Jun 25, 2018

A new accurate technique for determination of crystallographic orientation of surfaces of single crystal wafers

A technique based on high resolution X-ray diffractometry employing multicrystal X-ray diffractometers is described. The wafer is mounted against the flat surface of a device and is aligned for diffraction of X-rays from lattice planes that are nearly parallel to its surface. The device is rotated azimuthally around an axis perpendicular to the wafer surface in a stepwise manner. The specimen has to be reoriented after each step to be on the peak of the diffraction curve due to finite angle alpha between the visible surface and the lattice planes. A plot of the reorientation angle as a function of the azimuthal position gives a sinusoidal curve. From three such plots at different known azimuthal orientations of the wafer with respect to the device, the value of angle alpha can be determined. The spatial orientation of the normal to the lattice planes is obtained. A general mathematical formulation has been given for the first time. The finite angle between the axis of rotation of the device and its flat surface against which the specimen is held, is determined. Once a device has been characterised only two azimuthal positions of the wafer are sufficient to determine its crystallographic orientation. Illustrative results of characterisation of a device and determination of orientation of a (111) silicon wafer are described. An overall uncertainty of +or-6 arc sec in the determination of alpha is achieved.


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