Growth precursors

The substrate temperature is a very important deposition parameter, as it directly affects the kinetics of ad- and desorption of growth precursors, surface diffusion, and incorporation. Actual substrate temperatures may differ from substrate heater setpoints. Calibration of temperature readings is needed, so as to report the correct substrate temperature. 

Enhancement of surface diffusion of the growth precursors is considered as one of the beneficial effects of ion bombardment [246,428]. The potential energy of ions, which is released when the ion is neutralized, is typically 10 eV. This energy can be a substantial fraction of the total energy transferred. The release of this ionization energy is sufficient to excite atoms into excited electronic states, thereby weakening their bonds and enhancing their mobilities [429]. 

Nowadays, it is generally accepted that device quality a-Si H is obtained under PECVD conditions where the SiH radical is the predominant growth precursor [123, 137, 192]. At typical deposition temperatures and pressures the a-Si H surface is almost completely terminated by hydrogen atoms. The SiHj radical... 

As the speed of the reactions at the growing surface is increased when the temperature is raised, a temperature-dependent growth rate should basically be observed for LP-CVD process. In Fig. 6.19, the deposition rate and the consumption of DEZ (defined as the percentage of DEZ effectively used for ZnO growth, the rest of DEZ being pumped out of the chamber) are shown as a function of the substrate temperature for the LP-CVD process developed at IMT Neuchatel, which operates at 0.5mbar and uses DEZ and water vapors as growth precursors. 

The following paragraph discusses the particular case of boron-doped LP-CVD ZnO developed at IMT Neuchatel, for which DEZ and H2O are used as growth precursors. It describes in more detail the structural, optical, and electrical properties of the resulting ZnO films when the gas flow ratio H2O/DEZ is varied. 

Another emerging film growth technique that employs metal-organic film growth precursors is termed CBE (chemical beam epitaxy). CBE is a variant of the widely used MBE (molecular beam epitaxy) technique, except that metal-organic... 

Film growth precursors for lithium are limited owing to the tendency of lithinm componnds to form highnuclearity species... 

Interest in the development of metal-organic precursors for the lanthanide elements is due to the many important apphcations of lanthanide-containing materials. These include erbium-doped semiconductors for use as optical fiber communications, lanthanide-doped GaN for fiiU color displays, high-temperature superconductors, and lanthanide-doped ferroelectric see Ferroelectricity) phases. Despite the importance of these materials, lanthanide film growth precursors... 

The most common technique used to grow epitaxial SiC is CVD. The standard gas chemistry used is hydrogen-propane-silane, or TG-CsHs-SiEG, respectively. In this chemistry, C3H8 is the carbon growth precursor while SiTC is the silicon precursor. 

Gas-phase activation above the deposition surface is essential for achieving appreciable diamond growth rates. The various CVD methods differ primarily in the way they produce gas-phase activation. The most abundant carbon-containing gaseous species present in most activated systems are methyl radicals and acetylene molecules which are also considered to be predominant growth precursors for diamond, almost independent of the deposition methods used. However, in systems that dissociate a significant fraction of H2, such as DC plasma arc-jet CVD, carbon atoms, aside from acetylene, are also abundant in the gas phase. 

The SiHg radical is the dominant growth precursor for the formation of the a-Si H films in a low-temperature silane plasma [32]. Silane molecules are dissociated by energetic plasma electrons ... 

The substrate can either be positioned outside of (few mm) or immersed within the intense discharge region. The plasma is where the reaetive growth precursor(s) is formed and transported to the substrate surface. The key deposition parameters to control are the source gas composition, microwave power, system pressure, and substrate temperature. 

---