High Power Pulsed Magnetron Sputtering (HPPMS)(excerpt)

The following text was excerpt from the webpage:
http://www.ifm.liu.se/plasma/reshppms.html
Glow discharge thin film deposition processes are technologically very important and are extensively used for industrial production of layers as well as in materials research, especially in facilitating in the creation of new advanced materials. Unlike evaporative techniques glow discharge plasmas can be tailored to obtain impinging particles with energies comparable to typical surface and molecular binding energies. This in turn gives yields increased adatom mobility as well as increased surface chemical reaction rates which give rise to epitaxial growth at reduced temperatures and synthesis of chemically metastable materials. Compound formation, in which the reactivity between constituents is the rate-limiting step also becomes easier. For instance, dissociation can occur as a result of energetic plasma processes, such as electron, ion, and photon irradiation.

An even greater advantage can be achieved if the deposition material itself is ionized (ionized sputtering). In this case the material can be accelerated to desired energies and guided in direction, using electrical or magnetical fields, to facilitate e.g. film substrate intermixing, nano- and microstructural modifications, and creation of metastable phases.Due to this interest in achieving a deposition flux in the form of ions rather than neutrals, several new ionized physical vapor deposition (IPVD) techniques have emerged giving this possibility [1]. These techniques are all based on the formation of very high plasma densities which makes it virtually impossible for the deposition atoms to escape from the vapor generation zone without becoming ionized by energetic electrons. The first IPVD systems consisted of a magnetron cathode for physical sputtering of atoms and a secondary inductively coupled plasma (ICP) discharge[2], by a secondary microwave driven discharge[3], or by shaping the cathode target in a particular way in order to confine the electrons, referred to as hollow cathode magnetron discharge[4]. High-power pulsed dc magnetrons in unipolar mode have been proposed for highly ionized sputtering[5,6]. In a conventional dc magnetron the power density is limited by the thermal load on the target, since most of the energy of the positive ions accelerated to the target is transformed into heat. In unipolar pulsing the power supply operates at low (or zero) power level and then pulses to a significantly higher level for a short period each cycle. When the peak power densities exceed 1 kW/cm2 we refer to the process as HPPMS. The peak power density is generally in the range 1-3 kW/cm2 at peak target voltage in the range 300-1500 V. Thus substantial increase in the instantaneous plasma density is achieved without increasing the thermal load of the target. The pulsed magnetron has been demonstrated for use in high-aspect-ratio filling applications and improved thickness homogeneity of the deposited films compared to conventional dc magnetrons[5].For a list of our recent publication in this field see the publication list.
[1] See for example: Ionized Physical Vapor Deposition, Ed. by JA Hopwood (Academic Press, London, 2000) or JM Schneider, SL Rohde, WD Sproul, and A Matthews, Recent Developments in Plasma Assisted Physical Vapour Deposition, Journal of Physics D 33, 2000, R173.
[2] Magnetron sputter deposition with high levels of metal ionization, S.M. Rossnagel and J. Hopwood, Appl. Phys. Lett. 63 (1993) 3285.
[3] Development of a cylindrical DC magnetron sputtering apparatus assisted by microwave plasma, A. Yonesu, H. Takemoto, M. Hirata, and Y. Yamashiro, Vacuum 66 (2002) 275.
[4] Hollow cathode magnetron, Z. Wang and S.A. Cohen, J. Vac. Sci. Technol. A 17 (1999) 77.
[5] novel pulsed magnetron sputter technique utilizing very high target power densities, V. Kouznetsov, K. Macák, J.M. Schneider, U. Helmersson, and I. Petrov, Surface and Coatings Technology 122 (1999) 290.