Molecular layer deposition of polymeric thin films for applications in semiconductor fabrication [electronic resource]
Keywords: Chemistry.

The electronics industry has been developing improvements in its products at a rapid pace for five decades, an achievement that stems from its ability to continuously decrease the smallest feature sizes in microelectronic devices. To keep step with the miniaturization of next-generation devices, the constituent polymeric films of microelectronics need to meet requirements such as providing conformal, uniform, pinhole-free and ultrathin coatings. Molecular layer deposition (MLD), as an analogue to atomic layer deposition, is a layer-by-layer technique that utilizes sequential, self-limiting reactions of organic precursors to deposit films with one molecular unit at a time, which in turn allows for fine tuning of the position and concentration of various functionalities in the deposited film. Hence MLD can be a powerful method for deposition of polymer films used in semiconductor device fabrication. In this thesis, novel MLD processes are developed for fabricating ultrathin films and improving the film properties with applications in semiconductor manufacturing. The first part of this thesis explores the application of MLD films as chemically amplified photoresist materials. Acid-labile groups are embedded in the backbone of the precursor and incorporated into the photoresist film with a uniform distribution. Two methods of incorporating photo acid generator (PAG) are employed. The first method is to directly soak the PAG into the resist film after deposition and the second approach is to form in-situ polymer-bound PAG. By this novel synthetic approach, several polyurea films were deposited by MLD and tested for patterning, including an aromatic polyurea film with a soaked-in PAG, an aromatic polyurea film with an in-situ polymer-bound PAG, and an aliphatic polyurea film with soaked-in PAG. All these films were successfully deposited and characterized for both materials properties and resist response. Ellipsometry measurements show that the film thicknesses have a linear dependence on the number of MLD cycles. The presence of the urea linkage is confirmed by infrared (IR) spectroscopy, and x-ray photoelectron spectroscopy (XPS) show that the films are deposited with stoichiometric composition. Both of the aromatic films show cross-linking behavior under e-beam exposure, probably due to reaction at the aromatic rings. Moreover, the in-situ polymer-bound aromatic PAG has a lower activity than the soaked-in aromatic PAG, likely due to a lower photoacid yield. Finally, among the three MLD films studied, the aliphatic film performs best as a photoresist material and good sensitivity and resolution are achieved. To be applied in semiconductor device fabrication, polymeric thin films need to be thermally stable. Two approaches are investigated to improve the thermal stability of the MLD films. First, a series of cross-linked polyurea thin films are deposited by using multifunctional precursors. The cross-linked films show constant growth rate, urea chemical bonding, and stoichiometric compositions. More importantly, they exhibit higher film density and thermal stability compared to the non-cross-linked polyurea film. Second, a MLD process for depositing inorganic-organic hybrid carbosiloxane films is developed. Characteristic MLD growth behavior such as a constant growth rate and saturation behaviors are observed with this process as well. Significant improvement of film stability is achieved with the carbosiloxane films. This thesis concludes with thoughts and perspectives on the future of MLD in semiconductor device fabrication.