Sample preparation

All the samples were prepared in a similar manner. A film was grown on the silicon substrate and then silicon from the back side of the wafer was etched away in a circular opening approximately 0.5 centimeter in diameter. The etching stops when the film is reached. This results in an extremely thin film sitting on the top of the silicon frame. The cross section of such structure is shown in Fig. 4.55.

  

Figure 4.55: Cross section of the thin film sample.

The following samples were prepared at Lincoln Lab for the transmission measurements:
1. Thin SiO₂ film (dry oxidation of Si wafer at 1000^o C, a process identical to the one used for CCD gate oxide growth), nominally 0.14 microns thick.
2. Thick SiO₂ film (wet oxidation at 1000^o C, a process used for channel stop oxide growth), approximately 1.5 microns thick.
3. A sandwich of SiO₂+Si₃N₄+SiO₂, a copy of the CCD gate insulator structure, nominal thicknesses 0.06 + 0.03 + 0.015 microns.
4. Phosphorus doped polycrystalline silicon, 0.6 microns thick.
5. The same polycrystalline silicon film partially oxidized, nominally 0.46 + 0.2 microns of Si+SiO₂ respectively.