JPH09292347A - Foreign-material inspecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable extracting only the foreign materials, without being affected by a circuit pattern by condensing and receiving the light rays emitted from a photomask by lighting, and measuring the phase distribution or the phase differential distribution of the received light. SOLUTION: Parallel light rays 3 emitted from a light source 1 are condensed on a circuit-pattern drawing surface 6 of a photomask 4 through a half mirror HM1, lenses L3 and L2, a vibration mirror Mm and a lens L1. An optical spot is formed on a point-shaped inspecting region Pi. Then, reflected light rays 30 advance in the reverse direction through the half mirror HM1 and lens L4 and form the image at one point Pi' on an incident edge 13 of a waveguide element 2. Then, the difference of the amounts of the incident lights on two photoelectric conversion elements 16 and 17 is calculated by a differential circuit 7, and a two-dimensional difference signal Do in the x-y plane of the photomask 4 is obtained. The difference signal Do is stored in correspondence with the position of the optical beam, and the image is formed. Thus, the two-dimensional phase distribution image is obtained and can be readily discriminated as foreign materials.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foreign matter inspection apparatus, and more particularly to an apparatus for optically detecting a foreign matter on a photomask on which a circuit pattern of a semiconductor device or the like is drawn.

[0002]

2. Description of the Related Art A conventional apparatus of this type erases an image of a defect-free circuit pattern by using a bright-field transmission image and a bright-field reflection image obtained by beam scanning to detect a foreign substance.

[0003]

However, the conventional foreign matter inspection apparatus has a problem that the image of the defect-free circuit pattern cannot be completely erased.

The present invention has been made in view of such conventional problems, and provides a foreign matter inspection apparatus capable of extracting only foreign matter by simple signal processing without being affected by a defect-free circuit pattern. The purpose is to do.

[0005]

To achieve the above object, according to the present invention, there is provided a foreign matter inspection device for optically detecting a foreign matter on a photomask having a predetermined pattern drawn on only one surface. Therefore, the illumination optical system that illuminates the photomask, the condensing optical system that condenses the light rays emitted from the photomask, and the light condensed by the condensing optical system is received, and the phase distribution or phase of the received light Provided is a foreign matter inspection apparatus including a phase distribution or phase differential distribution measuring means capable of measuring a differential distribution. In this case, the illumination optical system is a reflection optical system that illuminates the photomask by the reflection illumination method,
Alternatively, it is a transmission optical system that illuminates the photomask by a transmission illumination method. Furthermore, it is preferable that the condensing optical system condenses a light beam emitted from one surface of the photomask and transmitted through the other surface of the photomask.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, an image of a circuit pattern and an image of a foreign substance are obtained by means of the phase distribution or phase differential distribution measuring means. In this case, since the circuit pattern observed from the substrate side of the photomask does not have the slope of the edge portion, it can be represented by a simple phase distribution. For this reason, a simple 2
Only the image of the circuit pattern can be erased by the digitizing circuit,
Therefore, it becomes possible to easily detect only the foreign matter.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. Referring to FIG. 1 showing a first embodiment of the present invention, a parallel light beam 3 emitted from a light source 1 including a laser and a beam expander is a half mirror HM1.
And a lens L that is arranged along the optical axis Ax2.
After passing through L3 and L2, it reaches the vibrating mirror Mm. The vibrating mirror Mm vibrates in the direction of the arrow in FIG. 1 about the rotation center Mp. The rotation center Mp is parallel to the y-axis and is positioned near the rear focal position of the objective lens L1. The light beam 3 reflected by the vibrating mirror Mm is refracted by the objective lens L1 and is condensed on the circuit pattern drawing surface 6 of the photomask 4 to form a light spot on the dot-shaped inspection region Pi.

The reflected light ray 30 reflected by the circuit pattern drawing surface 6 traces the original optical path to the half mirror HM1. The reflected light ray 30 is reflected by the half mirror HM1, refracted by the lens L4, and forms an image at a point Pi ′ on the incident end face 13 of the waveguide element 2 in which the channel waveguide is formed. The channel waveguide in the waveguide element 2 manufactured based on a predetermined design parameter includes a double mode waveguide area extending from the incident end face 13 and two single mode waveguide areas extending to the two photoelectric conversion elements 16 and 17. And a waveguide branch region that branches the double mode region into two single mode regions. The method of designing these waveguides is disclosed in, for example, Japanese Patent Laid-Open No. 20891/1992.
No. 3 describes in detail.

