JP2020193809A - Trace metal detection device and trace metal detection method - Google Patents

Abstract

To provide a trace metal detection device and a trace metal detection method capable of detecting trace metals in a liquid sample in real time.SOLUTION: A liquid sample 20 is placed on a base material 50. A laser irradiation unit 110 irradiates the liquid sample 20 with a laser pulse. A control circuit 120 allows continuous irradiation with laser pulses from the laser irradiation unit 110 multiple times. A spectroscope 130 divides light emitted by plasma generated by the continuous irradiation with laser pulse multiple times.SELECTED DRAWING: Figure 1

Description

The present invention relates to a trace metal detection device and a trace metal detection method.

Devices and methods for measuring the substances contained in a sample by applying Laser Induced Breakdown Spectroscopy (LIBS) are known.

For example, in the concrete-containing substance measuring method described in Patent Document 1, two laser beams are applied to the concrete surface to be inspected. The first laser beam is focused on the concrete fracture surface 6a to generate a plasma plume. The second laser beam is focused in the plasma plume generated by the first laser beam irradiation. Emissions from plasmatized material are decomposed for each wavelength.

In the method for preparing a test specimen plate described in Patent Document 2, a binder layer is formed on a substrate, and a liquid sample is dropped onto the binder layer and evaporated to dryness to prepare a specimen preparation. The contained substance measuring device described in Patent Document 2 irradiates the surface of the sample preparation with a laser beam to ablate the sample-containing substance into plasma, and decomposes the emission of the brazed substance for each wavelength. Obtain the emission spectrum.

JP-A-2009-68969 Japanese Unexamined Patent Publication No. 2016-95139

In the semiconductor manufacturing process, a cleaning liquid is used to keep the surface of a substrate such as a silicon wafer in a clean state in order to improve the quality and yield of the product. The cleaning liquid is used repeatedly, but a small amount of metal is mixed in the cleaning liquid every time the semiconductor wafer is cleaned. It is important to detect trace metals in the cleaning solution in order to measure (know) the timing of changing the cleaning solution.

The method described in Patent Document 1 is for measuring the concentration of a substance contained in a solid such as concrete, and cannot detect a trace amount of metal in a liquid sample such as a cleaning liquid.

Since the method described in Patent Document 2 requires preparation of a specimen preparation, a step for preparing a sample such as a step of drying a liquid sample to make a solid sample is required, and for detecting trace metals in the liquid sample. It takes time. On the other hand, in order to meet the demand for monitoring the waste liquid of the production line, it is necessary to detect trace metals in the liquid sample in real time.

Therefore, an object of the present invention is to provide a trace metal detection device and a trace metal detection method capable of omitting a sample preparation step and detecting trace metals in a liquid sample in real time.

The first aspect of the present invention is a trace metal detection device that detects a trace metal in a liquid sample, a base material on which the liquid sample is placed, and a laser irradiation unit that irradiates a laser pulse toward the liquid sample. The present invention relates to a trace metal detection device including a control circuit for continuously irradiating a laser pulse a plurality of times from a laser irradiation unit and a spectroscope for dispersing the light emitted by plasma generated by irradiating the laser pulse a plurality of times continuously. ..

A second aspect of the present invention is a trace metal detection method for detecting a trace metal in a liquid sample, in which a step of dropping the liquid sample onto a base material and a laser pulse toward the liquid sample are continuously applied a plurality of times. The present invention relates to a trace metal detection method including a step of irradiating and a step of dispersing light emitted by plasma generated by irradiating a liquid sample with a plurality of consecutive laser pulses.

According to the present invention, plasma can be generated by irradiating a liquid sample with a laser pulse a plurality of times in succession. As a result, the sample preparation step can be omitted, and trace metals in the liquid sample can be detected in real time.

It is a block diagram explaining the structure of the trace metal detection apparatus which concerns on embodiment. It is a figure which shows one form of the laser pulse which the laser irradiation unit 110 irradiates. It is a figure which shows the spectroscopic spectrum when one laser pulse is irradiated. It is a figure which shows the spectral spectrum at the time of irradiating two laser pulses continuously. It is a flowchart which shows the procedure of the trace metal detection method of embodiment. It is a figure which shows another form of the laser pulse which a laser irradiation part 110 irradiates.

Hereinafter, embodiments will be described with reference to the drawings.
FIG. 1 is a block diagram illustrating a configuration of a trace metal detection device according to an embodiment.

