JPS6171342A - Method for evaluating surface of wafer of crystalline material - Google Patents

Abstract

PURPOSE:To evaluate the surface of a wafer accurately, based on the diffracted image of a reflected electron beam, by projecting the electron beam from the surface of the water to an arbitrary point on an edge, which is formed by a cleaved plane of the wafer of a crystalline material that is cleaved in extremely low temperature liquid and the surface of the waver of the crystalline material, at a specified angle. CONSTITUTION:A crystalline material, e.g., a GaAs ingot, is sliced, and a sliced GaAs wafer, whose surface is (100), is obtained. The wafer is cleaved in an extremely low temperature liquid such as liquid nitrogen, and a sample piece 2 of about 5X5mm<2> is obtained. An electron beam is projected from the upper part of the well surface on an edge 5, which is formed by the (100) surface and the (110) cleaved plane 4, at an angle of 0=1 deg.. Then the diffracted image is observed. Thus the dislocation of the surface and the introduction of strain are well suppressed in the extremely low temperature liquid. The change in crystalline property caused in the wafer during the machining processes can be evaluated without relation to the inside of the wafer and the crystalline property of the back surface. When the crystalline property of the surface is good, diffraction spots 7 simultaneously appear together with Kikuchi lines. A debye ring appears on the polycrystalline surface.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to a method for evaluating the crystallinity of a wafer surface of a crystalline material, such as a compound semiconductor single crystal, by reflection electron beam diffraction.

[Prior Art] Conventionally, as a method for evaluating the crystallinity of the surface of a crystalline material wafer such as a compound semiconductor single crystal, a transmission electron beam is used to evaluate the crystallinity from a diffraction image obtained by transmitting an electron beam through a thin film wafer. Examples include a diffraction method and a reflected electron diffraction method in which crystallinity is evaluated from a diffraction image obtained when an electron beam irradiated onto the wafer surface is reflected by the wafer surface.

However, in the transmission electron diffraction method, crystallinity is evaluated based on the diffraction image obtained when an electron beam passes through the crystal, so dislocations on the J5 and back surfaces of the crystal appear in the diffraction image along with the dislocations on the surface of the crystal that are to be evaluated. .

Therefore, it is not suitable for evaluating the crystallinity of only the crystal surface, and the crystal needs to be made extremely thin, so it cannot be said to be a simple evaluation method.

On the other hand, in contrast to the transmission electron beam diffraction method, the reflected electron beam diffraction method evaluates crystallinity from the diffraction image obtained when an electron beam irradiated onto the surface of a crystal wafer is reflected by the surface of the crystal wafer. , it is possible to evaluate the crystallinity of only the crystal surface. However, if the surface is extremely smooth due to chemical etching or the like, it is often difficult to obtain a diffraction image.

Therefore, generally, as shown in FIG. 1, an arbitrary point 5a of an edge 5 formed by a surface 3 of a sample piece 2 prepared by cleaving a wafer and a cleavage surface 4 is placed at an angle θ from above the surface 3. A diffraction image is obtained by irradiating an electron beam 1 at an arbitrary point 5a so that the electron beam reflected at an arbitrary point 5a appears as a diffraction spot 7 on the film 6. Note that θ is usually about 1°
That's about it.

However, in the backscattered electron beam diffraction method, the sample piece 2 must fit on a sample stage approximately 5 meters square due to the equipment (generally an electron microscope). Therefore, when the wafer is cleaved or broken at room temperature, new strains and dislocations are introduced into the wafer 2, and changes in crystallinity occur on the wafer surface due to wafer processing steps such as slicing, lapping, or polishing before cleaving or breaking. could not be detected and had low reliability.

[Object of the Invention] In view of the problems of the prior art, the present invention provides a method for slicing, lapping, or polishing that is performed on the surface of a crystal wafer without introducing dislocations or strains into the sample piece when producing the sample piece from the crystal wafer. It is an object of the present invention to provide an evaluation method capable of appropriately evaluating the crystallinity of the crystal wafer surface by detecting changes in crystallinity that occur on the surface of the crystal wafer through processing steps such as the above.

