commonly used transmittance measuring apparatus having a spectroscopic optical system, the size of the measurement region in the sample to be measured is limited to a spot having a diameter of about 1 mm due to design restrictions of the optical system. Since it is difficult to measure the transmittance of a fine pattern of the order of microns, the transmittance of the phase shift photomask in the semi-shielded area is measured using a transmittance measuring device with this spectroscopic optical system, and after pattern formation. By measuring in a large area other than the fine pattern, the value at the required wavelength was obtained from this.

[0003]

Under the above circumstances, the present invention provides a transparent region for light having a predetermined wavelength and a semi-transparent region for giving a phase difference to the transparent region for transmitted light having the predetermined wavelength. The present invention provides a method and apparatus for measuring the light transmittance of a member having the same in a semi-transparent region, and in particular, a method and apparatus for measuring the transmittance of a minute semi-transparent area in a halftone type phase shift photomask. Is provided.

[0004]

The transmittance measuring method of the present invention is a member having a transparent region for light of a predetermined wavelength and a semi-transparent region for imparting a phase difference to the transparent region of transmitted light of the predetermined wavelength. Of the light transmissivity at a predetermined wavelength of the micro semi-transparent region, in the vicinity of the micro translucent region, represented by a light intensity ratio based on the transmitted light of the transparent region, a method for measuring relative transmissivity, Two light fluxes having the same amplitude and phase and a coherent predetermined wavelength, which pass through the minute semitransparent region and the transparent region near the minute semitransparent region, respectively, and then pass through the minute semitransparent region. And the light flux after passing through the transparent region in the vicinity of the minute semi-transparent region are interfered with each other to adjust the phase of the obtained interference light, thereby obtaining the maximum value I _max and the minimum value I _min of the intensity of the interference light. And obtain the relative transmittance from these two values It is. Specifically, this maximum value I
_The value of _max and the minimum value I _min , and (I _max −I _min ) / (I
_max + I _min ) = 2 (a) ^1/2 / (1 + a), the relative transmittance a is calculated by arithmetic processing, or the maximum value I _max and the minimum value I _min are calculated. At this time, the light intensity I _{0 of the} transparent region near the minute semi-transparent region and a =
The relative transmittance a is obtained from the relational expression of (I _max + I _min ) / 2I ₀ −1. Regarding the light intensity I ₀ of the transparent area near the minute semi-transparent area, the two light beams after passing through the transparent area near the minute semi-transparent area are caused to interfere with each other, and the phase of the interference light thus obtained is adjusted. It is also possible to obtain the maximum value 4I ₀ of light intensity and obtain I ₀ from this value. In particular,
In the halftone type phase shift photomask,
As shown in FIG. 2, in a minute area, the light flux A having a predetermined wavelength after passing through the semi-shielded area and the light flux B having the above-mentioned predetermined wavelength after passing through the transparent area are caused to interfere with each other, and the phase of the obtained interference light is adjusted. Thus, the maximum value and the minimum value of the intensity of the interference light are obtained, and the relative transmittance is obtained from this value and the light intensity of the transparent area at that time. The transmittance measuring device of the present invention is a member having a transparent region for light having a predetermined wavelength and a semi-transparent region for imparting a phase difference to the transparent light for transmitted light having the predetermined wavelength, and a predetermined wavelength of a minute semi-transparent region. Is a device for measuring relative transmittance, in which the light transmittance in the above is represented by a light intensity ratio based on the transmitted light in the transparent area in the vicinity of the minute semi-transparent area, and a mercury lamp light source and a filter extracting only a single wavelength. A linearly polarized light supplying means for supplying linearly polarized light of the predetermined wavelength, and a birefringence separating means for separating the linearly polarized light into two light beams having different polarization directions,
A single condenser lens system that irradiates the projection original plate with each of the two light fluxes, a single lens system that forms the pattern image by the two light fluxes, and the two light fluxes that have passed through the objective lens Birefringent coupling means for recombining;
Phase difference adjusting means for changing the phase difference of the light beam, and detection for measuring the contrast of the pattern of the light beam recombined by the birefringence coupling means in correspondence with the adjustment by the phase difference adjusting means. And a calculation processing unit that performs a calculation process on the measured value. In particular, the transmittance measuring apparatus of the present invention is a phase shift photomask having a phase shift pattern with controlled phase difference and transmittance,
It is possible to measure the transmittance of the semi-shielded shifter pattern area as the relative transmittance of the semi-shielded area to the transparent non-patterned area in the vicinity of the shifter pattern area. And a polarizer at a single wavelength, i-line 365 nm,
A linearly polarized light supplying means for supplying linearly polarized light, and a birefringence separating section for separating the linearly polarized light into two light beams having different polarization directions,
A lens for projecting the two light beams onto the pattern to be measured, an objective lens for forming an image of the two light beams transmitted through the pattern to be measured, a birefringent coupling part for recombining the two light beams transmitted through the objective lens, and the two light beams The apparatus is provided with a phase difference adjusting section for changing the phase difference of the above, and a detecting section and a calculating section for measuring the contrast of the interference pattern of the two light fluxes. In this device, an interference pattern is generated with a certain width adjacent to the pattern edge of the pattern to be measured after the two light beams are combined, corresponding to the distance on the sample of the two light beams separated by the birefringence. The phase difference plate that adjusts the contrast of this interference pattern maximizes the light intensity of the interference pattern,
The minimum value can be measured and calculated.

