JP2001221755A - Secondary ion mass spectrometry - Google Patents

Abstract

PROBLEM TO BE SOLVED: To calculate secondary ion intensity of interfering ion relative to a measuring object element without using a standard sample including no measuring object element. SOLUTION: A first secondary ion intensity of ion having a mass number roughly equal to that of the measuring object element and a second secondary ion intensity of molecular ion which is an isotope of the interfering ion relative to the measuring object element are measured, and thereafter correlation between the second secondary ion intensity and an isotope abundance of the molecular ion is obtained, and then a third secondary ion intensity of the interfering ion is calculated by using the correlation. Then, the third secondary ion intensity is subtracted from the first secondary ion intensity, to thereby calculate a fourth secondary ion intensity of the measuring object element, and the concentration of the measuring object element in the sample is obtained by using the fourth secondary ion intensity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary ion mass spectrometry used for quantitative analysis of impurity concentration in a solid material.

[0002]

2. Description of the Related Art Secondary ion mass spectrometry (Secondary Ion
Mass Spectrometry (hereinafter referred to as SIMS method)
In this method, secondary ions emitted by irradiating the solid material with primary ions are subjected to mass analysis to analyze impurities contained in the solid material, that is, elements to be measured. The SIMS method is widely used in the depth direction analysis of impurity concentration in a semiconductor or metal as an analysis method capable of detecting a trace impurity in a solid material with the highest sensitivity.

[0003] In the SIMS method, when a solid surface is irradiated with primary ions, molecular ions or polyvalent ions composed of elements other than the element to be measured are released together with monoatomic ions composed of the element to be measured. . Among these molecular ions or polyvalent ions, ions having a mass number substantially equal to the element to be measured are generally called interfering ions. When the secondary ion intensity of the element to be measured is measured by the SIMS method, the measured value of the actual secondary ion intensity usually includes the intensity component of the interfering ion, that is, the background.

[0004] Therefore, in order to increase the sensitivity of detecting trace impurities by the SIMS method, the secondary ion intensity may be increased or the background included in the secondary ion intensity may be reduced.

[0005] In the following, a depth direction distribution of As implanted as an impurity was measured for a sample having a laminated structure of TiSi ₂ film and polysilicon film (hereinafter referred to as TiSi ₂ / Si structure) shown in FIG. For example, the conventional SI
The MS method will be described.

As shown in FIG. 8, a polysilicon film 3 is formed on a silicon substrate 1 with a silicon oxide film 2 interposed therebetween.
An iSi ₂ film 4 is formed. The polysilicon film 3
Is ion-implanted with As, which is an impurity,
After the ion implantation, an annealing process is performed on the silicon substrate 1.

The As concentration in the sample shown in FIG.
When analyzing using the MS method, the element to be measured, that is, ⁷⁵ A
With respect to s (As ions having a mass number m of 75 (omitted below the decimal point ... the same applies hereinafter)), ⁴⁶ Ti ²⁹ Si having a mass number substantially equal to ⁷⁵ As (Ti having a mass number m of 46 and mass number m of 46 2
9 molecular ions made of Si) and ⁴⁷ Ti ²⁸ Si (molecular ions made of Ti having a mass number m of 47 and Si having a mass number m of 28) become interference ions.

In order to remove the intensity component of interfering ions when measuring the secondary ion intensity of the element to be measured, the following (1) high-resolution measurement method, (2) offset potential method, or (3) A method for examining the intensity ratio of molecular ions to monoatomic ions is usually used. (1) High-resolution measurement method In the high-resolution measurement method, a double-focusing SIMS device capable of obtaining a mass resolution m / Δm of up to about 10,000 is used. Thereby, the difference Δm of the mass number between the element to be measured and the interfering ion is 1/1 of the mass number m of the element to be measured.
When it is larger than 0000, the secondary ion intensity of the element to be measured can be measured while removing the intensity component of the interfering ions. (2) Offset potential method However, when analyzing the As concentration in the sample shown in FIG. 8, the mass resolution m / Δm required to separate ⁷⁵ As from interfering ions reaches about 10,000 (interfering ions). Is ⁴⁶ Ti ²⁹ Si, the required mass resolution m / Δm is 9950, and the interfering ions are ⁴⁷ Ti ²⁸ Si
In this case, the required mass resolution m / Δm is 10555), so that it becomes difficult to remove the intensity component of the interfering ions even by using the high-resolution measurement method.

