Magnetron Reactive Ion Etching of GaAs: Plasma Chemical Aspects and Surface Damage Studies
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MAGNETRON REACTIVE ION ETCHING OF GaAs: PLASMA CHEMICAL ASPECTS AND SURFACE DAMAGE STUDIES G. F. McLI.,ie, M. Meyyappan*, M. Taysing-Lara, M. W. Cole, C. Wrenn , L Yerke, and D. Eckart U. S.Army Electronic Technology and Devices Laboratory, Fort Monmouth, NJ Scientific Research Associates, Inc., Glastonbury, CT 06033 ** Vitronics, Inc., Eatontown, NJ 07724
ABSTRACT Using a magnetic field to confine the plasma closer to the cathode has been shown to be advantageous in dry etching technology since this yields a high degree of ionization at low pressures. We report here the results of a study of magnetron reactive ion etching of GaAs using a freon discharge. Various characterization techniques have been employed to understand the etching process and identify the extent of surface damage. The results show that magnetron etching is capable of yielding high etch rates with low damage. INTRODUCTION Reactive ion etching (RIE) is widely used at present for etching silicon, and a variety of EIl-V compounds. RIE has desirable features such as high etch rate, controllability and anisotropy, but ion induced damage to the wafer in RIE is not acceptable for many device applications. This led to the development of down-stream plasma reactors where creation of the plasma and actual etching take place in different locations, and magnetron reactors. In the latter, a magnetic field is used to confine the electrons close to the powered electrode, which increases ionization at low pressures. The dc self-bias is characteristically lower than in RIE, and the discharge contains low to moderate energy ions. This allows wafer processing with less ion-induced damage while maintaining the desirable features of conventional RIE. While magnetron reactive ion etching (MIE) has been investigated for etching Si and Si0 2 [1,2,3] there has been relatively little work on exploiting this technique in GaAs processing. Contolini and D'Asaro [4] reported high etch rates for GaAs (up to 7 pm/min etch rate for unpatterned samples) using MIE. Though MIE is a modification of RIE with a magnetic field, the knowledge base developed for RIE is not directly transferable. The low characteristic energies in MIE may result in
different mechanisms which, in turn, may result in different etch rates and selectivity [2]. Hence, there is a strong incentive to undertake studies looking into reaction mechanisms, and wafer damage characteristics. We have recently initiated a comprehensive study to understand MIE of GaAs using various chlorine-bearing discharges. Results using a freon discharge are reported here. EXPERIMENTAL DETAILS The experiments were performed in a Materials Research Corporation MIE-710 reactor. The reactor has been described in detail in refs 1, 2 and 4. The powered electrode (13.56MHz rf) contains two bar magnets with two more located outside the chamber, at the top of the chamber cover. These magnets aid in maintaiing a uniform magnetic field above the cathode. The cathode is water-cooled andcovered with an Al plate and Al pedestal which supports t
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