JPH01128341A - Mass analyzer - Google Patents

Abstract

PURPOSE:To make fine optical axis alignment for ion beams very easy by performing the optical axis alignment as monitoring a beam quantity by each electrode piece of a beam monitor electrode and ammeters installed in a sample and a Faraday cup. CONSTITUTION:When ion beams are irradiated each of electrode pieces 41-44 of a beam monitor electrode 40, an electric current in proportion to the irradiation value is generated there, flowing into each of ammeters 111-114. Accordingly, an optical system is mechanically electrically adjusted as monitoring these ammeters and optical axis alignment for a focusing lens is carried out. Next, since Faraday cup 100 is installed on the extension of each optical axis of the focusing lens 20 and the monitor electrode 40, it adjusts a focal distance of the lens 20 so as to cause the ion beam to be maximized as monitoring an ammeter 116 of the cup 100 in that state that voltage is not impressed on a neutron eliminating deflecting electrode 52. Furthermore in this state, voltage is impressed on the electrode 52, and this voltage is adjusted as monitoring a beam quantity by the ammeter 115 installed in a sample 90, and an optical axis for these ion beams is accorded with that of an objective lens 80.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a mass spectrometer used for mass spectrometry of a solid sample using an ion beam.

(Prior Art) Conventional devices of this type emit a primary ion beam such as Ar ions using an ion gun, and convert this primary ion beam into a primary ion beam optical system consisting of a focusing lens, a beam limiting aperture, etc. A secondary ion quality analyzer is common, which irradiates a sample through a system, detects secondary ions generated from the sample, and performs mass analysis.

(Problems to be Solved by the Invention) In the conventional apparatus described above, it is necessary to efficiently irradiate the sample with the primary ion beam, and for this purpose, the optical axis of the focusing lens and the optical axis of the beam limiting aperture must be aligned. Therefore, it is desirable that the optical axis of the ion beam after passing through the neutral particle removal deflection electrode be aligned with the optical axis of the objective lens to form a fine beam diameter on the irradiated sample surface. However, due to dimensional tolerances in structural design, assembly tolerances, etc., the above-mentioned deviation of the optical axis cannot be avoided.

Conventionally, the optical axis was aligned based on the amount of ion beam reaching the sample, but if the ion beam optical system includes an electrode to deflect the beam, alignment for alignment becomes extremely difficult. It requires skill and a lot of effort and time. Also, once the optical axis shifts during measurement,
Readjusting requires breaking the ultra-high vacuum of the device, making it an extremely difficult task. As a result, they were often forced to continue working in an unstable state.

Taking these points into consideration, a method has been proposed for aligning the optical axes of the focusing lens and the beam limiting aperture by adjusting the current flowing into the shield plate of the beam deflection electrode. It was difficult to align the optical axis of the deflection tangent.

This invention has been made to solve the above-mentioned problems of conventional devices, and allows for easy and quick adjustment.
Next, the ion beam is efficiently irradiated onto the sample to enable highly accurate interrogation analysis. The purpose is to provide a question analysis device.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, the present invention provides a primary ion beam emitted from an ion gun with a focusing lens, a beam limiting aperture, and a neutral particle removal device. In a mass spectrometer that performs mass analysis of the sample by irradiating the sample with a primary ion beam through a primary ion beam optical system consisting of a deflection electrode and an objective lens and detecting a secondary ion beam generated from the sample, the above-mentioned focusing lens and the above-mentioned A disk-shaped beam monitor electrode is provided between the beam limiting averter layer and has an aperture in the center for passing the ion beam, and is composed of a plurality of equally divided electrode pieces each connected to an ammeter; A Faraday cup is provided on an extension of the optical axis of the lens and the beam monitor electrode and is connected to an ammeter, and an ammeter is connected to the sample. The gist is that the optical axis of the system is mechanically and electrically aligned.

(Operation) Since the beam monitor electrode is composed of multiple electrode pieces that are each connected to an ammeter and divided into equal parts, the deviation of the optical axis of the focusing lens is shown as a difference in the indicated value of each ammeter. .Thus, while monitoring the ammeter,
By adjusting the optical system mechanically or electrically,
The optical axis of the focusing lens is aligned, that is, the optical axis of the focusing lens and the optical axis of the beam monitor electrode are aligned. Furthermore, since the Faraday cup is installed on the extension of the optical axis of the focusing lens and the beam monitor electrode, the current meter of the Faraday cup can be monitored while no voltage is applied to the deflection electrode for neutral particle removal. Adjust the focal length of the focusing lens to maximize the ion beam that reaches it. In this state, a voltage is applied to the neutral particle removal deflection electrode to deflect the ion beam toward the sample, and while the beam end is monitored by an ammeter installed on the sample, the voltage of the deflection electrode is adjusted to ionize the ion beam. Align the optical axis of the beam with the optical axis of the objective lens. This makes it possible to precisely align the axis of the primary ion beam without breaking the vacuum of the apparatus, and to perform highly accurate mass spectrometry.

