JP2763907B2 - Breakdown spectroscopic analysis method and apparatus - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method and an apparatus for breakdown spectroscopy, and more particularly to a method and apparatus suitable for identifying a component of a sample and quantifying its concentration. The present invention relates to an apparatus and a monitor for impurity concentration in a semiconductor manufacturing process comprising a breakdown spectrometer.

[Conventional technology]

Conventionally, an apparatus for analyzing a sample by spectroscopically analyzing the emission of breakdown plasma is described in Applied Spectroscopy, Vol. 38, No. 5, (1984), pp. 721 to 729 (Appl.
ied Spectroscopy, vol 38, No. 5 (1984) pp. 721-729). This conventional apparatus includes a light source that generates light for inducing a breakdown plasma, a spectroscope that disperses light emitted from the breakdown plasma induced by the light, and a photodetector that detects light emission from the dispersed plasma. And a photodetector is used to detect the intensity of the bright line based on the transition between specific levels of the sample, and to quantify the sample concentration using this signal.

[Problems to be solved by the invention]

In the above conventional technique, the signal used for quantifying the sample concentration is only the bright line intensity based on the transition between specific levels of the sample. Therefore, when the measurement time is fixed, the emission line intensity changes due to the change in the number of generated breakdown plasmas, and when measuring particulate matter, the emission line intensity changes due to the change in the position of the generated breakdown plasma. This causes a problem that the quantification range and accuracy of the concentration are deteriorated.

An object of the present invention is to correct a variation in the emission line intensity due to a variation in the number of times and position of generation of the breakdown plasma,
An object of the present invention is to provide a breakdown spectroscopic analysis method and apparatus with improved quantitative accuracy.

Another object of the present invention is to provide an impurity concentration monitor for a semiconductor manufacturing process comprising a breakdown spectroscopic analyzer with improved quantification accuracy, which corrects fluctuations in the emission line intensity due to fluctuations in the number and position of generation of breakdown plasma. It is to be.

[Means for solving the problem]

The object is to separate the emission line generated by the transition between the specific levels of the sample and the white light generated by the recombination of the plasma from the light generated from the breakdown plasma, measure the respective intensities, and emit light. This is achieved by taking the ratio between the intensity of the bright line and the intensity of the white light, and quantifying the sample concentration using the value of the ratio.

Further, the above object is to provide a light source for generating light for inducing a breakdown plasma, a spectroscope for dispersing light emission from the breakdown plasma induced by the light, and a light detection for detecting light emission from the dispersed plasma. And a calculating means for calculating the ratio of the intensity of the bright line generated by the transition between the specific levels of the sample and the intensity of the white light generated by the recombination of the plasma. You.

Further, the above object is to provide a breakdown spectroscopic analyzer, in which an acoustic detector for detecting a sound generated from the breakdown, an intensity of a bright line of the sample detected by the photodetector, and a sound of the sound detected by the acoustic detector. This is achieved by providing a calculation means for obtaining a ratio with the intensity.

Further, the above object is achieved by configuring an impurity concentration monitor in a semiconductor manufacturing process with the above-configured breakdown spectrometer.

[Action]

The light source generates light for inducing breakdown. The light is sent to a sample cell containing a sample and collected. A plasma is generated by the breakdown in the light condensing portion, and the plasma generates a bright line-like light emission caused by a transition between specific levels of the sample and a white continuous light emission caused by the recombination of the plasma. The light is split by a spectroscope and detected by a photodetector. Then, the ratio between the intensity of the bright line and the intensity of the white light is determined by the calculating means, and the sample concentration is determined using the value of the ratio.

In addition, in the configuration provided with the acoustic detector, the intensity of the emission line is detected by the spectroscope and the photodetector from the emitted light from the generated breakdown plasma, and the intensity of the acoustic wave generated from the breakdown is detected by the acoustic detector. Then, the ratio between the intensity of the bright line and the intensity of the acoustic wave is obtained by the calculation means, and the sample concentration is obtained using the value of the ratio, whereby the quantification can be performed with high accuracy.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS.