The trace metal detection device 100 according to the embodiment detects the trace metal in the liquid sample 20 to be inspected by LIBS. For example, the liquid sample 20 is a cleaning liquid used for cleaning a semiconductor wafer used in the cleaning apparatus 10 in the semiconductor manufacturing process.

The semiconductor manufacturing process consists of a front end of line (FEOL) until a device (transistor, capacitor, resistor, etc.) is formed as a pattern on a semiconductor wafer, and a wiring process (FEOL: Front End Of the Line) that forms a multilayer wiring thereafter. BOOL: Back End Of the Line) and included. Contaminants such as inorganic substances containing various metals are generated in each manufacturing process of semiconductor devices. When such a pollutant adheres to the semiconductor device, the electrical characteristics of the semiconductor device are deteriorated, which greatly affects the quality of the semiconductor device. Therefore, removal of contaminants by the cleaning device 10 is indispensable in the semiconductor manufacturing process. As the structure of semiconductor devices becomes finer, more advanced cleaning technology is required.

As a cleaning process in the semiconductor manufacturing process, so-called wet cleaning, in which a semiconductor wafer is cleaned with a liquid, is widely used. For example, in order to remove metal contamination, a mixed solution of ammonia, hydrogen peroxide solution and pure water, or a mixed solution of hydrochloric acid, hydrogen peroxide solution and pure water is used as the cleaning solution. The cleaning device 10 circulates the cleaning liquid and is used repeatedly, but every time the semiconductor wafer is cleaned, a small amount of metal is mixed in the cleaning liquid. In cleaning in the wiring process, as an example, Cu (copper), which is a wiring material, is mixed in the cleaning liquid. When the same cleaning liquid is repeatedly used in circulation, the Cu concentration in the cleaning liquid gradually increases, and the cleaning liquid becomes contaminated with Cu. As the cleaning liquid becomes contaminated, the cleaning capacity of the cleaning liquid also decreases.

On the other hand, since the amount of cleaning liquid used in the semiconductor manufacturing line is enormous, it is not desirable to dispose of the cleaning liquid from the viewpoint of environmental load as well as increasing the manufacturing cost if the cleaning liquid is frequently replaced. .. Therefore, the user of the cleaning device 10 wants to use the cleaning liquid repeatedly for as long as possible within a range in which the quality of the semiconductor device as a final product can be maintained. For this reason, there is an increasing need to grasp trace metals in the cleaning liquid in real time.

With reference to FIG. 1, the trace metal detection device 100 according to the embodiment detects trace metals in a liquid sample. The trace metal detection device 100 includes a sample stage 51, a base material 50, a laser irradiation unit 110, a control circuit 120, a condenser 150, an optical fiber 160, a spectroscope 130, a data processing device 190, and the like. It is provided with a display device 195.

An irradiation window 115 is formed in the chamber 200. A condenser 150 is attached to the chamber 200. The condenser 150 may be arranged inside the chamber 200.

A sample stage 51 is arranged inside the chamber 200. The base material 50 can be placed on the sample stage 51. The sample stage 51 can be moved in the horizontal and vertical directions by a driving means (not shown).

A laser irradiation unit 110, an optical fiber 160, a spectroscope 130, a control circuit 120, a data processing device 190, and a display device 195 are arranged outside the chamber 200.

A certain amount of cleaning liquid is collected as a liquid sample 20 from the cleaning apparatus 10 and dropped onto the base material 50. As the base material 50, for example, a chip made of silicon (Si) can be used. The collection of the liquid sample 20 from the cleaning liquid and the dropping of the collected liquid sample 20 onto the base material 50 can be performed manually as appropriate. Alternatively, the liquid sample 20 may be automatically collected from the cleaning liquid while the cleaning device 10 is in operation, and the collected liquid sample 20 may be dropped onto the base material 50. The base material 50 is placed on the sample stage 51.

The laser irradiation unit 110 irradiates a laser pulse toward the liquid sample 20 placed on the base material 50. The laser irradiation unit 110 includes a laser oscillator 112 and a condenser lens 114.

The laser oscillator 112 emits a laser pulse. The laser oscillator 112 may be composed of, for example, a laser medium, an excitation source, and an optical resonator. As the laser oscillator 112, a YAG laser having a Q switch, a CO ₂ laser, an excimer laser, or the like can be used.

