High Temperature (1100C) Dry Oxide Uniformity Issue

[HowardHiew]

Hi all,

I am from Diffusion Module, process engineer.
Recently i encountered an issue on oxide uniformity.
There are total 4 monitoring wafers in this run, 2nd wafer showed bad uniformity while other 3 wafers showed typical trend.
Total 5 production lot in this batch, the affected control wafer is in between the production wafer.

Due to production is not able to measure, TEM has been proceed on the product wafer neigbouring the 2nd test wafer, result showed normal.

Target is around 800A, total 9 site measure, out of this 9 sites, 2 sites showed around 900A.

Mainly suspect on test wafer issue or wafer back side condition affect the test wafer.

The product back side is 2000A　nitride.

I want a machanism to explain this phenomenon, can anybody encountered similar issue before? thanks

 

[IRstuff]

What kind of production line is this? 10 wafers, of which 5 are monitor does not sound like high volume. Have there been similar problems recently?

As with many similar processes, variances are often due to inadequate surface prep or contamination. Other possibilities are that the substrates are not what they;re supposed to be. Were they all from the same supplier batch?

TTFN
faq731-376

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[HowardHiew]

Hi IRstuff,

Thanks for the reply.

This product is mass production, the affected run having 125 wafers (max. loading 150 wafers)
Total 4 monitoring wafers which cover from top to bottom zone accross whole tube (vertical furnace)

On and off we do observed the issue but this time round the uniformity went higher than historical trend.
1 of the observation is unique recipe structure which 1100C N2/O2/TLC.

It might be enhance effect with this unique recipe since do not observed similar issue on pure dry or wet oxidation.

Hope to solve this puzzle with a convincing mechanism.