JP4864336B2 - Depth element distribution measurement method - Google Patents

Description

The present invention relates to a depth element distribution measuring method, in particular, secondary ionization rate in measuring the distribution in the depth direction of the elements in a minute region by using a secondary ion mass spectrometry method (SIMS method) those concerning the depth direction element distribution measuring method characterized by the configuration to increase.

  In semiconductor devices, the impurity concentration and distribution in the well region and channel dope region have a great influence on the device characteristics, but the surface of the semiconductor substrate and the deposited thin film with the progress of miniaturization and thinning in recent years. Therefore, it is required to form an impurity concentration distribution in a shallow region with high accuracy.

  In order to meet such demands, it is necessary to grasp the impurity concentration distribution in the measurement target region with high accuracy. For this reason, the distribution of elements such as impurities in the depth direction from the surface of the semiconductor substrate or the deposited thin film is required. Since secondary ion mass spectrometry (SIMS), which is a representative means for measurement, is mainly used, the conventional SIMS method will now be described with reference to FIG.

See FIG.
FIG. 6 is a schematic configuration diagram of a conventional SIMS apparatus, in which a sample 41 to be measured is fixed and held, a sample holder 42 capable of moving, tilting, and rotating in the X, Y, and Z directions, and primary ions. Source oxygen ion gun 43 and cesium ion gun 44, quadrupole mass analyzer 45 for mass analysis of secondary ions, detector 46 for measuring the amount of analyzed ions, electron gun for correcting charging by ion irradiation 47.
Note that an oxygen ion gun 43 is used when generating positive secondary ions, and a cesium ion gun 44 is used when generating negative secondary ions.

  In this secondary ion mass spectrometry method, composition analysis is performed by performing mass analysis of secondary ions generated by irradiating the sample surface with ions. Analysis is possible.

  In addition, as described above, in the analysis of a minute region, a liquid metal having a high convergence property, such as Ga (gallium), is used for the primary ions. When used as, there is a problem that atoms and molecules emitted from the sample surface cannot be detected by a mass spectrometer because most of them are neutral.

  In addition, since the measurement region is as small as one-tenth to one-hundredth of that of a normal SIMS analysis, there is a problem that the amount of secondary ions emitted is reduced and sufficient intensity cannot be obtained.

  Therefore, the present applicant reduced the work function of the sample surface by adding an alkali metal or attaching an alkali metal film to the surface of the sample, and also added alkali metal ions rich in reactivity with the sample as primary ions. It has been proposed to increase the negative secondary ionization rate, that is, the probability of becoming negative ions by irradiation (see, for example, Patent Document 1).

In this case, the negative secondary ionization rate γ ^-1 is generally given by assuming that φ is the work function of the sample surface, χ is the electron affinity, and ε ₀ is a factor related to the vertical component of the secondary ion release rate. ,
γ ^-1 ∝exp [-(φ-χ) / ε ₀ ]
It is represented by

Therefore, in order to improve the negative secondary ionization rate γ ⁻¹ , it is necessary to lower the work function φ, and in order to lower the work function φ, the sample surface is coated with an alkali metal having a low electronegativity. Is effective.
JP 2004-294275 A

However, in the case of using an alkali metal as a primary ion source, there is a problem that the alkali metal ions other than Cs ⁺ ions are not suitable for analysis of poor small area convergence, whereas, the convergence of such Ga ⁺ ions When ions with high properties are used, there is a problem that the sensitivity is lowered due to the small secondary ionization rate.

  Although the work function of the sample surface is reduced by adding an alkali metal or adhering an alkali metal film to the surface of the sample, it is not always sufficient as the analysis region is further miniaturized. Decrease in the amount of released ions becomes a problem.

  In other words, when the measurement area is small, the conventional assistance with alkali metal or halogen single element has a limit in ionization efficiency, and the element type to be supplied differs depending on the polarity of the ion. There is a problem of becoming an element.

  Accordingly, an object of the present invention is to increase the convergence of primary ions and lower the work function of the sample surface to further increase the negative secondary ionization rate.

