KR20050033699A - Method for forming sample using analysis by tem - Google Patents

Abstract

A method of fabricating a sample for a TEM is provided to form a uniform thin film by overcoming a differential etching rate between a metal pattern and an insulation layer pattern of the sample. A preliminary sample(130) is prepared by attaching a dummy wafer to upper and lower surfaces of a semiconductor substrate. A position of an analysis area to be observed is marked on the upper surface of the preliminary sample(130). Then, an FIB etching is carried out from an upper outer peripheral portion of the preliminary sample towards a center portion of the preliminary sample. The semiconductor substrate includes a metal pattern(80a) and an insulation pattern(90a) of a metal insulator semiconductor capacitor.

Description

Method for forming sample using analysis by TEM

The present invention relates to a method for preparing a specimen for transmission electron microscope (TEM) analysis, and more particularly, to fabricate the specimen for TEM analysis using a focused ion beam (FIB). It relates to a method of making a specimen.

 Recently, as semiconductor devices and device materials are rapidly becoming highly integrated and miniaturized to realize high functions and large capacities, in semiconductor FAB processes, particles and voids appear on the surface of semiconductor substrates, and not fill phenomenon of contacts. Various defects such as these have occurred. Accordingly, the importance of analytical equipment and technology capable of structural and chemical analysis of finer regions is increasing.

As an analysis method for identifying defects of the semiconductor device, there is an analysis method using an optical microscope, a scanning electron microscope (SEM), or a transmission electron microscope (TEM). Among various analytical methods, TEM is used as a very powerful tool for analyzing the microscopic defects, because the TEM can obtain an image or diffraction pattern using electrons transmitted through the analytical specimen, as well as structural information. One of the best technologies in terms of disassembly and application has received great attention.

Since the TEM obtains the information of the analytical specimen from the image formed by transmitting the accelerated electrons into the analytical specimen, the analytical specimen should prepare an optimal specimen in order to obtain an analytical result for the desired purpose. Success depends on the outcome. Therefore, the situation in which the manufacturing method of the specimen applied to the TEM is emphasized more.

To date, as a method of fabricating a specimen for transmission electron microscopic analysis of semiconductor substrate specimens such as silicon wafers, argon ion milling, chemical polishing, chemical etching, cleavage system, electron polishing, etc. Until now, argon ion milling has played a large role in the preparation of TEM specimens.

However, as semiconductor devices become more highly integrated and defects become more and more minute, the defect analysis technique of the submicron unit has a small probability of accurately obtaining a TEM specimen in a specific region when argon ion milling is used. . For this reason, recently, TEM specimens are manufactured by using a focusing ion beam (FIB) device capable of etching the periphery of the analysis point and adjusting the thickness of the specimen while observing the analysis point electronically.

1A to 1D are views for explaining a method for fabricating a TEM specimen using a conventional FIB, and FIG. 2 is an SEM photograph showing the film quality in which an analysis point of FIG. 1D is formed.

Referring to FIG. 1A, a location of an analysis point to be analyzed is roughly found by using a TEM on a substrate, and marked 5 may be identified to identify the location of the analysis point. Then, the substrate is cut to a size that can be mounted on the specimen holder provided in the TEM. The analysis point must be included in the first preliminary test sample 10 formed by cutting the substrate.

Referring to FIG. 1B, the first preliminary specimen 10 is polished to reduce the thickness of the portion including the analysis point to form a second preliminary specimen 10a.

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

Referring to FIG. 1D, the center structure to be analyzed by locally etching the front and rear surfaces of the second preliminary specimen 10a using FIB while leaving analysis points included in the second preliminary specimen 10a. Complete the TEM analysis specimen 20 comprising a. In this case, the central structure includes an insulating film pattern 16 and a metal pattern 18.

However, when the specimen for TEM classification is formed by the above-described method, the central structure does not have a uniform thickness because it has an uneven shape. This means that when the patterns made of various materials are arranged in the vertical direction on the substrate, even if the patterns are etched with FIB having the same current density, the etch rates vary depending on the respective patterns. Specifically, when the film is etched using the FIB, the metal pattern 18 is relatively slow to be etched compared to the insulating film pattern 16.

For this reason, the metal film pattern of the second preliminary specimen has a slower etching rate than the insulating film pattern and has a thicker thickness than that of the insulating film pattern (see FIG. 2). Therefore, it is difficult for the final central structure to have a uniform thickness. Therefore, it is difficult to obtain accurate TEM analysis results.

Accordingly, an object of the present invention is to provide a method for fabricating a specimen for TEM analysis, including a thin film having a uniform thickness by overcoming the difference in etching rates between the metal pattern and the insulating film pattern of the specimen to be analyzed.

