JP4863494B2 - Preparation method for microstructure observation sample - Google Patents

Description

  The present invention relates to a method for producing a microstructure observation sample in which a microstructure is processed by a FIB method from a sample having a microstructure formed on a substrate surface.

In the FIB processing technique, a finely focused gallium ion beam is irradiated onto the surface of an observation target, and fine processing can be performed by sputtering.
Since this method only processes the target area, it can greatly eliminate the conventional processes such as cutting and mechanical polishing, and realizes faster and more precise processing. On the other hand, many problems have been reported that the formation of defect layers and changes in physical properties occur by irradiating the sample surface with a focused ion beam.
Therefore, at present, by applying a coating protective film by carbon vapor deposition or plasma polymerization or FIB-CVD method (a method of forming a protective film by irradiating gallium ions while supplying a raw material gas in the FIB), the surface generated during FIB processing is applied. To reduce the negative effects of However, there are many cases where it is difficult to cut even before the FIB processing with respect to a laminated multilayer film that easily peels off or a sample in which a brittle nanostructure is formed on the surface.
Microscopy and Microanalysis (2006), 12: 504-505. Kaiser, M .; A. Verheijen, A .; L. Roest, E .; P. A. M.M. Bakers

  As described above, in the well-known FIB method, the fine structure of the focused ion beam irradiation surface must be damaged, and the present invention aims to prevent such damage from occurring. .

  The method for producing a microstructure observation sample according to the first aspect of the present invention includes embedding a microstructure surface with an energy curable resin, disposing a dummy substrate facing the surface having the microstructure, and vacuum degassing, After removing the gap between the sample and the resin and the dummy base material, and then curing the resin by irradiating energy, the wedge type is formed at a low angle from the back surface of the base material of the sample (the surface not provided with the fine structure). The surface is mirror-polished, and then the fine structure is processed by irradiating the polished surface with a focused ion beam.

  The present invention 2 is characterized in that in the method for producing a microstructure observation sample of the present invention 1, the microstructure is processed by irradiating the focused ion beam perpendicularly to the polished surface.

In the present invention 1, since the focused ion beam is irradiated from the back side of the sample surface having a fine structure, the fine structure can be processed in a wide region while protecting the fine structure.
In addition, since the wedge mold is angled, there is an advantage that the optimum thickness of the protective substrate can be arbitrarily selected during the FIB processing.
In addition to the observation of the fine structure, the evaluation at the atomic level has become possible even at the interface between the substrate and the fine structure, which has been considered difficult so far.

  In the conventional FIB processing technology, a sample with irregularities on the ion-irradiated surface has a processing spot called curtain effect due to the interaction between the shape of the structure and ion sputtering, and it is uniform and uniform in all areas. Although it was difficult to obtain thinness, in the present invention 2, since the focused ion beam is irradiated perpendicularly to the mirror-polished surface, it is possible to obtain a uniform thickness without processing unevenness. It was.

As shown in the examples, the present invention provides a technique for the FIB pretreatment technique that is effective for a sample having a microstructure with extremely low adhesion to the interface. Until now, various pretreatments have been tried in the FIB pretreatment technology, but in this method, one specimen to be observed and one reinforcing sheet are bonded to each other so that the microstructure is embedded in the resin. By polishing the resulting sample into a wedge shape from the back surface and performing FIB processing from that surface, it became possible to perform cross-sectional microfabrication that has not existed before without damaging the fine structure.
In the examples, a semiconductor material is used, but in the future, any material can be used as long as it can withstand thermosetting, such as metal (magnetic / nonmagnetic), ceramic, and polymer.
In addition, powdered samples can be finely processed by FIB, even if they are magnetic materials, by mixing them with resin in advance and curing them in a plate shape, and then using an optimal material for reinforcement. It becomes.
Furthermore, for samples that are weak against the focused ion beam, even if the final processing is not FIB, the joint block that has been wedge-polished by this technique is cut from the side surface, and further polished by a wedge. Access by polishing is also expected to be possible.
In this embodiment, a thermosetting epoxy resin is used, but an ultraviolet curable resin can be used as well.

