Yizhou Song

High-rate automated deposition system for the manufacture of complex multilayer coatings.

A previously described automated thin-film deposition system based on rf-magnetron sputtering could deposit quite complex optical multilayer systems with good precision and with no one in attendance [Sullivan and Dobrowolski, Appl. Opt. 32, 2351-2360 (1993)]. However, the deposition rate was slow, and the uniform area on the substrate was limited. We describe an ac-magnetron sputtering process in which the same deposition accuracy has been combined with significantly better film uniformity and a fivefold or sevenfold increase in the deposition rate. This makes the equipment of commercial interest. Experimental results are presented for several difficult coating problems.

Syntheses and optical properties of low-temperature SiOx and TiOx thin films prepared by plasma enhanced CVD

Abstract SiOx, TiOx and SiOx–TiOx mixed thin films were prepared by PECVD at a substrate temperature below 80°C using tetraethoxysilane (TEOS) and ethyltrimethylsilane (ETMS) for SiOx and titaniumtetraisopropoxide (TTIP) for TiOx, respectively. Optimal deposition conditions for preparing SiOH free ETMS SiOx are control of the external magnetic field and use of Ar as a excitation gas. The refractive index of SiOx increased with the ratio of infrared absorption intensity of Si–C to that of Si–O, which is related to the stoichiometry of SiOx determined by Si–O–Si stretching absorption frequency and XPS analysis. The refractive index (n) of SiOx varied from 1.459–1.559 with extinction coefficient (k) lower than 3.0×10−4. This index of TiOx was from 1.750–2.047 and k lower than 2.0×10−3. The refractive index of mixed SiOx–TiOx thin film can be varied from 1.460–1.820 by controlling fraction constituents content.

Manufacture of complex optical multilayer filters using an automated deposition system

Abstract It is now possible to design complex thin film multilayer coatings that can achieve almost any desired spectral performance. Moreover, these coatings can consist of tens or hundreds of layers each of which may have a different thickness. It is a challenge to accurately manufacture such complex coatings. An automated deposition system (ADS) has been developed which is able to fabricate complex optical coatings on a routine basis. This deposition system uses a wideband optical monitor to accurately determine the deposited layer thickness and to re-optimize the remaining layer thicknesses, if required. One advantage of this process is that no operators are required during the manufacture of a filter. For this technique to work, however, an energetic deposition process such as sputtering is necessary in order to achieve thin films with a bulk-like refractive index with little or no porosity or inhomogeneity. As well, the optical constants of the thin film materials must be accurately known. A number of thin film filters have been manufactured using this ADS. These include all-dielectric coatings as well as metal/dielectric filters. In this paper, the ADS and the real-time process control algorithms will be described in more detail and several examples of manufactured complex thin film filters will be described for different applications.

Optical and structural properties of low-temperature PECVD ETMS SiOx thin films

Abstract SiOx thin films were prepared via a PECVD system at a substrate temperature below 70°C using ethyltrimethylsilane (ETMS). The refractive index (n) of SiOx increased with increasing carbon concentration in the film, which is related to the stoichiometry of SiOx determined by both Si–O–Si stretching absorption frequency and XPS analysis. No notable Si–OH FTIR absorption was observed in ETMS SiOx. FTIR carbon free SiO2 film, which showed a bulk-like refractive index, was prepared with a deposition rate of 0.16 nm/s. The external magnetic field and Ar inert gas strongly influence SiOx physical properties. Such effects may be due to the enhancement of the excited atomic oxygen and Ar in situ monitored by optical emission spectroscopy (OES).

Development of large diameter radical beam sources

We developed radical beam sources with beam diameters larger than 100 mm intending to increase the productivity for thin film processes. Radical species were generated by using inductively coupled plasma generators driven by a RF (13.56 MHz) power supply. The relative density of oxygen radical was evaluated by OES (optical emission spectroscopy) peak at 845 nm, which is related to oxygen radiation from 3p3P to 3s3S, and the absolute density by Ag oxidization. The properties of the radical source depend strongly on the shape and volume of the plasma chamber and the configuration of the RF antenna. The maximum oxygen radical density is 1.24 × 10 15 atoms/cm 2 s at 100 mm from the end of beam source. It is two orders of magnitude higher than the ion density.