JP2000230891A - Method for preparing sample for transmission type electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preparing a samaple for microscopic observation using a transmission type electron microscope facilitating the observation of a planar microstructure with a specific depth in a semiconductor device. SOLUTION: A sample 2 is cut from a semiconductor chip to be made thin by mechanical polishing and the thin sample is attached to a single-ported mesh 6 for transmission type electron microscope observation and a Pt film 7 is formed to the part with specific depth of an end surface and irradiated with gallium ion beam 8 parallel to the main surface of the sample to make the part other than a principal part thin by etching. After etching by gallium ion beam, when the sample is irradiated with argon ions at a low angle, the damaged layer at a time of etching is removed to enable observation of higher resolving power.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preparing a sample for observing a planar microstructure at a specific depth of a sample having a thickness such as a semiconductor device by a transmission electron microscope.

[0002]

2. Description of the Related Art Semiconductor devices are usually formed in and on a substrate such as silicon through a number of processes. Among these processes, for example, crystal defects caused by the ion implantation process greatly affect the characteristics of semiconductor devices. Therefore, it is important to examine the presence and distribution of defects, and planar observation with a transmission electron microscope is indispensable. is there.

In order to observe a sample with a transmission electron microscope, it is necessary to make the sample thin so that an electron beam can pass through the sample. In the case of a transmission electron microscope with an acceleration voltage of several hundred thousand V class, the thickness through which electrons can be transmitted and clearly observed is about 100 nm.

[0004] As a sample preparation method therefor, an ion milling method is generally used. The ion milling method is a method of thinning a solid material using the sputtering effect of ionized ions such as an inert gas.A small amount of inert gas introduced from the anode is ionized between the anode and the cathode and accelerated. It is emitted from the hole cathode as an ion beam, and is irradiated with a sample under vacuum to form a thin film. Argon (hereinafter referred to as Ar) is used as the inert gas, and the general milling conditions are as follows:
kV, ion current 50 to 200 μA, irradiation angle 2 to 15 °.

FIG. 2 is an explanatory view showing a method of manufacturing a sample for a transmission electron microscope using an ion milling method. Punching: A sample 2 to be observed is punched out of a semiconductor device chip 1 into a predetermined size (for example, a 3 mm diameter disc) using an ultrasonic disc cutter.

Backside polishing: The backside of the sample 2 has a thickness of about 10
Roughly polished flat to 0 μm and 30
Polished in a dimple shape until the particle size becomes equal to or less than μm.
Finish the mirror surface with 1 μm abrasive. Reinforcement ring attached: Reinforcement ring 3 made of epoxy resin (for example, made of stainless steel) to reinforce sample 2
Glue. The dimensions of the ring 3 are, for example, an outer diameter of 3 mm and an inner diameter of 2
mm.

[0007] Ion milling: While rotating the sample 2, an Ar ion beam 4 is irradiated at a low angle (irradiation angle 2 to 15 °) from the back side of the sample, and thinned until a minute hole 5 is opened in the center. . As a result, the area around the hole is sufficiently thinned,
This is an observation area with a transmission electron microscope.

[0008]

The above-described ion milling method is the most common method for thinning a sample for observing the planar structure of the surface of various semiconductor devices with a transmission electron microscope.

However, 0.1 to several 1
It has been extremely difficult to make the internal structure down to 0 μm thin so that a planar structure at a specific depth can be observed. An object of the present invention is to provide a method for manufacturing a sample for a transmission electron microscope, which facilitates observation of a planar microstructure having a specific depth in a semiconductor device.

[0010]

In order to solve the above-mentioned problems, a method for preparing a sample for a transmission electron microscope according to the present invention is directed to a method for forming a sample on a specific portion of one end face of a plate-like sample, for example, a portion other than a portion having a specific depth. Then, a thin film sample of a specific portion of the plate sample is manufactured by irradiating a parallel ion beam to the main surface of the plate sample and etching.

In this case, a thinned sample capable of observing a plane at a specific depth, which has been extremely difficult in the past, can be obtained. Gallium (Ga) focused for etching
An ion beam can be used.

Further, if etching is performed through a step in which the ion beam current is gradually reduced, a smooth surface can be obtained.
High-precision observation becomes possible. After etching with an ion beam, another ion beam such as argon may be irradiated at a low angle to remove a damaged layer due to processing.

