Generating large-area uniform microwave field for plasma excitation

Abstract

This study proposes a distributed input system to generate large-area uniform microwave field for the applications of plasma excitation or material processing. A microwave source is divided into four equal-amplitude and equal-phase waves through cascaded H-plane and E-plane power dividers. The wave in rectangular TE 10 mode is subsequently converted into cylindrical TE 11 mode and then propagates through a slightly deformed waveguide to form a circularly polarized wave. The four circularly polarized waves with a 2  2 input array are led into a reaction chamber to excite plasma or an applicator to process materials. An experiment was conducted, which verified the simulated results. The idea of generating uniform microwave field can be scaled to a much larger area if an n  n input array is used V C 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3692231] I. INTRODUTIONSince the invention of microwave sources, microwave energy has been widely used in various applications and research fields. Microwave can be used to generate various plasma sources based on different mechanisms, like microwave plasma systems 1-5 and electron cyclotron resonance (ECR) systems. 6-11 It can also be employed directly to process or anneal materials, such as ceramics, ferrites, thin films, or even metal powders. 12-23 Thus, exciting large-area and uniform microwave field has been pressingly required for many applications.Generating large-area uniform plasma hinges on several factors in that the microwave field is very crucial. Microwave field can be built up as waves traveling in cylindrical waveguide or waves standing in a resonant cavity. In a cylindrical waveguide, a high-order transverse mode, like TE 01 , TE 21 , TE 41 , TM 01 , or a mixed-mode system 1,7,8,24-26 is favorable for a much larger waveguide radius at a given frequency. In the microwave/plasma system, a circularly polarized TE 11 or TE 21 wave is a promising candidate of generating uniform density plasma with azimuthal symmetry. 2,10,24,26 Many researchers like to use TE 01 or TM 01 mode for its intrinsic symmetry. 7,8,24,25 In addition to these waveguide modes, a periodical vane-type structure which generates surface wave was used to excite planar plasma. 3,4 Microwave energy can also be used to process (either sinter or anneal) materials more effectively than the conventional counterpart. 12,13,20 It can be used not only to deal with bulk materials like ceramics, ferrites, or even metal powders 18-22 but also to anneal thin films like silicon or lead zirconate titanate thin films. 14-17 Comparing with conventional oven annealing, the required annealing temperature is lower and the processing time is shorter in general. Why the microwave annealing is so effective is not well understood to date. Nevertheless, large-area and uniform microwave field is believed to facilitate the applications of microwave/ material processing.This study proposes a scheme to generate large-area and uniform microwave field using a distributed input array, as illustrated in Fi...

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