Michelle Marie S. Villamayor

Process stabilization by peak current regulation in reactive high-power impulse magnetron sputtering of hafnium nitride

A simple and cost effective approach to stabilize the sputtering process in the transition zone during reactive high-power impulse magnetron sputtering (HiPIMS) is proposed. The method is based on real-time monitoring and control of the discharge current waveforms. To stabilize the process conditions at a given set point, a feedback control system was implemented that automatically regulates the pulse frequency, and thereby the average sputtering power, to maintain a constant maximum discharge current. In the present study, the variation of the pulse current waveforms over a wide range of reactive gas flows and pulse frequencies during a reactive HiPIMS process of Hf-N in an Ar-N2 atmosphere illustrates that the discharge current waveform is a an excellent indicator of the process conditions. Activating the reactive HiPIMS peak current regulation, stable process conditions were maintained when varying the N2 flow from 2.1 to 3.5 sccm by an automatic adjustment of the pulse frequency from 600 Hz to 1150 Hz and consequently an increase of the average power from 110 to 270 W. Hf-N films deposited using peak current regulation exhibited a stable stoichiometry, a nearly constant power-normalized deposition rate, and a polycrystalline cubic phase Hf-N with (111)- preferred orientation over the entire reactive gas flow range investigated. The physical reasons for the change in the current pulse waveform for different process conditions are discussed in some detail.

High Dynamic Range Imaging of Magnetized Sheet Plasma

High dynamic range (HDR) imaging was used to obtain a wide intensity map of a magnetized sheet plasma. A set of 12 low dynamic range (LDR) photographs with various shutter speeds (1/200-1/2 s) was captured with an Olympus FE-19 digital camera. The LDR images were processed to recover color channel response functions of the camera needed to produce RGB radiance maps. The HDR image was finally generated from the combined radiance maps via linear tone mapping. By comparison of histograms, the HDR image uses the whole range of intensity values compared with the underexposed and overexposed LDR images.

Sheet Plasma Configurations Suitable for Materials Processing

A sheet plasma device can produce a steady state high density plasma with strong density and temperature gradients. These characteristics provide efficient formation of negative hydrogen (H) ions over a wide beam extraction area through the so called electron volume process [1]. The device configuration is suitable for plasma based materials processing. Concentrated plasma flow of the magnetized sheet plasma realizes rapid sputtering of target materials, and the produced flux of sputtered atoms can form thin functional films [2]. The cathode structure injects mono-energetic electron beam into sheet plasma that enables production of specific species of ions, excited neutral atoms and molecules in the produced plasma. A small sheet plasma device has been built to produce H ions, and was utilized to demonstrate the capability of controlling the surface structure of a Si substrate [3].

Color-based tracking of plasma dust particles

Color-based tracking to observe agglomeration of deposited particles inside a compact planar magnetron during plasma discharge was done by creating high dynamic range (HDR) images of photos captured by a Pentax K10D digital camera. Carbon erosion and redeposition was also monitored using the technique. The HDR images were subjected to a chromaticity-based constraint discoloration inside the plasma chamber indicating film formation or carbon redeposition. Results show that dust deposition occurs first near the evacuation pumps due to the pressure gradient and then accumulates at the positively charged walls of the chamber. This method can be applied to monitor dust formation during dusty plasma experiments without major modification of plasma devices, useful especially for large fusion reactors.

Transparent ZnO thin film deposition by a compact planar magnetron plasma device

A 120 mm diameter by 80 mm compact planar DC magnetron device capable of maintaining a pure H2O discharge was used to deposit conducting transparent ZnO thin film on glass substrates via plasma enhanced chemical vapor deposition (PECVD). A square Zn target with an area of 55 × 55 mm2 placed at the cathode was sputtered by argon-oxygen plasma at 100 mA discharge current and −550 to −680 V discharge potential. Gaseous H2O was introduced into the system as a source of reactive oxygen at 600 mPa in addition to argon fed at 100 mPa. For the deposition duration of 3, 5, and 7 min, the thickness measured was 21.5, 15, and 16 nm, respectively. The interface between the glass and oxide layer was dependent on the deposition duration — smooth for the 3-min deposition and rough for the 5 and 7 min durations. FTIR and UV–vis spectrometries show % transmittance in UV to IR range is inversely proportional to deposition time. The thin films exhibited electrical conductance.

Enhancement mechanism of H- production and suitable configurations for materials processing in a magnetized sheet plasma

A magnetized sheet plasma ion source was developed for steady state high density plasma with strong density and high temperature gradients. This feature provides efficient formation of negative hydrogen (H-) ions over a wide beam extraction area through the electron volume process. A hexapole confinement at the cathode, addition of argon and magnesium seeding led to the increase of H- yield. The device configuration is suitable for plasma based materials processing namely, synthesis of TiN, SiH, SnO2, and the formation of advanced MAX phase materials Ti2AlC, Ti2CdC and NbAlC.