Band offsets for ultrathin SiO2 and Si3N4 films on Si(111) and Si(100) from photoemission spectroscopy

High resolution soft x-ray photoelectron spectroscopy with synchrotron radiation is used to study the interfaces of ${\mathrm{SiO}}_{\mathrm{2}}\mathrm{/Si}\text{(111),}$ ${\mathrm{SiO}}_{\mathrm{2}}\mathrm{/Si}\text{(100),}$ ${\mathrm{Si(111)/Si}}_{\mathrm{3}}{\mathrm{N}}_4,$ and ${\mathrm{SiO}}_{\mathrm{2}}{\mathrm{/Si}}_{\mathrm{3}}{\mathrm{N}}_4$ for device-quality ultrathin gate oxides and nitrides. The thin oxides and nitrides were grown by remote plasma deposition at a temperature of 300 °C. Aftergrowth samples were further processed by rapid thermal annealing for 30 s at various temperatures from 700 to 950 °C. The ${\mathrm{Si(111)/Si}}_{\mathrm{3}}{\mathrm{N}}_4$ samples were air exposed and formed a thin ∼6 Å ${\mathrm{SiO}}_2$ layer with a $\mathrm{Si}\text{(2p)}$ core-level shift of 3.9 eV, thus allowing us to study both the ${\mathrm{Si(111)/Si}}_{\mathrm{3}}{\mathrm{N}}_4$ and ${\mathrm{SiO}}_{\mathrm{2}}{\mathrm{/Si}}_{\mathrm{3}}{\mathrm{N}}_4$ interfaces with a single type of sample. We obtain band offsets of 4.54±0.06 eV for ${\mathrm{SiO}}_{\mathrm{2}}\mathrm{/Si}\text{(111)}$ and 4.35±0.06 eV for ${\mathrm{SiO}}_{\mathrm{2}}\mathrm{/Si}\text{(100)}$ with film thicknesses in the range 8–12 Å. The ${\mathrm{Si(111)/Si}}_{\mathrm{3}}{\mathrm{N}}_4$ nitrides show 1.78±0.09 eV valence-band offset for 15–21 Å films. This value agrees using the additivity relationship with our independent photoemission measurements of the nitride–oxide valence-band offset of 2.66±0.14 eV. However, we measure a substantially larger ${\mathrm{SiO}}_{\mathrm{2}}{\mathrm{/Si}}_{\mathrm{3}}{\mathrm{N}}_4$ ${\mathrm{\Delta E}}_V$ value of 3.05 eV for thicker (∼60 Å) films, and this indicates substantial differences in core-hole screening for films of different thickness due to additional silicon substrate screening in the thinner (15–21 Å) films.