Gas flow sputtering

Fig. 9.4.11 Apparatus for the gas flow-sputtering method. A sputtering gas (mixture of He and 40% H2) was supplied from nozzle A. Produced particles are flowed into the other port B and trapped by a solution trap apparatus cooled at approximately - 50°C. (From Ref. 16.)...

Hollow cathode gas flow sputtering operates in the pressure range of 0.1-1 mbar. The particles are thermalized at the substrate. Plasma activation of growth processes can be achieved either by applying a substrate bias or by pulsed mode operation of the discharge. 

Fig. 5.33. Schematic diagram of hollow cathode gas flow sputtering. Total pressure pt.ot, 0.1 — lmbar. Gas flow q( Ar) fsl — 5slm for 75 cm target length...

Ishii, K., 1989. High-rate low kinetic energy gas-flow-sputtering system. J. Vac. Sci. Technol. A... 

The sputtered vapor may be entrained in a gas (1 Torr) flow to give gas flow sputtering Figure 7.7 shows one such arrangement. 

Figure 7.7 Gas Flow Sputtering. Adapted from Leyens et al. (2008) ...

K. Ishi, H. Hamakake, Gas flow-sputtering for vapor deposition and cluster deposition, in Proceedings of the 43rd Aimual Technical Conference, Society of Vacuum Coaters, 2000, p. 107. 

A tubular hollow sputtering cathode with a gas flow through it is used in the gas flow sputtering source (Figure... 

Synthesis of nano-structured alloys by the inert gas evaporation technique A precursor material, either a single metal or a compound, is evaporated at low temperature, producing atom clusters through homogeneous condensation via collisions with gas atoms in the proximity of a cold collection surface. To avoid cluster coalescence, the clusters are removed from the deposition region by natural gas convection or forced gas flow. A similar technique is sputtering (ejection of atoms or clusters by an accelerated focused beam of an inert gas, see 6.9.3). 

The glass coating process requires high gas flows for the sputter processes as well as low hydrocarbon concentration. The only vacuum pump which satisfies these requirements as well as high pumping speed stability over time are turbo-molecular pumps which are used almost exclusively. 

Cong and co-workers [54] have prepared a ternary library of transition metals by sputter deposition on a quartz wafer. The catalyst samples were supplied with reactants through a concentric tube that also delivered the product gas flow to a sensor for spectroscopic analysis (see Chapter 3). The catalysts could be activated by a C02 heating laser from the backside of the wafer. 

Formation of metal clusters by gas aggregation, in which metal atoms are evaporated or sputtered into a cooled inert gas flow at relatively high pressure, has been well established in last decade. By repeated collisions with the carrier gas, the supersaturated metal vapor nucleates and forms clusters. The mechanism of cluster formation can be explained with homogeneous and heterogeneous nucleation theories. The gas aggregation methods have been applied extensively to produce small clusters of metals such as zinc, copper, silver etc. [23-26]. In some cases this method was used in combination with a mass filter such as a quadruple or a time-of-flight spectrometer [27, 28], The metal vapor for cluster source can be produced by either thermal evaporation [23-28] or sputter discharge [22, 29]. 

Fig. 5.6. Reactive sputter process for depositing the compound film AB. (a) Balance of reactive gas flow Qtot, which is partially gettered at the target (Qt) and at the substrate (Qc) and partially pumped by the vacuum pump (Qp). The fraction of the target surface At that is covered by the compound AB is 6>t. The fraction of the collecting area Ac covered is Gc. j is the sputter current density, (b) Definition of particle fluxes that alter the target and collecting area coverage fractions 6>t and 6>c (see text), (modified from [70])...

Figure 5.13 shows the dependence of O2 partial pressure on discharge power and the growth rate achieved for ZnO deposition at different substrate temperatures using reactive MF magnetron sputtering. The O2 partial pressure was measured with a A-probe and the discharge power was controlled at constant gas flow. The experimental conditions are summarized in Table 5.3. 

The transition mode process control described above is the key to reactive magnetron sputtering of ZnO Al films. Several approaches have proven to be useful, either adjusting the reactive gas flow or the discharge power as a function of appropriate process variables. 

Fig. 5.25. Dual magnetron configuration for MF reactive magnetron transitionmode sputtering. Fast PEM control of the reactive gas flow inlet is applied via a piezoelectric valve for the gas inlet between the targets is used. Either all oxygen can be introduced between the cathodes or the total flow can be divided such that most of the reactive gas is introduced via the outer gas lines...

Understanding the dependence of film structure and morphology on system layout and process parameters is a core topic for the further development of ZnO technology. Work is being performed on in situ characterization of deposition processes. Growth processes are simulated using Direct Simulation Monte-Carlo (DSMC) techniques to simulate the gas flow and sputter kinetics simulation and Particle-ln-Cell Monte-Carlo (PICMC) techniques for the plasma simulation [132]. 

Fig. 8.20. SEM micrographs of etched ZnO Al surfaces. The films were prepared by reactive MF-sputtering at different working points with decreasing oxygen partial pressure from left to right. The etching was done in KOH (top), HC1 (middle), or by an ion beam of 3keV (oxygen/argon gas mixture, gas flows 50 seem each) in a vacuum chamber (bottom). More details can be found in [124]...

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