Semiconductor electrochemical etching processes employing closed loop control
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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Abstract
Methods and apparatus for providing closed-loop control over an electrochemical etching process during porous semiconductor fabrication enhance the quality of the porous semiconductor materials, especially those contained structural variations (such as porosity or morphology variations) along the thickness of said porous semiconductors. Such enhancement of the control over the electrochemical etching process is highly desired for many applications of porous semiconductor materials.
12 Citations
27 Claims
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1. A method of providing closed-loop control over an electrochemical etching process during porous semiconductor fabrication comprising:
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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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2. A method of providing closed-loop control over an electrochemical etching process during porous semiconductor fabrication comprising:
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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, and wherein said adjustment of the electrochemical etching parameters is performed according to the measured absolute amplitude value of the resistivity of the electrochemical etching system. - View Dependent Claims (3, 4)
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5. A method of providing closed-loop control over an electrochemical etching process during porous semiconductor fabrication comprising:
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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, counter electrode as a cathode and necessary hardware and/or software;
wherein at least part of said first surface of the semiconductor wafer is exposed to electrolyte,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 some temporal length, measuring the voltage oscillation frequency of the electrochemical etching system at least once during the electrochemical total process temporal length by setting the system to galvanostatic process conditions for at least some period of time and analyzing the temporal characteristics of the voltage needed by the electrochemical system in order to achieve a set level of electrical current density, and adjusting the electrochemical etching parameters according to the measurements of the voltage oscillation frequency of the electrochemical etching system at least once during the electrochemical total process temporal length. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A method of providing closed-loop control over an electrochemical etching process during porous semiconductor fabrication comprising:
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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, counter electrode as a cathode and necessary hardware and/or software, wherein at least part of said first surface of the semiconductor wafer is exposed to electrolyte, setting the electrochemical etching parameters to the electrochemical etching system comprising the semiconductor wafer as an anode, electrolyte, and counter electrode as a cathode, and performing the electrochemical etching process over a total process temporal period, measuring and storing the current-voltage curve of the electrochemical etching system at least once during the electrochemical total process temporal period, and adjusting the electrochemical etching parameters according to the voltage and current values of a characteristic feature of the measured current-voltage curve of the electrochemical etching system at least once during the electrochemical process temporal length, wherein said current-voltage curve measurements are performed by fixing all the electrochemical etching parameters at preliminarily set values, except for the current and applied voltage, tuning the applied voltage within a range, and measuring and recording the current obtained at each value of applied voltage.
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24. A method of providing closed-loop control over an electrochemical etching process during porous semiconductor fabrication comprising:
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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, counter electrode as a cathode and necessary hardware and/or software, wherein at least part of said first surface of the semiconductor wafer is exposed to electrolyte, setting the electrochemical etching parameters to the electrochemical etching system comprising the semiconductor wafer as an anode, electrolyte, and counter electrode as a cathode, and performing the electrochemical etching process over a total process temporal period, measuring and storing the current-voltage curve of the electrochemical etching system at least once during the electrochemical total process temporal period, and adjusting the electrochemical etching parameters according to the voltage and current values of a characteristic feature of the measured current-voltage curve of the electrochemical etching system at least once during the electrochemical process temporal length, wherein said characteristic feature of the current-voltage curve is the first peak of current and the current and voltage positions of said first peak are determined by mathematically processing the measured current-voltage curve.
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25. A method of providing closed-loop control over an electrochemical etching process during porous semiconductor fabrication comprising:
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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, counter electrode as a cathode and necessary hardware and/or software, wherein at least part of said first surface of the semiconductor wafer is exposed to electrolyte, setting the electrochemical etching parameters to the electrochemical etching system comprising the semiconductor wafer as an anode, electrolyte, and counter electrode as a cathode, and performing the electrochemical etching process over a total process temporal period, measuring and storing the current-voltage curve of the electrochemical etching system at least once during the electrochemical total process temporal period, and adjusting the electrochemical etching parameters according to the voltage and current values of a characteristic feature of the measured current-voltage curve of the electrochemical etching system at least once during the electrochemical process temporal length, wherein said characteristic feature of the current-voltage curve is the curve inflection point positioned between zero voltage and the first peak of current and the current and voltage positions of said inflection point are determined by mathematically processing the measured current-voltage curve.
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26. A method of providing closed-loop control over an electrochemical etching process during porous semiconductor fabrication comprising:
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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, counter electrode as a cathode and necessary hardware and/or software, wherein at least part of said first surface of the semiconductor wafer is exposed to electrolyte, setting the electrochemical etching parameters to the electrochemical etching system comprising the semiconductor wafer as an anode, electrolyte, and counter electrode as a cathode, and performing the electrochemical etching process over a total process temporal period, measuring and storing the current-voltage curve of the electrochemical etching system at least once during the electrochemical total process temporal period, and adjusting the electrochemical etching parameters according to the voltage and current values of a characteristic feature of the measured current-voltage curve of the electrochemical etching system at least once during the electrochemical process temporal length, wherein said adjustment of the electrochemical etching parameters is performed according to the measured relative change in the current and voltage positions of a characteristic feature on the measured current-voltage curve of the electrochemical etching system.
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27. A method of providing closed-loop control over an electrochemical etching process during porous semiconductor fabrication comprising:
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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, counter electrode as a cathode and necessary hardware and/or software, wherein at least part of said first surface of the semiconductor wafer is exposed to electrolyte, setting the electrochemical etching parameters to the electrochemical etching system comprising the semiconductor wafer as an anode, electrolyte, and counter electrode as a cathode, and performing the electrochemical etching process over a total process temporal period, measuring and storing the current-voltage curve of the electrochemical etching system at least once during the electrochemical total process temporal period, and adjusting the electrochemical etching parameters according to the voltage and current values of a characteristic feature of the measured current-voltage curve of the electrochemical etching system at least once during the electrochemical process temporal length, wherein said adjustment of the electrochemical etching parameters is performed according to the measured absolute values of current and voltage positions of a characteristic feature on measured current-voltage curve of the electrochemical etching system.
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Specification