L6 Resistor Fabrication
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Transcript of L6 Resistor Fabrication
Rochester Institute of Technology - MicroE © REP 3/15/2007
Resistor Fabrication
Device Fab. 1 page-1
ROCHESTER INSTITUTE OF TECHNOLOGYMICROELECTRONIC ENGINEERING
Resistors
Dr. Robert Pearson
9-19-05 Resistor fabrication.ppt
Rochester Institute of Technology - MicroE © REP 3/15/2007
Resistor Fabrication
Device Fab. 1 page-2
OUTLINE
DefinitionsResistor I-V CharacteristicsThe Semiconductor Resistor
ResistivityCarrier Mobility
The Diffused Semiconductor ResistorResistor Design and Cross-SectionsResistor Fabrication Sequence (micrographs)Resistor Networks, Terminations
Rochester Institute of Technology - MicroE © REP 3/15/2007
Resistor Fabrication
Device Fab. 1 page-3
DEFINITIONS
Voltage - The force applied between two points causing charged particles (and hence current) to flow. Units - Volts, and the symbol used is V. Sometimes called the potential
Current - A measure of the number of charged particles passing a given point per unit time. Units - Amperes or Coulombs per second. The symbol I is usually used to denote a current.
Resistance - A measure of the ability of a sample of a material to allow a current to pass through it when an external force or potential is applied. The units are Ohms and the symbol R is used for a resistance.
Ohm’s Law V = I (R) or R = V / I or I = V / R
Rochester Institute of Technology - MicroE © REP 3/15/2007
Resistor Fabrication
Device Fab. 1 page-4
MEASURING RESISTOR I-V CHARACTERISTIC
Data TableVolts Amperes Resistance
V I (V/I) in Ohms-5 -0.005 1000-4 -0.004 1000-3 -0.003 1000-2 -0.002 1000-1 -0.001 10000 0 ?1 0.001 1000
variable Voltage Supply
5
010
- +
Ammeter (measures current)
(Volts)V
(Amperes)I
resistor
controlknob
5
010
+ -
Rochester Institute of Technology - MicroE © REP 3/15/2007
Resistor Fabrication
Device Fab. 1 page-5
PLOT OF I-V RESISTOR CHARACTERISTIC
I
V
Resistor a two terminal device that exhibits a linear I-V characteristic that goes through the origin. The inverse slope is the value of the resistance.
R = V/I = 1/slope
Rochester Institute of Technology - MicroE © REP 3/15/2007
Resistor Fabrication
Device Fab. 1 page-6
THE SEMICONDUCTOR RESISTOR
Resistance = R = ρ L/Area = ρs L/w ohms
Resistivity = ρ = 1/( qµnn + qµpp) ohm-cm
Sheet Resistance = ρs = 1/ ( q µ(N) N(x) dx) ~ 1/( qµ Dose) ohms/square
L Area
R
wt
ρs = ρ / t
q = 1.6E-19 coulombs
Note: sheet resistance is convenient to use when the resistors are made of thin sheet of material, like in integrated circuits.
integral
Rochester Institute of Technology - MicroE © REP 3/15/2007
Resistor Fabrication
Device Fab. 1 page-7
RESISTIVITY OF SILICON
1021
1020
1014
1015
1016
1019
1018
1017
1013
100 101 102 103 10410-3 10-2 10-110-4
Boron doped silicon
PhosphorousDoped silicon
ρ = 1/(qµN)
Because the carrier mobility, µis a function of N and N is the doping, the relationship between resistivity ρ and N is given in the figure shown to the left, or calculated from equations for µ as a function of N (see next page)Im
purit
y C
once
ntra
tion,
N, c
m-3
Resistivity, ohm-cm
Rochester Institute of Technology - MicroE © REP 3/15/2007
Resistor Fabrication
Device Fab. 1 page-8
ELECTRON AND HOLE MOBILITY
Electron and hole mobilities in silicon at 300 K as functions of the total dopant concentration (N). The values plotted on the next page are the results of the curve fitting measurements from several sources. The mobility curves can be generated using the equation below with the following parameter values:
Parameter Arsenic Phosphorous Boronµmin 52.2 68.5 44.9µmax 1417 1414 470.5Nref 9.68X10^16 9.20X10^16 2.23X10^17α 0.680 0.711 0.719
µ(N) = µ min + (µmax-µmin)
1 + (N/Nref)α
Rochester Institute of Technology - MicroE © REP 3/15/2007
Resistor Fabrication
Device Fab. 1 page-9
ELECTRON AND HOLE MOBILITY
Carrier Mobilities versus Doping Concentration
0.00E+00
2.00E+02
4.00E+02
6.00E+02
8.00E+02
1.00E+03
1.20E+03
1.40E+03
1.60E+03
1.00E+14 1.00E+15 1.00E+16 1.00E+17 1.00E+18 1.00E+19
Doping Concentration (Na or Nd)
Car
rier M
obili
ty (c
m2/
V-se
c)
mu_nmu_p
Rochester Institute of Technology - MicroE © REP 3/15/2007