The measuring principle of the present invention is as follows.
When the measurement light having linearly polarized light is birefringently separated into two light beams, the polarization planes thereof are different by 90 °. When the two light fluxes are recombined after passing through the sample, interference occurs, and the pattern image changes brightly and darkly to form interference fringes. The light intensity I of the interference fringes is 1 and 2 after the sample is transmitted.
Intensity of each of I ₁ , I ₂ and light wave of E
_1, when _{E 2, E 1 = A 1} exp (-2πω 1 t) E 2 = A 2 exp than be expressed as (-2πω ₂ t), I = [E ₁ + E _2] ² = [A ₁ exp (-2πω
₁ t) + A ₂ exp (−2πω ₂ t)] ² = A ₁ ² +
A ₂ ² + 2A ₁ A ₂ cos (Δφ), where Δφ is the phase difference according to the position at which the interference fringes of the two light beams are observed and the optical path, I = I ₁ + I ₂ +2 [(I ₁ × I ₂ )] ^1/2 cos (Δφ) (1) The intensity I is maximum (bright) at cos (Δφ) = 1, cos
It becomes the minimum (dark) when (Δφ) = − 1. Normally, Δφ = 0 °
Is the maximum (bright), and Δφ = 180 ° is the minimum (dark). Therefore, the light intensity I ₁ of the light flux 1 and the light flux 2 that pass through the transparent region
When the light flux 2 has the same light intensity I ₂ and passes through the transparent region of the sample, the phase adjusting unit is changed to record the values at which I becomes maximum (I _max ) and minimum (I _min ). At this time, I ₁ = I ₂ = I ₀ , and from (1), I _max = 4I ₀ (2) I _min = 0 Then, the light flux 1 is allowed to pass through the transparent area, and the light flux 2 is left in the semi-shielded area. When the position of the sample is set so as to pass through, an interference pattern having a light intensity corresponding to a is generated at the edge portion of the semi-shielding pattern. At this time as well, the phase adjustment unit is changed and the values at which I becomes maximum (I _max ) and minimum (I _min ) are recorded. Where the relative transmittance is
, I ₂ = aI ₁ (a: relative transmittance, 0 <a ≦ 1) If defined as (3), the light intensity of the light flux 1 transmitted through the formula (1) and the transparent region is I ₁ = I _{0 Therefore} , I _max = [1 + a + 2 (a) ^1/2 ] I ₀ (4) I _min = [1 + a-2 (a) ^1/2 ] I ₀ (5) When the contrast C is defined by the following equation, C = ( I _max −I _min ) / (I _max + I _min ) (6) From equations (4), (5) and (6), C = 2 (a) ^1/2 / (1 + a) (7) Further, the relative transmittance a is represented by a = (I _max + I _min ) / 2I ₀ −1 (8), and eventually I _max and I from the equations (6) and (7).
The value of _min , or I _max , I _min , and I from equation (8)
_The relative transmittance a can be obtained from the value of ₀ . As described above, the transmittance measurement of the present invention is performed by measuring the above-mentioned I _max and I _min when the sample position is set so that the light flux 1 passes through the transparent region and the light flux 2 passes through the semi-shielded region, or I _max, as the measurement of I _min, the light beam 1 is a transparent region, with the I ₀ from the measurement of the I _max in the case of setting the sample position so that the light beam 2 is also transmitted through the transparent region, the relative transmission a Is to seek.

