JP4244305B2 - Illumination optical system and pattern defect inspection apparatus using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pattern inspection for detecting a defect (short, disconnection, etc.) and foreign matter in a photomask pattern, an illumination optical system used for foreign matter inspection, a pattern defect device, and an optical fiber.
[0002]
[Prior art]
Conventionally, in a pattern defect inspection apparatus, a mask pattern image is formed by illuminating a sample such as a photomask using an illumination optical system having a performance equivalent to that of a high resolution microscope, and this mask pattern image is formed by a CCD camera or a line sensor. It is acquired as image information using an image receiving sensor such as, and a reference image without defects / foreign matter acquired in advance or a reference image without defects / foreign matter prepared in advance is compared with image information obtained by measurement to produce An inspection is performed to determine whether or not there is a defect or foreign matter in the photomask or the like.
[0003]
In a mask pattern defect inspection apparatus having a performance equivalent to, for example, a high resolution microscope as a pattern defect inspection apparatus, a sample is illuminated at once and a mask pattern image is formed with an objective lens having a large numerical aperture, that is, an objective lens having a high NA. I am doing so. In such a pattern defect inspection apparatus, with the progress of miniaturization of semiconductor devices in recent years, the wavelength of light used for exposure and inspection has been shortened, and deep ultraviolet (DUV) light has come to be used. ing.
[0004]
However, in this light wavelength region, if an ordinary lamp light source (discharge lamp) is used, the amount of DUV light in the total light emission amount is small, and the area of the light emission bright spot increases even if the output is increased. As a result, the laser is often used as a light source.
[0005]
For example, a laser scanning microscope that focuses laser light on the surface of the sample and scans it as a high-resolution microscope is commercially available. It is conceivable to use this to scan and illuminate the sample. For example, there is a disadvantage that the sample cannot be scanned within the required inspection time even if a relatively high-speed means such as AOD (acousto-optic element) is used.
[0006]
Therefore, it has been proposed to perform collective illumination using laser light, but when collective illumination is performed using laser light, overshoot and undershoot due to ringing at speckle patterns and pattern edges due to the coherence of the laser light. Shooting occurs, resulting in uneven lighting.
[0007]
In addition, an integrator may be used in the illumination optical system to improve the numerical aperture of the illumination light beam and at the same time ensure the uniformity of the collective illumination. It is formed on the top, resulting in uneven illumination. This uneven illumination is high in contrast, and if the sample is photographed in this state, the photographed image is uneven.
[0008]
Therefore, in order to reduce the coherence of the laser beam, the random phase plate is rotated at the condensing point of the integrator, the diffusion plate is installed at the condensing point, and the length is different according to each element of the integrator. A configuration in which optical fibers are arranged side by side has been proposed (see, for example, Patent Document 1).
[0009]
According to these optical systems, the phase difference is controlled while the laser beam as the illumination beam passes through each element of the integrator, and uneven illumination due to the interference fringe pattern is reduced.
[0010]
[Patent Document 1]
JP 2002-39960 A (FIG. 11)
[0011]
[Problems to be solved by the invention]
However, in the case of using a random rotating phase plate, a mechanism for rotating the random rotating phase plate is required, and in the case of using a diffusion plate, the illumination light beam is greatly diffused and is projected onto the sample by a condenser lens. In the case where the light intensity of the illumination light beam is greatly reduced and the length of the optical fiber is changed, the coherence distance changes when the performance of the laser light source changes, so the length of the fiber must be changed accordingly. In addition, there is a disadvantage that causes an increase in the size of the apparatus.
[0012]
The present invention has been made in view of the above circumstances, and an object of the present invention is to eliminate the need for a movable mechanism and to reduce the efficiency of laser light without impairing the utilization efficiency of the illumination light beam and without enlarging the apparatus. An object of the present invention is to provide an illumination optical system, a pattern defect inspection apparatus, and an optical fiber that can reduce illumination unevenness due to coherence.
