Meeting Microcool LHCb

Status update 28.03.2012Tushant Singh

Wafer Status - Fabrication#3426 #3694 #3427 #3434 #3442

Sphagetti Problem Yes Yes No No No

Bonding To be analysed with EDX* and cleaned thereafter

To be analysed with EDX* and cleaned thereafter

Ready for bonding

Bonded Bonded

Inlets -- -- -- To be done Inlets etched

Dicing -- -- -- -- To be done

*EDX = Energy-dispersive X-ray spectroscopyTo be done at CSEM Neuchatel on 2nd April

Sphagetti Problem – Recall

Wafer#3426

White colored ‘Sphagetti’ observed coming out of the channels

Oxide strip – wet etch (BHF)

SEM pictures

SEM pictures of structures were taken and this is what the side-walls of the channel look like.

Sphagetti Problem

Wafer with Sphagetti Problem #3694 Wafer without Sphagetti problem #3442

You can see dirty sidewalls and dirty surface in this picture

Sphagetti Problem

• Possible causes –– WE DONT UNDERSTAND, but the guess is :• Contamination in dry etch machine• Contamination in wet etch bath

For now we are not observing any such problems

Surface Roughness Problem

• During SEM imaging for looking at Sphagetti problem it was observed that the Wafer surface was very rough. – This could cause bad bonding.

Compare surface roughness (Top surface)

Wafer with Sphagetti problem #3694 Wafer without Sphagetti problem #3442

Surface Roughness Problem

• Preliminary investigations show that this problem is associated with wafers that had the Sphagetti problem.

• The wafer which did not have sphagetti problem looked OK in terms of Surface roughness.

• Further investigation needed with more wafers.

Further activities

• New batch of 3 wafers• Modified process flow – Slight modification in process flow has been

proposed and is under discussion with Alessandro.