JPS62108442A - Electrostatic lens - Google Patents

Abstract

PURPOSE:To enable the precise and quick adjustment of the diameter of a beam, which includes focusing, by applying the potential of the ground to both end electrodes, applying a potential near the potential of the ground to one of electrodes next to both the end electrodes, and applying a prescribed potential to the other electrode. CONSTITUTION:An electrostatic lens 5a for converging emitted ions from the emitter 1 of an ion source onto a sample 7 comprises four electrodes 6, 6', 6'', 6''' having circular holes coaxial with each other. The potential of the ground is applied to the first and the fourth electrodes 6, 6''', which are numbered from the side of the emitter 1. An optimal potential is applied from a lens power supply 9 to the electrode 6'' to perform rough adjustment for focusing. A potential DELTAVL is applied from an auxiliary lens power supply 14 to the electrode 6'. Secondary electrons 11 emitted from the sample 7 are detected at 12 correspondingly to a beam scanning signal to measure the diameter of a beam by a beam control section 15. The potential DELTAVL is set by a control signal supplied from the control section 15 and corresponding to the diameter of the beam, to equalize the diameter to the minimum or a prescribed value.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention is suitable for performing dynamic focus correction when scanning a beam on a sample in a focused ion beam device used for implantation or exposure using a focused ion beam. Regarding electrostatic lenses.

[Background of the invention]

Conventional electrostatic lenses are used by being incorporated into focused ion beam devices and the like. An outline of a focused ion beam device is shown in FIG. 1, and a conventional electrostatic lens will be explained. For example, 10K is applied between the emitter 1 of the ion source and the extraction electrode 2.
A voltage of approximately V is applied by an extraction power source 3, and the ions extracted from the emitter 1 are accelerated by an acceleration power source 4 to, for example, approximately 100 KV. Ion is an electrostatic lens 5
is focused onto the sample 7 by The focused beam is scanned by a deflection electrode 8. The electrostatic lens 5.

It is composed of two or more electrodes, but here we use three
An Einzel lens consisting of a single electrode is used. In this electrostatic lens 5, both end electrodes 6 and 6' are at ground potential, and a high voltage of about 80 KV is applied from a lens power source 9 to the center electrode 6'. Secondary electrons 11 are emitted from the sample 7 by ion beam irradiation, and a secondary electron detector 12 is detected.
Detected by secondary electron image NI! The measuring section 13 observes information regarding the sample surface and monitors the beam diameter. In the ion microbeam device, the beam diameter is reduced. That is, it is often used by deflecting the beam to a predetermined location on the sample 7 with the deflection electrode 8 and focusing it accurately with the lens 5. To this end, prior to operations such as ion implantation and exposure, the lens voltage VL must be scanned between about 100 V before and after the optimum lens voltage, and the minimum value of the beam diameter must be searched for in advance while monitoring the beam diameter. However, with this conventional electrostatic lens, 100K
In order to scan a range of only about ±100 V with an accuracy of 0.5 V or less using a lens source 9 with a high voltage of about V, it takes about 1.0 seconds or more because the time constant is large. There was a drawback in terms of shortening the focusing time.

Strictly speaking, the distances between the beam irradiation point and the center of the lens 5 are slightly different between the center of beam deflection on the sample 7 and its periphery. Therefore, the beam diameter is set to 0.1
When carrying out work such as ion implantation or exposure with extremely focused light on the order of μm, it is necessary to correct the focus of the lens 5 as a function of the deflection position 6, that is, dynamic focus correction. In this conventional electrostatic lens, a time constant of several IQmsec is required to change the range of about ±100V with an accuracy of ±2Vv1 degree using the lens power supply 9 with a high voltage of about 100KV, and it is necessary to use a time constant of several IQ msec to change the range of about ±100V with an accuracy of ±2Vv1 degree. However, there was a problem with responsiveness.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrostatic lens that has excellent focusing capabilities and can accurately and quickly adjust the beam diameter.

[Summary of the invention]

In order to also achieve the above object, in the present invention.

In a lens consisting of electrodes with n (where n is an integer greater than or equal to 4) circular holes arranged coaxially, the first and nth electrodes at both ends, counting sequentially from one side of the beam axis, are ground,
The potential of either the second or (n-1,)th electrode is closer to the ground potential than the potential of the other remaining electrodes, and the potential is applied from a control power source that can be varied at high speed;
The other remaining electrodes are characterized in that they are connected to a high voltage power source so that a predetermined potential is applied to them.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. FIG. 2 is a schematic diagram of a focused ion beam device, showing an electrostatic lens 5a according to an embodiment of the present invention. Ions emitted from the emitter 1 of the ion source are focused onto the sample 7 by an electrostatic lens 5a.