The difference between the amounts of light incident on the two photoelectric conversion elements 16 and 17 arranged in the waveguide element 2 is the differential circuit 7
Is calculated by The difference signal D0 has an output value proportional to the optical tilt component of the object in the point-shaped inspection region Pi in the x direction. While scanning the light spot in the x direction by the vibrating mirror Mm, the photomask holding unit RH and the driving unit R
By moving the photomask 4 in the y direction by A, a two-dimensional difference signal D0 in the xy plane is obtained.
Then, the difference signal D0 is stored in correspondence with the position of the light beam and imaged to obtain a two-dimensional phase distribution image.

Here, consider one scanning line in the x direction in the phase distribution image obtained as described above. In observing the circuit pattern drawing surface 6 of the photomask 4 of FIG. 2A, in the present invention, the incident direction of the illumination light is I1 or I2, and the observing direction is C2. This is the edge portion 5E1,5 of the circuit pattern 5.
This is to eliminate the influence of E2. Since the circuit pattern of the photomask is usually formed by photolithography,
Due to the etching process, the edge portion does not become a vertical wall surface but has an oblique inclination component. In order to avoid the influence of this inclination component, in the present invention, observation is performed from the C2 direction.

The difference signal D0 in the first embodiment is shown in FIG.
As shown in (b), at the pattern edge portion, an output having a width δ determined by the beam size and a minute signal value ± EL is centered on the zero level. The signal from the pattern edge portion represents a minute phase shift due to a metal such as chrome, and each has a rectangular shape. Therefore, as shown in FIG. 2C, the window comparator level ± TH is set and the output value is set. Is binarized to detect a signal DU0 ′ related to the foreign substance DU attached to the photomask 4 such as a light-transmitting foreign substance without detecting the signal from the pattern edge portion, and the portion DU0 ′ exceeding the window comparator level ± TH. Only can be detected. The signal of a foreign substance does not have a rectangular shape but generally has a waveform having a curved line.

The signal processing unit 8 in FIG. 1 incorporates the above-mentioned window comparator and the like, and detects only the signal of foreign matter. The computer 10 controls the signal processing unit 8, the drive unit RA, the vibrating mirror Mm, and the like to perform a foreign matter inspection.
The display 11 displays the inspection result on a map.
The interface 12 is a portion where an operator inputs an inspection area, sensitivity, etc., and the input information is supplied to the computer 10.

FIG. 3 shows a second embodiment of the present invention. While the reflection illumination method is used in the above-described first embodiment, the transmission illumination method is used in the second embodiment. The light ray 3 emitted from the light source 1 passes through the lenses L5 and L6 to become a parallel light ray, and is further reflected by the mirror M1 to the optical axis Ax1.
It becomes a ray along. The light ray 33 generated from the circuit pattern drawing surface 6 of the photomask 4 is refracted by the objective lens L1 and reaches the vibrating mirror Mm. The vibrating mirror Mm whose angle can be changed centering on the point Mp is
i is scanned in the x direction within the region where the illumination light 3 is incident. The light ray 33 is reflected by the vibrating mirror Mm, condensed by the second objective lens L2, and imaged at a point Pi ′ on the incident end face 13 of the waveguide element 2. The second embodiment is different from the above-described first embodiment only in the illumination method, and is otherwise common to the first embodiment, and therefore the description thereof will be omitted. Book second
In the embodiment, since the phase, that is, the optical path difference does not change in the metal chrome portion forming the circuit pattern 5, the signal processing becomes simpler than in the first embodiment.

FIG. 4 shows a third embodiment of the present invention. The light ray 3 emitted from the light source 1 has a polarization component parallel to the paper surface and a polarization component perpendicular to the paper surface. The polarization beam splitter PSB1 transmits a polarization component parallel to the paper surface and reflects a polarization component perpendicular to the paper surface. The light beam 3 is polarized and separated by the polarization beam splitter PSB1 and divided into a linearly polarized light beam 46 having a polarization plane parallel to the paper surface and a linearly polarized light beam 50 having a polarization plane perpendicular to the paper surface. The light ray 46 passes through the λ / 4 wave plate QW2 and becomes a clockwise circularly polarized light ray 48, which is reflected by the mirror M3, refracted by the lens L7, and condensed at the focal point of the lens L7. The half mirror HM2 near the focus of the lens L3 reflects a part of the light ray 48. The reflected light ray 48 is refracted by the lens L2 to become a substantially parallel light ray, is reflected by the vibrating mirror Mm, is refracted by the objective lens L1, and is on the inspection area Pi on the circuit pattern drawing surface 6 on the photomask 4. Collect light.

