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Junction Depth Measurement by Anodic Oxidation and Light Induced Voltage Measurement Technique

IP.com Disclosure Number: IPCOM000091917D
Original Publication Date: 1968-Jul-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Duffy, MC: AUTHOR [+3]

Abstract

The junction depth of a semiconductor wafer is measured by successively removing layers and measuring the voltage induced by a source of light at each layer. The waveform obtained by this measurement is shown. The following is a sequence of steps performed to determine the junction depths in diffused silicon wafers. There is anodic oxidation of a wafer to form a known thickness of SiO(2) on the surface. The SiO(2) is removed with HF acid. The wafer is enclosed in complete darkness and two probes are placed on the surface, the distance between the probes on the surface being constant for every measurement. Light of a given intensity is shined on the surface of the wafer the induced voltage is recorded. The four steps are repeated. As the emitter-base junction is approached, a negative voltage is induced by the light.

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Junction Depth Measurement by Anodic Oxidation and Light Induced Voltage Measurement Technique

The junction depth of a semiconductor wafer is measured by successively removing layers and measuring the voltage induced by a source of light at each layer. The waveform obtained by this measurement is shown. The following is a sequence of steps performed to determine the junction depths in diffused silicon wafers. There is anodic oxidation of a wafer to form a known thickness of SiO(2) on the surface. The SiO(2) is removed with HF acid. The wafer is enclosed in complete darkness and two probes are placed on the surface, the distance between the probes on the surface being constant for every measurement. Light of a given intensity is shined on the surface of the wafer the induced voltage is recorded. The four steps are repeated. As the emitter-base junction is approached, a negative voltage is induced by the light. When the emitter-base junction is traversed, a positive voltage is induced. The positive voltage increases as the base-collector junction is approached. As the junction is passed, the induced voltage drops sharply to a negative level. The test points on the waveform indicate measured values of induced voltage at each layer. By removing the silicon in 0.3 micro-inch steps, the accuracy of this method is approximately +/- 0.1 micro-inches.

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