Therefore, the offset potential method (SF Corcoran, DP Griffis, a
nd RW Linton, Secondary Ion Mass Spectrometry,
SIMS VI, A. Benninghoven, AM Huber, and H.
W. Werner, Eds., Wiley, New York (1988) pp. 283-28
6.) has been used to measure the secondary ion intensity of the element to be measured.

Generally, molecular ions serving as interfering ions have a narrower energy distribution than monoatomic ions consisting of the element to be measured. In the offset potential method utilizing this property, a slit position of a mass spectrometer in a double focusing SIMS apparatus is set so that secondary ions in a high energy region can be detected. As a result, the ratio of detected molecular ions (interfering ions) to monoatomic ions (elements to be measured) can be reduced, so that the secondary ion intensity of the element to be measured can be measured while removing the intensity component of the interfering ions. it can.

FIG. 9 shows the depth of the secondary ion intensity of ions having a mass number substantially equal to As (m = 75) with respect to the sample shown in FIG. 8 using the conventional secondary ion mass spectrometry. The result of having measured the profile is shown.

In FIG. 9, the solid line represents the depth profile of the secondary ion intensity obtained by the measurement with the normal resolution, and the broken line represents the depth profile of the secondary ion intensity obtained by the offset potential method. I have. Note that the depth profile of any secondary ion intensity is the same as that of the double focusing type SI.
This is obtained by using a Cs ⁺ beam as a primary ion beam and detecting a negative ion as a secondary ion in an MS device.

As shown in FIG. 9, in the depth profile of the secondary ion intensity obtained by the measurement at the ordinary resolution, ⁴⁶ T generated as an interfering ion with respect to ⁷⁵ As is obtained.
Since the intensity components of i ²⁹ Si and ⁴⁷ Ti ²⁸ Si have not been removed, the secondary ion intensity is relatively high in the TiSi ₂ film 4 (depth 0 nm to about 40 nm), while the polysilicon film 3 (depth) is low. (About 40 nm or more), the secondary ion intensity gradually decreases and approaches a constant value as the depth increases, that is, as the distribution of Ti decreases.

[0014] On the other hand, as shown in FIG. 9, in the depth profile of the secondary ion intensity obtained by the offset potential method, the intensity component of the interfering ions are removed for ⁷⁵ As, TiSi ₂ film 4 The secondary ion intensity in the polysilicon film 3 becomes substantially constant. That is, by using the offset potential method, a depth profile of the secondary ion intensity of ⁷⁵ As from which the intensity component of the interfering ions is removed can be obtained. (3) Method for Investigating the Intensity Ratio of Molecular Ions to Monoatomic Ions By the way, with the miniaturization of LSI, it is required to increase the resolution in the depth direction of the SIMS method in the measurement of the depth profile of the dopant concentration and the like. Have been S
In order to increase the resolution in the depth direction of the IMS method, it is effective to reduce the incident energy of the primary ion beam. Therefore, a quadrupole mass spectrometer is required rather than using a double focusing SIMS apparatus. It is generally advantageous to use a SIMS device having the same (hereinafter referred to as a quadrupole SIMS device).

However, in the quadrupole SIMS apparatus, since the mass resolution m / Δm is about 2, the high-resolution measurement method cannot be used, and the offset potential method cannot be used. When the secondary ion intensity of the element to be measured is measured by a quadrupole SIMS device, it is impossible to directly remove the intensity component of the interfering ions.

Therefore, in a quadrupole SIMS apparatus, "a method for examining the intensity ratio of molecular ions to monoatomic ions" (SF Corcoran, DP Griffis, and RW Lin)
ton, Secondary Ion Mass Spectrometry, SIMS VI,
A. Benninghoven, AM Huber, and HW Werner, E
ds., Wiley, New York (1988) pp. 283-286.), the secondary ion intensity of the element to be measured has been measured.

The flow chart of FIG. 10 will be described below with respect to the "method for examining the intensity ratio of molecular ions to monoatomic ions" by taking as an example the case of analyzing the As concentration in a sample having a TiSi ₂ / Si structure shown in FIG. This will be described specifically with reference to FIG. In the following description,
It is assumed that a Cs ⁺ beam is used as a primary ion beam and negative ions are detected as secondary ions.