Light ray 49 reflected by the inspection area Pi
Is a point P near the half mirror HM2, which traces the original optical path.
Image at i '. A part of the light ray 49 is reflected by the half mirror HM2 and refracted by the lens L7 to become a substantially parallel light ray. The parallel light ray 49 is reflected by the mirror M3, passes through the λ / 4 wave plate QW2 and becomes a light ray 47 having a polarization plane perpendicular to the paper surface, is reflected by the polarization beam splitter PBS1, and is analyzed by the analyzer A.
Head for.

On the other hand, the light ray 50 reflected by the polarization beam splitter PBS1 passes through the λ / 4 wave plate QW1 and becomes a clockwise circularly polarized light ray 44. The light ray 44 is reflected by the mirror M2, passes through the optical path length correction plate LA1, and reaches the half mirror HM2. A part of the light ray 44 passes through the half mirror HM2, is refracted by the lens L2, and is condensed near the rear focus of the objective lens L1. Ray 4
4 is reflected by the vibrating mirror Mm, and the objective lens L
The light rays are refracted by 1 and become substantially parallel rays, reach the circuit pattern drawing surface 6 of the photomask 4, and illuminate a wide illumination region Pr on the circuit pattern drawing surface 6.

The light ray 44 is reflected by the circuit pattern drawing surface 6 to become a light ray 45, and the light ray 45 traces the original optical path. The light ray 45 enters the objective lens L1, is condensed near the rear focal point, is reflected by the vibrating mirror Mm, and becomes a substantially parallel light ray by the lens L2. Ray 45
A part of the light passes through the half mirror HM2, the light path length correction plate LA1, and the light is reflected by the mirror M2.
It reaches the wave plate QW1. The light ray 45 is a λ / 4 wave plate QW1.
Through the light beam and becomes a linearly polarized light ray 51 having a polarization plane parallel to the paper surface.
It goes through BS1 and goes to analyzer A.

The light ray 51 and the light ray 47 are two linearly polarized lights having polarization planes orthogonal to each other, which are reflected by different areas on the circuit pattern drawing surface 6. The light ray 51 becomes a reference light wave. The light ray 51 and the light ray 47 are transmitted through the analyzer A and become a coherent light ray 52.
Enters the photoelectric conversion element 22. Photoelectric conversion element 22
Outputs a signal 18 proportional to the intensity of the light wave on the light detection surface 23. If ray 3 has a single frequency, signal 18 is modulated by the optical path difference between rays 51 and 47,
It becomes a homodyne interference signal. When the light ray 3 has two different frequencies of linearly polarized light which are orthogonal to each other, the signal 18 becomes a beat signal, and the optical path difference between the light ray 51 and the light ray 47 is obtained by the known heterodyne interferometer technique. Can be detected.

The optical path difference between the light ray 51 and the light ray 47 is determined by the wide illumination area P of the circuit pattern drawing surface 6 of the photomask 4.
The phase difference between the average phase of r and the phase in the inspection area Pi, which is a minute spot, is represented. Therefore, the two-dimensional phase distribution can be measured by measuring the optical path difference between the light ray 51 and the light ray 47 by combining the beam scanning by the vibrating mirror Mm and the translational movement of the photomask 4 in the y direction. it can. This is because the optical path length of the light ray 51 is an average value, so that the position of the illumination region Pr is almost the same regardless of where on the circuit pattern drawing surface 6 of the photomask 4, the optical path of the light ray 47 is changed. The length is the inspection area Pi
This is because it is sensitive to the minute objects inside. The signal 18 in FIG. 4 is converted by the light quantity / phase converter 19 into
It becomes an electrical signal representing the phase and is input to the signal processing unit 8. The processes after the signal processor 8 are the same as those in the first and second embodiments described above, and the description thereof will be omitted.