[Summary of the Invention] The method for evaluating the surface of a crystalline material wafer of the present invention includes: cleaving a crystalline material wafer in a cryogenic liquid (1) to provide a cleavage plane, and forming a surface formed by the cleavage plane and the surface of the crystalline material wafer. An electron beam diffraction image obtained by irradiating an electron beam at an appropriately set angle from above the surface of the crystalline material wafer to an arbitrary point on the edge and being reflected at an arbitrary point on the edge. This method is characterized in that the crystallinity of the surface of the crystalline substance is evaluated.

Note that the cryogenic liquid includes liquid oxygen, liquid air,
Liquid nitrogen or liquid helium is suitable.

For C work Next, the operation of the present invention will be explained.

Generally, when a semi-centered single crystal wafer is cleaved or fractured at room temperature, dislocations and strains are introduced into the wafer. However, when a cleavage or fracture occurs in a cryogenic liquid such as liquid nitrogen or liquid helium, almost no dislocations or strains are introduced into the wafer, and even after the wafer is removed from the cryogenic liquid, there are almost no dislocations or strains. It has never been introduced.

Therefore, when the reflected electron beam diffraction shown in FIG. This allows the crystallinity of the wafer surface to be evaluated with high reliability.

Next, the principle of reflected electron beam diffraction method will be explained. Figure 1 shows
FIG. 2 is an explanatory diagram showing the principle of reflected electron beam diffraction. Surface 3 and cleavage plane 4 of sample piece 2 prepared by cleaving a crystal wafer
An arbitrary point 5a of the edge 5 formed by the electron beam 1 is irradiated with the electron beam 1 from above the surface 3 at an angle θ. Different crystal planes exist on the surface 3, so that the electron beam is reflected in directions corresponding to the respective crystal planes and appears as diffraction spots 7 on the film 6, making it possible to obtain an electron beam diffraction image. Further, the origin 8 is obtained when the electron beam 1 directly reaches the film 6 in order to irradiate the sample piece 2 at an angle of about 1°.

The diffraction spots 7 are determined by the crystal plane, so if the crystallinity is good, the electron beam will be directed to the diffraction spot 7 corresponding to the crystal plane.
At the same time, the Kikuchi line began to appear. Furthermore, if the crystallinity of the surface 3 is poor as in the case of polycrystalline material, diffraction spots are not defined and appear as Debye rings. By utilizing such a phenomenon, the crystallinity of the wafer surface can be evaluated.

[Example] Examples of the present invention will be described below.

Note that the horizontal Bridgman method (H) is used as a crystalline material.

GaAs single crystal (Si-doped, E
PD≦500CI114) was used.

Example 1 A GaAS ingot was sliced with an internal diamond cutter to form an as-sliced Ga S wafer with an <ioo> surface in liquid nitrogen (about -196°C).
110) and was cleaved into <11o> to produce a sample piece of approximately 5# x 5 shoes.

Next, by backscattered electron beam diffraction shown in FIG. was irradiated.

The reflected electron beam appears as an electron beam diffraction image like the reflection electron micrograph shown in FIG.

This electron diffraction image has many Debye rings, indicating that the wafer surface is polycrystalline without uniform crystallinity.

Example 2 S wafer (100) to as-sliced Ga of Example 1
From the surface, HN40il-Hz OHz02 system is 90.
After removing the sample by etching 5 μm, a sample piece was prepared in liquid nitrogen in the same manner as in Example 1, and reflected electron beam diffraction was performed.

In the diffraction image obtained as shown in the reflection electron micrograph shown in FIG. 3, no Debye ring is seen at all, and sharp Kikuchi lines are clearly seen. Therefore, it can be seen that by etching the S wafer by 90.5 μm onto the as-sliced Ga substrate whose surface was polycrystalline, the polycrystalline layer was removed and a single-crystalline layer with good crystallinity appeared on the surface.

