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Studie van de oppervlakte mechanismes bij selectieve atomaire laagafzetting na organische film passivatie / Study of surface mechanisms in organic film mediated area selective atomic layer deposition

  • Pasquali, Mattia; 118396;
Publication Date
Feb 19, 2024
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Modern chips are likely the most complex man-made devices ever produced. Their manufacturing heavily relies on top-down patterning techniques, which struggle to meet the ever-increasing requirements for alignment and minimum feature size imposed by the never-ending device miniaturization. Area-selective deposition (ASD), a bottom-up substrate-selective material deposition technique, has the potential to alleviate such manufacturing challenges, by enabling ultra- thin film deposition on nanopatterns exclusively where it is needed. In ASD a film is selectively deposited on the targeted areas of a prepatterned substrate, the growth areas (GAs), while no material deposition is observed on the remaining non-growth areas (NGAs). For instance, surface-sensitive deposition techniques, like chemical vapor deposition (CVD) and atomic layer deposition (ALD), are exploited in conjunction with well-distinguished local surface chemistries within the nanopattern to achieve selective material growth. In this example, the selectivity of a deposition process can be further enhanced if altering the chemical specificities of the NGA to delay the material nucleation, by grafting, or forming, non-reactive functionalities on top of the NGA. In this research project, we study various fundamental aspects of ASD while tackling the challenges behind ASD-enabled fully self-aligned via (FSAV) integration, an application of great relevance for back-end-of-line technology. The work described in this Ph.D. thesis delves into AS-ALD enabled by self-assembled monolayer-mediated (SAM) passivation. Specifically, octadecanethiol-derived (ODT) SAM is employed to inhibit ALD on Cu, while not interfering with the material nucleation on SiO2. This Ph.D. dissertation focuses on three research objects. First, a systematic study is conducted to elucidate the link between the Cu surface proprieties, the fundamental qualities of the grafted ODT-SAM, and its effectiveness as an ALD inhibitor. Second, it is tackled a critical challenge in ASD metrology: the scarcity of characterization methods to study the ASD mask on technology-relevant nanopatterns. Third, the study and development of novel ALD processes to enable SAM-based ASD of FSAV-relevant materials on Cu over SiO2. The fundamental mechanisms driving the ODT-Cu interaction are investigated with the aim of identifying, and understanding, the conditions that allow the ODT-mask to exhibit superior ALD inhibition properties. Cu is treated either with acids or oxidizing agents to produce a multiplicity of surfaces, and their chemical compositions and morphological properties are investigated. Similar investigations are carried out as these substrates are modified by dip-coating in an ODT solution. As the ODT masks are tested against hafnium nitride ALD, the organic blocking layer better delays the material growth if coating oxidized Cu. The superior performance of the ODT mask on the metal oxide is attributed to the formation of a denser and more thermally stable SAM compared to the one obtained on oxide-free Cu. Pulsed force atomic force microscopy (AFM) is employed to perform a nanomechanical (NM) characterization of the ODT blocking layer. The scope of this study is to enable the monitoring of the SAM on Cu/SiO2 patterns, by providing crucial insights into its thermal stability, selectivity, and inhibition performance against ALD. Specifically, we show that by recording the adhesion force evolution of an ODT-coated Cu/SiO2 pattern undergoing ASD, it is possible to accurately estimate the SAM coverage on the NGA, something otherwise unachievable by other characterization techniques. The insights provided by the NM-characterization of the passivated patterns are corroborated by X-ray photoelectron spectroscopy, whereas top-down scanning electron microscopy (SEM) highlights the strong relationship between ASD quality upon hafnium nitride ALD and pulsed force AFM-derived ODT coverage. The blocking capabilities of ODT are also investigated on various substrates with different feature dimensions, ranging from blanket Cu samples to 10 nm critical dimension (CD) Cu/SiO2 planar patterns. Hafnium nitride ALD serves as the test deposition process for these experiments. Testing the considered ASD strategy on state-of-the-art complementary metal-oxide semiconductor substrates allows to gain insights into the opportunities and challenges faced in ASD at technology-relevant nanodimensions, which are of utmost importance for ASD applications in semiconductor manufacturing. The pulsed force AFM metrology, in combination with top-down SEM inspection, is used to study the selectivity loss mechanisms observed on 50 nm Cu/SiO2 patterns. These findings are critical to enable a ∼5 nm hafnium nitride ASD on 10 nm-wide SiO2 spacings, a CD never explored in ASD before. Moreover, this study highlights the "monolayer tradeoff " faced at such small CDs. On one hand, a desirable SAM passivation should have a thickness close to a monolayer to confine its ALD inhibition properties exclusively to the NGAs. On the other hand, at such a nanoscale, the extremely detrimental later expansion of the ALD film over the GAs could be effectively hampered by a blocking layer with a thickness comparable to that of the ASD film. Finally, our investigation delves into ASD of materials relevant to FSAV technology. A dimethylaluminum isopropoxide (DMAI) and H2O-based deposition process is explored to deposit AlOx, whereas a quaternary ALD process with dimethoxydiazasilacyclooctane as Si-precursor is studied to deposit an Al-silicate film under ASD-favorable deposition conditions. A fundamental study of the metal-oxide ASD process is carried out to enhance the selectivity of both ALD processes. We highlight the critical role played by the Al-precursor dose during AlOx ALD, showing how reduced DMAI dose during ASD is critical to hamper both the undesired generation and the growth of metal oxide nanoparticles that form on ODT-Cu. As both AlOx and Al-silicate ALD processes are feasible at the ASD-favorable temperature of 100 °C, and they do not rely on strong oxidizers or plasma activation, ASD is achieved on 50 nm Cu/SiO2 patterns. In addition, both ALD films' electrical properties are investigated using planar capacitor structures. The analysis reveals that the AlOx film is a robust dielectric, comparable to analogous dielectrics available in the industry, while the Al-silicate exhibits the desired electrical properties to enable the FSAV technology. In conclusion, this Ph.D. dissertation presents findings that could extend our comprehension of the fundamental mechanisms occurring during ASD, along with dedicated studies aimed at developing ASD processes for a specific semiconductor manufacturing application. An emphasis is put on the need for innovative characterization methods to gain insights into the phenomena taking place during ASD on technology-relevant nanopatterns. Moreover, this research underscores the importance of "ASD-favorable" material deposition processes to pave the way for potential breakthroughs in semiconductor applications for ASD. / status: published

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