The condenser lens 114 collects the laser pulse emitted from the laser oscillator 112. The focused laser pulse is irradiated toward the liquid sample 20 on the base material 50 through the irradiation window 115 provided on the side surface of the chamber 200. The laser pulse is incident on the liquid sample 20 from an oblique direction.

The control circuit 120 continuously emits two laser pulses from the laser irradiation unit 110. The control circuit 120 can control the intensity of the laser pulse, the pulse width (= half width) of the laser pulse, and the pulse interval.

Conventionally, it has been known that plasma is generated by irradiating a solid sample with a laser pulse. In Patent Document 1, the S / N of the emission spectrum of plasma is improved by irradiating a solid sample with a laser pulse twice in succession. In Patent Document 1, the width tw of the laser pulse is set to a value in the range of several tens of nm or several tens of fs to several hundred ps, and the interval td of two adjacent laser pulses is set to a value in the range of 500 ns to 2 μs. The interval td (500 ns to 2 μs) between two adjacent laser pulses is such that white light noise is reduced and excited atoms remain in the plasma plume after the plasma plume is generated by the first laser pulse. It is said that it is time to be secured.

In Patent Document 2, in consideration of the fact that plasma is not generated even when a liquid sample is irradiated with a laser pulse (see paragraphs 0011 and 0012 of Patent Document 2), a binder layer is formed on the substrate to form a binder layer. A test specimen preparation is prepared by dropping a liquid sample and evaporating to dryness. In Patent Document 2, since it is necessary to prepare a test specimen, real-time measurement cannot be performed.

FIG. 2 is a diagram showing one form of a laser pulse irradiated by the laser irradiation unit 110 of the embodiment.

The inventor of the present application sets the width of the laser pulse and the interval between two adjacent laser pulses to an appropriate value so that the first laser pulse irradiation of the liquid sample 20 does not generate plasma. It was discovered that the liquid sample 20 was turned into plasma by the second laser pulse and emitted light.

The inventor of the present application sets the width tw of the laser pulse to a value in the range of 0.5 ns or more and 1.5 ns or less, and sets the interval td of two adjacent laser pulses to a value in the range of 100 μs or more and 250 μs or less. It was discovered that the peak of the spectral spectrum was sufficiently large. The width tw of the laser pulse and the distance td between the two adjacent laser pulses are not limited to the above range. Since it may be possible to detect the peak of the spectroscopic spectrum even if it deviates from the above range, those skilled in the art will be able to detect the width tw of the laser pulse and the interval td of two adjacent laser pulses depending on the required accuracy and the like. Can be adjusted as appropriate. However, what is important is the combination of the range of the width tw of the laser pulse of Patent Document 1 (several tens of nm or several tens of fs to several hundred ps) and the range of the interval td between two adjacent laser pulses (500 ns to 3 μs). The combination of the laser pulse width tw range (0.5 ns to 1.5 ns) and the laser pulse interval td range (100 μs to 250 μs) by the inventor of the present application is significantly different.

In Patent Document 1, a plasma plume is generated by irradiating a concrete sample with a first laser pulse. After that, the second laser pulse is irradiated when the white light noise is reduced and the excited atoms remain in the plasma plume. The combination of the range of the width tw of the laser pulse of Patent Document 1 and the range of the interval td of two adjacent laser pulses can cause such a phenomenon.

On the other hand, in the present application, plasma is not generated by irradiating the liquid sample 20 with the first laser pulse, but the liquid sample 20 shifts to some transition state. By irradiating the liquid sample 20 with the second laser pulse, the transition state shifts to the plasma plume. The combination of the range of the width tw of the laser pulse of the present application and the range of the interval td of two adjacent laser pulses can cause such a phenomenon.

Further, in Patent Document 1, the first laser pulse and the second laser pulse are emitted from separate laser oscillators. When irradiating two lasers from two separate laser oscillators as described in Patent Document 1, it is difficult to control the pulse interval even if two pulses are irradiated, and a sample of each pulse is used. The irradiation point in the above will be misaligned. Therefore, in the prior art, it was considered that the step of drying the sample was an essential step. Alternatively, even if the liquid sample is experimentally irradiated with two pulses to form plasma, the accuracy of plasma conversion is low. On the other hand, in the present application, a plurality of laser pulses are irradiated to the liquid sample 20 from a single laser oscillator 112 in the laser irradiation unit 110. In Patent Document 1, it is necessary to adjust the timing of emitting laser pulses in the two laser oscillators. Since the interval between laser pulses is extremely short, it is not easy to adjust this timing, and an error may occur. On the other hand, in the present application, since a plurality of laser pulses are emitted from a single laser oscillator 112, it is not necessary to adjust the timing. As a result, the laser pulse interval td can be easily adjusted with high accuracy. Further, since the deviation of the irradiation (collision) portion of each of the two pulse laser samples is small, the accuracy of plasma conversion of the sample is improved.

