Buried contacts:

The buried contact is a method to make direct ohmic contact between the polysilicon gate material and the junctions, in silicon-gate integrated circuits.

With this method – requiring an additional masking layer – it was possible to use the polysilicon as an additional layer of interconnection, greatly improving the circuit density, particularly in random logic circuits.

Here gate length is dependent upon the alignment of the buried contact mask relative to the poly silicon and therefore vary by ± λ.

Butting contact:

The gate and source of a depletion device can be connected by a method known as butting contact.

Here metal makes contact to both the diffusion forming the source of the depletion transistor and to the poly silicon forming this device’s gate.

Its advantage is that no buried contact mask is required and it avoids associated processing.