Substrate-dependent nucleation during CVD has been heavily studied, and several strategies for selective growth are known. Compared to CVD, atomic layer deposition generally allows more precise control over surface reactions, but to date, the most successful selective-area deposition processes are based on CVD and not ALD mechanisms. Most ALD processes have an inherent substrate bias during nucleation, leading to problems in process development. Better understanding of this native substrate bias can be used to promote and enhance selective-area ALD. We have studied nucleation of ALD metals and dielectrics to promote native substrate bias and improve selectivity. Tungsten ALD using WF6/SiH4 onto SiO2 proceeds when surface Si-H (from SiH4) begins to form, allowing WF6 reduction to W and elimination of SiF4. We hypothesized that the introduction of a H2 or H-plasma exposure into the ALD sequence may help remove Si from the SiO2, which could extend the nucleation delay on SiO2, while not affecting W growth on Si. Using ellipsometry, XPS, high resolution SEM and in-situ quadrupole mass spectrometry we find that a H2 exposure during W ALD on ex-situ prepared SiO2 decreased the rate of W nucleation compared to growth without the H2 step, effectively increasing the selectivity window. Also, using XPS in-situ FTIR, we explored how various oxide ALD precursors react with different surfaces. For example, doing TiO2 ALD using TiCl4 with titanium isopropoxide as the oxygen source (instead of water), we find that eliminating water slows the substrate oxidation in areas where TiO2 deposition is not desired, thereby promoting the nucleation delay to as much as 200 ALD cycles at 170°C, resulting in a maximum selectivity thickness, ts,max ≈ 2–3 nm. We will discuss other details of initial reactions obtained from in–situ infrared spectroscopy, quartz crystal microbalance, TEM, SEM, ellipsometry and other tools to better understand and improve “inherent” substrate selective ALD of metals and metal oxides.

Using inherent substrate-dependent nucleation to promote selective-area atomic layer deposition

253rd National Meeting (2017)

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