L09 Wires - Wires 6.371 Fall 2002 L09 Wires 1 Modern...

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L09 – Wires 1 6.371 – Fall 2002 10/2/02 Wires
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L09 – Wires 2 6.371 – Fall 2002 10/2/02 Modern Interconnect Stack IBM CMOS7 process 6 layers of copper wiring 1 layer of tungsten local interconnect © IBM © IBM Metal 1 Metal 6 Metal 5 Metal 4 Metal 2 Metal 3 Via 5-6 Via 1-2 Tungsten local interconnect
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L09 – Wires 3 6.371 – Fall 2002 10/2/02 Interconnect Problems A lot of circuit designers are very worried about what’s happening with wires Device technology has been scaling well, with gate performance increasing linearly with decreasing feature size Wires scale differently, and long wires have been getting relatively slower over time Wire delay is a function of wire resistance and capacitance
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L09 – Wires 4 6.371 – Fall 2002 10/2/02 Wire Resistance bulk aluminum 2.8x10 -8 -m bulk copper 1.7x10 -8 -m bulk silver 1.6x10 -8 -m Width Length Height ( ) ( ) width height y resistivit length resistance × × = Thickness fixed in given manufacturing process Resistances quoted as /square TSMC 0.18 µ m 6 Aluminum metal layers M1-5 0.08 /square (0.5 µ m x 1mm wire = 160 ) M6 0.03 /square (0.5 µ m x 1mm wire = 60 )
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L09 – Wires 5 6.371 – Fall 2002 10/2/02 Local Interconnect Use contact material (tungsten) to provide extra layer of connectivity below metal 1 Can also play same trick with silicided poly to connect gates to diffusion directly in RAMs Typically used to shrink memory cells or standard cells Contacts directly to poly gate or diffusion Contact plug Local Wire
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L09 – Wires 6 6.371 – Fall 2002 10/2/02 Contact Resistance Contact resistance significant TSMC 0.18 µ m 6-Al Diff-M1 11.0 Poly-M1 10.4 M2-M1 4.5 M3-M1 9.5 M4-M1 15.0 M5-M1 19.6 M6-M1 21.8 Resistance of two via stacks at each end of M1 wire equivalent to about 0.1 mm wire (~20 ) Resistance of two via stacks at each end of M6 wire about the same as 1 mm narrow M6 wire (~60 )!!! Use more vias in parallel to reduce effective contact resistance Copper processes have lower via resistance Vias made from Tungsten in Aluminum processes.
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