Comparison of advanced plasma sources for etching applications. I. Etching rate, uniformity, and profile control in a helicon and a multiple electron cyclotron resonance source

Abstract

We have studied the etching performance of two commercially available low pressure, high density plasma sources and their application for the etching of 0.35 μm features in polysilicon films. The two sources are a rf-inductively coupled helicon made by Lucas Labs of Sunnyvale, CA and a multipole electron cyclotron resonance (ECR) source made by Wavemat of Plymouth, MI. The sources are mounted on a dual chamber etching platform to remove platform dependent effects. Performance metrics consist of measuring the polysilicon etching rate, etching rate uniformity, and profile control in HBr gas-phase chemistry. The effect of applied source power, applied rf-bias power, and reactor pressure on the etching rate and uniformity is examined using a response surface experiment. Profile control is determined by examining nested and isolated lines and trenches using oxide mask/polysilicon/oxide structures. In both sources, high uniformity and vertical profiles are obtained at low reactor pressure, high applied source power, and applied rf-bias powers between 50 and 60 W. To decrease the lateral etching rate and increase the anisotropy of the etching process, approximately 3% of O2 is added to the feed-gas. For the helicon, the operating point for best uniformity is at 2.0 mTorr, 2500 W applied source power, and 57 W applied rf-bias power resulting in a measured etching rate of 2340 Å/min and uniformity of ±3.3%(2σ). For the ECR, the operating point for best uniformity is at 2.8 mTorr, 1370 W applied source power, and 60 W applied rf-bias power resulting in a measured etching rate of 2580 Å/min and uniformity of ±1.4%(2σ). Since both sources exhibit remarkably similar performance for the etching of polysilicon films, other factors such as ease of operation, plasma stability, and plasma ignition sequence become relatively more important when deciding which source to use for a particular application.