Multiple-surface interferometry of highly reflective wafer by wavelength tuning

Area of Science:

• Optical metrology
• Materials science
• Semiconductor manufacturing

Background:

• Accurate measurement of wafer surface topography and optical thickness is critical for semiconductor device fabrication.
• Highly reflective materials like lithium niobate (LNB) present challenges in optical testing due to significant harmonic signals and crosstalk.
• Existing interferometry methods struggle to effectively suppress these unwanted signals in LNB wafer testing.

Purpose of the Study:

• To develop and validate a novel phase-shifting algorithm for simultaneous measurement of surface shape and optical thickness variation of LNB wafers.
• To effectively suppress harmonic signals and crosstalk generated by highly reflective LNB samples during interferometric testing.
• To achieve high-accuracy measurements of optical thickness variation in LNB wafers.

Main Methods:

• Simultaneous measurement of surface shape and optical thickness using a wavelength-tuning interferometer.
• Implementation of a new phase-shifting algorithm with flexible phase-shift interval selection.
• Suppression of harmonic signals and crosstalk for highly reflective samples (LNB wafer in optical contact with fused-silica plate).

Main Results:

• The new phase-shifting algorithm successfully suppressed harmonic signals and crosstalk.
• Experimental validation demonstrated the capability of the method for simultaneous measurement.
• Optical thickness variation of the LNB wafer was measured with a high accuracy of 2 nm.

Conclusions:

• The developed phase-shifting algorithm offers an effective solution for metrology of highly reflective wafers like LNB.
• This technique enhances the accuracy and reliability of surface shape and optical thickness measurements.
• The method has significant implications for quality control and process optimization in LNB wafer manufacturing.