First, in step S1, a first auxiliary secondary ion intensity I _{Si of Si} and T 1 are measured using a sample to be measured having a TiSi ₂ / Si structure shown in FIG.
the second auxiliary secondary ion intensity I of i (monoatomic ion)
_Ti and a first secondary ion intensity I ₇₅ of an ion having a mass number substantially equal to As (m = 75) are measured.

Next, in step S2, a third auxiliary secondary ion of Ti (monoatomic ion) is formed using a first standard sample having a TiSi ₂ / Si structure shown in FIG. The strength J _Ti and the mass number substantially equal to As (m = 7
4th auxiliary secondary ionic strength J of the molecular ion having 5)
₇₅ (secondary ion intensity of interfering ions for As in the first standard sample).

Next, in step S3, the second secondary ion intensity I _i of the interfering ion with respect to As in the sample to be measured is calculated by the following formula: I _i = I _Ti × (J ₇₅ / J _Ti ) (Equation 1) calculate.

Next, in step S4, the third secondary ionic strength I _As of As in the sample to be measured is calculated by the following formula: I _As = I ₇₅ −I _i (2) calculated by the ionic strength I ₇₅ subtracting the second secondary ion intensity I _i.

Next, the As concentration is determined using the relative sensitivity coefficient RSF.

Specifically, in step S5, FIG.
To have a TiSi ₂ / Si structure shown, with the second standard sample As is injected (As concentration C _As ⁰ known), Si
The fifth auxiliary secondary ion intensity K _Si of As and the sixth auxiliary secondary ion intensity K _{As of As} are measured.

Next, in step S6, the Si of As
Is calculated by the following equation: RSF = (K _Si / K _As ) × C _As ⁰ .

Next, in step S7, the As concentration C _As in the sample to be measured is calculated by the following equation: C _As = (I _As / I _Si ) × RSF (Equation 4)

As described above, as described in “Monoatomic ion
The method of determining the intensity ratio of molecular ions to
Using a standard sample that does not contain
Secondary ionic strength of the monatomic ion of the atoms that make up the on
(Third auxiliary secondary ionic strength J _Ti) And interfering ions
Secondary ion intensity of the molecular ion acting by
Next ionic strength J₇₅), That is, "for a monoatomic ion
And the "single atom"
Measurement ratio based on the “intensity ratio of molecular ions to ions”
Secondary of interfering ions for the element to be measured in elephant samples
Ionic strength (second secondary ionic strength I_i)
And

The "method for examining the intensity ratio of molecular ions to monoatomic ions" can also be used in a double focusing SIMS apparatus.

[0028]

[Problems to be solved by the invention]
Method for determining the intensity ratio of molecular ions to molecular ions
If used, the secondary ionic strength of the target element obtained
(Third secondary ion intensity I _As) Is converted to impurity concentration
Sample (the second standard sample into which As was injected)
In addition, "Intensity ratio of molecular ions to monoatomic ions"
Sample (first standard sample not containing As)
Fees), which makes the process complicated.
Problem.

When the "method for examining the intensity ratio of molecular ions to monoatomic ions" is used, the dependence of the secondary ion intensity of molecular ions serving as interfering ions on the element to be measured on the measurement conditions or the state of the sample, etc. Is strong, the “intensity ratio of molecular ions to monoatomic ions (J ₇₅ / J _Ti )” in the standard sample not containing the element to be measured and the “intensity ratio of molecular ions to monoatomic ions (I _i / I _Ti ) "does not necessarily coincide with each other, which causes a factor that the accuracy of quantitative determination of the secondary ion intensity of the element to be measured in the sample to be measured decreases.

In view of the above, it is an object of the present invention to be able to calculate the secondary ion intensity of interfering ions for an element to be measured without using a standard sample containing no element to be measured.

[0031]

Means for Solving the Problems The present invention has been made by paying attention to the fact that, in many cases, a plurality of isotopes are present in molecular ions serving as interfering ions with respect to an element to be measured.

Specifically, the secondary ion mass spectrometry according to the present invention uses the sample containing the element to be measured to determine the first secondary ion intensity of ions having a mass number substantially equal to the element to be measured. A first step of measuring a second secondary ion intensity of a molecular ion which is made of an element other than the element to be measured and which is an isotope of an interfering ion having a mass number substantially equal to that of the element to be measured; A second step of determining a correlation between the secondary ion intensity of No. 2 and the abundance ratio of molecular ions in all isotopes including the interfering ion, and a third secondary ion of the interfering ion using the correlation. A third step of calculating the intensity, and a fourth step of calculating a fourth secondary ion intensity of the element to be measured by subtracting the third secondary ion intensity from the first secondary ion intensity; Using the fourth secondary ionic strength, And a fifth step of determining the concentration of the measurement target elements that.

