GP Plasma needed to improve the cross-web uniformity of some planar cathodes. The as-built uniformity on a web roughly the length of the straightaways of the target was in the range of +/-12% due to the deposition rate drop-off at the turnarounds. With the planar cathodes and surrounding deposition area modeled in COMSOL Multiphysics, static magnetic fields and electric fields were used to determine the Lorentz forces. The magnitude of these forces on the surface of the target was then used to generate a molecular flow model to simulate material deposition from the cathodes onto the substrate. While this was a good first-order uniformity plot that followed the trend of the measured uniformity on the web, it was more uniform than actual results due to the lack of a cross-corner effect. Nevertheless, trim shields designed to improve the uniformity by a factor of two in the model translated directly to the measured results.

Plasma photography offers a captivating glimpse into the intricate dynamics of magnetic confinement systems. These images, produced from a single processed imaged of a titanium planar cathode, reveal the underlying processes that shape the plasma's behavior. Original lmage, left: The initial image showcases a vibrant blue-white glow, primarily attributed to the light emission from sputtered titanium. The i intensity off this glow correlates with the rate Of sputtering, With brighter regions indicating higher levels ofr material removal. A subtle pinkish-purple hue, visible in/ areas of lower titanium emission in the turnarounds, is due to argon light emission, suggesting reduced sputtering in those regions. Overall, the plasma appears relatively uniform when highly intense.

Enhanced Contrast: By deepening the image's blacks, the shape of the higher-intensity plasma becomes more pronounced. A clear counterclockwise pattern emerges, indicative of the Hall current electron motion. The reduced plasma intensity in the upper left and lower right portions of the racetrack corresponds to regions of lower Hall current, where electron loss occurs in the turnarounds. This is knows as the Cross-Corner effect. Focused on Shape: Further emphasis on the plasmas shape reveals variations h its width along the straightaways. These fluctuations arise from the additive and subtractive effects of electron current density along the magnetic confinement. Electrons, traveling counterclockwise, ionize argon and sputter target material, releasing secondary electrons into the strongest magnetic fields near the target surface. This process enhances ionization efficiency as electrons progress down the left racetrack. The plasma reaches maximum width near1 the center of the left : straightaway, influenced by factors such as magnetic field strength, operating pressure, and target material's secondary electron emission The resulting plasma intensity closely mirrors the expected erosion profile on the target.

Filtered View: By applying additional filtering, the tapered growth of plasma in each straightaway and its partial exten sion into the turnarounds becomes strikingly clear. he bright section in the lower left straightaway represents a region where electrons are pushed into weaker magnetic fields, reducing ionization efficiency beyond that point. However, this process also carries more electrons into the bottom turnaround, slightly increasing its plasma intensity. Conversely,the right-hand straightaway starts with fewer electrons in the Hall current.

These images offer a fascinating visual representation off the complex interplay between various factors that govern plasma behaviori inr magnetic confinement systems. By analyzing images like this and comparing them to COMSOL Simulations Arizona Thin Film Research can help you gain valuable insights into optimizing you sputtering performance.

In 20 years of working with various plasma sources this is by far my favorite picture. This is an early iteration of the Thermal Plasma Deposition (TPD) source that I was developing to deposit high purity materials directly onto the outside of cylindrical backing tubes to make cylindrical sputtering targets.

Years of working to optimize sputtering processes and solve customer sputtering problems helped me identify a key problem when reactively sputtering aluminum oxide from aluminum targets, the grain size. High purity aluminum likes to form really large grains with most target manufacturing processes. If the cylindrical target material is cut down to size on a lathe the mechanical cutting process tends to break up the grains within the first milimeter or so of the target surface. This initial finer grain structure would enable fantastic arc free control of the reactive sputtering process but as soon as the target eroded away and exposed the larger grains the aluminum would sputter preferentially from the exposed grain boundaries and oxides would redeposit on the centers of the grains leading to arcing on the target surface. This lead me to ask, how can I control the grain size when making a target? Of course, there are several solutions that already exist like adding silicon and other dopants to disrupt the grain coalescence, cold working, and cold spraying but all of these processes can add impurities, trapped gas, and incorporate oxides. I wanted a no compromise solution to control the grain size without sacrificing purity and thus I came up with the TPD process.

In the picture, a copper induction coil is surrounding a ceramic crucible filled with high purity aluminum metal. The induction current is used to melt and evaporate the aluminum metal in the crucible, the voltage differential from coil to coil helps form a plasma from the evaporated aluminum flux and accelerate the ionized species out the end of the coil. The magnetic field generated by the coil help confine the plasma primarily within the opening of the crucible. This process operates only from evaporated flux and no other gas is introduced into the vacuum system.

Unfortunately, aluminum was one of the worst materials to work with because in it's liquid state it aggressively attacks and destroys all high temperatures ceramics making the process extremely difficult to sustain. Ultimately we abandoned aluminum and created a refined implementation of this process that was able to successfully deposit ITO directly onto cylindrical backing tubes with a controlled grain size and oxide reduction.

Arizona Thin Film Research would like to help improve your sputtering process if you answered yes to any of these questions.

Forced to sacrafice sputter target utilization in order to acheive a required depositon uniformity? Arizona Thin Film Research is ready to help you increase the target utilization through advanced plasma simulations to show how the cross-corner and or cross-cathode effects may be alleiviated in your specific application. #COMSOL #Sputtering