JP2000123773A - Secondary ion mass spectrometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary ion mass spectrometer capable of analyzing in the depth direction with high sensitivity as well as high depth-resolution. SOLUTION: This mass spectrometer has such as arrangement that an angle αformed by a primary ion beam 2 and the center axis of a secondary ion collecting system 5 and the position of the cross point (p) of both of them are variable by making an ion gun 1 movable when the primary ion beam 2 from the ion gun 1 is irradiated on a sample 4 held on a sample holding part 3, and secondary ions 8 released from the sample 4 are separated based on their mass by a mass spectrograph 6 via the secondary ion collecting system 5 comprising a secondary ion extraction electrode 5a and an electrostatic lens 5b, and detected by a secondary ion detector 7.

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 spectrometer and, more particularly, to the simultaneous optimization of the angle of incidence of primary ions on a sample and the relative position between the sample and a secondary ion collection system.

[0002]

2. Description of the Related Art As shown in FIG. 2, a secondary ion mass spectrometer conventionally used for collecting secondary ions comprises an ion gun 1, a sample holder 3, a secondary ion extraction electrode 5a and an electrostatic lens 5b. It mainly comprises a system 5, a mass analyzer 6, a secondary ion detector 7, and the like. The sample 4 held by the sample holder 3 is movable, but the ion gun 1 and the secondary ion collection system 5 are fixed, and the angle of incidence of the primary ion beam, that is, the trajectory of the primary ion beam, the sample normal and In order to change the angle formed, the method of inclining the sample 4 with respect to the primary ion beam is used.
For this reason, when the incident angle of the primary ions is changed, the relative position between the sample 4 and the secondary ion collection system, that is, the distance and the angle between them are also changed.

[0003] In depth analysis using a secondary ion mass spectrometer, mixing of primary ions with atomic molecules constituting a sample is one of the main factors for lowering the resolution in the depth direction (for example, MG). Dowsett e
tal., J. Vac. Sci. Tech. B, 10, 336 (1992)).
Therefore, suppressing this mixing is indispensable for improving the resolution in the depth direction. In general, when performing depth analysis using secondary ion mass spectrometry, it is effective to increase the incident angle of primary ions in order to suppress mixing and obtain high depth resolution. (E.g., WR Morinville et al., Secondar
y Ion Mass Spectrometry, SIMS XI, Wiley, Chicheste
r 1998, p. 297). On the other hand, the secondary ion detection efficiency largely depends on the relative position between the sample 4 and the secondary ion collection system 5.

[0004]

In the conventional secondary ion mass spectrometer, since the ion gun and the secondary ion collection system are fixed, the incident angle of the primary ions and the relative angle between the sample and the secondary ion collection system are determined. It was not possible to change the position independently. In particular, when analyzing at the optimal primary ion incidence angle to obtain high depth direction resolution, the component of the kinetic energy of secondary ions emitted from the sample in the normal direction of the sample is small and enters the secondary ion collection system. Hateful. Therefore,
Although it is desirable to reduce the distance between the sample and the secondary ion collection system, in a conventional secondary ion mass spectrometer,
Since the inclination angle of the sample is determined by determining the incident angle of the primary ions, the distance and angle between the sample and the secondary ion collection system cannot be freely changed.
That is, it was impossible to simultaneously achieve the optimal primary ion incidence angle for obtaining high depth direction resolution and the optimal arrangement of the sample and the secondary ion collection system for obtaining high detection sensitivity. Therefore, when the measurement is performed with the conventional secondary ion mass spectrometer under the condition where the primary ion incident angle is increased, there is a problem that the secondary ion intensity is significantly reduced.

SUMMARY OF THE INVENTION The present invention makes it possible to independently change the angle of incidence of primary ions and the positional relationship between a sample and a secondary ion collection system, thereby achieving high resolution in the depth direction and high sensitivity at the same time. To provide a secondary ion mass spectrometer capable of performing the following.

[0006]

Means for Solving the Problems To solve the above-mentioned problems, means adopted by the present invention is to irradiate a sample held by a sample holding section with a primary ion beam from an ion source, In the secondary ion mass spectrometer, the released secondary ions are mass-separated by a mass analyzer through a secondary ion extraction electrode, a secondary ion collection system including an electrostatic lens, and detected by a secondary ion detector. Secondary ion mass, characterized in that the ion gun is movable so that the angle between the primary ion beam and the central axis of the secondary ion collection system and the position of the intersection of the two are variable. It is configured as an analyzer.

