KR20040004931A - Method for forming sample using analysis by TEM - Google Patents

Abstract

PURPOSE: A method for fabricating a sample for a transmission electron microscope(TEM) sample is provided to more precisely analyze an analysis point by making the thickness of a portion of the TEM sample including the analysis point uniform and thin so that an electron beam can transmit the sample. CONSTITUTION: A layer located over the analysis point of a process target for analysis is eliminated. The front and back surfaces of the resultant structure are etched while the analysis point is left. The process target including the analysis point has such a thickness that accelerated electrons can transmit the sample.

Description

Method for forming sample using analysis by TEM

The present invention relates to a method for preparing a sample for transmission electron microscopy (TEM) analysis, and more particularly, a sample for preparing a TEM sample using a focused ion beam (FIB). It is about a method.

In recent years, with the rapid spread of information media such as computers, semiconductor devices are also rapidly developing. In terms of its function, the semiconductor device is required to operate at a high speed and to have a large storage capacity. In response to such demands, manufacturing techniques have been developed for semiconductor devices to improve the degree of integration, reliability, and response speed.

With the higher integration of semiconductor devices, the line width of the circuit is getting finer. As a result, the source causing various defects in the semiconductor device is further refined and diversified, thereby increasing the difficulty caused by failure analysis of the semiconductor device. Generally, an optical microscope, a scanning electron microscope (SEM) or a transmission electron microscope (TEM) is used to identify the defect of the semiconductor device. Among them, the TEM is used as a very powerful tool for analyzing the minute defects because the TEM can obtain an image or a diffraction pattern using electrons transmitted through the analytical sample to obtain structural information as well as the shape of the material.

Since the TEM obtains information of the analytical sample from the image formed by transmitting the accelerated electrons into the analytical sample, the analytical sample must be so thin that the electrons are transmitted. Therefore, prior to performing the analysis, a predetermined sample preparation process must be performed to reduce the thickness of the analysis sample.

Sample preparation methods for TEM analysis which are widely used conventionally include argon ion milling method, chemical polishing method, chemical etching method, electropolishing method and the like. However, as semiconductor devices have been highly integrated and defects generated have become increasingly finer, it has become very difficult to produce a TEM sample including an analysis region in which the fine defects are generated by the above method. Therefore, in recent years, TEM analysis samples have been prepared using FIB, which can control the thickness of a sample by etching the periphery of the analysis point while observing the analysis point in an electronic image.

1A to 1E are views for explaining a TEM sample preparation method using a conventional FIB.

1A to 1B, the location of an analysis point to be analyzed is roughly found by using a TEM on a substrate and marked 5 so as to identify the location of the analysis point. Then, the substrate is cut to a size that can be mounted on the sample holder provided in the TEM. The analysis point 10 formed by cutting the substrate must include the analysis point.

Referring to FIG. 1C, the object 10a is polished to reduce the thickness of the portion including the analysis point.

Referring to FIG. 1D, a protective film 12 is formed on a surface portion of the genital workpiece 10a corresponding to the upper portion of the analysis point in the workpiece 10a. The protective layer 12 may be formed of a material such as tungsten or carbon.

Referring to FIG. 1E, the front and rear surfaces of the workpiece 10a are locally etched using FIB while leaving analysis points included in the workpiece 10a, thereby analyzing the sample 11 for analysis. Complete At this time, the analysis sample 11 should be formed to have a thickness enough to transmit the electron beam to the analysis point.

By the way, a film made of various materials is stacked on the substrate to form a semiconductor device. Various films formed on the substrate may have different rates at which the respective films are etched even if they are etched by the FIB having the same current density. Specifically, when the film is etched using the FIB, the metal film is etched at a slower rate than the nitride film and the oxide film. Therefore, when a part of the metal film is included in the object to be processed, the film located below the metal film has a slow etching rate compared to the surrounding film in which the metal film is not formed, and remains thicker than the surrounding film. In other words, if the metal part is partially included in the object to be processed, the phenomenon that the thickness of the completed analysis sample becomes uneven appears.

In addition, when etching is performed using the FIB, the finished sample for analysis has a thicker thickness between the front side and the rear side of the sample toward the bottom of the membrane.

