Ion Beam Sputtering (IBS) offers a deposition process yielding optical thin films with stable optical parameters, near bulk density, and ppm level optical loss. Recently higher throughput systems with higher deposition rate and larger substrate fixtures have been developed. The higher deposition rates make accurate layer control essential. This is most readily achieved by using an optical monitoring system (OMS).
Multiple optical bandpass, edge filters and notch filters have been deposited in a high throughput IBS system with four 333mm diameter planetary using both a single wavelength (SWLOMS) as well as a broadband OMS (BBOMS). A wavelength repeatability of less than 0.1% for five subsequent short wave pass filters is demonstrated. Results for a multi notch filter coated using the BBOMS are also presented. A control strategy utilizing a mix of a broadband and a single wavelength model was used successfully in the deposition.
Spectral performance of multiple bandpass filters using turning point control is presented. A 2D mapping of a 15nm FWHM bandpass filter centered at 830nm shows a +/-0.05% variation in the center wavelength across the central 180mm diameter and a +/-0.35nm variation in the FWHM to the edge of the wafer. A variation of the standard turning point monitoring that enables control of filters with narrower bandwidth than the spectral resolution of the OMS system has been developed. A 0.8nm FWHM bandpass filter centered at 532nm controlled using a BBOMS with a ~1.5nm FWHM spectral resolution of the spectrometer is demonstrated.
In this work we report on the damage threshold of ion beam deposited oxide films designed for high peak power short pulse laser systems. Single layers of ZrO2, SiO2, Al2O3, TiO2, and Ta2O5 and multilayers of Al2O
3/TiO2, SiO2/Ta2O5, and SiO2/ZrO2 were grown on polished borosilicate glass substrates using ion beam sputter deposition. Deposition conditions were optimized to yield fully oxidized films as determined from x-ray photoelectron spectroscopy (XPS). Damage threshold testing was performed using an amplified Ti:Sapphire laser producing a train of 120 picosecond pulses at a wavelength of 800 nm. The laser output was focused with a lens to generate fluences ranging from 0.1 to 24 J/cm2. The highest damage threshold of 15.4 J/cm2 was measured for a single layer film of SiO2. The damage threshold of high reflectance and anti-reflection multilayer coatings fabricated for 800 nm applications was evaluated using the same procedure as for the single layer films. Highest damage thresholds of 2.5 and 3.5 J/cm2 were measured for a 6-pair ZrO2/SiO2 high reflectance coating and a 5 layer anti-reflection coating of the same materials.
Silicon nanocrystals have been prepared in thermally oxidized hydrogenated amorphous silicon (a-Si:H) and annealed silicon-rich oxynitride (SRON) films with [O/Si]=0.17 [N/Si]=0.07, in the temperature range 400-800°C and 850-1150°C respectively. Glancing Angle X-ray Diffraction (GAXRD) measurements show the presence of silicon nanocrystals embedded in silicon oxide films. Warren-Averbach Analysis of GAXRD data indicates the presence of ~9 nm silicon crystallites in a-Si:H films oxidized at 800°C. Room temperature photo-luminescence (PL) was observed from silicon nanocrystals embedded in oxidized a-Si:H films. Modeling the PL data indicates the presence of 6 nm silicon nanocrystals. This discrepancy is attributed to the columnar growth of silicon nanocrystals in thermally oxidized a-Si:H films. Silicon nanocrystals were not formed by thermal oxidation of SRON films under similar reaction conditions. However, silicon nanocrystals could be fabricated by annealing SRON films for 4 h in vacuum over the temperature range 850-1150°C. Silicon crystallite sizes remained constant (~4 nm) for films annealed below 1050°C and increased to 9 nm for films annealed at 1150°C. The presence of nitrogen played an important role in the silicon nanocrystal precipitation in SRON films. While the nanocrystal formation in a-Si:H films was due to oxidation and crystallization progressing simultaneously in the films, nanocrystal formation in SRON films appears to be due to the high temperature precipitation of excess silicon in the film.