JP2907176B2 - Calibration curve creation method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for preparing a calibration curve when mass spectrometry is performed by ionizing impurities in the order of ppt to ppb contained in an inert gas at atmospheric pressure.

[0002]

2. Description of the Related Art When ionizing a trace amount of impurities in the order of ppt to ppb contained in an inert gas under atmospheric pressure and performing mass spectrometry, not all of the contained impurities are ionized. To make measurements
A calibration curve must be created in advance.

Conventionally, to prepare a calibration curve, as shown in FIG. 5, a standard gas 7 containing impurities on the order of several ppm is used.
Are diluted using a carrier gas 4 such as 10-fold dilution, 100-fold dilution, and 1000-fold dilution. A calibration curve was created from the linearity. Typical examples of impurities in the inert gas include water (H ₂ O), O ₂ , and CH ₄ . FIG.
Among them, 5 is a gas purification device, and 6 is a mass flow controller.

[0004]

In the conventional method shown in FIG. 5, a calibration curve for impurities in an inert gas must be prepared by a dilution method. However, in this method, the target of the impurities is boron or boron. In the case of fluorine, there was a problem that it was impossible to prepare a calibration curve.

[0005] The reason is that when the target of impurities in the inert gas is boron or fluorine, it is impossible to prepare a standard gas on the order of several ppm because there is no other measuring means at the ppm level. It is.

Further, even if it is possible to prepare a standard gas by containing impurities in the inert gas in the order of several percent, there is a problem that it is impossible to prepare a calibration curve with such a standard gas.

The reason is that the content of boron or fluorine is pp
If the order exceeds m, the danger increases, handling becomes difficult, and the flow rate used for measurement is 1 l / m.
dilution, the dilution is 1000 from the mass flow accuracy.
The doubling dilution is the limit, and when the impurity content exceeds the ppm order, in order to dilute to the ppt to ppb level, it is necessary to use a double dilution method. This is because an accurate calibration curve cannot be created.

It is an object of the present invention to provide a method for preparing a calibration curve for quantitatively measuring a trace amount of boron or fluorine when ionizing impurities in the order of ppt to ppb in an inert gas at atmospheric pressure and performing mass spectrometry. And a device.

[0009]

In order to achieve the above object, a method for preparing a calibration curve according to the present invention is directed to a method for mass spectrometry for ionizing trace impurities in an inert gas at atmospheric pressure and performing mass spectrometry. A line forming method, comprising a sample forming step, a temperature raising step, and a desorption step, wherein the sample forming step forms a film containing a small amount of impurities on the substrate surface or does a small amount of impurities on the substrate. Thereby, a process for preparing a sample for mass spectrometry, and the temperature raising step is a process for heating the sample for mass spectrometry at a constant rate of temperature raising to gasify impurities contained in a substrate or a film. ,
The desorption process is a process of supplying gasified impurities as a gas to be ionized at a fixed flow rate using a carrier gas.

[0010] A calibration curve creating apparatus according to the present invention is a calibration curve creating apparatus in a mass spectrometer for ionizing a trace amount of impurities in an inert gas under atmospheric pressure and performing mass analysis. It has a heating part and a desorption part, and the sample preparation part forms a film containing a trace amount of impurities on the substrate surface,
Alternatively, a sample for mass spectrometry is produced by doping a trace amount of impurities into a substrate.
The mass spectrometry sample is heated to gasify impurities contained in a substrate or a film, and the desorption section supplies the gasified impurities as a gas to be ionized by a carrier gas. .

[0011]

In the present invention, a film containing a certain amount of impurities is formed on the surface of a substrate, or a certain amount of impurities is doped into a substrate, and this is used as a sample for mass spectrometry.

The mass spectrometry sample is heated to remove impurities from the substrate or the film as a gaseous substance, and this is supplied as a gaseous substance for mass spectrometry using a carrier gas.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a configuration diagram showing Embodiment 1 of the present invention.

Referring to FIG. 1, a calibration curve creating apparatus according to Embodiment 1 of the present invention uses a trace amount (pp.
(t to ppb order) to supply a gaseous substance as a calibration curve to a mass spectrometer for ionizing impurities in the order of t to ppb, and having a sample preparation unit 2a, a heating unit 2b, and a desorption unit 2c. ing.

The sample preparation section 2a forms a film 1a containing a trace amount of impurities on the surface of the substrate 1b to prepare a sample for mass spectrometry. In the first embodiment, a silicon oxide film (SiOF) 1a containing fluorine as an impurity
Is formed on the surface of the substrate 1b, and this is used as a sample for mass spectrometry.

The temperature raising section 2b heats the sample for mass spectrometry to gasify impurities contained in the film 1a of the substrate 1b. In the first embodiment, the mass spectrometry sample is heated from room temperature (23 ° C.) to 1000 ° C. at a heating rate of 20 ° C.
/ Min.

The desorption section 2c introduces the gasified impurities into the atmospheric pressure ionization mass spectrometer 3 at a flow rate of 1 l / min by a carrier gas, for example, high-purity air supplied through the gas purification device 5. Is what you do.

Hereinafter, a method of mass spectrometry will be described. As a sample for mass spectrometry for elevating and desorbing fluorine, a silicon wafer or a fragment thereof (hereinafter, referred to as a silicon sample) in which a silicon oxide film (SiOF) 1a containing fluorine as an impurity is grown on a substrate 1b is used.

