Comparison of the Phase Metrics DFHT IV and Zygo Pegasus 2000 fly height testers

The performance of the Phase Metrics DFHT IV (DFHT) fly height tester was c ompared with the performance of the Zygo Pegasus 2000 (P2000) fly height te ster. The testers showed comparable repeatabilities (0.25 mn for the DFHT a nd 0.30 nm for the P2000) and correlated well at all points except at the c enter rail trailing edge. The DFHT had a measurement uncertainty of 0.76 ru n at a fly height of 25 nm and 0.35 nm near contact. Similarly the P2000 ex hibited an uncertainty of 1 nm at 25 nm and 0.5 run at contact. The measure ment uncertainty of the DFHT is due to calibration at a location different from the measurement location; for the P2000, it is primarily due to residu al uncertainty in the correction for stress-induced birefringence in the te st disk. The P2000 did not recognize the presence of small diamondlike carb on bumps on the air bearing surface. There was a consistent 3-nm absolute o ffset between the fly height measurements of the two testers. Neither teste r possessed a clear advantage over the other in the approaching era of near -contact recording. (C) 2001 Optical Society of America.