(Embodiment) FIG. 1 is a block diagram of a primary ion optical system according to an embodiment of the present invention.

In the drawing, reference numeral 10 denotes an ion gun that emits a primary ion beam such as Ar ions, and is composed of a filament (cathode) 11, an intermediate electrode 12, an anode 13, and an extraction electrode 14 that determines the extraction direction of the ion beam. There is. 20 is a focusing lens for focusing the ion beam emitted from the ion gun 10, 30 is a deflection mechanism for deflecting the ion beam focused by the lens 20, and includes a pair of X-direction deflection electrodes 31a and 31b. It consists of a pair of Y direction deflection electrodes 32a and 32b. Reference numeral 40 denotes a beam monitor electrode, which has four fan-shaped electrode pieces 4 divided into equal parts.
1,42,43,44, and has an aperture 45 in the center that is large enough for the ion beam to pass through. Although not shown, the anode electrode 13 and extraction electrode 14 of the ion gun 10 are provided with directional screws for mechanical axis alignment, and the direction of adjustment of the ion beam by these screws is , the direction in which the optical axis is moved so that the beam passing through the aperture 45 of the beam monitor electrode 40 passes through the center of the aperture 45.

In addition, as shown in FIG. 2(a), the beam monitor electrode 40
Each electrode piece 41, 42, 43, 44 has an ammeter 111
．． 112, 113, and 114 are connected, and when each electrode piece 41, 42, 43, 44 is irradiated with an ion beam, the amount of current generated in proportion to the ion beam irradiation m is detected.

Reference numeral 50 denotes a beam limiting aperture, in which an opening 51 is formed to guide the ion beam to the sample 90. Note that between the beam monitor electrode 40 and this beam limiting aperture 1750 there is a pair of beam deflection electrodes Ifi 52 for deflecting the ion beam that has passed through the aperture 45 and guiding it to the aperture 51 of the aperture 50; A shield plate 53 is provided to shield the electric field of the electrode 52.

60 is a drawing of an ion beam scanning machine, which includes a pair of X-direction scanning electrodes 61a and 61b, another pair of X-direction scanning electrodes 71a and 71b, and a further pair of Y-direction scanning electrodes 62a.
, 62b and another pair of Y-direction scanning electrodes 72a, 72
b are provided in a double arrangement as shown in the figure. Reference numeral 80 denotes an objective lens, which in this embodiment consists of three electrode pieces 81, 82, and 83. Each electrode piece 8L8
2.83 has openings 81a, 82a, 83a for guiding the ion beam to the sample 90, and openings 81b, 82b, 83b for passing the ion beam not deflected by the deflection electrode 52. There is.

100 is the aperture 81b, 82b of the objective lens 80,
This is an electrode called a Faraday cup provided on the extension of 83b, and is used to convert the irradiation amount of the ion beam into a current amount for detection. In addition, Fig. 2(b) and (
As shown in C), sample 90 and Faraday cup 100
Ammeters 115 and 116 are connected to these, and the amount of ion beam incident on each is converted into a current m and detected.

Note that the optical axis of the beam scanning mechanism 60 and the optical axes of the apertures 81a, 82a, and 83a in the objective lens 80 coincide with the optical axis of the ion beam deflected by the deflection electrode 52.

Next, the operation of the above embodiment will be explained. First, when a primary ion beam is emitted from the ion gun 10, this ion beam is focused by the focusing lens 20, and the deflection mechanism 3
0, the respective apertures 45.5 of the beam monitoring electrode 40 and the beam limiting aperture 50
1 and reaches the sample 90. At this time, the ion beam is deflected by the deflection electrode 52 to remove neutral particles contained in the beam. When the sample 90 is irradiated with the ion beam, the sample 90 generates secondary ions, and these secondary ions are detected and subjected to mass spectrometry. Note that means for mass spectrometry including a secondary ion beam detection mechanism is not shown.

Here, in order to efficiently irradiate the sample 90 with the ion beam, adjustment of the ion beam optical system, that is, adjustment of the optical axis of the focusing lens 20 and adjustment of the focal position, and roughly adjustment of the optical axis of the beam limiting aperture t750. is necessary.

