AFM Analysis of ECR Dry-Etched InGaP, AlInP and AlGaP
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(1)AT&T Bell Laboratories, Murray Hill NJ 07974 (2)University of Florida, Gainesville FL 32611 (3)US Army Research Laboratories, Ft. Monmouth NJ 07703 ABSTRACT The etch rates of InGaP, AlInP and AlGaP increases dramatically with microwave power in ECR BCI3- or CH 4/H2 -based discharges, reaching values near I m-min-1 at 1000W, The surface morphologies of these materials however behave much differently as the microwave power is increased. For BC13 etching of InGaP the surface RMS roughness decreases from 36nm at 250W to 2nm at 1000W. For AlInP, there is little change in surface morphology, whereas for the common binary component of these two materials, InP, the surface becomes very rough at high powers (>60nm RMS). By contrast, the morphologies of the three ternaries remain smooth over a wide range of conditions with CH 4 /H2/Ar. The AFM analysis, coupled with AES enables us to understand these different responses in terms of volatility of the respective chloride, metalorganic and hydride etch products. INTRODUCTION Virtually all advanced III-V semiconductor devices are based on heterostructures containing one or more ternary or quaternary materials. This makes it difficult to develop dry etching processes, since traditionally two completely different plasma chemistries have been employed for In-containing materials (CH 4/H 2) and Ga- or Al- based materials (Cl 2 and related gases).(1) While CH 4/H2 is a universal etchant for III-V semiconductors, the rates are too slow for many (2 4) photonic or electronic (5 6) power devices(7)in which the required etch depths are relatively large. - Constantine et al. ( and Shul et al. have reported combined C12/CH 4/H 2 plasma chemistries, generally with the sample held at a slightly elevated temperature, for etching of materials containing both In and Ga or Al. Under Electron Cyclotron Resonance (ECR) conditions the role of the CH 4 in this chemistry is basically to produce a sidewall protective layer for elimination of undercut. (8) Reproducible etching with elevated temperature mixtures requires good thermal contact between the heated electrode and the sample. An enduring problem is the possibility of transferring heat conductive grease from the back of the sample onto the front at some point in the etch process. Considerable simplification of III-V etch processes could be achieved if In-containing materials could be removed at high rates in polymer-free plasma chemistries that do not require elevated sample temperatures. There have been recent reports of high-rate etching of InP or InGaP in C12/Ar or BCI 3/Ar ECR discharges at temperature of 1.2[tm/min at -300V). Similar results were obtained for both InP and InAlP, and indicates that at 100 0 C there is still a need for some energy provided by incident ions to efficiently 0 desorb the InClx etch products.( ) While the three materials displayed similar trends in terms of etch rate dependencies on different plasma parameters, we observed much different responses of their surface morphologies. Figure 3 shows AFM scans (7x7[tm
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