FIG. 1 is a diagram illustrating the basic configuration of the present invention. Means for solving the problems in the present invention will be described with reference to FIG.
In order to solve the above-mentioned problem, the present invention detects the secondary ions 4 generated by the irradiation of the primary ions 3 and measures the depth direction distribution of the elements constituting the sample 1 in the depth direction. In the element distribution measurement method, ions of a metal element having higher convergence than Ar are used as primary ion species, and an oxide of an alkali metal element is attached to the surface of the sample 1.

In this way, by using ions of a metal element having a higher convergence than Ar as a primary ion species, it is possible to perform highly accurate analysis in a minute region, and the detection sensitivity is reduced due to it, which is highly reactive with the sample 1. It is possible to cover by lowering the work function by attaching an oxide of an alkali metal element, which is the oxide 2 of the element, to the surface of the sample 1.

  As the primary ion species in this case, any ion of a metal element having higher convergence than Ar may be used, but from the viewpoint of ease of handling or environmental pollution, liquid metals such as Ga and Cs, A metal that can be easily melted, such as Au, Bi, or In, is desirable.

Further, as means for supplying the alkali metal element to the surface of the sample 1, either heating evaporation or ion beam may be used.
For example, an alkali metal element oxide may be attached to the surface of the sample 1 by supplying an alkali metal element as an ion beam in an oxygen atmosphere.

Alternatively, an alkali metal element oxide may be attached to the surface of the sample 1 by supplying an alkali metal element as an ion beam and oxygen as an ion beam.

Alternatively, an alkali metal element may be attached to the surface of the sample 1 by supplying the alkali metal element by heating and evaporation in an oxygen atmosphere, and further, the alkali metal element may be an oxide of the alkali metal element. The oxide of the alkali metal element may be attached to the surface of the sample 1 by sputtering in an oxygen atmosphere using as a target.

In this case, the highly reactive element is preferably an alkali metal element or alkaline earth element having a high electronegativity, but an alkali metal element having a higher electronegativity is more preferable.
As the alkali metal element, Li, Na, or Cs is particularly desirable from the viewpoint of easy handling.

Further, it is desirable to optimize the oxygen composition ratio in the oxide of the alkali metal element according to the element type to be analyzed constituting the surface of the sample 1.
That is, in the case of A alkali metal, by controlling the oxygen at the time of film formation or ion irradiation from having a plurality of oxidized form, to form an alkali metal oxide film having an optimal work function in accordance with the analyzed element species Thus, the secondary ionization efficiency can be stably improved.

The thickness of the oxide of an alkaline metal element to be deposited on the surface of the sample 1, usually, the work function decreases with increasing coverage of oxides, coverage is minimized at 1.0 mL (monolayer) Therefore, the thickness of the oxide is desirably 2 nm or less, more preferably 1 nm or less.
Note that if it exceeds 2 nm, it is not preferable because it takes time for the sputter etching of the oxide during the sputter etching in the analysis of the surface of the sample 1.

  In the present invention, the decrease in secondary ionization rate due to the use of highly convergent ion species as primary ions is compensated by using oxides of highly reactive elements, particularly alkali metal oxides, as sensitizing elements. Therefore, it is possible to perform the element distribution measurement in the depth direction of the minute region by SIMS with higher sensitivity.

  The present invention uses ions of metal elements having higher convergence than Ar, in particular, Ga, Cs, Au, Bi, or In as primary ion species, and elements rich in reactivity with a sample, particularly Li, Na. Alternatively, an oxide of an alkali metal element such as Cs is attached to the surface of the sample with a thickness of 2 nm or less, more preferably 1 nm or less, and primary ions are applied to the sample surface in a state where the work function of the sample surface is lowered. Irradiation is performed, and the secondary ions generated therewith are subjected to mass spectrometry to measure the element distribution in the depth direction.

