Closed-loop control of composition and temperature during the growth of InGaAs lattice matched to InP

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Abstract

Spectroscopic ellipsometry (SE) and diffuse reflection spectroscopy (DRS) are used to control the Ga mole fraction and substrate temperature, respectively, during the growth of InGaAs lattice matched to InP. Ga mole fraction is controlled to within ±0.002 of its target value and substrate temperature is controlled to within ±2 °C of its target value. The same growth under constant thermocouple control would result in a 50 °C rise in real substrate temperature and a Ga composition 1% above its target value. In both cases, feedback control is achieved using a nested proportional-integral-derivative (PID) control loop, where, the inner loop consists of the conventional Eurotherm-thermocouple feedback loop and the outer loop updates the thermocouple setpoint using a PID control loop implemented in the control software. For composition control, the Ga cell thermocouple setpoint is increased (decreased) 0.2 °C for every 0.002 that the Ga mole fraction, given by the SE sensor, deviates below (above) the target value. During substrate temperature control, the thermocouple setpoint is updated based on the temperature difference between the DRS sensor and the user setpoint. Frequency loop shaping, based on a dynamical model of the system obtained from an identification experiment, is used to tune the outer PID loop.

Original languageEnglish (US)
Pages (from-to)1237-1240
Number of pages4
JournalJournal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures
Volume17
Issue number3
StatePublished - Dec 1 1999

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Thermocouples
thermocouples
Chemical analysis
Spectroscopic ellipsometry
Substrates
Derivatives
Temperature
temperature
ellipsometry
Spectroscopy
Sensors
Temperature control
sensors
temperature control
Feedback control
feedback control
Identification (control systems)
spectroscopy
temperature gradients
Feedback

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Electrical and Electronic Engineering

Cite this

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title = "Closed-loop control of composition and temperature during the growth of InGaAs lattice matched to InP",
abstract = "Spectroscopic ellipsometry (SE) and diffuse reflection spectroscopy (DRS) are used to control the Ga mole fraction and substrate temperature, respectively, during the growth of InGaAs lattice matched to InP. Ga mole fraction is controlled to within ±0.002 of its target value and substrate temperature is controlled to within ±2 °C of its target value. The same growth under constant thermocouple control would result in a 50 °C rise in real substrate temperature and a Ga composition 1{\%} above its target value. In both cases, feedback control is achieved using a nested proportional-integral-derivative (PID) control loop, where, the inner loop consists of the conventional Eurotherm-thermocouple feedback loop and the outer loop updates the thermocouple setpoint using a PID control loop implemented in the control software. For composition control, the Ga cell thermocouple setpoint is increased (decreased) 0.2 °C for every 0.002 that the Ga mole fraction, given by the SE sensor, deviates below (above) the target value. During substrate temperature control, the thermocouple setpoint is updated based on the temperature difference between the DRS sensor and the user setpoint. Frequency loop shaping, based on a dynamical model of the system obtained from an identification experiment, is used to tune the outer PID loop.",
author = "Shane Johnson",
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AB - Spectroscopic ellipsometry (SE) and diffuse reflection spectroscopy (DRS) are used to control the Ga mole fraction and substrate temperature, respectively, during the growth of InGaAs lattice matched to InP. Ga mole fraction is controlled to within ±0.002 of its target value and substrate temperature is controlled to within ±2 °C of its target value. The same growth under constant thermocouple control would result in a 50 °C rise in real substrate temperature and a Ga composition 1% above its target value. In both cases, feedback control is achieved using a nested proportional-integral-derivative (PID) control loop, where, the inner loop consists of the conventional Eurotherm-thermocouple feedback loop and the outer loop updates the thermocouple setpoint using a PID control loop implemented in the control software. For composition control, the Ga cell thermocouple setpoint is increased (decreased) 0.2 °C for every 0.002 that the Ga mole fraction, given by the SE sensor, deviates below (above) the target value. During substrate temperature control, the thermocouple setpoint is updated based on the temperature difference between the DRS sensor and the user setpoint. Frequency loop shaping, based on a dynamical model of the system obtained from an identification experiment, is used to tune the outer PID loop.

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