| This dissertation presents a study of the scaling limit of Phase Change Materials (PCM) for non-volatile memory device application. The approach is to obtain isolated true nano size Phase Change Materials through controllable deposition of PCM onto a template - nano pitted substrate. The fabrication of nano pitted substrate started from a di-block copolymer (DBC) film in hexagonal nano arrangement coated on thin SiO2 on Si (100) substrate. Then the DBC pattern was transferred to SiO2 - Si substrate by anisotropic dry oxide etch. Subsequently, a wet KOH etch with high crystallographic selectivity changed the circular pattern into an inverted pyramidal pit substrate. Thus, the dimension of the pits are controlled by the hole size of DBC, and the density of the pits are controlled by the interspacing between holes. Characterization tools such as SEM and TEM are intensively used to analyze the morphology, crystallographic, atomic ratio and phase transformation of the PCM. The dissertation discusses the critical fabrication tricks to produce high yield nano pitted substrate, illustrating the size effect of phase change materials upon crystallization and melting as well as the scaling limit of PCM. A proposal is also discussed for extending the study to device fabrication level and branch out the nano pitted substrate for the study of other materials in size and pressure effect. |