In this case, not only the damaged layer due to the processing is removed, but also the surface excluding the influence of the gallium ions implanted at the time of etching can be obtained, and high-resolution observation can be performed.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory view showing a method for producing a sample for a transmission electron microscope and an observation method according to the present invention. The description will be made in the following order.

Cutting out and polishing the back surface: about 2 mm so as to include the target area of the semiconductor device to be observed.
A sample 2 having a size of × 1 mm is cut out. Next, the back side of the sample 2 (or the front side if the front side is unnecessary) has a thickness of 5 mm.
The thickness is reduced by mechanical polishing with sandpaper or the like until the thickness becomes 0 μm or less. This mechanical polishing is for reducing the amount of etching by the subsequent ion beam.

Fixation to a single-hole mesh: A single-hole mesh 6 for a transmission electron microscope is cut out into a fan shape of about 240 ° so that the observation target portion of the sample 2 faces the opening of the single-hole mesh 6. Adhere with epoxy resin.

Applying a protective film: A platinum (Pt, about 1 μm thick) film 7 is formed on the target portion to be processed, for example, by vapor deposition.
To form This is for protecting the end face portion, and may be omitted in some cases.

Processing by irradiation with a focused ion beam: A focused ion beam 8 of gallium (Ga) is irradiated in a direction parallel to the sample surface, and etching is performed so as to leave only a target depth. For the etching, the beam current is adjusted to perform rough processing (ion beam current 6600 to 11500 pA),
Medium processing (1000-2700pA), finishing (1)
It is preferable to carry out in three stages of 50 to 350 pA). With this device, secondary electrons generated when irradiating with an ion beam are detected by a secondary electron detector, and the target depth is specified while observing on a monitor as a secondary electron image of tens of thousands of times, Can be processed. Observation part thickness is 50nm
Finish as follows. Processing time is 10-20μ
In the case of the observation area of m square, it takes about 6 hours.

^* If damage to the sample by the Ga ion beam becomes a problem, an Ar ion beam is subsequently irradiated at a low angle of 2 to 15 ° to the processing surface. As a result, a damaged layer on the surface and the implanted Ga ions are removed, and a sample that can be observed with high resolution can be obtained.

Through the steps of or, ^* , a sample for observing a wide range of a planar microstructure having a specific depth can be prepared. Transmission electron microscope (TEM) observation: A thinned region is irradiated with an electron beam 9 to observe a transmission electron image. The actually fabricated sample was mounted on a transmission electron microscope, and good observation was performed.

[0021]

As described above, according to the present invention, a portion of a plate-like sample such as a semiconductor device other than a portion at a specific depth is irradiated with an ion beam parallel to the main surface of the plate-like sample. By performing the etching, a thinned sample for a transmission electron microscope can be easily prepared, and a planar fine structure at a specific depth, which has been extremely difficult in the past, can be observed in a wide range.

For example, it has become possible to observe the presence or absence of crystal defects and the like generated in the ion implantation process and their two-dimensional distribution. Therefore, the present invention greatly contributes to further technical progress of semiconductor devices.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a sample preparation method and an observation method according to the present invention.

FIG. 2 is an explanatory view showing a conventional sample preparation method.

[Explanation of symbols]

 Reference Signs List 1 semiconductor chip 2 sample 3 reinforcing ring 4 Ar ion 5 hole 6 single hole mesh 7 Pt film 8 Ga ion 9 electron beam

Claims (5)

[Claims] 1. A method for irradiating an ion beam parallel to a main surface of a plate-like sample on a portion other than a portion of a specific depth to be observed on one end surface of the plate-like sample, thereby etching the plate-like sample. A method for preparing a sample for a transmission electron microscope, characterized by preparing a thinned sample at a portion having a specific depth. 2. The method for producing a sample for a transmission electron microscope according to claim 1, wherein etching is performed using a focused gallium ion beam. 3. The method for preparing a sample for a transmission electron microscope according to claim 2, further comprising an etching step in which an ion beam current is gradually reduced. 4. The transmission electron microscope according to claim 1, wherein after etching with the ion beam, another ion beam is irradiated at a low angle to remove a damaged layer due to processing. Method of preparing sample for use. 5. The method for preparing a sample for a transmission electron microscope according to claim 4, wherein argon ions are used as another ion.