JPS6010252B2 - Method for preparing specimens for transmission electron microscopy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preparing a semiconductor crystal specimen for transmission electron microscopy.

Generally, in order to use a semiconductor crystal (including one with an epitaxial crystal layer) as a sample for electron microscopy, the thickness of the semiconductor through which an electron beam can pass must be determined, for example, in the case of potassium sulfide, at an acceleration voltage of 10 V. It needs to be extremely thin, less than 0.5 microns, and less than 1 micron even at 200 KV.

Conventionally, chemical etching methods, jet polishing methods, ion bombardment methods, and the like have been used as methods for preparing samples of such thin semiconductor crystals, but these methods have the following drawbacks. That is, for the chemical etching method, as shown in Fig. 1, a sample wafer A is pasted on a glass plate B with a thermofusible wax C such as Picane wax, and only the part D is covered except for the other parts. Then, it is immersed in corrosive liquid F in container E to perform chemical corrosion, creating a corroded surface with a hole in the center like part G, and the area around the hole as an area that can be observed through transmission. However, in this case, the slope of the corroded area is quite steep, so the permeable area is very narrow. The jet polishing method shown in Figure 2 was developed with the aim of widening this area, and by applying a powerful stream of corrosive liquid to the sample surface using a nozzle, the jet polishing method By widening the flat surface G, it was possible to slightly expand the observable area. However, these two methods have a common problem in that the success rate of creating thin section samples is low due to the difficulty of maintaining constant corrosion conditions.
Furthermore, since the transmissible area is not wide enough, it is very difficult to observe a desired narrow specific area. A more recently developed ion bombardment method is
This method uses an ion sputtering device to spray high-speed argon ions, which are created by heating and accelerating high-purity low-pressure argon gas in a vacuum with a discharge between high-pressure electrodes, onto the target crystal. Since the etching rate is extremely slow at 2 to 3 microns/hour, it is rarely used except in the final step of thinning a sample, for example. On the other hand, in the manufacturing of semiconductor devices, there is a phenomenon in which deterioration of device characteristics occurs due to various causes, and this deterioration of characteristics is often caused by defects in specific local regions of devices or material wafers. In such a case, in order to observe this specific local area with an electron microscope, the thin section must include that narrow area. For example, as shown in FIGS. 3a (top view) and b (side view) of a light emitting device, there are non-conformities called dark lines (DL) and dark spots (DS) K in the Ga ship-GaNASDH laser device 1. There are problems with the generation and growth of the light-emitting region, and these are considered to be one of the factors that cause device deterioration, so there are cases where it is necessary to observe and study this part using an electron microscope. In this case, the non-light-emitting region L that requires observation is an extremely narrow local region as shown in the figure.

In order to observe such an extremely narrow specific region of a semiconductor crystal, it is almost impossible to do so using conventional sample preparation methods, and a special procedure is required. The present invention aims to provide a method for creating a sample for electron microscopy that can observe an extremely narrow specific area, for which it was not possible to create a sample suitable for observation using conventional methods. By using a combination of chemical etching and chemical mechanical polishing methods, we were able to successfully obtain a thin sample containing a narrow specific area with a relatively high success rate.

The present invention will be explained below with reference to FIG.

First, the procedure of the sample preparation method according to the present invention is as follows.

'1' First, the specific area 1 to be observed is placed on the semiconductor wafer 2.
Determine the three-dimensional position within.

(2) Next, the portion 4 above the region 1 is removed by chemical etching from the surface 3 on the side closer to the specific region 1 to the vicinity of the region 1.

If it cannot be removed by chemical corrosion, it can be removed by ion bombardment. '3' Next, the surface layer 6 of the back surface 5 is removed by chemical mechanical polishing or chemical etching to make the surface 7 clean and flat,
In addition, the thickness of the entire surface should be 50 microns or less.

'4} Next, approximately 100 to 50
It is cut into 0 micron square plates 8 by man-cutting or cutting.

(2) This thin plate is pasted onto a disk 10 having a diameter of 3 mm and having a smaller circular hole 9 in the center, with the specific area 1 facing upward and the specific area 1 being located at the center of the circular hole 9.

(2) Finally, ion bombardment is performed from the bottom of the circular hole 9 as shown in FIG. 4f to obtain a desired sample 11 with a thickness that allows the electron beam to pass through the portion including the specific region 1.

Most of the thin section samples il prepared as described above can be observed through transmission, and the success rate is extremely high.

As mentioned above, the sample preparation method according to the present invention including the steps (1) to [6- above] is highly recommended as a method with an extremely high success rate for preparing samples for transmission electron microscopy of semiconductor crystals. It is something to do.

[Brief explanation of the drawing]

Figures 1 and 2 are explanatory diagrams showing the conventional method, Figure 3 is an explanatory diagram of a crystal defect part of a laser emitting device which is an example of the method according to the present invention, and Figure 4 is a diagram showing sample preparation according to the present invention. FIG. 2 is an explanatory diagram showing the method in the order of steps. 1... Narrow specific area, 2... Semiconductor wafer,
3,5..."Wafer surface, 9...Small circular hole, 10...
Small disk, 11... Completed sample. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. In a method for preparing a specimen for a transmission electron microscope for observing an extremely narrow specific region of an inner layer of a semiconductor wafer, one side of the semiconductor wafer is treated from the side closer to the specific region by a chemical etching method or an ion bombardment method. , remove the wafer in parallel layers close to a specific area, and then remove the back side of the wafer in layers by chemical mechanical polishing or chemical etching to form a smooth surface with a thickness of 50 microns or less, and then cleave or cut. 100 to 5 approximately centered on a specific area, etc.
Cut the thin plate into a rectangular thin plate of 0.00 micron square, and place the thin plate on a small disk having a circular hole smaller than the size of the thin plate in the center, with the specific area facing upward and so that the thin plate covers the small circular hole. A transmission electron transmission method characterized by comprising a step of attaching the sample and etching it from the back side of the small circular hole by ion etching until the specific area has a thickness that allows the electron beam to pass through, thereby completing sample preparation. Method for preparing specimens for microscopy.