Here, with reference to FIG.2 and FIG.3, the secondary ion mass spectrometry method of Example 1 of this invention is demonstrated.
See Figure 2
FIG. 2 is a conceptual configuration diagram of a secondary ion mass spectrometer used in the secondary ion mass spectrometry method of Example 1 of the present invention. A measurement chamber 11 having an exhaust port 12 and a gas inlet 13 and a sample 15 are shown. A sample holder 14 to be placed and fixed, a Ga ion gun 16 that irradiates Ga ⁺ ions 17 as primary ions, a quadrupole mass analyzer 19 that performs mass analysis of secondary ions 18 generated from the sample 15, and a mass analysis. A detector 20 that measures the amount (number) of ions and a Cs ion gun 21 that supplies Cs ⁺ ions 22 to the surface of the sample 15 are configured.
Here, a silicon substrate in which As was ion-implanted with an acceleration energy of 5 keV and a dose amount of 5 × 10 ¹⁴ cm ⁻² was used as the sample 15.

First, oxygen gas is introduced from the gas inlet 13 into the measurement chamber 11 evacuated to a base pressure of 1 × 10 ⁻⁹ Torr, and the degree of vacuum is lower than 1 × 10 ⁻⁸ Torr, for example, 6.0 × 10 ^{−. In} the oxygen atmosphere of ⁵ Torr, ⁵ keV or less, for example, 1 keV Cs ⁺ ions 22 and 25 keV Ga ⁺ ions 17 are alternately supplied and generated by the quadrupole mass analyzer 19 and the detector 20. Secondary ion 18 is detected and analyzed.

In this case, by irradiating the surface of the sample 15 with Cs ⁺ ions 22 in an oxygen atmosphere, a Cs-O film 23 is formed on the surface of the sample, and the work function of the surface of the sample 15 is attached alone. Decrease than if.

Usually, the work function decreases as the coverage increases, and the coverage is minimal at 1.0 ML (monolayer), so that the thickness of the Cs-O film 23 is 2 nm or less, more preferably 1 nm or less. In particular, it is necessary to determine the dose amount of the Cs ⁺ ions 21 so as to be in the vicinity of 1.0 ML.

  Note that if the thickness of the Cs-O film 23 exceeds 2 nm, it is not preferable because it takes time for sputter etching of the Cs-O film 23 itself. This is not desirable because of the large fluctuations.

In this case, the irradiation time of Cs ⁺ ions 22 is, for example, 2 seconds, the irradiation time of 25 keV Ga ⁺ ions 17 is, for example, 5 seconds, and irradiation is performed alternately until the analysis at a predetermined depth is completed. Since the work surface is lowered by covering the sample surface exposed to Ga ⁺ ions 17 for 5 seconds with the Cs-O film 23 again, secondary ions 18 are always generated in a low work function state. Can be made.
In this case, As to be analyzed is detected as secondary ions 18 in the form of molecular ions AsSi ⁻ .

See Figure 3
FIG. 3 is a profile (AsSi—Cs + O) in the depth direction of AsSi ⁻ ions measured under the above conditions, and here, the depth is expressed as time.
For comparison, when oxygen is not introduced into the measurement chamber 11 and 1 keV Cs ⁺ ions 22 and 25 keV Ga ⁺ ions 17 are alternately irradiated so that only Cs exists on the surface (AsSi-Cs), A case where only an oxygen atmosphere is used (AsSi-O) and a case where neither Cs ⁺ ion irradiation nor an oxygen atmosphere is used (AsSi-Ga) are also illustrated.

  As is clear from the figure, comparing the peak-top intensity of ion-implanted As, it can be seen that the intensity is the highest in Example 1 (AsSi-Cs + O) of the present invention. It can be seen that the secondary ionization rate is improved even when compared with adhesion (AsSi-Cs).

In Example 1 of the present invention, the Cs—O film 23 is attached to the sample surface and irradiated with highly converged Ga ⁺ ions in a state in which the work function is lowered. Can be done with precision.