Again, with reference to FIG. 1, the light emitted by the plasma is input to the spectroscope 130 through the condenser 150 and the optical fiber 160. The spectroscope 130 outputs a spectroscopic spectrum by dispersing the light emitted by the generated plasma. The spectral spectrum represents the light intensity for each wavelength. The peak wavelength differs in the spectroscopic spectrum depending on the metal component contained. For example, Cu (copper) has peaks at wavelengths of 324.7 (nm) and 327.4 (nm). The data processing apparatus 190 can identify the type of metal contained in the liquid sample 20 from the peak wavelength appearing in the spectral spectrum.

The data processing device 190 stores in the memory a table in which the correspondence between the light intensity of the peak wavelength and the corresponding metal concentration is determined. The data processing apparatus 190 detects the concentration of the metal corresponding to the light intensity of the peak wavelength of the obtained spectral spectrum by referring to the table. For example, the data processing device 190 refers to a calibration curve showing the correspondence between the concentration of the metal and the light intensity, which is created and stored in advance, and the metal corresponding to the light intensity of the peak wavelength of the obtained spectral spectrum. It may be used to specify the concentration of.

The data processing device 190 is composed of a personal computer, a microcomputer, or the like having an I / O port, an A / D converter, a D / A converter, a memory, and a CPU (Central Processing Unit) (not shown). be able to.

The display device 195 displays a spectrum, a detected metal concentration, and the like. The display device 195 can be typically configured by a display screen such as a liquid crystal display.

Next, when Cu is contained in the liquid sample 20, the spectral spectrum when one laser pulse is irradiated and the spectral spectrum when two laser pulses are continuously irradiated will be described.

FIG. 3 is a diagram showing a spectral spectrum when one laser pulse is irradiated.
As shown in FIG. 3, the liquid sample 20 is not converted into plasma by irradiating only one laser pulse, so that no peak is detected in the spectral spectrum.

FIG. 4 is a diagram showing a spectral spectrum when two laser pulses are continuously irradiated. Here, as described above, the width tw of the laser pulse is set to a value in the range of 0.5 ns or more and 1.5 ns or less, and the interval td between two adjacent laser pulses is set to a value in the range of 100 μs or more and 250 μs or less. And said.

As shown in FIG. 4, peaks P1, P2, and P3 can be detected in the liquid sample 20 by irradiating two laser pulses in succession. The peak P1 is a peak due to Cu (324.7 nm). The peak P2 is a peak due to Cu (327.4 nm). The peak P3 is a peak due to the base material silicon (Si). Thereby, it is possible to detect that Cu is contained in the liquid sample 20.

FIG. 5 is a flowchart showing the procedure of the trace metal detection method of the embodiment.
In step S101, the liquid sample 20 is dropped onto the base material 50.

In step S102, the control circuit 120 continuously irradiates the liquid sample 20 with the laser pulse twice from the laser irradiation unit 110. The control circuit 120 sets the width tw of the laser pulse to a value within the range of 0.5 ns or more and 1.5 ns or less, and sets the interval td between two adjacent laser pulses within the range of 100 μs or more and 250 μs or less. Set to the value of.

In step S103, the spectroscope 130 disperses the light emitted by the plasma generated by irradiating the liquid sample with two consecutive laser pulses, and outputs a spectroscopic spectrum.

In step S104, the data processing device 190 detects the concentration of trace metals such as Cu contained in the liquid sample 20 based on the spectral spectrum. The data processing device 190 displays the detected trace metal concentration on the display device 195.

As described above, according to the present embodiment, the liquid sample is irradiated with a laser pulse twice in succession to generate plasma, and the light emitted by the plasma is separated to generate a trace amount of metal in the liquid sample. Can be detected in real time.

In the above description, the laser irradiation unit 110 irradiates the liquid sample 20 with the laser pulse twice, but the present invention is not limited to this.