The present invention to achieve the above object,

Preparing a preliminary specimen by attaching dummy wafers to upper and lower surfaces of the substrate including the analysis region; Marking a position of an analysis region to be observed on an upper surface of the preliminary specimen that is perpendicular to an upper surface of the substrate and includes a side surface of the substrate; And irradiating the FIB to form a central structure including an analysis region having a thickness through which electrons are transmitted by FIB etching from the outer side of the upper surface of the preliminary test piece to the center direction.

The method of manufacturing the TEM analysis specimen described above can minimize damage due to the difference in etching rate of the analysis film quality including the metal pattern and the insulating film pattern, thereby forming a test specimen for TEM analysis including an analysis central structure having a uniform thickness. can do.

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

3A to 3E are cross-sectional views illustrating a method for fabricating a specimen for TEM analysis according to an embodiment of the present invention, and FIG. 4 is a SEM photograph showing a central structure including an analysis point of FIG. 3E.

Referring to FIG. 3A, after preparing a substrate W including a metal pattern and an insulating layer pattern of a metal-insulator-semiconductor (MIS) capacitor, first through an optical microscope to analyze defects and defects of the metal pattern and the insulating layer pattern Check the analysis position to analyze.

Subsequently, the substrate is cut to a predetermined size to include the metal pattern 80 and the insulating film pattern 90, and then the bottom surface of the cut substrate is polished to have a width of 3 mm x 2 mm and a thickness of about 0.6 mm. To form a substrate piece 100 having. The substrate may be cut using an ultrasonic cutter or a diamond cutter, and polishing may be performed using, for example, a Tripod polisher.

 The size of the substrate piece 100 formed by the cutting and polishing process is a minimum size that can form the cut substrate piece 100 without damaging the analysis region of the substrate when using a cutter. The metal pattern 80 and the insulating layer pattern 90 are disposed to be perpendicular to the upper surface of the substrate. Since the polishing is an etching process of rapidly etching the lower surface of the substrate, the surface of the lower surface of the substrate is roughly formed.

 Here, the upper surface of the substrate is a surface confirming the analysis position, and the lower surface is a surface facing the upper surface.

Referring to FIGS. 3B and 3C, two dummy wafers 110a, each of the upper and lower surfaces of the substrate piece 100 including an analysis region in which defects in the metal pattern 80 and the insulating film pattern 90 can be observed. 110b) to form a first preliminary specimen 120 having a width of 3 mm x 3 mm and a thickness of about 2 mm.

Subsequently, the analytical area to be observed by grinding each of the lower surfaces and the two side surfaces of the first preliminary specimen except for the upper surface of the first preliminary specimen 120 is positioned at the center and has a width of 3 mm × 40 μm. A second preliminary specimen 130 having a size and a thickness of about 1 mm is formed.

Here, an upper surface of the first preliminary specimen 130 is a surface including a side surface of the substrate piece 100, and a lower surface of the first preliminary specimen 130 is a surface facing the upper surface of the first preliminary specimen. Four sides of the first preliminary specimen are planes perpendicular to the top surface of the first preliminary specimen.

In the second preliminary specimen 130, the smaller the distance (P) between the sides perpendicular to the top and bottom surfaces of the second preliminary specimen, the thickness to be etched by the FIB in the subsequent process is reduced, thereby reducing the time required for fabrication of the specimen. do. However, when the gap P between the front and rear surfaces is too small in the second preliminary specimen 130 formed by grinding, handling of the second preliminary specimen is not easy by the operator.

In addition, there is a limit in reducing the distance P between the side surfaces facing each other without damaging the analysis region included in the second preliminary specimen 130 by the grinding method. For this reason, in order to prevent the damage of the 2nd preliminary test piece 130, the damage of an analysis point, etc., it is preferable to have the above-mentioned space | interval.

Subsequently, the metal pattern 80a and the insulating film pattern 90a of the metal insulator semiconductor (MIS) capacitor included in the substrate piece of the second preliminary specimen 130 are observed in electronic form to indicate the exact position of the analysis region to be analyzed. Marking 145 is formed on the upper surface of the second preliminary specimen.

Referring to FIG. 3D, the passivation layer 150 is deposited on the analysis region including the metal pattern 80a and the insulating layer pattern 90a on the top surface A of the second preliminary specimen 130. The protective film 150 serves to minimize damage that may occur on the surface of the TEM analysis specimen by the FIB when observing a specific region of the TEM analysis specimen or later micro milling using the FIB. Do it. The protective film 150 may be a tungsten (W) film, a platinum (Pt) film, a carbon (C) film, an aluminum (Al) film, or the like.

Referring to FIG. 3E, the FIB is irradiated from the outer surface of the upper surface of the two preliminary specimens 130 toward the center of the analysis region in which the protective film is formed, and has a thickness for transmitting electrons. The metal pattern 80a and the insulating film pattern 90a Form a specimen for TEM analysis with a central structure comprising a).