Next, with reference to FIG. 4, the secondary ion mass spectrometry method of Example 2 of this invention is demonstrated.
See Figure 4
FIG. 4 is a conceptual configuration diagram of a secondary ion mass spectrometer used in the secondary ion mass spectrometry method of Example 2 of the present invention. A measurement chamber 11 having an exhaust port 12 and a gas inlet 13 and a sample 15 are shown. A sample holder 14 to be placed and fixed, a Ga ion gun 16 that irradiates Ga ⁺ ions 17 as primary ions, a quadrupole mass analyzer 19 that performs mass analysis of secondary ions 18 generated from the sample 15, and a mass analysis. A detector 20 that measures the amount (number) of ions, a Cs ion gun 21 that supplies Cs ⁺ ions 22 to the surface of the sample 15, and an O ion gun 24 that supplies O ⁺ ions 25 to the surface of the sample 15. .

First, in the measurement chamber 11 evacuated to a base pressure of 1 × 10 ⁻⁹ Torr, 5 keV or less, for example, 1 keV Cs ⁺ ions 22 and 5 keV or less, for example, 1 keV O ⁺ ions 25 are simultaneously supplied. Alternatingly, 25 keV Ga ⁺ ions 17 are supplied to attach the Cs-O film 23 to the surface of the sample 15, and the secondary ions 18 generated by the quadrupole mass analyzer 19 and the detector 20 are detected and analyzed. I do.

Also in this case, the dose amounts of the Cs ⁺ ions 22 and the O ⁺ ions 25 are determined so that the film thickness of the Cs—O film 23 is 2 nm or less, more preferably 1 nm or less, particularly in the vicinity of 1.0 ML. There is a need to.

In this case, the irradiation time of the Cs ⁺ ions 21 and the O ⁺ ions 24 is 2 seconds, for example, and the irradiation time of the 25 keV Ga ⁺ ions 17 is 5 seconds, for example, and the analysis at a predetermined depth is completed. Alternately.

Also in this Example 2, since the work surface is lowered by covering the sample surface exposed by the Ga ⁺ ions 17 again with the Cs—O film 23 in the same manner as in Example 1, the work function is always in a low work function state. Secondary ions 18 can be generated, and highly sensitive measurement is possible.

Next, a secondary ion mass spectrometry method according to Example 3 of the present invention will be described with reference to FIG.
See Figure 5
FIG. 5 is a conceptual configuration diagram of a secondary ion mass spectrometer used in the secondary ion mass spectrometry method of Example 3 of the present invention. A measurement chamber 11 having an exhaust port 12 and a gas inlet 13 and a sample 15 are shown. A sample holder 14 to be placed and fixed, a Ga ion gun 16 that irradiates Ga ⁺ ions 17 as primary ions, a quadrupole mass analyzer 19 that performs mass analysis of secondary ions 18 generated from the sample 15, and a mass analysis. A detector 20 that measures the amount (number) of ions, a Cs source 26 that supplies Cs 27 to the surface of the sample 15, an electrode 28 that supplies a heating current to the Cs source 26, a current introduction terminal 29, and a shutter 30 Is done.

First, oxygen gas is introduced from the gas inlet 13 into the measurement chamber 11 evacuated to a base pressure of 1 × 10 ⁻⁹ Torr, and the degree of vacuum is lower than 1 × 10 ⁻⁸ Torr, for example, 6.0 × 10 ^{−. In} the oxygen atmosphere of ⁵ Torr, a current is supplied from the current introduction terminal 29 to the electrode 28 to heat and evaporate the Cs source 26 and supply Cs27 to form the Cs-O film 23 on the surface of the sample 15. .

  Also in this case, it is necessary to control the supply amount and the supply time of Cs27 so that the film thickness of the Cs-O film 23 is 2 nm or less, more preferably 1 nm or less, particularly in the vicinity of 1.0 ML.

Next, 25 keV Ga ⁺ ions 17 are irradiated for 5 seconds, for example, with the shutter 30 closed, and the secondary ions 18 are detected and analyzed by the quadrupole mass analyzer 19 and the detector 20. 30 is opened, a new Cs-O film 23 is deposited, and again 25 keV Ga ⁺ ions 17 are irradiated, for example, for 5 seconds to detect and analyze the secondary ions 18.

