JPH0896739A - Secondary ion mass spectrometry device - Google Patents

Abstract

PURPOSE: To provide a secondary ion mass spectrometry method capable of measuring true concentration distribution from the outermost surface of a sample. CONSTITUTION: With a sample 3, a target 19 having the same quality or the same sputter rate to the sample is held in a sample chamber 30 exhausted to be vacuumized, to sputter the target by deflecting a primary ion beam 20 in a deflecting means 18, and a thin film of thickness two times or more a primary ion implanting range is formed in a surface of the sample 3. Thereafter, the sample is irradiated with a primary ion from a thin film side in the sample chamber, to mass spectrometrically analyze a secondary ion emitted from the sample.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to secondary ion mass spectrometry widely used for surface analysis.

[0002]

2. Description of the Related Art Various devices such as LSI are
As the device becomes smaller and thinner, the surface and interface characteristics have a great influence on the device function. In the fabrication of more advanced devices, surface characterization is extremely important, and surface management and control are essential for the development of next-generation LSIs. Secondary ion mass spectrometry plays an important role in evaluating the characteristics of the substrate material of various devices such as LSI and the material surface in each manufacturing process.

FIG. 2 shows an outline of a secondary ion mass spectrometer. The primary ion beam irradiation system 1 is composed of an ion source 2 for the primary ion beam, a converging lens unit, and a sample 3. The primary ion beam irradiation system 1 forms a convergent ion beam and irradiates the sample 3 with a controlled ion beam. The secondary ion optical system 4 separates ions based on sample atoms emitted from the surface of the sample 3 upon irradiation with the primary ion beam according to mass and charge ratio, and performs mass analysis. For mass spectrometry, the entrance slit 5, sector electric field 6, sector magnetic field 7
And a sector type mass spectrometer comprising a collector slit 8 and
Alternatively, a quadrupole mass spectrometer 13 or the like is used. As a method of detecting the separated ions, the ion intensity passing through the collector slit 8 and the neutral particle removing slit 9 is determined by the ion detector 1.
2 and a method of directly measuring the emission pattern of the secondary ions at the position of the collector slit 8,
The image is magnified by the projection lens system 10 and the screen 11
There are two methods of observing and detecting the specific element image above.
The detection signal from the ion detector 12 is processed by the CPU 17, and the CRT is synchronized with the irradiation of the primary ion beam.
It is displayed on the screen 15 or recorded on the recorder 16 for use.

O ₂ ⁺ and Cs ⁺ are mainly used as primary ion species for irradiating the sample 3 from the ion source 2. When the detection element is a positive element, O ₂ ⁺ irradiation and positive ion detection are advantageous, and when the detection element is a negative element, Cs ⁺ irradiation and negative ion detection are advantageous. This is because when O ₂ ⁺ irradiation is performed as the primary ion species, O adheres to the sample surface and changes depending on the sample constituent elements, but in the steady state it is about 10 ²²
The concentration is atoms / cm ³ . Generally, when oxygen is adsorbed on the metal surface, the work function of the sample surface increases. As a result, when the ionization energy of the emitted ion species is lower than the work function, the transition of electrons to the emitted positive ions is not possible and the neutralization of positive ions does not occur. That is, the probability of survival of positive ions is high and the ionization rate is high. On the other hand, in the case of Cs ⁺ irradiation, Cs adheres to the sample in the steady state and lowers the work function of the sample surface (the work function of Cs is 3.9 eV). As a result, the electrons easily transition to the emitted particles and the ionization rate of negative ions is improved. In this case, the ion affinity is directly related to the electron affinity, and the larger the value, the higher the ionization rate. Furthermore, the relationship between the implantation concentration of the primary ion species and the ionization rate shows that the ionization rate tends to improve as the concentration increases. When the primary ion implantation range is Rp, the measurement is performed after performing sputter etching to a depth of 2 Rp or more.

[0005]

Since the secondary ion mass spectrometer uses high-energy ions as the primary excitation source, the incident primary ion species are injected into the sample together with the sputtering phenomenon during analysis, and The concentration of the injected primary ion species monotonically increases according to the error function up to a depth (2Rp) which is about twice the range of the primary ions, and then reaches a constant value after being saturated.

FIG. 3A is a schematic diagram for explaining the concentration distribution of the primary ion species implanted in the depth direction, and shows how the concentration distribution changes with time. Hatched part 4 in the figure
0 represents the concentration of the primary ion species in the width of the depth, and changes with time to the distribution shown on the right side. The surface position of the sample 3 becomes lower as it moves to the right because the etching progresses. As shown in the figure, the concentration of the implanted primary ion species on the surface of the sample, until the etching progresses to a depth of about twice the implantation range Rp of the primary ions,
It changes rapidly and then saturates to a constant value.

