Ion Implantation and Synthesis of Materials - Studium

9.2 Defects 1179.2.5 Planar DefectsPlanar defects include grain boundaries, stacking faults, and twins. These defectsare formed during ion implantation and thermal and processing. All three types ofplanar defects are enclosed by a single dislocation or by an array of dislocationsseparating the faulted area from the normal area or delineating the misorientationbetween various areas of the semiconductor.Stacking faults are created during crystal growth processes, such as epitaxialgrowth and during the annealing of ion-implanted regions. Extrinsic stackingfaults also are formed in Si due to oxidation. Silicon self-interstitials are createdduring oxidation; these interstitials then coalesce to form extrinsic stacking faults.Twins are related to stacking faults and also are formed during crystal growth.A twin fault is therefore formed by inserting a fault plan every other plane in thenormal FCC stacking sequence.9.2.6 Volume DefectsVolume defects include voids and local regions of different phases, such as aprecipitate or an amorphous phase. In Si, oxygen precipitation is the mostimportant volume defect. Silicon crystals are grown by either the Czochraskitechnique or by the float-zone technique. The typical concentration of oxygen inCzochraski Si crystals is about 10–20 ppm (parts per million) or 5 × 10 17 –1 × 10 18 cm −3 . The float-zone technique introduces less oxygen in Si than doesthe Czochraski technique. Most of the oxygen in the as-grown crystal is atomicallyFig. 9.9. Edge dislocation created by inserting an extra half-plane of atoms