Design and Development of Novel Atomic Layer Deposition Equipment & Processes for Biomedical Applications

Ultra-thin films grown using Atomic Layer Deposition (ALD) have gained a lot of ground in recent years. This technology, which is still relatively new, has created a benchmark for depositing pure, conformal, pin-hole free films on almost any substrate with atomic scale precision. One of the major applications of this deposition technique has been in the biomedical implant industry where ALD can be used to functionalize many commonly used biomaterials to enhance their surface properties. These biomaterials have special applications but due to their organic nature, they are not receptive to cell proliferation. ALD has become indispensable mostly because of its ability to coat organic substrates with enough material to induce cell proliferation but not enough to induce a cytotoxic response. During research into low temperature ALD reactions, work was done to produce ultra-thin films of Titanium dioxide (TiO2) or titania, magnesium oxide (MgO), titanium oxynitride(TiOxNy) and silver (Ag) metal. Each metal or oxide explored provided some enhancement to the underlying substrate in terms of hydrophobicity, cell response and osteointegration. The as-deposited films were characterized by spectroscopic ellipsometry (SE) for thickness and refractive index. Films were also characterized using X-ray Photoelectron Spectroscopy (XPS) to study its chemical composition. Furthermore, density and absolute thickness of as-deposited films were also measured using X-Ray Reflection (XRR). Mechanical testing included measurement of the tensile strength of the material before and after deposition. Leaching of the coated material in Phosphate Buffer Solution (PBS) was also studied using Inductively Coupled Plasma- Quadrupole Mass Spectrometry (ICP-QMS). Through these studies, low temperature reactions were demonstrated on substrates such as polymethylmethacrylate (PMMA), bone particles and collagen membrane that are temperature sensitive. A reactor for bilayer ALD of metal oxide/nitride is also presented. With this reactor, a novel approach was used to control the reactor using a custom code written in Python and executed using a commonly available single board computer (SBC) and microcontrollers. This led to the design being more compact and robust. This reactor was used to deposit Titanium oxynitride and this reaction was studied using a QMS attached to the downstream of the reactor to get insights into the ALD reaction.