In FIG. 1, a light source 1 generates light for inducing a breakdown, and a laser is used because a high energy is required to induce a breakdown. As this laser, it is preferable to use a Palace laser capable of instantaneously obtaining a high energy density. The excitation light 20 from the light source 1 is condensed by the condenser lens 11 and sent to the cell 2. A sample is placed in the cell 2, and a breakdown occurs in a region (referred to as a beam waist) where the energy sample of the excitation light 20 exceeds a threshold that causes the breakdown. FIG. 2 shows an enlarged view of a beam waist portion. Light is generated from the plasma generated by the breakdown, that is, the breakdown plasma. The light includes a bright line-like emission caused by a transition between specific levels of the sample and a white light (continuous light) caused by the recombination of the plasma. ). Therefore, in order to separate these lights, the light is split by the spectroscope 3 and detected by the photodetector 4. The spectroscope 3 generally uses a diffraction grating, and the photodetector 4 uses a photomultiplier tube or a photodiode array. The plasma emission spectrum of the sample detected by the photodetector 4 is recorded in the recorder 8 via the arithmetic unit 4, and the component of the sample is identified from the wavelength of the bright line. Further, the bright line intensity of the sample and the white light intensity of the plasma coupling detected by the photodetector 4 are sent to the arithmetic unit 6, and the ratio between the bright line intensity and the white light intensity is obtained, and the concentration of the sample is quantified from this ratio. It is recorded in recorder 8.

Here, the principle of the breakdown light emission will be described with reference to FIG. FIG. 3 schematically shows an atom model and electron orbital levels before and after light irradiation. First, before light irradiation, an electron exists on an electron orbit around a nucleus, and the electron is at a ground level. Light is illuminated,
When a breakdown occurs, electrons jump out of orbital levels and even exceed the ionization potential. At this time, the nuclei (or ions) and the electrons are separated from each other and enter a plasma state. Immediately after the light irradiation, recombination of the plasma starts. That is, the collision between the separated electron and the atomic nucleus (or ion) captures the electron at the orbital level. Electrons before being captured in orbital levels have different energies, but when captured in orbital levels, emit that energy as light. Because this light has various energies,
Observed as white light. After the plasma recombination, a phenomenon occurs in which electrons at the excited level return to the ground level. This phenomenon also involves light emission. In this case, an energy difference between a specific excitation level and a ground level is determined by a substance, and light having a wavelength corresponding to the energy is generated. This is the bright line. Therefore, the substance can be identified from the wavelength of the bright line, and the concentration of the substance can be obtained from the intensity. Therefore, even in a multi-component system, since a bright line corresponding to each substance is generated, it is possible to identify and quantify each substance from the wavelength and intensity of the bright line.

In the present embodiment, based on the above principle, when the components of the sample are unknown, the plasma emission spectrum of the sample is first recorded in the recorder 8 in the first breakdown spectroscopic analysis, and the components are identified from the result. Breakdown spectroscopy is performed to determine the ratio between the intensity of the emission line and the intensity of the white light of plasma coupling for the identified component, and the concentration of the sample is quantified from this ratio. If the components of the sample have been identified, the concentration of the sample is directly quantified.

Next, the principle of the present invention will be described with reference to FIG.

When the sample to be measured is a solution, since the breakdown occurs in the entire beam waist area as shown in FIG. 4A, the generation position does not change. However, since the measurement is usually performed with the measurement time kept constant, if the number of times of plasma emission within the measurement time changes, the measured bright line intensity also changes. At this time, the bright line intensity E is expressed by the following equation.

E∝C _s · I ₀ ⁿ · φ (1) where, C _s : concentration of the sample component in the solution I ₀ : excitation light intensity n: order based on the excitation potential of the sample component φ: number of times of plasma generation n is a value that increases as the excitation potential of the sample component increases.

On the other hand, the white light intensity B at this time is expressed as follows.

B∝M · I ₀ · φ (2) M: matrix concentration Here, the matrix concentration refers to the concentration of a component other than the substance to be measured, and specifically, the solvent refers to the concentration of a coexisting substance. Since the white light intensity is considered to be affected by the components and the density of the matrix, it is expressed as in the above equation (2).

Therefore, taking the ratio (E / B) between the intensity of the bright line and the intensity of the white light, E / B∝ (C _s / M) · I ₀ ^n-1 (3) It is possible to do. Therefore, if the matrix density M, and the irradiation light intensity I ₀ constant, thereby enabling the concentration quantified using a proportional relationship between the sample component concentrations and E / B value.

Next, the case where the measurement sample is a particle will be described. In the case of particles, component analysis must be applied on a particle-by-particle basis. Therefore, as shown in FIG. 4 (b), the position where the particles are turned into plasma is not constant, and the energy of the excitation light absorbed varies depending on the position.
Bright line intensity fluctuates. The bright line intensity E at this time is expressed as follows.

E∝C _P · I ₀ ⁿ · f (x) (4) C _P : Concentration of sample component in particles f (x): Change rate of excitation light energy density at plasma generation position x On the other hand, white intensity B at this time _{is, BαM · I 0 · f (} x) ... (5) next, taking the ratio of the same E and B in the case of a _{solution, E / Bα (C P /} M) · I 0 n-1 .. (6), the fluctuation of the plasma generation position can be corrected. Therefore, as in the case of the solution, the component concentration in the particles can be determined.

