JPH09257670A - Sample preparation equipment for electron microscope - Google Patents

Abstract

(57) Abstract: An electron microscope sample preparation apparatus using FIB is provided, which can efficiently reduce the amorphous layer that can be processed by FIB. An ion milling mechanism is provided in a sample chamber of an FIB apparatus, and after an electron microscope sample is prepared by the FIB, the ion milling mechanism is irradiated with ions having an acceleration voltage lower than that of the FIB to form an amorphous layer. remove. Further, a shutter is provided between the ion milling mechanism section and the sample to control so that stable ion milling can be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for preparing a sample for an electron microscope using a focused ion beam.

[0002]

2. Description of the Related Art When observing a cross section of a semiconductor device or the like using a transmission electron microscope (hereinafter abbreviated as TEM), a focused ion beam (hereinafter abbreviated as FIB) processing apparatus is used to form a thin film at a desired position. It can be made reliably in a short time. For details of this method, for example, “If you prepare a sample for TEM with a focused ion beam” (Surface Science: Vol. 1
6, No. 12, pp.755-760, 1995) and "Tra
nsmission Electron Microscope Sample Prepara
tion Using a Focused Ion Beam ”(J ElectronMicrosc
43, pp.322-326, 1994).

When processing a cross-section observation sample for TEM with the FIB, first, as shown in FIG. 2, a sample 5 having a portion including a desired position 7 of about 40 μm left is prepared, and thinning processing is performed using the FIB. To do. The ion species used for FIB is G
There are many a, and the energy is about 30 keV to 50 keV. Here, in order to perform observation using a TEM, the width of the thin film 8 including a desired position needs to be 100 nm or less. However, when FIB processing is performed, an amorphous layer 9 having a thickness of a dozen nm or more is formed near the processing position by ion beam irradiation, and the proportion of the amorphous layer becomes large in a thin film having a thickness of 100 nm or less which is suitable for TEM observation. It becomes difficult to observe the lattice image. In order to remove this amorphous layer, there is a method in which an ion milling device other than the FIB device is used to irradiate the sample with Ar ions 3 of several keV and the like, and the sample surface is milled for about a dozen nm.

[0004]

In general, an ion milling apparatus is used which discharges Ar gas to ionize it and irradiates a sample. Conventionally, the ion milling device and the FIB processing device are separate devices, and the sample mounting method of each device is different, so that the sample replacement work is complicated. Further, the milling rate of the ion milling device is about 10 to 100 nm / min, and the thin film sample itself is deleted after irradiation for several minutes. Therefore, a thin film of 100 nm or less with a small amorphous layer is produced while preventing loss of the sample. To do this, it is necessary to control the irradiation time with high accuracy. However, there is a problem that the discharge current is not stable for several minutes after the start of discharge, and it is difficult to control the ion irradiation time.

[0005]

SUMMARY OF THE INVENTION The above-mentioned problem is that the same sample chamber as the FIB device is equipped with an ion milling device and the sample holder is shaped so that it can be used in a TEM device. The problem can be solved by providing a shutter composed of electrodes, deflection coils, a shielding plate, etc., and opening / closing the shutter according to the discharge time.

