JP2022128325A - Inspection device and inspection method - Google Patents

Abstract

An object of the present invention is to perform accurate measurement even when the surface position of an object to be inspected fluctuates during inspection. An inspection apparatus for analyzing the concentration of an element contained in an object to be inspected by irradiating the object to be inspected with a laser beam from a laser light source, wherein the laser beam is condensed on a focal plane to an irradiation optical system having a condensing lens for irradiating the laser light, a condensing optical system for condensing the plasma emission generated from the object to be inspected by the laser beam, and the intensity of the plasma emission condensed by the condensing optical system for each wavelength and a measuring unit for measuring the light-condensing optical system, wherein the condensing optical system has an aperture member arranged at a position optically conjugate with the focal plane of the condensing lens. [Selection drawing] Fig. 1

Description

The present invention relates to an inspection apparatus and an inspection method.

2. Description of the Related Art There is known an apparatus for inspecting the types of elements contained in an object to be inspected by measuring plasma emission due to laser ablation (for example, Patent Document 1).
[Prior art documents]
[Patent Literature]
[Patent document 1] JP-A-7-167785

However, when the surface position of the object to be inspected fluctuates during inspection, the positional relationship between the focus position of the laser and the surface position of the object to be inspected fluctuates. Difficult to measure accurately.

A first aspect of the present invention is an inspection apparatus for analyzing the concentration of an element contained in an object to be inspected by irradiating the object with a laser beam from a laser light source, wherein the laser beam is focused on a focal plane. An irradiation optical system having a condensing lens for irradiating an object to be inspected with light, a condensing optical system for condensing the plasma emission generated from the object to be inspected by laser light, and plasma condensed by the condensing optical system. and a measuring unit for measuring the intensity of emitted light for each wavelength, wherein the condensing optical system has an aperture member arranged at a position optically conjugate with the focal plane of the condensing lens. .

a second measuring unit that measures the intensity of the plasma emission at a predetermined wavelength; and a correcting unit that corrects the intensity measured by the measuring unit based on the intensity measured by the second measuring unit. You may have more.

The measurement unit may perform measurements a plurality of times at predetermined time intervals to calculate an emission peak of the plasma emission, and use the intensity measured at the emission peak as the intensity of the plasma emission for each wavelength.

The apparatus may further include a shutter for controlling incidence and blocking of plasma emission to the measurement unit by opening and closing, and a delay generation unit for delaying the time from irradiation of the object to be inspected with laser light to opening of the shutter.

The shutter may be an image intensifier that amplifies the plasma emission.

The laser irradiation unit may further include a beam shaper that shapes the beam profile of the laser light irradiated onto the object to be inspected into a Gaussian beam.

The beam shaper may have a beam expander that expands the beam diameter of the laser light, and a second aperture member arranged at a position optically conjugate with the focal plane of the condenser lens.

The condenser lens is shared by the condenser optical system, and the focal plane of the condenser lens may be set closer to the condenser lens than the surface of the object to be inspected.

In a second aspect of the present invention, there is provided an inspection method for analyzing the concentration of an element contained in an object to be inspected by irradiating the object to be inspected with a laser beam from a laser light source, comprising an irradiation optical system having a condenser lens. a step of condensing a laser beam onto a focal plane by a system and irradiating the object to be inspected; and measuring the intensity for each wavelength of the illuminated plasma emission, wherein the condensing optical system has an aperture member arranged at a position optically conjugate with the focal plane of the condensing lens. I will provide a.

It should be noted that the above summary of the invention does not list all the necessary features of the invention. Subcombinations of these feature groups can also be inventions.

It is a figure showing a schematic structure of inspection device 100 in this embodiment. (a) and (b) are diagrams showing an example of inspection when the thickness of an object to be inspected 27 varies in this embodiment. 4 is a diagram showing a schematic configuration of a beam shaper 12 and a condensing optical system 42 in this embodiment; FIG. 4 is a graph showing an elemental spectrum of plasma emission P in this embodiment. (a) is a diagram showing an example of temporal changes in the intensity of plasma emission P in a comparative example, and (b) is a timing chart showing laser excitation timing and measurement timing in the comparative example. (a) is a diagram showing an example of temporal changes in the intensity of plasma emission P in this embodiment, and (b) is a timing chart showing laser excitation timing and measurement timing in this embodiment.

