JPH07243982A - Photo-mask inspecting device and inspecting method - Google Patents

Abstract

PURPOSE:To provide a photo-mask inspecting device and an inspecting method imaging the pattern of desired phase and transmittance by providing a measuring means of the phase, amplitude transmittance, and energy transmittance. CONSTITUTION:A linearly polarized beam passes through a contraction optical system 103, and it is split in two by a splitting means. One beam rotated 90 deg. in the beam polarization direction or the other unrotated beam passes through a photo-mask 109 to be inspected, then both beams are synthesized, and the change quantities of the transmittance and phase are obtained by an analyzer 113 and a light intensity detector 114.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photomask inspecting apparatus and method for inspecting a structural defect in a shape or a thickness direction of a pattern in a photomask plane used for a lithography technique.

[0002]

2. Description of the Related Art With the miniaturization of patterns of semiconductor integrated circuits and the like, high resolution of reduction projection exposure apparatuses used in lithography technology has been attempted. One way to do this is to form a chromium film on the glass substrate, which is usually used and has a thickness that absorbs almost all of the exposure light, and then replace it with a transparent mask instead of a photomask. A technique using a photomask which gives a phase difference to light passing through the photomask or a photomask which gives a pattern part a certain degree of transparency and phase change is in the spotlight. The technique of using a photomask that gives the improved former phase difference is called a phase shift technique, and it is from page 103 to page 1 of the monthly issue of Nikkei Microdevices, July 1990.
It is disclosed on page 14 and JP-A-58-173744. Further, the technique of using the latter photomask, which is improved to give the transparency and the phase change in the pattern portion, is described in the J4 paper at the 36th International Symposium on Electron / Ion / Photon Beam, JP-A-4-136854 and Japanese Patent Laid-Open No. It is disclosed in Kaihei 4-162039.

These techniques using the improved photomask are techniques for improving the light intensity distribution on the image plane obtained as a result of the interference of light from various parts of the photomask. The description will be made in comparison with the case where the photomask of (1) is used. FIG. 4A shows an amplitude distribution when a line / space pattern is imaged using a normal photomask. The dotted line shows the amplitude distribution of the transmitted light from each space, and the solid line shows the amplitude distribution as a result of interference. The light intensity distribution is the square of the amplitude distribution shown by the solid line. FIG. 4B is an explanatory diagram when a phase shift photomask is used. The shaded portion is a light-shielding pattern, and the pattern provided between the two central light-shielding patterns is a pattern for shifting the phase. Figure 4
Similar to (a), the dotted line shows the amplitude distribution of the transmitted light from each space, and the solid line shows the amplitude distribution as a result of interference. The light intensity distribution is the square of the amplitude distribution shown by the solid line. As is apparent from FIGS. 4A and 4B, in the normal photomask, the diffracted light from the adjacent transmissive portions are superposed in the same phase, so that the light intensity of the light shielding portion does not become 0, but the phase shift photomask Then, since the diffracted lights from the adjacent transmission parts are superimposed in the opposite phase, the light intensity of the light shielding part becomes zero. As a result, the phase shift photomask can improve the image contrast.

It should be noted here that the more the phase difference between the light from the adjacent transmitting portions deviates from π, the more the light transmitted through the phase shift member due to absorption of the phase shift member. That is, the greater the decrease in the amplitude of, the less the contrast improvement effect. Furthermore, unless the pattern for shifting the phase is formed in a desired shape at a desired position, the desired effect of improving the contrast cannot be obtained.

Although the phase shift mask has been described above as an example, the contrast improving effect decreases as the transmittance of each part of the photomask and the amount of phase change received by light passing therethrough deviate from a predetermined value. What to do is
This is a phenomenon common to other improved photomasks. Similarly, if the pattern in which the phase and the transmittance are controlled is not formed at a desired position and in a desired shape, the expected effect of improving contrast cannot be obtained.

[0006]

As described above, in the improved photomask, it is extremely important to control the phase and transmittance of the transmitted light in each part. Further, it is important that each pattern of the photomask is formed in a desired shape at a desired position with a controlled position and transmittance.

