Transcript Sputtering - edunano.ru

Equipment and technological processes for manufacturing GaAs MMICs
METALISATION TWO
TALK 9
Equipment and technological processes for manufacturing GaAs MMICs
METALLISATION 2
Sputtering
• Sputtering: When a solid or liquid
is bombarded by high energy
atomic particles, it is possible for
individual atoms to obtain enough Plasma
energy to escape from the surface
of the material being bombarded.
Substrate
Magnetic
Field
High
negative
potential
Target
Magnets
Argon Atoms
Target Atoms
Ions
Electrons
Equipment and technological processes for manufacturing GaAs MMICs
METALLISATION 2
Sputtering
When power is supplied to a magnetron a negative voltage of
typically -300V or more is applied to the target. This negative
voltage attracts positive ions to the target surface at speed.
Generally when a positive ion collides with atoms at the
surface of a solid an energy transfer occurs. If the energy
transferred to a lattice site is greater than the binding energy,
primary recoil atoms can be created which can collide with other
atoms and distribute their energy via collision cascades.
A surface atom becomes sputtered if the energy transferred to
it normal to the surface is larger than about 3 times the surface
binding energy (approximately equal to the heat of sublimation).
Equipment and technological processes for manufacturing GaAs MMICs
METALLISATION 2
• Advantages
–
–
–
–
–
–
Sputtering
Good film adhesion
Accurate control of process
Good ‘step’ coverage, e.g. coats round corners
Lift off Possible with long throw distance and coating chimneys
Easily automated
With appropriate power input virtually anything can be sputtered
• Disadvantages
– Small source to substrate distance can make film thickness
uniformity difficult
– Films thicker than 5 microns difficult
– Hardware & target material costs are high
Equipment and technological processes for manufacturing GaAs MMICs
METALLISATION 2
Sputtering
• There are two basic methods for sputtering
materials
– DC Sputtering - limited to materials which are
electrically conductive. Can’t be used to sputter
insulators. Generally high deposition rate.
– RF Sputtering - Used to sputter non-conductive
materials. Will also work for conductive (anything can
be RF sputtered).
Deposition rate lower than DC for metallic materials.
Equipment and technological processes for manufacturing GaAs MMICs
METALLISATION 2
• Magnetron sputtering - Magnets enable lower pressures to be
used
During the sputter process a magnetic field can be used to trap
secondary electrons close to the target. The electrons follow helical
paths around the magnetic field lines undergoing more ionizing
collisions with neutral gaseous near the target than would
otherwise occur.
This enhances the ionisation of the plasma near the target leading
to a higher sputter rate. It also means that the plasma can be
sustained at a lower pressure. The sputtered atoms are neutrally
charged and so are unaffected by the magnetic trap.
Equipment and technological processes for manufacturing GaAs MMICs
METALLISATION 2
What a magnetron looks like
Equipment and technological processes for manufacturing GaAs MMICs
METALLISATION 2
Key parts of a magnetron
Equipment and technological processes for manufacturing GaAs MMICs
METALLISATION 2
Magnetrons come in all sorts of shapes and sizes!!
Equipment and technological processes for manufacturing GaAs MMICs
METALLISATION 2
Also during the sputtering process a glow is observed , this is caused by excited
ions relaxing to a lower energy state and emitting energy in the form of light.
Different elements emit the visible light at a different wavelength and therefore a
different colour will be observed.
However this highlights one of the problems of magnetron the so called
“racetrack” – caused by non–uniformity of the magnetic field behind the target
This means parts of the target get sputtered way faster than others which leads
to reduced efficiency and poor use of material – if the target is an expensive
material (e.g. Au) this is a problem
Equipment and technological processes for manufacturing GaAs MMICs
METALLISATION 2
Many very complex designs of
magnets have been employed
by vendors in order to improve
this effect.
Usage can be as low as low as
30% if nothing is done
High usage around 80% is
possible but at a price!
Equipment and technological processes for manufacturing GaAs MMICs
METALLISATION 2
Magnetron Concepts
The term balanced and unbalanced magnetrons are
commonly used
The balanced term is generally used to describe conventional
magnetrons
The term unbalanced is used to describe magnetrons that are
also capable of producing ion bombardment of the thin film at
the same time as deposition
Equipment and technological processes for manufacturing GaAs MMICs
METALLISATION 2
Unbalanced magnetrons
An unbalanced magnetron possesses stronger magnets on the outside
resulting in the expansion of the plasma away from the surface of the
target towards the substrate.
The effect of the unbalanced magnetic field is to trap fast moving secondary
electrons that escape from the target surface. These electrons undergo
ionizing collisions with neutral gas atoms away from the target surface and
produce a greater number of ions and further electrons in the region of
the substrate considerably increasing the substrate ion bombardment.
Effectively a secondary plasma is formed in the region of the substrate. When
a negative bias is applied to the substrate, ions from this secondary
plasma are accelerated to the substrate and bombard it; this ion
bombardment is used to control the many properties of the growing film.
Equipment and technological processes for manufacturing GaAs MMICs
METALLISATION 2
An unbalanced magnetron, the outer North
poles are stronger than the inner South poles
therefore the field lines stretch further into
the vacuum chamber
Equipment and technological processes for manufacturing GaAs MMICs
METALLISATION 2
Completely
balanced
Type 1. unbalanced
Type 2. unbalanced.
Equipment
COATING
and technological
GEOMETRIES
processes for manufacturing GaAs MMICs
METALLISATION 2
ON AXIS COATINGS & UNIFORMITY
WAFER
LOW DENSITY FLUX
HIGH DENSITY FLUX
RELATIVE THICKNESS
100%
EDGE OF WAFER
EVAPORATION FLUX
ATOM SOURCE
VACUUM CHAMBER
CENTER OF WAFER
Equipment and
COATING
technological
GEOMETRIES
processes for manufacturing GaAs MMICs
METALLISATION 2
OFF AXIS COATINGS AND UNIFORMITY
HIGH DENSITY FLUX
LOW DENSITY FLUX
RELATIVE THICKNESS
100%
ROTATING
WAFER
EDGE OF WAFER
EVAPORATION FLUX
ATOM SOURCE
VACUUM CHAMBER
CENTER OF WAFER
Equipment and technological processes for manufacturing GaAs MMICs
METALLISATION 2
Relative Deposition (%)
00378-13-h001-100ht-130sepn
101
100
99
Approx1
±2%
98
97
Approx2
Fig. 1. 6” source, 8” substrate, 100mm
height separation (target to substrate),
130mm offset distance(centre of
target to centre of substrate)
96
95
0
20
40
60
80
100
Distance from wafer centre (mm)
Relative Deposition (%)
00378-13-h001-175ht-130sepn
102
100
Approx1
98
Approx2
96
±4.5%
94
92
90
0
20
40
60
80
100
Distance from wafer centre (mm)
Fig. 2. 6” source, 8” substrate, 175mm
height separation (target to substrate),
130mm offset distance(centre of
target to centre of substrate)
Equipment and technological processes for manufacturing GaAs MMICs
METALLISATION 2
VACUUM PUMPING OPTIONS
ROUGH VACUUM
2 STAGE ROTARY PUMPING
1.5-80 cu m3 h-1 2 STAGE ROTARY PUMPS
Oxygen pumping options (Fomblinised systems using
Fomblin oils)
SCROLL PUMPING WITH OIL FREE OPERATION
These pumps are totally oil free to avoid oil contamination
inside the vacuum chamber. They are suited for oxygen
pumping and have reduced maintenance schedules.
Equipment and technological processes for manufacturing GaAs MMICs
METALLISATION 2
VACUUM PUMPING OPTIONS
HIGH VACUUM PUMPING
DIFFUSION
LOWEST COST HIGH VACUUM PUMPS. MEDIUM BASE VACUUM WITH
GOOD WATER VAPOUR PUMPING SPEED
TURBO MOLECULAR
FAST START UP TIMES WITH MAGNETICALLY LEVITATED BEARING
OPTIONS. THESE PUMPS HAVE POOR WATER VAPOUR PUMPING
PERFORMANCE WITH HIGH BASE VACUUM LEVELS.
CRYOGENIC PUMPING
SLOW START UP TIMES, NO BACKING REQUIRED WITH FASTED WATER
VAPOUR PUMPING. HIGH BASE VACUUM.
Equipment and technological processes for manufacturing GaAs MMICs
METALLISATION 2
PROCESS PRESSURE OPTIONS – MORE IMPORTANT THAN YOU THINK!
BASIC OPEN LOOP CONTROL
Fixed gas flow from Auto Gas Bleed, and fixed vacuum pumping speed
UP-STREAM PRESSSURE CONTROL
Mass flow gas control with closed loop connection to process vacuum gauge
Constant vacuum pumping speed
Pressure is maintained constant by varying the process gas flow in a PID closed loop
control system
DOWN-STREAM PRESSURE CONTROL
Operator selectable mass flow values for process gas flow.
Operator selectable pumping speed via continuously variable throttle valve in
high vacuum pumping line, with PID closed loop control from process pressure gauge
Individual settings for both process gas flow and process pressure.
Equipment and technological processes for manufacturing GaAs MMICs
METALLISATION 2
Pressure control
Equipment and technological processes for manufacturing GaAs MMICs
workholders
Simple rotation
Planetary motion
METALLISATION 2
Equipment and technological processes for manufacturing GaAs MMICs
METALLISATION 2
Reactive sputtering and alloys -1
You can carry out sputtering in the presence of
a reactive gas (like O2) instead of the usual Ar
Its one way of creating oxides – but be
warned!!
Reactive sputtering is hard to control – final
stoichiometry of deposited films tends to vary
a lot and the process is hard to make
reproducible
Equipment and technological processes for manufacturing GaAs MMICs
METALLISATION 2
Co-sputtering
Equipment and technological processes for manufacturing GaAs MMICs
METALLISATION 2
Reactive sputtering and alloys -2
Same goes for alloys. You can co-sputter alloys by having 2
magnetrons working at once but again be warned that its hard to:-
Get the geometry of the system right
Get the sputter rate of the two films right and in the correct ratio
and stable at that
Get good uniformity over a large substrate
If you want to sputter an alloy buy a composite target but be careful
again as the composition of the target may well not be the
composition of the film you get but it will be reproducible!
Equipment and technological processes for manufacturing GaAs MMICs
METALLISATION 2
Sputter data – different materials
Target
Sputter
Power
Target
Total
Crystal
Atomic
interatomic
Static rate different
separations
material
yield
density
diameter
power
structure
radius
spacing
microns per
minute
-600V
W/cm2
cm
watts
nm
nm
6 cm
10 cm
rate factor
14 cm
atoms/ion
Ag
3.4
2
10
157
FCC
0.144
0.289
0.354
0.214
0.139
0.128
Al
1.2
2
10
157
FCC
0.143
0.286
0.124
0.075
0.049
0.128
Au
2.8
2
10
157
FCC
0.144
0.288
0.290
0.176
0.114
0.128
C
0.2
2
10
157
HEX
0.077
0.154
0.011
0.007
0.004
0.128
Co
1.4
2
10
157
CPH
0.125
0.25
0.126
0.076
0.050
0.128
Cr
1.3
2
10
157
BCC
0.128
0.25
0.117
0.071
0.046
0.128
Cu
2.3
2
10
157
FCC
0.128
0.255
0.211
0.128
0.083
0.128
Fe
1.3
2
10
157
BCC
0.128
0.248
0.116
0.070
0.046
0.128
Ge
1.2
2
10
157
DIAMOND
0.139
0.278
0.120
0.073
0.047
0.128
Mo
0.9
2
10
157
BCC
0.14
0.275
0.089
0.054
0.035
0.128
Nb
0.65
2
10
157
BCC
0.147
0.286
0.067
0.041
0.026
0.128
Ni
1.5
2
10
157
FCC
0.125
0.249
0.134
0.082
0.053
0.128
Os
0.95
2
10
157
CPH
0.135
0.27
0.092
0.056
0.036
0.128
Pb
2.15
2
10
157
FCC
0.174
0.348
0.269
0.163
0.106
0.128
Pd
2.4
2
10
157
FCC
0.137
0.274
0.237
0.144
0.093
0.128
Pt
1.6
2
10
157
FCC
0.138
0.277
0.160
0.097
0.063
0.128
Re
0.9
2
10
157
CPH
0.138
0.276
0.089
0.054
0.035
0.128
Rh
1.5
2
10
157
FCC
0.134
0.269
0.145
0.088
0.057
0.128
Si
0.5
2
10
157
DIAMOND
0.117
0.234
0.042
0.026
0.017
0.128
Ta
0.6
2
10
157
BCC
0.147
0.286
0.062
0.037
0.024
0.128
Th
0.7
2
10
157
FCC
0.18
0.36
0.091
0.055
0.036
0.128
Ti
0.6
2
10
157
CPH
0.147
0.299
0.065
0.039
0.025
0.128
U
1
2
10
157
ORTHO
0.138
0.275
0.099
0.060
0.039
0.128
W
0.6
2
10
157
BCC
0.141
0.274
0.059
0.036
0.023
0.128
Y
0.6
2
10
157
CPH
0.181
0.362
0.078
0.047
0.031
0.128
Zr
0.75
2
10
157
CPH
0.16
0.318
0.086
0.052
0.034
0.128
Equipment and technological processes for manufacturing GaAs MMICs
METALLISATION 2
Do it yourself sputtering!!
Unlike many technologies described in these talks there is
nothing so difficult about sputtering that does not allow
anybody with a decent understanding of vacuum and thin films
to build their own system
Many suppliers of sputter systems, especially for smaller size
substrates, are just assemblers of parts and add very little
value to the process that is being carried on inside the system
There is so much literature on the properties of sputtered
films and the conditions needed to create them, you should be
able to establish exactly what you want quite easily – SO if
money is short do it yourself!!