Protecting frontside features during backside etch for the P5000 etcher

cm_richter at cm_richter at
Tue Jul 19 12:53:29 PDT 2005

Dear SpecMat Committee:

I spoke to Jim regarding this after my inquiry. I asked if I could use resist to protect the frontsides of my wafer. From what I understood in our discussion, I was told that thinner resist is better since there is a less chance of reticulation on the surface which could result in shedding. I asked if I could try both 1um and 3 microns. I was told that in order to do this process I would need to have maintenence around to watch me do this. The test wafers were hardbaked overnight at 110C (~12 hours) instead of carbonizing it since I was told that I may have difficulty removing the resist.

Elmer and I placed some test wafers into the blue loading cassette so the vacuum wand can take these wafers into and out of the loadlock and back into the loading cassette. He found that the the major sources of scratches were coming from the vacuum wand as it is placing the wafer back to the blue loading cassettes. Elmer made some adjustments to the wand to mechanically release the wafers better, however, the results were not consistent. Some wafers were scratched more than others when these wafers were placed one at a time in the same slot in the blue cassette. Some wafers showed no scratches at all.

The scratches are located at the center of the wafer (about 0.5-1" diameter). Some new test wafers were then loaded manually into loadlock elevator and allow the vacuum wand take the wafers into the etching chamber. When the etch run was done and the wafers loaded back into the loadlock elevator by the vacuum wand, we saw very little to no scractching of the wafers..for either 1um or 3um resist. Some of these wafers that went through the test were my "good" wafers. After ashing the wafers, I saw very little to no scratching on the wafers. This working process continued a few more times with help from maintenence.

It looks like this process works, however when I relayed this information to Jim today, there was a concern about a buildup of particle contamination in the chamber(s) by scratched resist by the vacuum wand. Also, there was a concern how this can affect other processes. I was asked to discontinue the frontside resist protection until further notice. 

I have a hard deadline coming up at the end of this month and would like to proceed with some more wafers that need to go into the P5000 for backside etching. If possible, I'd like to continue my processing as soon as possible and an approved process in writing agreed by all members of the Specmat committee.

Best regards,


 -------------- Original message ----------------------
From: Ed Myers <edmyers at>
> Claudia,
> SpecMat has reviewed your request.  The request has been approved with the 
> following limitations.  We recommend the use of only 1um photoresist 
> thickness and the bake be at least 90 minutes.  There is concern it you 
> will be able to remove the coating after the bake.
> Regards,
> At 06:50 PM 6/28/2005, you wrote:
> >Dear Specmat,
> >
> >I am working on a second round of wafers where I need to dryetch features 
> >on the frontside and backsides of wafers on the P5000. The wafers are DSP 
> >silicon with 3 microns of thermal oxide and about a half micron of 
> >amorphous silicon on both sides. On the frontside, I have submicron 
> >features etched into the oxide that will eventually be sealed with another 
> >wafer by fusion bonding. I am ready to start etching the backsides, 
> >however I would really want to minimize scratching on the frontsides. My 
> >previous batch of wafers I processed cannot be used since there are both 
> >fine and major scratches on most of the wafers.
> >
> >Is there a way to protect these frontside features so I can etch the 
> >backsides? What would the consequences be if there was thick resist 
> >(3-4um) applied over these features that was carbonized by baking it at 
> >about 200C for about 90min in the smaller Blue-M oven in the litho room? 
> >The resist should be fully crosslinked and not likely to be removed with 
> >acetone....I can test this first to make sure the resist isn't soluable. 
> >Any other ideas? I'd appreciate any help on this.
> >
> >Best regards,
> >
> >Claudia

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