The lens 5a is composed of four electrodes 6.6', 6', 6"', which are coaxial and have circular holes. These four electrodes are arranged as 6.6', 6", 6"'. Counting from the ion source side, the first and fourth electrodes, 6°6'', are at ground potential. A potential close to the optimum potential is applied to the 311i pole 6'' from the lens power supply 9, and coarse adjustment is made for focusing.A potential ΔV is applied to the second electrode from the auxiliary lens power supply 14.
+, is given. The beam diameter is measured by the beam controller 15 by detecting the secondary electrons 11 emitted from the sample 7 with the detector 12 and making them correspond to the beam scanning signal. The output voltage ΔVL of the auxiliary lens power supply 14 is set so that the beam diameter becomes the minimum or a predetermined value for a predetermined beam deflection position by a control signal according to the beam diameter from the beam control section 15. Ion implantation.

Prior to operations such as fogging, all beam deflection positions within the beam scanning range on the sample 7 are measured in advance.

The beam controller 15 determines the set value of Δv1 and writes it into the memory.

During actual writing, the control signal of ΔVL is read out from the memory in the beam control unit 15 in response to the scanning signal from the deflection power source 10, and this control signal is sent to the auxiliary lens power source 14 to irradiate the beam. Blanking electrodes are required to deflect the beam from the beam axis in order to turn the beam on and off, but this is not shown in FIG.

In this example, a Ga liquid metal ion source was used and 100K
For focusing of the Ga+ beam accelerated by V, the potential of the 3fi-th lens electrode 6' of the electrostatic lens 5a is 81
KV was roughly adjusted, and then the potential Δv of the second lens electrode 6' was applied from the auxiliary lens power source 14, and the optimum value of Δv, 540 V, which gave the minimum beam diameter at the center of deflection was obtained. The minimum beam diameter at this time was 0.5 μm, and the beam current was about 0.4 nA. Maximum voltage I to auxiliary lens power supply 14
To adjust with an accuracy of ±2v using a KV power supply, use the following formula:
Qmsec, which enables high-speed beam diameter adjustment, that is, dynamic focus correction.

Next, another embodiment of the present invention will be described with reference to FIG. 3(a) is a side view of the schematic structure of the electrostatic lens of the present invention, and corresponds to the electrostatic lens 5a of FIG. 2. FIG. 3(b) is a front view of the schematic configuration of the second electrode 6' of FIG. 3(a). The electrode 6' is composed of a plate-like electrode with a circular hole divided into eight equal parts, and each of the electrodes 1 to 2 has the potential written in FIG. 3(b) to the auxiliary lens power source 14'. (not shown)
given from. Here, Va=Vs-cos(2θ+), Vb=Vs-cos
(2θ-1), Vs is variable DC from 0 to 2oOv, θ is O
It is a variable amount of ~27c. Further, ΔVo is a variable DC of 0 to IKV as in the case of FIG. This electrostatic lens in Fig. 3 is used as the electrostatic lens 5 of the focused ion beam device in Fig. 2.
By incorporating it into a, it became possible to perform not only dynamic focus correction but also astigmatism correction. Here, astigmatism correction refers to the correction of beam spread due to asymmetric components with respect to the beam axis due to deviations from the beam axis in the fabrication of lens electrodes, etc., deviations from axial symmetry of the circular hole shape of the lens electrodes, etc. It is.

Furthermore, the electrostatic lens of the present invention has the advantage that the characteristics of the electrostatic lens are not affected by the electric field distribution around the lens because both ends of its constituent electrodes are necessarily at ground potential.

〔Effect of the invention〕

According to the present invention, the diameter adjustment of the bead 11 including focusing can be performed accurately and quickly, and by incorporating it into a focused ion beam device, etc., it has become possible to perform ion implantation, exposure, etc. with high efficiency.

[Brief explanation of drawings]

FIG. 1 is a basic configuration diagram of a focused ion beam device using a conventional electrostatic lens, and FIG. 2 is a basic configuration diagram of a focused ion beam device using an electrostatic lens showing an embodiment of the present invention. FIG. 3 shows another embodiment of the electrostatic lens of the present invention. 1... Emitter, 2... Extracting electrode, 3... Extracting power source, 4... Accelerating power source, 5a... Electrostatic lens, 6.
6', 6'. 6″'... Lens electrode, 7... Sample, 8... Deflection electrode, 9... Lens power supply, 10... Deflection power supply, 11
...Secondary electron, 12...Secondary electron detector, 13...
・Secondary electron image viewing side part, 14...Auxiliary lens power supply, 15
... Beam control unit, 16... Vacuum vessel. Jth part

Claims (1)

[Claims] 1. In an electrostatic lens consisting of an electrode having n coaxially arranged circular holes (where n is an integer of 4 or more), counting sequentially from one side of the beam axis, the first and the nth electrode is grounded,
The potential of either the second or (n-1)th electrode is closer to the ground potential than the potential of the other remaining electrodes, and the potential is applied from a control device that can vary rapidly. An electrostatic lens characterized in that the electrodes are connected to a high voltage power source so that a predetermined high potential is applied. 2. Either the second or (n-1)th electrode is divided into eight equal parts around the beam axis, and each electrode is connected to a control power source that applies a potential independently. An electrostatic lens according to claim 1.