Introduction to metallographic sectioning, ion milling, FIB cutting three kinds of sample making methods

Metallographic sectioning

The working principle of metallographic slicing method: Select a typical representative area on the sample to be measured, after inlay grinding and polishing and other sample processing, the sample sliced into a smooth cross-section, and then through the metallographic microscope or scanning electron microscope (SEM) on the thickness of the coating to be measured.

Measurement procedure of metallographic sectioning method：

Figure 1: Measurement steps of metallographic sectioning method

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Figure 2: Typical metallographic section and SEM results

Ion milling

Ion milling is also called argon ion polishing cross-section sampling, the principle of using ion beams of high-energy impact on the surface of the material, so as to achieve the purpose of removing surface impurities, leveling the surface and so on. Ion milling CP sample cutting diameter of about 1000 microns, with SEM + EDS can be realized on the chip structure layer measurement and elemental analysis.

Argon ion polishing machine can be realised in two forms: flat polishing and cross-section grinding polishing:

Figure 3: Argon ion plane grinding and polishing

Figure 4: Argon ion cross-section grinding and polishing

Ion milling sample preparation can avoid the mechanical milling sample preparation will cause scratches and soft metal ductile deformation problems of the impact of ion milling CP (argon ion polishing cutting) can avoid the impact of stress in the milling process. Particularly for samples to be observed at the same time there is a large difference in the hardness of the material, ion milling CP can be solved in the grinding process of soft materials caused by the stress of the extension. In addition, the sample profile processed by ion milling CP can be more accurately analyzed for the material properties of the sample surface because it is not affected by stress.

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Figure 5: For TEM, SEM, EBSD and LM sample preparation, cross section after Ar ion milling

Focused Ion Beam FIB Cutting and Sampling

Focused Ion Beam FIB test principle:

Focused Ion Beam (FIB) system utilizes a gallium ion source and a dual-lens focusing column to bombard the surface of the specimen with an intense focused ion beam for precision material removal, deposition and high-resolution imaging. It simply aggregates the functions of FIB processing of samples and SEM observation of phase formation. In FIB, the Ga element is ionized into Ga+, then accelerated by an electric field, and then focused by an electrostatic lens to deliver the high-energy Ga+ to the designated point to achieve the function of sample treatment. Focused Ion Beam FIB test principle: Focused Ion Beam (FIB) system utilizes a gallium ion source and a dual-lens focusing column to bombard the surface of the specimen with an intense focused ion beam for precision material removal, deposition and high-resolution imaging. It simply aggregates the functions of FIB processing of samples and SEM observation of phase formation. In FIB, the Ga element is ionized into Ga+, then accelerated by an electric field, and then focused by an electrostatic lens to deliver the high-energy Ga+ to the designated point to achieve the function of sample treatment. FIB thinning TEM slice + TEM observation and analysis

Figure 6: FIB-SEM slice test procedure

For the chip film layer is very thin structural layer, generally a few nanometers of the chip film thickness, has exceeded the scanning electron microscope SEM analysis limit, then need to use transmission electron microscope TEM chip structure observation. Transmission electron microscope TEM resolution than the scanning electron microscope SEM high, transmission electron microscope resolution than the optical microscope is much higher, can reach 0.1 ~ 0.2nm, magnification of tens of thousands to millions of times. Therefore, the use of a transmission electron microscope can be used to observe the fine structure of a sample, or even the structure of just one row of atoms, tens of thousands of times smaller than the smallest structure that can be observed with an optical microscope.

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Figure 7: FIB TEM lamellar preparation for sample

FIB-TEM test process:

the chip to select the appropriate location to do FIB thinning TEM sheet, TEM sheet size is usually in the 5 * 8 microns, the thickness of about 100 nm, through the FIB thinning of the sample selection of the appropriate TEM sheet, and then on the TEM to do observation and analysis.

The process of FIB preparation of TEM samples:

1. Platinum deposition: E-beam or ion-beam assisted deposition method is used to vaporize Pt protective coating on the surface of the TEM specimen to be prepared, in order to avoid the irradiation damage caused by Ga ion beam on the final TEM specimen. 2;
2. Bulk-out: Rapidly digging a "V" shaped pit on both sides of the prepared TEM specimen with a large example beam current. 3;
3. U-cut: excise the ends and the bottom of the TEM thin section cut out in step (2);
4. Lift-out: Lift the TEM specimen out of the block substrate with a micromanipulation needle, and bond the specimen to the needle by vaporizing Pt. 5;
5. Mount on Cu half-grid: the lifted-out TEM sheet is transferred and bonded to a pre-prepared TEM mount using a micromanipulator needle;
6. Final milling: further thinning of the TEM slice with a smaller interest beam current until the thickness is about 100 nm.

Comparison of three different sample preparation methods: metallographic sectioning, ion milling and focused ion beam FIB cutting

Metallographic Sectioning:

The diameter of the cut sample is generally below 3 cm. Damage scratches may occur in the sample-making process. It is not suitable for ductile metal sample preparation as deformation may occur. The sample-making process can introduce impurity contamination, which is not conducive to failure analysis. Samples need to undergo pre-treatment, inlay curing, grinding, and polishing processes, taking about 4 hours to process a sliced sample. This method is suitable for large-area cross-section analysis, incoming material inspection, and product sampling.

Argon Ion Grinding:

The diameter of the cut sample is generally about 1 mm, with almost no damage to the sample in the sample-making process. The sample surface shows a smooth mirror surface with less stress residue, making it suitable for EBSD sample preparation, soft and hard composite materials, vacuum environment sample preparation, and avoiding secondary pollution of the sample by the system. Low-temperature environment for sample preparation eliminates the influence of heat on sample preparation. Sample preparation time depends on the sample area, usually taking 2-3 hours. This method is suitable for micro-sectioning, failure analysis, research and development analysis, competitive analysis, and quality control.

FIB (Focused Ion Beam):

This method can precisely cut the sample according to the required sample size, with almost no damage to the sample during the sample preparation process. The sample surface shows a smooth mirror surface with little stress residue, suitable for EBSD sample preparation. The sample is prepared in a vacuum environment, preventing secondary contamination of the sample. Precise positioning of the cutting position can be achieved, facilitating the analysis of failure anomalies. It can be thinned to prepare TEM thin section samples, achieving nanometer precision cutting, and precise positioning of the cut under the SEM. The sampling time depends on the sampling area, usually taking 1-2 hours. This method is suitable for micro-area slicing, failure analysis, research and development analysis, competitive analysis, and quality control.