VLSI Systems #7
Design rules and layout
P.J. Drongowski

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Materials (review)
*********

  Material	Graphic			Color
  --------	-------			-----
  diffusion	solid line		green
  poly		crosshatch		red
  implant	line with dots		yellow
  metal		dotted line		blue
  overglass	line with strokes	violet

  oxide		none			none

  contact	box with crisscross	black with crisscross
  buried	reverse crosshatch	brown reverse crosshatch

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Cross sections
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  Draw cross sections for diffusion, poly, metal, contact, and
  buried contact. (Do cross sections at board to illustrate
  monochrome composite style.)

  Metal can run over poly and diffusion. However, when poly crosses
  diffusion, a transistor will be formed!

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Design rules
************

  * Design rules are geometric constraints which must be satisfied
    if a circuit is to work correctly after fabrication.
  * They are motivated by potential errors in the fabrication process
    and the electrical properties of the semiconductor materials.
  * Design rules represented accumulated experience with a
    particular process or fabrication line.

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Highlights
**********

  * Mead and Conway rules should work over a variety of fabrication
    lines.
  * They are, however, gross simplifications of the real world.
    Industrial designers want to be as "aggressive" as possible to
    minimize the size of their designs.

  Diffusion.

    Min wire width		2
    Min sep diff from diff	2

  Depletion (implant.)

    Min overlap			1
    Min sep from gate		2

  Buried contact.

    Min overlap			1
    Min sep from gate		2

  Polysilicon.

    Min wire width		2
    Min sep poly from poly	2
    Min overlap beyond gate	2
    Min sep poly from diff	2

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Parameters and material constants
*********************************

Minimum feature size		4 microns
Mead and Conway lambda		2.0 micron
Minimum transistor dimensions	4 x 4 microns

Enhancement threshold (VTO)	+1 Volts
Depletion threshold (VTO)	-3 Volts

Channel length reduction	1.00 microns (0.25 * 4 microns)
Channel width reduction		0.60 microns (0.15 * 4 microns)

Diffusion sheet resistance	9-18 ohms/square
Poly sheet resistance		20-60 ohms/square
Metal sheet resistance		0.028 ohms/square
Channel resistance		10K ohms/square

Gate oxide capacitance		0.40 ff/square-micron
Thick field oxide capacitance	0.025 ff/square-micron
Junction area capacitance	0.12 ff/square-micron

Poly to substrate capacitance	0.057 ff/square-micron
Diffusion capacitance		0.1 ff/square-micron
Metal to substrate capacitance	0.03 ff/square-micron
Gate-channel capacitance	0.4 ff/square-micron

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Other DR items
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  * Alignment marks.
  * Test devices.
  * Copyright notice.

Copyright (c) 1984 Paul J. Drongowski