Dielectric materials by Atomic Layer Deposition for microelectronic applications

The Atomic Layer Deposition (ALD) is an innovative technique to deposit thin film materials for several application fields. The rapid affirmation of the ALD process is related to the peculiarities of the deposition mechanism. In particular, because of the self-limiting principle and of the layer-by-layer growth mode, ALD guarantees the conformal and uniform film deposition on large area, with precise thickness control at relatively low deposition temperatures. The described ALD features play a fundamental role in several new generation industrial fields. In particular, the progressive scaling down of the microelectronic devices, according to the Moore s law, is the most significant reason for the increased attention towards the ALD processes. The semiconductor industry currently demands for novel materials and manufacturing techniques in order to achieve high performance and reliability. According to the miniaturization at the nanometric scale, the need of deposition methods with atomic level accuracy has become an important issue. In this perspective, the ALD is the most promising deposition technique. Among the huge number of microelectronics fields, the ALD found mainly application in the deposition of the dielectric materials with high permittivity values, also known as high k dielectrics. These materials have been widely employed as insulator layer in the new generation of power devices, such as dynamic random access memories (DRAMs) and in metal-oxide-semiconductor field effect transistors (MOSFETs). In this context, the PhD research activity has been devoted to the study of the ALD deposition of high k dielectrics, including Al2O3, HfO2 and AlN, as gate dielectric layers in power transistors. In particular, both thermal and plasma deposition modes have been explored as well as the structural, morphological and compositional film properties have been evaluated and finally the consequent dielectric behaviour has been measured on electrical test-patterns (capacitors). Moreover, the dielectric films have been investigated as simple single layers but also as nanolaminated Al2O3/HfO2 structures. Each dielectric material has been initially deposited and characterized on silicon substrate and after preliminary tested on wide band gap semiconductors (WBGs). The description of the PhD research activity has been divided in the following parts: the first and the second chapters are focused on the description of the theoretical principles of the ALD technique and of the related employment in the microelectronics field. In particular, the properties for each high k dielectric materials, grown by ALD, and its combination with the wide band gap semiconductors have been described. The third and the fourth chapters are dedicated to the experimental parts. In particular, the fourth chapter provides the details of the ALD reactor and of the properties of the used metal precursors. Moreover, it further contains an illustration of the reaction mechanisms involved in the growth of each material of the deposition parameters as well as a description of the chemical, structural and electrical properties of each dielectric material deposited on the silicon substrate. Similar studies have been carried out depositing the same dielectric films onto the wide band gap (WBGs) semiconductors and the related characterization data are presented in the fifth chapter. In the appendix the description of the different characterization methods, used for the investigation of the dielectric films, is presented.