Hereinafter, the present invention will be described through embodiments of the invention, but the following embodiments do not limit the invention according to the claims. Also, not all combinations of features described in the embodiments are essential for the solution of the invention.

FIG. 1 is a diagram showing a schematic configuration of an inspection apparatus 100 according to this embodiment. As shown in FIG. 1, the inspection apparatus 100 includes a laser light source 11, a beam shaper 12, a condenser lens 13, a mirror 14, beam splitters 15 and 16, a bandpass filter 17, and a second measurement unit. a photodiode 18 as a function, a condenser lens 19, an aperture 20 as a diaphragm member, a condenser lens 21, an image intensifier 22, a spectrometer 23 as a measuring unit, a computer 24, a delay It has a generator 25 and a laser controller 26 . The inspection apparatus 100 of the present embodiment is an apparatus for analyzing the types and concentrations of elements contained in an object 27 to be inspected by irradiating the object 27 to be inspected with a laser beam R from a laser light source 11 . The inspection apparatus 100 of the present embodiment particularly identifies a small amount of elements such as impurities mixed in known elements serving as a base material and their concentrations.

The laser light source 11 is connected to a laser power source (not shown). The laser light source 11 may be a pulse width nanosecond oscillation solid-state laser. The laser light R emitted by the laser light source 11 may be pulsed laser light. The laser light source 11 and laser power supply are connected to a laser controller 26 . The laser controller 26 generates a timing signal for oscillating the laser light R. This timing signal is transmitted from the laser controller 26 to the laser light source 11 .

A laser beam R emitted from a laser light source 11 is shaped into a Gaussian beam by a beam shaper 12 . Here, if the beam profile is not properly shaped, Gaussian-shaped light cannot be collected on the surface of the object 27 to be inspected. becomes a disturbance component when

As shown in FIG. 1, the beam shaper 12 has a condenser lens 31, an aperture 32 as a second diaphragm member, a condenser lens 33, and a beam expander . A beam expander 34 expands the beam diameter of the laser light R emitted from the laser light source 11 to an appropriate size, and the condensing lenses 31 and 33 and the aperture 32 shape the laser light R into a Gaussian beam. The aperture 32 is arranged at a position optically conjugate with the focal plane of the condenser lens 13 . For the aperture 32, for example, a thin metal plate having minute pinholes formed therein may be used. Aperture 32 may be a slit.

The condenser lens 13 , the mirror 14 , and the beam splitters 15 and 16 together constitute an irradiation optical system 41 . The condenser lens 13 , the mirror 14 , and the beam splitters 15 and 16 are arranged so that the laser beam R emitted from the laser light source 11 is focused on the surface of the object 27 to be inspected.

When the object to be inspected 27 is irradiated with the laser beam R through the irradiation optical system 41 composed of the condenser lens 13, the mirror 14, and the beam splitters 15 and 16, a so-called breakdown occurs due to laser ablation. , part of the surface of the object to be inspected 27 is turned into plasma. Plasma light emission P is generated from the object 27 to be inspected by plasmatizing a part of the surface of the object 27 to be inspected. In this plasmification, recombination starts when the irradiation of the laser beam R ends, and the constituent elements of the object to be inspected 27 become excited atoms for several microseconds to several tens of microseconds. Atoms in this excited state emit plasma light emission P having an emission intensity (light amount) proportional to the number of atoms when transitioning to a lower level.

