Lasers Solutions for Annealing

The application of lasers for annealing of wafer-based and thin-film microelectronic devices is steadily increasing. Excellent control of material characteristics (for example, dopant activation profile) can be achieved through proper selection of laser parameters, such as wavelength, pulse duration and fluence, which directly influence the laser material interaction. In this paper, we present several lasers and optical systems from Coherent that have proven to be useful for annealing in both microelectronic and macroelectronic applications. These laser systems include Excimer Lasers in the ultraviolet and our unique high-power continuous-wave laser system that delivers scalable output power of multiple hundreds of Watts in the visible wavelength range. We will present results from recent work involving dopant activation, and will present several application examples from Flat Panel Display annealing and crystallization, which we propose are directly applicable to wafer-based microelectronics as well.

Introduction

Lasers are ideally suited for applications in microelectronics where low-thermal-budget processing is required, because the laser wavelength, fluence and interaction time can be appropriately selected to ensure an extremely localized deposition of energy. For example, in the vast majority of Flat Panel Display (FPD) applications, the substrates are low-cost high-temperature-intolerant glasses and plastics. However, it is often desirable to form high-quality crystalline Si films on these substrates without resorting to expensive processes that involve transferring monolithic Si wafers. In FPD manufacturing, Excimer lasers have long been employed to convert as-deposited amorphous-Si films into polycrystalline Si films, by inducing extremely rapid film melting which is then followed by subsequent rapid re-solidification. The selection of a UV wavelength, which is strongly absorbed in the first few nanometers of the Si film, and appropriate laser pulse duration (10's to 100's of nanoseconds) allows the process to be entirely compatible with glass and plastic substrates that have softening points well below the melting point of Si.