Why is it so hard and hence expensive to control the TTV under 0.5 µm? 

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Looking for Si wafer that has thickness control of 1.0mm +/- 0.5um

For 3"Ø or 4"Ø wafers we can achieve TTV<0.5µm (with 3mm edge exclusion),
for either lapped, or ground or double-side-polished wafers, but it is expensive.

To achieve absolute thickness of 1,000.0±0.5µm is another matter.
We would have to agree on a common calibration standard.

We cannot achieve Bow/Warp<0.5µm. It is impossible to measure these parameters with such precision.

silicon substrate total thickness variation


For 3"Ø and 4"Ø wafers we can certainly achieve Bow<5µm, Warp<10µm.
Anything less would require careful definition of how these parameters would be measured.

The above conversation was a question and answer session between our engineer and a research client.

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Why is it so hard and hence expensive to control the TTV under 0.5 µm?

Total Thickness Variation TTV is a measure of flatness. It is the difference between thickest and the thinnest portion of the wafers. It is harder to make a wafers that has a TTV<5µm than it is to make one that is TTV<10µm. It is harder still to make TTV<1µm. It is harder still to make TTV<0.5µm. It is harder still to make TTV<0.05µm. And so on. If it was easy to make TTV<0.5µm then that would be the standard. It is not easy and so the standard is <10µm. Please confirm that you understand this concept that tighter specifications are harder to achieve and thus more expensive.

1,000.0±0.5µm means that all of the wafers when measured have a center point thickness of 1,000µm with a 0.5µm tolerance. So, every wafer will be in the range of (999.5-1,000.5). The standard range is ±25µm (975-1,075). It is more difficult to make ±10µm. It is even more difficult to make ±5µm. More difficult to make ±1µm. Even more difficult to make ±0.5µm. Please confirm that you understand of a lower thickness tolerance is harder to achieve and thus more expensive.

We can do much better than SEMI standard for Bow/Warp. Standard is <40µm and we can do Bow<5µm and Warp<10µm. There are limits to what can be made and measured.

We do have a large selection of 1 micron TTV substrates