Etch stop in via-hole etching on aluminum interconnection using inductively coupled C₂F₆ plasma with O₂ additive gas

This article describes an etch stop in via-hole etching on an aluminum interconnection line using inductively coupled C₂F₆ plasma with O₂ additive gas under the following conditions: 2700 W source power, 5 mTorr operational pressure, and a total gas flow of 43 SCCM (SCCM denotes cubic centimeter per minute at STP). Via-hole etching is performed with a change in the aspect ratio (AR) under identical etching conditions. Etch-stop behavior in a manufacturing process is investigated as a function of a cumulative etch time. To estimate the etch-stop degree, the etch depth was measured using different structure in a wafer (etch-stop test wafer) from that in a production wafer and by using the test etching conditions. Those conditions are different from the production etching conditions to enhance the detection sensitivity for the etch stop as follows: 2100 W source power, 5 mTorr operational pressure, and 1 SCCM O₂ flow rate reduction. As a result, no etch stop in a via-hole fixed at 2.8 AR was seen up to 76.6 h of cumulative etch time. But etch stops occurred in via holes of 0.01 and 1.31 ARs at 0.28 and 1.65 h, respectively. X-ray photoelectron spectroscopy measurements clarified that aluminum from a via hole at 0.01 AR is emitted and adheres to the chamber components of an upper electrode and a quartz wall. Since the etch stop depends on the via-hole AR, the amount of aluminum emitted from the via hole affects the etch stop. Moreover, after etch stops occur in via holes at 0.01 and 1.31 ARs, the authors confirmed that dummy etching using a bare Si wafer could eliminate the etch-stop state and was an effective method to avoid etch stops. In conclusion, etch stop was induced by aluminum emitted from wafers. The aluminum adheres to the chamber components and functions as a fluorine scavenger. Since the carbon-to-f- luorine ratio is increased by aluminum, etch stop occurs in via-hole etching using fluorocarbon plasma.