FIG. 6 is a diagram showing another form of the laser pulse irradiated by the laser irradiation unit 110.
As shown in FIG. 6, the laser irradiation unit 110 may irradiate the liquid sample 20 with a laser pulse three or more times. In this case, the width tw of the laser pulses and the interval td between two adjacent laser pulses may be constant values or may be changed.

Further, in the above description, the liquid sample 20 is a cleaning liquid used for cleaning the semiconductor wafer used in the cleaning apparatus 10 in the semiconductor manufacturing process, but the present invention is not limited to this. The liquid sample 20 contains various liquids. For example, the liquid sample 20 may be factory wastewater or the like.

(Aspect)
It will be understood by those skilled in the art that the above-described exemplary embodiments are specific examples of the following embodiments.

(Section 1)
The trace metal detection device (100) for detecting the trace metal in the liquid sample of one embodiment includes a base material (50) on which the liquid sample (20) is placed and a base material (50).
A laser irradiation unit (110) that irradiates a laser pulse toward the liquid sample,
A control circuit (120) that continuously irradiates the laser pulse from the laser irradiation unit a plurality of times.
It may be provided with a spectroscope (130) into which light emitted by plasma generated by irradiation of the laser pulses consecutively a plurality of times is input.

According to the trace metal detection device of the first item, trace metals in a liquid sample can be detected in real time.

(Section 2)
In the trace metal detection device of the first item, the width of the laser pulse is 0.5 ns or more and 1.5 ns or less, and the distance between two adjacent laser pulses is 100 μs or more and 250 μs or less. May be good.

According to the trace metal detection device of the second term, the peak of the spectroscopic spectrum output from the spectroscope can be sufficiently increased.

(Section 3)
In the trace metal detection device according to any one of the first and second terms, the laser irradiation unit may irradiate the laser pulse emitted from a single laser oscillator (112) a plurality of times in succession.

According to the trace metal detection device of the third item, the interval between two adjacent laser pulses can be easily adjusted with high accuracy.

(Section 4)
In the trace metal detection device according to any one of items 1 to 3, the liquid sample may be a cleaning liquid for a semiconductor wafer.

According to the trace metal detection device of the fourth item, trace metals such as Cu in the cleaning liquid of the semiconductor wafer can be detected.

(Section 5)
A trace metal detection method for detecting a trace metal in a liquid sample according to one embodiment is
The step of dropping the liquid sample onto the base material and
A step of continuously irradiating the liquid sample with a laser pulse a plurality of times,
It may include a step of splitting the light emitted by the plasma generated by irradiating the liquid sample with the laser pulse that is continuous a plurality of times.

According to the trace metal detection method of the fifth item, trace metals in a liquid sample can be detected in real time.

It should be considered that the embodiments disclosed this time are exemplary in all respects and not restrictive. The scope of the present invention is shown by the scope of claims rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

10 Cleaning device, 20 Liquid sample, 50 Base material, 51 Sample stage, 100 Trace metal detector, 110 Laser irradiation unit, 112 Laser oscillator, 114 Condensing lens, 115 Irradiation window, 120 Control circuit, 130 Spectrometer, 150 Condenser, 160 optical fiber, 190 data processor, 195 display, 200 chambers.

Claims (5)

A trace metal detector that detects trace metals in a liquid sample.
The base material on which the liquid sample is placed and
A laser irradiation unit that irradiates a laser pulse toward the liquid sample,
A control circuit that continuously irradiates the laser pulse from the laser irradiation unit a plurality of times.
A trace metal detection device including a spectroscope that disperses light emitted by plasma generated by irradiation of the laser pulses continuously a plurality of times. The width of the laser pulse is 0.5 ns or more and 1.5 ns or less.
The trace metal detection device according to claim 1, wherein the distance between two adjacent laser pulses is 100 μs or more and 250 μs or less. The trace metal detection device according to claim 1 or 2, wherein the laser irradiation unit irradiates the laser pulse emitted from a single laser oscillator a plurality of times in succession. The trace metal detection device according to any one of claims 1 to 3, wherein the liquid sample is a cleaning liquid for a semiconductor wafer. A trace metal detection method that detects trace metals in a liquid sample.
The step of dropping the liquid sample onto the base material and
A step of continuously irradiating the liquid sample with a laser pulse a plurality of times,
A method for detecting a trace metal, comprising a step of dispersing light emitted by plasma generated by irradiating the liquid sample with a plurality of consecutive laser pulses.

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