In this paper we propose a novel pre-etch method to determine the [100] direction on the surface of 
110
silicon wafers with a diameter of 100 mm for precise bulk etching. A series of circular windows is arranged in an arc with a radius of 48.9 mm, and bulk etched to form hexagonal shapes for the indication of crystal orientation. The hexagons, which have two angles of 109° and four other angles of 125.5°, are surrounded by four {111} vertical planes and two {111} planes inclined 35.5° to the wafer surface. The corners of the hexagons are used as an alignment reference to indicate the [100] direction on the 110 silicon wafers. Using a calculation from the relationship between the circular windows with different diameters of 153, 74 and 35 μm and the circle center distances of 192, 96 and 48 μm, the alignment accuracy can be determined as ±0.11°, ±0.06° and ±0.03° to the projected [100] orientation, respectively. Experimental results also demonstrate the feasibility of accurately aligning long etching slots along the 111 direction. The misalignment has been determined to be 0.02° from 20 experimental samples, much less than the estimated value of ±0.03° on a 100 mm 110 wafer. This simple, accurate and fast alignment technique is applicable to long slot fabrication on 110wafers with tight geometry tolerance.
Source:IOPscience
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Silicon x‐ray analyzer crystals were microfabricated by dicing and etching 10.3 cm (4‐inch) diam, 1.35 mm thick, undoped float zone (111) silicon wafers. These analyzer crystals are intended for a beam line at the Advanced Photon Source synchrotron accelerator ring under construction at the Argonne National Laboratory. Parallel and perpendicular, 1 mm spaced grooves were cut on the silicon wafers using an automated dicing saw. The grooves were cut at 15° and 105° to the '110' primary flat to avoid crystallographic cleavage directions because mechanical strength was desired. The depth of the grooves was 1.15 mm, which was 85% of the wafer thickness. The two cutting parameters, progressive cutting thickness, and feed rate were optimized to reduce saw damage and chipping. Saw damage, which extended over a region of about 30 μm from grooves was removed by isotropic etching. The quality of the single crystal was tested by measuring the width of x‐ray rocking curves with a double‐crystal diffractometer. The best width obtained with 11.2 arc‐s. Since the ideal full width at half maximum (FWHM) according to x‐ray dynamical diffraction theory is 9.7 arc‐s, a broadening function with a FWHM of only 5.6 arc‐s is present due to residual strains (quadrature addition is assumed).
Source:IOPscience
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Si wafers with boron concentrations up to 2 ⋅ 1019 cm−3 were characterized by delineating defects with SC1 solution and analyzing them with respect to crystal originated particles (COP). No oxidation induced stacking fault (OSF) ring appears, and the whole wafer displays a homogeneous COP density after SC1 treatment for low boron doped ingots in a resistivity range of several ohms centimeter and appropriate pulling conditions. Without modification of the crystal pulling process but increasing boron concentration the radial COP distribution changes. The area with a high COP density shrinks and vanishes in the center of the wafer when the boron concentration approaches a level of about 1019 cm−3. Adjacent to the area of high COP density an OSF ring is found, similar to the case of low boron doped material at reduced pulling rate. It is assumed that boron doping at a sufficiently high level modifies the balance of vacancies and interstitials generated in the crystal pulling process and changes the radial defect distribution in the silicon crystals.
Source:IOPscience