Here, the phase, amplitude transmittance and energy transmittance can be controlled by controlling the thickness of each material if the refractive index and the extinction coefficient of each material used for manufacturing the photomask are accurately known. However, it is often difficult to accurately measure the refractive index and extinction coefficient of each material, and impurities are mixed into each material during the manufacturing process, resulting in an error in the refractive index and the extinction coefficient. In addition, manufacturing tolerances are always associated with the thickness of each material. Therefore, a desired photomask is realized by repeating the steps of actually measuring the phase, amplitude transmittance, and energy transmittance of each part of the manufactured photomask and feeding the results back to the manufacturing process. However, there is a problem that there is no effective means for measuring the phase / amplitude transmittance / energy transmittance. In addition, each pattern of the photomask has a controlled phase and transmittance,
In order to confirm that the pattern is formed in the desired shape at the desired position, only the phase and transmittance pattern of interest are imaged, or the phase and transmittance pattern of interest are emphasized and imaged. However, there was a problem that the technology was not available.

An object of the present invention is to obtain a simple and accurate measuring means for phase, amplitude transmittance and energy transmittance, and image only the phase and transmittance patterns of interest, or emphasize these patterns. It is to obtain a photomask inspection apparatus and an inspection method for forming an image.

[0009]

The above object is to provide a means for generating a linearly polarized beam, a means for reducing the cross-sectional area of the beam, a means for dividing the reduced beam into two, and one of the divided beams. A means for rotating the polarization direction of the beam by 90 degrees and a photomask to be inspected are installed in the beam having any one of the polarization directions, and the photomask is moved in a plane perpendicular to the beam without hindering the progress of the beam. A stage, means for synthesizing the beam of the polarization direction rotated by 90 degrees and the other beam of the polarization direction which does not rotate, a rotatable analyzer and a light intensity detector provided in the optical path of the synthesized light. Achieved by

The means for reducing the cross-sectional area of the linearly polarized beam reduces or increases the cross-sectional area, and
It is a means for shaping the cross-section into a desired shape, and the beam divided into two reduces or expands the cross-sectional area, and
By having a beam whose cross section is shaped into the desired shape,
Further, the means for shaping the beam cross section into a desired shape is achieved by arranging cells made of a substance whose transmittance can be controlled by an external signal in a two-dimensional array.

Further, the above-mentioned object is to make a linearly polarized beam into two beams.
Into a first linearly polarized light having a first polarization direction and a second linearly polarized light having a second polarization direction different from the first polarization direction. The inspection target pattern in the inspection target mask is irradiated with one of the linearly polarized lights, and the linearly polarized light that has passed through the inspection target mask and the other linearly polarized light that does not pass through are combined to form combined light, and the phase change from the combined light In the method of inspecting a photomask for determining the amount and the energy transmittance, it is achieved by moving the mask to be inspected and stopping it at a predetermined position, and repeatedly measuring the amount of phase change and the energy transmittance from the combined light. In addition, the combined light is adjusted to the linearly polarized light by adjusting the optical path length of the first or the second linearly polarized light, and the mask to be inspected is continuously moved with the analyzer held at a specific angle. Yo Further, the irradiation of the inspection target pattern in the inspection target mask is performed by reducing or expanding the beam cross-sectional area and shaping the cross section into a desired shape or the shape of the inspection target pattern, and then dividing the beam into two. The linearly polarized light is achieved by moving the mask to be inspected, stopping it at a predetermined position, and irradiating it.

[0012]

According to the present invention, the linearly polarized light is divided into two parts to pass through two different optical paths, and linearly polarized lights having polarization directions orthogonal to each other in a plane perpendicular to the traveling direction are obtained. A photomask to be inspected is installed in the optical path of one of the linearly polarized lights, and the linearly polarized light that has passed through the above photomask and the linearly polarized light that does not pass through the other photomask are combined into a combined light, but they are superimposed. The combined light is generally elliptically polarized.

By measuring the polarization state of the elliptically polarized light formed by the linearly polarized light that has passed through the inspection target portion on the photomask and the linearly polarized light that has not passed through the photomask,
It is possible to calculate the amplitude transmittance or the energy transmittance of the inspection target portion, and to obtain the phase change amount due to the light passing through each part of the photomask. Further, the two-dimensional distribution of the phase and the transmittance can be obtained by repeating the above measurement while sequentially moving the photomask.

