JPH10281951A - Preparation of membrane sample for electron microscope observation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To permit a TiW alloy part to be formed into membrane with priority by polishing composite material which has interface of the TiW alloy which includes a specific percent of Ti and O, whose remainder is W, a semiconductor, or an insulator, forming it into a membrane shape by ion-milling for electroplating. SOLUTION: Composite material involving interface of a TiW alloy 1 which has Ti contents of approx. 0 to 70 wt.%, O contents of approx. 0 to 15 wt.%, and the remainder of W, and a semiconductor or an insulator 2 is split into two pieces of several millimeters around, and the TiW alloys 1 are bonded with each other by an adhesive 3. The thickness with the interface being put vertically is polished into approx. 50 μm by abrasive paper such as SiC particles, and platinum or stainless steel 4 is attached to a sample so as to be brought into contact with the TiW alloy 1. The thickness of the sample at the interface part is formed to be about. 5 to 10 μm by conducting dimpling with a dimpler 5, and the thickness of the semiconductor or insulator 2 in the vicinity of the interface is formed to be approx. 0.2 μm or smaller by an Ar ion milling. The sample and a negative plate 8 are immersed in NaOH aqueous solution 9 for electroplating. It is thus possible to form the TiW alloy 1 part into a membrane shape with priority.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for preparing a thin film sample for observing an interface between a TiW alloy and a semiconductor or an insulator with a transmission electron microscope.

[0002]

2. Description of the Related Art It is important in the development of semiconductor devices to clarify the structure of the interface between different materials at the atomic level. For example, DRAM (Dynamic Random Access Me
mory), T is used as a barrier film material.
i, TiW, structure of interface between TiN and Si substrate, Al
The structure of the interface between the wiring and the Si wiring dominate the characteristics of the DRAM, and it is essential to clarify these interface structures at the atomic level in the development of the DRAM.

In order to clarify the structure of the interface between dissimilar materials at the atomic level, a cross-sectional observation using a high-resolution transmission electron microscope is the most effective means. However, in order to perform observation with a high-resolution transmission electron microscope, it is necessary to reduce the thickness of the sample in the region to be observed to a thickness that allows the electron beam to be sufficiently transmitted. This thickness is such that the accelerating voltage of the electron microscope is 20
In the case of 0 kV, it is about 0.2 μm or less.

Conventionally, as a thin film sample preparation method for observing the cross-section of the interface structure of different materials with a high-resolution electron microscope, for example, as shown in Osamu Ueda, Boundary, November 1993, pp. 31-38, Prepare two pieces of the sample cut out to an appropriate size, stick them together with an adhesive, mechanically grind the sample to about 50 μm using abrasive paper coated with SiC particles, etc., and dimple it A technique has been used in which dimpling is performed until the sample thickness at the interface becomes about 20 μm, and ion milling is performed by Ar ion irradiation until the thickness at the interface becomes 0.2 μm or less. However, in this method, since the speed of thinning by ion milling differs depending on the material, it was impossible to uniformly thin the film on both sides of the interface.

As a method for solving this problem, for example, as disclosed in Japanese Patent Application Laid-Open No. 7-174677, there has been proposed a method which combines mechanical polishing, thinning by ion milling, and thinning by chemical etching. In this method, a thin film is formed uniformly by using a chemical etching solution which preferentially etches a material having a lower film formation speed by ion milling. However, Ti
In the case of a W alloy and a semiconductor such as Si, or a TiW alloy and an insulator such as SiO ₂ , no matter what etchant is used for chemical etching, the interface portion is preferentially etched, Since the TiW alloy separates from the semiconductor or the insulator before the TiW alloy portion is thinned, a uniform thin film cannot be obtained. Similar problems occur with materials other than TiW alloys depending on the material system. For example, Ta
And W and a semiconductor or an insulator.

In these material systems, it is difficult to produce a uniform thin film sample near the interface by the conventional method, and the interface structure cannot be observed with a transmission electron microscope.

[0007]

SUMMARY OF THE INVENTION The present invention provides a method for producing an optimum thin film sample only by observing an interface between a TiW alloy and a semiconductor or an insulator with a uniform transmission electron microscope.

