how to prevent growing poly-si on the backside of the wafer

Chienliu Chang clchang6 at
Wed Oct 26 23:09:58 PDT 2011

Dear Miss Ran,

Hi, I am Chienliu.
It is impossible not to deposit polysilicon on the back side.
The only and easiest way is blank-etching away the backside polysilicon 
after deposition.

There are some selective deposition method to date in the world, but they 
are not applicable in SNF.

I think to bond any material on the back-side is unwise.
It would introduce wafer cracking in the furnace.
Even though it might be uncracked after deposition, it would be tightly 
bonded after high-temperature annealing, and then hardly separate them.
Besides, no any nobel-metal clamp can tightly fix on the wafer in these 
high-temperature ambient.
It also introduces contamination.

Please discuss with me if anything I could help you.

Chienliu Chang, Ph.D.

Khuri-Yakub Laboratory
Edward L. Ginzton Laboratory, Box 125
Center for Nanoscale Science & Engineering, room 101
Stanford University
348 Via Pueblo, Stanford, CA 94305-4088

Phone: 650-725-2265
Email: clchang6 at
      clchang6 at

----- Original Message ----- 
From: "Qiushi (Helen) Ran" <qran at>
To: <thermcopoly1 at>
Sent: Wednesday, October 26, 2011 10:43 PM
Subject: how to prevent growing poly-si on the backside of the wafer

> Hi, All
> sorry to spam. I have a question about how to prevent growing poly-Si on 
> the backside of the wafer. I tried to put two wafer back-to-back in the 
> same slot, but it didn't help. Is there some nobel-metal clamp I can use 
> to stick two wafer together? Or Is there any bonding method to bond two 
> wafer together, then part them after the growth? Any suggestions are 
> welcomed.
> Best,
> Helen
> Qiushi(Helen) Ran
> =========================================
> Department of Electrical Engineering
> Stanford University, Stanford, CA 94305.
> Mobile: +1-650-796-1439
> Email: qran at

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