JP2008014899A - Sample preparing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sample preparing method capable of processing a cross section after plane observation more inexpensively and easily than existing technology. <P>SOLUTION: The sample 1 is cut to a block shape in a chamber of a focused ion beam (FIB) device, the sample block (bulk) 4 is taken out of vacuum and is brought into contact with a glass probe 5 set at the tip of a manipulator to be supported. Next, the bulk 4 is fixed through epoxy resin to the tip of a cylindrical pin 6 as a sample stand. Next, a thin film sample for plane observation is prepared by FIB processing. Next, an internal defective position is two-dimensionally observed and identified by a TEM/STEM. Then, the pin 6 is manually rotated by 90°, and then the position including the defective part is cross-sectionally processed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a sample preparation method for preparing a sample having a shape suitable for analysis and observation using a focused ion beam (FIB).

  One method for preparing a sample for a transmission electron microscope is to use a focused ion beam (FIB). This is a method of precisely milling a rectangular region with a Ga ion beam while observing a scanning ion microscope image with a focused ion beam device. In sample preparation using this focused ion beam apparatus, the target portion of the sample material is irradiated with an ion beam from the upper surface side (sample material processing surface side) of the sample material, and the target portion is cut out as a thin film sample.

  By the way, semiconductor devices are becoming finer and more complex, and failure analysis is also difficult. Even if the cell of the defective portion can be identified from the electrical characteristics, the detailed position in the cell is not known, and there are many cases where the sample cannot be prepared by direct focused ion beam processing for TEM observation.

  In such a case, a semiconductor device is mounted on a focused ion beam apparatus, a sample is once prepared for planar observation using an ion beam, and then observed with a TEM or the like to determine the position of a defective portion two-dimensionally, and then again FIB. Then, the thin film portion of the same sample is formed for cross-sectional observation including a defective portion by an ion beam, and observed with a TEM or the like.

  FIG. 6 is a diagram showing a step of observing a cross section after planar observation of the same place. After the portion marked with the laser marker is processed into a block shape by an ion beam, it is fixed to a mesh or the like using a manipulator and processed into a thin film (about 1 μm) thicker than usual.

  When the defective part can be specified, the thin film is cut off with an ion beam, rotated 90 ° with a manipulator, and fixed again to a mesh or the like. Thereafter, thin film processing is performed for cross-sectional observation so as to include the defect site specified at the time of planar observation.

  When such a conventional technique is used, a sample once fixed for plane observation is separated by an ion beam after thin film processing, rotated and fixed again by 90 degrees using a manipulator, and then again for cross-sectional direction observation by ion beam processing. It required a complicated process of thinning.

Patent Document 1 below discloses a technique in which a sample is made into a thin film, observed with a TEM, a target region is cut out, the portion (thin film) is fixed to a sample stage, and cross-section processing is performed. . Specifically, a thin film sample is observed by a planar TEM using a TEM or STEM, a minute thin piece sample including a desired target portion is taken out from the thin piece sample, the minute thin piece sample is fixed to a sample holder, and the minute thin piece sample including the target portion is included. This is a technique in which a cross-sectional thin sample having a thickness substantially perpendicular to the surface and capable of transmitting electrons is processed by a focused ion beam.
JP 2000-146781 A

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a sample preparation method capable of processing a cross section after observation after performing planar observation much cheaper and easily than existing techniques. . It is another object of the present invention to provide a sample preparation method that facilitates positioning of a target site.

  In the sample preparation method according to the present invention, in order to solve the above-described problem, the first step irradiates the sample material with the ion beam to cut out the sample block, and the second step is cut out in the first step. The sample block is picked up, the third step attaches the sample block picked up by the second step to the sample stage, and the fourth step irradiates the sample block attached to the sample stage by the third step. Then, the thin film sample for plane observation is cut out, the thin film sample cut out by the fourth step is plane-observed to identify the defect position, and the sixth step is identified by the fifth step. On the sample table, the sample table is manually rotated by 90 ° in order to machine the cross section of the defect position, and the seventh step is rotated by 90 ° in the sixth step. The position of the thin film sample including the defect site is processed in cross section.

