This document discusses the fabrication of passive elements like resistors, capacitors, and inductors in integrated circuits. Resistors are fabricated using doped polysilicon or metal layers on a silicon wafer. Capacitors can be made by growing a thin silicon dioxide layer between conductors. Inductors are fabricated as copper or aluminum coils on the wafer similar to a spiral micro inductor. The precision of components made using IC fabrication is limited due to variations in processes like ion implantation doses, layer thicknesses, and photolithography widths across wafers.

1. Fabrication of Passive Elements
(Resistor ,Capacitors & Inductors)

2. • Integrated Circuit
• Resistors
• Capacitors
• Inductors
• Uncertainty in IC Fabrication
Content

3. Integrated Circuit
An integrated circuit (IC) is a miniature ,low cost electronic circuit
consisting of active and passive components fabricated together on
a single crystal of silicon. The active components are transistors
and diodes and passive components are resistors, inductors and
capacitors.

4. Advantages of Integrated Circuit
1. Miniaturization and hence increased equipment
density.
2. Cost reduction due to batch processing.
3. Increased system reliability due to the elimination
of soldered joints.
4. Improved functional performance.
5. Matched devices.
6. Increased operating speeds.
7. Reduction in power consumption

5. Fabrication of Monolithic Integrated Circuit
1. Silicon wafer (substrate) preparation
2. Epitaxial growth
3. Oxidation
4. Photolithography
5. Diffusion
6. Ion implantation
7. Isolation technique
8. Metallization
9. Assembly processing & packaging

6. Resistors
(ohms)

7. Introduction
A resistor is a passive two-terminal electrical component that implements
electrical resistance as a circuit element.
The current through a resistor is in direct proportion to the voltage across the
resistor's terminals. This relationship is represented by Ohm’s law (I=V/R)
I is the current through the conductor in units of amperes, V is the potential
difference measured across the conductor in units of volts, and R is the resistance
of the conductor in units of ohms.

8. Resistance of Material
Other conducting materials Ohm
N+ polysilicon (t=500 nm) 20
Aluminum 0.07
Silicided Polysilicom 5
Silicided Source/drain diffusion 3
MOSIS 1 um CMOS PROCESS

9. IC Resistor
Given the sheet resistance, we need to find the number of squares for this layout
L / W = 9 squares

10. Laying Out a Resistor
Rough approach:
R known(Ns) = R / Rs(Sheet Resistance)
Select a width W (possibly the minimum to save area)
the length L = W N and make a rectangle L x W in area
Add contact regions at the ends ... ignore their contribution to R

11. Layout of Resistor
More careful approach:
Account for the contact regions and also, for corners
Measurement shows that the effective number of squares of the “dogbone” style
contact region is 0.65 and for a angle 90 corner is 0.56.
For the resistor with L / W = 9, the contact regions add a significant amount to
the total square count:
Ns= 9 + 2 (0.65) = 10.3

12. Capacitors
(Columns/Volts or Farads)

13. Introduction
Capacitor is a basic storage device to store electrical charges and
release it as it is required by the circuit. In a simple form it is made of
two conductive plates (Electrodes) and an insulating media
(Dielectrics) which separate the electrodes.
The charges (Q) on the capacitor plates depend on the voltage (V)and
the capacitance value (C) and is as follows:
Q=C.V

14. Fabrication
B+
n-Si
SiO2
n-Si
GROW 4000 A OXIDE ON N-TYPE SILICON MATERIAL PATTERN AND ETCH OXIDE<THEN ION IMPLANT 50 KeV
BORON TO FROM P+ REGION

15. Thin SiO2
Al
n-Si n-Si
GROW THIN OXIDE (2000 A) PATTERN AND
ETCH OXIDE TO FROM CONTACT
DEPOSIT 5000A ALUMINUM PATTERN AND
ETCH ALUMINUM
Fabrication

16. Poly-Poly Capacitors Layout
Substrate
FOX
Poly
Poly2
Cross section
tins
Poly2
Area A2
Poly
Top View
Cp-Cp2=Eins/tin*A2

17. Metal-Metal Capacitors
This type of structure is easily built in multiple-metal layer processes. The capacitors are formed using
patterns on two metal layer.
Cmm = Cxy *Aov
Where Cxy is the capacitance per unit area and
Aov is overlap area.

18. MOSFET Capacitors
The gate implementation of capacitance of MOSFET also can be used to create a capacitor by shorting both
the drain and source connections
C=Eox/tox*Ag=CoxWL

19. Inductors
(Henry)

20. Introduction
 An inductor (also choke, coil or reactor) is a passive two
terminal electrical component that stores energy in its magnetic
field. For comparison, a capacitor stores energy in an electric
field, and a resistor does not store energy but rather dissipates
energy as heat.
 Any conductor has inductance. An inductor is typically made of
a wire or other conductor wound into a coil, to increase the
magnetic field.

21. Construction of an inductor
An inductor is usually constructed as a coil of conducting
material, typically copper wire, wrapped around a core either of
air or of ferromagnetic or ferrimagnetic material. Core materials
with a higher permeability than that of air increase the magnetic
field and confine it closely to the inductor, thereby increasing the
inductance.

22. Silicon wafer Deposit 100nm of SiO2
Fabrication

23. Spin coat photo resist Mask exposure and develop the pattern
Fabrication

24. Deposit aluminum and copper alternately Photo resist removal.
Fabrication

25. Spiral Micro Inductor
Spiral micro
inductor.

26. Schematic layer Structure
Microphotograph of the spiral inductor fabricated on the A1203 substrateSchematic layer structure of the spiral inductor fabricated on the A1203 substrate

27. The precision of transistors and passive components fabricated using IC
technology is surprisingly, poor!
Sources of variations:
 Ion impant dose varies from point to point over the wafer and from wafer to
wafer.
Thicknesses of layers after annealing vary due to temperature variations across
the wafer.
Widths of regions vary systematically due to imperfect wafer flatness (leading to
focus problems) and randomly due to raggedness in the photoresist edges after
development.
Uncertainties in IC Fabrication