Immersion diffractometry for determining nanoscale grating pitch.

Area of Science:

• Optics and Photonics
• Metrology
• Nanotechnology

Background:

• Laser diffractometers are crucial for calibrating grating pitch standards.
• Conventional Littrow configuration diffractometers face a half-wavelength limit for measuring fine gratings in air.
• This limitation hinders the precise calibration of sub-wavelength grating structures.

Purpose of the Study:

• To propose and demonstrate an immersion diffractometer technique for overcoming the conventional half-wavelength limit.
• To enable accurate measurement of grating pitches smaller than half the laser wavelength.
• To enhance the capabilities of grating pitch calibration in optical metrology.

Main Methods:

• Development of an immersion diffractometer by increasing the environmental refractive index.
• Calibration of a 288 nm grating using the proposed immersion diffractometer with a 633 nm laser.
• Comparison with measurements from a conventional diffractometer using a 543 nm laser.

Main Results:

• The immersion diffractometer successfully measured a 288 nm grating, overcoming the half-wavelength limitation.
• The proposed method demonstrated feasibility and effectiveness in grating pitch calibration.
• Pitch measurements showed a high degree of agreement, with a difference of approximately 0.05 nm between methods.

Conclusions:

• The immersion diffractometer is an effective solution for calibrating grating structures with pitches below the half-wavelength limit.
• This technique significantly improves the precision and range of grating metrology.
• The study validates the practical application of immersion diffractometry for advanced optical component calibration.