Optical and ion beam studies of excimer laser irradiated hexagonal silicon carbide

Walton, Christopher Derek

Abstract

The realisation of doped regions, specifically Nitrogen, in Silicon Carbide (SiC) for transistor and p-n junction applications is a serious problem. Difficulty arises because of the low value of the diffusion coefficient and consequently the excessive temperatures required for substantial diffusion to take place can cause dissociation of the material. Coincidently, the robustness of Silicon Carbide makes it a suitable material for use in harsh environments, where excessive radiation and temperatures exist especially for high power and high frequency applications. Diffusion and
activation using thermal processes in equilibrium is not a practicable solution and therefore one feasible alternative technique is that of ion-implantation and laser annealing. However, the incorporation of dopants by ion implantation can cause damage to the crystal lattice. In the work that follows, excimer laser processing of Silicon Carbide has been employed to address these problems from two quite different approaches.

Experimental investigations are carried out to investigate the laser interaction of Silicon Carbide over a range of laser fluence close to the ablation threshold. These experiments serve as preliminary investigations to establish the experimental process parameters for the fourth coming work. As a first approach, work was carried out in an attempt to introduce vacancy type defects into the lattice of 4H-SiC using both Argon Fluoride (193nm) and Xenon Chloride (308nm) excimer lasers, a technique we refer to here has "Laser Induced Defect Mediated Diffusion". The introduction of defects using ion beams to displace host atoms has previously been undertaken by other workers where it has been shown that the diffusion of dopant species can be enhanced, however, no such studies on Silicon Carbide exist at the present time using an excimer laser to specifically disrupt the lattice in this way. Photoluminescence (PL) and Positron Annihilation (PA) measurements are adopted as the diagnostic techniques to measure and quantify the response of Silicon Carbide subsequent to laser irradiation, hence help determine the nature of any defects that might have been introduced. PL measurements of ArF laser irradiated Silicon Carbide revealed the evolution of an emission band that correlates with the laser fluence which was tentatively associated with laser induced damage below the ablation threshold. Work is driven by these latter results and a technique for gaining further information on the nature of this band was adopted. The technique of PA is carried out on both ArF and XeCl laser irradiated material. On a microscopic scale the laser induced 'damage' consists of di-vacancy clusters at the near surface. The damage consists of large voids, essentially holes, which are not suitable for mediating the diffusion of dopant species in Silicon Carbide.

Secondly, an alternative way of introducing Nitrogen dopants is carried out. Samples of 4H- and 6H-SiC were implanted with Nitrogen ions and later annealed using a Xenon Chloride excimer laser. The laser annealing experiments serve the purpose of removing/reducing implantation damage. Fourier Transform Infrared Reflection (FTIR) spectrometric and visible reflection measurements have been undertaken in an attempt to determine the optimum parameters for lattice recovery. We show that excimer laser annealing can be considered as an alternative method of removing ion-implantation damage when annealed at a optimum laser fluence and above this optimum the photon flux imparts detrimental damage to the lattice.

Citation

Walton, C. D. (2000). Optical and ion beam studies of excimer laser irradiated hexagonal silicon carbide. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4222761

• Thesis Type: Thesis
• Deposit Date: Nov 16, 2020
• Publicly Available Date: Feb 23, 2023
• Keywords: Physics
• Public URL: https://hull-repository.worktribe.com/output/4222761
• Additional Information: Department of Physics, The University of Hull
• Award Date: Sep 1, 2000