[0008]

Means for Solving the Problems Ti: 0 to 7 by weight%.
When thinning a composite material having an interface between a semiconductor or an insulator and a TiW alloy containing 0% and O: 0 to 15% with the balance being W and unavoidable impurities, either of mechanical polishing or ion milling is used. Alternatively, a method for producing a thin film sample for transmission electron microscope observation, characterized in that the entire sample is thinned using both of them, and the TiW alloy portion is preferentially thinned by electrolytic polishing of the sample, and A gist of the present invention is a method for producing a thin film sample for observation by a transmission electron microscope, wherein platinum or stainless steel is adhered to the TiW alloy portion on the surface of the sample during polishing and electrolytic polishing is performed.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have found that in a composite material having an interface between a TiW alloy and a semiconductor or an insulator, the TiW alloy portion is uniformly thinned by electrolytic polishing, and completed the present invention.

Hereinafter, the present invention will be described in detail. First, the reasons for limiting the components will be described. If the Ti: TiW alloy contains more than 70% of Ti, the difference in hardness from Si becomes so large that a uniform thin film sample can be formed by mechanical polishing and ion milling without using chemical etching or electrolytic polishing. can get.
For this reason, the Ti content was set to 0 to 70%.

O: O is contained in an amount of about 10% by being placed in the atmosphere after the TiW alloy is produced or after the TiW alloy is produced. If it is 15% or less, no oxide is formed and there is no influence on electrolytic polishing. Also, Ti
Since the W alloy is manufactured in an ultra-high vacuum and covered with an antioxidant film such as Mo after the manufacture, the oxygen concentration can be reduced to almost negligible level, so the content range is 0 to 15%.

FIG. 1 schematically shows a thinning process. First,
(A) A composite material having an interface between a TiW alloy 1 and a semiconductor or an insulator 2 is cut out into an appropriate size of several mm square to prepare two sheets, and (b) these are bonded with an adhesive 3. It is preferable to bond the TiW alloys to obtain a uniform thin film sample. next,
(C) Using abrasive paper coated with SiC particles,
The thickness of the sample is reduced to 50 μm by mechanically polishing the interface between the W alloy and the semiconductor or insulator so that the interface is perpendicular to the polishing paper.
m.

Next, (d) platinum or stainless steel 4 is adhered to the whole or a part of the sample. At this time, it is necessary that platinum or stainless steel 4 be attached so as to touch the TiW alloy 1. Next, (e) dimpling is performed by the dimple 5 until the sample thickness at the interface becomes about 5 to 10 μm. At this time, a part of platinum or stainless steel 4 is not polished by the dimpling. Next, (f) the thickness of the semiconductor or insulator 2 near the interface is reduced to 0.2 μm or less by ion milling using Ar ions or the like. At this stage, the semiconductor or insulator portion is sufficiently thin, but the TiW alloy portion is not sufficiently thin.

Next, (g) the portion of the sample such as platinum or stainless steel 4 remaining at the end of the sample is pinched with metal tweezers 6, and the tweezers 6 is connected to the + terminal of the DC power source 7 to form platinum or stainless steel. Is connected to the negative terminal, and the sample and the cathode plate are immersed in an electrolytic polishing liquid 9 such as a 2 to 5% NaOH aqueous solution to perform electrolytic polishing. In electropolishing, the semiconductor or insulator part is hardly thinned,
The TiW alloy portion is preferentially thinned. By performing electropolishing for an appropriate time, the semiconductor or insulator portion and the TiW alloy portion have a uniform thickness. It is desirable to determine the electropolishing time while observing the thickness by observation with a transmission electron microscope. In addition, electrolytic polishing has the feature of preferentially polishing protruding parts of the sample surface, and flattening the sample whose surface roughness has increased by ion milling etc., so that a uniform thin film sample over a wide area around the interface Can be obtained. Finally, (h) if necessary, ion milling is performed again to remove an oxide film formed on the surface of the sample during electrolytic polishing, so that an interface between TiW and a semiconductor or insulator can be observed. An observation thin film sample can be prepared.

[0015]

【Example】

(Example 1) A TiW alloy was vapor-deposited to a thickness of about 20 nm by a magnetron sputtering apparatus on a SiO ₂ film having a thickness of 1.5 nm to ₂ nm grown on a Si substrate by natural oxidation. Table 1 shows the chemical composition of the TiW alloy. Sample 2
Two pieces were cut out into a size of mm × 2 mm, and these were bonded with an epoxy resin. Approximately 50μ sample thickness by mechanical polishing
After that, platinum was deposited on a part of the sample by a sputtering apparatus. The thickness of the deposited platinum was about 1 μm. This was subjected to dimpling by a dimpler apparatus to reduce the thickness of the interface portion to about 7 μm. next,
Reduce the thickness of SiO ₂ near the interface to about 0.2 by ion milling.
The thickness was reduced to μm. Ar ions were used as the milling gas, the acceleration voltage was 3.5 kV, and the amount of ion current was about 1.5 A. The thickness of the SiO ₂ portion was determined as follows.
First, the sample was observed with a transmission electron microscope, the EELS spectrum was measured at the SiO ₂ portion, and the log-ratio method (RFEgerton, Electron Energy Loss Spectroscopy i) was used.
n the Electron Microscope, Plenum Press, New York a
nd London, 1986, P.291).