This is not a problem when the sample holder is of a type in which a sample is simply placed on a table and exposed, but in the case of a type in which the sample holder has an opening and holds the sample on a lower surface. It is preferable to make the opening as wide as possible because it allows a higher angle of incidence. In the same manner, in the conventional secondary ion mass spectrometer, similarly, by widening the opening of the sample holding portion, it is possible to perform incidence at a higher angle, but it is said that the device of the present invention is more preferable. It is as follows.

[0008]

Next, embodiments of the present invention will be described with reference to the drawings.

[0009]

Embodiment 1 FIG. 1 is a block diagram of an embodiment of the present invention.
In FIG. 1, a primary ion beam 2 extracted from an ion gun 1 irradiates a sample 4 held in a sample holding unit 3. The secondary ions 8 released from the sample 4 pass through a secondary ion collection system 5 including a secondary ion extraction electrode 5a and an electrostatic lens 5b, are separated in mass by a mass analyzer 6, and detected by a secondary ion detector 7. You. Here, the ion gun 1 is movable by a bellows 10 corresponding to an ultra-high vacuum, so that the position of the angle α between the trajectory of the primary ion and the central axis of the secondary ion collection system and the intersection point p of both can be changed. It has become. This makes it possible to independently change only the incident angle of the primary ion while maintaining the relative position between the sample 4 and the secondary ion collection system 5 so that the detection sensitivity of the secondary ion is maximized. I have.

Next, a case in which a depth direction analysis is performed with a high resolution in the depth direction using this apparatus will be described. As described above, increasing the incident angle of the primary ion beam is effective for improving the resolution in the depth direction. In order to obtain a high depth resolution, the angle of incidence must be especially between 80 ° and 90 °.
Is desirably within the range. By using this apparatus, it is possible to set the incident angle of the primary ions by moving the position of the ion gun 1 while keeping the sample horizontal so that the resolution in the depth direction is optimized. By using this method, the distance and angle between the sample and the secondary ion collection system can be arbitrarily selected without being limited by the tilt angle of the sample, and after selecting a location where the detection sensitivity is optimal. , The incident angle of the primary ions can be set. This makes it possible to perform the depth direction analysis with a high depth resolution and a high detection limit.

[0011]

[Embodiment 2] FIG. 3 shows an example in which the results of the depth direction analysis by the conventional apparatus and the apparatus of the present invention are compared. The example in FIG.
Using Cs ⁺ with an accelerating voltage of 1.5 kV as the primary ion, the depth distribution of O in the 45 ° -thick oxide film formed on the Si
It was measured by detecting sO ⁺ . Fig. 3 (a)
Fig. 3 shows a measurement at an incident angle of primary ion of 75 ° using a conventional apparatus, and Fig. 3B shows a measurement at an incident angle of 85 ° using the apparatus of the present invention. The attenuation of the intensity of CsO ⁺ at the interface between the oxide film and the substrate is clearly steeper with the device of the present invention than with the conventional device. The depth resolution when the apparatus of the present invention is used is 12 °, and the depth resolution when the conventional apparatus is used is 21 °. It can be seen that the resolution in the depth direction is significantly improved by the apparatus of the present invention. In addition, since the profile of CsO ⁺ has less variation in intensity in the present invention, it can be seen that the measurement accuracy is higher in the present invention than in the conventional method.

[0012]

As described above, according to the present invention, in the secondary ion mass spectrometer, by making the ion gun movable, the incident angle of the primary ions and the relative position between the sample and the secondary ion collection system are determined. By changing them independently, there is an effect that high-resolution depth direction analysis can be performed simultaneously with high depth resolution.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an outline of a configuration of a secondary ion mass spectrometer according to the present invention.

FIG. 2 is a schematic diagram showing an outline of a configuration of a conventional secondary ion mass spectrometer.

FIG. 3 is a graph showing the results of depth analysis using a conventional device (a) and the device (b) of the present invention.

[Explanation of symbols]

 1 Ion gun 2 Primary ion beam 3 Sample holder 4 Sample 5a Secondary ion extraction electrode 5b Electrostatic lens 5 Secondary ion collection system 6 Mass analyzer 7 Secondary ion detector 8 Secondary ion 9 Vacuum tank 10 Bellows

Claims (1)

[Claims] A sample held in a sample holder is irradiated with a primary ion beam from an ion source, and secondary ions emitted from the sample are converted into a secondary ion formed by a secondary ion extraction electrode and an electrostatic lens. In a secondary ion mass spectrometer that separates mass by a mass analyzer through an ion collection system and detects by a secondary ion detector, by moving an ion gun, the primary ion beam and the center of the secondary ion collection system A secondary ion mass spectrometer having an arrangement in which an angle between the axis and an intersection between the two is variable.