According to the secondary ion mass spectrometry of the present invention,
Using a sample containing the element to be measured, a first secondary ionic strength of ions having a mass number substantially equal to the element to be measured,
After measuring the second secondary ion intensity of the molecular ion which is an isotope of the interfering ion with respect to the element to be measured, the correlation between the second secondary ion intensity and the isotope abundance ratio of the molecular ion is obtained, and then Since the third secondary ion intensity of the interfering ion is calculated using the correlation, the third secondary ion intensity, that is, the element to be measured, can be obtained without using a standard sample containing no element to be measured. The secondary ion intensity of the interfering ions with respect to. Therefore, by subtracting the third secondary ion intensity from the first secondary ion intensity, the fourth secondary ion intensity of the element to be measured, that is, the concentration of the element to be measured in the sample can be easily and accurately determined. Can be.

Further, according to the secondary ion mass spectrometry of the present invention, the secondary ion intensity of the element to be measured from which the intensity component of the interfering ions has been removed without using a method for increasing the mass resolution such as the offset potential method. Because you can ask for
Since the resolution in the depth direction can be increased by using a quadrupole SIMS device, the impurity distribution on the surface or interface of a semiconductor used for an LSI or the like can be accurately evaluated.

In the secondary ion mass spectrometry of the present invention,
Preferably, the correlation is represented by a linear function.

This makes it possible to easily calculate the secondary ion intensity of the interfering ions with respect to the element to be measured.

In the secondary ion mass spectrometry of the present invention,
The correlation is preferably represented by a quadratic function.

In this way, even when the correlation deviates from a simple proportional relationship, the secondary ion intensity of interfering ions in the sample to be measured can be calculated accurately.

[0039]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) Hereinafter, an As concentration in a sample having a TiSi ₂ / Si structure shown in FIG. 8 will be described for a secondary ion mass spectrometry according to a first embodiment of the present invention. An example in which the analysis is performed will be described with reference to the drawings. In the following description, it is assumed that a Cs ⁺ beam is used as a primary ion beam and a negative ion is detected as a secondary ion.

The feature of the first embodiment is that, using a sample containing an element to be measured (hereinafter, referred to as a sample to be measured), the secondary ion intensity of molecular ions serving as isotopes of interfering ions with respect to the element to be measured is determined. After measurement, the correlation between the measured secondary ion intensity of molecular ions and the abundance ratio of molecular ions in all isotopes including interfering ions (hereinafter referred to as the isotope abundance ratio of molecular ions) is shown. A linear function expression is obtained, and thereafter, the secondary ion intensity of the interfering ion is calculated using the linear function expression.

Incidentally, the Ti atom has a mass number m of 46,
There are 47, 48, 49, and 50 isotopes, and S
Since the i atom has isotopes with mass numbers m of 28, 29, and 30, the molecular ion composed of Ti atom and Si atom (hereinafter referred to as TiSi molecular ion) has mass number m of 74 to 80. There are seven types of isotopes. The isotope abundance ratio of these TiSi molecular ions is represented by the product of the isotope abundance ratio of Ti atoms and the isotope abundance ratio of Si atoms.

FIG. 1 shows the isotopic composition and isotopic abundance ratio of TiSi molecular ions.

In the first embodiment, since the mass number m of As, which is the element to be measured, is 75, the isotope composition is
^The mass number m represented by ⁴⁶ Ti ²⁹ Si or ⁴⁷ Ti ²⁸ Si is 7
The TiSi molecular ion of No. 5 becomes an interfering ion for As, and the TiSi molecular ion having a mass number m other than 75 becomes an isotope of the interfering ion.

FIG. 2 shows secondary ions of six types of TiSi molecular ions (TiSi molecular ions which are isotopes of interfering ions with As) having a mass number m other than 75, measured using the sample shown in FIG. This shows the dependence of strength on the isotopic abundance ratio of TiSi molecular ions. In FIG. 2, the solid line indicates a linear function expression representing a correlation between the secondary ion intensity of TiSi molecular ions having a mass number m other than 75 and the isotope abundance ratio of TiSi molecular ions.

