Sub Micron Polishing Technology (SµPT^TM) enables full automation of the polish-clean-inspect cycle for significantly increased success rates in manufacturing fiber-optic planar devices.

SµPT^TM is the preferred methodology in the semiconductor industry in using automated polishing for increased success rates, surface quality and accuracy. The extensive application of this technique is primarily attributed to its high reproducibility and yields.

This technique today is also being used by fiber optic component manufacturers to approach higher yields through automation.

Sagitta provides the SµPT^TM technology on the Gemini-Pi, the first fully automated multi-station polish and inspection system for photonic devices. Integration and automation of three major steps in a single system will be described:

To polish planar devices such as Arrayed Wave guide Grating, splitters, filters, multiplexeres as well as fiber optics components (V-grooves, fiber tips) to an optical surface finish. General requirements for the polishing finish would be as follows:

Standard process should vary between 3 to 4 step process:
The optimization of the process flow is vital to minimize grain structure deformation in the surface of contact.
- Rough grinding: Should remove the bulk material and form the required geometry.
- Planar Polishing (up to 2 stages): Smooth the surface by removing the damages caused during grinding. The depth of defects in this stage is significantly reduced.
- Final lapping: generates the final surface quality.

Polishing materials are chosen according to their compatibility to the device structure: Mechanical properties, chemical compatibility, support of the abrasive as well as hardness and composition of the abrasive bonding for firm abrasives.
We chose in our polishing process flow firm abrasives during the first polishing stages and loose abrasive in the final lapping with 0.05 micron colloidal silica on soft pad to reach high surface quality.

The motion of the sample on the polishing wheel is important to reach high surface qualities as well as equal polishing rates across the device. The relative motion of the sample vs. the polishing wheel when both move in circular motion is given by the formula below:

V _relative = V _polisher - V _head

V _relative X = - r sin φ ( ω _polisher - ω _head )

V _relative Y = r cos φ ( ω _polisher - ω _head ) + ω _polisher R

The ideal relative motion for high surface quality is when the vector of velocity varies between zero to II radians where as for equal polishing rates one velocity throughout the device is necessary (ω _polisher = ω _head). Optimization between surface quality and equal polishing rates can be done by using  ω _polisher « ω _head .

Avoiding cross contamination, especially before the final lapping stage, is critical to surface quality and overall yields. While some devices may require lower frequencies to protect fragility, SµPT^TM achieves this goal through ultrasonic cleaning generally done in 30-40 kHz, along with detergent media and followed by a rinse and dry cycle. The particles targeted for removal are 1um organic and inorganic based particles, e.g. Silicon, Silicon Oxide and Diamond.

The optical inspection integrated in SµPT^TM detects pre-defined defects, such as scratches and particles in the wave guide area, and characterizes the quality of the cut. Moreover, inspection is used between batches to create statistical process control (SPC) and monitoring, to increased production yields.

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ASM Surface Roughness Measurement