Describe pros and cons of any two wafer thinning techniques

Describe pros and cons of any two wafer thinning techniques for 8-in. silicon wafers. What extra precautions would have to be considered if the wafer diameter were to increase to 12-in.

Solution

One of the most common technique for wafer thinning is mechanical grinding.

PROS

Because of its high thinning rate, mechanical grinding currently is the most common technique for wafer thinning.

cost benefit and cleanliness is more.

For conventional grinding the thinning is a two-step process.

1200 grit is a rough finish where the grind striations are clearly visible. 2000 grit has improved roughness compared to 1200 grit and the grind marks are less apparent. Poligrind is a near-mirror finish with the smoothest roughness. Poligrind also provides the highest wafer and die strength as the high grit wheel removes the most subsurface damage. As a rule, as the grit increases the wafer strength and smoothness improves while the wafer warpage and subsurface damage decreases.

CONS

Mechanical polishing cannot be done . It requires a separate process and equipment from mechanical grinding.

Mechanical polishing is a minimal removing process.

Another technique used is chemical-mechanical planarization (CMP).

PROS:

In CMP, abrasive chemical slurry is used with a polishing pad to perform material removal.

CMP provides greater planarization compared to mechanical grinding.

CMP does have the advantage of being more forgiving when it comes to processing
hard or exotic materials.

CONS

It is considered a dirtier and most costly process.

The wafers are mounted to a backing film, such as a wax mount, which can be difficult to remove or leave a residue on the front side of the wafer.