In this embodiment, the focal plane 13 a of the condenser lens 13 is arranged so as to match the surface position of the inspection object 27 . However, the focal plane 13a of the condenser lens 13 may be set closer to the condenser lens 13 than the surface of the object 27 to be inspected. Specifically, the focal plane 13a of the condenser lens 13 may be set on the side closer to the condenser lens 13 than the surface of the object 27 to be inspected. As a result, laser ablation can be generated at a position close to the surface of the object 27 to be inspected. The emitted light P can be easily condensed.

Of this plasma emission P, only that generated in a predetermined area on the surface of the object to be inspected 27 passes through the aperture 20 and reaches the condenser lens 21, and after being amplified by the image intensifier 22, Incident into spectrometer 23 . The plasma emission P incident on the spectroscopic device 23 is spectrally separated, converted into electrical signals corresponding to the intensity of each wavelength, and transmitted to the computer 24 .

The condenser lens 19, the aperture 20, and the condenser lens 21 constitute a condenser optical system 42 for condensing the plasma emission P generated from the object 27 to be inspected by laser ablation. The condensing lens 13 is also shared by the condensing optical system 42 . A plasma light emission P generated in a predetermined area of the surface position of the object to be inspected 27 is made incident on the spectrometer 23 by the condensing optical system 42 . Aperture 20 is arranged at a position optically conjugate with focal plane 13 a of condenser lens 13 . As a result, of the plasma emission P generated when the object 27 to be inspected is irradiated with the laser beam R, only the plasma emission P generated in the region of the object 27 to be inspected that coincides with the focal plane 13a of the condenser lens 13 is It reaches the condensing lens 21 through the aperture 20 . For the aperture 20, for example, a thin metal plate having minute pinholes formed therein may be used. Aperture 20 may be a slit.

FIGS. 2A and 2B are diagrams showing an example of inspection when the thickness of the object 27 to be inspected varies in this embodiment. In FIGS. 2A and 2B, the object to be inspected 27 is transported and moved from left to right by the transport unit 43 . In FIGS. 2(a) and 2(b), it is assumed that the thickness of the inspected object 27 varies. The thickness of the object to be inspected 27 is t1 at maximum and t2 at minimum. 2(a) and 2(b), the focal plane 13a of the condenser lens 13 is located at the tip of the arrow of the laser beam R. In FIG. In the inspection when the object to be inspected 27 moves, it is desirable that the object to be inspected 27 is intermittently moved, and the irradiation and measurement of the laser beam R are performed when the object to be inspected 27 is stationary.

In FIG. 2A, the focal plane 13a of the condenser lens 13 coincides with the surface position 27a of the inspection object 27, and laser ablation occurs at an ideal position. Therefore, plasma emission P1 having a high emission intensity is generated by laser ablation. On the other hand, in FIG. 2B, the object 27 to be inspected is being transported, so the focal plane 13a of the condenser lens 13 does not match the surface position 27b of the object 27 to be inspected. The laser beam R is focused at a position above the surface position 27b of the body 27. FIG. In this case, no laser ablation occurs at the ideal position. Therefore, plasma emission P2 having a low emission intensity is generated by laser ablation.

As described above, when the thickness of the object to be inspected 27 varies, such as when inspecting the object to be inspected 27 being transported, the focal plane 13a of the condenser lens 13 and the surface position of the object to be inspected 27 are , the variation in the emission intensity of the plasma emission P increases. If all the plasma emission P with large fluctuations is made incident on the spectrometer 23 and measured, the measurement cannot be performed with good quantification. This is not limited to the case where the thickness of the object to be inspected 27 varies, but the variation in the shape of the object to be inspected 27 causes the focal plane 13a of the condenser lens 13 and the surface position of the object to be inspected 27 to be transported to change. The same applies when the positional relationship changes.

