Silicon-carbide diffraction grating for the vacuum ultraviolet: feasibility

High reflectance ta-C coatings in the extreme ultraviolet

“…One is that there is no significant reflectance difference over the samples grown with approximate average ion energies in the 70 to 140 eV range, and the differences over the samples are within the measurement uncertainty. This is attributed to the highest sp 3 bonding that has been reported for films deposited with C ion energies in the ~50-150 eV range [35,36]. The other feature is that the films grown with ~70 eV or higher average energy have a substantially higher reflectance in the whole spectral range than the film grown with 0-V bias voltage, hence ~20-eV ion energy.…”

“…The reason may be that the average ion energy of sample 1, ~20 eV, even though insufficient to produce C films with highest sp 3 bonding, it is somewhat larger than the average atom energy in an ion-beam sputtering system such as in [29], which may reach only few eV; again, the smaller thickness of the IBD-C sample (24 nm thick) cannot explain a reflectance difference larger than 0.6% (relative) above 55 nm, whereas present sample 1 exceeds IBD C film reflectance an average of 16%. The large reflectance of the ta-C film compared to IBD C is attributed to the high sp 3 bonding content in ta-C films; in this way, diamond represents the limit of 100% sp 3 bonding. The proportion of sp 3 bonding content has been correlated with the energy of the ions in ta-C films [37], and for the present films grown with non-zero bias, the proportion of sp 3 bonding is expected to be in the ~80-85% [34].…”

“…The large reflectance of the ta-C film compared to IBD C is attributed to the high sp 3 bonding content in ta-C films; in this way, diamond represents the limit of 100% sp 3 bonding. The proportion of sp 3 bonding content has been correlated with the energy of the ions in ta-C films [37], and for the present films grown with non-zero bias, the proportion of sp 3 bonding is expected to be in the ~80-85% [34].…”

“…Aluminum is an exception to this rule, with a high reflectance down to its plasma wavelength at 83 nm [1]; however, Al slightly oxidizes in contact with the atmosphere, which destroys its EUV reflectance and which is unavoidable since no protective coating is available that is transparent below ~105 nm, the cutoff of LiF [2]. In the EUV range, chemical-vapordeposited (CVD) SiC coatings [3,4] and hot-pressed B 4 C [5] are among the few stable materials that provide the largest known reflectance below ~100 nm down to ~60 nm, which is in the range of ~30-50%. However, CVD SiC films must be deposited onto substrates at very high temperatures, whereas hot-pressed B 4 C is a bulk material that is prepared at an extremely high temperature.…”

“…Ion-beam-sputter deposited (IBD) C films have a higher EUV reflectance than films deposited by evaporation, which has been attributed to the larger average energy of condensing C atoms in IBD compared to evaporation [29]; for IBD C films, a slight increase in the average energy of condensing atoms was seen to result in an increase in the EUV reflectance of the resulting films and this was attributed to a larger content of sp 3 bonding, the bonding of C in diamond [29]. This behaviour suggested that C films grown with impinging C atoms with optimum energy for the highest proportion of sp 3 bonding might result in a higher EUV reflectance [29]. C films with largest sp 3 bonding can be prepared by filtered cathodic vacuum arc (FCVA), among other techniques.…”