Setting the orientation of crystals

Details Setting the orientation of crystals Setting the orientation of crystals

1985-05-14

1987-12-01

Straub, Gary P.

Adhesive bonding and miscellaneous chemical manufacture

Delaminating processes adapted for specified product

Delaminating in preparation for post processing recycling step

156617SP, 156DIG65, 378 73, C30B 3300, C30B 1520

Patent

active

047102594

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a method and apparatus for setting the orientation of the crystallographic axes of a single-crystal such as may be required preparatory to cutting a boule or polishing a wafer. It is applicable in both laboratory and industrial contexts and is especially relevant to the production of microchips from boules.
Current practice is to affix the boule to a base plate with epoxy-resin as a means of holding it while cutting, to determine the errors in the orientation of its crystallographic axes by means of an X-ray diffraction technique, and, having transferred the specimen on its base plate to the cutter/polisher, to make angular correctons on that instrument to ensure that the resulting surface has the desired orientation. Such methods usually employ monochromatic (characteristic) radiations and involve measurement of the Bragg angle of one diffracted beam at a time. Where comparison of two such beams is made they are profiled separately and, when accuracy is needed, this is a relatively slow process that calls for a stabilized X-ray source which is expensive. It also necessitates duplication of the angular correction facilities on the cutter/polisher.
The rate of deposition of epitaxial layers (or the depth of penetration of ion implantation) during the subsequent formation of integrated circuits on the surface of a wafer is markedly dependent on the degree of misalignment between the growth face and the crystallographic planes in the substrate, and the electronic switching speeds achievable in the finished product depend on the thickness of such deposits. It has become important, therefore, especially in the batch production of microprocessors, to control the orientation of the prepared surface of the wafers, and to make any deliberate misalignments that are desirable in the interests of high switching speeds as reproducible as possible: and that requires precise angular measurements. Sufficient accuracy is achievable with some of the current techniques but always at a high price in time.
One object of the invention is to enable high-precision setting to be achieved routinely, much more rapidly, and in a preferred embodiment, in a manner that lends itself to adjustment under computer control.
We have found that the orientation of a crystal can be determined with reference to a position in which a pair of symmetrical reflexions simultaneously satisfy Bragg's law at the same wavelength of X-ray radiation and propose therefore, in accordance with the invention to ascertain the orientation of a crystal by irradiating the crystal with an X-ray beam and detecting a pair of symmetrical reflexions which occurs at the same wavelength of X-ray radiation.
According to this invention a method of setting the orientation of a single crystal comprises directing onto the crystal an X-ray beam comprising a peak of energy at a given wavelength, adjusting the orientation of the crystal while relatively moving the crystal and the beam about an axis perpendicular to an equatorial plane containing the X-ray beam until any pair of relexions that are symmetrical with respect to the equatorial plane occur simultaneously (ie. at the same azimuth) at the said wavelength of X-ray radiation.
It will be understood that some or all of the energy in the X-ray beam must be confined to a very narrow bandwidth, in which case the pair of reflexions will occur simultaneously only when one of the crystallographic planes of symmetry is set in a predetermined or determinable orientation relative to a datum.
Most X-ray diffraction tubes will, in addition to white radiation, generate intense peak energy at a wavelength or wavelengths characteristic of the target material in the tube when operated above a critical voltage, so that in a preferred embodiment using a conventional X-ray diffraction tube it is possible to detect a pair of reflexions before making adjustments to establish a relative position of the beam and crystal in which the pair of relexions "flash" simultaneously in response to the peak energy, at the waveleng

REFERENCES:
patent: 3213278 (1965-10-01), Spielberg
patent: 3345613 (1967-10-01), Bucholtz et al.
patent: 3788890 (1974-01-01), Mader et al.
patent: 3870880 (1975-03-01), Merigoux et al.

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