| US 7,560,018 B2 | ||
| Semiconductor electrochemical etching processes employing closed loop control | ||
| Vladimir Kochergin, Westerville, Ohio (US); and Marc Christophersen, Westerville, Ohio (US) | ||
| Assigned to Lake Shore Cryotronics, Inc., Westerville, Ohio (US) | ||
| Filed on Jan. 21, 2005, as Appl. No. 11/38,500. | ||
| Claims priority of provisional application 60/537508, filed on Jan. 21, 2004. | ||
| Prior Publication US 2005/0199511 A1, Sep. 15, 2005 | ||
| Int. Cl. B23H 3/02 (2006.01) | ||
| U.S. Cl. 205—645 [205/641; 205/646] | 27 Claims |
| 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, and
adjusting 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, and
wherein 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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