Why Is The Structural Process of High Aspect Ratio More Difficult

In the TSV process, it is often mentioned that the through hole of the high aspect ratio, what is the high aspect ratio? Why is the higher the depth-to-width ratio, the more difficult it is to fill?

What is the depth to width ratio of the through hole?

Depth-to-width ratio = depth of through hole/diameter of through hole. For example, the diameter of the through hole we want to make is 20um and the depth is 100um, then the depth to width ratio of the hole is: 100/20=5:1

We often say that the high aspect ratio refers to the ratio of depth to width is larger, generally more than 5:1.

What are the problems caused by the high aspect ratio?

Structures with high aspect ratios are more difficult to process:

1, in the filling process such as electroplating, chemical vapor deposition (CVD) or physical vapor deposition (PVD), the structure with a high aspect ratio is more likely to have gaps.

2, in the dry etching process, the transport efficiency of gas and byproducts is reduced in the deep-hole structure, resulting in uneven etching rate and insufficient etching at the bottom.

3, the glue, exposure, development process is more difficult.

Which chip products have a high aspect ratio structure?

1, TSV(silicon through hole), TGV (glass through hole)

2, FinFET (fin-type field-effect transistor), fin depth to width ratio is very high

3, deep slot isolation of memory chips

4. Some microstructures of MEMS

5, microfluidic chip

And so on