FIG. 5 shows a fourth embodiment of the present invention. The fourth embodiment is similar to the third embodiment described above in that
The foreign matter inspection device measures the phase distribution by the optical path difference between two light waves. However, in the fourth embodiment, since the transmission illumination and the beam spot scan are combined, the illumination area of the photomask of the reference light wave is circular in the third embodiment, whereas the fourth embodiment is different. In the embodiment, it is a linear illumination area extending in the y direction. The light beam 3 emitted from the light source 1 is polarized and separated by the polarization beam splitter PBS3, and the light beam 54 has a plane of polarization parallel to the plane of paper.
The light beam 55 has a plane of polarization perpendicular to the plane of the paper.

A light ray 55 is a light ray for a probe, and includes a mirror M7, a lens L8, and a polarization beam splitter PBS.
5, the light passes through the lens L9 and the vibrating mirror Mm, enters the objective lens L10, and forms a beam spot in the inspection region Pi on the circuit pattern drawing surface 6 of the photomask 4. The light ray 55 passes through the photomask 4, is refracted by the objective lens L1, becomes a substantially parallel light ray, is reflected by the polarization beam splitter PBS4, passes through the mirror M4 and the optical path length correction plate LA2, and is reflected by the polarization beam splitter PBS2. And get out of the system.

On the other hand, the reference light beam 54 is reflected by the mirror M6 and is polarized by the cylindrical lens SL1 having no refracting power in the y direction.
In the vicinity of 5, the light is condensed into a linear shape having a longitudinal direction in the y direction.
The light ray 54 includes a lens L9, a vibrating mirror Mm, and a lens L1.
After passing 0, the light is linearly focused again on the circuit pattern drawing surface 6 of the photomask 4. The light ray 54 passes through the photomask 4, the lens L1, and the polarization beam splitter PBS4. The light beam 54 is the polarization beam splitter PBS4.
In the vicinity, the light is condensed into a linear shape having a longitudinal direction in the x direction and reaches the cylindrical lens SL2 having no refractive power in the x direction. The light ray 54 is refracted by the cylindrical lens SL2 to become a parallel light ray similar to the light ray 55, and the mirror M
After passing through 5, the light beam passes through the polarization beam splitter PBS2.
The rays 55 and 54 are transmitted through the analyzer A and become a coherent ray 56.

Also in the fourth embodiment, the light ray 55 relating to the minute inspection area Pi and the light ray 54 relating to the linear illumination area Pr.
The phase distribution of the object is measured by detecting the optical path difference between and. The inspection area Pi and the illumination area Pr simultaneously optically scan the circuit pattern drawing surface 6 of the photomask 4 as the vibrating mirror Mm is deflected. The optical system in the fourth embodiment can be constituted by homodyne or heterodyne. Further, the photoelectric conversion element 22 and the subsequent elements have substantially the same function as that of the third embodiment, and thus the description thereof will be omitted. In the fourth embodiment, since the phase difference at the edge portion of the circuit pattern 5 is not detected, the signal processing becomes easier than that in the third embodiment.

FIG. 6 shows a fifth embodiment of the present invention. The fifth embodiment is essentially equivalent to the third embodiment shown in FIG. In the third embodiment, there was a significant difference between the inspection area Pi in the photomask of the light beam for the probe and the illumination area Pr in the photomask of the light beam for the reference. In the fifth embodiment, the magnifications of the expanders respectively arranged in the two optical paths in the Mach-Zehnder interferometer constituted by the mirrors M8 and M9 and the polarization beam splitters PBS6 and PBS7 are set to different values. The area of the inspection area Pi and the area of the illumination area Pr are set to be different from each other. Therefore, the opening angle when illuminating the inspection region Pi and the opening angle when illuminating the illumination region Pr are made different.

The light ray 57 emitted from the light source 1 passes through the half mirror HM3 and is polarized and separated by the polarization beam splitter PBS7 to be a light ray 58 and a light ray 59. The light ray 59 is a reference light ray, passes through the lens L14, the aperture AP2, the lens L13, the reflection mirror M8, and the polarization beam splitter PBS6, is reflected by the vibrating mirror Mm, is refracted by the objective lens L1, and illuminates the illumination region Pr. It is illuminated and reflected by the circuit pattern drawing surface 6 of the photomask 4 to become a light ray 60. The light ray 60 traces the original optical path to reach the analyzer A. On the other hand, the light beam 58 for the probe includes the lens L12, the aperture AP1, the lens L11, the mirror M9, and the polarization beam splitter PB.
The vibration mirror Mm is reached via S6. The light ray 58 is refracted by the objective lens L1 and illuminates the inspection area Pi on the circuit pattern drawing surface 6 of the photomask 4. Ray 5
8 is reflected by the circuit pattern drawing surface 6 and
It becomes 1. The light ray 61 goes back to the original optical path and passes through the analyzer A.
Leading to.

