Glancing angle deposition (GLAD) is a nanofabrication technique that is an extension of oblique angle deposition in which the substrate incline is manipulated during film deposition. Oblique depositions are typically performed with a fixed substrate. The GLAD process involves actively managing both the substrate incline angle and rotation rate during deposition to manipulate columnar structure growth. This requires a system with real time feedback and computer control such as the Intlvac Nanoquest platform. One of the key advantages of GLAD films is the ability to control overall thickness (micron size), as well as column dimensions (nanometer size) and growth angles.

Applications where GLAD technique is utilized:

• artificially enhanced birefringence, high laser damage threshold coatings;
• active and passive optical devices such as high quality optical filters;
• sensor devices including pressure sensors, optical resonators and humidity sensors, and;
• energy devices such as electrochemical supercapacitors, micro battery charge storage, fuel cells, and solar energy conversion.

Electron-beam evaporation systems are widely used for GLAD depositions to fabricate high quality structures. Ion beam or magnetron sputtering has also been used, however E-beam systems are generally preferred as they operate at very low pressures. This is important to keep mean free path high (prevent background gas from colliding with the vapor flux). Since E-beams don’t require background gas to function and they are able to be placed at a longer distance from the substrate, the resulting columns are more precisely controlled.

Ion beam systems or Sputtering systems are generally used for GLAD when electron-beam or other evaporation methods are not suitable. In those cases when sputtering techniques are utilized, the substrate must be closer to the sputter source. This may cause wider angular distribution in which case a physical screen might be implemented to restore collimation.

The growth of GLAD columns depends on a number of factors such as shadowing between columns, deposition temperature, deposition rate, deposition pressure, vacuum composition, substrate type, substrate preparation, and preferred crystallinity of the deposited material.

Basic GLAD structures can be categorized in three ways, depending on the deposition angle (α) and the substrate rotation angle (ø): constant, discrete and continuous. Constant means the substrate remains stationary during deposition. Discrete means the substrate undergoes periodic changes in a given angle but is stationary otherwise. Continuous means the substrate is continuously in motion during deposition for a specified angle. There are six basic GLAD structures noted in literature: slanted posts, chevron, vertical posts, slanted post stack, high-low stacks, and rugate. By combining these structure types it is possible to create novel material results, such as single-material films that have both high and low refractive index layers by adjusting film density using effective medium theory.

The features of a GLAD-capable physical vapor deposition (PVD) system will vary depending on the required result. Key considerations are pressure requirements, vapor sources, substrate motion, monitoring requirements, and substrate motion algorithms. In some cases, retrofits can be performed on existing deposition systems to accommodate the need for GLAD.

If you are interested in learning more about how Intlvac Thin Film can provide a customized GLAD-capable system for your application, or if your existing system is eligible for GLAD modifications, contact sales@intlvac.com

Source: Glancing Angle Deposition of Thin Films: Engineering the Nanoscale by M.M. Hawkeye, M.T. Taschuk, M.J. Brett; © 2014 John Wiley & Sons Ltd.