More MEMS: Dicing Challenges

30th August 2016

Back to Singapore.

Traditional Malay Style House in Geylang. Probably the last of its kind.

Colourful Shophouse 

Feeding the Hungry Ghosts

99 Red Lanterns? 

One of the big challenges in MEMS is how to  dice the wafers. Unlike conventional IC wafers:

•       MEMS may contain minute and extremely delicate structures such as cantilevers, bridges, hinges, gears, membranes and other sensitive features that necessitate special handling and care.

•          MEMS may contain membranes, high aspect-ratio topography and other pressure-sensitive components that cannot withstand the impact of water encountered during dicing and the subsequent cleaning cycle, and raise the need for a protective mechanism to shield them from the constant flow of liquid.

•          MEMS often have moving parts that are super sensitive to contamination, and in which the presence of tiny debris particles may hinder or even halt movement altogether.

•          Some MEMS (e.g. electrostatic  actuators) are highly sensitive to ESD phenomena and may fail upon spontaneous electrostatic discharges.

MEMS Dicing Challenges
From: Stealth Dicing for MEMS, Hammamatsu

Dicing damage to MEMS membranes
 From Stealth Dicing for MEMS, Hammamatsu

Dicing Options

1. Temporary protective layer on wafer before dicing, dice and remove protective layer
2. Scribe and break
3. Stealth dicing
4. Cap before dicing

Considering each in turn:

1. Temporary protective layer

•          Temporary protective sacrificial layer covers the MEMS wafer during dicing step and cleaning

•          Later removed or washed away

•          Usually polymer film

•          Remove by dry (plasma) or wet techniques.

2. Scribe and Break

• There are commercial systems for this eg Dynatex StreetSmart™ Breaker 
• Applies controlled amount of stress localized to the partial saw cut one street at a time
• As stress is applied, the remaining silicon directly below the partial saw cut breaks

Scribe and Break Schematic

3.      Stealth dicing

4 Cap before dicing

• Individual caps or capping
• wafer placed over the MEMS wafer
• Caps or capping wafer can be  attached by adhesive, solder, or anodic bonding methods
• Conventional dicing can then be applied

Cap before Dicing