This makes the thickness of the sample at the analysis point thick, making it difficult to obtain accurate analysis results.

Accordingly, an object of the present invention is to provide a method for preparing a sample for TEM analysis, which is thin and uniform in thickness of a sample at an analysis point.

1A to 1E are views for explaining a TEM sample preparation method using a conventional FIB.

2A to 2F are views for explaining a method for preparing a sample for TEM analysis according to an embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

32: mark 40b: object to be processed

42: sample for analysis

The present invention to achieve the above object,

Removing the membrane located on top of the assay point in the analyte to be treated; And

Etching the front and back of the resultant while leaving the analysis point, to form a sample to be processed to include the analysis point to have a thickness enough to transmit the accelerated electrons to prepare a sample for TEM analysis Provide a method.

Each of the steps is performed by focusing an ion beam on the surface of the workpiece.

According to the said method, since the membrane located in the upper part of the analysis point of the to-be-processed object is removed, the film | membrane of the said analysis point site | part can be prevented from becoming thick due to the membrane located in the upper part of the said analysis point. In addition, since the film located above the analysis point is removed, the thickness of the workpiece is reduced. Therefore, the phenomenon in which the thickness between the front and rear surfaces of the sample becomes thicker toward the bottom of the membrane in the finished TEM analysis sample can be minimized.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2A to 2F are views for explaining a method for preparing a sample for TEM analysis according to an embodiment of the present invention.

Referring to FIG. 2A, the position of the analysis point in the object 30 is confirmed through an optical microscope. The FIB is then used to mark 32 the perimeter of the analysis point.

Referring to FIG. 2B, the workpiece 30a is cut to a predetermined size to include the analysis point. The object 30a includes a semiconductor device or a wafer on which the semiconductor device is formed. The object 30a may be cut using an ultrasonic cutter or a diamond cutter.

At this time, the cut workpiece 30a has a distance A between both sides parallel to the analysis direction of the analysis point at least 3 mm, and a distance B between the front and back surfaces perpendicular to the analysis direction of the analysis point is About 2 mm. The size of the presented workpiece 30a is such that the gap B between the front and rear surfaces of the workpiece can be minimized without damaging the analysis point of the workpiece when the cutter is used. The analysis point is positioned at the center of the cut workpiece 30a.

In the following description, the workpiece 30a has an upper surface, a surface opposite to the surface marked with an analysis point, and a front surface and a rear surface with a side perpendicular to the analysis direction of the analysis point. Sides parallel to the analysis direction of the analysis point are referred to as both sides.

As shown in FIG. 2C, in the workpiece 30a cut to the predetermined size, the front and rear surfaces of the workpiece 30a are polished while leaving the analysis point. The front and rear surfaces of the workpiece 30a are polished to have a predetermined interval that is easy to mount on the sample holder provided in the TEM, and specifically, to have a distance D of 70 to 100 μm. At this time, the analysis point is located in the center between the front and back. The polishing can be performed using, for example, a Tripod grinder.

In the polished workpiece 40, the smaller the distance D between the front and back surfaces, the thickness to be etched by the FIB in a subsequent process is reduced, thereby reducing the time required for sample preparation. However, when the distance D between the front and back surfaces of the polished workpiece 40 is too small, handling of the workpiece 40 by the operator is not easy. In addition, there is a limit in reducing the distance D between the front and back surfaces without damaging the analysis point in the workpiece by the polishing method. Therefore, in order to prevent the damage of the workpiece 40 and the damage of the analysis point, it is preferable to have the above-described intervals.

Referring to FIG. 2D, the front and back surfaces of the polished workpiece 40a are locally first etched by FIB to adjust the thickness from the analysis point to the analysis direction.

Specifically, the polished workpiece 40a is mounted on a sample holder of an FIB device, and an ion beam is scanned onto an upper surface of the polished workpiece 40a to front and back of the workpiece 40a. Etch the site. At this time, the current density of the FIB is increased to 2000 to 3000 pa (pico ampere) to quickly reduce the thickness of the workpiece 40a. Subsequently, when the thickness of the workpiece 40a is reduced to some extent, the current density is reduced to about 500 to 1500 pa (pico ampere) to reduce the etching rate of the workpiece 40a.

