COMPARISON OF ADVANCED PLASMA SOURCES FOR ETCHING APPLICATIONS .1. ETCHING RATE, UNIFORMITY, AND PROFILE CONTROL IN A HELICON AND A MULTIPLE ELECTRON-CYCLOTRON-RESONANCE SOURCE

We have studied the etching performance of two commercially available low pressure, high density plasma sources and their application for th e etching of 0.35 mum features in polysilicon films. The two sources a re a rf-inductively coupled helicon made by Lucas Labs of Sunnyvale, C A and a multipole electron cyclotron resonance (ECR) source made by Wa vemat of Plymouth, MI. The sources are mounted on a dual chamber etchi ng platform to remove platform dependent effects. Performance metrics consist of measuring the polysilicon etching rate, etching rate unifor mity, and profile control in HBr gas-phase chemistry. The effect of ap plied source power, applied rf-bias power, and reactor pressure on the etching rate and uniformity is examined using a response surface expe riment. 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 lo w reactor pressure, high applied source power, and applied rf-bias pow ers between 50 and 60 W. To decrease the lateral etching rate and incr ease the anisotropy of the etching process, approximately 3% of O2 is added to the feed-gas. For the helicon, the operating point for best u niformity is at 2.0 mTorr, 2500 W applied source power, and 57 W appli ed rf-bias power resulting in a measured etching rate of 2340 angstrom /min and uniformity of +/-3.3%(2sigma). For the ECR, the operating poi nt for best uniformity is at 2.8 mTorr, 1370 W applied source power, a nd 60 W applied rf-bias power resulting in a measured etching rate of 2580 angstrom/min and uniformity of +/-1.4%(2sigma). Since both source s exhibit remarkably similar performance for the etching of polysilico n films, other factors such as ease of operation, plasma stability, an d plasma ignition sequence become relatively more important when decid ing which source to use for a particular application.