Deposition rates

Optical trapping can also be used as a hthographic tool (90). For example, a combination of optical molasses and an optical standing wave have been used to focus a beam of neutral sodium atoms and deposit them in the desired pattern on a suitable substrate (eg, siUcon). Pattern resolutions of the order of 40 nm with good contrast (up to 10 1 between the intended features and the surrounding unpattemed areas) and deposition rates of about 20 nm /min were obtained (90). 

Deposition rates using this process are limited by the fact that each electrode contains a finite amount of filler metal. The time required both to change electrodes and to remove the slag coating between each weld pass lowers the overall productivity of the process. 

The result is the formation of a dense and uniform metal oxide layer in which the deposition rate is controlled by the diffusion rate of ionic species and the concentration of electronic charge carriers. This procedure is used to fabricate the thin layer of soHd electrolyte (yttria-stabilized 2irconia) and the interconnection (Mg-doped lanthanum chromite). 

Pa (10 10 ° Torr)) condition such that the volatile species travels at a relatively high velocity to the substrate wafer. The growth rate is 0.01-0.3 ///min which starts to be competitive with CVD deposition rates. 

Dielectric Film Deposition. Dielectric films are found in all VLSI circuits to provide insulation between conducting layers, as diffusion and ion implantation (qv) masks, for diffusion from doped oxides, to cap doped films to prevent outdiffusion, and for passivating devices as a measure of protection against external contamination, moisture, and scratches. Properties that define the nature and function of dielectric films are the dielectric constant, the process temperature, and specific fabrication characteristics such as step coverage, gap-filling capabihties, density stress, contamination, thickness uniformity, deposition rate, and moisture resistance (2). Several processes are used to deposit dielectric films including atmospheric pressure CVD (APCVD), low pressure CVD (LPCVD), or plasma-enhanced CVD (PECVD) (see Plasma technology). 

Polysilicon. Polysihcon is used as the gate electrode material in MOS devices, as a conducting material for multilevel metallization, and as contact material for devices having shallow junctions. It is prepared by pyrolyzing silane, SiH, at 575—650°C in a low pressure reactor. The temperature of the process affects the properties of the final film. Higher process temperatures increase the deposition rate, but degrade the uniformity of the layer. Lower temperatures may improve the uniformity, but reduce the throughput to an impractical level. 

The cobalt deposition rate on new, replacement, or decontaminated recirculation piping surface has been reduced by pretreating the piping using an atmosphere of oxygenated wet steam to form an oxide film (25). Studies have been conducted for both PWRs and BWRs to reduce the cobalt content of materials used in the nuclear parts of the plants, particularly in hardened and wear surfaces where cobalt-base alloys ( 50% Co) are used (26). Some low cobalt materials have been developed however, the use of the materials is limited to replacement parts or new plants. 

The key determinants of future cost competitiveness of a-Si H PV technology are a-Si H deposition rates, module production yields, stabilized module efficiencies, production volume, and module design. Reported a-Si H deposition rates vary by more than a factor of 10, but most researchers report that the high quaUty films necessary for high stabilized efficiencies require low deposition rates often due to high hydrogen dhution of the Si (and Ge) source gases (see Semiconductors, amorphous). 

Fibrous stmctures represent a grain refinement of columnar stmcture. Stress-reHeving additives, eg, saccharin or coumarin, promote such refinement, as do high deposition rates. These may be considered intermediate in properties between columnar and fine-grained stmctures. 

The state-of-the-art i -Si H films (Table 3) are deposited at the rate of 1—3 A/s with the gas utilization rate on the order of 15%. Larger gas utilization rates, hence larger deposition rates, usually result in inferior properties than those indicated in Table 3. Increasing the deposition rate by merely increasing the power leads to dust formation. The use of higher excitation frequency can lead to deposition rates in excess of 15 A/s and still give relatively good film properties (7). 

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