JP3664433B2 - Compact time-of-flight secondary ion mass spectrometer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a small time-of-flight secondary ion mass spectrometer.
[0002]
[Prior art]
A time-of-flight secondary ion mass spectrometer (Time of Flight Mass Spectrometer, TOF-MS) combined with a time-of-flight mass spectrometer (Time of Flight Mass Spectrometer, TOF-MS) in one of the secondary ion mass spectrometry (SIMS). Hereinafter, this TOF-SIMS also includes a large TOF-SIMS and a small TOF-SIMS such as 1 m (vertical) × 1 m (horizontal) × 1.5 m (height). .
[0003]
The small TOF-SIMS is configured, for example, as shown in FIG. 1 so that the entire flight configuration is made compact and small by shortening the ion flight stroke as much as possible.
[0004]
That is, FIG. 1 schematically shows a general configuration of a main part of a small-sized TOF-SIMS. In this figure, 1 is a source of primary ions 2 and is formed in an annular shape. Is provided with a detector 4 for detecting secondary ions 3. Reference numeral 5 denotes a holding table for the sample 6 provided on the upstream side of the primary ion generation source 1. Reference numerals 7 and 8 denote a pulsed ion optical system and a primary ion acceleration electrode provided between the primary ion generation source 1 and the sample holder 5. Reference numeral 9 denotes a flight tube provided on the front side of the primary ion generation source 1, and reference numeral 10 denotes an extension flight tube provided on the inner side of the primary ion generation source 1. Reference numeral 11 denotes a reflector that refracts the primary ions 2 flying from the primary ion source 1 and the secondary ions 3 flying from the sample 6 in the direction of the sample 6 and the ion detector 4, respectively.
[0005]
The operation of the small TOF-SIMS will be described with reference to FIG. In this figure, for convenience of explanation, the sample 6, the acceleration electrode 8, and the detector 4 are arranged on a straight line.
[0006]
Conventionally, a sample (for example, a semiconductor wafer) 6 is held at a ground potential, and the surface 6a is irradiated with primary ions 2 accelerated with appropriate energy (for example, several keV to 20 keV). The secondary ions 3 emitted from 1a are caused to fly in the direction of the detector 5 by applying a pulse voltage to an acceleration electrode (also referred to as a secondary ion extraction electrode) 8. In this figure, reference numeral 12 denotes a generation source of a pulse voltage to be applied to the acceleration electrode 8, 13 denotes a switch for switching on / off the power source, and 14 denotes a circuit for controlling the switch 7.
[0007]
By the way, as a primary ion 2 used in a conventional small-sized TOF-SIMS, an ion beam such as Ar (argon) or Xe (xenon) is used. As shown by reference numeral 2A in FIG. It is a bundle of state waves. The sample surface 6a is irradiated with the primary ions 2 in the wave packet state within an extremely short time such as 30 nsec (nanoseconds).
[0008]
In the TOF-SIMS, all of the bundles (wave packets) of the primary ions 2 in the Gaussian distribution state reach the sample surface 6a from the viewpoint of improving the mass resolution performance of an element having a mass number of 16 or more, for example. Once you have finished (indicated by symbol T _E in FIG. 4), with respect to the accelerating electrode 8, as shown at (a) in FIG. 4, by applying a predetermined pulse voltage, the sample 6 of the primary ion 2 The secondary ions 3 generated as a result of irradiation with respect to are accelerated.
[0009]
[Problems to be solved by the invention]
However, as described above, when a pulse voltage for accelerating the secondary ions 3 is applied to the accelerating electrode 8 at the time T _E when all of the primary ions 2 in one wave packet 2A reach the sample surface 6a, for example, Light elements (indicated by 3L in FIG. 6) such as H (hydrogen), He (helium), B (boron), and C (carbon) having a small mass number are applied when the pulse voltage is applied to the acceleration electrode 8. In FIG. 4, the light element has reached a position far away from the sample surface 6 a, so that a sufficient acceleration voltage is not applied and the acceleration is hardly performed. Therefore, in the conventional small TOF-SIMS, the light element is represented by a curve I in FIG. As shown by, almost no detection was possible. In FIG. 6, 3H indicates an element having a mass number larger than 16.
[0010]
The present invention has been made in consideration of the above-described matters, and an object thereof is to provide a small-sized TOF-SIMS capable of reliably measuring so-called light elements having a mass number of 16 or less, for example.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, accelerated primary ions are irradiated onto the sample surface, and the secondary ions released from the sample surface at this time are applied with a pulse voltage to the accelerating electrode, thereby detecting the detector direction. In a small time-of-flight secondary ion mass spectrometer that is allowed to fly, the pulse voltage is applied to the accelerating electrode at a time earlier than the completion of irradiation of the primary ions. ).
[0012]
In small TOF-SIMS above configuration, for example, if (3, indicated by reference numeral T _B) when the irradiation of the primary ions is started which is adapted in, applies a pulse voltage to the accelerating electrode, wherein Since a predetermined acceleration voltage is applied to light elements such as H, He, B, and C generated by the irradiation of primary ions, acceleration is ensured and detection efficiency is greatly improved.
[0013]
