Near‐surface damage and contamination of silicon following electron cyclotron resonance etching

Abstract

Damage and contamination produced after electron cyclotron resonance (ECR) etching of Si using CF4 gas has been studied using electrical characterization, Rutherford backscattering spectroscopy (RBS), secondary ion mass spectroscopy (SIMS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and etch pit density measurement techniques. Due to the small dc self‐bias voltage generated across the plasma sheath, ECR etching is expected to produce low damage and contamination levels. RBS measurements show that ECR etching does indeed produce less structural damage than that produced by conventional reactive ion etching (RIE). It is found that the damage and contamination levels from an ECR etching process are actually reduced by the addition of radio frequency (rf) power to the wafer. The metallic impurity levels are shown to be greatly reduced by covering the stainless steel wall of the ECR source near the resonance region with an anodized Al liner. The plasma density in the resonance region of the reactor during ECR processes is much higher than that during RIE processes. Therefore, the ECR processes produce heavy metal contamination, which is mainly from the portion of the stainless steel wall of the reactor in contact with the plasma. Schottky diodes fabricated on the etched samples exhibit high leakage currents implying some damage and/or impurities are present in the near‐surface region. Relationships that exist among the generation current of the metal–oxide–silicon (MOS) capacitors, the etch pit density and the metallic impurity level were studied. Some wafers were exposed to an Ar ECR/RIE plasma to compare the effects of pure physical sputtering and ion‐assisted chemical etching, as when CF4 was used. A possible explanation for the observed behavior is given.