[0006]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a usage pattern of the present invention. The Ga ion beam 100 extracted from the liquid metal ion source 101 is accelerated to, for example, 30 kV,
Focusing lens 102, beam limiting diaphragm 103, aligner
Stigma electrode 104, deflection electrode 105, objective lens 1
The sample 5 is focused and deflected by an ion optical system such as 06 to scan an arbitrary position of the sample 5. By changing the hole diameter of the beam limiting diaphragm 103, switching from a large current beam having a beam current of a few dozen nA to a beam having a beam current of about 1 pA and a fine diameter beam having a beam diameter of several nanometers for processing and observing a sample. You can The sample 5 is fixed to the sample holder 12 and mounted in the sample chamber 6. Since the sample holder 12 can be attached to the electron microscope as it is, it is not necessary to replace the sample 5 with the sample holder for the electron microscope when observing with the electron microscope, and the process from sample preparation to observation can be simplified.
When processing the TEM sample in cross section, FIB processing is performed until the thickness of the thin film 8 including a desired position becomes about 100 nm as shown in FIG. At this time, an amorphous layer 9 having a thickness of 30 nm to 15 nm is formed on the sample by FIB irradiation, which is an obstacle to the observation of the lattice image by TEM. Ir ions 3 are irradiated to remove this. Ar gas introduced from the gas cylinder 10 is a flow rate controller 11
The flow rate is controlled by and the gas is introduced into the ion gun 1. Here, when Ar gas is introduced into the FIB column, F
Since the ion pump 107 that evacuates the IB column is adversely affected, the valve 108 is closed during gas introduction. An arbitrary high voltage between 1 kV and 6 kV is applied to the ion gun 1 from the control unit 4. This high voltage causes the Ar gas to be ionized by the discharge and irradiate the sample 5. Since the discharge current is not stable for several minutes after the start of discharge, the milling mechanism control unit 4 sets the shutter closed state 2'to Ar.
Prevent the ions 3 from hitting the sample 5. The discharge current value is fed back to the control unit 4, and when the discharge current stabilizes, the control unit 4 puts the shutter in the open state 2, starts measuring the discharge time, and ends the discharge after a lapse of a predetermined time.

[0008]

By using the apparatus of the present invention, the operator can easily control the time of ion milling. In the case of TEM sample preparation, it became possible to form a thin film having a low proportion of an amorphous layer, and it became easy to observe a lattice image even when using a TEM having a relatively low acceleration voltage. In addition, the loss of the sample due to excessive shaving can be prevented, which increases the certainty of the cross-sectional TEM sample preparation.

Further, even when a sample of a scanning electron microscope (hereinafter abbreviated as SEM) is produced by the apparatus of the present invention, a cross-section sample with a small number of amorphous layers can be provided, so that observation with higher resolution can be performed. Has the effect of enabling.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of an apparatus to which the present invention is applied.

FIG. 2 is an explanatory view showing a processing procedure for explaining the present invention.

[Explanation of symbols]

1 ... Ion gun, 2 ... Shutter (open), 2 '... Shutter (closed), 3 ... Ar ion, 3' ... Deflected Ar ion, 4 ... Ion milling device controller, 5 ... Sample, 6 ... Sample chamber, 7 ... Desired cross-section position, 8 ... Thin film including desired cross-section position, 9 ... Amorphous layer, 10 ... Ar gas cylinder, 11
... Gas flow rate controller, 12 ... Sample holder, 100 ... Ga ion beam, 101 ... Liquid metal ion source, 102 ... Focusing lens, 103 ... Beam limiting diaphragm, 104 ... Aligner / stigma electrode, 105 ... Deflection electrode (FIB optical system) ), 106
... objective lens, 107 ... ion pump, 108 ... valve.

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display area H01L 21/302 D

Claims (6)

[Claims] 1. A sample preparation device for an electron microscope having a function of observing the shape of a sample surface by scanning a focused ion beam and performing a sputtering process on the sample, wherein the sample is irradiated with ions having an energy lower than that of the focused ion beam. A sample preparation device for an electron microscope, which is provided with an ion milling mechanism capable of performing the above. 2. The sample preparation device for an electron microscope according to claim 1, wherein a shutter made of at least one of an electric field, a magnetic field and other physical barriers is provided between the ion milling mechanism section and the sample. 3. A sample preparation device for an electron microscope according to claim 1, wherein the sample holder used in the electron microscope can be mounted. 4. An electron microscope according to claim 1, wherein a valve is provided between the focused ion beam lens barrel and the sample chamber, and the valve is closed when the ion milling mechanism is operated. Sample preparation device. 5. The sample preparation device for an electron microscope according to claim 1, 2, 3 or 4, wherein the ion species of the focused ion beam is Ga. 6. The method of claim 1, 2, 3, 4, or 5,
An electron microscope sample preparation device in which the ion species of the ion milling mechanism is Ar.