Figure 12
Micrograph of a dry-pit sample and magnification of the side profile. The dry-pit line shows a higher reflectance than the dry-tip results. For the dry etching method, nanostructures can be fabricated on most of the pit profiles; however, nanostructures cannot grow on a small area of the profile, as shown in Fig. 12. Because the plasma is accelerated by the ICP bias power, with a high speed in the vertical direction and a low speed in the horizontal direction, the plasma cannot reach the region that is shielded under the mask or the top silicon surface. In the magnified side profile, the white arrow shows the boundary of the grass growth. Grass can grow on the right side of the arrow but cannot grow on the left side of the arrow. Therefore, the absorption efficiency of a dry-pit sample is lower than that of a sample with tips that grow well over all of the side profile, as shown in Fig. 6(b).
