Freeze Drying of High Aspect Ratio Structures

As semiconductor devices continue to scale down to smaller sizes, high aspect ratio (HAR) structures are required to achieve the desired device performance. As such, wet processing becomes a very challenging process step due to the capillary forces that are generated during drying. The strength of the capillary force is dependent on the surface tension and contact angle of the fluid that is being dried, as well as the feature spacing and AR. If the drying forces are too high (Figure 1), then the features may break or collapse onto each other resulting in poor device yield. Other factors affecting a structure’s susceptibility to collapse include pattern geometry and material composition [1].