In order to protect the target fine structure, an epoxy resin is dropped on the silicon wafer to be observed so as to cover the entire surface.
Next, a reinforcing base material (dummy) is further placed thereon and bonded together so that the fine structure is embedded in the epoxy resin.
The two bonded silicon wafers are defoamed in a vacuum desiccator in order to bring the fine structure and the resin into close contact with each other more precisely. (Figure 1)
After defoaming, the two bonded silicon wafers are baked in an oven in order to thermally cure the resin.
In the conventional method, pressure bonding is performed, but in this case, the point is to cure without applying pressure so as not to damage the microstructure.

Next, of the two bonded silicon wafers, the wafer is polished into a wedge shape at a low angle from the back surface of the silicon wafer to be observed.
The polishing method is performed until the tip of the base material to be observed is lost by precision polishing according to the stage using a diamond sheet and mirror finishing by CMP. At this time, the thickness of the tip of the substrate on the observation target side is on the order of nanometers. (Figure 2)

After adjusting the above pretreatment, a cross-sectional sample is prepared using FIB. (Figure 3)
By using such a pretreatment technique, it has become possible to perform focused ion beam processing without damaging the surface tissue to be observed.

The formation of the uppermost carbon film was performed to measure the thickness of the tip of the silicon substrate this time. (Fig. 6, 7, 8)
In FIG. 6, a film layer: a carbon film, a silicon substrate, a gallium nitride nanowire (fine structure) in the resin, and a reinforcing silicon wafer (reinforcing base material) can be confirmed from above.
In the present invention, the silicon substrate itself serves as a protective film. Therefore, it is possible to process under a desired thickness condition due to the difference in thickness of the sample substrate controlled by the wedge processing.

  In recent years, it is expected that nano-level control of the film thickness, composition, etc. of microstructures constituting devices will be indispensable in the development of next-generation materials that are increasingly miniaturized. Along with this, development of analysis and evaluation technology at the nano level of fine structure has become an urgent task, and it is requested to construct a high-speed and large-capacity advanced information processing system. In order to realize this, it is necessary to dramatically improve the performance of each device used in the current information processing system. In the field of device research, the present invention can further contribute to the application of next-generation devices based on the creation of nanostructures and precise evaluation of microstructures by further advancing TEM observation sample preparation technology. Be expected. In addition, this will become a basic technology that supports technological innovation in a wide range of industrial fields such as IT, environment, and biotechnology, which will lead the next-generation social economy, and is expected to have a very large economic effect.

The schematic diagram which shows the state which bonded together the silicon substrate with which the gallium nitride nanowire grew on the surface, and the sample for reinforcement (dummy) with the epoxy resin. The schematic diagram which showed the grinding | polishing direction of the bonded bonding block shown in FIG. The schematic diagram which shows the state grind | polished to the wedge type | mold at the low angle from the back surface of the base material which has the fine structure used as observation object. At this time, the thickness of the tip of the sample to be observed is on the order of nanometers. The schematic diagram which shows a mode that FIB processing is carried out from the grinding | polishing surface (back surface of a fine structure) by the side of the base material which has the fine structure used as observation object. The schematic diagram which shows sectional drawing of the thin piece produced by FIB process. Transmission electron micrograph of a thin piece produced by FIB processing. A cross-sectional observation photograph showing an enlarged interface between silicon and gallium nitride nanowire, which is a sample substrate that can be confirmed in FIG. A further enlarged view of FIG.

Claims (2)

  A method for producing a microstructure observation sample in which a microstructure is processed by a FIB method from a sample formed with a microstructure on a substrate surface, wherein the microstructure is embedded with an energy curable resin, A reinforcing substrate is placed opposite the surface having the structure, and vacuum deaeration is performed to eliminate a gap between the sample and the resin and the reinforcing substrate, and then the resin is cured by applying curing energy. Later, the sample is mirror-polished into a wedge shape at a low angle from the back surface of the substrate (the surface where no microstructure is provided), and then the focused surface is irradiated with a focused ion beam to process the microstructure. A method for producing a sample for microstructural observation. 2. The method for producing a microstructure observation sample according to claim 1, wherein the microstructure is processed by irradiating a focused ion beam perpendicularly to the polished surface.