The element concentration distribution C (0, t) of the incident primary ion species on the surface of the sputter crater at time t is Vs for the sputtering rate, Rp for the primary ion implantation range, ΔRp for the standard deviation of Rp, and the primary ion beam. When the irradiation density is Jp and the elementary charge (1.6 × 10 ⁻¹⁹ C) is q, it is represented by the following formula (1) [FIG. 3 (b)]. C (0, t) = (Jp / 2q ・ Vs) [erf [(t ・ Vs-Rp) / 2 ^1/2・ ΔRp] + erf [Rp / 2 ^1/2・ ΔRp]] (1)

By the way, since the ionization rate of the contained element, that is, the number of ionized atoms with respect to the total number of sputtered atoms of the specific element greatly changes depending on the concentration of the implanted primary ion species, the conventional secondary ion mass spectrometry method It was difficult to evaluate the concentration in the region from the sample surface where (0, t) was changed to the depth of 2Rp. FIG. 4 shows a result calculated from the equation (1) assuming that a Si wafer is irradiated with a Cs ⁺ beam of 20 keV. Primary ion current density of 480 μA
/ Cm ² , 112 μA / cm ² , 48 μA / cm ² and 3
The calculation is performed by changing the type, and in any case, the sputter depth at the time of giving the saturation value is about 2 Rp. The measured value was adopted as the sputtering speed Vs.

As described above, in the region from the sample surface to the depth of 2Rp, the concentration of the injected primary ion species changes rapidly with the depth, and the ion intensity of the element to be analyzed in the sample also changes irrespective of the concentration accordingly. . Si containing B uniformly
FIG. 5 shows an example of the results of measuring the B and Si distributions in the depth direction of the wafer by the secondary ion mass spectrometer shown in FIG. FIG. 5A shows the measurement result of the concentration distribution of the impurity B in the depth direction, and FIG. 5B shows the measurement result of the concentration distribution of the Si as a matrix in the depth direction. The secondary ion mass spectrometry uses O ₂ ⁺ as the primary ion species, the primary ion energy is 7 keV, and the primary ion current density is 1 × 10 5.
^It was performed under the condition of ^-4 A / cm ² . The B concentration in Si is 2.5 × 10 ¹⁷ atoms / cm ³ . From FIG. 5, it can be seen that the B and Si ion intensities show an abnormal change in the 10 nm region from the surface. The intensity change in this region does not reflect the concentration distribution. The above-mentioned region corresponds to the etching depth region in which the primary ion species for excitation is injected into the sample, and the concentration thereof changes with the depth. In this region, the ionization rate of the contained element changes significantly. However, the secondary ion signal cannot reflect the concentration. As a result, the true depth profile is 10n in which the implantation concentration of the primary ion species (here, oxygen) shows a constant value.
It will be obtained only at a depth of m or more.

As described in detail above, the ionization rate of the contained element changes significantly in the region up to a depth about twice the implantation range of the primary ion beam used for analysis, and true information can be obtained. Absent. This is an essential problem of secondary ion mass spectrometry, and in the past, data in the depth region from the sample surface to 2Rp was either discarded or qualitatively evaluated by an empirical method. Absent. The region of 2 Rp in depth corresponds to a region of several tens of nm from the surface, and since true information cannot be obtained in the thin surface layer, there is a limit in the secondary ion mass spectrometry as a material surface analysis method. An object of the present invention is to solve the above problems and provide a secondary ion mass spectrometry method capable of measuring a true concentration distribution from the outermost surface of a sample.

[0011]

According to the present invention, in the sample chamber evacuated to the ultrahigh vacuum (<10 ⁻⁷ Pa) of the secondary ion mass spectrometer, the primary ion is attached to the surface of the sample to be analyzed prior to the analysis. The above object is achieved by producing a thin film of a substance having the same quality or the same sputter rate as the sample over a thickness twice or more the implantation range (Rp).

The thin film is formed on the surface of the sample by utilizing the sputtering phenomenon by the ion beam emitted from the primary ion source mounted on the secondary ion mass spectrometer. As the sputtering material, a sample piece obtained by cutting out a part of the sample itself, or a material having the same composition as the sample is used. The surface of the sample to be analyzed and the sputtered material are placed facing each other in the sample chamber of the secondary ion mass spectrometer, and the surface of the sputtered material is irradiated with static or scanning primary ion beam, and 2R
A sputtered film having a film thickness of p or more is formed. Rp can be uniquely calculated if the composition of the sample or sputter material and the incident ion species and energy are determined. The film thickness of the sputtered film considers the type of the sample or sputter material to be analyzed and the ion species and energy during analysis. To decide.