[0006]

According to the transmittance measuring method of the present invention, by adopting such a constitution, the transmittance of a microscopic semi-light-shielding area (pattern area) such as a halftone type phase shift photomask can be measured. Using a transparent region (non-patterned region) near the semi-shielded region as a reference, it is possible to directly measure at that position at a wavelength used for transfer such as i-line 365 nm. The transmittance measuring device of the present invention comprises a linearly polarized light supply means for supplying linearly polarized light of a predetermined wavelength, which comprises a mercury lamp light source, a filter for extracting only a single wavelength, and a polarizer, and the linearly polarized light having different polarization directions. It has a birefringence separating means for separating it into two light beams, and produces two light beams with good coherence. Further, by using the contrast detector, it is possible to easily find the maximum and minimum values of the intensity of the interference light in correspondence with the phase difference adjustment of the two light fluxes. After all, with such a configuration, it is possible to easily measure the transmittance in a minute region having a width of the order of microns.

[0007]

EXAMPLES Examples of the transmittance measuring method of the present invention will be described below with reference to the drawings. 1 is a schematic view of a measuring apparatus, FIG. 2 is a sectional view of a region including a semi-shielding pattern portion in a halftone type phase shift photomask, and the halftone type phase shift photomask shown in FIG. 2 is used as a measurement sample. The transmittance of the translucent pattern area was measured using the apparatus of No. 1. First, a halftone type phase shift photomask, which is a measurement sample, is attached to the XYZ stage 1 of FIG.
Then, the stage 15 is moved to determine a predetermined position to be measured. Then, the amplitude transmitted through the objective lens 5,
As shown in FIG. 2, two light fluxes having the same phase and coherent wavelengths and having coherence are passed through the semitransparent pattern area 21 and the adjacent transparent pattern area 22, respectively, and the light flux A and the light flux B which have respectively passed therethrough. Rejoin. The interference pattern image of the recombined light is photographed by the image pickup tube 12, and 2
The light intensity was measured on a 56-tone TV monitor.
The measured values are displayed in the range of levels 0 to 255. Since the phase change amount due to the phase shifter layer is added to the intensity of this interference pattern, the phase adjusting plate 9 measures the maximum and minimum values of the optical intensity of the interference pattern,
The relative transmittance of the non-pattern area and the shifter pattern area of the measurement sample was calculated by arithmetic processing.
In the sample of FIG. 2, the luminous flux A transmitted through the transparent area
And the maximum value I _max of the light intensity of the interference pattern of the light flux B transmitted through the semi-shielded region is 95, and the minimum value I _min is 30, the relative transmittance is 7.9%. I was able to. Hereinafter, the measuring device used for the above measurement will be described in detail with reference to FIG. In order to perform measurement at the i-line (365 nm), the high-pressure mercury lamp 1 and the interference filter 2 are used as the light source, and the light source for supplying the single-wavelength i-line (365 nm) is used.
m) linearly polarized light. Then, the Nomarski prism 4 separates the two light beams with different polarization directions, and the x50 ultraviolet objective lens 5 separates the two light beams into the sample 6 to be measured.
Projected on. At this time, the shearing amount of the two light fluxes on the measured sample 6 was 0.5 μm. The sample 6 is X so that any pattern of the sample 6 to be measured can be measured.
It is installed on the YZ stage 15. The same ultraviolet objective lens as the inspection light projection lens is used for the ultraviolet light objective lens 7 that forms two light beams that have passed through the pattern to be measured, and that is used for two light beam separation to recombine the two light beams that have passed through the objective lens. The Nomarski prism 8 having the same shear ring amount was used. The phase adjusting unit 9 and the analyzer 10 are rotated to obtain an interference pattern image of the same component of the polarization planes of the two light fluxes, and the linear polarization plane is selected. This interference image is projected by the magnifying lens 11 onto the image pickup tube 12 that is sensitive to ultraviolet rays, and the light intensity is set to 2 in the image processing unit 13 for measuring the contrast.
Measure with 56 gradations. The value obtained by the measurement is arithmetically processed by the arithmetic processing unit 14 to obtain the relative transmittance.

[0008]

With the above-described structure, the transmittance measuring method and apparatus of the present invention enable the transmittance measurement in a minute area, and is a halftone type phase shift photometer. It is possible to measure the transmissivity of the semi-transparent part of the fine pattern in Fuku.

