The use of Metal Additions to Phosphoric Acid to Etch Polysilicon in Poly Buffered Locos Processes


The use of poly-buffered LOCOS processing is a common feature of many sub-micron integrated circuit fabrication processes. However, the silicon layer interposed between the nitride oxidation mask and the pad oxide is often difficult to remove. Different strategies involve dry and/or wet etching of the film. We have demonstrated the utility of adding metals such as Fe or Cu to a conventional phosphoric bath used to etch silicon nitride. Briefly, the presence of the metals is thought to result in a classic oxidation-reduction reaction between the metal and the silicon. Additions of 60ppm of Cu+2 resulted in etch rates of 20Å /min. on undoped polysilicon at a process temperature of 165°C, whereas, the etch rate of SiO2 was less than 1Å/min. Similar results were obtained for additions of Fe+3 and other metals.

This is a preview of subscription content, access via your institution.


  1. 1.

    R. H. Havemann and U.S. Patent 4,541,167 (1986).

  2. 2.

    R. L. Guldi et al., J. Electrochem. Soc., 136, 3815 (1989).

    Article  Google Scholar 

  3. 3.

    Cotton and Wilkinson, Advanced Inorganic Chemistry, Interscience Publishers, USA, 1962.

    Google Scholar 

  4. 4.

    T. Lin, N. Tsai and C. Yeo, J. Electrochem. Soc., 138, 2145 (1991).

    CAS  Article  Google Scholar 

  5. 5.

    J. Nagel et al., J. Electrochem. Soc., 138, 2145 (1991), 140, 2356 (1993).

    Article  Google Scholar 

Download references


We would like to thank A. Rhodes and P. Chromiak for the polysilicon controls and measurements, J. K. Haas for the thermal oxide controls and measurements.

Author information



Corresponding author

Correspondence to Charles W. Pearce.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Pearce, C.W., Chung, B.C. The use of Metal Additions to Phosphoric Acid to Etch Polysilicon in Poly Buffered Locos Processes. MRS Online Proceedings Library 477, 459–464 (1997).

Download citation