The secondary ion mass spectrometer according to the present invention comprises:
A sputtering mechanism is provided in the sample chamber in order to easily form a thin film on the sample surface. Specifically, the target support means, the primary ion beam deflecting means for irradiating the target supported by the ion beam, and the sample surface directly faces the target during sputtering, and the sample surface faces the secondary ion extraction electrode during analysis. A sample support base driving means for changing the attitude of the sample so as to face the sample is provided.

[0014]

When a sample having a dummy thin film having a film thickness of 2 Rp or more formed on the surface is analyzed by a secondary ion mass spectrometer, the primary ion implantation effect (altered layer) in the region of less than 2 Rp is
Sputtering occurs in the dummy thin film before reaching the actual sample. Therefore, in the measurement area of the actual sample, the primary ion implantation concentration shows a constant value and the ionization rate change of the contained element can be removed, so that a true depth direction distribution can be obtained even in the surface thin layer area of 10 nm or less from the surface. To be

A sample piece obtained by cutting out a part of the sample itself or a material having the same composition as the sample is used as the material of the dummy thin film because the sputtering rate is kept at the same rate as the sample and the dummy film and the sample surface are kept in a steady state. This is in order to obtain the same oxygen concentration in and the ionization rate of each element should be the same in both regions. If a thin layer is formed on the sample surface by another sputtering device and the sample is once taken out into the air and then mounted on a secondary ion mass spectrometer for analysis, expose the sample to the air. Then, the surface of the sample is contaminated by gas phase substances such as H, N, O and heavy metals from the dust due to moisture in the air, suspended dust, etc., and the measurement accuracy of the element to be analyzed in the surface layer is remarkably reduced. In addition, when a dummy thin layer is formed by a sputtering device different from the secondary ion mass spectrometer, a sputter device is required separately, which causes a cost problem, and a pretreatment process for forming the dummy thin layer. Since measurement and measurement are performed independently in time series,
There is also a problem that operations such as exhaustion of the device and mounting of a sample are complicated, and measurement takes time.

In the present invention, a sputtering mechanism is provided in the sample chamber of the secondary ion mass spectrometer, a dummy thin film forming process is performed in the sample chamber, and then the analysis is immediately started without breaking the vacuum. With a simple operation, it is possible to avoid contamination of the sample surface and perform highly accurate surface layer analysis.

[0017]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows an outline of the sample chamber. FIG. 1A shows the positional relationship between the beam deflection and the sample to be analyzed when the capping film is formed (the position where sputtered particles tend to adhere), and FIG. 1B shows the measurement result after the capping film has been formed. The positional relationship between the beam deflection (scanning) state and the sample to be analyzed is shown.

In the sample chamber 30 that has been evacuated, a sample support table 35 that holds the sample 3 to be analyzed, and the sputtering material 1
A sputter material support base 33 for holding 9 is provided. The sample support base 35 is controlled by a sample support base drive mechanism 38 that adjusts the three-dimensional position and inclination of the sample. The sputter material support base 33 is mounted on the transmission shaft 39 from outside the vacuum.
It is driven by the drive mechanism 37 via the, and adjusted to the irradiation position of the ion beam 20. The primary ion deflection electrode 18 is formed of a sputtered material 19 by the large-angle deflection of the primary ion beam 20.
It has a small-angle scanning deflection function during irradiation and measurement.

When forming a capping film by sputtering, first, one side of the analysis sample 3 or a sputter material 19 having the same composition as the analysis sample 3 is mounted on the sputter material support 33, and the ion beam 20 irradiates the sputter material 19 under optimum conditions. Fine adjustment is performed by the drive mechanism 37 so that it can be performed. Next, the sample support base 35 on which the analysis sample 3 is mounted is driven by the sample support base drive mechanism 38 so that the analysis target surface of the sample faces the target material surface. 1 × 10 ^-7 in the sample chamber 30
Evacuate below Pa. Then, the potential of the primary ion deflection electrode 18 is adjusted to an optimum deflection state, and the target material 19 is irradiated with ions. The particles 21 sputtered from the target material 19 adhere to the surface of the sample 3 to form a thin film. The ion beam 20 is scanned so that a uniform thin film is produced. The sputtering amount or the sputtering film thickness is set by the ion current and the sputtering time by utilizing the previously obtained sputtering yield.

When the thin film formation on the sample surface is completed, the sample 3 is driven and rotated by the sample support base drive mechanism 38 while maintaining the vacuum of the sample chamber 30, and as shown in FIG. The secondary ion extraction electrode 23 is directly faced. Thereby, the secondary ions 24 due to the sample atoms emitted from the sample 3
Can be efficiently guided to the secondary ion optical system 4. In the measurement, the primary ion deflection electrode 18 performs small-angle scanning deflection of the beam to perform secondary ion mass spectrometry.

