Chemical dry cleaning and pretreatment on the electrical and reliability characteristic of high-k gate dielectrics in MOS device

Abstract

Effect of chemical dry cleaning (CDC) and pre-treatment (NH3 annealing) on the interface property of high-K gate dielectrics (NiTiO3) in MOS device have been investigated. A surface layer is damaged due to oxide dry etching (CHF3/CF4/Ar) process in active region formation. This damaged layer was generally removed by wet etching (HF) however it creates a rough layer on the substrate surface. It appears that the surface roughness by plasma dry etching is better then that by HF wet oxide etching. When the metal is directly deposited on the silicon substrate, a poor interface quality leads to a high leakage current. A damage-free, smooth surface, and thin interfacial layer formed on substrate surface are important for high-k gate dielectric process. Therefore, a method using Chemical Dry Cleaning (CF4/O2) is adopted after dry oxide etching (CHF3/CF4/Ar). In addition, CDC can then be adopted to effectively remove fluorocarbon residue and Si-F and Si-C bonds on the silicon surface etched in fluorocarbon plasma chemistry. After CDC, pre-deposition treatment can be employed to inhibit the growth of the interfacial layer. The pre-treatment strategies (NH3 annealing) are used to prevent silicide formation and to elevate the interface property of the devices. Finally, post deposition annealing (N2 annealing) can be performed to reduce the leakage current. These approaches not only strengthen the structure of Si-N bonds, but also improve the smoothness and uniformity at the interface of the metal oxide/silicon substrate.