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Cold spray has been used to manufacture more than 800 Cu-In-Ga (CIG) sputter targets for deposition of high-efficiency photovoltaic thin films. It is a preferred technique since it enables high deposit purity and transfer of non-equilibrium alloy states to the target material. In this work, an integrated approach to reliability assessment of such targets with deposit weight in excess of 50 lb. is undertaken, involving thermal-mechanical characterization of the material in as-deposited condition, characterization of the interface adhesion on cylindrical substrate in as-deposited condition, and developing means to assess target integrity under thermal-mechanical loads during the physical vapor deposition (PVD) sputtering process. Mechanical characterization of cold spray deposited CIG alloy is accomplished through the use of indentation testing and adaptation of Brazilian disk test. A custom lever test was developed to characterize adhesion along the cylindrical interface between the CIG deposit and cylindrical substrate, overcoming limitations of current standards. A cohesive zone model for crack initiation and propagation at the deposit interface is developed and validated using the lever test and later used to simulate the potential catastrophic target failure in the PVD process. It is shown that this approach enables reliability assessment of sputter targets and improves robustness.

In this work the Brazilian disc test technique is applied to mechanical characterization of cold-sprayed Cu-In-Ga deposits. The main advantage of the test is that the material can be tested in its end product form while naturally attending to the distribution of micro-structural phases and flaws by choosing an appropriate specimen size. The stress state of the test specimen can be obtained in analytical closed form and testing can be readily extended to obtain the stress-strain curve. While limited to low ductility materials the Brazilian disc test appears ideal for testing as-sprayed cold spray deposits due to their typically brittle nature.

Conventional magnetron sputter deposition with a rf inductively coupled plasma (ICP) has demonstrated that ionized metal fluxes can be effectively utilized to fill trenches and vias with high aspect ratios. The ICP is created with a seven turn (1/2 wavelength), water cooled coil located between the magnetron cathode and the substrate. A large fraction of the metal atoms sputtered from the magnetron cathode are ionized by the ICP. These ions are accelerated across the sheath toward the substrate and deposited at normal incidence, by placing a negative bias on the substrate. A gridded energy analyzer configured with a quartz crystal microbalance is located in the center of the substrate plane to determine the ion and neutral deposition rates. While keeping the magnetron power, rf coil, target to substrate distance, pressure and diagnostic location constant, the ionization fraction was measured for two metal targets: Cu and Ti using three different working gases: Kr, Ar and Ne. Variations in target materials...

A helicon antenna that sits remotely outside the vacuum system is attached to a magnetron sputtering system. This increases the electron temperature, which increases the ionization of the sputter flux for achieving ionized physical vapor deposition (IPVD). There are no shadowing and contamination problems, unlike other IPVD devices with immersed coils, since the helicon antenna is outside the vacuum system. Furthermore, the target to substrate distance can be kept small. At 2 kW magnetron power, 4 kW helicon power, 45 mTorr argon gas, and with a copper target, ionization fractions to the substrate of 51±10% and a deposition rate of 847±42 A/min are measured using a quartz crystal oscillator (QCO) and a multi-grid filter. Without the antenna, the ionization fraction to the QCO is 30±6% and the deposition rate is 815±41 A/min. Multiple remote sources are envisioned to be positioned radially around a sputtering chamber, controlling uniformity while increasing the ionization further. Since 21% additional ionization is achieved using only one source, with no threat of contamination inside the vacuum chamber, the helicon source has good potential for a secondary plasma source in IPVD applications.

A rotating magnet dc planar magnetron with a 33-cm diameter aluminum target is coupled with a secondary plasma source to ionize the sputtered metal neutral flux to control the angular distribution of the flux arriving at the surface of the substrate. For this purpose, a radio-frequency (rf) plasma is created between the sputtering target and substrate by a three-turn coil located in the vacuum chamber. The rf plasma increases the electron temperature and density, which results in significant ionization of the neutral metal flux from the sputtering target. By applying a small negative bias to the substrate, metal ions are drawn to the substrate at normal incidence. A gridded energy analyzer and a quartz crystal microbalance (QCM) were used to determine the ion and neutral deposition rates. From this, the ionization fraction of the flux incident onto the QCM is determined.