  In the second step, it is preferable that the sample block cut out in the first step is brought into contact with and supported by the probe set at the tip of the manipulator, the probe is lifted and picked up, and the picked up probe is rotated. In the third step, the sample block picked up by the second pickup is preferably fixed to a pin used as a sample stage. In the third step, it is preferable that the pin to which the sample block is fixed is attached to the chip-on cartridge using a leaf spring.

  In the fifth step, it is preferable to identify the defect position of the thin film sample cut out in the fourth step by two-dimensional observation with a TEM / STEM. In the fifth step, when the defect position of the thin film sample cut out in the fourth step is observed, it is preferable that the defect position portion is marked. In the fifth step, it is preferable to arrange the marking width and interval in the marking process asymmetrically.

  According to the present invention, by employing a manual sample rotation mechanism, it can be realized at a much lower cost than existing techniques (microsampling / 360 ° rotation holder). By using the bulk pickup method, plane observation can be performed much more easily than existing techniques (microsampling). In addition, the target portion can be easily positioned by the marking method that is asymmetrically arranged.

  The best mode for carrying out the present invention will be described below with reference to the drawings. This embodiment is performed by a focused ion beam (FIB) apparatus.

  First, Example 1 will be described. The focused ion beam apparatus has a function of finely focusing an ion beam from an ion source and two-dimensionally scanning the thinly focused ion beam on a sample. The focused ion beam apparatus also includes a secondary ion detector generated from the sample by the ion beam scanning, and a sample image (SIM image) of the ion beam scanning region is displayed on the CRT screen based on the output of the ion detector. It has a function to display.

  Furthermore, this focused ion beam apparatus is configured such that a processing region can be arbitrarily designated with a mouse or the like on the SIM image.

  Hereinafter, a procedure for preparing a sample using such a focused ion beam apparatus will be described. FIG. 1 is a flowchart showing a sample preparation procedure. FIG. 2 is a schematic diagram showing an actual work procedure.

  First, as shown in step S1 of FIG. 1, the sample is cut into a block shape in the chamber of the focused ion beam apparatus. As shown in FIG. 2A, the sample material (Specimen) 1 is scanned with the ion beam 2 in the direction of the cross arrow to dig out the periphery of the target portion in the sample 1 to produce the prism 4. Further, the stage of the focused ion beam apparatus is tilted by 60 °, a slit is cut into the bottom of the prism by ion beam processing (bottom cut), and the prism is cut into a block.

  Next, in step S2, the sample block (bulk) 4 is taken out of the vacuum and brought into contact with and supported by the glass probe 5 set at the tip of the manipulator as shown in FIG. Thereafter, the hydraulic handle is operated, the probe 5 is picked up by picking up in the direction of arrow U, and the picked up glass probe 5 is rotated in the direction of arrow T in order to fix the pin 5 to a pin 6 to be described later at a stable position.

  Next, in step S3, the bulk 4 is fixed with an epoxy resin to the tip of a cylindrical pin 6 which is a sample stage shown in FIG. FIG. 2D shows a fixed state. This cylindrical pin 6 is mounted on a chip-on cartridge 7 shown in FIG. 3 and can be rotated manually. The chip-on cartridge 7 has a structure in which pins can be attached to the mesh mounting portion. As a result, the FIB / TEM reciprocation becomes simple and the processing / observation can be easily repeated. As will be described later, the pin 6 may be a cylindrical pin 6-1 or may be a pin 6-2 whose mounting portion is a prism and the rest is a cylinder, or a prism 6-3 as a whole. Each pin 6-1, 6-2, 6-3 is inserted into the hole 8 formed in the chip-on cartridge and attached. Moreover, you may make it attach with a leaf | plate spring.

  Next, in step S4, a thin film sample for plane observation is produced by FIB processing. A thin film is cut out by the ion beam 2 as shown in FIG.

  Next, in step S5, the defect position of the thin film sample cut out in step S4 is two-dimensionally observed by TEM / STEM ((E) in FIG. 2) and identified.

  Thereafter, in step S6, the pin 6 is manually rotated by 90 ° to obtain the state shown in FIG. 2F, and in step S7, the position including the defective portion is processed in cross section. That is, a thin film for observing a cross section in a target region is manufactured using FIB. Thereafter, the cross section of the defective portion is observed with a TEM.