The light ray 61 and the light ray 60 become a coherent light ray 62 by the analyzer A and enter the photoelectric conversion element 22. The photoelectric conversion element 22 outputs the output signal 18.
Since the signal processing and the like are the same as those in the third embodiment described above,
The description is omitted.

FIG. 7 shows a sixth embodiment of the present invention. The sixth embodiment is a modification of the above-mentioned fifth embodiment. The only difference between these is the objective lens L1,
In the sixth embodiment, a double focus lens is used as the objective lens L1. The focus of the light ray 58 having the plane of polarization perpendicular to the paper surface is on the circuit pattern drawing surface 6, while the focus of the light ray 59 having the plane of polarization parallel to the paper surface is on the non-circuit pattern drawing surface g of the photomask 4. The light ray 59 is a reference light ray, and in the present embodiment, the inspection area Pi and the illumination area P.
r are provided on different surfaces. Reference ray 59
Illuminates an illumination region Pr having a larger area than the inspection region Pi so that the optical path length is not changed by foreign matter on the non-circuit pattern drawing surface g. In the sixth embodiment, the reference light beam is not phase-modulated by the metal circuit pattern.

[0028]

As described above, according to the present invention, a circuit pattern can be obtained as an image of a simple phase distribution,
It can be easily distinguished from foreign matter. Further, according to the present invention, since the phase distribution of the circuit pattern drawing surface of the photomask is observed from the substrate side, it is not affected by the slope of the edge portion of the circuit pattern.

According to the first and second embodiments, since the phase distribution is measured by using the waveguide element, the measurement error does not occur even if there is fluctuation in the optical path length of the optical system. According to the second and fourth embodiments, since the transillumination method is used, the image of the light blocking member (for example, CrOx film) forming the circuit pattern is not detected, and therefore the phase change due to the light blocking member is not considered. Signal processing can be performed. According to the sixth embodiment, the reference light beam used in the interferometric method is reflected from the non-circuit pattern drawing surface of the photomask substrate, so that it is almost the same as the first embodiment without using the waveguide element. A system of performance can be configured.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of a first embodiment of a foreign matter inspection device according to the present invention.

FIG. 2 is a diagram illustrating the inspection principle of the foreign matter inspection apparatus according to the present invention.

FIG. 3 is a schematic diagram showing a configuration of a second embodiment of the foreign matter inspection apparatus according to the present invention.

FIG. 4 is a schematic diagram showing the configuration of a third embodiment of the foreign matter inspection device according to the present invention.

FIG. 5 is a schematic diagram showing the configuration of a fourth embodiment of the foreign matter inspection device according to the present invention.

FIG. 6 is a schematic diagram showing a configuration of a fifth embodiment of the foreign matter inspection device according to the present invention.

FIG. 7 is a schematic diagram showing a configuration of a sixth embodiment of the foreign matter inspection apparatus according to the present invention.

[Explanation of symbols]

 2 Waveguide element 4 Photomask 5 Circuit pattern 6 Circuit pattern drawing surface 13 Incident end face 16 Photoelectric conversion element 17 Photoelectric conversion element 22 Photoelectric conversion element A Analyzer D0 Differential signal LA Optical path length correction plate Pi Inspection area Pr Illumination area QW λ / 4 Wave plate RH Photomask holding section SL Cylindrical lens

Claims (4)

[Claims] 1. A foreign matter inspection apparatus for optically detecting a foreign matter on a photomask having a predetermined pattern drawn on only one surface, the illumination optical system illuminating the photomask, and the photomask. A condensing optical system for condensing a light beam emitted from the optical system, and a phase distribution or phase differential distribution measuring means capable of receiving the light condensed by the condensing optical system and measuring the phase distribution or phase differential distribution of the received light. A foreign matter inspection apparatus comprising: 2. The reflection optical system, wherein the illumination optical system illuminates the photomask by a reflection illumination method.
A foreign matter inspection device according to item 1. 3. The illumination optical system is a transmission optical system that illuminates the photomask by a transmission illumination method.
A foreign matter inspection device according to item 1. 4. The condensing optical system condenses a light beam emitted from the one surface of the photomask, which is transmitted through the other surface of the photomask. The foreign matter inspection device according to the item.