And in said small-sized TOF-SIMS, as described in claim 2, the timing of applying the pulse voltage to the accelerating electrode is a time point earlier than the completion of the primary ion irradiation and a time point when the primary ion irradiation is completed. When switching to, it becomes possible to detect elements and molecules over a wide range from light elements to heavy elements, and a small TOF-SIMS with a wide detection range can be obtained.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings. In the small-sized TOF-SIMS of the present invention, the basic apparatus configuration is the same as that shown in FIG. The small TOF-SIMS of the present invention is significantly different from the conventional one in that the pulse voltage is applied to the acceleration electrode 8 at a time earlier than the completion of the irradiation of the primary ions 2. FIG. 2 is a diagram for explaining the operation in such a manner. Also in this figure, the sample 6, the acceleration electrode 8, and the detector 4 are arranged on a straight line for convenience of explanation.
[0015]
For example, when the application of the pulse voltage is performed at the time T _B when the irradiation of the primary ions 2 is started, as indicated by reference numeral (b) in FIG. 4, as shown in FIG. A predetermined acceleration voltage is applied to ions 3L of light elements such as H, He, B, and C generated by the irradiation. Therefore, the light element ions are surely accelerated, and the detection efficiency is greatly increased.
[0016]
FIG. 2 shows the output of the detector 4 in the compact TOF-SIMS of the present invention, where the horizontal axis represents time and the vertical axis represents intensity. As can be seen from this figure, according to the small TOF-SIMS of the present invention, light elements such as B and C, which are difficult to detect in the conventional small TOF-SIMS, and CH, CH ₂ , CH Even molecules with a relatively low molecular weight such as ₃ can be detected with high sensitivity (reliable).
[0017]
Therefore, according to the present invention, as shown by reference numeral II in FIG. 5, even when the mass number is 16 or less, 100% detection efficiency can be maintained.
[0018]
In the embodiment described above, the application of the pulse voltage for accelerating electrode 8, but be performed when T _B where irradiation of the primary ion 2 is started, the invention is not limited thereto, What is necessary is to carry out at least before the irradiation of the primary ions 2 is completed. For example, it may be performed at a time substantially at the center of the wave packet 2A, which is indicated by a symbol T _M in FIG. The point of application of the pulse voltage, the closer to the primary ion irradiation start time T _B, the acceleration efficiency is improved for the smaller mass of the element (or molecules), closer to the primary ion irradiation end point T _E, more The acceleration efficiency of small mass elements etc. is reduced. Therefore, the application timing of the pulse voltage to the acceleration electrode 8 may be set according to the type of light element or molecule to be detected.
[0019]
When the timing of applying the pulse voltage to the accelerating electrode 8 is switched between a time point earlier than the completion of the irradiation of the primary ions 2 and a time point when the irradiation of the primary ions 2 is completed, Elements and molecules can be detected over a wide range up to heavy elements, and a small TOF-SIMS with a wide detection range can be obtained.
[0020]
【The invention's effect】
As described above, in the small TOF-SIMS of the present invention, it is possible to measure light elements or low molecular weight molecules, which is impossible in the conventional small TOF-SIMS of this type. It is possible to detect metal elements such as boron and carbon and hydrocarbons that play an important role in organic substance evaluation. Therefore, by using the small TOF-SIMS of the present invention, more accurate quantitative analysis becomes possible.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing a configuration of a main part of a small time-of-flight secondary ion mass spectrometer according to the present invention.
FIG. 2 is a diagram for explaining the operation of the apparatus.
FIG. 3 is a diagram illustrating an example of a detection output of the device.
FIGS. 4A and 4B are explanatory diagrams showing the relationship between the wave packet and the timing of voltage application, where FIG. 4A shows a conventional example, and FIG. 4B shows the present invention.
FIG. 5 is a diagram for explaining detection efficiency.
FIG. 6 is a diagram for explaining the operation of a conventional apparatus.
[Explanation of symbols]
2 ... primary ion, 3 ... secondary ion, 4 ... detector, 6 ... sample, 6a ... sample surface, 8 ... acceleration electrode, _TE ... primary ion irradiation completion point.

Claims (2)

A small time-of-flight type two-beam type in which the accelerated primary ions are irradiated onto the sample surface, and the secondary ions emitted from the sample surface at this time are caused to fly in the direction of the detector by applying a pulse voltage to the acceleration electrode. In the secondary ion mass spectrometer, the pulse voltage is applied to the accelerating electrode at a time earlier than the completion of the primary ion irradiation. 2. The small time-of-flight type according to claim 1, wherein the application timing of the pulse voltage to the accelerating electrode is switched between a time point earlier than completion of primary ion irradiation and a time point when primary ion irradiation is completed. Secondary ion mass spectrometer.

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