Here, by setting the intensity of light to be irradiated higher than the intensity at which the particle breaks down and lower than the intensity at which the medium in which the particle exists breaks down, only the particles are selectively broken down. It is possible to do.

Based on the above principle, the arithmetic unit 6 has the following equation C _s = (1 / K _s · I ₀ ^{n -1} ) · (E / B) obtained from the above equations (3) and / or (6). (7) C _p = (1 / K _p · I ₀ ^n-1 ) · (E / B) (8) is stored. Here, K _s and K _p are composed of an apparatus constant S and a matrix concentration M based on the measurement sensitivity of the apparatus,
It is expressed as follows.

K _s or _{K p = S / M (9} ) Next, the procedure for actually measured on the basis of the present embodiment. Here, a description will be given using a Na ⁺ solution as an example.

FIG. 5 shows an example of the result of spectral analysis of breakdown plasma emission in a Na ⁺ solution. In this figure, it can be seen that emission lines between the specific levels of Na ⁺ are measured at 589.0 nm and 589.6 nm, and white light is measured over the entire wavelength range. Here, the bright line intensity and the white light intensity can be separated as shown in FIG.

It is necessary to obtain in advance n and K _s in (7) before measuring the sample. Therefore, a solution having the same matrix concentration as the sample and having a known sample concentration is prepared. First, when the sample concentration constant, by changing the irradiation light intensity I _0, E / B
Measure the ratio. One example is shown in FIG. In this figure, since E / B is linearly proportional to I ₀ , it can be seen from equation (3) that n is 2. Next, when I _{0 is} constant, K _s in the following equation can be obtained from a change in the value of the E / B ratio when the sample concentration is increased.

_{E / B = K s · C} s · I 0 n-1 (10) Therefore, in the measurement, stores n was first determined in advance, the K _p and the irradiation light intensity I ₀ to the computing unit 6, described above ( 7) is given to the equation. And the equation (7), by substituting the value of the measured E / B, it is possible to determine the C _s.

Also in the case of particles, _Cp is determined by the same procedure as described above.

As described above, according to the present embodiment, there is an effect that the variation in the intensity of the bright line due to the number of times and the position where the breakdown plasma is generated can be corrected, and the component can be accurately quantified.

Another embodiment of the present invention will be described with reference to FIG.

In this embodiment, the intensity of the emission line is measured by the spectroscope 3 and the photodetector 4 from the emitted light from the generated breakdown plasma, and the intensity of the acoustic wave generated from the breakdown plasma is detected by the acoustic detector 5.

The acoustic wave intensity A is expressed as follows: A∝I ₀ · φ (11) when the sample is a solution, and A∝I ₀ · f (x) (12) when the sample is a particle. Become. Therefore, using the formulas (1) and (4), the ratio with the bright line intensity E is given by: E / A∝C _s · I ₀ ^n-1 (13) E / A∝C _p · I ₀ ^n-1 (14), and the influence of fluctuations in φ and f (x) can be corrected to quantify the concentration. The arithmetic unit 6 stores the same expressions as the above-mentioned expressions (7) and (8) obtained from the expressions (13) and (14), and obtains the density by detecting E and A. .

Therefore, according to the present embodiment, there is an effect that the fluctuation of the bright line intensity can be corrected by the acoustic wave generated from the plasma.

Next, still another embodiment of the present invention will be described with reference to FIG.

In the present embodiment, a time resolution processing device 7 for time-resolving the signal from the photodetector 4 is provided. A signal is sent from the light source 1 to the time-resolved processing device 7 when the pulse light is oscillated. The time-resolved processing device 7 measures the time-dependent change of the light generated after the signal reception as a starting point. As described above with reference to FIG. 3, white light is generated at the time of plasma recombination, and a bright line is generated at the final stage. Therefore, according to the time-resolved measurement, it is possible to temporally separate the white light and the bright line. The S / B ratio obtained by this time resolution is sent to the arithmetic unit 6 to obtain the sample concentration.

According to the present embodiment, the white light intensity and the bright line intensity can be easily separated, the weak bright line can be prevented from being buried in the white light, and the lower detection limit of the bright line can be improved.

Next, still another embodiment of the present invention will be described with reference to FIG.

In this embodiment, the excitation light 20 from the light source 1 is transmitted to the probe 13 using an optical fiber, and the light emission 21 from the breakdown plasma is transmitted to the spectroscope 3 using an optical fiber.

According to the present embodiment, there is an effect that the place where the breakdown is emitted can be easily moved, and in-situ analysis can be performed at the place where measurement is desired.

Finally, application examples of the present invention will be described. The breakdown spectrometer of the present invention is used as an impurity concentration monitor in a semiconductor manufacturing process, for example. In this case, the cell 2 of the above-described embodiment, for example, the cell 2 of the embodiment shown in FIG. 1, is a pipe portion through which ultrapure water for semiconductor manufacturing processing flows in a semiconductor manufacturing process. There is no substantial change in other configurations. This makes it possible to identify the impurity component contained in the ultrapure water and accurately quantify the concentration.

