The Influence of Doping on the Etching of Si(111)
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THE INFLUENCE OF DOPING ON THE ETCHING OF Si(111) Harold F. Winters* and D. Haarer** * IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120-6099 ** Universitaet Bayreuth, Lehrstuhl fuer Experimentalphysik IV, Postfach 3008, D-8580 Bayreuth, F.R.G. EXTENDED ABSTRACT It has been recognized for some time that the doping level in silicon influences etch rate in plasma environments[1-81. We have now been able to reproduce and investigate these doping effects in a modulated-beam, mass spectrometer system described previously [9] using XeF 2 as the etchant gas. The phenomena which have been observed in plasma reactors containing fluorine atoms are also observed in our experiments. The data has led to a model which explains the major trends. The influence of doping could be related to the electronic structure of the surface, the chemical influence of the dopant atoms, or some sort of impurity related phenomena. Using Auger spectroscopy, we have been unable to find a correlation between the surface concentration of dopant atoms or impurities and etching characteristics. Therefore, it is concluded that these doping phenomena are related to the electronic structure of the surface. Similar conclusions have been drawn previously. [1,2,4,71 It was previously suggested [10] that etching reactions were similar to the growth of thin oxide layers and could therefore be described by the ideas proposed by Mott and Cabrera, [11,12] i.e., that the presence of negative ions and/or an electric field at the surface strongly influences the reaction rate. This abstract summarizes data and ideas which will be described in more detail in ref. 13 and which show that there is a strong correlation between the estimated negative ion concentration at the surface and the etch rate. The experimental results which are related to the influence of doping on etch rate are summarized in this paragraph. References 13 and 14 refer to the etching of silicon with XeF2 while the other references deal with plasma assisted etching of silicon with fluorine and chlorine. In situations where the XeF 2 and plasma experiments overlap, they give similar results. The symbol nt -Si(111) means degenerately doped, n-type Si(111). 1. n÷-Si(111) etches much faster than undoped, lightly doped or p*-Si(111). (See refs. 1,2,3,4,6,5,7,13) 2. Lightly doped p-type silicon etches faster than p+-Si(111). (See refs. 13,2,4,7) 3. Both lightly doped p-type and n-type silicon have similar etch rates. (See refs. 13,4,7.) Mat. Res. Soc. Symp. Proc. Vol. 75. @,1987Materials Research Society
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The etch rates for n+-Si(111) and p+-Si(111) are similar when the fluorosilyl layer on the silicon surface is thin but differ greatly when the layer is thicker. (See ref. 13.) 5. Ion bombardment reduces the influence of doping on etch rates. (See refs. 13,2.) 6. Exposure of silicon to high intensity light increases the etch rate. (See ref. 14.) 7. The presence of alkali metals on the silicon surface increases the etch rate. (See ref. 8.) The experimental trends described a
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