Anisotropic Si Etching by a Supersonic Cl 2 Beam
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ANISOTROPIC Si ETCHING BY A SUPERSONIC C12 BEAM
YUDEN TERAOKA, FUMIHIKO UESUGI, AND IWAO NISHIYAMA NEC Corporation, Opto-Electronics Basic Research Laboratory, Opto-Electronics Research Laboratories, 34 Miyukigaoka, Tsukuba, Ibaraki 305, Japan
ABSTRACT Perpendicular etching profiles of n÷-Si(100) are obtained with a supersonic C12 beam at substrate temperature of 900°C. Although small undercuts are observed just below the SiO2 mask, the side wall etching caused by the background Cl 2 is almost negligible. An aspect ratio of greater than 6 and selectivity of greater than 8000 are obtained with 0.5 Itm line & space mask pattern. From Arrhenius plots of etch rates, an effective activation energy of the nozzle beam etching is determined to 0.53 eV. Assuming that the reaction product is SiCl2, the reaction probability is estimated to be 19% at 900'C. Highly anisotropic etching of the Si(100) obtained here is due to the large reaction probability. INTRODUCTION Research and development of semiconductor dry-etching techniques are devoted to obtain high anisotropy, low damage, and high selectivity. Plasma etching techniques have been improved along the course of these demands. Magnetic field containing plasma etching methods, e.g., microwave excited ECR and magnetron plasma etchings, are known as promising technologies. In these methods the ion kinetic energy is relatively lower than a conventional RIE and the mean free path of the ions is effectively long so that the etching damage and anisotropy are improved. Recently, an electron beam excited plasma etching technology has been developed [1]. The most advantage of this method is in a point of very low kinetic energy of the ions such as 10 eV. Attributing to such a low kinetic energy it has been succeeded to prevent the damage to some extent caused by the bombardment of energetic ions [2]. On the other hand, significant efforts have also been applied to the technological characterization of etching processes with neutral species. Some methods utilizing the neutral species as an etchant are examined in order to prevent completely some effects of ion bombardment. For example, the charge build-up effect on a dielectric thin film, which is often observed in a gate etching, is suppressed by assistance of high speed rare gas atoms which are made through a resonance charge exchange reaction between the accelerated rare gas ion and same kind of rare gas [3]. Moreover, a hot molecular beam is also applied to poly-Si gate etching [4]. The authors suggest the energy transfer of molecular vibration to the surface enhances the reaction probability on the bottom rather than the side wall so that anisotropic profiles are obtained in the etching method. The vibrational energy (less than 0.1 eV), however, is so small that whether the vibrational energy transfer accelerates the reaction or not is still a problem to be solved. Understanding of surface reactions of semiconductor with halogen containing molecules or radicals and the structure of etchant adsorbed layer is of fundamental impor
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