A process for improved Al (Cu) reactive ion etching

Abstract

The standard reactive ion etching (RIE) process for etching Al and its alloys in a single-wafer tool is basically a high-pressure (> 100 mTorr), multistep etching process. A significant modification to this process is reported which incorporates the standard high-pressure Al (Cu) etch followed by a low-pressure overetch step. The etch gases used for Al(Cu) etching are a mixture of (BCI3 /Cl2 /CHCI3 /N2). At pressures < 100 mTorr, the cathode dc self-bias voltage is increased, enhancing the ion bombardment energy and hence directionality normal to the substrate. Then the component of etching by ion assisted or reactively sputtered etching increases relative to the reactive component, increasing the ability to remove Cu-rich residues. The low-pressure overetch step also exhibits a factor of 2 smaller etch bias than the standard process. This is estimated to be 0.05 μm/image in RIE of l-μm-thick Al(Cu) films. We have demonstrated that lowering the pressure of the overetch step, hence increasing the ion energies but keeping the same reactive species, offers a more effective clearing process. Combining this clearing process with the overetch does not increase the total time required for the process. Using this process, 1.5-μm-thick metal lines of Ti/Al (2.5% Cu)/Si 0.6 μm wide were obtained with vertical sidewalls. © 1989, American Vacuum Society. All rights reserved.