Projection optics design for tilted projection of fringe patterns

Abstract

A challenge in the semiconductor industry is 3-D inspection of the miniaturized solder bumps grown on wafers for direct die-to-die bonding. An inspection mechanism proposed earlier requires the projection of a binary fringe grating to the inspected surface from an inclined angle. For high speed and accuracy of the mechanism, the projection optics has to meet these requirements: ͑1͒ it allows a tilt angle between the inspected surface and the projector's optical axis; ͑2͒ it has a high bandwidth to let high-spatial-frequency harmonics contained in the binary grating pass through the lens and be projected onto the inspected surface properly; ͑3͒ it has a high modulation transfer function; ͑4͒ it has a large field of view; and ͑5͒ it has an adequate depth of field that matches the depth range of the inspected surface. In this paper, we describe a projection optics design, consisting of a fringe grating and several pieces of spherical lens, that addresses the requirements. To reduce the lens aberrations, the grating is laid out with an angle chosen specifically to make the grating, the lens, and the average plane of the inspected surface intersect in the same line. Performance analysis and tolerance analysis are shown to demonstrate the feasibility of the design.

An illumination-invariant phase-shifting algorithm for three-dimensional profilometry

“…And in real systems, a projection optics design tilted projection of fringe pattern can ensure the measuring plane is uniformly focused. 16 Then we focus on the dominant uneven effect from illumination in experiments.…”

Regularized multiframe phase-shifting algorithm for three-dimensional profilometry

“…However, surface reconstruction at the low fringe contrast region is often important such as for surface defect inspection and volume measurement. Therefore, a tilted optics system has been designed to improve the image quality [18]. In this paper, we improve the accuracy and robustness for the surface profile from a signal processing point of view by solving a constrained optimization problem.…”

“…When ϕx 1; y ϕx; y and ϕx; y 1 ϕx; y, the above expressions can be simplified to Eqs. (18) and (19). For locally smooth surfaces with homogeneous reflectivity, these approximations are suitable for an initial estimation.…”

Three-dimensional microscopy and sectional image reconstruction using optical scanning holography

“…However, the three-dimensional image is formed by a three-dimensional raster scan of the entire object, which is a slow process. This is a major disadvantage of confocal microscopy in applications that demand fast processing or high throughput, such as in [2]. Similarly, optical coherence tomography (OCT) achieves such true-depth slicing by rejecting the out-of-focus information before detection, this time by interference between two beans with short temporal coherence.…”