Sub-nanometre double shearing heterodyne interferometry for profiling large scale planar surfaces

Abstract

A novel interferometric method, called a double shearing interferometry, is presented for profiling large-scale quasi-planar surfaces, such as semiconductor wafers, optical flats and x-ray mirrors. The surface profile is measured even under existence of the inclination of a scanning stage. By adopting the common-path optical configuration and the heterodyne detection, the proposed method realizes excellent resolution in sub-nanometer order and enables a robust measurement against unwanted disturbances due to the measurement environments. A height resolution of 0.1nm was experimentally achieved. A standard deviation of the analytical surface profiles was found to be 1.3nm, even when using a conventional screw-lead scanning stage. The measured results show that the surface profile and stage inclination are separately determined.We confirmed resultant profile was well consistent with the one measured with Fizeau interferometer.

Interaction Between Line Soliton andY-Periodic Soliton: Solutions to the Asymmetric Nizhnik–Novikov–Veselov Equation

“…In contrast to the reflection method described above, an imaging method [7], a laser interferometry method [3,4] and a two-laser light method [8,9] can all be successfully used for almost all the samples, since a rough surface can be examined by means of the scattered light on the surface. Figure 4 shows the basic optics of this method.…”

“…Many optical methods and devices have been developed and manufactured for this purpose. Some representative devices for the measurement of longitudinal resolution on a sub-nm scale have been developed, which are all based on laser interferometry employing sub-nanometre double shearing heterodyne interferometry [3] or a phase shift method [4]. Another device has been developed by the present authors, which is based on laser reflection [5].…”

“…Another device has been developed by the present authors, which is based on laser reflection [5]. Both methods [3,4] utilizing laser interferometry are based on the imaging of an irradiated area, and thus can obtain two-dimensional information instantaneously. However, the data processing involved with these methods is relatively time consuming since analysis of the interferogram is moderately difficult.…”

“…However, the data processing involved with these methods is relatively time consuming since analysis of the interferogram is moderately difficult. Also, these methods and devices [3][4][5] for nm measurement are very complicated and expensive. Our method, on the other hand, though it can scan only a line on a surface and requires many measurements to scan a two-dimensional region, is relatively simple and inexpensive, and provides a real-time technique for data acquisition.…”

A double common-path heterodyne interferometer for the measurement of flying height modulation

“…The resolution reaches 0.1 nm in terms of phase measurement [21], and the frequency of data sampling can be higher than 500 kHz. The Abbe error which resulted from the rotating pitch of the disk [22] is in situ compensated by the double interferometers that are symmetrically placed [23]. Both interferometers share the same Wollaston prism, which divides the measurement and reference beams by a very small angle so that the whole system provides strong ability to resist environmental disturbance.…”