As shown in FIG. 2, the secondary ion intensity of TiSi molecular ions having a mass number m other than 76 has a good proportional relationship with the isotope ratio of TiSi molecular ions.

Therefore, when the mass number m is other than 75 and 76, T
By measuring the secondary ion intensity I _X for any one of the iSi molecular ions (assuming that the isotope abundance ratio is R _X ), the mass number m serving as an interfering ion for As is 75 Secondary ion intensity I _{i of} TiSi molecular ion
I _i = (R ₇₅ / R _X ) × I _X (Equation 5) Here, in (Equation 5), R ₇₅ is an isotope ratio of TiSi molecular ions having a mass number m of 75.

Hereinafter, a method of analyzing the As concentration in a sample having a TiSi ₂ / Si structure using the secondary ion mass spectrometry according to the first embodiment will be described with reference to FIG.
This will be specifically described with reference to the flowchart of FIG.

First, in step S11, a first auxiliary secondary ion intensity I _{Si of Si} is obtained by using a sample to be measured having a TiSi ₂ / Si structure shown in FIG.
A first secondary ion intensity I ₇₅ of an ion having a mass number substantially equal to As (m = 75), and a Ti having a mass number m other than 75
The second secondary ion intensity _{IX of} Si molecular ions (isotopes of TiSi molecular ions having a mass number m of 75 serving as interfering ions for As) is measured.

Next, in step S12, the correlation between the second secondary ion intensity I _X and the isotope abundance ratio R _X of the TiSi molecular ion is examined, and the second secondary ion intensity I _X is determined.
_X selects TiSi molecular ions that is proportional to the isotope abundance ratio R _X.

Next, in step S13, using the second secondary ion intensity I _X and the isotope abundance ratio R _X of the TiSi molecular ions selected in step S12, the mass number m serving as an interfering ion for As is determined. the third secondary ion intensity I _i of 75 TiSi molecular ion is calculated by _{I i = (R 75 / R} X) × I X ...... ( equation 6). However, in (Equation 6), R ₇₅ is an isotope abundance ratio of a TiSi molecular ion having a mass number m of 75.

Next, in step S14, the fourth secondary ion intensity I _As of As in the sample to be measured is calculated by the following equation (I _As = I ₇₅ −I _i ), that is, the first secondary ion intensity I _As calculated by subtracting the third secondary ion intensity I _i of the ionic strength I _75.

Next, the relative sensitivity coefficient RS is calculated by a known method.
The As concentration is determined using F.

More specifically, in step S15, a second auxiliary sample of Si is formed using a standard sample (having a known As concentration C _As ⁰ ) having a TiSi ₂ / Si structure shown in FIG. The secondary ion intensity K _Si and the third auxiliary secondary ion intensity K _{As of As} are measured.

Next, in step S16, S of As
The relative sensitivity coefficient RSF for i is calculated by RSF = (K _Si / K _As ) × C _As ⁰ (Equation 8).

Next, in step S17, the As concentration C _As in the sample to be measured is calculated by C _As = (I _As / I _Si ) × RSF (Equation 9).

FIG. 4 shows the results obtained by using the secondary ion mass spectrometry according to the first embodiment, specifically, the method having the TiSi ₂ / Si structure shown in FIG. Shows the results of the analysis of the As concentration in FIG. In the step S12, the mass number m as TiSi molecular ions second secondary ion intensity I _X is proportional to the isotope abundance ratio R _X has selected the TiSi molecular ion of 74.

In FIG. 4, the solid line (with a black circle) indicates A obtained by the secondary ion mass spectrometry according to the first embodiment.
The dashed line represents the depth profile of the As concentration obtained by the offset potential method as a first comparative example, and the dashed line represents the second profile as the first comparative example.
Represents a depth profile of the As concentration obtained from the first secondary ion intensity I ₇₅ (secondary ion intensity of ions having a mass number substantially equal to As (m = 75)).

As shown in FIG. 4, the depth profile of the As concentration obtained by the secondary ion mass spectrometry according to the first embodiment is the first comparative example, that is, the As concentration obtained by the offset potential method. Well matched with the depth profile.

On the other hand, as shown in FIG. 4, in the second comparative example, since the intensity component of the interfering ions was not removed, the As concentration in the TiSi ₂ film 4 (depth 0 nm to about 40 nm) was excessively high. Has been evaluated.

