JP2003185635A - Apparatus and method for analyzing heated and desorbed gas using electron attachment mass spectrometry - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and a method for analyzing heated and desorbed gases capable of easily identifying the types and amount of parent molecules. <P>SOLUTION: In an electron attachment mass spectrometry, a mass spectroscopic part for analyzing the components of the desorbed gases comprises an ionizing chamber and a filament for generating thermoelectrons for ionizing the desorbed gases in the ionizing chamber. A mesh is arranged between the ionizing chamber and the filament. This apparatus is used to ionize the desorbed gases generated from a sample by electron attachment reactions in the ionizing chamber. Electron attachment mass spectrometry is performed through the use of created anions to evaluate the components of the gases desorbed from the sample. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal desorption gas analyzer and an analytical method, and more particularly to a thermal desorption gas analyzer and an analytical method utilizing electron attachment mass spectrometry. .

[0002]

2. Description of the Related Art In the conventional thermal desorption gas analysis method, the molecules (AB) of the desorption gas are subjected to electron bombardment to obtain the following formula: AB + e → A ⁺ + B + 2e or AB + e.
→ Utilizing the ordinary ionization process of ionization such as AB ⁺ + 2e, the generated positive ions are analyzed by the mass-to-charge ratio (M / q),
This is to evaluate the sample components.

A thermal desorption gas analyzer (TDS) used in such a thermal desorption gas analysis method is a molecule or atom that is desorbed from the surface of a solid sample while increasing the temperature of the surface of the solid sample at a constant rate. Information on the adsorbed molecules and atoms on the solid surface, the adsorption amount and adsorption state, the desorption process from the surface, etc. by measuring the change in pressure and the amount of desorbed molecules and atoms depending on the type of Is an analyzer for obtaining According to this gas analyzer, the order of desorbed molecules and atoms with respect to temperature is obtained as a thermal desorption spectrum, and by analyzing the shape of this spectrum and the change in the spectral shape when the heating rate is changed, Knowledge about the adsorption state and the like can be obtained.

As a mass spectrometer used in a conventional thermal desorption gas analyzer, one which analyzes the generated positive ions by utilizing the above-mentioned ionization process is used. The configuration of such an entire apparatus is shown in FIG. As shown in FIG. 1, the sample 3 placed in the quartz tube 2 is heated by the heating device 1 such as an infrared image furnace, and the gas desorbed from the sample surface is guided to the mass spectrometer 4. The thermoelectrons emitted from the filament 5 attached to the mass spectrometer are accelerated to about 70 eV, bombard gas molecules and atoms in the ionization chamber 6, and positively ionize them. After the positive ions have their orbits converged by the lens system, in the case of a quadrupole mass spectrometer, the quadrupole column 7
And are mass separated according to the mass / charge ratio. The current value of the mass-separated positive ions is amplified by the secondary electron multiplier 8 and measured by the control / measurement device 9.

FIG. 2 shows an example of the structure of the main part of the ionization chamber in such a mass spectrometer. 2, the same components as those in FIG. 1 have the same reference numerals. As shown in FIG. 2, the ionization chamber 6 arranged in a vacuum atmosphere is set to 10 V, the filament 5 is set to −60 V, and the thermoelectrons emitted from the filament are accelerated,
It becomes 70 eV in the ionization chamber. Due to this electron impact, the gas molecules and atoms released from the sample are positively ionized,
It is carried to the quadrupole column 7 and subjected to mass spectrometry. In FIG. 2, 10 is a lens system and 11 is a vacuum vessel wall.

Conventionally, in the manufacture of semiconductor devices, for example, in order to analyze impurities contained in a film formed on the surface of a substrate, the above-mentioned thermal desorption gas analyzer is used. Has been. As described above, this temperature-programmed desorption gas analyzer heats the sample to a high temperature in the vacuum chamber and analyzes the gas desorbed from the film by the mass spectrometer. That is, the adsorbed molecules and atoms in the vicinity of the surface of the sample that have obtained heat energy by heating are desorbed from the surface of the sample in order from the one having the weakest adsorption force. This desorption of gas molecules can be detected by a pressure increase in the vacuum chamber. By mass spectrometric analysis of the gas molecules thus desorbed, it is possible to obtain information on the adsorption state of the sample surface, surface adsorption gas, impurities contained in the sample film, etc., and evaluate the semiconductor device manufacturing process.

