ICMCTF2004 Session B9/TS1: Pulsed Plasmas for Vapor Deposition

High power pulsed magnetron sputtering (HPPMS) has created growing interest, because it can generate highly ionized plasmas with high target material ion content. HPPMS applies a high power pulse (up to several megawatts) with short pulse width to the target. The result is a high degree of ionization of the plasma, consisting of sputtered species and process gas. The ions can improve the structure and properties of the deposited film. It has been shown that a significant flux of low energy ions to the substrate can result in dense equi-axed films. The HPPMS technique can generate large numbers of ions with essentially conventional magnetron sputtering apparatus. An experimental power supply was built in order to investigate HPPMS. It is capable of peak powers up to 3 megawatts with nominal pulse widths of 100-150 µsec. Average delivered power is up to 20 kW, at frequencies from single shot to 500 Hz. Temporally resolved optical spectroscopy of the plasma provides evidence of the ionization of the sputtered species. The degree of ionization is a function of the peak power delivered to the process. Very thin carbon films for potential hard disk applications have been deposited by HPPMS. The films have a density of 2.7 g/cm³, very high for sputtered carbon.¹ The power supply can detect and suppress arcs which enables HPPMS deposition of important materials which are prone to arcing, such as carbon and aluminum. In addition, the pulsing power supply circuitry incorporates wave-shaping to prevent arcing. This enables the pulse to transition directly from the glow to the highly ionized state without accessing the arc regime. Pulse discharge circuit considerations, optical spectra, electrical waveforms, process characteristics, and deposited film properties will be presented.

¹B. M. DeKoven, et al., accepted for publication in the Proceedings of the Society of Vacuum Coaters Technical Conference, San Francisco, May 2003.

High power pulsed magnetron-sputtering (HPPMS) offers the opportunity of producing a highly ionized metal plasma. The degree of ionization of the plasma is a function of the peak power in the pulse, and for sputtered metals such as aluminum the degree of ionization can exceed 50%. Previous work¹ with the reactive sputtering of aluminum oxide in an ionized PVD system demonstrated that it is possible to deposit crystalline alumina at temperatures below 500 degrees C. In this study, an experimental high power pulse power supply with special arc handling and pulse rise time features combined with partial pressure control of the reactive gas was used to evaluate the feasibility of reactively depositing crystalline alumina in an HPPMS system. Target arcing is particularly debilitating to the control of any reactive sputtering process, and the experimental power supply was capable of detecting and quenching arcs, which brought stability to the deposition process. In addition, the rising edge of the pulse was controlled to prevent the plasma from going from the abnormal glow discharge mode into the arc regime. The combination of these features allowed the reactive sputter deposition of aluminum oxide films using HPPMS. Details of the deposition process and results of the characterization of the deposited films will be reported.

¹J. M. Schneider, W. D. Sproul, A. A. Voevodin, and A. Matthews, "Crystalline Alumina Deposited at Low Temperature by Reactive Ionized Magnetron Sputtering," J. Vac. Sci. Technol. A, 15(3) (1997) 1084.

With the increasing popularity of pulsed plasma discharges a growing interest in time-resolved process characterization arose. Langmuir single and double probes enable one to determine plasma density and electron temperature as well as (in case of single probes) the plasma potential. Owing to the dimensions of the probe tips (typically 1 - 10 mm) a certain spatial resolution can be achieved. During the past years, time-resolved Langmuir probe technuiques have been developed and applied to pulsed magnetron sputtering processes. The talk is organised as follows:

i) As an introduction, a concise description of the Langmuir probe measurement and data evaluation techniques is given and it is shown how plasma parameters can be derived from the current-voltage characteristics of the probe. Peculiarities of Langmuir single and double probes are presented and practical problems to be faced in depositing plasma are discussed.

ii) In the past years, few groups have done time-resolved Langmuir probe investigations of pulsed magnetron discharges. These results are shortly reviewed, including own results of a time-resolved Langmuir double probe technique which was applied to a pulsed magnetron discharge at several 100 kHz used for MgO deposition. The tungsten probe tips were 500 µm in diameter, 10 mm in length and where placed parallel to each other in a distance of 5 mm. The time-resolved measurement was done by fixing the probe voltage and recording the probe current as a function of time. This was repeated for different voltages. Then, the matrix of the I_U(t) curves was transposed with a computer to yield for each time step the usual I(U) characteristic, from which plasma density and electron temperature were determined.

iii) All results are critically discussed in connection with the discharge characteristics as well as time-dependent processes in the plasma which may influence the time-resolved measurement.