A silicon sample is set on the retainer 2d of the desorption section 2c, and the silicon sample is heated from room temperature (23.degree. C.) to 1000.degree.
Heat at ° C / min.

The heated silicon sample is approximately 200
At a temperature of ° C., fluorine gas (F ₂ ) begins to desorb from the SiOF grown on the surface.

The desorbing section 2c is provided with an atmospheric pressure ionization mass spectrometer 3 using fluorine gas (F ₂ ) desorbed as a gaseous substance from the substrate film at a flow rate of 1 l / min using high-purity air used as a carrier gas. Introduce within.

The atmospheric pressure ionization mass spectrometer 3 detects the mass of fluorine ions ( ¹⁹ F ⁻ ) generated by ionization as an ion current.

During the heating at a fixed heating rate from room temperature to 1000 ° C., the ion current due to ¹⁹ F ⁻ was constantly measured.
The intensity distribution of the ion current as shown in FIG.

(Embodiment 2) Embodiment 2 of the present invention will be described with reference to FIG. Embodiment 2 shows a case in which boron (impurity) in an inert gas is quantitatively measured by using thermal desorption.

In the second embodiment, a wafer or a fragment thereof obtained by doping (ion-implanting) boron into a silicon substrate is used as the mass spectrometric sample 1 for heating and desorbing boron.

The mass spectrometry sample 1 is heated from room temperature to 1000 ° C. at a temperature rising rate of 20 ° C./min by the temperature raising section 2a. The heated silicon sample is about 700-80
At a temperature of 0 ° C., boron begins to desorb from the substrate surface. The desorption part 2c is. The desorbed boron is introduced into the atmospheric pressure ionization mass spectrometer 3 at a flow rate of 1 l / min with argon (Ar) used as a carrier gas.

The atmospheric pressure ionization mass spectrometer 3 detects the mass of boron ions ( ¹¹ B ⁺ ) generated by ionization as an ion current.

During heating at a constant heating rate from room temperature to 1000 ° C., the ion current due to ¹¹ B ⁺ was constantly measured.
The intensity distribution of the ion current as shown in FIG.

The ion current obtained according to the embodiment of the present invention has the distribution shown in FIG. 3 for fluorine ions ( ¹⁹ F ⁻ ) and FIG. 4 for boron ions ( ¹¹ B ⁺ ).

Next, the samples for mass spectrometry before and after heating were
By performing other quantitative analysis such as MS, a relationship between the intensity of the desorbed ion current and the amount of the desorbed element as shown in the following equation is obtained, and a quantitative measurement can be performed.

[0032]

(Equation 1)

[0033]

As described above, according to the present invention, a film containing an impurity is formed on a substrate without diluting a standard gas, or an impurity is doped on a substrate, and the temperature is raised to remove the impurity into a gaseous substance. Is desorbed and ionized and analyzed.
Corresponding to other quantitative analysis such as MS, quantitative measurement can be performed, and ppt in inert gas can be measured.
~ppb order of fluorine ion ⁽¹⁹ F ^-) and boron (
¹¹ B ⁺ ) can be quantitatively measured.

Further, at atmospheric pressure, ppt to p in an inert gas
In a method of ionizing impurities in the order of pb and performing mass spectrometry, the present invention is characterized in that a quantitative measurement is performed by using thermal desorption. With this method, it is possible not only to perform quantitative measurement on non-refinable light elements such as boron and fluorine of a standard gas on the order of several ppm in the case of the conventional dilution method, but also to measure its volatility. From the height, more optimal quantitative measurement can be realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a view showing a distribution of an ion current of fluorine and an average ion current obtained according to the first embodiment of the present invention.

FIG. 3 is a configuration diagram showing a second embodiment of the present invention.

FIG. 4 is a diagram showing a distribution of ion current of boron and an average ion current obtained according to a second embodiment of the present invention.

FIG. 5 is a diagram showing mass spectrometry by a conventional dilution method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mass spectrometry sample 1a Impurity containing film 1b Substrate 2a Sample preparation part 2b Heating part 2c Desorption part 3 Atmospheric pressure ionization mass spectrometer 4 High-purity carrier gas (Ar or air) 5 Gas purifier

Claims (2)

(57) [Claims] 1. A method for preparing a calibration curve in a mass spectrometry method for mass-analyzing a small amount of impurities in an inert gas under atmospheric pressure and comprising a sample preparation step, a temperature raising step, and a desorption step. The sample preparation step is a process of forming a film containing a small amount of impurities on the substrate surface or doping the substrate with a small amount of impurities to prepare a sample for mass spectrometry. The mass spectrometry sample is heated at a constant heating rate to gasify the impurities contained in the substrate or film. The desorption process ionizes the gasified impurities with the carrier gas at a constant flow rate. A method for preparing a calibration curve, wherein the process is a process of supplying as a gas body. 2. A calibration curve creating apparatus for a mass spectrometer for mass-analyzing a small amount of impurities in an inert gas under atmospheric pressure and having a sample creating section, a heating section, and a desorbing section. The sample preparation unit is for preparing a sample for mass spectrometry by forming a film containing a small amount of impurities on the substrate surface or by doping the substrate with a small amount of impurities. The mass spectrometry sample is heated to gasify impurities contained in the substrate or film, and the desorption section supplies the gasified impurities as a gas to be ionized by a carrier gas. A calibration curve creating apparatus characterized by the following.