Thamban, P. L. Stephan

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Dr. P. L. Stephan Thamban is a Senior Lecturer in the Department of Mechanical Engineering. His research interests include: materials processing with low temperature plasmas and process control diagnostics in semiconductor device manufacturing.


Recent Submissions

Now showing 1 - 3 of 3
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    Silicon Etch Using SF₆/C₄F₈/Ar Gas Mixtures
    Bates, Robert L.; Thamban, P. L. Stephan; Goeckner, Matthew J.; Overzet, Lawrence J.; 0000 0000 5396 3610 (Goeckner, MJ); 0000 0003 5379 4329 (Overzet, LJ); 0000 0001 2766 4681 (Thamban, PLS); 2008008261‏ (Goeckner, MJ)
    While plasmas using mixtures of SF₆, C₄F₈, and Ar are widely used in deep silicon etching, very few studies have linked the discharge parameters to etching results. The authors form such linkages in this report. The authors measured the optical emission intensities of lines from Ar, F, S, SFx, CF₂, C₂, C₃, and CS as a function of the percentage C₄F₈ in the gas flow, the total gas flow rate, and the bias power. In addition, the ion current density and electron temperature were measured using a floating Langmuir probe. For comparison, trenches were etched of various widths and the trench profiles (etch depth, undercut) were measured. The addition of C₄F₈ to an SF₆/Ar plasma acts to reduce the availability of F as well as increase the deposition of passivation film. Sulfur combines with carbon in the plasma efficiently to create a large optical emission of CS and suppress optical emissions from C₂ and C₃. At low fractional flows of C₄F₈, the etch process appears to be controlled by the ion flux more so than by the F density. At large C₄F₈ fractional flows, the etch process appears to be controlled more by the F density than by the ion flux or deposition rate of passivation film. CF₂ and C₂ do not appear to cause deposition from the plasma, but CS and other carbon containing molecules as well as ions do.
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    Electron Beam Excitation Method to Study Gas Phase During Etch Processes
    Stephan Thamban, P. L., 1975-; Padron-Wells, Gabriel; Yun, Stuart; Hosch, Jimmy W.; Goeckner, Matthew J.; 0000 0000 5396 3610 (Goeckner, MJ); 0000 0001 2766 4681 (Thamban, PLS); 2008008261‏ (Goeckner, MJ)
    In process optical emission spectroscopy (OES) measurements, excitation mechanisms as dictated by the process plasma can be complex to analyze optical signals quantitatively. Applications of a new electron beam excitation method demonstrate distinct merits for plasma process diagnostics and process control. The electron energy control attribute of the method provides the means to optimize and monitor specific species optical emission in process chemistries to achieve process control such as endpoint. The authors present gas phase results from photoresist ash and SiO2 etch using O-2 and CF4/Ar discharges, respectively. The effluent density variations as measured with the e-beam method during process stages demonstrate process endpoint detection. Simultaneous measurements with FTIR spectroscopy and direct plasma OES is also presented for comparison.
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    Comparison endpoint study of process plasma and secondary electron beam exciter optical emission spectroscopy
    (American Vacuum Society, 2012-10-03) Thamban, P. L. Steven; Padron-Wells, Gabriel; Hosch, Jimmy W.; Yun, Stuart; Goeckner, Matthew J.; 0000 0001 2766 4681 (Thamban, PLS); 0000 0000 5396 3610 (Goeckner, MJ); 2008008261‏ (Goeckner, MJ)
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