Augmented reality glassed based on waveguides with diffraction gratings are the technology of choice for many device makers. They have evolved to provide excellent picture quality and large field of view to the users. However, the field of view is a key criterion for such waveguides and to further increase it the refractive index of the used materials has to be increased. With current manufacturing methods mostly nanoimprinted permanent polymers with inorganic high refractive nanoparticles are used. Commercial materials can already achieve refractive index of n=1.9 but it seems difficult to achieve refractive indices of n=2.0 and above. On the other side the glass substrates or coating are already available with a refractive index n=2.0 and higher and thus could be utilized directly for structuring the needed diffraction gratings. In this case a pattern transfer by etching is required which should enable binary grating designs as well as slanted grating. In this work the nanoimprint lithography patterning is investigated in combination with subsequent etching processes to achieve binary or slanted nanograting in high refractive TiO2 and glasses.
Ion Beam Sputter Deposition (IBSD) is a versatile technique particularly suited to applications requiring high quality, high performance layer materials as it allows independent and accurate control of the process parameters. Vanadium oxides, used for example in the fabrication of microbolometers, optical switches or optical storage, exhibit interesting properties such as a high Temperature Coefficient of Resistance (TCR), relatively low 1/f noise and a semiconductormetal phase transition close to room temperature. However, it is very challenging to control the stoichiometry of the deposited film as there are at least 25 different oxidation states of vanadium, few of which display the required electrical characteristics. In the present study, vanadium oxide thin layers were deposited by IBSD using an Oxford Ionfab300+ and analyzed with regard to their electrical properties. The impact of the system parameters on the resistance repeatability, wafer-to-wafer and batch-to-batch, was thoroughly investigated to provide the end user with a clear understanding of the factors affecting film resistivity while ensuring at the same time a steep variation of resistance with temperature, as notably required for uncooled bolometers. These parameters were balanced to also achieve a good deposition rate, throughput and uniformity over large device areas, compatible with the requirements of industrial applications.
The conventional wisdom to guarantee high purity thin films in IBSD has been to use a large vacuum chamber usually in excess of 1 m3. The chamber size was important to minimise the effect of reflected high energy particles from the target surface sputtering chamber materials onto the substrate and to allow the use of large targets to avoid beam overspill onto chamber furniture. An improved understanding of beam trajectories and re-sputtered material paths has allowed the deposition of thin films with very low metallic impurity content in a chamber volume below 0.5 m3. Thus, by optimizing the sputter ion source, target and substrate configuration, and by arranging suitable shielding made of an appropriate material in the process chamber, the levels of contaminants in the deposited films have been reduced to a minimum. With this optimum hardware arrangement, the ion beam process parameters were then optimized with respect to the ppm levels of contaminants measured in the films by SIMS analysis. Using the deposition of SiO2 as a standard material for DSIMS composition analysis and impurity level determination, it has been shown that our IBS deposition tool is capable of depositing films with contamination levels of <50ppm for the total of all metal impurities in the deposited films.
We show that asymmetric dual cavity filters, comprising one cavity of Ta2O5 (H) and the other of SiO2 (L), can be designed so that the asymmetry in the transmission intensity between the two peaks is sensitive enough to detect H/L ratio changes down to 1.0001. This accuracy is necessary for precise uniformity determinations for 100 GHz filter production. We show that interpretation of asymmetry changes is still valid despite small absorption or scatter losses due to either of the materials, and also despite small layer thickness errors which have been optically compensated by the optical monitoring system during deposition of the filter. We illustrate the use of asymmetry in adjusting the H/L ratio within 1.0001 at larger and smaller radii away from the optical monitor band on an 8" diameter disc, and also for checking azimuthal variations. Combining the asymmetry data with the wavelength shift data enabled the individual H and L calibrations to be deconvoluted from the multilayer data. This technique is far more accurate than measuring individual material calibration runs, and also takes account of multilayer effects such as interfacial mixing and process sequencing. Ion beam sputtering process parameters were varied to maximize the uniformity and increase the yield for cost-reduction of 100 GHz filters, and the application to 50 GHz filter yield enhancement is discussed.
Etching of patterned doped poly-Si and of patterned W or Al metal wafers with high selectivity, high anisotropy, and high rate is achieved using the newly developed MORI rf plasma source. The source operates at low pressure (typically 1 - 3 mtorr) and at 13.56 MHz while achieving high efficiency through the generation of an m equals 0 Whistler wave often referred to as the m equals 0 helicon wave. The chlorine etch selectivity of poly-Si to SiO2 can exceed 100, the selectivity of poly-Si to photoresist can exceed 10, and the poly-Si etch rate ranges from 2500 A/m to about 4000 A/m, depending upon wafer characteristics. The uniformity is less than 2% (1 sigma) and the chlorine ion saturation current exceeds 15 mA/cm2 above the wafer location. Uniform, anisotropic etching of Al-1% Si-0.5% Cu using pure Cl2 or Cl2-(5-20%) BCl3 at 1.5 - 3 mtorr achieves rates exceeding 6000 A/m with selectivity to photoresist (PR) of 9 and selectivity to oxide of 22 using a wafer rf bias power of 30 w at 13.56 MHz. Similarly excellent results are found in the etching of patterned W using SF6 at 3 mtorr. Etch rates exceed 2500 A/m with selectivity to PR greater than 2 and selectivity to oxide greater than 10.