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The goal of this project is to create thin films to improve resolution for 3-color lithography (3CL). Lithography is a technique that is used to pattern semiconductor chips. The current methods used to manufacture chips use deep and extreme ultraviolet light to create patterns on a photoresist. 3CL is an alternative that creates patterns using easily-accessible visible light instead of dangerous radiation that requires specialized and prohibitively expensive equipment. This work focuses on improving the resolution of the 3CL technique by using thin negative tone acrylate photoresist films. Modern microelectronic devices require semiconductor chips that have individual features less than 100 nm wide and patterns with features that pack closely together. The industry is moving to shorter wavelengths because feature size is directionally proportional to the wavelength of the light used. However, 3CL uses visible light, which has larger wavelengths than the desired feature size. One way to reduce the size of features is to shape and overlap the beams so that not all irradiated areas result in fabricated features. Two beams are used to excite the photoinitiator in the photoresist to initiate radical polymerization in the acrylate monomers. The third beam is used to deactivate the photoinitiator, thus inhibiting polymerization before it can occur. Another requirement for semiconductor chip patterns is high resolution, or closely packed features. To prevent unwanted polymerization between features in 3CL, and thereby increase resolution, initiation and deactivation should occur from different photoinitiator excited states. Therefore, a 3CL photoinitiator should have a long-lived chemically inactive excited state where either deactivation can relax it back down to the ground state, or further excitation can bring it to the chemically active excited state. We examine isopropylthioxanthone (ITX) and its excited states to probe for 3CL behavior. Deactivation limits the feature width, but the deactivated features in the bulk material are taller than their width and collapse. Thin films are employed to correct the aspect ratio and further improve resolution. This project focuses on ITX’s performance as a 3CL photoinitiator, the procedure to produce 40 nm thin films, and how polymerization and deactivation are different in thin film samples compared to the micron-thick bulk samples. |