When the film is etched using the FIB, the metal film is etched at a slower rate than the nitride film and the oxide film. Therefore, when a part of the metal film is included in the object to be processed, the film located below the metal film has a slow etching rate compared to the surrounding film in which the metal film is not formed, and remains thicker than the surrounding film. 50a) That is, when the object is partially included in the metal film, the phenomenon that the thickness of the analytical sample after the etching is completed is not uniform.

Referring to FIG. 2E, in the first etched object 40a, the second etching is performed to remove the film located above the analysis point.

Specifically, the sample holder of the FIB device is tilted at a predetermined angle. This is to facilitate removal of only the membrane located above the analysis point. That is, the sample holder is tilted so as to have an angle of about 90 ° with an ion beam provided with the upper film of the analysis point exposed on the front and rear surfaces of the object 40b. The tilt angle of the sample holder is 60 to 90 degrees.

At this time, the provided ion beam may be tilted at a predetermined angle without tilting the sample holder. However, the tilting of the ion beam requires modification of the equipment and may adversely affect the stability of the ion beam.

Subsequently, the membrane located above the analysis point in the object 40b is removed using the ion beam.

As the above process is performed, when the etching is performed by the ion beam, the film located above the analysis point, which has lower etching efficiency than the surrounding film, is removed in advance. Therefore, the thickness of the sample for analysis can be prevented from being uniform by the film located above the analysis point. In addition, the height of the analysis sample is lowered, when the etching is performed using the FIB, the less the etching of the membrane toward the lower portion of the membrane, the thickness of the lower portion of the membrane can be minimized.

Referring to FIG. 2F, by performing third-order etching of the treated material 40b from which the film located on the upper part of the analysis point is removed, the TEM analysis device has a thickness that allows the electron beam to pass through the analysis point in the analysis direction. The sample 42 is completed.

The object 40b has already been reduced in thickness by the primary etching and the secondary etching. Therefore, when performing the etching, the current density of the FIB is very small, such as 50 to 100 pa (pico ampere), to finely etch the object 40b.

When etching using FIB as described above, it is possible to prevent the thickness of the analytical sample 42 from being uniform by the membrane located above the analysis point. In addition, the phenomenon in which the lower portion of the membrane becomes thicker in the sample for analysis 42 may be minimized.

As described above, according to the present invention, the sample for TEM analysis may be made thin and uniform so that the thickness of the portion including the analysis point is transparent to the electron beam. Therefore, using the analysis sample, it is possible to analyze the analysis point more accurately in the TEM equipment.

As described above, although described with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified without departing from the spirit and scope of the invention described in the claims below. And can be changed.

Claims (9)

i) removing the membrane located above the assay point in the analyte to be treated; And ii) etching the front and rear surfaces of the resultant while leaving the analysis point, thereby forming a workpiece including the analysis point to have a thickness such that accelerated electrons are transmitted. Analytical Sample Preparation Method. The method for preparing a sample for TEM analysis according to claim 1, wherein the step i) is performed by focusing an ion beam on the surface of the workpiece. The sample preparation method of claim 2, wherein the step i) is performed by tilting an ion beam focused on the workpiece. The method for preparing a sample for TEM analysis according to claim 1, wherein the step i) is performed by tilting the workpiece. The method for preparing a sample for TEM analysis according to claim 4, wherein the tilt angle of the workpiece is 60 to 90 degrees. The method of claim 1, wherein the step ii) is performed by focusing an ion beam on a surface of the workpiece. The method of claim 1, further comprising adjusting the thickness of the workpiece by locally etching the front and back surfaces of the workpiece, while leaving the analysis point of the workpiece before performing step i). Sample preparation method for TEM analysis, characterized in that. The method of claim 7, wherein the adjusting of the thickness of the workpiece comprises adjusting the ion beam current density focused on the surface of the workpiece, such that the etching speed of the workpiece becomes slower as it approaches an analysis point of the workpiece. Method for producing a sample for TEM analysis, characterized in that the etching. The method for preparing a sample for TEM analysis according to claim 1, wherein the film located above the analysis point comprises a metal film.