[0014]

Embodiments of the present invention will now be described with reference to the drawings. 1 is a diagram showing a first embodiment of a photomask inspection apparatus according to the present invention, FIG. 2 is a diagram showing a second embodiment of the present invention, and FIG. 3 is a diagram showing a third embodiment of the present invention.

First Embodiment In FIG. 1 showing a first embodiment of the present invention, 101 is a laser for generating unpolarized light, 102 is a polarizer, 10
3 is a reduction optical system, and 104 is a beam splitter. The laser light linearly polarized by the laser 101 and the polarizer 102 becomes a beam having a small cross-sectional area by the reduction optical system 103, and is split into two optical paths by the beam splitter 104 to become a beam 105 and a beam 106. 107a and 107b are total reflection mirrors, 108 is a half-wave plate, and the polarization plane of the beam 105 is rotated by the half-wave plate 108 in a direction orthogonal to the beam 106. Reference numeral 109 is a photomask to be inspected, 110 is a stage, 111 is a drive circuit for the stage 110, and the photomask 109 is the stage 110 and its drive circuit 111.
Move in a plane perpendicular to 6. Reference numeral 112 denotes a half mirror that superimposes the beam 105 and the beam 106 that has passed through the inspection target photomask 109 to form a combined light. 113
Is a rotatable analyzer, and 114 is a light intensity detector which is installed on the optical path of the combined light. Reference numeral 115 is a computer for controlling the analyzer 113, the light intensity detector 114, and the stage 110.

If the linear polarization direction of the beam 106 passing through the photomask 109 to be inspected is the x direction and the linear polarization direction of 105 passing through the half-wave plate 108 is the y direction, the beam 106 will have a phase delay in the half mirror 112. δ
_x , and the phase delay of the beam 105 is δ _y , the time-varying functions E _x and E _y of the linearly polarized light intensity in the x direction and the y direction
Are as follows:

[0017]

[Equation 1]

[0018]

[Equation 2]

Where a _x and a _y are the amplitudes of the above E _x and E _y ,
t is the time measured from the reference time, and ω is the beam 1
The angular frequencies of 05 and 106 are shown. Δ _x and δ _y are in the x direction and y
3 shows the initial phase of linearly polarized light in the direction. The beam 106 that has passed through the photomask to be inspected and the half-wave plate 10
The combined light obtained by overlapping the beam 105 that has passed through 8 is

[0020]

[Equation 3]

[0021] However

[0022]

[Equation 4]

It is A _x , a _y in the above formula (3),
δ is the first of Applied Optics
It was determined by the method described on page 201 of Volume 3 (1962). That is, as shown in FIG. 1, the analyzer 113 is installed perpendicularly to the optical axis, and 1 / n is provided around the optical axis.
Rotation × n times = 1 rotation (n is an integer), and the output of the light intensity detector 114 at each analyzer tilt is read. The i-th rotation of the analyzer 113 (i = 1, 2, 3, ... N)
At the time, the direction of the analyzer is (360 ° / n) × i = with respect to the reference direction assumed in the plane perpendicular to the optical axis.
The output when α _i (n is an integer) is I _i, and k ₀ = (1 /
n) ΣI _i , k ₁ = (2 / n) ΣI _i cos2α _i , k ₂ = (2
From / n) ΣI _i sin2α _i, the determined k _0, k _1, k _2, respectively, can be determined from the equation δ and a _x Hatsugi, a _y can also be determined similarly.