[Brief description of drawings]

FIG. 1 is a schematic view of an apparatus according to an embodiment of the present invention.

FIG. 2 is a sectional view of the sample to be measured in the example of the present invention.

[Explanation of symbols]

 1 High-pressure mercury lamp 2 Interference filter 3 Polarizer 4 Nomarski prism 5 Ultraviolet objective lens 6 Sample to be measured 7 Ultraviolet objective lens 8 Nomarski prism 9 Phase adjusting plate 10 Analyzer 11 Magnifying lens 12 Image pickup tube 13 Image processing unit 14 Arithmetic processing unit 15 XYZ stage A semi-transparent pattern area transmitted light flux B transparent non-pattern area transmitted light flux 21 semi-transparent pattern area 22 transparent non-pattern area

Claims (7)

[Claims] 1. A light transmittance at a predetermined wavelength of a minute semitransparent region of a member having a transparent region for a light of a predetermined wavelength and a semitransparent region for giving a phase difference between the transmitted light of the predetermined wavelength and the transparent region. Is a method for measuring relative transmittance, which is represented by a light intensity ratio based on transmitted light in a transparent region in the vicinity of the minute semi-transparent region, and has a predetermined wavelength with equal coherence and amplitude and phase. After passing through the minute semitransparent region and the transparent region in the vicinity of the minute semitransparent region, the light fluxes after passing through the minute semitransparent region and the transparent region in the vicinity of the minute semitransparent region are Interferes with the light flux after passing,
By adjusting the phase of the obtained interference light, the maximum value I _max and the minimum value I _min of the intensity of the interference light are obtained, and the relative transmittance is determined from these two values, the transmittance measuring method. . 2. The binary value of the maximum value I _max and the minimum value I _min of the intensity of the interference light according to claim 1, and (I _max −I _min ).
A transmittance measuring method characterized in that the relative transmittance a is obtained by a calculation process from a relational expression of / (I _max + I _min ) = 2 (a) ^1/2 / (1 + a). 3. The binary value of the maximum value I _max and the minimum value I _min of the intensity of the interference light, the light intensity I ₀ of the transparent region transmission near the minute semi-transparent region at this time, and a = (I
A transmittance measuring method, characterized in that a relative transmittance a is obtained by arithmetic processing from a relational expression of _max + I _min ) / 2I ₀ −1. 4. The interference light obtained according to claim 3, wherein the transmitted light intensity I ₀ in the transparent region in the vicinity of the minute semi-transparent region is caused to interfere with two light beams after passing through the transparent region in the vicinity of the minute semi-transparent region. A transmittance measuring method characterized in that a maximum value 4I ₀ of the intensity of interference light is obtained by adjusting the phase, and the maximum value 4I ₀ is obtained from this value. 5. The member to be measured according to claim 1, wherein the member to be measured is a halftone type phase shift photomask, and the transmittance at a predetermined wavelength of the semi-shielded region of the photomask is represented by a light intensity ratio with the transparent region. A method for measuring transmittance, which is expressed as relative transmittance. 6. A light transmissivity at a predetermined wavelength of a minute semitransparent region of a member having a transparent region for light of a predetermined wavelength and a semitransparent region for imparting a phase difference between the transmitted light of the predetermined wavelength and the transparent region. In the vicinity of the minute semi-transparent region, which is represented by a light intensity ratio based on the transmitted light in the transparent region, which is a relative transmittance measuring device, wherein a mercury lamp light source, a filter for extracting only a single wavelength, and a polarizer are provided. A linearly polarized light supplying means for supplying linearly polarized light of the predetermined wavelength, a birefringence separating means for separating the linearly polarized light into two light beams having different polarization directions, and the two light beams to the projection original plate, respectively. A single condenser lens system for irradiating, a single lens system for forming the pattern image by the two light fluxes, a birefringence coupling means for recombining the two light fluxes passing through the objective lens, and the two light fluxes Phase of A phase difference adjusting means for changing the difference, and a detector for measuring the contrast of the pattern of the light beam recombined by the birefringence combining means, corresponding to the adjustment by the phase difference adjusting means, A transmittance measuring device, comprising: an arithmetic processing unit that arithmetically processes measured values. 7. The i-line 36 according to claim 6, wherein the predetermined wavelength is i-line.
A transmittance measuring device having a thickness of 5 nm.