As described above, according to the first embodiment, using the sample to be measured, the first secondary ion intensity of ions having a mass number substantially equal to the element to be measured, and the After measuring a second secondary ion intensity of a molecular ion to be an isotope of an interfering ion, a correlation between the second secondary ion intensity and an isotope abundance ratio of the molecular ion is determined, and then the correlation is determined. And the third of the interfering ions
Since the secondary ion intensity is calculated, it is possible to calculate the third secondary ion intensity, that is, the secondary ion intensity of interfering ions with respect to the element to be measured, without using a standard sample not containing the element to be measured. it can. Therefore, by subtracting the third secondary ion intensity from the first secondary ion intensity, the fourth secondary ion intensity of the element to be measured, that is, the concentration of the element to be measured in the sample to be measured can be accurately and easily obtained. You can ask.

According to the first embodiment, the correlation between the second secondary ion intensity and the isotope abundance ratio of molecular ions is represented by a linear function, so that the third secondary ion intensity That is, the secondary ion intensity of the interfering ions with respect to the element to be measured can be easily calculated.

Further, according to the first embodiment, without using a method for increasing the mass resolution such as the offset potential method,
Since the secondary ion intensity of the element to be measured from which the intensity component of the interfering ions has been removed can be obtained, the quadrupole SIM
Since the resolution in the depth direction can be increased using the S apparatus, the impurity distribution on the surface or interface of a semiconductor used for an LSI or the like can be accurately evaluated.

(Second Embodiment) Hereinafter, a secondary ion mass spectrometry according to a second embodiment of the present invention will be described with reference to a sample having a TiSi ₂ / Si structure shown in FIG.
The case where the analysis of the concentration is performed will be described with reference to the drawings. In the following description, it is assumed that a Cs ⁺ beam is used as a primary ion beam and a negative ion is detected as a secondary ion.

The feature of the second embodiment is that after measuring the secondary ion intensity of the molecular ion which is an isotope of the interfering ion with respect to the element to be measured using the sample to be measured, the secondary ion intensity of the measured molecular ion is measured. A quadratic function expression representing the correlation between the ion intensity and the isotope abundance ratio of the molecular ion is obtained, and then,
The purpose is to calculate the secondary ion intensity of the interfering ions using the quadratic function equation.

FIG. 5 shows six types of TiSi molecular ions other than 75 having a mass number m (interfering ions against As (TiSi molecules having a mass number m of 75) measured using the sample shown in FIG.
The graph shows the dependence of the secondary ion intensity of TiSi molecular ion (which is an isotope of molecular ion) on the isotope abundance ratio of TiSi molecular ion. In FIG. 5, the solid line indicates a quadratic function equation representing a correlation between the secondary ion intensity of TiSi molecular ions having a mass number m other than 75 and the isotope abundance ratio of TiSi molecular ions.

Specifically, assuming that the isotope abundance ratio of the TiSi molecular ion is x, the quadratic function f (x) shown in FIG.
That is, the secondary ion intensity of the TiSi molecular ion is f (x) = − 50529x ² + 187201x + 94.806 (Equation 10).

Accordingly, the secondary ion intensity I of the TiSi molecular ion having a mass number m of 75 as an interfering ion for As is obtained.
_i can be calculated by I _i = f (R ₇₅ ) (Equation 11). However, in (Equation 11), R ₇₅ is the isotope abundance ratio of a TiSi molecular ion having a mass number m of 75.

Hereinafter, a method of analyzing the As concentration in a sample having a TiSi ₂ / Si structure using the secondary ion mass spectrometry according to the second embodiment will be described with reference to FIG.
This will be specifically described with reference to the flowchart of FIG.

First, in step S21, as in step S11 of the first embodiment shown in FIG. 3, a Si sample having a TiSi ₂ / Si structure shown in FIG. A first auxiliary secondary ionic strength I _Si ,
A first secondary ion intensity I ₇₅ of an ion having a mass number substantially equal to As (m = 75), and a Ti having a mass number m other than 75
The second secondary ion intensity _{IX of} Si molecular ions (isotopes of TiSi molecular ions having a mass number m of 75 serving as interfering ions for As) is measured.

Next, in step S22, a quadratic function f (x) ((Equation 1) representing the correlation between the second secondary ion intensity I _X and the isotope abundance ratio R _{X of} TiSi molecular ions.
0)).