[0013]
[Means for Solving the Problems]
The illumination optical system according to claim 1 includes an incident side lens array that collects illumination light from a laser light source to generate a plurality of pseudo light sources, a plurality of elements, and is incident on each element. An integrator that mixes illumination light and guides it to a condenser lens, an exit side lens array facing each element of the integrator, an entrance surface facing each lens element of the entrance side lens array, and each lens of the exit side lens array An optical fiber array having a plurality of optical fibers each having an emission surface facing the element and a piezoelectric material film formed on the outer peripheral portion and the refractive index of which is changed, and the piezoelectric material film of each of the optical fibers is controlled And a control circuit.
The pattern defect inspection apparatus according to claim 2, comprising an incident side lens array for condensing illumination light from a laser light source to generate a plurality of pseudo light sources, a plurality of elements, and incident on each element An integrator that mixes the illuminating light and guides it to the condenser lens, an exit side lens array that faces each element of the integrator, an entrance surface that faces each lens element of the entrance side lens array, and each of the exit side lens array An optical fiber array having a plurality of optical fibers each having an exit surface facing the lens element and a piezoelectric material film formed on the outer peripheral portion and the refractive index of which is changed, and the piezoelectric material film of each of the optical fibers is controlled A control circuit for condensing, a condenser lens for condensing the illumination light beam emitted from the integrator and irradiating the sample, and condensing the illumination light beam irradiated to the sample An objective lens, a detection optical system that forms an image of a light beam condensed by the objective lens on a detection sensor, and a signal processing device that processes a signal imaged and photoelectrically converted on the detection sensor. It is characterized by being.
The pattern defect inspection apparatus according to claim 3, wherein the control circuit generates a phase difference pattern generation circuit that generates a random phase difference pattern, and a voltage that applies a voltage corresponding to the random phase difference pattern to each piezoelectric material film. Comprising a control circuit, and controlling the phase difference of the illumination light beam passing through each of the optical fibers in synchronization with the photoelectric accumulation time of the detection sensor to average the light amount distribution of the illumination light beam on the detection sensor. Features.
The pattern defect inspection apparatus according to claim 4, wherein the control circuit generates a phase difference pattern generation circuit that generates a regular phase difference pattern, and a voltage corresponding to the regular phase difference pattern is applied to the piezoelectric element between columns. It consists of a voltage control circuit applied to the material film, giving the same phase to the illumination light beam passing through the optical fiber existing in each row and giving a predetermined phase difference to the illumination light beam passing through the optical fiber existing in a different row from that row The light quantity distribution of the illumination light beam on the detection sensor is averaged by changing the phase difference in synchronization with the photoelectric accumulation time of the detection sensor while maintaining the phase difference between the columns. And
The pattern defect inspection apparatus according to claim 5, wherein the detection sensor is a one-dimensional line sensor, and the sample is moved in a direction orthogonal to a direction in which the one-dimensional line sensor extends.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a schematic diagram of a pattern defect inspection apparatus according to the present invention. In FIG. 1, 1 is a laser light source unit, 2 is an illumination optical system, 3 is a condenser lens, 4 is a sample, 5 is an objective lens. , 6 is a detection optical system, 7 is a detection sensor (sensor), and 8 is a signal processing device.
[0020]
The laser light source unit 1 has a beam expander optical system (not shown), and the laser beam P emitted from the laser light source unit 1 is incident on the illumination optical system 2 with its beam diameter enlarged.
[0021]
The illumination optical system 2 includes an incident side fly-eye lens array 9, an output side fly-eye lens array 10, an optical fiber array 11, and an integrator 12, as shown in detail in an enlarged manner in FIG.
