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Focused Ion Beam (FIB) has been in use for a long time, as a convenient way of altering silicon, for pre-mask validation, verification, design modifications, or probe point creation.

However, with increased number of metal layers, access to buried metal lines (known as "frontside" FIB) is becoming almost impossible. A novel way to use FIB has been first deployed in the mid-90s: backside FIB, or backside circuit edit.

The idea is to perform FIB from the silicon side. While frontside FIB is a fairly straightforward operation, usually performed within a day (as a walk-in type of activity), backside FIB requires a few additional steps:

1. Provide silicon access (available with flip-chip; requires backside packaging for wire-bonded devices)
2. Sample preparation: thin down silicon to (typically) 50-25μm, then polish
3. Test electrically to ensure the device is still functional after sample prep
4. On the backside FIB system:
   1. Navigate optically to the region of interest (requires infra-red capability)
   2. Trench down to 2-5μm of diffusion
   3. Open up access holes to metal
   4. Perform traditional FIB operation(s)

The IDS OptiFIB has been designed to support backside FIB; its ion column incorporates a coaxial optical path for simulatneously live optical and ion images. This allows precise backside alignment and beam placement, for modifications down to the 45nm process node.

Our team has been at the origin of the development of the IDS OptiFIB at Schlumberger, and has seen its deployment at over 20 customers since 1999. We have successfully performed hundreds of backside circuit edits.