In this embodiment, the condensing optical system 42 has the aperture 20 arranged at a position optically conjugate with the focal plane 13a of the condensing lens 13, so that the object 27 to be inspected is irradiated with the laser beam R. Of the plasma luminescence P generated by this, only the plasma luminescence P generated in the area of the inspection object 27 coinciding with the focal plane 13 a of the condenser lens 13 reaches the condenser lens 21 through the aperture 20 . do. Therefore, the light deviating from the focal plane 13a of the condensing lens 13 is not guided to the spectroscopic device 23, thereby suppressing the mixing of disturbance components. As a result, only the plasma emission P having a constant intensity can be made incident on the spectroscopic device 23 and measured, and the measurement can be performed with good quantitativeness. The area of the inspection object 27 that coincides with the focal plane 13a of the condensing lens 13 is an area including a certain width, for example, an area having a thickness of 0.1 to 2 mm in the thickness direction.

Returning to FIG. 1 , the image intensifier 22 amplifies the plasma emission P that has entered the image intensifier 22 and enters the spectral device 23 . The image intensifier 22 has a shutter (not shown) that controls the incidence and blocking of the plasma emission P to the spectroscopic device 23 by opening and closing. The image intensifier 22 is connected to the delay generator 25 and receives commands from the delay generator 25 .

The delay generator 25 delays the time from when the object 27 to be inspected is irradiated with the laser light R to when the shutter is opened, and transmits to the image intensifier 22 a gate signal for opening and closing the shutter of the image intensifier 22 . Thus, the timing of incidence and cutoff of the plasma emission P to the spectroscopic device 23 is controlled. The gate signal is a signal for measuring the plasma light emission P delayed by a predetermined time from the timing signal for oscillating the laser light R transmitted from the laser controller 26 . The spectrometer 23 measures the emission intensity of the plasma emission P amplified by the image intensifier 22 for each wavelength. The spectroscopic device 23 is composed of, for example, a distributed spectroscope and an array sensor of silicon elements.

A bandpass filter 17 and a photodiode 18 are devices for monitoring the emission intensity of the plasma emission P. FIG. For the band-pass filter 17, for example, a dielectric multilayer film added to calcium fluoride as a base material may be used. The photodiode 18 may be, for example, a PIN photodiode made of silicon. Plasma light emission P emitted from the inspected object 27 passes through the beam splitter 16 , is reflected by the beam splitter 15 , and enters the bandpass filter 17 and the photodiode 18 . The photodiode 18 measures the emission intensity of the incident plasma emission P. FIG. The emission intensity of the plasma emission P measured by the photodiode 18 is transmitted to the computer 24 and monitored.

The computer 24 monitors the luminescence intensity of atoms other than the element of interest, preferably the most abundant element contained in the object 27 to be inspected (for example, the base material element of the object 27 to be inspected). is corrected. For example, by dividing the emission intensity from the target element by the emission intensity from the matrix element, the concentration of the target element can always be stably measured. The computer 24 corrects the intensity of the plasma emission P when the surface position of the object 27 to be inspected is changed by using the monitored emission intensity from the base material element. When the surface position of the object 27 to be inspected deviates from the focal plane 13a of the condensing lens 13, the intensity of the laser ablation becomes weak, so the intensity of the plasma emission P received by the photodiode 18 becomes small. At this time, by correcting the decreased intensity of the plasma emission P by the computer 24, it is possible to correct the emission light amount of the target element of the object 27 to be inspected, and to maintain the quantitativeness of the measurement.

FIG. 3 is a diagram showing a schematic configuration of the beam shaper 12 and the condensing optical system 42 in this embodiment. 3, in order to show the correspondence relationship between the beam shaper 12 and the condensing optical system 42, the arrangement position of the beam shaper 12 is changed (rotated left and right) from that in FIG. 1 for the sake of convenience. . As shown in FIG. 3, each component of the beam shaper 12 and each component of the condensing optical system 42 are arranged at corresponding positions.

