Effect of substrate composition on atomic layer deposition using self-assembled monolayers as blocking layers

Abstract

The authors have examined the effect of two molecules that form self-assembled monolayers (SAMs) on the subsequent growth of TaNx by atomic layer deposition (ALD) on two substrate surfaces, SiO2 and Cu. The SAMs that the authors have investigated include two vapor phase deposited, fluorinated alkyl silanes: Cl3Si(CH2)2(CF2)5CF3 (FOTS) and (C2H5O)3Si(CH2)2(CF2)7CF3 (HDFTEOS). Both the SAMs themselves and the TaNx thin films, grown using Ta[N(CH3)2]5 and NH3, were analyzed ex situ using contact angle, spectroscopic ellipsometry, x-ray photoelectron spectroscopy (XPS), and low energy ion-scattering spectroscopy (LEISS). First, the authors find that both SAMs on SiO2 are nominally stable at Ts ∼ 300 °C, the substrate temperature used for ALD, while on Cu, the authors find that HDFTEOS thermally desorbs, while FOTS is retained on the surface. The latter result reflects the difference in the head groups of these two molecules. The authors find that both SAMs strongly attenuate the ALD growth of TaNx on SiO2, by about a factor of 10, while on Cu, the SAMs have no effect on ALD growth. Results from LEISS and XPS are decisive in determining the nature of the mechanism of growth of TaNx on all surfaces. Growth on SiO2 is 2D and approximately layer-by-layer, while on the surfaces terminated by the SAMs, it nucleates at defect sites, is islanded, and is 3D. In the latter case, our results support growth of the TaNx thin film over the SAM, with a considerable delay in formation of a continuous thin film. Growth on Cu, with or without the SAMs, is also 3D and islanded, and there is also a delay in the formation of a continuous thin film as compared to growth on SiO2. These results highlight the power of coupling measurements from both LEISS and XPS in examinations of ultrathin films formed by ALD.

Chemical Treatment of Low-k Dielectric Surfaces for Patterning of Thin Solid Films in Microelectronic Applications

“…The surface chemistry of SiO 2 has been studied extensively, but not always optimally used in microelectronic fabrication. For instance, selectivity in film deposition by chemical means, either via chemical vapor deposition (CVD) − or by using the newer atomic layer deposition (ALD) version, − can in principle be controlled by conditioning the initial substrate prior to its exposure to the film deposition chemicals. − This is often accomplished by using organic masking agents, either polymers or self-assembled monolayers (SAMs), − but simpler chemistry may be possible.…”

Competitive Adsorption as a Route to Area-Selective Deposition

“…In this case, there is no reason to expect that one could not identify a suitable family of chemical species that would bind preferentially to SiO 2 vs Cu. As discussed in the Introduction, a number of previous studies have investigated the use of molecules that form SAMs on SiO 2 , binding strongly to −OH­( a ) species. ,,, We have reported, for example, that vapor-phase delivery of alkyl silanes can selectively hinder ALD growth of TaN x thin films on SiO 2 , while not affecting their growth on Cu. In this case, these blocking layers were formed once, before growth, and coexposure was not investigated.…”

“…Another method that has been explored involves “reversing” chemisorption of the precursor by introducing an “etch-back” step, − which possesses several similarities to the reversibility exploited in some AS-CVD processes. Perhaps the most examined approach in AS-ALD to date involves the use of blocking layers in the form of self-assembled monolayers (SAMs). ,,, While this approach has its merits, it often suffers from very slow solution-phase formation of the SAMs, degradation over time and exposure to the coreactant (catastrophic with exposure to a plasma), and undesirable effects of surface topography where blocking effects break down …”

“…Perhaps the most examined approach in AS-ALD to date involves the use of blocking layers in the form of selfassembled monolayers (SAMs). 8,9,22,23 While this approach has its merits, it often suffers from very slow solution-phase formation of the SAMs, degradation over time and exposure to the coreactant (catastrophic with exposure to a plasma), and undesirable effects of surface topography where blocking effects break down. 24 In this work, we explore an alternative strategy that involves the introduction of a third chemical species (referred to as the coadsorbate), that primarily competes with the thin-film precursor (and potentially the coreactant species) for surface binding sites.…”

Area-Selective Atomic Layer Deposition Using an Inductively Coupled Plasma Polymerized Fluorocarbon Layer: A Case Study for Metal Oxides

“…Since ALD relies heavily on surface chemistry, it is possible to chemically modify the surface to achieve AS-ALD. Such ALD-enabled nanopatterning approaches have been classified into two categories; (i) area-activated AS-ALD ,− and (ii) area-deactivated AS-ALD. ,− So far, most of the AS-ALD studies have been performed with area deactivation, where part of the substrate is blocked/deactivated by certain coatings allowing film to grow only on the uncovered areas. Surface deactivation has been typically achieved by selectively attaching self-assembled monolayers (SAMs) on the substrate surface.…”