M ask D esign T raining M ask D esign T raining Page 1 Quality Layout.

Quality Layout

What is Quality Layout ?Quality Layout Consist Of These Elements : Meet Circuit Performance Requirements

Minimize parasitic RC Analog

Efficient Area Usage Anticipate ECO changes Prepare future process/optical shrink Meet or beat allocated area

Manufacture-able Layout (DFM) Debug-able Layout (DFD)

Probe & FIB Fulfill Reliability Guidelines

Electro Migration & Self Heating ESD

OUTLINES Engineering Layout Checklist

Poly Guidelines Contact Guidelines Diffussion Guidelines Metal and Vias Guidelines Summary

Electromigration and Self Heating Layout Review Checklist

Poly GuidelinesPolysiliconsIn general, poly has much higher resistance then metal and

therefore much higher delay.

Using poly as an interconnect level can be advantageously used to create very compacts layout. But, poly should never be used as interconnect when the capacitance is high.

Gate driving Gate driving

Gates should be driven from the middle so that long poly lines are minimized. This means they should be driven between the p’s and n’s not through them.

Gate spacing Gate Spacing

Stacked series gates should be minimally spaced at Yu apart. Parallel gates need a spacing of Xu between gates (i.e. series gates can be closer).

No field poly in high speed path

•Gate poly is worse, gate oxide is 10X then field oxide RC.

Leg device is needed

There is a Design rule limitation on the poly length. The transistor

performance is very sensitive to the gate width.

No field poly to connect diffusion

Function of the IC may be jeopardized. EM (electromigration) rule is likely to be violated.

Significant performance impact.

No bend gates Even the process today allow bent gates and will not give any

significant impact to the performance, the analysis tool make no provision for them.

Contacts Guidelines There are two kinds of contacts: partially covered and fully

covered. Partially covered contacts cannot carry as much current as fully covered contacts.

Definitions

Fully/Partially Covered: A fully covered contacts has at least 0.16u coverage on all sides. A partially covered contact has 0.0 metal coverage past the edge of the contact. This mean that during process, if the mask moves, the partially covered contact may not be covered all the way with metal.

Fully/Partially Strapped: Strapping is a term indicating how many contacts connect the device to metal1. Fully strapped means that as many contact as will fit have been placed on the device. Partially strapped means that some of the contacts is missing.

Strapping Guidelines At least 40% of length with minimum-spaced fully-covered contacts. At least 80% of length with minimum-spaced partially-covered contacts. Do not break S/D strapping Based on simulations of conductivity degradation Static Timing Analysis tool assumes all junctions are fully strapped in its transistor

models.

Diffusion stretching Only stretch VCC/VSS (not signal) diffusion to make room for

signal routes. Based on observation of the impact on diffusion loading on the

output node We don’t care about diffusion loading on the VCC/VSS

Supply and Interleaving guideline

Connect signal diffusions inside and supplies outside Signals are sensitive to diffusion loading, supplies are not Typical diffusion loading

area = 0.48fF/u2periphery = 0.05fF/u

Metal and Vias Guidelines Ohm per square resistance

P86X process

Contact 15.0

Via1 7.0

Via2 7.0

Via3 7.0

Via4 7.0

Via5 6.0

Poly 16.10

Metal1 0.085

Metal2 0.062

Metal3 0.062

Metal4 0.062

Metal5 0.062

Metal6 0.020

MetalsMetal1 will be unusable for longer routes as refer to the chart of

ohm/square.Metal1 is more resistive compared to others metal layer, therefore

move to Metal2 as soon as possible when do a signal routing to minimize the RC delay.

ViasVias are allowed to be stacked.Via stacking rules:1. Via1 may stack on well, diff and poly and directly on top of

contact.2. Via2 may stack on contact and directly Via1 without constraint.3. Via3 may stack on contact, Via1 and directly Via2 without

constraint.4. Via4 may stack on contact, Via1, Via2 and directly Via3 without

constraint.

BKM on metal routingAvoid Small Jog Segments (< 1x MDR width)

- Small jog segments are defined as being less than 1X minimum design rule line width.

- No small jog segments on diffusion, poly, metal1 – metal5.< 1X MDR Width

Insufficient room for “Serifs and “Cutouts”

Pinching Risk

Small Jog Segment Recommendations

1X MDR Width 2X MDR Width

0.5X MDR Width

2X MDR Width

Increase Jog Separation Distance

Increase Jog Segment Size

Minimize the Total Number of Jog Segments

Fewer number of vertices to correct. Less pattern distortion risk.

BetterUndesirable

Undesirable Better

Landing Pad Recommendations

Layer changes / Jumpers Layer Changes / Jumpers

Minimize the number of metal layer changes while routing a signal.

– Metal layer changes are expensive in area. – Every extra via increases resistance quite a bit and impacts

signal timing. No Poly jumpers

– Poly is very resistive

What’s Wrong With This Layout ?

Summary Shareable Power/Ground

Ensure shareable power/ground at diffusion edges if possible. Always connect to bigger supply (ie: metal2 with 2 vias width).

Well Taps & Substrate Taps Have well taps connect to VDD or signal specified in schematic. Have substrate taps connect to GND.

Shareable Nodes Share nodes both internally and externally as much as possible.

– Sharing nodes can reduce cell or block size/area.– Sharing nodes can reduce contacts, vias and metal layers

used. Help to improve circuit performance. Not applicable for special circuit (ie: analog – matching layout).

Metal Directions Use consistent metal directions for M1, M2, and M3. Make

sure that tracks are not blocked by using inconsistent directions. M1 and M3 vertical, M2 and M4 horizontal.

Routing Jogs / turning points Avoid making unnecessary jogs in routing (i.e. if a wire can go

straight it should). This will help performance and area. Aligned the placement of connectors to signal to avoid creating

unnecessary curves / corners.

Signal Width Try to maintain uniform/even width for a signal. Check with DE or layout lead on critical / HV signal width

requirement.

EM and SH

EM definitionsEM is a problem that occurs when current only moves in one

direction and pulls the atoms of the metal along with it. This movement will eventually leave gaps in the meatl causing open circuits failures. It can also cause increase resistance especially in contact and Via’s causing a speed failure over time.

SH definitionsSH or self heat is a problem that occurs when current is alternating

or not just flowing in the same direction all the time. Whereas in EM the metal only moves in one direction, in SH the atoms move in one direction and then back again making a net movement of zero. The problem occurs when too much currents flows heating up the metal and causing it to deteriorate and increase the resistance.

Layout checklistItems to check Status

1 Half design rules to cell boundary

2 Diffussion

a. Minimize source/drain width

b. Power source should be at both ends of the cell.

c. Shared diffussion

d. Diffussion height align

3 Poly

a. Poly gate driving in the middle

b. No poly jumpers

c. No poly bends

d. P & N devices orientation are the same

4 Contact

a. Full strapping contact and centralized.

b. At least two contact for each input/connection.

5 Metal

a. No notches

b. No metal jogs

c. Use uniform width of metal routing.

6 Labeling

a. Label all the nodes as the schematic has and case-sensitive.

b. All IO pins must have pin name.

7 Power/Ground source

a. Power/ground must directly connected from the main vcc/vss bus, insteads of connect from the wellTab or substrate tap.

M ask D esign T raining M ask D esign T raining Page 1 Quality Layout.

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