In this embodiment, first, the amount of ion beam incident on each electrode piece of the beam monitor electrode 40 is monitored to detect a shift in the optical axis of the ion beam, and alignment is performed. That is, when each electrode piece 41 to 44 of the beam monitor electrode 40 is irradiated with an ion beam, each mm piece 41 to 44 is irradiated in proportion to this irradiation M.
A current is generated, and its value is detected by each ammeter 111-114. Now, assuming that the indicated value of the ammeter 111 is the maximum, and the following indicated values are larger in the order of ammeter 114, 112, and 113 (114>112>113), the light of the ion beam that has passed through the focusing lens 20 The shaft is electrode piece 4
It can be seen that it is shifted to the 1 side. Therefore, each ammeter 11
While monitoring the indicated values 1 to 114, the optical axis is mechanically adjusted by shifting the optical axis in the direction of the electrode piece 43 using adjustment screws provided on the anode 13 and the extractor 1 (i14).This procedure By repeating this, the indicated values of each ammeter are made equal, and the optical axis is aligned with the center of the aperture 45.Next, the focusing lens 20 is electrically activated,
Change the focal length of the lens. At this time, if the amount of current flowing into each of the electrode pieces 41 to 44 is equal regardless of the change in focal length, the ion beam is aligned with the optical axis of the beam monitor electrode 40. On the other hand, if the amount of current differs between each electrode piece, the ion beam and the optical axis of the beam monitor electrode 40 are not parallel, so the deflection mechanism 30 is operated to adjust them so that they are parallel.

Next, the focal position of the focusing lens 20 is determined.

When no potential is applied to the neutral particle removal deflection electrode 52,
The ion beam that has passed through the aperture 50 heads toward the Faraday cup 100, but when the ion beam is located on the adjusted optical axis, the illumination f toward the Faraday cup 100 is
iffl increases. Therefore, Faraday Cup 100
Readjust the focusing lens 20 and deflection mechanism 30 so that the current value becomes the maximum using the ammeter 116 provided in the
The focal position of the focusing lens 20 is adjusted.

Next, a potential is applied to the neutral particle removal deflection electrode 52 to align the ion beam with the optical axis of the objective lens 80. First, with no potential applied to the objective lens 80, the potential applied to the neutral particle removal deflection electrode 52 is gradually increased to change the amount of beam current reaching the sample 90. At this time,
Sample 901. : The provided ammeter 115 has a peak at a certain deflection voltage value of the electrode 52. In this deflection voltage state, each electrode 61a, 61b, 62a, 6 of the scanning mechanism 60
2b.

Bias voltage L is applied to 71a, 71b, 72a, and 72b.
f is given so that the amount of beam current reaching the sample 90 is maximized. Thereby, the optical axis after deflection by the electrode 52, that is, the optical axis of the beam limiting aperture 50, coincides with the optical axis of the objective lens 8O. Note that after this, the objective lens 8
A voltage for focusing the ion beam is applied to the scanning mechanism 60, and a scanning potential for controlling the scanning width is applied to the scanning mechanism 60 in addition to the bias voltage determined in step 1 to prepare for mass spectrometry.

As explained above, in this embodiment, the focusing lens 20
fine optical axis adjustment and focal position adjustment, and further optical axis adjustment of the beam limiting aperture 1750.
0 each electrode piece, sample 90 and Faraday cup 100
While monitoring the beam current amount with an ammeter installed in the ion gun 10 and the focusing lens 2,
0, by neutral particle removal electrode, beam scanning mechanism, etc.
It can be implemented mechanically or electrically. Moreover, the procedure and scanning are extremely easy.

[Effects of the Invention] As explained above with reference to the embodiments, according to the present invention, fine optical axis alignment of an ion beam can be carried out extremely easily without breaking the vacuum property of the apparatus, and therefore a high Accurate mass spectrometry can be performed.

[Brief explanation of the drawing]

FIG. 1 shows a mass spectrometer according to an embodiment of the present invention.
A block diagram of the next ion optical system, and FIG. 2 is an explanatory diagram of the main parts of the apparatus shown in FIG. 1. 10... Ion gun 20... Focusing lens 40...
・Beam monitor electrode 41.42.43.44...I pole piece 45...Aperture 50...Beam limiting aperture 52...Deflection electrode for neutral particle removal 80...Objective lens 90... Sample 100...Faraday cup 111.112.113.114.115.116...
・Ammeter agent Patent attorney Nori Chika Ken Shu
Kenji Maru 17 (b) 〒〜100 ＼−116 (C) Figure 2

Claims (2)

[Claims] (1) The primary ion beam emitted from the ion gun is irradiated onto the sample through a primary ion beam optical system consisting of a focusing lens, a beam limiting aperture, a deflection electrode for removing neutral particles, and an objective lens, and generated from the sample. A mass spectrometer that performs mass analysis of the sample by detecting a secondary ion beam, which is provided between the focusing lens and the beam limiting aperture, has an aperture in the center for passing the ion beam, and each has an aperture for passing the ion beam. a disk-shaped beam monitor electrode consisting of a plurality of equally divided electrode pieces connected to the meter; and a Faraday cup provided on an extension of the optical axis of the focusing lens and beam monitor electrode and connected to the ammeter. , and an ammeter connected to the sample, and the mechanical and electrical optical axis alignment of the optical system is performed while monitoring the beam current with each of the ammeters. Device. (2) The primary ion beam optical system has a beam scanning mechanism for scanning and irradiating the sample, and this beam scanning mechanism is provided with bias voltage application means for adjusting the ion beam optical axis. A mass spectrometer according to claim 1, characterized in that: