Lab 3 : Annealing
Height Measurement
Hall Bar Geometry Measurement
TFE4180 - Semiconductor Manufacturing Technology
Prepared by
Andreas Liudi Mulyo
andreas.liudi-mulyo@iet.ntnu.no
Flow chart over the lab sessions
2
Our sample
• Hall bar pattern: Complete 3D structure of
channel connecting metal contact
3
What we want to achieve
• Dopant activation (influencing electrical properties) on
our sample.
→ Annealing process by rapid thermal processing
• Height measurement of the etched profile
→ Profilometer
• Hall bar geometry
→ Optical microscope
+++ Cross-section and compositional analysis of our
sample
→ Scanning electron microscope (SEM) +
energy-dispersive X-ray spectroscopy
4
Annealing (I)
Jipelec-JetFirst
• Process of heating wafer to high temperature
(1200°C or greater) in several seconds with the
goal of activating doping, continued with cooling to
room temperature in slower rate to avoid wafer
breakage due to thermal shock.
→ Interface as well as metal can be altered
(reducing unintentional barrier)
→ An alloy is formed between metal and
semiconductor
→ possibility to repair damage from ion implantation
• Annealing usually being done with rapid thermal
processing, where the rapid heating is provided by
Halogen lamps
5
Annealing (II)
Reflector
Halogen lamps
Wafer
Process chamber
Susceptor
Thermocouple
Water cooling
Vacuum inlet
Pyrometer
The cross-section of rapid thermal processing
6
Gases which are available for the annealing process, are N2, O2 and H2 diluted with Ar. N2 normally used for this
kind of process as well as cooling. No mixing be happened between O2 and Ar diluted in H2, as they can trigger
an explosion.
Susceptor: absorb electromagnetic energy (radio frequency or microwave) efficiently → heat.
Thermocouple: two different conductors are in contact → ΔV → ΔT (Seebeck effect), see here for more.
Pyrometer: based on the blackbody radiation (cool object does not glow and hot object does-red),
Thermal Oxidation During Annealing
• Thermal oxidation is a process of producing a thin
layer of oxide on the surface of a wafer.
• The oxidizing component diffuses into the wafer at
high temperature.
• The thermal oxidation influences the distribution of
impurities. It is important to control and minimize
oxidation temperature in the minimal thermal
budget which can be achieved using this method.
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Metal
•
•
•
•
•
Pd
Ge
Ti
Pt
Au
(200 Å)
(400 Å)
(400 Å)
(300 Å)
(2000 Å)
Ohmic contact, with the advantages of:
→ No oxygen are observed
→ Diffusion barrier for the outdiffusion of As
→ Smooth morphological surface
→ Good thermal stability
Contact resistance is the lowest (order of < 10-6):
n-GaAs, with the annealing temperature of 400°C for ~17 sec
p-GaAs, with the annealing temperature of 450°C for ~39 sec
J. Appl. Phys. 74, 754 (1993)
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Schottky to Ohmic Contact (I)
Pd/Ge/Ti/Pt/Au
GaAs
• Metal -- semiconductor junction → barrier
• Two possibility types forming junction:
1. Schottky contact has rectifying characteristics
→ One bias polarity (diode)
type of contact is used
2. Ohmic contact is non-rectifying This
to get signal (current) in and out
(electrical measurement)
from semiconductor device
I-V
→ Two polarities
Resistivity
Hall bar
• Ohmic contact can be achieved by:
Solar cell
1. Lowering barrier height (by annealing)
2. Narrowing the barrier (by high doping)
→ Tunneling
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Schottky to Ohmic Contact (II)
• Example: metal-semiconductor (n-type), forward-bias
Schottky contact
qΦm > qΦs
qΦs
qΦm
metal
Ohmic contact
qΦm < qΦs
qΦm
qΦs
metal
sc
Forward-bias
sc
Evac
- qV0
- ++ +
EFm
qV0
Evac
Ec
EFs
qV
EV
EFm
-- -
qV
+
+
+
EV
e- can flow much easier
Note: in thermal equilibrium condition, EFs=EFm
10
Ec
EFs
Schottky to Ohmic Contact (III)
Flash animation for better insight:
• http://www.doitpoms.ac.uk/tlplib/semiconductors/p
n.php
• http://www.doitpoms.ac.uk/tlplib/semiconductors/ju
nction_rectifying.php
• http://www.doitpoms.ac.uk/tlplib/semiconductors/ju
nction_ohmic.php
• http://www.cleanroom.byu.edu/ohmicschottky.phtml
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Schottky to Ohmic Contact (IV)
• Current-voltage (I-V) characteristic of
Schottky (green) and Ohmic contact (red)
I
Low R
High R
V
Breakdown
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Reverse bias
Forward bias
Geometry Measurement (I)
• Profilometer
- Tool to measure surface profiles
(roughness) of surfaces.
- This is a contact stylus-type (made from
diamond) profilometer.
Piezoelectric-based transducers
Monitor
13
Geometry Measurement (II)
• Optical microscope (differential interface contrast)
- Principle: interferometry
- It is able to enhance the contrast and gain
optical path length of the sample
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Geometry Measurement (+++)
• SEM
Electron gun source → electron beam
Vacuum chamber
- Anode
- Condenser lens
- Scanning coils
- Objective lens
Magnetic lens
system
Vacuum chamber* (during measurement)
- 3-4 detectors, for different type of
electron signals
- Sample stage
* Air can be introduced and vented
15
Scanning Electron Microscopy &
Transmission Electron Microscopy (TEM) (I)
• Electron interaction with specimen (SEM-left and TEM-right)
Incident
electrons (100-200 keV)
Incident
electrons (5-30 keV)
Secondary
Auger electrons
electrons
Backscattered
electrons Characteristic
X-rays
Secondary
Auger electrons
electrons
Backscattered
electrons Characteristic
X-rays
Visible
light
Visible
light
100 nm or less
Thickness:
order of mm or less
Scattered
electrons
(elastically)
at high angle
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Bremsstrahlung
X-rays
Scattered
Scattered
electrons
electrons
Direct
(elastically)
(inelastically)
transmitted
at low angle
electrons
Scanning Electron Microscopy &
Transmission Electron Microscopy (TEM) (I)
• Signal information (SEM-left and TEM-right)
Incident
electrons (100-200 keV)
Incident
electrons (5-30 keV)
Secondary
Auger electrons
electrons
Topological
Composition
Backscattered
electrons Characteristic
X-rays
Topological
Composition
Visible
light
Secondary
Auger electrons
electrons
Topological
Composition
Backscattered
electrons Characteristic
X-rays
Topological
Composition
Visible
light
100 nm or less
Thickness:
order of mm or less
Scattered
electrons
(elastically)
at high angle
HAADF
17
Scattered
electrons
Direct
(elastically)
transmitted
at low angle
electrons
ADF,
BF
HRTEM
Bremsstrahlung
X-rays
Composition
Scattered
electrons
(inelastically)
EELS
EFTEM
Scanning Electron Microscopy &
Transmission Electron Microscopy (II)
• The setup (SEM-left and TEM-right)
Electron gun
Condenser lens
Scanning coil
Electron gun
Condenser lens
Specimen
Objective lens
Objective lens
Detector
Intermediate +
Projection
lenses
Specimen
Detector
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