Plasma-enhanced molecular layer deposition (PEMLD) of boron carbide dielectrics from carboranes for interconnect and patterning applications
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Abstract
The dimensional scaling of semiconductor devices following Moore’s law has resulted in smaller, faster, and cheaper integrated circuits (IC) chips, going from ~3000 transistors in an IC chip in the early 1970s, to ~100 billion per chip today. But this has come at a price of introducing complex patterning processes for achieving feature sizes not accessible through traditional lithography. Also, to connect these huge numbers of transistors, single-level interconnect was not sufficient so multi-level interconnects were introduced that require complex process. Such processes require multiple materials that can act as diffusion barriers, copper capping layers, etch stops, hard masks, etc. Currently, silicon-based materials are being used to fulfill the majority of these needs, but complex next-generation multi-patterning schemes demand new materials and new methods to deposit them. In this work we have investigated the development of a so far unprecedented plasma-enhanced molecular layer deposition (PEMLD) process for boron carbide from carboranes. This novel method will allow for the deposition of thin films of boron carbide with molecular-level control. Boron carbide, which lies outside the silicon class of materials, has appealing chemical, mechanical, electrical, dielectric, and etch properties, making it a candidate for various patterning-support layers. We have demonstrated the deposition of monolayers from three different types of carborane derivatives: 1,2-dithiol-o-carborane on copper, 9-thiol-m-carborane on copper, and 1,2-bis(hydroxymethyl)-o-carborane on SiO₂. Monolayer formation is supported by an increase in hydrophobicity observed via contact angle measurements, an increase in thickness observed with ellipsometry, and an increase in boron coverage determined by X-ray photoelectron spectroscopy (XPS). Toward developing a PELMD process, we further investigated multilayer growths. We treated all three types of monolayers with cycles of nitrogen plasma followed by ortho-carborane-1-carbonylchloride. The 1,2-bis(hydroxymethyl)-o-carborane monolayer was treated with oxygen plasma followed by second dosing of the same precursor. All growths demonstrated continuous thickness increase observed by ellipsometry, supported by the continuous increase in the B:Cu/B:Si ratio obtained from XPS. With each half cycle of the PEMLD process, i.e., plasma treatment or exposure to precursor vapor, we observed an alternating increase and decrease in the N:B/O:B ratio, which distinguished each half cycle. Hence, we were able to develop and demonstrate two novel PEMLD process for the deposition of boron carbide films from carboranes.
Table of Contents
Introduction -- Methods -- Deposition of monolayers of boron carbide from carboranes -- Effect of heat and plasma treatment on carboranethiol self-assembled monolayers on copper -- Multilayers of boron carbide from carboranes -- Conclusion and future work
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Ph.D. (Doctor of Philosophy)