Development of a Microwave-Laser Measurement Technique and Contactless Measurement of Conductivity of Silicon Wafer in an Infinitesimal Area

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1.Development of a microwave-laser measurement systemA measurement system for detecting the phase variation of a laser light occurring in an electro-optic crystal was developed. The phase variation is induced by the changed index of refraction when a microwave beam is applied to the electro-optic crystal. The variation of the polarized light of a femtosecond pulse laser generated due to the electro-optic effect was successfully detected; thereby the sampling of a high frequency microwave (millimeter-wave) becomes possible.2. Contactless measurement of conductivity of silicon wafer independent of the thicknessA method for quantitative measurement of electrical conductively of semiconductor wafers in a contactless fashion by using millimeter waves was developed, A high-frequency millimeter wave was used in order to ensure the transmitted millimeter wave attenuated rapidly inside the wafer so that the reflection from the bottom surface of the wafer can be neglected. Thereby it becomes possible only to consider the reflection on the top surface of the wafer and thus the millimeter wave response signal is not affected by the thickness of the wafer. In addition, in the experiment, both the amplitude and phase of the reflection coefficient are measured, and by using these two parameters it is possible to determine the conductivity independent of the permittivity of the semiconductor wafers.3. Measurement of conductivity distribution of silicon wafer with high spatial resolution and sensitivityDistribution of the conductivity of silicon wafer was measured by microwave imaging. An open-ended coaxial line sensor was used to increase the spatial resolution and the sensitivity of the measurement. The relationship of the amplitude of the reflection coefficient and the conductivity of a wafer was found to be linear. The demonstrated method could be used to determine conductivity distribution in the process of wafer manufacturing or during device fabrication.