Specifically, the condenser lens 31 of the beam shaper 12 and the condenser lens 19 of the condenser optical system 42 are arranged at corresponding positions. Also, the aperture 20 of the beam shaper 12 and the aperture 32 of the condensing optical system 42 are arranged at positions optically conjugate with the focal plane 13 a of the condensing lens 13 . Also, the condenser lens 33 of the beam shaper 12 and the condenser lens 21 of the condenser optical system 42 are arranged at corresponding positions. In this manner, the beam shaper 12, which is an optical system for shaping the beam profile of the laser light R, is arranged in an optical system corresponding to the condensing optical system 42 for the plasma emission, so that the focal plane 13a of the condensing lens 13 coincides with the beam shaper 12. It is possible to correctly measure the spectrum of the plasma emission P in the region where

FIG. 4 is a graph showing an elemental spectrum of plasma emission P in this embodiment. The spectrum of the plasma emission P generated from the object 27 to be inspected by laser ablation differs for each emitting element. FIG. 4 shows the relationship between the wavelength and intensity of plasma emission P from various elements. As shown in FIG. 4, the emission from the matrix element has an emission peak at wavelength n1. Emission from element A has emission peaks at wavelengths n2 and n3. Emission from element B has emission peaks at wavelengths n3, n4, and n5. The spectroscopic device 23 measures the elemental spectrum of the plasma emission P. By measuring the element spectrum of the object 27 to be inspected, when the object 27 to be inspected contains a plurality of elements, it is possible to measure the concentrations of the plurality of elements at the same time. In general, one element emits a plurality of emission spectra, and by analyzing the plurality of spectra, it becomes possible to quantify the amount of the element more precisely.

FIG. 5(a) is a diagram showing an example of temporal changes in the intensity of the plasma emission P in the comparative example. As shown in FIG. 5(a), the emission intensity of the plasma emission P changes over time. After the irradiation of the laser beam R, the emission intensity of the plasma emission P once increases with the passage of time and then decreases. The change over time in the emission intensity of the plasma emission P, that is, the time constant between plasma generation and emission differs depending on the element that emits the plasma emission P. As shown in FIG. 5A, the emission from element A peaks at time t1, while the emission from element B peaks at time t2. Even for the same element, the time constant may differ depending on the plasma excitation concentration.

FIG. 5B is a timing chart showing laser excitation timing and measurement timing in a comparative example. In the comparative example shown in FIG. 5B, the laser excitation timing is time t0, and the measurement timing is once at time t3 between time t1 and time t2. It is desirable to measure the plasma emission when the emission intensity of the plasma emission P is at its peak. By measuring the plasma emission at the peak, the ratio of noise components can be reduced and the concentration of the object to be measured can be accurately analyzed. However, when measuring at the timing of time t3 as shown in FIG. 5(b), the time t3 is later than the time t1, so the emission peak from the element A cannot be captured, and the time t3 is the time t2. , the emission peak from the element B cannot be caught.

FIG. 6(a) is a diagram showing an example of temporal changes in the intensity of plasma emission P in this embodiment, and FIG. 6(b) is a timing chart showing laser excitation timing and measurement timing in this embodiment. be. Note that FIG. 6(a) is the same as FIG. 5(a), so the description is omitted. In this embodiment shown in FIG. 6B, measurements are performed multiple times at predetermined time intervals. Specifically, the laser excitation timing is time t0, and the measurement timing is nine times from time ta to time ti. Here, as shown in FIGS. 6A and 6B, time tb is the timing that coincides with time t1, which is the emission peak from element A, and time te is time t2, which is the emission peak from element B. It is the timing that coincides with Therefore, emission peaks from element A and element B can be captured. The computer 24 calculates the emission peaks from the multiple measurements, and stores the emission intensities measured at the emission peaks as the emission intensities of the plasma emission P for each wavelength.

As described above, in the present embodiment, by performing measurements a plurality of times at predetermined time intervals, it is possible to capture emission peaks from a plurality of types of elements contained in the object to be inspected 27, and reduce noise components. By reducing the ratio, the concentrations of various elements contained in the object to be inspected 27 to be measured can be analyzed with high accuracy.

