Area selective atomic layer deposition: use of lithographically defined polymer masking layers for the deposition of titanium dioxide

Abstract

Atomic layer deposition (ALD) is a promising method for depositing high quality, conformal, ultra-thin films. The ability to perform area selective ALD would provide a number of benefits including a reduction in the cost and number of process steps required for patternwise deposition of materials, elimination of possible substrate and device damage induced by plasma etching of thin films, and ability to direct pattern materials that are difficult to etch. Previous attempts have been made to develop area selective ALD processes based on the use of self-assembled monolayers (SAMs). In these schemes, the SAM layers were used to selectively passivate specific regions of a substrate surface and thus prevent ALD. However, the process times required for SAM deposition and problems with SAM defectivity have limited the practical application of such methods. This paper presents a new approach to area selective atomic layer deposition techniques (ASALDT) based on the use of lithographically definable polymeric masking layers that allow deposition only in selected areas of a substrate. It is shown that there are a number of factors that must be considered in designing such patternable polymeric masking materials and processes including: reactivity of the polymer with the ALD precursor species, diffusion of ALD precursors through the polymer mask, and remnant precursor content in the masking film during ALD cycling. Finally, successful direct patterned deposition of TiO₂ is demonstrated using a poly(methyl methacrylate) masking layer that has been patterned using deep-UV lithography.