title: Femtosecond laser pulses for fast 3-D surface profilometry of microelectronic step-structures.
abstract: Fast, precise 3-D measurement of discontinuous step-structures fabricated on microelectronic products is essential for quality assurance of semiconductor chips, flat panel displays, and photovoltaic cells. Optical surface profilers of low-coherence interferometry have long been used for the purpose, but the vertical scanning range and speed are limited by the micro-actuators available today. Besides, the lateral field-of-view extendable for a single measurement is restricted by the low spatial coherence of broadband light sources. Here, we cope with the limitations of the conventional low-coherence interferometer by exploiting unique characteristics of femtosecond laser pulses, i.e., low temporal but high spatial coherence. By scanning the pulse repetition rate with direct reference to the Rb atomic clock, step heights of ~69.6 μm are determined with a repeatability of 10.3 nm. The spatial coherence of femtosecond pulses provides a large field-of-view with superior visibility, allowing for a high volume measurement rate of ~24,000 mm3/s.
authors.affiliation: Ultrafast Optics for Ultraprecision Group, Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Science Town, Daejeon, 305-701, South Korea.
authors.forename: Woo-Deok
authors.initials: WD
authors.lastname: Joo
authors.forename: Seungman
authors.initials: S
authors.lastname: Kim
authors.forename: Jiyong
authors.initials: J
authors.lastname: Park
authors.forename: Keunwoo
authors.initials: K
authors.lastname: Lee
authors.forename: Joohyung
authors.initials: J
authors.lastname: Lee
authors.forename: Seungchul
authors.initials: S
authors.lastname: Kim
authors.forename: Young-Jin
authors.initials: YJ
authors.lastname: Kim
authors.forename: Seung-Woo
authors.initials: SW
authors.lastname: Kim