[0022]
The incident side fly-eye lens array 9 and the exit side fly-eye lens array 10 have lens elements 9a and 10a regularly arranged. The incident side fly-eye lens array 9 condenses the illumination light P from the laser light source unit 1 to generate a plurality of pseudo light sources. The exit-side fly-eye lens array 10 faces each element 12 a of the integrator 12. The optical fiber array 11 includes a plurality of regularly arranged optical fibers 13. Here, the optical fiber array 11 is composed of nine optical fibers 13 arranged three by three vertically and horizontally. Here, reference numeral 13A denotes a row of the first optical fiber, reference numeral 13B denotes a second optical fiber row, and reference numeral 13C denotes a third optical fiber row.
[0023]
Each optical fiber 13 has an incident surface 13 a facing each lens element 9 a of the incident side lens array 9 and an output surface 13 b facing each lens element 10 a of the output side lens array 10. A piezoelectric material film 14 is formed on the outer peripheral portion 13 c of each optical fiber 13. Each optical fiber 13 is distorted by the expansion and contraction of the piezoelectric material film 14 and its refractive index is changed.
[0024]
A voltage is periodically applied to each piezoelectric material film 14 by the control circuit 15. The control circuit 15 includes a phase difference pattern generation circuit 16 and a voltage control circuit 17. The phase difference pattern generation circuit 16 has a function of calculating a phase difference given to each optical fiber 13. The voltage control circuit 16 generates an applied voltage corresponding to the phase difference signal from the phase difference pattern generation circuit 15 and applies an applied voltage corresponding to the phase difference signal to each piezoelectric material film 14.
[0025]
As a result, each optical fiber 13 is given a distortion corresponding to the applied voltage applied to the piezoelectric material coating 14. As a result, the illumination light beam P is given a phase difference while passing through each optical fiber 13. The phase difference is preferably such that the phase difference (2π) of one wavelength of light is given in order to avoid an increase in the size of the piezoelectric material film 14 and an increase in the size of the optical fiber array 11.
[0026]
Here, the phase difference pattern generation circuit 15 is assumed to generate a random phase difference pattern. The illumination light beam P is given a random phase difference when passing through each optical fiber 13 and is incident on the integrator 12. The illumination light beam P is mixed by the integrator 12 and guided to the condenser lens 3. The illumination light beam is condensed by the condenser lens 3 and the sample 4 is illuminated by the illumination light beam P. According to the illumination optical system 2, the same effect as that of the conventional random phase plate can be obtained.
[0027]
The illumination light beam P transmitted through the sample 4 is condensed by the objective lens 5 and guided to the detection optical system 6, and is imaged on the detection sensor 7 by the detection optical system 6. Here, the detection sensor 7 is composed of an area sensor, and the output of the area sensor is input to the signal processing device 8 and subjected to image processing in the same manner as in the prior art.
[0028]
As described above, in the embodiment of the invention, a random phase difference is given to the illumination light beam passing through each optical fiber 13, but for each optical fiber 13, for example, each optical fiber 13 and row 13B forming the horizontal row 13A. Each optical fiber 13 to be formed and each optical fiber 13 to form the row 13C are given the same phase, and a predetermined phase difference is given to the optical fiber 13 forming the row 13A and the optical fiber 13 forming the row 13B. Further, different predetermined phase differences are given to the optical fibers 13 forming the row 13A and the row 13B and the optical fibers forming the row 13C, and the phase difference between the columns is maintained in synchronization with the photoelectric accumulation time of the area sensor 7. Alternatively, the phase may be swept by changing the phase from 0 to 2π.
[0029]
If the detection sensor 7 is configured to use a line sensor instead of an area sensor and move the sample 4 in a direction orthogonal to the direction in which the line sensor extends to capture a two-dimensional image, each optical fiber 13 array The same phase difference is given to each of 13A, 13B, and 13C, and the phase is changed from 0 to 2π while maintaining the phase difference between the columns in synchronization with the photoelectric accumulation time of the area sensor. As shown in FIG. 3, the light quantity distribution Q corresponding to the interference fringes formed on the detection sensor 7 can be continuously moved by one pitch, and if configured in this way, the interference as shown in FIG. By averaging the light quantity distribution Q corresponding to the stripes, illumination unevenness can be removed.
