Lambda design rule

Here we explain the design of Lambda Rule

1. Layout Design Rules
The physical mask layout of any circuit to be manufactured using a particular
process must conform to a set of geometric constraints or rules, which are
generally called layout design rules.
These rules usually specify the minimum allowable line widths for physical
objects on-chip such as metal and polysilicon interconnects or diffusion areas,
minimum feature dimensions, and minimum allowable separations between
two such features.
The design rules are usually described in two ways :
• Micron rules, in which the layout constraints such as minimum feature sizes
and minimum allowable feature separations, are stated in terms of absolute
dimensions in micrometers.
• Lambda rules, in which the layout constraints such as minimum feature sizes
and minimum allowable feature separations, are stated in terms of absolute
dimensions in () .
Lambda based design rules :
The following diagram show the width of diffusions(2) and width of the
polysilicon (2).
And it also represent the minimum separation between layers and they are
1.Separation between P-diffusion and P-diffusion is 3
2.Separation between N-diffusion and N-diffusion is 3
3.Separation between P-diffusion and Polysilicon is 1
4. Separation between N-diffusion and Polysilicon is 1
5. Separation between Polysilicon and Polysilicon is 2

2. The following diagram show the width of metals 1 (3) and metal2 (4).
1. Separation between Metal1 and Metal1 is 3
2. Separation between Metal2 and Metal2 is 4



Transistor design rules:-
By overlapping the polysilicon with N-diffusion form the NMOS
And overlapping the polysilicon with P-diffusion form the PMOS
After forming the enhancement NMOS if it was implant then it converts to depletion NMOS

3. Contact Cuts:-
• When making contacts between polysilicon and diffusion circuits it should be recognized
that there are three possible approaches
1.Polysilicon to metal then metal to diffusion
2.Buried contact polysilicon to diffusion
3.Butting contact (Polysilicon to diffusion using metal)

1.Polysilicon to metal then metal to diffusion :-
When contact cut is created between metal to polysilicon and metal to diffusion is 2 x 2
and it was superimposed with 4 x 4.
And the minimum separation between contact cuts is 2


2.Buried contact polysilicon to diffusion :-
i.The contact cut in these case indicating where the thin oxide is etched to
reveal the surface of the silicon wafer before polysilicon is deposited.
ii.Then diffusion is carried out into the exposed surface. when diffusion takes
place impurities will diffuse into polysilicon as well as diffused area within the
contact area.
iii.It tell that connection between polysilicon and diffusion .

4. 3.Butting contact (Polysilicon to diffusion using metal):-
Butting contact is complex .A 2 x 2 contact cut is made down to each layers to be joined. Layers
are butted together so that two contact cuts become contiguous.
The polysilicon and diffusion layers are butted together. And the contact between two butting layers
is then made by a metal overlays