A. Palmero

One-dimensional analysis of the rate of plasma-assisted sputter deposition

In this article a recently developed model [A. Palmero, H. Rudolph, and F. H. P. M. Habraken, Appl. Phys. Lett. 89, 211501 (2006)] is applied to analyze the transport of sputtered material from the cathode toward the growing film when using a plasma-assisted sputtering deposition technique. The argon pressure dependence of the deposition rate of aluminum, silicon, vanadium, chromium, germanium, tantalum, and tungsten under several different experimental conditions has been analyzed by fitting experimental results from the literature to the above-mentioned theory. Good fits are obtained. Three quantities are deduced from the fit: the temperature of the cathode and of the growing film, and the value of the effective cross section for thermalization due to elastic scattering of a sputtered particle on background gas atoms. The values derived from the fits for the growing film and cathode temperature are very similar to those experimentally determined and reported in the literature. The effective cross sectio...

On the ion and neutral atom bombardment of the growth surface in magnetron plasma sputter deposition

The energy distribution of positive argon ions bombarding the substrate during radiofrequency magnetron sputter deposition has been measured as a function of the argon pressure. The results are related to measurements of the plasma potential distribution and understood invoking the occurrence of resonant charge transfer reactions. This effectively lowers the ion bombardment energy and causes the bombardment of the growth surface with neutrals of a few eV kinetic energy in the pressure range of 0.1–1Pa.

Characterization of the plasma in a radio-frequency magnetron sputtering system

In order to understand the fundamental mechanisms in a radio-frequency magnetron sputtering system, the main properties of the argon plasma used in the process have been measured. A complete three-dimensional map of the ion density, electron temperature, and plasma potential has been obtained using a Langmuir probe. The electron temperature as well as the ion density have been found to increase in the region of the so called race track at the cathode. Furthermore, from the plasma potential map, the time-averaged local electric field has been obtained, pointing out the race track as the region where the most intense ion bombardment takes place. Besides, only the ions produced near the race track are accelerated towards the cathode, whereas those produced in the remaining volume move towards the anode. Finally, the dependence of the plasma quantities on the incident radio-frequency power and deposition pressure has been studied. The plasma potential measured using the Langmuir probe has been found to agree ...

Generalized Keller-Simmons formula for nonisothermal plasma-assisted sputtering depositions

A general description of the relation between the sputtering rate and the deposition rate in plasma-assisted sputtering deposition has been developed. The equation derived yields the so-called Keller-Simmons [IBM J. Res. Dev. 23, 24 (1979)] formula in the limit of zero thermal gradients in the deposition system. It is shown that the Keller-Simmons formula can still be applied to fit the experimental results if the characteristic pressure-distance product, p0L0, is related to the temperature of the sputter cathode and the growing film. Using this relation, it is found that the variations in the values for p0L0 for different experimental conditions agree with the thus far not well understood experimental trends reported in the literature.

Characterization of a low-pressure argon plasma using optical emission spectroscopy and a global model

The excitation mechanisms of the lower lying excited levels in a low-ionized, low-pressure, argon plasma are modeled and studied in order to characterize the plasma through optical emission spectroscopy. It is found that the lower lying excited states of argon play an important role in the excitation and that they must be taken explicitly into account for an accurate determination of the excitation rates. The possible influence of radiative cascades from upper argon excited states, which are not included in the model, has been studied by introducing an effective level in the description and studying its influence on the results. The model has been used to calculate the electron density and electron temperature in an argon magnetron sputtering plasma produced at different electromagnetic powers and gas pressures, as a function of the intensity of the optical emission lines λ1=750.38nm and λ2=696.54nm. The results obtained from the model have been compared with Langmuir probe measurements, showing a good ag...

Study of the a-Si/a-SiO2 interface deposited by r.f. magnetron sputtering

Abstract Samples of a-Si/a-SiO2 have been deposited on (100) c-Si substrates by r.f. magnetron sputtering from a polycrystalline-silicon target in an Ar/O2 gas mixture. Samples were either multi-layered stacks of a-Si/a-SiO2 or consist of a 50 nm a-Si intermediate layer covered by a single thin a-SiO2 (between 1 and 12 nm) layer. Two different procedures are used for deposition: (a) the transition from a-Si to SiO2 is made by addition of oxygen while the plasma is kept uninterrupted; (b) the transition is made by interrupting the r.f. power and Ar flow, followed by pumping the chamber to high vacuum before starting the combined Ar/O2 flow until process pressure is reached. Then the plasma is re-ignited. The atomic neighbors of Si in the top layer are investigated by X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR). We find that the interface region is best characterized by a SiOx layer with x gradually increasing from 0 to 2 when the distance to the surface increases from 0 up to 3 nm for procedure (b) and 6 nm for procedure (a). The large interface width is attributed to the 40 s necessary to obtain a steady state concentration of atomic oxygen in the plasma as monitored in-situ by optical emission spectroscopy (OES).

Distinct processes in radio-frequency reactive magnetron plasma sputter deposition of silicon suboxide films

A detailed investigation of the distinct processes in radio-frequency reactive magnetron plasma sputter deposition of SiOx films in a O2∕Ar atmosphere has been carried out, using the experimental evaluation of the individual growth rates of silicon and oxygen and of the ion impingement on the growth surface. Experimental variables are the total pressure, the oxygen partial pressure necessary to grow layers with 0⩽x⩽2, the RF power, the substrate temperature during deposition and the height of the cathode with respect to the growth surface. The various possible contributions to the silicon and oxygen incorporation on the growth surface have been distinguished and the magnitude of their contribution estimated, including that of sputtered SiO molecules. A model concerning the oxygen coverage on the cathode erosion area during sputtering is discussed, including the transition from the metallic cathode to the poisoned, nonmetallic, cathode.