Next, in step S23, the third secondary ion intensity I _i of a TiSi molecular ion having a mass number m of 75 as an interfering ion with respect to As is calculated as follows: I _i = f (R ₇₅ ) (Equation 12) ) Calculated by. However, in (Formula 12), R ₇₅ is the isotope abundance ratio of TiSi molecular ions having a mass number m of 75.

Next, in step S24, as in step S14 of the first embodiment shown in FIG. 3, the fourth secondary ion intensity I _As of As in the sample to be measured is calculated as I _As = I ₇₅ −I _i (13), that is, by subtracting the third secondary ion intensity I _i from the first secondary ion intensity I ₇₅ .

Next, the relative sensitivity coefficient RS is calculated by a known method.
The As concentration is determined using F.

More specifically, in step S25, as in step S15 of the first embodiment shown in FIG. 3, a standard sample (As) having the TiSi ₂ / Si structure shown in FIG. using the density C _as ⁰ known), to measure a third auxiliary secondary ion intensity K _as the second auxiliary secondary ion intensity K _Si and as of Si.

Next, in step S26, as in step S16 of the first embodiment shown in FIG.
The relative sensitivity coefficient RSF for i is calculated by RSF = (K _Si / K _As ) × C _As ⁰ (Equation 14).

Next, in step S27, as in step S17 of the first embodiment shown in FIG. 3, the As concentration C _As in the sample to be measured is calculated as follows: C _As = (I _As / I _Si ) × RSF. ... (Equation 15)

FIG. 7 shows the results of a secondary ion mass spectrometry according to the second embodiment, more specifically, a sample having a TiSi ₂ / Si structure shown in FIG. Shows the results of the analysis of the As concentration in FIG.

In FIG. 7, a solid line (with a black circle) indicates A obtained by the secondary ion mass spectrometry according to the second embodiment.
The dashed line indicates the depth profile of the As concentration obtained by the offset potential method as a third comparative example, and the dashed line (with a white square) indicates the fourth profile.
As a comparative example, the depth profile of the As concentration obtained by the secondary ion mass spectrometry according to the first embodiment (in the case where a TiSi molecular ion having a mass number m of 76 is selected in step S12 shown in FIG. 3). Is represented.

As shown in FIG. 7, the depth profile of the As concentration obtained by the secondary ion mass spectrometry according to the second embodiment is the third comparative example, that is, the As concentration obtained by the offset potential method. Well matched with the depth profile.

On the other hand, as shown in FIG. 7, in the fourth comparative example, the intensity component of the interfering ion calculated based on the secondary ion intensity (see FIG. 4) of the TiSi molecular ion having a mass number m of 76 is As a result of being underestimated, the TiSi ₂ film 4
The As concentration in (at a depth of 0 nm to about 40 nm) is overestimated.

As described above, according to the second embodiment, using the sample to be measured, the first secondary ion intensity of ions having a mass number substantially equal to the element to be measured, and the After measuring a second secondary ion intensity of a molecular ion to be an isotope of an interfering ion, a correlation between the second secondary ion intensity and an isotope abundance ratio of the molecular ion is determined, and then the correlation is determined. And the third of the interfering ions
Since the secondary ion intensity is calculated, it is possible to calculate the third secondary ion intensity, that is, the secondary ion intensity of interfering ions with respect to the element to be measured, without using a standard sample not containing the element to be measured. it can. Therefore, by subtracting the third secondary ion intensity from the first secondary ion intensity, the fourth secondary ion intensity of the element to be measured, that is, the concentration of the element to be measured in the sample to be measured can be accurately and easily obtained. You can ask.

According to the second embodiment, the correlation between the second secondary ion intensity and the isotope abundance ratio of molecular ions is expressed by a quadratic function, so that the correlation is simple. Even when the proportional relationship is deviated, the third secondary ion intensity, that is, the secondary ion intensity of interfering ions with respect to the element to be measured can be accurately calculated.

Further, according to the second embodiment, without using a method for increasing the mass resolution such as the offset potential method,
Since the secondary ion intensity of the element to be measured from which the intensity component of the interfering ions has been removed can be obtained, the quadrupole SIM
Since the resolution in the depth direction can be increased using the S apparatus, the impurity distribution on the surface or interface of a semiconductor used for an LSI or the like can be accurately evaluated.

