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Feedback Control for Silicon Doping

IP.com Disclosure Number: IPCOM000062178D
Original Publication Date: 1986-Oct-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Iyer, SS: AUTHOR

Abstract

This article relates generally to silicon molecular beam epitaxy (Si MBE) and, more particularly, to a closed loop system for controlling the level of doping. Improved control of the doping process in Si MBE results from monitoring the dopant desorption rate and dynamically varying the dopant flux concentration or substrate temperature in response to that rate. In the figure, a substrate 1 being subjected to Si MBE is supported on heater assembly 2 in an evaporator unit. A dopant flux beam is directed from effusion cell 3 to the substrate. Beam flux detector 4, that may be either a beam flux monitor, similar to an ion gauge, or a quadrapole mass spectrometer, measures the amount of desorbing dopant and issues an output signal proportional to the desorption rate.

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Feedback Control for Silicon Doping

This article relates generally to silicon molecular beam epitaxy (Si MBE) and, more particularly, to a closed loop system for controlling the level of doping. Improved control of the doping process in Si MBE results from monitoring the dopant desorption rate and dynamically varying the dopant flux concentration or substrate temperature in response to that rate. In the figure, a substrate 1 being subjected to Si MBE is supported on heater assembly 2 in an evaporator unit. A dopant flux beam is directed from effusion cell 3 to the substrate. Beam flux detector 4, that may be either a beam flux monitor, similar to an ion gauge, or a quadrapole mass spectrometer, measures the amount of desorbing dopant and issues an output signal proportional to the desorption rate. This output signal is compared with a reference signal in a summing device 5 that issues a correction signal to vary the output of either the effusion cell or substrate temperature or both. This technique maintains the proper amount of surface phase of the dopant to achieve sharp doping profiles. Since the control is dynamic, correction signals are not large, and changes in flux or substrate temperature are small and effectively executed without delay due to thermal inertia.

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