  As described with reference to step S6 and FIGS. 2E and 2F, the pin 6 can be manually rotated 90 ° by being mounted on the chip-on cartridge 7 and manually rotated. For this reason, the sample once fixed can be rotated without being separated.

  As described above, according to the sample preparation method of the present invention, a sample can be prepared at a much lower cost than existing techniques (microsampling / 360 ° rotation holder) by employing a manual sample rotation mechanism. Further, by using the bulk pickup method, plane observation can be performed much more easily than the existing technique (microsampling).

  Next, Example 2 will be described. In the second embodiment, the processing procedure can be described with reference to the flowchart shown in FIG. 1 and the schematic diagram shown in FIG. However, the second embodiment is characterized by the planar observation process in step S5.

  4 and 5 are diagrams for explaining the marking process in the plane observation process. When a two-dimensional position of a place for cross-sectional observation such as a defect is specified at the time of plane observation and the next cross-section processing is performed, it is convenient that some marking processing is performed on the deposition portion in advance. However, a TEM or SEM image observes a transmission image, and if the marking width and interval are symmetrical as shown in FIG. 4, the position cannot be specified.

  Therefore, in the sample preparation method according to the second embodiment, as shown in FIG. The marking position is clearly different between the planar image A and the planar image B that are visible on the left side of the page. This can also be seen from the fact that the SIM image viewed from the top is that of the flat image B and not that of the flat image A because it is distinguished by the distance b from the notch to the marking. In this way, it is possible to specify the position of a TEM image irradiated with an electron beam from the front surface or a TEM image irradiated with an electron beam from the back surface.

  In addition, you may make the shape of the pin used in Example 1 and Example 2 the whole or only a front-end | tip part into a prism. If the entire shape of the pin or only the tip portion is a prism, the pin can be accurately rotated 90 ° when it is manually rotated 90 ° in step S6 in FIG. Also, the rotation operation itself is easy. Furthermore, a memory at equal intervals may be imprinted around the pins so that the rotation angle can be easily recognized.

3 is a flowchart showing a sample preparation procedure in Example 1. FIG. 3 is a schematic diagram illustrating an actual work procedure in the first embodiment. It is an external view of a chip-on cartridge. It is a figure for demonstrating the marking process in a plane observation process It is the figure which has arrange | positioned the width and space | interval of marking asymmetrically. It is a figure which shows the process of carrying out cross-sectional observation after plane observation of the same place.

Explanation of symbols

1 Sample 2 Ion beam 4 Sample block (bulk)
5 Glass probe 6 pin

Claims (7)

Irradiating a sample material with an ion beam to cut out a sample block;
Picking up the cut sample block;
Attaching the picked-up sample block to a sample stage;
Irradiating an ion beam to a sample block attached to the sample stage to cut out a thin film sample for plane observation;
Observing the cut out thin film sample in plan and identifying a defect position;
Rotating the sample stage by 90 ° to cross-section the identified defect position;
Cross-sectionally processing a position including the defect portion of the thin film sample on the sample stage rotated by 90 °.   In the step of picking up the sample block, the sample block cut out in the step of cutting out the sample block is brought into contact with and supported by the probe set at the tip of the manipulator, the probe is lifted and picked up, and the picked-up probe is rotated. The sample preparation method according to claim 1.   The sample preparation method according to claim 1, wherein the step of cutting out the thin film sample includes fixing the sample block picked up in the step of picking up the sample block to a pin used as a sample stage.   4. The sample preparation method according to claim 3, wherein in the step of cutting out the thin film sample, a pin to which the sample block is fixed is attached to a chip-on cartridge using a leaf spring.   2. The sample preparation according to claim 1, wherein the step of identifying the defect position identifies the defect position of the thin film sample cut out by the step of cutting out the thin film sample two-dimensionally by TEM / STEM. Method.   The step of identifying the defect position is characterized in that when the defect position of the thin film sample cut out by the step of cutting out the thin film sample is observed, marking processing is performed on the defect position portion. Sample preparation method. The sample preparation method according to claim 6, wherein in the step of identifying the defect position, the marking width and interval in the marking process are arranged asymmetrically.

Images