Next, the sample was electrolytically polished to reduce the thickness of the TiW portion near the interface to about 0.2 μm. The electropolishing liquid uses a 3% NaOH aqueous solution, and the applied voltage is about 38
V, the amount of current was about 100 mA. The thickness of the TiW portion was determined in the same manner as the thickness measurement of the SiO ₂ portion. Next, the sample was subjected to ion milling again to remove an oxide film on the surface generated during electrolytic polishing. The sample thus prepared was observed with a transmission electron microscope having an acceleration voltage of 200 kV. FIG. 2 shows the observed high-resolution image. FIG. 2 shows that the interface between SiO ₂ and the TiW alloy was observed at the atomic level.

Further, after the sample is thinned only by mechanical polishing, dimpling and ion milling without electrolytic polishing, and after the entire sample is thinned by mechanical polishing, dimpling and ion milling, 0.5 mol / mol A sample in which the TiW portion was thinned by chemical etching with a mixed solution of 1 l of hydrogen peroxide and 1.04 mol / l of an aqueous ammonia solution was observed with a transmission electron microscope having an acceleration voltage of 200 kV. Table 2 shows the results of these observations. In the sample thinned by mechanical polishing, dimpling and ion milling, high-resolution interface observation is impossible because the TiW portion is not thinned. In the sample thinned by mechanical polishing, dimpling, ion milling and chemical etching, TiW is used. Was separated from SiO ₂ and high-resolution interface observation was not possible, and high-resolution interface observation was possible only for the sample prepared by the sample preparation method of the present invention.

[0018]

[Table 1]

[0019]

[Table 2]

Example 2 A sample (sample A) in which a SiO ₂ film grown on a Si substrate by natural oxidation was removed by washing with a hydrogen fluoride aqueous solution, and a TiW alloy was immediately deposited to a thickness of about 20 nm by a magnetron sputtering apparatus (sample A)
A and B), the Si ₃ N ₄ and 10nm deposited by CVD on a Si substrate, to produce a sample of about 20nm deposited TiW alloy (Sample C and D) by immediately magnetron sputtering apparatus. Table 3 shows the chemical composition of the deposited TiW alloy. Using these samples, a thin film sample for transmission electron microscope observation was prepared in the same manner as in Example 1. Four types of etchants were used for chemical etching. Table 4 shows the results of observing the prepared sample with a transmission electron microscope. All the samples prepared by the sample preparation method of the present invention were capable of high-resolution image observation of the interface between the TiW alloy and Si or Si ₃ N ₄ , but the samples prepared by the sample preparation methods other than the sample preparation method of the present invention. Were not able to observe the interface at high resolution.

[0021]

[Table 3]

[0022]

[Table 4]

[0023]

According to the method for preparing a thin film sample according to the present invention described above, a uniform interface can be obtained without separation of the interface between the TiW alloy and the semiconductor or insulator. The most suitable sample can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a thinning process of the present invention.

FIG. 2 is a high-resolution interface image of SiO ₂ and a TiW alloy observed using a thin film sample manufactured by the thin film sample manufacturing method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 TiW alloy 2 Semiconductor or insulator 3 Adhesive 4 Platinum or stainless steel 5 Dimples 6 Tweezers 7 DC power supply 8 Cathode plate 9 Electropolishing liquid

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI G01N 1/28 F

Claims (2)

[Claims] 1. A composite material having an interface between a semiconductor or an insulator and a TiW alloy containing 0 to 70% by weight of Ti and 0 to 15% of O and the balance being W and unavoidable impurities. When thinning, the entire sample is thinned using one or both of mechanical polishing and ion milling, and
A method for preparing a thin film sample for transmission electron microscope observation, characterized in that the TiW alloy portion is preferentially thinned by electropolishing the sample. 2. The method for producing a thin film sample for transmission electron microscopy observation according to claim 1, wherein platinum or stainless steel is adhered to the TiW alloy portion on the surface of the sample during the electropolishing, and the sample is electropolished.