Magnetron-Enhanced Reactive-Ion-Etching of Al-1%Si-2%Cu Alloy
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MAGNETRON-ENHANCED REACTIVE-ION-ETCHING OF AI-l%Si-2%Cu ALLOY C.Y. Fu,R. Hsu, and V. Malba
Lawrence Livermore National Laboratory University of California Livermore, CA 94550 ABSTRACT Plasma etching of Al-1%Si-2%Cu presents serious challenges in corrosion, residue, and critical dimension (CD) control in single wafer etchers. One approach is to pattern the metal with oxide mask so chlorine can no longer be trapped in resist and sidewall polymers to cause corrosion. The magnetron-enhanced reactive-ion-etching (MERIE) offers a high degree of ionization at very low pressure, so anisotropic etching with reasonably high etch rate can be achieved even without sidewall protection. This paper summarizes our MERIE process characterization in terms of the effects of SiC14 flow rate and plasma power on selectivity and CD control using an oxide mask. Typical etching was performed at 1000 watts and 40 sccm SiCI4 with the unthrottled pressure at 4.0 mTorr and a self-induced dc bias of 75 V. A 2-minute NF3 plasma at 250 watts and 100 sccm of NF 3 flow served as the passivation step. This metal etch process has been successfully implemented in a doublelayer-metal interconnect technology. INTRODUCTION Plasma etching of Al-i%Si-2%Cu presents serious challenges in corrosion, residue, and critical dimension (CD) control in single wafer etchers. One approach is to pattern the metal with oxide mask so chlorine can no longer be trapped in resist and sidewall polymers to cause corrosion. However, since Al also reacts with atomic and molecular chlorine, tight profile control becomes difficult without polymer sidewall protection derived from resist or carbon-containing gases. The magnetron-enhanced reactive-ion-etching (MERIE) offers a high degree of ionization at very low pressure, so anisotropic etching with reasonably high etch rate can be achieved even without sidewall protection[1,2]. In addition, the high flux of low energy ions helps to remove the hard-to-etch residue with little or no substrate damage. The elimination of resist and polymer also minimizes corrosion problems and polymer-related residues. In addition, the selectivity of metal to mask can be significantly improved in comparison to resist masking. This paper summarizes the basic MERIE process characterization in terms of the effects of SiC14 flow rate and plasma power on selectivity and CD control using an oxide mask. EXPERIMENTAL All Si wafers used were 4-inch (100) P-type with 1 um thermal oxide. 800 nm of Al1%Si-2%Cu was cold deposited in a magnetron sputter machine. Then 400 nm SiO 2 was deposited by plasma-enhanced chemical vapor deposition at 200'C and subsequently patterned by resist mask in a RIE. The chamber of the MRC ARIES etcher is shown in Fig. 1. The wafer was located on a cathode which was coupled with 13.56 MHz power. The magnetic field strength at the wafer was about 230 Gauss. The external magnet was positioned to achieve a 5% metal etch uniformity. Both the chamber wall and the cathode were maintained at 50*C with no He backside cooling. We have invest
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