For example, when a plasma process apparatus is used as a plasma etching apparatus, a gas containing a halogen atom such as chlorine or bromine is generally introduced into the apparatus as an etchant to generate plasma by high frequency discharge, thereby generating plasma. Etching is performed by irradiating the substrate with halogen as radicals or ions from the generation region. In this case, in plasma etching with a halogen-based gas such as a metal film or an insulating film in a semiconductor device, a halide or other substance at a molecular level remains on the substrate surface after etching. Since this residual halide adversely affects the device characteristics, it is necessary to inspect for the presence of residual halide on the substrate surface. Therefore, a thermal desorption gas analyzer is used.

Identification of desorbed gas molecules using a conventional thermal desorption gas analyzer is performed by electron impact (for example, 70 eV).
This gas molecule is ionized by the above, and the positive ion species (A ⁺ and AB ⁺ ) generated through the above ionization process are identified by a mass analyzer such as a quadrupole mass spectrometer. In this case, generally, the gas molecules are dissociated by electron impact to generate a plurality of positive ion species, and therefore the original parent molecule is estimated from the measured plurality of positive ion species. When there is only one kind of parent molecule, there is a known database (NIST (National Institute
fStandards and Technology) Chemistry WebBook (htt
p: //webbook.nist.go/chemistry/)), it is easy to estimate the parent molecule using it.

In the thermal desorption gas analysis, however, a plurality of types of gas molecules are generally desorbed from the surface of the sample. Therefore, a large number of positive ion species generated from these gas molecules are measured and the above-mentioned known database is used. The types and amounts of the original multiple parent molecules must be estimated. In this case, the number of measured positive ion species is arbitrarily combined, the type of each parent molecule is estimated from the above database, and the assumption is made for the time being. Next, if the cross-sectional area of each ionic species is known, a simultaneous linear equation with the amount of each parent molecule as an unknown number is established for the amount of each positive ion species, and this is solved to obtain the amount of each parent molecule. In practice, a mass spectrum assuming the type and amount of each parent molecule is obtained using the above database, and this is compared with the actually measured mass spectrum. Then, the type and amount of each parent molecule are determined so as to be closest to the measurement result while changing the type and amount thereof.

[0010]

However, in the conventional method, as described above, the type of each parent molecule is estimated,
However, there is a problem in that complicated work is required to make a hypothesis and finally determine the type and amount of the parent molecule. Therefore, for example, in a semiconductor device manufacturing process, it is difficult to use the analysis result in real time. An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a thermal desorption gas analyzer and an analysis method capable of easily identifying the type and amount of a parent molecule. is there.

[0011]

[Means for Solving the Problems] The inventors of the present invention have conducted extensive studies on an apparatus and a method for identifying the type and amount of a parent molecule by a simple operation in the thermal desorption gas analysis. As a result, the target of measurement is not the positive ion species dissociated through the dissociative ionization process, but the target of measurement is the negative ion species dissociated through the dissociative electron attachment process. We succeeded in identifying the kind and amount of the parent molecule of each ion obtained by ionizing the desorbed gas extremely easily, and completed the present invention.

In the present invention, the molecules (AB) of the desorbed gas are
By the electron impact, the dissociative electron attachment process of dissociating and ionizing as in the following formula: AB + e → (AB ⁻ ) ^* → AB ⁻ → A ⁻ + B is used to generate a negative electron attachment reaction. By measuring the ions, the type and amount of the parent molecule of each ion is identified.

The temperature programmed desorption gas analyzer of the present invention comprises a heating section for heating a sample to generate a desorption gas and an electron for analyzing a component of the desorption gas generated from the sample. A thermal desorption gas analyzer including an attached mass analysis unit, wherein a mesh is arranged between an ionization chamber of the electron attachment mass analysis unit and a filament. The electron attachment mass spectrometer is an electron attachment mass analyzer having an ionization chamber arranged in a vacuum chamber and a filament that generates thermoelectrons for ionizing the desorbed gas in the ionization chamber, A mesh is arranged between the ionization chamber and the filament.

The above mesh may be any mesh that can generate a potential sufficiently higher than that of the filament in the space between the filament and the ionization chamber. Therefore, the mesh should not be so coarse. This is because, in the case of the electric potential of the space at the center of the mesh net, unlike the electric potential of the wires forming the mesh, if the eyes are too coarse, a high electric potential cannot be created in the space. Further, the size of the mesh is sufficient as long as it covers the space between the filament and the ionization chamber, and the arrangement position is not particularly limited as long as it is between the filament and the ionization chamber.

