The semiconductor industry uses a large amount of perfluoro compounds (PFCs), and their impact on global warming has become a major environmental concern. In the semiconductor industry, PFC are used to periodically remove deposits from the chamber walls of chemical vapor deposition (CVD) reactors after film deposition. These chamber clean processes account for typically 50%–70% of the PFC usage in a semiconductor wafer fabrication site, the rest being mainly used for wafer-etching processes. With a conventional parallel plate radio frequency (rf) plasma reactor, the PFC gas utilization is incomplete and a large fraction of unreacted gas can be emitted in the atmosphere. This paper describes a microwave plasma source that provides as high as 99.9% utilization removal efficiency (URE) of the reactant gas (NF3) during chamber clean. This technology brings the million metric tons carbon equivalent (MMTCE) of a chamber clean to negligible levels and also enhances the chamber clean efficiency and the system throughput. Here we review the requirements for the manufacturability of a remote plasma clean process. Gaseous Fourier transform infrared and quadrupole mass spectroscopy techniques have been used to characterize the clean process, the by-products of the reaction, and the efficiency in reducing the MMTCE of CVD chamber cleans.

The fluorine atomic radical reactions to form molecular fluorine and hydrogen fluoride are examined by time-of-flight mass spectroscopy (TOFMS) and kinetically modeled for various reaction orders. Fluorine radicals are generated from NF 3 or F 2 in microwave-generated and low-frequency (LF)-generated plasmas and are passed through flow tubes under various flow, pressure, and dilution conditions. In general, the concentrations of the mass spectroscopically measured products F, F 2 , and HF do not depend on the specific wall material (e.g., Teflon, stainless steel, Al, Ni, Al 2 O 3 , SiO 2 ); the only variations of [F]/[F 2 ]/[HF] ratios with wall material are found at pressures below 1 Torr. The most significant changes in these ratios are observed upon varying flow rates and pressures. Specifically, the F relative concentration decreases from ∼80% to ∼20%, and the F 2 relative concentration increases from ∼20% to ∼80%, as the pressure is varied over the range 0.5-10 Torr. In all cases, the HF concentration is found to decrease as the pressure increases. Data suggest that the composition of the tube surface material does not contribute significantly to the generation of F 2 ; however, since the wall surface carries adsorbed hydrogen sources such as H, H 2 O, H 2 , and OH, it becomes important in the generation of HF. A simple kinetic analysis of the experimental data suggests a combined two-reaction mechanism for F 2 and HF generation: (1) a pseudo-second-order volume reaction (k v ) to generate F 2 , and (2) a zero-or first-order wall reaction (k w ) to generate HF. Thus, both surface and volume reactions contribute to the overall F atom loss mechanism in the gas flow from the plasma source. The model fits our data best for a k v /k w ratio of about 75. The reaction order for the loss of F atom is found to be 1.68, while the reaction order for the formation of F 2 is found to be ∼2.

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The cost of photovoltaic (PV) energy generation has been steadily reduced with the increase of solar cell power conversion efficiency and the drop of manufacturing cost. An effective way of lowering the cost of Si thin film solar cells is to increase the solar panel size by growing thin films on large area substrates, where it is important to maintain uniform film properties to ensure efficient and consistent PV performance. In this study, we control the thickness and crystalline volume fraction uniformities of Si films grown on 5.7 m 2 glass substrates in ratio-frequency (RF) plasma enhanced chemical vapor deposition (PECVD) chambers by balancing the RF power distribution. Crystalline volume fraction uniformity of 3% was obtained in µc-Si:H films. Tandem junction (TJ) solar cells of the structure glass/SnO2:F/a-Si:H/µc-Si:H/ZnO:Al/Ag were grown with the balanced RF feed. With the uniform film deposition, the 5.7 m 2 solar panels achieved stabilized aperture efficiency η > 8%.