[0024]

[Equation 5]

[0025]

[Equation 6]

Now, when δ, a _x when the photomask 109 to be inspected is not installed on the stage 110 are expressed as δ ′, a _x ′, the amount of phase change caused by the beam 106 passing through the photomask 109. Δδ
And energy transmittance T is

[0027]

[Equation 7]

[0028]

[Equation 8]

It is calculated by Therefore, the photomask 1
09 is set on the stage 110, δ ′ and a _x ′ are obtained, and then the photomask 109 is set on the stage 11
Set it to 0. The control computer 115 issues a command to the drive circuit 111 to control the stage 110 so that the measurement starting portion of the photomask 109 overlaps the beam 106, and the stage 1 is controlled at that position.
Stop 10. After that, δ and a _x are obtained, and (7)
The phase change amount Δδ and the energy transmittance T are calculated by the equation and the equation (8). Subsequently, the control computer 115 issues a command to the drive circuit 111 to control the stage 110 so that the position where the next measurement of the inspection target photomask 109 is to be performed overlaps the beam 106, and the stage 11 is controlled at that position.
Stop 0. Then, δ and a _x are obtained and the above Δδ and T are calculated by the equations (7) and (8). By repeating the above procedure, the transmittance distribution and the phase change amount distribution of the inspection target photomask 109 are obtained. By comparing the designed transmittance distribution and the phase change amount distribution of the photomask 109 with the two distributions actually obtained by the present invention, defects and the like caused by the manufacturing of the photomask become clear. Further, if a certain range is provided for the value of the transmittance or the amount of phase change and only the portion showing the measured value included in the range is displayed, only the pattern of the desired phase or the transmittance can be imaged.

Second Embodiment In FIG. 2 showing a second embodiment of the present invention, 201 is a laser for generating unpolarized light, 202 is a polarizer, 20
3 is a reduction optical system, and 204 is a beam splitter. The laser light linearly polarized by the laser 201 and the polarizer 202 becomes a beam having a small cross-sectional area by the reduction optical system 203, and is divided into two optical paths by the beam splitter 204 to be a beam 205 and a beam 206. Become. 20
Reference numerals 7a and 207b are total reflection mirrors, 208 is a half-wave plate, and the beam 205 is rotated by the half-wave plate 208 in the direction of polarization orthogonal to the beam 206. 20
9 is a photomask to be inspected, 210 is a stage, 211 is a drive circuit for the stage 210, and the photomask 209 is moved in a plane perpendicular to the beam 206 by the stage 210 and the drive circuit 211. Reference numeral 212 denotes a half mirror that superimposes the beam 205 and the beam 206 to form a combined light. 213 is a rotatable analyzer, and 214 is a light intensity detector, which is installed on the optical path of the combined light. Reference numeral 215 is a computer for controlling the analyzer 213, the light intensity detector 214 and the stage 210. Reference numeral 216 inserted in the optical axis of the beam 205 is an optical path length adjusting device. If the polarization direction of the beam 206 is the x direction and the polarization direction of the beam 205 that has passed through the half-wave plate 208 is y, it can be handled in the same manner as in the first embodiment. Now, the desired pattern on the inspection target photomask 209 is the beam 206.
The stage 210 is controlled so as to come to a position overlapping with, and stopped at that position. Next, to measure a _x, a _y, [delta] using the above analyzer 213 and the optical intensity detector 214. At this time, if a _x , a _y , and δ are values as designed,
You can see that it is a correctly manufactured pattern. The phase delay δ _y of the beam 205 in the half mirror 212 is adjusted by the optical path length adjusting device 216, and δ in the equation (4) is 0.
Or 2π. In this case, as is clear from the equation (3), the polarization resulting from the beam 205 and the beam 206 being superposed on each other by the half mirror 212 becomes a linear polarization. The analyzer 213 is fixed in a direction orthogonal to the polarization direction of the linearly polarized light generated by overlapping. Next, the stage 210 is continuously moved. That is, considering the inspection target photomask 209, the beam 206 scans the photomask 209. When the desired pattern produced correctly comes to the position of the beam 206, its output becomes 0 because no light is incident on the light intensity detector 214. A desired pattern that is not manufactured correctly or an undesired pattern may be the beam 206.
When the position is reached, light is incident on the light intensity detector 214 and its intensity is detected. Therefore, by displaying only the portion of the output 0 of the light intensity detector 214, only the correctly manufactured desired pattern is imaged. Defects can be detected when compared with the shape of the desired pattern in the design stage.