The temperature-programmed desorption gas analysis method of the present invention comprises heating a sample to heat it to generate a desorption gas, ionizing the desorption gas generated from the sample in an ionization chamber, and using the generated ions. In the temperature programmed desorption gas analysis method for analyzing the components of the desorbed gas from the sample, the desorbed gas generated from the sample is ionized by an electron attachment reaction in the ionization chamber to generate negative ions, and the generated negative ions are Electron attachment mass spectrometry is used to evaluate the components of the desorbed gas. This analysis method uses the above-mentioned temperature programmed desorption gas analyzer to analyze the negative ions produced by ionizing the gas desorbed from the sample by electron attachment mass spectrometry to evaluate the desorbed gas components. It is done by

According to the present invention, since the predetermined mesh is arranged between the ionization chamber and the filament as described above, electrons can escape from the filament, and the intended purpose can be achieved. it can. Since the mesh is arranged and the potential is set to be higher than the potential of the filament, in order to reduce the electron energy in the ionization chamber, even if the potential difference between the filament and the ionization chamber is made small Get out and head for the mesh.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of an analysis method using the thermal desorption gas analyzer of the present invention will be described below with reference to the flowchart shown in FIG. As the analyzer, the analyzer of FIG. 1 in which a mesh 43 is arranged between the filament 41 and the ionization chamber 42 as shown in FIG. 4 is used. The sample is heated by a heating device such as an infrared image furnace, and the gas desorbed from the sample surface is analyzed by electron attachment mass spectrometry. Since the temperature programmed desorption analysis is performed, electron attachment mass spectrometry is performed while increasing the sample temperature. In electron attachment mass spectrometry, electron energy must be swept, and multiple negative ion species may be observed, so the mass spectrometer setting mass is also swept to measure all negative ion species. There is a need. An example of the measurement procedure at this time is shown in the flowchart of FIG.

However, as described in Example 1 below,
In the case of fluorocarbon gas, since the parent molecule can be identified from the peak position (electron energy value) of the F ⁻ signal, the set mass is not swept, and only the F ⁻ signal is set while m / q is set to 19. Just measure. Further, even when measuring a plurality of types of negative ions, the number of negative ion species is limited, and therefore the sweep of the mass number may be performed discretely only for the mass number at which the negative ion species can exist. The case of measuring only F ⁻ will be specifically described below. As shown in FIG. 3, the measurement starts at room temperature and the mass number set in the mass spectrometer is set to 19
Then, the electron energy is swept from 0 eV to 10 eV, and the signal of the ion current of F ⁻ is taken into the computer connected to the measuring instrument. The sweeping of the electron energy and the capturing of the ion current signal are repeatedly performed while raising the sample temperature. The computer also controls the sweeping of electron energy and the heating device. The measurement ends when the sample temperature reaches the set maximum temperature. The electron energy is swept by sweeping the electric potential of the filament. By sweeping the filament potential from -5 V to -15 V with the ionization chamber potential of -5 V and the mesh potential of 0 V, the electron energy in the ionization chamber becomes 0 eV to 10 eV.

[0019] By this measure, F and sample temperature T and electron energy E _e as a function with a variable ^- so that the ion current value I _F- (T, E _e) is taken into the computer. By three-dimensionally plotting T and E _e on the x and y axes and I _F− on the z axis, the dependence of I _{F −} on T and E _e can be seen. The parent molecule is determined from the peak position of I _{F −} with respect to E _{e, and} the temperature change of the desorption amount of the parent molecule desorbed from the sample surface from the change of the peak height of the I _{F −} with respect to T.
That is, a temperature programmed desorption spectrum in which a desorption molecular species is identified can be easily obtained.

[0020]

Example (Example 1) As a thermal desorption gas analyzer,
The desorbed gas was analyzed using a conventional device in which a mesh was placed between the ionization chamber and the filament. FIG. 4 shows the structure of the ionization source and the main part of potential distribution in the apparatus used in this example. Analysis of the gas molecules desorbed from the sample was performed using the filament 4
1 using an electron attachment mass spectrometer having a mesh 43 arranged between the ionization chamber 42 and the ionization chamber 42. In order to monitor the generated negative ions, the potential of the ionization chamber was set to -5 V below the center potential (0 eV) of the Q pole, and the mesh potential was set to 0 V. Also, the filament potential was swept to -5V. That is, the electron energy in the ionization chamber was swept up to 0 eV. Even in that case, the potential of the mesh was higher than that of the filament, so that the electrons stably escaped from the filament. The electron current to the ionization chamber was monitored and the measurement result was corrected later.

