Purpose of TAP or tank contact in a Standard Cell Layout

[ukint]

tap cell

Hi,
I am a beginner in standard cel layout.I have observed the presence of Tap but not sure of its purpose.Can anyone letme know the importance of tap.Would appreciate if the purpose of other layers such as metal,poly,active region,contact,via is explained.

Waiting for a reply.
Thanks in advance
ukint

 

[road_0506]

tap cell layout

pertaining to MOS layout design, tap is the body of the device. this is important to isolate the device from any other neighboring device.
metal - used for wiring the desired connections
poly - a layers used to indicate the gate
active - a layers used to indicate diffusion ( P-diff for PMOS and N-diff for (NMOS) or P+ active / N+ active
contact - used to connect poly/active and 1st metal
via - used to connect diff metals; eg: 1st to 2nd metal; 2nd to 3rd metal, etc..