Iodine-Based dry Etching Chemistries for InP and Related Compounds
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IODINE-BASED DRY ETCHING CHEMISTRIES FOR InP AND RELATED COMPOUNDS S. J. PEARTON, U. K. CHAKRABARTI, A. KATZ, C. R. ABERNATHY, W. S. HOBSON, F. REN AND T. R. FULLOWAN AT&T Bell Laboratories, Murray Hill, NJ 07974 ABSTRACT A comparison is given of the dry etching characteristics of InP and related materials in high ion density (>1011 cm- 2 ) microwave discharges of HI, CH 3 I, C2 H5 1, C3 H7 1 and C2 H 3 I. The InI, species are more volatile than their InClx counterparts near room temperature and rapid etch rates can therefore be achieved without the need for sample heating. HI discharges provide faster etch rates than the halocarbon-based mixtures, but are more corrosive. All of these gas chemistries offer faster rates than conventional CH 4 /H 2 mixtures. Halocarbon-iodide discharges still suffer from polymer deposition on the mask and within the reactor, as with CH 4 /H 2 . AES analysis shows an absence of contaminating residues with all of the iodine-based chemistries, and highly anisotropic features are obtained since the etching is driven by ion-enhanced desorption of the reaction products.
INTRODUCTION Chlorine-based dry etch mixtures normally only yield smooth surface morphologies for In-containing III-V semiconductors when the sample temperature is > 130°C.('-7) This is the temperature needed to promote desorption of InCI3 , which otherwise will remain on the surface and lead to rough morphologies.( 6 ) By contrast, CI- /H2 mixtures provide smooth etching of all Ir-V semiconductors, but the rates are prohibitively low for applications such as etched mesa buried heterostructure lasers in which deep features (a3.5 gtm) are required. The fact that relatively long (Q 100 min) runs are needed means that erosion of the dielectric or metal masks used can also be a problem. It is clear from this discussion that more aggressive plasma chemistries need to be examined in order to obtain rapid, smooth etching of InP and related compounds. Mixtures based on HBr have been reported,(s- °) but the etch rates were relatively slow at low dc biases, and the extremely corrosive nature of this gas means that its handling is a problem. Very promising results have been obtained with HI-based discharges, first reported by Flanders et al.(I") The indium iodide species have higher vapor pressures than their chloride counterparts at low temperature and hence fast etch rates can be achieved.( 12 ' ) However the HI is also very corrosive and will attack the gas delivery lines, mass flow controllers and the mechanical backing pump. In addition, the shelf life of HI is -6 months because it decomposes to hydrogen and iodine and as a result there are problems in achieving reproducible results. It is of interest therefore to explore alternative iodine-containing plasma chemistries for dry etching of III-V materials. Prime candidates include methyl iodide (CH 3 I), ethyl iodide (C2 H3 I), vinyl iodide (C2 H3 1) and propyl iodide (C3 H 7 I). In particular these can be used in conjunction with H 2 and Ar addition to obtain a direct comparison
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