Nanometer-precision pattern registration for scanning-probe lithographies using interferometric-spatial-phase imaging

Abstract

The authors propose a solution to drift and disturbances between a scanning-probe tip and a substrate that commonly distort scanned images and undermine effective lithographic patterning. An interferometric position detection method is employed to continuously suppress drift and control the tip-scanning trajectory with nanometer precision, relative to the substrate. An associated interferometric method is used to control tip height during approach to the substrate. Patterns with arbitrary geometries are written by means of a tap-imprint method, using probes with sub-0.7-nm tip diameters.

Back-scattered detection provides atomic-scale localization precision, stability, and registration in 3D

“…Then, a PZT stage would generate displacements that compensate for the locally measured drift. One implementation of this general method uses an optical grating as a sensor for both lithographic [9] and, more recently, atomic force microscope (AFM) applications [10]. But, such gratings and their accompanying optics are cumbersome, often are not local to the measurement point, and do not achieve atomic-scale stabilities, but rather stabilities of 0.28 nm, 0.39 nm, and <1 nm in x, y, and z, respectively [10].…”

High precision dynamic alignment and gap control for optical near-field nanolithography

“…10 As shown in Fig. 3(a), the ISPI grating pattern consists of a pair of two dimensional checkerboards, whose y-periodicity is uniform and the x-periodicity is chirped oppositely.…”

“…The ISPI gapping is based on the detection of interference fringes from a set of specially designed gratings on an optical mask. [9][10][11][12] By analyzing interference signals, the frequency and phase information of the interference fringes can be obtained and used to derive the value of the gap between the mask and the substrate. The ISPI system employs oblique light incident geometry so that it can be integrated with the lithography system without interfering with the lithography process.…”

Nanometer-level alignment using interferometric-spatial-phase-imaging (ISPI) during silicon nanowire growth

“…The mask and substrate alignment must be achieved with nanometer-level accuracy in all six degrees of freedom (X, Y, Z, yaw, pitch, and roll). Several alignment methods rely on interference of light to detect subwavelength alignment [1][2][3][4][5]. A white-light scanning interferometer measures the air gap thickness acting as a modulator from the source and eliminates any chromatic dispersion issue [5].…”

“…Alignment is determined from Fourier-based phase-difference analysis. ISPI has been proved to achieve alignment better than 1 nm sensitivity in gap and lateral alignments [1][2][3][4]. Advantages of the ISPI method include non-scanning scheme, high signal-to-noise ratio, and fluctuation tolerance.…”