Third Embodiment In FIG. 3 showing a third embodiment of the present invention, 301 is a laser which emits polarized light, 302 is a scaling optical system, and 30
3 is a beam shaping system, and 304 is a beam splitter.
The laser light emitted as linearly polarized light from the laser 301 becomes a beam with a large cross-sectional area by the expansion / contraction optical system 302,
The beam shaping system 303 shapes the cross-sectional shape into a rectangle,
Beam 305 and beam 306 at beam splitter 304
It is divided into two. 307a and 307b are total reflection mirrors, 308 is a half-wave plate, and the beam 305 is rotated by the half-wave plate 308 in a direction orthogonal to the beam 306. Reference numeral 309 is a photomask to be inspected, 310 is a stage, 311 is a drive device for the stage 310, and the photomask 309 is the stage 310 and its drive device 3.
11 moves in a plane perpendicular to the beam 306. Reference numeral 312 denotes a half mirror that superimposes the beam 306 that has passed through the inspection target photomask 309 and the beam 305 that has passed through the half-wave plate 308 into combined light. Three
Reference numeral 13 denotes a rotatable analyzer, 314 denotes a light intensity detector, which is installed on the optical path of the combined light. 315 is an analyzer 313,
It is a computer for controlling the light intensity detector 314 and the stage 310.

If the polarization direction of the beam 306 is x and the polarization direction of the beam 305 that has passed through the half-wave plate 308 is y, it can be handled in the same manner as in the first embodiment. Therefore, before the inspection target photomask 309 is installed on the stage 310, the aforementioned δ ′ and a _x ′ are obtained. Here, since a _x ′ depends on the cross-sectional area of the beam 306,
The amount per unit cross-sectional area is stored in the control computer 315, and then the photomask 309 is attached to the stage 31.
Set to 0. The control computer 3 is arranged so that the measurement starting portion of the photomask 309 overlaps the beam 306.
15 issues a command to the drive circuit 311 to output the stage 310
Is controlled, and the stage 310 is stopped at that position. At this time, since the shape of the desired pattern overlapping the beam 306 can be grasped by the control computer 315, the beam shaping system 303 is also controlled by the control computer 315 to form a beam having the same cross section. afterwards,
The above δ and a _x are obtained, and the amount per unit cross-sectional area is calculated for a _x . Based on these, the phase change amount Δδ and the energy transmittance T are calculated using the equations (7) and (8). Subsequently, the control computer 3 is controlled so that the portion of the photomask to be inspected 309 to be measured next overlaps the beam 306.
15 issues a command to the drive circuit 311 to output the stage 310.
Is controlled, and the stage 310 is stopped at that position. Then, the beam shaping system 303 is controlled so that the desired pattern overlapping the beam 306 and the cross-sectional shape of the beam 306 match, and δ and a _x are obtained, and the amount per unit cross-sectional area is calculated for a _x. To do. Next, using equations (7) and (8), Δδ and T are calculated in the same manner as above. By repeating the above procedure, the transmittance distribution and the phase change amount distribution of the photomask 309 are obtained. Comparing the designed transmittance distribution and the phase change amount distribution of the inspection target photomask 309 with both distributions actually obtained by the present invention, the defects and the like caused by the manufacturing of the photomask 309 are clarified. Become. Furthermore, if a certain range is set for the value of the transmittance or the amount of phase change, and only the part showing the measured value included in the above range is displayed, only the phase or transmittance pattern of interest is imaged. You can

In the third embodiment, the beam shaping system has been described as generating a beam having a rectangular cross section. However, if the desired pattern overlapping the beam 306 is not rectangular, the desired pattern is rectangular. You can divide it into Alternatively, if the beam shaping system 303 is configured such that cells such as liquid crystals are arranged in a two-dimensional plane and the transmittance of each cell is changed by a signal from the outside, the beam 306 that matches the shape of a desired pattern is obtained. The cross-sectional shape of can be realized.

