STS2 undercut?

[Sora Kim]

Hi, 

I am just wondering about how much undercut I get when I etch 5 um polysilicon in STS2. 
A long time ago, I heard that the undercut is 0.5um. Is there a recipe that gives smaller undercut than 0.5um? 
Is there difference about undercut between having a photo-resist mask and an oxide mask? 
I have 4um wide features, so 1um undercut from both sides is detrimental to my devices. 

Thanks,

Sora
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