Influence of pulse duration on plasma chemistry and thin film growth of plasmonic titanium nitride deposited by constant-current regulated HIPIMS

This study documents the results of an investigation into the effect of pulse duration within constant-current reactive high power impulse magnetron sputtering of titanium discharges, specifically investigating the effects on plasma chemistry and its temporal evolution and on changes to thin film texture of titanium nitride thin films produced from these discharges. Pulse durations ranging from 40 to 200 μs were studied. The data obtained from the time-resolved optical emission spectroscopy and supported by time-resolved and time-averaged mass spectrometry show three stages that can be used to characterize the generation of the discharge: gas rarefaction, pumping, and steady state. The rise in higher excitation energy species populations when increasing pulse duration provides proof of increasing electron temperature and increasing prevalence of metal ions relative to gas ions. Increasing pulse duration is shown to strongly influence film grain sizes as determined by x-ray diffraction and increase the prominence of the (200) crystal plane. The produced films are shown to exhibit instrumental nano-hardnesses within 31–35 GPa, are optically metallic, and exhibit a high localized surface plasmon resonance quality factor of 2 as obtained from the ratio between the real and imaginary dielectric permittivity. All films were produced at room temperature making the synthesis process CMOS compatible.

What is it about?

The study focused on the deposition of plasmonic titanium nitride thin films using high power impulse magnetron sputtering (HIPIMS) with constant-current regulation. It explored the influence of pulse duration on plasma chemistry and thin film growth. A CS400S cluster deposition system was utilized, equipped with a titanium target and a HIPIMS power supply, that could control the current at a constant level within each pulse. Various substrates, including high-speed steel, stainless steel, silicon wafers, and glass plates, were used for titanium nitride coatings. Time-resolved optical emission spectroscopy and time-averaged mass spectrometry were employed to analyze ion flux and plasma characteristics and identify a pumping stage in the development of the HIPIMS discharge. XRD pole figure analysis was used to determine the crystallographic orientation of the films. Ellipsometry was used to evaluate the optical parameters through the real and imaginary components of the dielectric permittivity. The study demonstrated that high-quality, plasmonically active thin films can be produced at room temperature, suitable for temperature-sensitive substrates such as polymer webs.

Why is it important?

This study is important as it demonstrates a method to produce high-quality, plasmonically active titanium nitride (TiN) thin films at room temperature using high power impulse magnetron sputtering (HIPIMS). The research provides a solution to the challenge of depositing plasmonic materials on temperature-sensitive substrates, expanding the potential for practical applications across various industries. By achieving optical performance comparable to the best examples in the literature without requiring high temperatures, the study advances the development of plasmonic materials for use in fields such as sensing, photovoltaics, and biomedical applications, where environmental and mechanical stability is crucial.

Key Takeaways:

1. Room Temperature Deposition: The research successfully deposits high-quality TiN thin films at room temperature, making it feasible to coat temperature-sensitive substrates like polymer webs without compromising film quality.

2. Superior Optical Performance: The optical properties of the deposited TiN films are on par with the best available examples and achieved at substantially lower temperatures, indicating that the HIPIMS technique can match or exceed traditional methods in achieving plasmonic activity.

3. Versatile Substrate and Process Flow Compatibility: The ability to deposit TiN coatings onto various substrates, including metals, silicon, and glass, and at low process temperature highlights the versatility of the HIPIMS method for diverse applications in industrial and biomedical fields, allowing high optical property TiN to be incorporated in complex production chains including in semiconductor manufacturing.

4. Identify a Pumping stage in the development of the HIPIMS discharge whereby plasma emission and temperature increase whilst current and voltage remain constant, thereby reducing thermal load on the target.