During the past decade there has been a rapid growth of interest in poly-Si for the active device layer in thin film transistors (TFTS) for active matrix flat-panel displays. Whilst the early work, demonstrating the high carrier mobility of these devices, employed processing temperatures of approximately 1000 degrees C and quartz susbtrates, this was soon followed by the investigation of lower-temperature processes which were compatible with the use of glass substrates. Some of the key aspects of this work are reviewed in this article: the preparation of the material by direct deposition and by crystallization from a-Si precursors, the characterization of the defect-induced trapping states within the material and their passivation, and the present understanding of the TFT leakage current mechanisms. This work is put into the context of the requirements for active matrix liquid-crystal displays, and, with the understanding and control of poly-Si which has been achieved to date, its application in this area can be expected to increase rapidly in the coming years.

https://iopscience.iop.org/article/10.1088/0268-1242/10/6/001/pdf

Polycrystalline silicon thin film transistors

Ion-beam-induced amorphization in Si has attracted significant interest since the beginning of the use of ion implantation for the fabrication of Si devices. A number of theoretical calculations and experiments were designed to provide a better understanding of the mechanisms behind the crystal-to-amorphous transition in Si. Nowadays, a renewed interest in the modeling of amorphization mechanisms at atomic level has arisen due to the use of preamorphizing implants and high dopant implantation doses for the fabrication of nanometric-scale Si devices. In this paper we will describe the most significant experimental observations related to the ion-beam-induced amorphization in Si and the models that have been developed to describe the process. Amorphous Si formation by ion implantation is the result of a critical balance between the damage generation and its annihilation. Implantation cascades generate different damage configurations going from isolated point defects and point defect clusters in essentially ...

https://www.ele.uva.es/~mmm/papers/2004_Pelaz_JAP_96.pdf

Ion-beam-induced amorphization and recrystallization in silicon

A fabrication process polycrystalline silicon thin film transistors commences with the deposition of an ultra-thin nucleating-site forming layer onto the surface of an insulating substrate (e.g., 7059 glass). Next, an amorphous silicon film is deposited thereover and the combined films are annealed at temperatures that do not exceed 600° C. By patterning the deposition of the nucleating site forming material on the glass substrate, the subsequently deposited amorphous film can be selectively crystallized only in areas in contact with the nucleating-site forming material.

Low temperature crystallization and patterning of amorphous silicon films on electrically insulating substrates

The fabrication of thin-film-transistor (TFT) devices on a transparent substrate lies at the heart of active-matrix-liquid-crystal-display (AMLCD) technology. This is both good and bad. On one hand it is a difficult task to manufacture millions of intricate semiconductor devices reliably over such large display substrates. On the positive side, AMLCD technology can aspire to become much more than a “display” technology. The idea is as follows: It is possible for one to readily fabricate additional transistors to execute various electronic functions—those that would otherwise be handled by separate large-scale-integration (LSI) and very large-scale-integration (VLSI) circuits—on the periphery of the display. Since this can be done, in principle, with no—or a minimal number of—additional processing steps, substantial cost reduction is possible and significant value can be added to the final product.Doing so and doing it well can ultimately lead to “system-on-glass” products in which the entire electronic circuitry needed for a product is incorporated directly onto a glass substrate. This means that integrated active-matrix liquid-crystal displays (IAMLCDs) have the potential to bypass conventional Si-wafer-based products and may lead TFT technology to compete directly against Si-wafer-based monolithic integrated circuits.

Crystalline Si Films for Integrated Active-Matrix Liquid-Crystal Displays

A review is presented of the self‐implantation method which has been developed to achieve high‐quality polycrystalline silicon thin films on insulators with enhanced grain sizes and its applications to thin‐film transistors (TFTs). In this method, silicon ions are implanted into an as‐deposited polycrystalline silicon thin film to amorphize most of the film structure. Depending on ion implantation conditions, some seeds with 〈110〉 orientation remain in the film structure due to channeling. The film is then thermally annealed at relatively low temperatures, typically in the range of 550–700 °C. With optimized process conditions, average grain sizes of 1 μm or greater can be obtained. First, an overview is given of the thin‐film transistor technology which has been the greatest motivation for the research and development of the self‐implantation method. Then the mechanism of selective amorphization by the silicon self‐implantation and the crystallization by thermal annealing is discussed. An analytical mode...

Polycrystalline silicon thin films processed with silicon ion implantation and subsequent solid-phase crystallization: Theory, experiments, and thin-film transistor applications

This paper presents a theoretical and experimental study of the recrystallization behavior of polycrystalline silicon films amorphized by self‐implantation. The crystallization behavior was found to be similar to the crystallization behavior of films deposited in the amorphous state, as reported in the literature; however, a transient time was observed, during which negligible crystallization occurs. The films were prepared by low‐pressure chemical vapor deposition onto thermally oxidized silicon wafers and amorphized by implantation of silicon ions. The transient time, nucleation rate, and characteristic crystallization time were determined from the crystalline fraction and density of grains in partially recrystallized samples for anneal temperatures from 580 to 640 °C. The growth velocity was calculated from the nucleation rate and crystallization time and is lower than values in the literature for films deposited in the amorphous state. The final grain size, as calculated from the crystallization param...

R. Reif

Papers

Recrystallization of amorphized polycrystalline silicon films on SiO2: Temperature dependence of the crystallization parameters