In detail, the second preliminary specimen 130 is mounted on the specimen holder of the FIB device, and the second preliminary specimen 130 farthest from the analysis region is scanned by scanning the FIB to the upper surface of the second preliminary specimen 130. Locally and rapidly etching the front and rear surfaces of the second preliminary specimen 130 from the periphery of the upper surface of the second preliminary specimen 130 toward the center of the analysis region. The rapid etching is to quickly etch the outer surface of the upper surface of the second preliminary specimen 130 including the analysis region by setting the current density of the FIB to 2800 to 2400pa.

Subsequently, when the front surface and the back surface of the second preliminary specimen 130 are etched to some extent by the fast etching, the current density of the FIB is set to 1100 to 800 pa (pico ampere), so that the front and back surfaces of the fast etching process are performed. Etch slower than the fast etching.

Subsequently, when the front and rear surfaces of the second preliminary specimen 130 are etched to some extent by slow etching, the current density of the FIB is set to 300 to 100 pa (pico ampere) to fine the front and rear surfaces of the second preliminary specimen. By etching (fine milling) to form a specimen 200 for TEM analysis having a thickness of the central structure 160 including the metal pattern and the insulating film pattern is 70 to 100nm.

When the metal pattern 80a and the insulating film pattern 90a are simultaneously etched using the FIB, the etching speed of the metal pattern is relatively slower than the speed at which the insulating film pattern is etched. However, when the TEM analysis specimen 200 is formed by performing the above process, since the metal pattern and the insulating film pattern are stacked in a direction perpendicular to the etching direction of the ion beam, the metal pattern and the insulating film are independent of the etching rate. Patterns can be etched sequentially. For this reason, as shown in FIG. 4, the central structure 160 having a structure in which an insulating film pattern having a uniform thickness and a metal pattern are stacked may be formed without having an uneven structure.

The method of the present invention as described above is to provide a method for fabricating a specimen for TEM analysis comprising a thin film having a uniform thickness by overcoming the difference in etching rate between the metal pattern and the insulating film pattern of the specimen to be analyzed. That is, the central structure of the region to be analyzed does not have a concave-convex shape, and has a characteristic of easily forming a TEM analysis specimen having a thin and uniform thickness so as to transmit an electron beam. For this reason, if the TEM analysis specimen is used, defects and problems of the TEM analysis specimen can be analyzed more accurately in the TEM apparatus.

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.

1A to 1D are cross-sectional views illustrating a method of fabricating a specimen for TEM analysis using a conventional FIB.

FIG. 2 is a SEM photograph showing a defect of a central structure including the analysis point of FIG. 1E.

3A to 3E are cross-sectional views illustrating a method for fabricating a specimen for TEM analysis according to an embodiment of the present invention.

4 is a SEM photograph showing a central structure including the analysis point of FIG. 3e.

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

80: metal pattern 90: insulating film pattern

100: substrate fragment 110a, b: dummy wafer

120: the first preliminary specimen 130: the second preliminary specimen

145: marking 150: shield

160: central structure 200: specimens for TEM analysis

Claims (7)

(a) attaching dummy wafers to the top and bottom surfaces of the substrate including the analysis region to prepare a preliminary specimen; (b) marking a position of an analysis region to be observed on an upper surface of the preliminary specimen that is perpendicular to an upper surface of the substrate and includes a side surface of the substrate; And (C) a method of manufacturing a test specimen for TEM analysis comprising irradiating the FIB to the FIB etching in the center direction from the outer side of the upper surface of the preliminary specimen, forming a central structure having a thickness through which electrons pass and including an analysis region. The method of claim 1, wherein the substrate is a piece of a substrate including a metal pattern and an insulating layer pattern of a metal insulator semiconductor (MIS) capacitor. The method of claim 1, wherein the central structure includes metal patterns and insulating layers patterns stacked in a direction parallel to the upper surface of the preliminary specimen. The method of claim 1, wherein the dummy wafer is a dummy wafer having a plurality of overlapping dummy wafers. The TEM of claim 1, further comprising, after step (a) or (b), grinding both sides perpendicular to the top surface of the preliminary specimen so that the preliminary specimen has a predetermined size. Analytical Specimen Preparation Method. The method of claim 5, wherein after the step (b), during the etching process using the FIB of the preliminary specimen, a step of forming a protective film for preventing damage to the metal pattern and the insulating film pattern of the analysis region is performed. Method of making a specimen for TEM analysis. The method of claim 1, wherein the etching of the FIB is performed by adjusting an electric current density of the FIB focused on the upper surface of the preliminary specimen, so that an etching speed of the preliminary specimen becomes slower as it approaches the analysis region of the preliminary specimen. Method for producing a specimen for TEM analysis characterized in that.