[0034]

As described above, the photomask inspecting apparatus and method according to the present invention divides the reduced beam into two, a unit for generating a linearly polarized beam, a unit for reducing the cross-sectional area of the beam. Means, a means for rotating the polarization direction of one of the divided beams by 90 degrees, and a photomask to be inspected in the beam having one of the polarization directions, and the beam without impeding the progress of the beam. A stage moving in a plane perpendicular to the plane, means for synthesizing the beam of the polarization direction rotated by 90 degrees and the other beam of the polarization direction not rotating, and a rotatable analyzer provided in the optical path of the synthesized light. By including the light intensity detector, the transmittance and the phase change amount of each part of the photomask can be easily and accurately obtained. Further, since only a specific pattern is imaged or an image in which the specific pattern is emphasized is obtained, the shape inspection of the specific pattern can be performed. Further, if the measured thickness of the pattern is known, the refractive index, the absorption coefficient, or the extinction coefficient can be obtained from the obtained transmittance and the amount of phase change.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of a photomask inspection apparatus according to the present invention.

FIG. 2 is a diagram showing a second embodiment of the photomask inspection apparatus according to the present invention.

FIG. 3 is a diagram showing a third embodiment of the photomask inspection apparatus according to the present invention.

4A and 4B are diagrams for comparing and explaining a case using a phase shift technique and a case using a normal photomask, FIG. 4A is a diagram showing an amplitude distribution when an image is formed using a normal photomask, and FIG. FIG. 8B is a diagram showing an amplitude distribution when a phase shift photomask is used.

[Explanation of symbols]

 101, 201 Laser which emits unpolarized light 102, 202 Polarizer 103, 203 Reduction optical system 104, 204, 304 Beam splitter 108, 208, 308 Half-wave plate 109, 209, 309 Photomask to be inspected 110, 210, 310 Stage 112, 212, 312 Half mirror 113, 213, 313 Analyzer 114, 214, 314 Light intensity detector 216 Optical path length adjusting device 301 Laser emitting polarized light 302 Enlargement / reduction optical system 303 Beam shaping system

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01L 21/66 J 7630-4M C 7630-4M

Claims (6)

[Claims] 1. A means for generating a linearly polarized beam, a means for reducing the cross-sectional area of the beam, a means for dividing the reduced beam into two, and a polarization direction of one of the divided beams being rotated by 90 degrees. Means, a photomask to be inspected in a beam of any one of the polarization directions, a stage that moves in a plane perpendicular to the beam without hindering the progress of the beam, and the stage rotated by 90 degrees. An inspection device for a photomask, comprising: a means for combining a beam in a polarization direction and the other beam in a non-rotating polarization direction; a rotatable analyzer provided in the optical path of the combined light; and a light intensity detector. 2. A means for reducing the cross-sectional area of the linearly polarized beam is a means for reducing or expanding the cross-sectional area and shaping the cross-section into a desired shape. The photomask inspection apparatus according to claim 1, wherein the beam is a beam whose cross-sectional area is reduced or expanded and whose cross-section is shaped into a desired shape. 3. The means for shaping the cross section of a linearly polarized beam into a desired shape is a two-dimensional array of cells made of a substance whose transmittance can be controlled by a signal from the outside. The photomask inspection apparatus according to claim 2. 4. A linearly polarized beam is divided into two, a first linearly polarized light having a first polarization direction and a second linearly polarized light having a second polarization direction different from the first polarization direction. And irradiating the inspection target pattern in the inspection target mask with either the first or second linearly polarized light, and superimposing the linearly polarized light that has passed through the inspection target mask and the other linearly polarized light that does not pass through the inspection target mask. In the method of inspecting the photomask for obtaining the combined light and the phase change amount and the energy transmittance from the combined light, the mask to be inspected is moved and stopped at a predetermined position, and the phase change amount and the energy transmission from the combined light. A method for inspecting a photomask, which is characterized in that the measurement with the rate is repeated. 5. The combined light is adjusted to the linearly polarized light by adjusting the optical path length of the first or second linearly polarized light, and the mask to be inspected is continuously irradiated with the analyzer held at a specific angle. The photomask inspection method according to claim 4, wherein the photomask is moved. 6. The irradiation of the inspection target pattern in the inspection target mask reduces or expands the beam cross-sectional area of linearly polarized light,
5. The linearly polarized light of which the cross section is shaped into a desired shape or the shape of a pattern to be inspected, and which is then divided into two linearly polarized lights is irradiated while stopping the mask to be inspected at a predetermined position. Inspection method of the described photomask.