Abstract
This paper presents a calibration line between leaky surface acoustic wave (LSAW) velocities (V LSAW ) and coefficient-of thermal-expansion (CTE) characteristics for TiO 2 -doped SiO 2 (TiO 2 -SiO 2 ) glass to evaluate the absolute CTE by the line-focus-beam ultrasonic material characterization (LFB-UMC) system. Commercial TiO 2 -SiO 2 ultra-low-expansion glass and synthetic silica glass were selected as specimens. We measured V LSAW by the LFB-UMC system and CTE characteristics by dilatometers, and obtained relationships among V LSAW , CTE at 22°C {CTE(22°C){ and zero-CTE temperature {T(zero-CTE)}. Resolutions of CTE(22°C) and T(zero-CTE) determined by the LSAW velocity measurement were estimated as ±0.72 (ppb/K) and ±0.14°C (+2σ, σ. standard deviation) at 225 MHz. Both manufacturers and users can precisely inspect T(zero-CTE) for all EUVL-grade ultra-low-expansion glass substrates by this indirect evaluation method using the calibration line.
Published Version
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