In addition, the breakdown spectrometer of the present invention can be used for identification of components of various substances and quantification of the concentration in addition to the monitoring of the impurity concentration in the passive passive fabrication process. It can be used for monitoring the concentration of a solution.

〔The invention's effect〕

ADVANTAGE OF THE INVENTION According to this invention, when performing quantitative analysis by breakdown spectroscopy, since the fluctuation | variation of the bright line intensity of a sample by the fluctuation | variation of the frequency | count of generation or the generation position of breakdown plasma can be corrected, the quantification precision of breakdown spectroscopy can be improved. This has the effect.

Further, since the present invention is an internal standard method for correcting using white light or acoustic waves generated from breakdown plasma, there is an effect that correction can be performed accurately with a simple device.

Further, the present invention has an effect that an impurity component contained in ultrapure water can be identified in a semiconductor manufacturing process, and its concentration can be accurately quantified.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a breakdown spectrometer according to one embodiment of the present invention, FIG. 2 is an enlarged view of a beam waist in breakdown spectroscopy, and FIG. FIGS. 4A and 4B are diagrams for explaining the principle of breakdown light emission. FIGS. 4A and 4B are schematic diagrams of a breakdown plasma generation position when a sample is a solution and particles, respectively. FIG. is a diagram showing an example of a plasma emission spectrum of a Na ⁺ solution, FIG. 6 is a diagram showing an example of the excitation light-dependent measurements of E / B value in Na ⁺ solution, FIG. 7 is another invention FIG. 8 is a block diagram of a breakdown spectrometer according to another embodiment, FIG. 8 is a block diagram of a breakdown spectrometer according to still another embodiment of the present invention, and FIG. 9 is still another embodiment of the present invention. Breakdown spectroscopy according to embodiments It is a configuration diagram of a diffraction device. DESCRIPTION OF SYMBOLS 1 ... Light source 3 ... Spectroscope 4 ... Photodetector 6 ... Calculator 7 ... Time-resolved processing device 9,10 ... Optical fiber

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Masaharu Sakagami 1168 Moriyama-cho, Hitachi City, Ibaraki Prefecture Energy Research Laboratory, Hitachi, Ltd. (56) References JP-A-61-178645 (JP, A) JP-A-56- 114746 (JP, A) JP-A-60-209146 (JP, A) JP-A-63-81248 (JP, A) JP-A-1-259240 (JP, A) JP-A-5-184739 (JP, A) (58) Field surveyed (Int.Cl. ⁶ , DB name) G01N 21/62-21/74 G01N 15 JOIS

Claims (8)

(57) [Claims] 1. The method according to claim 1, wherein the emission from the breakdown plasma induced by the light irradiation is spectrally separated to determine a ratio of an intensity of a bright line generated by a transition between specific levels of the sample to an intensity of white light generated by recombination of the plasma. And performing a quantitative analysis of the sample using the value of the ratio. 2. The sample to be quantified is in the form of particles.
In the breakdown spectroscopic analysis method described, the intensity of the light to be irradiated is set higher than the intensity at which the particles break down, and the intensity is set lower than the intensity at which the medium in which the particles are present breaks down. Breakdown branch school analysis method. 3. A light source for generating light for inducing a breakdown plasma, a spectroscope for separating light emission from the breakdown plasma induced by the light, and a photodetector for detecting light emission from the separated plasma. And a calculating means for calculating a ratio of an intensity of a bright line generated by a transition between specific levels of the sample and an intensity of white light generated by recombination of the plasma. Breakdown spectrometer. 4. A light source for generating light for inducing a breakdown plasma, a spectroscope for separating light emission from the breakdown plasma induced by the light, and a photodetector for detecting light emission from the separated plasma. A sound detector that detects the intensity of the acoustic wave generated from the breakdown, the intensity of the bright line of the sample detected by the light detector, and the sound detected by the sound detector. A breakdown spectrometer comprising a calculating means for calculating a ratio with a wave intensity. 5. The breakdown spectrometer according to claim 3, wherein a time-resolved photodetector for time-resolved detection of emission from the breakdown plasma is used as the photodetector. Down spectrometer. 6. The breakdown spectrometer according to claim 3, wherein light for inducing a breakdown plasma is transmitted through an optical fiber. 7. The breakdown spectrometer according to claim 3, wherein the light emission generated by the breakdown is transmitted through an optical fiber. 8. An impurity concentration monitor for a semiconductor manufacturing process, comprising the breakdown spectrometer according to any one of claims 3 to 7.