Surface Modification for Area Selective Atomic Layer Deposition on Silicon and Germanium

Rong Chen
Abstract & Cover

Atomic layer deposition (ALD) is a powerful ultra-thin film deposition method that uses sequential self-terminating surface reaction steps for preparing a variety of materials. Typically, the process permits nano-scale control of materials in the vertical direction. To develop the method for three-dimensional control of materials, we have been investigating an area-selective ALD technique which will enable and ultimately nano-scale definition of the lateral structure. Many ALD processes are very sensitive to the conditions of the substrate surface. As a consequence, the surface functional groups can be manipulated prior to ALD to carry out an area selective ALD process. Our approach is to chemically modify the substrate surface in order to impart spatial selectivity to ALD. The materials we focus on are both dielectrics (e.g. Hf02 and Zr02 high-lc materials) and metals (e.g. Pt). We have investigated several different types of self-assembled monolayers (SAMs) as resists against ALD. Oxide-coated substrates (e.g. Si02) have been protected using organosilane-based SAMs by silylation reaction; hydrogen-terminated Si (Si-H) and hydrogen-terminated Ge (Ge-H) protected by reaction with Ialkenes or 1-alltynes via hydrosilylation and hydrogermylation, respectively. We have followed the SAM properties as a function of molecular structure and formation time using several experimental techniques and have correlated the properties of the SAMs with their efficacy as ALD resists for both classes of monolayers. With the successful ALD resists, area-selective ALD has been carried out using different patterning methods to define the lateral structure. Both micro-contact printing of the SAMs and selective functionalization of a Si02/Si structure by SAMs have been used to achieve area-selective ALD of Hf02 and Pt films. We have compared the selectivity between these methods, and have described the differences in the context of the SAM resist requirements. We have also shown that by choosing either silylation- or hydrosilylation-based chemical fimclionalization, a single patterned oxide substrate can be used for either positive or negative pattern transfer into the ALD film. The ability to achieve area selective ALD for both dielectrics and metals enables potential gate stack fabrication. Simple capacitor devices were fabricated using area selective ALD and their electrical performance was measured. The comparison of Hf02 electrical characteristics by different surface treatments prior to ALL) suggested further surface and interface modifications are important to achieve better electrical performance.

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Stanford Libraries
Stanford University
(Stanford, USA)
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