Silver Patterning by Reactive Ion Beam Etching for Microelectronics Application
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Silver Patterning by Reactive Ion Beam Etching for Microelectronics Application L. Gao, J. Gstoettner, R. Emling, P. Wang, W. Hansch, D. Schmitt-Landsiedel Institute for Technical Electronics, Technical University Munich D-80333, Munich, Germany ABSTRACT Dry etching of silver for the metallization in microelectronics is investigated. Etching is performed using an electron-cyclotron-resonance reactive-ion-beam-etching system (ECR-RIBE) in an Ar/CF4 or Ar/CF4/O2 mixture. The etch characteristics are strongly affected by ion energy (beam voltage and microwave energy); the O2 concentration in the reactive mixture has only a small effect. An anisotropic, smooth etch profile and clean surface are obtained. Focused ion beam (FIB) and atomic force microscopy (AFM) have been used to study the etched profile and the roughness, respectively. INTRODUCTION As devices continuously shrink in ultra large-scale integration (ULSI), the RC delay of the interconnection system becomes one of the most critical limitations on IC performance [1]. Because of its high electrical conductivity and its good electromigration properties, copper replaces aluminium in some microelectronic applications [2, 3]. Silver, with a lower bulk resistivity than that of aluminium and copper, is one of the candidates for future interconnect metallization [4-8]. It has been shown that a sputtered Ag metallization is possibly more suitable for ULSI than sputtered Cu due to a much higher electrical conductivity in features sizes below 100 nm [4]. Furthermore, it was measured that sputtered Ag can reach the same electromigration resistance as CVD or PVD deposited copper [5,8]. To evaluate the potential application of silver metallization, one of the important aspects is the pattern transfer by etch processing. Several investigations on Ag etching have been reported. The etching speed of wet etching using in a Fe(III)-nitride-H2O or in a NH4OH/H2O2-H2O can be very fast. However, it is very difficult to control and easily causes underetching [8]. A further work has been done with a hybrid dry-wet etching technique [7], which leads to a better result. However, it is complicated and time consuming. In another dry etching report a conventional technique of reactive ion etching (RIE) is established in an oxygen plasma [6]. The drawback here is that a low etch rate is obtained. To achieve anisotropic etching, physical sputtering along with radical reaction is essential. A plasma generation method using an ECR has been applied for etching and deposition [9,10]. In contrast to conventional RIE [11] the ion energy and flux can be controlled independently in the RIBE system [12] and yields better ion directionality due to its high mean-free path and high ionto-radical density ratio by a divergent magnetic field method. In order to optimise the etch rate and obtain smooth etch morphology in the RIBE process, it is important to know the effects of process variables such as beam voltage and current, and etching gas concentration. EXPERIMENTAL DETAILS In our investigati
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