Paper TF1-TuM12
Defect Mechanisms for Chlorosilane Based Self-Assembled Monolayers

Tuesday, October 19, 2010, 11:40 am, Room Pecos

Self-aligning manufacturing processes could allow smaller device structures to be made as well as significantly reduce the number of manufacturing steps required. By utilizing selective chemistry it is possible to control where growth occurs for many different materials. Self assembled monolayers (SAMs), such as octadecyltrichlorosilane (OTS), have been used to inhibit the atomic layer deposition (ALD) of materials spanning from high-k dielectrics to metals such as Ir or Pt. By tailoring the selective chemistry, it is possible to chemically activate and deactivate the surface for multiple materials. SAMs such as 3-mercaptopropyltriethoxysilane have been used to attach a variety of nanoparticles where desired, and when combined with other SAMs such as OTS can prevent adsorption or deposition where undesired. Simple patterning techniques such as photolithography, AFM lithography, or electron lithography can be combined with selective chemistries to allow high resolution spatial control over the growth and deposition of materials. One limitation of this technology is the long time scales required to fully deactivate deposition using SAMs, which are on the order of 48 hours. Molecular defects such as water in the SAM, unblocked hydroxyl groups, exposed Si-O bonds, misaligned boundaries between forming SAM islands, or polymerized SAM molecules in the SAM layers also leads to an eventual failure point for deposition deactivation. We found that they can be largely eliminated by forming the SAM on a uniformly hydroxylated surface, using a chloroform rinse step, and removing any polymerized or physisorbed SAM molecules from the surface during SAM formation. Using TiCl₄ as a probe for defect sites, the level of each defect type has been determined. The number of defects sites on the surface on a typical OTS SAM is on the order of 10¹² molecules/cm². 1/3^rd of the defects are associated with the physisorbed SAM molecules. Of the other 2/3^rds of SAM defects nearly half are unblocked hydroxyl groups while the other half are likely open Si-O bonds at grain boundaries. Water has been shown not to be a contributing cause for nucleation of deactivation failure. TiO₂ deposition from a TiCl₄ and H₂O ALD process at 170°C has been deactivated for at least 100 cycles after treating for only 4 hours in 10mM OTS in toluene solution, as long as the sample is removed every hour and rinsed. The extraction step removes unwanted SAM molecules and exposes open surface areas allowing for new SAM molecules to quickly fill the gaps. These improvements in both the quality and the time scale of SAM formation could it feasible to begin incorporating these technologies into manufacturing.