GROWTH AND ANALYSIS OF CEO2 THIN-FILMS ON SI(111) SUBSTRATE PREPARED BY ELECTRON-BEAM EVAPORATION

The microstructure of CeO2 layer grown on a (111) silicon substrate by using high-vacuum evaporation was studied for the cleaning and deposi tion conditions. The microstructure in CeO2 layer is an amorphous, nan o-crystalline, or columnar structure, depending on the growth conditio ns. The epitaxial CeO2 layer on Si(111) has good crystal quality for h ydrogen termination on the silicon surface(H-Si), two-step deposition and substrate heating at 400 degrees C. This epitaxial layer has a col umnar structure with high crystal quality. It is desirable to keep the H-termination on the silicon surface in order to prevent silicon surf ace oxidation during the initial growth step. However, the capacitance -voltage and the current-voltage curves of the film are noisy curve an d show a low oxide breakdown voltage owing to many dangling bonds on t he columnar grain boundaries. The CeO2 layer grown on Si(111) has a sl ightly larger and denser columnar structure for ramping up substrate t emperature at 400 degrees C. This epitaxial CeO2 layer shows the growt h of mainly a (111) crystallographic orientation in XRD pattern and ha s a stable C-V response and, from the I-V curve, a low dielectric stre ngth. If some intermediate SiO2 is in the as-deposited film, the C-V c urves have a hysteresis (Delta V) due to trapped charges near the inte rfaces (CeO2/SiO2 and SiO2/Si). In oder that the CeO2 layer have good electrical characteristics, it is desirable to increase the packing de nsity of the CeO2 layer during deposition, to anneal the film in an am bient (O-2 or N-2), and to make the intermediate SiO2 by oxidation. In the atomic force microscopic images, the films show smooth surfaces a nd increasing grain size with increasing substrate temperature. Since the evaporator have low-energy system (0.1 similar to 0.2 eV) for evap orating species (CeO2, Ce2O3), the grain size of CeO2 layer is small. To increase the grain size laterally, energy need to be supplied exter nally by the ion source in the evaporator.