AVS 46th International Symposium
    Electronic Materials and Processing Division Tuesday Sessions
       Session EM-TuM

Paper EM-TuM11
Removal of Native Oxide Employing Heated NH@sub 3@/NF@sub 3@ Mixture

Tuesday, October 26, 1999, 11:40 am, Room 608

Session: Si Surface Chemistry and Etching, Passivation, and Oxidation
Presenter: H. Ogawa, The University of Tokyo, Japan
Authors: H. Ogawa, The University of Tokyo, Japan
T. Arai, Toyo University, Japan
T. Ichiki, Toyo University, Japan
Y. Takamura, The University of Tokyo, Japan
Y. Horiike, The University of Tokyo, Japan
Correspondent: Click to Email
The removal of the native oxide employing a heated NH@sub 3@/NF@sub 3@ mixture was studied using in-situ XPS and FTIR-ATR/RAS. The mixture was heated in an 13 mm diameter Al@sub 2@O@sub 3@ tube whose surface was wound by a resistive heater, then being exposed to a sample set on a stage cooled by a N@sub 2@ gas with room temperature. The chemical oxide was grown in a H@sub 2@SO@sub 4@/H@sub 2@O@sub 2@ solution. The NH@sub 3@/NF@sub 3@ mixture with partial pressure ratio of unity at a pressure of 1 Torr started to remove the oxide from a Al@sub 2@O@sub 3@ tube temperature of 500 °C. For the Si surface after removal of the oxide, new XPS peaks appeared at 103.8 eV in Si2p and 402.2 eV in N1s, respectively. Absorption spectra of Si-H(2100 cm@super -1@), N-H(stretching; 3330 cm@super -1@, bending;1454cmcm@super -1@) and Si-F (783 cm@super -1@) were also observed in the IR measurement. These results exhibit the presence of a (NH@sub 4@)@sub 2@SiF@sub 6@ film deposited on the Si surface after removal of the oxide.@footnote 1@The film desorbed readily at 100 °C in a vacuum and then was terminated by hydrogen. The higher the partial pressure, the faster the oxide removal rate, whereas NH@sub 3@ or NF@sub 3@ alone did not demonstrate any etching reaction. The result that the Al@sub 2@O@sub 3@ tube heated at higher temperature led to the higher etch rate implies generation of the oxide etchant within the tube. Thus, NH@sub 3@ and NF@sub 3@ were introduced separately to two tubes, and when NF@sub 3@ alone was heated, the present reaction was confirmed. The result implies thermally decomposed NF@sub 3@ reacts with NH@sub 3@, generating the oxide etchant. The removal rate ratio of thermal grown SiO@sub 2@ to BPSG (boron phosphorus silicate glass) films was almost unity. It is well known that the usual HF solution produces about ten times higher etch rate for BPSG than for the thermal SiO@sub 2@. Accordingly, this technology allows us to offer a new dry cleaning method of the contact hole surface in ULSI multi-level interconnection process. @FootnoteText@ @footnote 1@M. Hirose, S. Yokoyama and Y. Yamakage: J. Vac. Sci. Technol., B3 (1985)1445.