In Example 3 as well, the sample surface exposed to Ga ⁺ ions 17 is again covered with the Cs—O film 23 to reduce the work function in the same manner as in Example 2, so that the work function is always in a low work function state. Secondary ions 17 can be generated, and highly sensitive measurement is possible.

  The embodiments of the present invention have been described above. However, the present invention is not limited to the configurations and conditions described in the embodiments, and various modifications can be made. For example, Ga is used as a primary ion. However, it is not limited to Ga, and any metal element having higher convergence than Ar may be used.

In particular, from the viewpoint of easy handling or environmental pollution, a liquid metal such as Ga and Cs, or a metal that can be easily melted such as Au, Bi, or In is desirable.
That is, since these metals are liquid metals or metals that can be easily melted, they can be melted in the ion gun to form a point-like ion source, so that the convergence is improved when converging with a lens.
In principle, there is no problem with Hg or Pb, but environmental pollution or the like becomes a problem.

In each of the above embodiments, Cs is used as the metal element constituting the oxide. However, the element is not limited to Cs, and the element having high reactivity with the element constituting the sample may be an electronegativity. A high alkali metal element or alkaline earth element is preferable, but an alkali metal element having higher electronegativity is more preferable.
Further, as the alkali metal element, Li or Na is preferable from the viewpoint of easy handling as in the case of Cs.

  In each of the above embodiments, the composition of the Cs-O film is not particularly mentioned, but Cs-O having a composition ratio satisfying the stoichiometric ratio may be used, or an O-rich Cs-O or O poor may be used. Cs-O may be used.

  In particular, in the case of alkali metal, since it has multiple oxidation forms, by controlling oxygen during film formation or ion irradiation, an alkali metal oxide film with an optimal work function is formed according to the element type to be analyzed By doing so, it is possible to stably improve the secondary ionization efficiency.

In each of the above embodiments, a method for forming the Cs-O film is described. However, the method is not limited to the method described in each of the embodiments, and for example, 1 × 10 ⁻⁹ Torr A state in which an oxygen gas is introduced from the gas inlet 13 into the measurement chamber 11 evacuated to the base pressure and the oxygen atmosphere is lower than 1 × 10 ⁻⁸ Torr, for example, 6.0 × 10 ⁻⁵ Torr. Thus, the Cs—O film may be deposited by sputtering using a Cs ₂ O target.

In this case, similarly to the third embodiment, the Cs—O film and the Ga ⁺ ion irradiation may be alternately performed using the shutter mechanism until the measurement of the element distribution up to a predetermined depth is completed.

  Further, although not mentioned in each of the above embodiments, it is desirable to provide an electron gun in order to correct charging associated with ion irradiation, as in the conventional example shown in FIG.

The detailed features of the present invention will be described again with reference to FIG. 1 again.
1 again (Appendix 1) In the depth direction element distribution measurement method for detecting the secondary ions 4 generated along with the irradiation of the primary ions 3 and measuring the depth direction distribution of the elements constituting the sample 1, A depth direction element distribution measuring method, wherein ions of a metal element having a higher convergence than Ar are used as a primary ion species, and an oxide of an alkali metal element is attached to the surface of the sample 1.
(Supplementary note 2) The depth direction element distribution measurement method according to supplementary note 1, wherein any one of Ga, Au, Cs, Bi, or In is used as the primary ion species.
(Additional remark 3) The depth direction element distribution measuring method of Additional remark 1 or 2 characterized by the means to supply the said alkali metal element to the surface of the said sample 1 being either heating evaporation or an ion beam.
(Supplementary Note 4) The alkali by providing an ion beam in an oxygen atmosphere a metal element, the depth direction elements according to Supplementary Note 3, wherein the attaching the oxide of the alkali metal element to the surface of the sample 1 Distribution measurement method.
(Supplementary Note 5) The above alkali metal element is supplied as an ion beam by the oxygen also supplied as an ion beam, Appendix 3, wherein the attaching the oxide of the alkali metal element to the surface of the sample 1 Depth direction element distribution measurement method.
(Supplementary note 6) The depth direction element according to supplementary note 3, wherein the alkali metal element is attached to the surface of the sample 1 by supplying the alkali metal element by heating and evaporation in an oxygen atmosphere. Distribution measurement method.
The oxide of the (Appendix 7) The alkali metal element of the alkali metal element as a target, by sputtering in an oxygen atmosphere, characterized by adhering an oxide of the alkali metal element to the surface of the sample 1 The depth direction element distribution measurement method according to attachment 3.
(Supplementary Note 8 ) The depth direction element distribution measurement method according to any one of Supplementary notes 1 to 7, wherein the alkali metal element is Li, Na, or Cs.
(Supplementary note 9 ) Any one of Supplementary note 1 to Supplementary note 8 , wherein the oxygen composition ratio in the oxide of the alkali metal element is optimized according to an element type to be analyzed constituting the surface of the sample 1. The depth direction element distribution measurement method according to 1.
(Additional remark 10) Depth direction element distribution measurement of any one of Additional remark 1 thru | or Additional remark 9 characterized by the film thickness of the oxide of the alkali metal element made to adhere to the surface of the said sample 1 having been 2 nm or less Way .