Example 3 The etched GaAS wafer of Example 2 was lapped, and then, as in Example 1, a sample piece was prepared in liquid nitrogen and subjected to backscattered electron diffraction.

The obtained diffraction image showed many Debye rings as in the reflection electron micrograph shown in FIG. 1, and it was found that the surface was polycrystalline.

Example 4 The lapped GaAS wafer of Example 3 was subjected to chemical polishing with an alkaline chemical, and the wrapped GaAS wafer of Example 1 was
A sample piece was prepared in the same manner as above and reflected electron beam diffraction was performed.

As can be seen from the reflection electron micrograph shown in Figure 4, diffraction spots appear regularly and clearly in the obtained diffraction image.
Moreover, the Kikuchi line also appears, indicating that the wafer surface is a single crystal with good crystallinity.

As described above, according to the embodiment of the present invention, since backscattered electron beam diffraction is performed on a sample piece prepared in liquid nitrogen, the wafer surface is By detecting only changes in crystallinity, the crystallinity of the wafer surface can be evaluated with high reliability.

Note that the present invention is applicable to all crystalline substances that can be diffracted by electron beam irradiation, regardless of whether they are metals or inorganic crystals.

Further, even if liquid oxygen, liquid air, liquid helium, or the like is used instead of liquid nitrogen, the introduction of dislocations and strains into the sample piece can be extremely effectively suppressed.

[Effects of the Invention] As described above in detail, the present invention provides the following significant effects.

(1) Since a sample piece is prepared from a wafer in a cryogenic liquid, the introduction of dislocations and strains into the sample piece can be extremely well suppressed.

(2) Since almost no dislocations or strains are introduced into the sample piece other than during the wafer processing process, only the changes in crystallinity that occur on the wafer surface during each wafer processing process can be detected, and the crystallinity of the wafer surface can be determined with high reliability. can be evaluated.

(3) Reflected electron beam diffraction is easier to prepare a sample than transparent electron diffraction, and it is possible to evaluate only the crystallinity of the wafer surface, regardless of the crystallinity of the back surface and inside of the wafer. can.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the principle of reflected electron beam diffraction. FIGS. 2, 3, and 4 are reflection electron micrographs showing electron diffraction images according to the present invention. 1... Electron beam, 2... Sample piece, 3... Surface. 4...-cleavage plane, 5... edge, 6... film. 7...Diffraction spots, 8...Origin. Agent Patent Attorney Fujio Sato No. 1, ll) + 2 Oichi-oh 13th P. 14th Case 1981 11g1 No. 193070 2 Name of the invention Method for evaluating the surface of a crystalline material wafer 3 Amendment Representative Tokugobu Mizukami 5 Date of amendment order January 29, 1985 6. Column for a brief explanation of the drawings in the specification subject to amendment. 7. Contents of amendment (1) “Details” on page 10, line 18 of the specification has been changed to “simple”
I am corrected. (2) On page 10, line 20 of the specification, insert ``Photographs available in place of drawings'' between ``Figure 4'' and ``This invention''. (3) "J according to the present invention" on page 10, line 20 of the specification is corrected to "obtained according to the present invention."that's all

Claims (2)

[Claims] (1) A crystalline material wafer is cleaved in a cryogenic liquid to provide a cleavage plane, and an arbitrary point on the edge formed by the cleavage plane and the crystalline material wafer surface is attached to the crystalline material wafer surface. The crystallinity of the surface of the crystalline substance is evaluated from an electron beam diffraction image obtained by irradiating an electron beam from above at an appropriately set angle and reflecting it at an arbitrary point on the edge. A method for evaluating the surface of a crystalline material wafer. (2) The method for evaluating the surface of a crystalline material wafer according to claim 1, wherein the cryogenic liquid is any one of liquid oxygen, liquid air, liquid nitrogen, or liquid helium.