2-Step algorithm for automatic alignment in wafer dicing process

Even in the semiconductor industry, free-space optical technology is nowadays seen as a prime option for solving the continually aggravating problem with VLSI chips, namely, that the interconnect technology has failed to keep pace with the increase in communication volume. To make free-space optics compatible with established lithography-based design and fabrication techniques the concept of planar integration was proposed approximately a decade ago. Here its evolution into a photonic microsystems engineering concept is described. For demonstration, a multichip module with planar-integrated free-space optical vector-matrix-type interconnects was designed and built. It contains flip-chip-bonded vertical-cavity surface emitting laser arrays and a hybrid chip with an array of multiple-quantum-well p-i-n diodes on top of a standard complementary metal-oxide semiconductor circuit as key optoelectronic hardware components. The optical system is integrated into a handy fused-silica substrate and fabricated with surface-relief diffractive phase elements. It has been optimized for the given geometrical and technological constraints and provides a good interconnection performance, as was verified in computer simulations on the basis of ray tracing and in practical experiments.

Multichip module with planar-integrated free-space optical vector-matrix-type interconnects

Self-imaging means image formation without the help of a lens or any other device between object and image. There are three versions of self-imaging: the classical Talbot effect (1836), the fractional Talbot effect, and the Montgomery effect (1967). Talbot required the object to be periodic; Montgomery realized that quasiperiodic suffices. Classical means that the distance from object to image is an integer multiple of the Talbot distance zT=2p2∕λ, where p is the grating period. Fractional implies a distance that is a simple fraction of zT: say, zT∕2,zT∕4,3zT∕2 … . We explore the most general case of the fractional Montgomery effect.

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Fractional Montgomery effect: a self-imaging phenomenon

An integrated three-dimensional optical multilayer system for optical data communications is presented. It is based on the use of free-space optical light propagation and combines two integration principles, namely, planar and stacked integration. The combination of both integration schemes aims at a maximal design flexibility for complex geometric layouts. On the other hand, packaging issues that stem from assembly and tolerance have to be considered. Here we describe the basic concept and demonstrate the implementation of an optical interface module in a processor-memory bus.

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Integrated three-dimensional optical multilayer using free-space optics.

Montgomery self-imaging effect using computer-generated diffractive optical elements

A method for aligning a photolithographic mask at the top of a transparent wafer that has a pattern on its bottom side is presented. The method is based on optical self-imaging of special alignment marks and provides submicrometer accuracy. The method is simple and robust and can conveniently be implemented on laboratory mask aligners for contact or proximity printing.

Precise and simple optical alignment method for double-sided lithography.

Talbot interferometer as a time filter

The Talbot interferometer consists of two gratings at a finite distance from each other. We consider a configuration of two phase gratings where the second coherently combines the diffraction orders generated by the first grating and discuss its use as a temporal filter. .

The flexibility of diffractive optics can offer interesting solutions to a variety of sensing problems. Here, we consider two examples: (1) the determination of the color of LEDs and (2) correlation spectroscopy. In both cases, optical setups are matched to a specific task which results in efficient and impulse systems. This makes them interesting for sensing applications in process control and monitoring. Compact micro-optical systems result by using lithographic fabrication and integration of the free-space optical components on single substrates. We describe principles and basic applications of our concept.

Detlev Hagedorn

Papers

Precise and simple optical alignment method for double-sided lithography.

Talbot interferometer as a time filter

Talbot interferometer as a time filter

Sensing applications of diffractive optics with broadband illumination