Drop In Deposition Rate Research Articles

EQCM and EIS characterization of electrochemical deposition of tin from aqueous solution containing pyrophosphate

Electroless plating of tin layers with thicknesses of more than 3 μm is becoming an important process in the production of circuit boards and semiconductor. Phosphonates constitute promising complexing agents for autocatalytic tin electrolytes. However, detailed time-resolved investigations or electrochemical impedance spectroscopy (EIS) measurements of tin deposition in this system are lacking. Here, deposition of tin was investigated by electrochemical quartz microbalance (EQCM) and electrochemical impedance spectroscopy. EQCM investigations showed a strong drop in deposition rate within the first ten minutes. Bath parameters had a significant effect on the drop of deposition rate. The results indicated an inhibitive pyrophosphate adsorption on the tin electrode surface which caused the observed drop of deposition rate. Impedance measurements confirmed this assumption. The equivalent circuit applied for the analysis of EIS data, included an increasing adsorbate resistance Rp, which can be related to the thickness of an adsorbed permeable pyrophosphate layer. Impedance measurements at selected frequencies revealed a linear relation between deposition rate and conductance 1/Rp. Subsequently, gluconate substituting for pyrophosphate was tested as complexing agent. Combined EQCM and EIS measurements during deposition using a gluconate containing electrolyte showed a stable rate with an invariant conductance.

Industrial-scale high power impulse magnetron sputtering of yttria-stabilized zirconia on porous NiO/YSZ fuel cell anodes

Yttria-stabilized zirconia (YSZ) thin films are reactively sputter-deposited by high power impulse magnetron sputtering (HiPIMS) in an industrial setup on porous NiO/YSZ fuel cell anodes. The influence of deposition pressure, cathode peak power density, and substrate bias voltage on the deposition rate and film morphology is studied. It is seen that increasing the deposition pressure from ~370mPa to ~750mPa results in a 64% increase in the deposition rate and denser film. Films are deposited at peak power densities ranging from 0.4kWcm−2 to 1.1kWcm−2. By increasing the peak power density the degree of ionization of both Ar and sputtered metallic species is significantly increased which results in denser films as open column boundaries are removed. The increase in peak power also results in a considerable drop in deposition rate. By combining a peak power density of 0.6kWcm−2 with the application of −180V substrate bias voltage a homogenous and essentially column-free coating can be deposited. These results demonstrate HiPIMS deposition as being capable of producing dense YSZ coatings on porous substrates as needed for solid oxide fuel cell applications.

Macroscopic Approach to Plasma Polymerization Using the Concept of Energy Density

AbstractThe film growth and the properties of plasma polymers are determined by gas phase and surface reactions. In order to gain more insights and to optimize plasma polymerization processes, some assumptions can be made that allow a macroscopic approach. Therefore, a concept was developed based on the energy input both into the gas phase (plasma) and during film growth (surface) that helps to distinguish between predominating gas phase or surface processes. Different experimental series using gas mixtures of C2H4 with CO2 or N2/H2 were performed at different power inputs W and gas flow rates F. Thereby, the same range of specific energy input W/F can be maintained at different ion bombardment to the substrate. The results indicate that changes in film growth were initiated by plasma chemical processes for CO2/C2H4 discharges (scavenger effects), while the obtained drop in deposition rate at high energy input values for N2/H2/C2H4 is caused by the energy dissipated in the film during growth pointing towards a threshold energy for chemical sputtering.magnified image

Growth Mechanism of Oxygen-Containing Functional Plasma Polymers

Regarding the recent debate on the usefulness of macroscopic kinetics for plasma polymerization, we further investigated the deposition of oxygen-containing functional plasma polymers based on low pressure CO2/C2H4 RF discharges in order to find differences and transitions in the growth mechanism. A reduction in deposition rate with increasing CO2/C2H4 ratio and a drop in deposition rate at enhanced energy input have been observed. Both effects are found to be mainly related to plasma-chemical processes such as the production of film-forming species and oxidation in the gas phase. In contrast to plasma etching with non-polymerizing gases, ion-enhanced etching effects were found to play a secondary role for the deposition of oxygen-containing functional plasma polymers.

The influence of the filament temperature on the structure of hot-wire deposited silicon

Exposure to hydrogen significantly cools the filament from the set temperature. This can mainly be explained by the power dissipation due to dissociation of hydrogen. The effect of silane on the filament temperature is more complicated. Below a certain threshold temperature (1850 K for W, 1750 K for Ta) a silicon-rich silicide is deposited on the filament, partially shielding it for further dissociation reactions. A drop in deposition rate accompanies this. Above another but higher threshold temperature (2000 K for W and 1950 K for Ta) the silicon-rich silicide is evaporated from the filament and the dissociation reactions occurred and thus the deposition rate are restored. Below these threshold temperatures (2 2 0) oriented materials can be produced.

Investigation of scaling-up issues in hot-wire CVD of polycrystalline silicon

In order to apply device quality polycrystalline silicon obtained by the hot-wire chemical vapour deposition technique in industrial processes a high deposition rate is desirable. Meanwhile it is important to maintain good thickness uniformity over large areas. To achieve this the catalytic area needs to be increased. The influence of increasing the catalytic area on the deposition rate and material properties was studied. Proportionally increasing the feedstock gas flows leads to an unexpected drop in deposition rate. The dissociation of the gases causes the filament temperature to decrease. Below 1850 K the dissociation process is limited by the silicon deposition on the filament. This leads to a drastic drop in deposition rate. By adjusting the process parameters to the increased catalytic area, device quality polycrystalline silicon is again obtained. The deposition rate of polycrystalline silicon has been increased from 6 to 21 Å/s while maintaining the material properties.

Organic-inorganic character of plasma-polymerized hexamethyldisiloxane

Plasma polymerization is a useful method for depositing thin films on substrates. The films formed are cross-linked, and their character depends on the plasma polymerization process conditions. The influence of power and monomer flow rate on the character of plasma-polymerized hexamethyldisiloxane (PPHMDSO) was investigated. The deposition rate increased strongly with HMDSO flow rate at low powers, indicating that the plasma is mono-mer-deficient. Increasing the power yielded a rapid drop in deposition rate, which reached a relatively flow rate-independent plateau at high power. At high flow rates and low powers, the similarity between the plasma polymer with its high hydrocarbon concentration and the monomer was greatest. At high powers, the monomer was more intensively fragmented yielding a more inorganic structure rich in silicon and oxygen. Generally, the plasma polymer seems to be a silicon-oxygen network with short hydrocarbon chains that may include hydroxyl and/or carbonyl groups attached to the silicon in the backbone. The inorganic nature of the plasma polymer at high powers and low flow rates is reflected in its relatively high polar component of surface tension. © 1996 John Wiley & Sons, Inc.