The mass number that can be transmitted by the mass analyzer of the gas analyzer is defined as "mass number of negative ions generated in the electron attachment process".
The kinetic energy of electrons in the ionization chamber 12 of the ionization source was swept from 0 to 10 eV. Generally, in the dissociative electron attachment process that occurs in the energy region of about 0 to 10 eV, there is a peak of the cross-sectional area at several eV, and the position of the peak (electron energy) differs depending on the type of parent molecule. For example, the cross-sectional area of F ⁻ generated from CF ₄ by the dissociative electron attachment process has a peak at 6.7 eV, and the cross-sectional area of F ⁻ generated from C ₂ F ₆ is 3.
It has a peak at 9 eV. Therefore, when the mass number of the mass spectrometer is set to 19, that is, F ⁻ , and the electron energy is swept while monitoring the ion current, 3.9e
If there are peaks at V and 6.7 eV, it can be understood that C ₂ F ₆ and CF ₄ are present in the gas to be analyzed, and the original parent molecule can be accurately identified without the need for complicated work. Will be possible. Also, if the values of the cross-sectional areas are known, their amounts can also be accurately derived, so if such a database is created using standard substances of compounds that may be present in the process, not only the types but also the types can be obtained. , The exact amount can also be identified.

For example, C ₃ F ₈ , n-C ₄ F ₁₀ , i-
C ₄ F _10, the _{n-C 5 F 12} and _{n-C 6 F 14,} respectively, 2.9,2.65,1.85 and 3.7,2.5 and 3.8, and 3 There is a peak at .45 eV (eg SM Spyrou, I. Sauers and LG
Christphorou: J. Chem. Phys. 78, 7200 (1983), S.
R. Hunter and LG Christphorou: J. Chem. Phys. 8
9, 6150 (1984)), if the peak of the negative ion species F ⁻ generated in the dissociative electron attachment process is at these values, the type of parent molecule can be easily identified.

It should be noted that the molecular weight is large and the electron affinity is positive.
In the molecule, non-dissociative electron attachment occurs and negative ions are generated.
It For example, SF₆Then the electron energy is almost 0 eV
SF ₆ ⁻Only generated. Therefore, in such cases
It is easier to identify the parent molecule. As mentioned above,
The electron energy at the time of child impact is
Energy: For example, lower than 70 eV) to reduce negative ions.
Nitration has made it possible to use conventional methods for thermal desorption gas analysis.
Easy identification of desorbed gas molecular species
It became so.

(Example 2) According to the method described in Example 1.
O generated by dissociative electron attachment from oxygen gas ⁻Measure
An example is shown below. That is, as shown in FIG.
A mesh between the filament 411 and the ionization chamber 42
43 was placed and performed using an electron attachment mass spectrometer. Raw
The potential of the ionization chamber to monitor the negative ions formed
Is lower than the center potential (0eV) of the Q pole and is -5V
It was Also, the filament potential was swept to -5V. Me
With the ground potential at 0 V, it is always higher than the filament potential.
Since it has been set, the electron energy in the ionization chamber is 0e.
Even under the condition of V, the electrons escape from the filament.
It was In addition, monitor the electron current to the ionization chamber.
Then, the measurement result was corrected later.

[0025] Figure 5 is a mass number of 16 mass analyzer, and may be set to a negative ion measurement mode, O when changing the energy (eV) of the electron impact ^- the ion current value
It is a graph which shows the change of (CPS: count / second). The measurement condition at that time is Ei (ionization chamber potential) = − 5 V;
Ef (potential of the focus electrode arranged under the ionization chamber) =-5V; Em (mesh potential) = 0V; Vsem
(Potential of secondary electron multiplier) =-2 kV; Vcon (conversion dynode voltage) = + 3.0 kV; If (filament current) = 2.52 A, voltage across filament = about 3.05 V, electron energy at this time 6.5 eV
And the electron current out of the filament is 0.09mA
Then, the electron current flowing into the wall of the ionization chamber is 0.021 m
It was A. ); Oxygen partial pressure = 1.9e-5 Torr; B
G (background pressure) = 1e-6 Torr. The cross-sectional area of dissociative electron attachment in oxygen is known to have a peak at an electron energy of 6.5 eV, and as shown in FIG. 5, the measurement results agree with it. From this, conversely, when O ⁻ was monitored, 6.5
If a peak appears at eV, the original parent molecule can be identified as O ₂ .

