Thick SiO2 etch

[Xiaoguang "Leo" Liu]

Dear all

For one of my projects, I need to pattern thick thermal oxide of
1.5um. I used 49%HF:DI = 1:6 as the etchant and 20um AZ9260 as a mask
(the reason of using this thick resist is that I need to do a through
wafer Deep RIE after patterning the SiO2).

The etching of the oxide takes more than half an hour in the etchant.
My problem is that the photoresist can not stand the HF solution and
start to peel off (especially the smaller features) after about 20min.
HF also attacks the photoresist reducing the overall thickness of the
photoresist, which can impact my later DRIE process.

Could anybody illuminate me with a better method to etch the oxide
layer without destroying the photoresist? I greatly appreciate your
help.

Best
--
Xiaoguang "Leo" Liu
Birck Nanotechnology Center
Purdue University
***@purdue.edu
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[Shao Guocheng]

according to my experience, when use HF solution to etch the SiO2 layer, you should monitor the process frequently. you want to take out the wafer as soon as the SiO2 is etched, since this process is istropic, which means the etchant can attack the SiO2 under your photoresist as well, and that's why the resist tends to peel off and make some saw-shape edge when u leave the wafer in the solution for too long. also, thick resist is easier to peel off than thin layer. (some one also mentioned that 49% HF solution tends to peel off ur resist)
I feel a little bit strange that you need 30 min to etch 1.5um SiO2, I remember that it took me about 10 minutes to etch 2um SiO2 when I was using BHF.

But since you have RIE, why dont you just use RIE for this process? I think that can make your life easier and safer. :)

Guocheng Shao

"Xiaoguang \"Leo\" Liu" <***@gmail.com> wrote:
Dear all

For one of my projects, I need to pattern thick thermal oxide of
1.5um. I used 49%HF:DI = 1:6 as the etchant and 20um AZ9260 as a mask
(the reason of using this thick resist is that I need to do a through
wafer Deep RIE after patterning the SiO2).

The etching of the oxide takes more than half an hour in the etchant.
My problem is that the photoresist can not stand the HF solution and
start to peel off (especially the smaller features) after about 20min.
HF also attacks the photoresist reducing the overall thickness of the
photoresist, which can impact my later DRIE process.

Could anybody illuminate me with a better method to etch the oxide
layer without destroying the photoresist?
_______________________________________________
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[VS Bhat]

Dear Mr.Xiaoguang "Leo" Liu,
For etching the thick oxide, BOE 6:1 would work better compared to the dil HF.
You may use dry etch with CF4 and CHF3 chemistry also for the oxide etch.
Bhat

Post by Xiaoguang "Leo" Liu
Dear all
For one of my projects, I need to pattern thick thermal oxide of
1.5um. I used 49%HF:DI = 1:6 as the etchant and 20um AZ9260 as a mask
(the reason of using this thick resist is that I need to do a through
wafer Deep RIE after patterning the SiO2).
The etching of the oxide takes more than half an hour in the etchant.
My problem is that the photoresist can not stand the HF solution and
start to peel off (especially the smaller features) after about 20min.
HF also attacks the photoresist reducing the overall thickness of the
photoresist, which can impact my later DRIE process.
Could anybody illuminate me with a better method to etch the oxide
layer without destroying the photoresist?

_______________________________________________
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provider of MEMS and Nanotechnology design and fabrication services.
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[P.E.M. Kuijpers]

Dear Xiaoguang "Leo" Liu,

A solution can be to use also a structured Cr mask below you resist
before etching the SiO2 layer.
We found that this gives better resulst than only a resist mask.

Regards,
Peter Kuijpers
MiPlaza
DTS/TFF
Phone.: [phone] (mobex)
mobile:[phone]
fax.: [[phone]
mailto:***@philips.com


"Xiaoguang \"Leo\" Liu" <***@gmail.com>

Subject [mems-talk] Thick SiO2 etch Classification

Dear all

For one of my projects, I need to pattern thick thermal oxide of
1.5um. I used 49%HF:DI = 1:6 as the etchant and 20um AZ9260 as a mask
(the reason of using this thick resist is that I need to do a through
wafer Deep RIE after patterning the SiO2).

The etching of the oxide takes more than half an hour in the etchant.
My problem is that the photoresist can not stand the HF solution and
start to peel off (especially the smaller features) after about 20min.
HF also attacks the photoresist reducing the overall thickness of the
photoresist, which can impact my later DRIE process.

Could anybody illuminate me with a better method to etch the oxide
layer without destroying the photoresist?
_______________________________________________
Hosted by the MEMS and Nanotechnology Exchange, the country's leading
provider of MEMS and Nanotechnology design and fabrication services.
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[Roger Brennan]

Hello Leo,

Thirty years ago, I was routinely etching 1.5um of thermal oxide in BOE
(buffered oxide etch --NH4F, HF, H2O) using negative photoresist (Waycoat, I
think). Good luck.

Roger Brennan

Applications Director
Solecon Labs
770 Trademark Drive
Reno, NV 89521-5926
Work: ***@Solecon.com
Work: 775-853-5900 ext 108


-----Original Message-----
From: mems-talk-***@memsnet.org
[mailto:mems-talk-***@memsnet.org]On Behalf Of Xiaoguang "Leo" Liu
Sent: Thursday, April 19, 2007 3:42 PM
To: General MEMS discussion
Subject: [mems-talk] Thick SiO2 etch


Dear all

For one of my projects, I need to pattern thick thermal oxide of
1.5um. I used 49%HF:DI = 1:6 as the etchant and 20um AZ9260 as a mask
(the reason of using this thick resist is that I need to do a through
wafer Deep RIE after patterning the SiO2).

The etching of the oxide takes more than half an hour in the etchant.
My problem is that the photoresist can not stand the HF solution and
start to peel off (especially the smaller features) after about 20min.
HF also attacks the photoresist reducing the overall thickness of the
photoresist, which can impact my later DRIE process.

Could anybody illuminate me with a better method to etch the oxide
layer without destroying the photoresist?
_______________________________________________
Hosted by the MEMS and Nanotechnology Exchange, the country's leading
provider of MEMS and Nanotechnology design and fabrication services.
Visit us at http://www.mems-exchange.org

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[Joe Lonjin]

CF4/CHF3 plasma in MERIE with backside He cooling.

Joe Lonjin
Penn State Nanofabrication Facility
190 MRI Building
230 Innovation Blvd
University Park, PA 16802

***@psu.edu
[phone]
Fax [phone]


-----Original Message-----
From: Xiaoguang "Leo" Liu [mailto:***@gmail.com]
Sent: Thursday, April 19, 2007 6:42 PM
To: General MEMS discussion
Subject: [mems-talk] Thick SiO2 etch

Dear all

For one of my projects, I need to pattern thick thermal oxide of
1.5um. I used 49%HF:DI = 1:6 as the etchant and 20um AZ9260 as a mask
(the reason of using this thick resist is that I need to do a through
wafer Deep RIE after patterning the SiO2).

The etching of the oxide takes more than half an hour in the etchant.
My problem is that the photoresist can not stand the HF solution and
start to peel off (especially the smaller features) after about 20min.
HF also attacks the photoresist reducing the overall thickness of the
photoresist, which can impact my later DRIE process.

Could anybody illuminate me with a better method to etch the oxide
layer without destroying the photoresist?
_______________________________________________
Hosted by the MEMS and Nanotechnology Exchange, the country's leading
provider of MEMS and Nanotechnology design and fabrication services.
Visit us at http://www.mems-exchange.org

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