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Semiconductor electrochemical etching processes employing closed loop control

  • US 7,560,018 B2
  • Filed: 01/21/2005
  • Issued: 07/14/2009
  • Est. Priority Date: 01/21/2004
  • Status: Active Grant
First Claim
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1. A method of providing closed-loop control over an electrochemical etching process during porous semiconductor fabrication comprising:

  • providing a substrate wafer of single-crystal semiconductor having a first surface and a second surface,disposing the substrate wafer in an electrochemical etching apparatus comprising the semiconductor wafer as an anode, electrolyte, and counter electrode as a cathode,executing an electrochemical etching process wherein at least part of said first surface of the semiconductor wafer is exposed to electrolyte to thereby etch high aspect ratio pores in said semiconductor wafer,setting the electrochemical etching parameters to the electrochemical etching system comprising the substrate wafer, electrolyte and counter electrode, and performing the electrochemical etching process at over a process time period,measuring the value of the resistance of the electrochemical etching system at least once during the electrochemical process time period, andadjusting the electrochemical etching parameters according to the measurements of the resistivity of the electrochemical etching system at least once during the electrochemical process time period,wherein said electrochemical etching adjustment parameters are one or more selected from the group consisting of electrical current density, illumination intensity, temperature of the electrolyte, applied voltage, the electrochemical etching process type, temporal characteristics of any or all of said parameters, and the electrochemical total process time period,wherein said adjustment of the electrochemical etching parameters is performed according to the measured relative change in the resistance of the electrochemical etching system in real time, andwherein the electrochemical etching parameter that is adjusted is the temporal characteristic of the applied electrical current density, more particularly said electrical current density varies in time according to a mathematical function having a characteristic temporal interval, said temporal interval of the mathematical function being adjusted according to the formula T(t)=T(t0

    R(t, I)/R(t0, I), wherein R(t, I))=U(t)/I is the measured resistance of the electrochemical etching system at time t taken at applied current density I, T is a temporal interval of said mathematical function, wherein values T(t0), I and t0 are set preliminary to the start of the electrochemical etching process.

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