Ion Implantation and Synthesis of Materials - Studium

11.4 The Mechanisms Behind the Ion-Cut Process 1555040DamagepeakAs-implanted3020H peakPlatelet Density (ab. units)10050403020DepthExfoliatedLayerAfter Ion-CutDepthDonorWafer1000.10 0.00 0.10 0.20Depth (µm)Fig. 11.11. Depth distribution of the platelet density in the as-implanted sample (solid line)(upper part) and also after ion-cutting in the exfoliated layer (dashed line) and the donorwafer (dash-dotted line) (lower part). The data was deduced from XTEM imagesDuring annealing, the single-hydrogen atoms at the bond-centered sites arereplaced with two-hydrogen atoms. In this state the atomic arrangement changesfrom Si–H–Si to Si–H–H–Si, forming two H atom layers, bonded only by theweak Van der Waals interaction between them. In-diffusing, H atoms split the twoH layers and agglomerate into a H 2 gas. Further in time or temperature, hydrogenatoms from other Si–H defects in the system are released from the traps, diffuse tothe H–H platelets and agglomerate, forming regions of highly pressurized H 2 gasbubbles. The high pressure in the H 2 gas bubbles provide the force needed togenerate a crack opening displacement, with cleavage occurring between theweakly bonded H–H atoms. As mentioned earlier, it has been shown that the H 2molecules that form within these bubbles do so with a bond length almost equal tothe H 2 bond length in vacuum (Leitch et al. 1999). The H 2 molecule formation inthe gas bubbles releases the energy necessary for the strain build up around thebubble in the silicon crystal (Cerofolini et al. 1992).