Dry Cleaning of Fluorocarbon Residues by Low-Power Electron Cyclotron Resonance Hydrogen Plasma

Reactive ion etching (RIE) using fluorocarbon chemistry is widely used to open contact holes in dielectric layers for very large scale integration (VLSI) since it provides high anisotropy and selectivity over Si. However, it is known that the RIE leaves fluorocarbon residues on the exposed surface after etching of silicon dioxide [1,2]. These residue layers were reported to be nonvolatile, chemically and thermally stable, and that they resulted in high contact resistance and degradation of metal-silicon interfacial quality [3]. Therefore, fluorocarbon residues need be removed prior to the metal deposition processes by appropriate means. Conventionally, fluorocarbon residues can be removed by a two step cleaning procedure. First, wafers are exposed to an oxygen plasma. During this process the residue layers are oxidized, and at the same time the silicon dioxide film is formed. Second, the oxide layer is subsequently removed by an HF solution. Although the oxidizing process is one of the most effective methods to remove the fluorocarbon residues, silicon consumption leads to changes in critical dimensions of the device structure [4]. Furthermore, wet cleaning processes such as HF dip may have limitations in cleaning high aspect ratio contact holes [5]. It is also difficult to integrate such wet processes with other dry processes in a cluster tool environment for the fabrication of VLSI [6]. Sputter cleaning techniques based on high density argon plasmas were reported for the removal of RIE residues [7,8], however, it is likely that the high power levels may deteriorate the electrical properties of the contacts by energetic ion bom bardment. Thus, an alternative plasma cleaning method at a much reduced power level is advantageous for this purpose. In this paper, we report the successful removal of fluorocarbon residues on silicon substrate using low power (50 W) electron cyclotron resonance (ECR) hydrogen plasma. The ECR plasma is advantageous over radio frequency plasma since it provides higher plasma density with lower incident ion energy.