Inductive sensor interface for on-wafer plating thickness measurements

A metrology chamber configured to retain a wafer chuck, the metrology chamber comprising:

• a sensor head assembly comprising a coil sensor configured to measure an oscillation frequency of a wafer;
• a swing arm configured to position the sensor head assembly above the wafer chuck;
• and
• a sensor interface configured to determine a thickness of plating on a wafer, comprising:
• an inductance to digital converter (LDC) configured to receive an input from the coil sensor, and configured to convert the input to data;
• a microcontroller (MCU) configured to receive the data and to convert the data into digital data;
• a digital to analog convertor (DAC) configured to convert the digital data to an analog signal;
• and
• an amplifier configured to amplify an input voltage range of the analog signal to an output voltage range of the analog signal, wherein the output voltage range is greater than the input voltage range, and
• an analog sensor configured to determine the thickness of plating on the wafer based on the output voltage range of the analog signal.

A method of determining a thickness of plating on a wafer with a sensor interface comprising an inductance to digital converter (LDC), a microcontroller (MCU), a digital to analog convertor (DAC), and an amplifier, the method comprising:

• converting an oscillation frequency into data with the LDC;
• reading the data into the MCU and converting the data into digital data;
• converting the digital data to an analog signal with the DAC;
• applying a selectable voltage offset and a gain to the analog signal with the amplifier;
• outputting the analog signal by the amplifier to an analog input, wherein an output voltage range of the analog signal is greater than an input voltage range of the analog signal;
• and
• determining the thickness of plating on the wafer.