Resistor Fabrication
Device Fab. 1 page-10
DIFFUSED RESISTOR
Aluminum contacts
The n-type wafer is always biased positive with respect to the p-type diffused region. This ensures that the pn junction that is formed is in reverse bias, and there is no current leaking to the substrate. Current will flow through the diffused resistor from one contact to the other. The I-V characteristic follows Ohm’s Law: I = V/R
n-wafer Diffused p-type region
Silicon dioxide
Rochester Institute of Technology - MicroE © REP 3/15/2007
Resistor Fabrication
Device Fab. 1 page-11
Layout/Mask Layer 1 - Diffusion (green)
L
W
L/W is the number of ‘squares’ long the resistor is said to be.The sheet resistance rhos, is the resistance of each square
5 squares in this case
If rhos is 100 ohms per square, R = 500 ohms
The resistance, R = rhos (L/W)
Top View
Side View
P type DiffusionN wafer
Resistortermination
Rochester Institute of Technology - MicroE © REP 3/15/2007
Resistor Fabrication
Device Fab. 1 page-12
Layout/Mask Layer 3 - Contacts (gray)
L
W
Remember, inside the green (diagonally shaded) regions is p type silicon, outside is n type
10 by 10 microns
Side View
Top View
Diffusion N wafer
contactopenings
Oxide
Rochester Institute of Technology - MicroE © REP 3/15/2007
Resistor Fabrication
Device Fab. 1 page-13
Layout/Mask Layer 4 - Metal (blue)
Resistor Symbol
10 by 10 microns
L
W
Top View
Side View
Diffusion N wafer
Oxide
Metal (Aluminum)
Rochester Institute of Technology - MicroE © REP 3/15/2007
Resistor Fabrication
Device Fab. 1 page-14
Metal (Aluminum) wiring to the Probe Pads
Probes
resistor 10 squares rhos for aluminum is0.01 Ohms per square
5 squares5 squares
rhos for diffusion = 100 Ohms per square
Rtotal = 10(100) + (5+5)(0.01) = 1000.1 Ohms, therefore Metal “wiring” does not add very much to the resistance
Aluminum Pads
Rochester Institute of Technology - MicroE © REP 3/15/2007
Resistor Fabrication
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Wafer with silicon dioxide, patterned and etched
Diffusion openings
This end of the resistor loops were cut off in the picture
This resistor is many, many squares long
20µm Green is oxide (glass)
Gray is bare silicon
MASK # 1
Rochester Institute of Technology - MicroE © REP 3/15/2007
Resistor Fabrication
Device Fab. 1 page-16
After dopants have been diffused in and a new oxide grown
Purple areas are diffused and pink areas are not (the oxide in this area did not allow the dopant to diffuse into the silicon)
Rochester Institute of Technology - MicroE © REP 3/15/2007
Resistor Fabrication
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After thin oxide openings have been patterned and etched
Bare Silicon
The thin oxide layer is actually part of the transistor fabrication sequence
MASK # 2
Rochester Institute of Technology - MicroE © REP 3/15/2007
Resistor Fabrication
Device Fab. 1 page-18
After thin oxide growth (part of the transistor process)
1000Å of SiO2
Rochester Institute of Technology - MicroE © REP 3/15/2007
Resistor Fabrication
Device Fab. 1 page-19
After the contact openings have been patterned and etched
Contact openingTo bare siliconMASK # 3
Rochester Institute of Technology - MicroE © REP 3/15/2007
Resistor Fabrication
Device Fab. 1 page-20
After Aluminum has been deposited
Aluminum
Particle on the microscope lens
Aluminum short circuits everything at this stage, until it is patterned and etched.
Rochester Institute of Technology - MicroE © REP 3/15/2007
Resistor Fabrication
Device Fab. 1 page-21
After aluminum is patterned and etched
Aluminum
ContactUnused
Pad
Rochester Institute of Technology - MicroE © REP 3/15/2007
Resistor Fabrication
Device Fab. 1 page-22
RESISTOR NETWORK
500 Ω 400 250 Ω
Desired resistor network
Layout
Rochester Institute of Technology - MicroE © REP 3/15/2007
Resistor Fabrication
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VARIATIONS ON THE BASIC RESISTOR LAYOUT
10.5
0.5
10987
6.5
5.5
4.5432
R = ρs (10+0.5+0.5)
Corner squares count ~ 1/2
Rochester Institute of Technology - MicroE © REP 3/15/2007
Resistor Fabrication
Device Fab. 1 page-24
RESISTOR TERMINATIONS
~ 0 squares ~ 0.5 squares
Field Mapping