As described above, according to the inspection apparatus 100 of the present embodiment, the condensing optical system 42 has the aperture 20 arranged at a position optically conjugate with the focal plane 13a of the condensing lens 13. , the light deviating from the focal plane 13a of the condenser lens 13 is not guided to the spectroscopic device 23, so that the mixing of disturbance components is suppressed. As a result, only the plasma emission P having a constant intensity can be made incident on the spectroscopic device 23 and measured, and the measurement can be performed with good quantitativeness.

Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It is obvious to those skilled in the art that various modifications and improvements can be made to the above embodiments. It is clear from the description of the scope of claims that forms with such modifications or improvements can also be included in the technical scope of the present invention.

The execution order of each processing such as actions, procedures, steps, and stages in the devices and methods shown in the claims, the specification, and the drawings is expressly expressed as “before”, “before”, etc. , and may be implemented in any order, as long as the output of a previous process is not used in a later process. Regarding the operation flow in the claims, the specification, and the drawings, even if the description is made using "first," "next," etc. for the sake of convenience, it means that it is essential to carry out in this order. not a thing

11 laser light source, 12 beam shaper, 13 condenser lens, 13a focal plane, 14 mirror, 15, 16 beam splitter, 17 bandpass filter, 18 photodiode, 19 condenser lens, 20 aperture, 21 condenser lens, 22 image intensifier, 23 spectroscopic device, 24 computer, 25 delay generator, 26 laser controller, 27 inspected object, 31 condenser lens, 32 aperture, 33 condenser lens, 34 beam expander, 41 irradiation optical system, 42 condensing optical system, 100 inspection device, R laser light, P plasma emission

Claims (9)

An inspection apparatus for analyzing the concentration of an element contained in an object to be inspected by irradiating the object to be inspected with laser light from a laser light source,
an irradiation optical system having a condenser lens for condensing the laser beam onto a focal plane and irradiating the object to be inspected;
a condensing optical system for condensing plasma emission generated from the object to be inspected by the laser beam;
a measurement unit that measures the intensity of each wavelength of the plasma emission condensed by the condensing optical system;
The inspection apparatus, wherein the condensing optical system has an aperture member arranged at a position optically conjugate with the focal plane of the condensing lens. a second measuring unit that measures the intensity of a predetermined wavelength of the plasma emission;
2. The inspection apparatus according to claim 1, further comprising a correcting unit that corrects the intensity measured by said measuring unit based on said intensity measured by said second measuring unit. The measurement unit calculates an emission peak of the plasma emission by performing the measurement a plurality of times at predetermined time intervals, and calculates the intensity measured at the emission peak as the intensity for each wavelength of the plasma emission. 3. The inspection device according to claim 1 or 2. a shutter that controls incidence and blocking of the plasma emission to the measurement unit by opening and closing;
4. The inspection apparatus according to any one of claims 1 to 3, further comprising a delay generator that delays the time from when the object to be inspected is irradiated with the laser light to when the shutter is opened. 5. The inspection apparatus according to claim 4, wherein said shutter is an image intensifier that amplifies said plasma emission. 6. The inspection apparatus according to any one of claims 1 to 5, wherein said irradiation optical system further includes a beam shaper that shapes a beam profile of said laser light irradiated onto said object to be inspected into a Gaussian beam. 7. The beam shaper has a beam expander that expands the beam diameter of the laser beam, and a second aperture member arranged at a position optically conjugate with the focal plane of the condenser lens. The inspection device described in . 8. The condenser lens is shared by the condenser optical system, and the focal plane of the condenser lens is set closer to the condenser lens than the surface of the object to be inspected. The inspection device according to any one of . An inspection method for analyzing the concentration of an element contained in an object to be inspected by irradiating the object to be inspected with laser light from a laser light source,
condensing the laser light onto a focal plane by an irradiation optical system having a condensing lens and irradiating the object to be inspected;
condensing the plasma emission generated from the object to be inspected by the laser beam using a condensing optical system;
measuring the intensity of each wavelength of the plasma emission collected by the collection optical system;
The inspection method according to claim 1, wherein the condensing optical system has an aperture member arranged at a position optically conjugate with the focal plane of the condensing lens.

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