In the case of fluorocarbon gas, F ⁻ ,
Since negative ions such as CF ₃ ⁻ are generated by dissociative electron attachment, the peaks of their ion currents with respect to electron energy are measured, and the measured values are compared with literature values to determine the original parent molecule before dissociation. Can be identified. In non-dissociative electron attachment, it is necessary to reduce the electron energy to 0 eV, but even in that case, a mesh is inserted between the filament and the ionization chamber so that the electrons can stably escape from the filament, and a higher potential than that of the filament is applied. For example, it can be carried out as in the case of dissociative electron attachment.

[0027]

According to the thermal desorption gas analyzer of the present invention, since the mesh is arranged between the ionization chamber and the filament, by applying a higher potential to the mesh than the filament, low energy electron This has the effect of enabling stable generation and supply. According to the thermal desorption gas analysis method of the present invention, the negative ion species dissociated through the electron attachment process is used as the measurement target by utilizing the electron attachment mass spectrometry for gas analysis. It is possible to easily identify the types and amounts of a plurality of types of parent molecules of each ion obtained by ionizing the separated gas with an extremely simple operation.

[Brief description of drawings]

FIG. 1 is a configuration diagram schematically showing the overall configuration of a conventional thermal desorption gas analyzer.

FIG. 2 is a configuration diagram schematically showing a configuration of a main part of an ionization chamber used in a conventional thermal desorption gas analyzer.

FIG. 3 is a flowchart showing an embodiment of a thermal desorption gas analysis method of the present invention.

FIG. 4 is an explanatory diagram showing a structure of an ionization source of a mass spectrometer and a main part of potential distribution in the thermal desorption gas analyzer of the present invention.

FIG. 5: O generated in the dissociative electron attachment process with oxygen
^The graph which shows the dependence of the signal (ion current) of-on electron energy.

[Explanation of symbols]

1 Heating Device 2 Quartz Tube 3 Sample 4 Mass Spectrometer 5 Filament 6 Ionization Chamber 7 Quadrupole Column 8 Secondary Electron Multiplier Tube 9 Control / Measuring Instrument 10 Lens System 11 Vacuum Vessel Wall 41 Filament 42 Ionization Chamber 43 Mesh

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yasuhiro Morikawa             1220-1 Suyama, Susono City, Shizuoka Al             Back Semiconductor Technology Laboratory F-term (reference) 5C038 EE03 EF26 GG01 GH02 GH06                 5F004 CB04

Claims (4)

[Claims] 1. An electron attachment device comprising: a heating unit for heating a sample to generate a desorption gas; and an electron attachment mass spectrometric unit for analyzing a component of the desorption gas generated from the sample. A thermal desorption gas analyzer utilizing mass spectrometry, characterized in that a mesh is arranged between an ionization chamber and a filament of the electron attachment mass spectrometry unit. . 2. A thermal desorption system comprising: a heating unit for heating a sample to heat it to generate a desorbed gas; and a mass spectrometric unit for analyzing components of the desorbed gas generated from the sample. In the gas analyzer, the mass spectrometer is an electron attachment mass spectrometer having an ionization chamber arranged in a vacuum chamber and a filament that generates thermoelectrons for ionizing the desorbed gas in the ionization chamber. A thermal desorption gas analyzer, wherein a mesh is arranged between the ionization chamber and the filament. 3. A sample is heated and heated to generate a desorbed gas, the desorbed gas generated from the sample is ionized in an ionization chamber, and the generated ions are used to analyze the components of the desorbed gas from the sample. In the thermal desorption gas analysis method described above, the desorption gas generated from the sample is ionized by an electron attachment reaction in an ionization chamber to generate negative ions, and the generated negative ions are subjected to electron attachment mass spectrometry to remove the ions. A thermal desorption gas analysis method, characterized in that the components of the released gas are evaluated. 4. A negative ion produced by ionizing the gas desorbed from the sample is analyzed by electron attachment mass spectrometry using the thermal desorption gas analyzer according to claim 1 or 2. 4. A method for evaluating a gas separation component.
The thermal desorption gas analysis method described.