Why Can Spin Coated Glass (SOG) Be Used To Flatten Wafers

The process of SOG?
SOG (Spin-on Glass), that is, Spin coated glass. SOG solution is a liquid compound of silicates based on silica.
The SOG solution is dropped in the center of the wafer, and then the wafer is rapidly rotated, and the solution is evenly coated on the surface of the wafer by centrifugal force, forming a uniform liquid film.
Soft drying to remove the solvent, so that the SOG film is called semi-solid.
Further heating at high temperature makes the SOG film completely solidified, and the organic groups in SOG undergo cross-linking reactions to form a solid glass layer.

What is the mechanism of SOG flattening?
In the process of soft baking, SOG solution flows into and fills the gaps and pits on the surface due to fluidity and capillary action, and can form a smooth and flat surface after full curing.
What does SOG do?
1, insulation: electrical isolation can be achieved between multi-layer metal interconnect structures to prevent electrical short circuit and capacitive coupling effect.
2, gap filling and flattening: SOG is a way of partial flattening, while cmp is global flattening.
3, improve light refraction and absorption: by adjusting the composition and thickness of SOG, control the absorption and reflection characteristics of light on its surface, optimize the exposure effect in the lithography process.
4, doping: SOG can be incorporated into impurities, used to adjust the electrical, optical or mechanical properties of the material.