In the conventional method, the results shown in FIG. 2 were obtained.
A Si sample uniformly containing B as described above was analyzed by the method of the present invention. A thin film is formed on the sample surface by using a fragment of the analysis sample as a target, and the target is subjected to A
It was performed by irradiating an r ⁺ beam. Energy of Ar ⁺ beam is 10 keV, ion current density is 1 × 10
^-3 A / cm ² . The thickness of the thin film formed on the sample surface is about 15 nm. FIG. 6 shows the measurement results of B ⁺ ionic strength distribution in the depth direction. FIG. 6 shows Si with a thin film attached.
A schematic diagram of the wafer is also shown. Abnormality due to primary ion implantation was about 15n attached to the sample surface by sputtering.
It occurs in the film thickness of m, and it can be seen that there is no abnormal effect due to the implanted ions in the sample to be analyzed. Si ⁺
The same results are obtained also for, and it can be seen that the present invention is effective in applying the secondary ion mass spectrometry to the surface layer analysis.

According to the present invention, a sputtered film forming function is added to the sample chamber of the secondary ion mass spectrometer, so that a sputtered film can be formed in a high vacuum. Since secondary ion mass spectrometry can be performed, changes in film composition and the like can be suppressed. Further, the analysis method of the present invention can be applied to all sample analysis.

According to the present invention, it becomes possible to analyze the depth direction of the surface layer of 10 nm or less, which has been difficult in the prior art by the secondary ion mass spectrometry, and analyze the shallow junction IC, the ultra-thin film and the passivation film. It can be performed. Moreover, according to the analysis method of the present invention, it becomes possible to quantitatively evaluate the surface contaminants and the oxide film.

[0024]

According to the present invention, it becomes possible to analyze the implantation depth region of primary ion species used as an excitation source in secondary ion mass spectrometry, and the field of application of secondary ion mass spectrometry is expanded.

[Brief description of drawings]

FIG. 1 is a schematic view of a sample chamber of a secondary ion mass spectrometer according to the present invention.

FIG. 2 is a schematic overall view of a secondary ion mass spectrometer.

FIG. 3 is a schematic diagram illustrating a depth direction implantation concentration distribution of primary ion species.

FIG. 4 is a diagram showing a concentration distribution in the depth direction on a sputtering surface of implanted primary ion species.

FIG. 5 is a diagram showing an analysis result by a conventional secondary ion mass spectrometry method.

FIG. 6 is a diagram showing measurement results according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Primary ion beam irradiation system, 2 ... Ion source, 3 ... Sample, 4 ... Secondary ion optical system, 5 ... Mass analysis system entrance slit, 6 ... Sector electric field, 7 ... Sector magnetic field, 8 ... Collector slit, 9 ... Neutral particle removing slit, 10 ... Projection lens system, 11 ... Screen, 12 ... Ion detector, 13
... Quadrupole mass spectrometer, 15 ... CRT, 16 ... Recorder, 17 ... CPU, 18 ... Primary ion deflection electrode, 19 ...
Sputtering material, 20 ... Primary ion beam, 21 ... Sputtered particles, 23 ... Secondary ion extraction electrode, 24 ... Secondary ion, 30 ... Sample chamber, 33 ... Sputtering material support, 35 ...
Sample base, 37 ... Drive mechanism, 38 ... Sample support base drive mechanism,
39 ... Transmission shaft, 40 ... Primary ion species concentration

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsumi Muto 832, Nagakubo, Horiguchi, Katsuta-shi, Ibaraki 2 Within Nissan Measurement Engineering Co., Ltd. Hiritsu Measurement Engineering Co., Ltd.

Claims (5)

[Claims] 1. A primary ion beam irradiation unit, a sample chamber to be evacuated, a sample support unit arranged in the sample chamber, a secondary ion extraction electrode for extracting secondary ions emitted from the sample, and a secondary. A secondary ion mass spectrometer including a secondary ion optical system for separating secondary ions extracted by an ion extraction electrode, and an ion detection means for detecting secondary ions separated by the secondary ion optical system, The secondary ion mass spectrometer, wherein the chamber has a target supporting means and has a function of producing a thin film of a target material having the same quality or the same sputtering rate as the sample on the surface of the sample supported by the sample supporting means. 2. The secondary ion mass spectrometer according to claim 1, further comprising a deflecting unit having a function of deflectively irradiating the target supported by the target supporting unit with the primary ion beam. 3. The secondary ion mass spectrometer according to claim 1, further comprising a driving unit that drives the target supporting unit. 4. The secondary ion mass spectrometer according to claim 1, further comprising drive means for directing the sample surface toward a target or a secondary ion extraction electrode. 5. A sample surface in a vacuum-exhausted sample chamber,
A thin film of a material having the same quality or the same sputtering rate as the sample is formed to a thickness twice or more of the primary ion implantation range, and then the sample is irradiated with primary ions from the thin film side in the sample chamber,
A secondary ion mass spectrometric method comprising mass spectrometric analysis of secondary ions emitted from a sample.