In the first and second embodiments, the correlation between the second secondary ion intensity and the isotope abundance ratio of molecular ions is expressed by a linear function or a quadratic function. Alternatively, the same effect can be obtained by using another function expression. Specifically, when analyzing the As concentration in the sample having the TiSi ₂ / Si structure shown in FIG.
Assuming that the correlation between the second secondary ion intensity and the isotope abundance ratio of molecular ions is represented by f ′ (x) (a function expression other than a linear function expression or a quadratic function expression), the third The next ion intensity I _i can be calculated by the following formula: I _i = f ′ (R ₇₅ ) (Equation 16) However, in (Equation 16), R ₇₅ is the isotope abundance ratio of TiSi molecular ions having a mass number m of 75.

[0085]

According to the present invention, the secondary ion intensity of interfering ions with respect to the element to be measured can be calculated without using a standard sample containing no element to be measured, so that the intensity component of the interfering ions can be removed. The secondary ion intensity of the measurement target element, that is, the concentration of the measurement target element in the sample can be accurately and efficiently obtained.

Also, according to the present invention, a quadrupole SIMS
Since the resolution in the depth direction can be increased using the apparatus, the impurity distribution on the surface or interface of a semiconductor used for an LSI or the like can be accurately evaluated.

[Brief description of the drawings]

FIG. 1 is a diagram showing an isotope composition and an isotope abundance ratio of TiSi molecular ions used in secondary ion mass spectrometry according to first and second embodiments of the present invention.

FIG. 2 shows secondary ion intensities of six types of TiSi molecular ions having a mass number m other than 75 and isotopes of TiSi molecular ions obtained by the secondary ion mass spectrometry according to the first embodiment of the present invention. It is a figure which shows the correlation with a body presence ratio.

FIG. 3 is a flowchart of a method for analyzing an As concentration in a sample having a TiSi ₂ / Si structure by using the secondary ion mass spectrometry according to the first embodiment of the present invention.

FIG. 4 is a diagram showing the results of analysis of the As concentration in a sample having a TiSi ₂ / Si structure using the secondary ion mass spectrometry according to the first embodiment of the present invention.

FIG. 5 shows the secondary ion intensities of six kinds of TiSi molecular ions having a mass number m other than 75 and isotopes of TiSi molecular ions obtained by the secondary ion mass spectrometry according to the second embodiment of the present invention. It is a figure which shows the correlation with a body presence ratio.

FIG. 6 is a flowchart of a method for analyzing an As concentration in a sample having a TiSi ₂ / Si structure by using the secondary ion mass spectrometry according to the second embodiment of the present invention.

FIG. 7 is a diagram showing a result of analysis of an As concentration in a sample having a TiSi ₂ / Si structure using a secondary ion mass spectrometry according to the second embodiment of the present invention.

FIG. 8 shows TiSi ₂ / Si used in the secondary ion mass spectrometry according to the first and second embodiments of the present invention.
It is sectional drawing of the sample which has a structure.

FIG. 9: Using conventional secondary ion mass spectrometry, TiS
the sample with i ₂ / Si structure diagrams showing the results of measurement of the depth profile of the secondary ion intensity of ions having an As substantially equal mass number (m = 75).

FIG. 10: Using conventional secondary ion mass spectrometry, Ti
FIG. 3 is a flowchart of a method for analyzing the As concentration in a sample having a Si ₂ / Si structure.

[Explanation of symbols]

Reference Signs List 1 silicon substrate 2 silicon oxide film 3 polysilicon film 4 TiSi ₂ film

Claims (3)

[Claims] A first secondary ion intensity of an ion having a mass number substantially equal to that of the element to be measured, and a sample other than the element to be measured; A first step of measuring a second secondary ion intensity of a molecular ion serving as an isotope of an interfering ion having a mass number substantially equal to the element to be measured; the second secondary ion intensity; and the interfering ion A second step of obtaining a correlation with the abundance ratio of the molecular ions in all the isotopes, and a third step of calculating a third secondary ion intensity of the interfering ion using the correlation. A fourth step of calculating a fourth secondary ion intensity of the element to be measured by subtracting the third secondary ion intensity from the first secondary ion intensity; and Using the secondary ionic strength of Secondary ion mass spectrometry, characterized in that it comprises a fifth step of determining the concentration of the measurement target element in the sample. 2. The secondary ion mass spectrometry according to claim 1, wherein the correlation is represented by a linear function. 3. The secondary ion mass spectrometry according to claim 1, wherein the correlation is represented by a quadratic function.