[0030]
【The invention's effect】
The illumination optical system and the pattern defect inspection apparatus according to the present invention do not require a movable mechanism, and do not impair the illumination efficiency due to the coherence of laser light without impairing the utilization efficiency of the illumination light beam and without increasing the size of the apparatus. Reduction can be achieved.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a pattern defect inspection apparatus according to the present invention.
FIG. 2 is an optical diagram showing a detailed configuration of an illumination optical system according to the present invention.
3A and 3B are explanatory diagrams showing an example of the operation of the illumination optical system according to the present invention, in which FIG. 3A is a diagram showing a movement state of a light quantity distribution corresponding to interference fringes, and FIG. It is a figure which shows the state averaged within the accumulation time.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Laser light source part 9 ... Incident side lens array 10 ... Output side lens array 11 ... Optical fiber array body 12 ... Integrator 13 ... Optical fiber 14 ... Piezoelectric material film 13a ... Incident surface 13b ... Outgoing surface 13c ... Outer peripheral part 15 ... Control circuit

Claims (5)

An incident-side lens array that collects illumination light from a laser light source to generate a plurality of pseudo light sources, and an integrator that has a plurality of elements and that mixes the illumination light incident on each element and guides it to a condenser lens And an exit-side lens array facing each element of the integrator, an entrance surface facing each lens element of the entrance-side lens array, and an exit surface facing each lens element of the exit-side lens array, and a piezoelectric An optical fiber array in which a plurality of optical fibers whose refractive index is changed by forming a material film on an outer peripheral portion are aligned, and a control circuit that controls the piezoelectric material film of each of the optical fibers. Lighting optical system. An incident-side lens array that collects illumination light from a laser light source to generate a plurality of pseudo light sources, and an integrator that has a plurality of elements and that mixes the illumination light incident on each element and guides it to a condenser lens And an exit-side lens array facing each element of the integrator, an entrance surface facing each lens element of the entrance-side lens array, and an exit surface facing each lens element of the exit-side lens array, and a piezoelectric An optical fiber array in which a plurality of optical fibers whose refractive index is changed by forming a material coating on the outer peripheral portion, a control circuit for controlling the piezoelectric material coating of each optical fiber, and illumination emitted from the integrator A condenser lens for condensing the light beam and irradiating the sample, an objective lens for condensing the illumination light beam irradiated to the sample, and the objective lens Has been a detection optical system for imaging the light beam on the sensor, said imaged on the detection sensor and the pattern defect inspection apparatus for a signal processing apparatus for processing a photoelectrically converted signal, characterized in that it comprises a.   The control circuit includes a phase difference pattern generation circuit that generates a random phase difference pattern, and a voltage control circuit that applies a voltage corresponding to the random phase difference pattern to each piezoelectric material film, and photoelectric storage of the detection sensor The pattern defect inspection according to claim 2, wherein the light intensity distribution of the illumination light beam on the detection sensor is averaged by controlling a phase difference of the illumination light beam passing through each of the optical fibers in synchronization with time. apparatus.   The control circuit comprises a phase difference pattern generation circuit that generates a regular phase difference pattern, and a voltage control circuit that applies a voltage corresponding to the regular phase difference pattern to the piezoelectric material film for each column, The illumination light flux passing through the optical fiber existing in each row is given the same phase, and the illumination light flux passing through the optical fiber existing in a row different from that row is given a predetermined phase difference to maintain the phase difference between the rows. 3. The pattern defect inspection apparatus according to claim 2, wherein the light intensity distribution of the illumination light beam on the detection sensor is averaged by changing the phase difference in synchronization with the photoelectric accumulation time of the detection sensor. .   The pattern defect inspection apparatus according to claim 4, wherein the detection sensor is a one-dimensional line sensor, and the sample is moved in a direction orthogonal to a direction in which the one-dimensional line sensor extends.

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