Etch Processing of III-V Nitrides

Abstract

As III-V nitride devices advance in technological importance, a fundamental understanding of device processing techniques becomes essential. Recent works have exposed various aspects of etch processes. The most recent advances and the greatest remaining challenges in the etching of GaN, AlN, and InN are reviewed. A more detailed presentation is given with respect to GaN high density plasma etching. In particular, the results of parametric and fundamental studies of GaN etching in a high density plasma are described. The effect of ion energy and mass on surface electronic properties is reported. Experimental results identify preferential sputtering as the leading cause of observed surface non-stoichiometry. This mechanism provides excellent surfaces for ohmic contacts to n-type GaN, but presents a major obstacle for Schottky contacts or ohmic contacts to p-type GaN. Chlorine-based discharges minimize this stoichiometry problem by improving the rate of gallium removal from the surface. In an effort to better understand the high density plasma etching process for GaN, in-situ mass spectrometry is employed to study the chlorine-based high density plasma etching process. Gallium chloride mass peaks were monitored in a highly surface sensitive geometry as a function of microwave power (ion flux), total pressure (neutral flux), and ion energy. Microwave power and pressure dependencies clearly demonstrate the importance of reactive ions in the etching of wide band gap materials. The ion energy dependence demonstrates the importance of adequate ion energy to promote a reasonable etch rate (≥ 100-150 eV). The benefits of ion-assisted chemical etching are diminished for ion energies in excess of 350 V, placing an upper limit to the useful ion energy range for etching GaN. The impact of these results on device processing will be discussed and future needs identified.

High Etch Rate Gallium Nitride Processing Using an Inductively Coupled Plasma Source

“…As plasma-assisted GaN etching is becoming more fully understood, it is generally accepted that the mechanism proceeds by a combination of radical induced chemical reactions and ion induced physical reactions [2]. The chemical nature of the etch can be identified by the fact that etching is moderately promoted by either increasing the ICP power (and hence increasing the degree of gas dissociation) or increasing the fraction of chlorine (reactive species) in the gas flow.…”

“…The chemical nature of the etch can be identified by the fact that etching is moderately promoted by either increasing the ICP power (and hence increasing the degree of gas dissociation) or increasing the fraction of chlorine (reactive species) in the gas flow. Evidence suggests the driving force behind this etch process is the dependence of product formation on incident ion energy [2,9,10]. Etch product formation has been observed using mass spectrometry to increase up to a maximum (at %350 eV) before decreasing at higher ion energies in an ECR system [2].…”

“…Evidence suggests the driving force behind this etch process is the dependence of product formation on incident ion energy [2,9,10]. Etch product formation has been observed using mass spectrometry to increase up to a maximum (at %350 eV) before decreasing at higher ion energies in an ECR system [2]. Many workers observed that the etch rate continues to increase over the same energy range, therefore concluding that the etch mechanism changed from an ion-assisted chemical process to physical sputtering.…”

“…Considerable research has been undertaken in recent years aimed at discovering the best route for this pattern transfer step of device fabrication. Two recent review articles have concisely documented these research efforts [2,3]. In summary there are two approaches to the GaN etch problem, wet processing and dry processing.…”

Very Low Pressure Magnetron Reactive Ion Etching of GaN and Al x Ga1−x N Using Dichlorofluoromethane (Halocarbon 12)

“…For instance, an ICP configuration would be optimal if there were a need to control the ion energy; an ECR configuration, instead, would be optimal if very high-density plasma were required. [8][9][10] In Fig. 1 the RF powered electrode is immersed in a 150 gauss magnetic field perpendicular to the plane of the drawing.…”