  As an application example of the present invention, analysis of impurity elements in a semiconductor integrated circuit device is typical, but it can also be applied to measurement of composition distribution in a film forming direction in a formed insulating film or silicide film. Furthermore, the present invention is also applied to the measurement of the composition distribution in the film forming direction of a multilayer structure film including a metal film such as a thin film magnetic head.

It is explanatory drawing of the fundamental structure of this invention. It is a notional block diagram of the secondary ion mass spectrometer used for the secondary ion mass spectrometry method of Example 1 of this invention. AsSi were measured in Example 1 of the present invention ^- is the depth direction of the profile of the ion. It is a notional block diagram of the secondary ion mass spectrometer used for the secondary ion mass spectrometry method of Example 2 of this invention. It is a notional block diagram of the secondary ion mass spectrometer used for the secondary ion mass spectrometry method of Example 3 of this invention. It is a schematic block diagram of the conventional SIMS apparatus.

DESCRIPTION OF SYMBOLS 1 Sample 2 Oxide of element rich in reactivity with sample 3 Primary ion 4 Secondary ion 5 Secondary ion detection means 11 Measurement chamber 12 Exhaust port 13 Gas inlet port 14 Sample holder 15 Sample 16 Ga ion gun 17 Ga ⁺ ion 18 Secondary ion 19 Quadrupole mass spectrometer 20 Detector 21 Cs ion gun 22 Cs ⁺ ion 23 Cs-O film 24 O ion gun 25 O ⁺ ion 26 Cs source 27 Cs
28 Electrode 29 Current introduction terminal 30 Shutter 41 Sample 42 Sample holder 43 Oxygen ion gun 44 Cesium ion gun 45 Quadrupole mass analyzer 46 Detector 47 Electron gun

Claims (6)

In a depth direction element distribution measurement method for detecting a depth direction distribution of elements constituting a sample by detecting secondary ions generated by irradiation with primary ions, ions of metal elements having higher convergence than Ar are used. A depth direction element distribution measuring method, wherein the element is used as a primary ion species, and an oxide of an alkali metal element is attached to the surface of the sample.   2. The depth direction element distribution measurement method according to claim 1, wherein any one of Ga, Au, Cs, Bi, and In is used as the primary ion species. The depth direction element distribution measuring method according to claim 1 or 2, wherein the means for supplying the alkali metal element to the surface of the sample is either heating evaporation or ion beam. The depth direction element distribution measuring method according to any one of claims 1 to 3 , wherein a thickness of the oxide is 1 nm or less and 0.3 ML or more. The depth direction element distribution measurement method according to any one of claims 1 to 4 , wherein the alkali metal element is supplied as an ion beam and an O ⁺ ion beam is also supplied. The depth direction element distribution measuring method according to claim 5 , wherein the alkali metal element is supplied simultaneously with the ion beam and the O ⁺ ion beam, and alternately with the primary ions.

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