AVS 63rd International Symposium & Exhibition
    Thin Film Friday Sessions
       Session TF-FrM

Paper TF-FrM1
Assessing the Role of Temperature and Pressure on the Tungsten ALD Selectivity Window on Si/SiO2 Substrates

Friday, November 11, 2016, 8:20 am, Room 105A

Session: CVD, ALD and Film Characterization
Presenter: Paul Lemaire, North Carolina State University
Authors: P.C. Lemaire, North Carolina State University
G.N. Parsons, North Carolina State University
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Operating conditions such as temperature and pressure are critical variables for atomic layer deposition (ALD) processes. The ALD “temperature window” describes the temperature range in which the growth per cycle is relatively constant. Yet the temperature window typically is in reference to the growth surface and does not include deposition on less thermodynamically favored surfaces. Pressure is typically maintained at ~1 Torr in order to maintain a balance between gas interdiffusion and entrainment, but there has been little work investigating how pressure affects ALD nucleation. In this work we discuss how process temperature and pressure can be adjusted to improve an ALD “selectivity window” aka deposit more material on a growth surface over a non-growth surface. We specifically study a tungsten hexafluoride (WF6) - silane (SiH4) ALD process (W-ALD) to selectively deposit tungsten on silicon (Si) over silicon oxide (SiO2). Ellipsometric and x-ray photoelectron spectroscopy (XPS) analysis shows that the W-ALD selectivity window increases at lower temperatures and at higher pressure. We suggest that this improved selectivity is due to the lowered probability of the WF6 reacting with defect sites on the non-growth SiO2 surface. In addition, we discuss how cyclic gas exposures during the ALD deposition can be used to rapidly change the operating pressure and temperature in order to improve the selectivity window. Results from ellipsometric, and XPS analysis show that dosing He, H2, and CH4 immediately prior to the WF6 exposure improves the selectivity window. We attribute the improved selectivity window to rapid substrate heating which assists in desorption of WFx species from the SiO2 surface and helps limit undesired tungsten nucleation.