Low temperature remote plasma cleaning of the fluorocarbon and polymerized residues formed during contact hole dry etching

Abstract

Reducing contact hole resistance in ultra large scale integration (ULSI) becomes very important due to the reduced contact hole. Reactive ion etching (RIE) using fluorocarbon is widely used to open contact holes due to its high anisotropic and selective silicon etching characteristics. However, the RIE process induces fluorocarbon residues and results in high contact resistance and defects at the metal-silicon interface. Furthermore, these residues polymerized after photo resist (PR) ashing process. These polymerized residues were reported to be non-volatile, and chemically and thermally stable. Therefore, these polymer residues must be removed prior to metal contact. In this study, we investigated the low temperature oxygen and hydrogen remote plasma cleaning of the polymer residues formed at the contact hole during RIE and PR ashing processes. Samples having shallow trench isolation structure were prepared by RIE using CHF3/CF4 gas. The efficiency of cleaning was systematically evaluated at various conditions such as plasma power, exposure time, gas flow rate and sample temperature. Polymer residues before and after cleaning were analyzed using in-situ Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM) systems. Also, the polymer residues were directly observed before and after cleaning using scanning electron microscope (SEM). Carbon and fluorine impurities were significantly reduced below detection limit of AES after remote plasma cleaning. Also, the C-C/C-H and C-Fx (x=1,2,3) types bonding were not observed by XPS. This paper presents the efficient remote plasma cleaning of the polymerized residues formed during RIE and ashing processes at the contact hole.