Endpoint detection of silicon wafer etching
Sinor, Timothy Wayne
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This thesis describes the results of an investigation into the use of plane polarized light for performing in situ endpoint monitoring of oxide thickness during the etching of silicon wafers. The continuous monitoring of the oxide thickness can be accomplished by analysis of the reflection characteristics of the plane polarized light. This information then allows the etching to be terminated when the oxide thickness approaches zero, thus, providing a means to control the etching process. To accomplish on line monitoring of the oxide thickness, plane polarized light from an argon ion laser passing through a rotating half-wave plate which alternately switches the polarization from transverse electric (TE) to transverse magnetic (TM). The modulated laser light is specularly reflected from the oxide-coated silicon wafer and is sensed by a silicon photo-detector. A.C. detection techniques are employed to measure the normalized reflectance intensity which is related to the thickness of the oxide coating. Oxide thicknesses on the order of 1000 A can be measured with the device to an accuracy of about 0.4%. Oxide thicknesses less than 50 A cannot be measured with accuracy.