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Chapter 8
UEEP2613
Microelectronic Fabrication
Metallization
Prepared by
Dr. Lim Soo King
29 Jul 2012
- i -
Chapter 8 ..........................................................................................193
Metallization ....................................................................................193
8.0 Introduction ............................................................................................ 193
8.1 Metal Selection ....................................................................................... 195
8.2 Aluminum Metallization ........................................................................ 196
8.3 Copper Metallization ............................................................................. 198
8.4 Tantalum Deposition .............................................................................. 198
8.5 Characteristics of Metal Thin Film ...................................................... 199
8.5.1 Thickness of Metal Film ................................................................................. 199
8.5.2 Uniformity of Metal Film ............................................................................... 202 8.5.3 Stress of Metal Film ........................................................................................ 203
8.5.4 Reflectivity of Metal Film ............................................................................... 203 8.5.5 Sheet Resistance and Capacitance of Metal Film ........................................ 204
Exercises ........................................................................................................ 210
Bibliography ................................................................................................. 212
- ii -
Figure 8.1: Cross sectional view of a CMOS integrated circuit showing tungsten via and
aluminum/copper interconnection ................................................................. 194 Figure 8.2: Cross sectional view of a CMOS integrated circuit showing copper
interconnection ............................................................................................... 195 Figure 8.3: Illustration of junction spiking caused by aluminum diffusion ..................... 197
Figure 8.4: Illustration of electromigration ...................................................................... 197 Figure 8.5: (a) Schematic of stylus profilometer and (b) the profile of thickness ............ 200 Figure 8.6: (a) Schematic of acoustic method for thin film measurement and (b) the
change of reflectivity with time ..................................................................... 202 Figure 8.7: The mapping pattern of wafer with (a) point measurement, (b) 9-point
measurement, and (c) 49-point measurement ................................................ 202 Figure 8.8: Hillock and crack caused by high stress ........................................................ 203 Figure 8.9: Metal film line................................................................................................ 205 Figure 8.10: Four point probe ............................................................................................. 205 Figure 8.11: Correcton factor versus t/s plot ...................................................................... 207 Figure 8.12: Interconnect metallic structure for RC analysis ............................................. 209
- 193 -
Chapter 8
Metallization
_____________________________________________
8.0 Introduction
A number of conductors such as copper, aluminum, tungsten etc, are used for
fabrication of semiconductor devices. Metal with high conductivity is widely
used for interconnection forming microelectronic circuit. Metallization is a
process of adding a layer of metal on the surface of wafer.
Metal such as copper and aluminum are good conductors and they are
widely used to make conducting lines to transport electrical power and signal.
Miniature metal lines connect million of transistors made on the surface of
semiconductor substrate.
Metallization must have low resistivity for low power consumption and
high integrated circuit speed, smooth surface for high resolution patterning
process, high resistance to electro-migration to achieve high device reliability,
and low film stress for good adhesion to underlying substrate. Other
characteristics are stable mechanical and electrical properties during subsequent
processing, good corrosion resistance, and relative receptivity to deposit and
etch.
It is important to reduce the resistance of the interconnection lines since
integrated circuit device speed is closely related with RC constant time, which is
proportional to the resistivity of the conductor used to form the metal line.
Although copper has lower resistivity than aluminum but technical
difficulties such as adhesion, diffusion problem, and difficulties with dry
etching etc have hampered copper application in microelectronics for long time.
Aluminum has dominated metallization application since beginning of the
semiconductor industry, In 1960s and 1970s, pure aluminum or aluminum-
silicon alloy were used as metal interconnection materials. By 1980s, when
device dimension shrank, one layer of metal interconnect was no longer enough
to route all the transistors and multi-layer interconnection became widely used.
To increase the pack density, there must be near-vertical contact and via holes,
which are too narrow for physical vapor deposition PVD of aluminum alloy to
fill the via without voids. Thus, tungsten become a widely used material to fill
08 Metallization
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contact and via holes and serves as the plug to connect different metal layers.
Titanium and titanium nitride barrier/adhesion layers are deposited prior to
tungsten deposition to prevent tungsten diffusion and peeling. Fig. 8.1 illustrates
a cross sectional view of a CMOS integrated circuit with aluminum
interconnection and tungsten via plug. Borophosphosilicate glass BPSG is used
as the insulating material separating the plugs.
Figure 8.1: Cross sectional view of a CMOS integrated circuit showing tungsten via and
aluminum/copper interconnection
In 1990s, the development of chemical mechanical polishing CMP has open the
avenue to use copper for interconnection with damascene or dual damascene
process, which gets around the demand of metal etching. Tantalum is used as
the barrier layer to prevent copper from diffusion through silicon dioxide.
Silicon niride is also used as an etch stop layer for dual damascene dielectric
etching process. Fig. 8.2 illustrates a cross sectional view of a CMOS device
with copper interconnection.
Since most of thin film depositions such as titanium, titanium nitride,
tungsten, silicidation have been discussed in previous chapter, we shall not
repeat them here. We shall concentrate to provide lecture on aluminum, copper,
and tantalum metal depositions. Besides these lectures, we will also be
discussing about the characteristics of metal film in terms of its thickness,
uniformity, stress, reflectivity, and sheet resistance. Note that FSG is
fluorosilicate glass, PSG is phosphorosilicate glass, and USG is undoped silicate
glass.
08 Metallization
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Figure 8.2: Cross sectional view of a CMOS integrated circuit showing copper
interconnection
8.1 Metal Selection
The importance of interconnection metallization has been briefly dicussed in the
earlier introductory section, which is controlling the propagation delay by virtue
of the resistance of interconnection line. The RC time constant of the line varies
with silicon dioxide as the dielectric material follows equation (8.1).
ox
ox
2
Line
Line
Line
d
L
dRC
(8.1)
where Line is the resistivity of the line material, dLine is the thickness of line,
LLine is the length of the line, dox is the thickness of oxide, and ox is the
permittivity of oxide.
The desired properties of the metallization for integrated circuit are as
follows.
Low resistivity.
Easy to form.
Easy to etch for pattern generation.
Should be stable in oxidizing ambient; oxidizable.
08 Metallization
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Mechanical stability; good adhersion and low stress.
Surface smoothness.
Stability throughout processing, including high temperature sinter,
dry and wet oxidation, gettering, phosphorous glass (or other
material), passiviation, metallization.
No reaction with final metal, aluminum.
Should not contaminate device, wafer, or working equipment.
Good device characteristics and lifetime.
For window contact – low contact resistance, minimal junction
penetration, low electromigration.
8.2 Aluminum Metallization
Aluminum is the most widely used metal in microelectronic industry particular
for interconnection and wire bonding. Aluminum is the forth most conductive
element with resistivity of 2.65-cm, after silver of resistivity 1.6-cm,
copper of resistivity of 1.7-cm, and gold of resistivity of 2.2-cm.
Aluminum can be easily dry etched than the other three elements to form tiny
metal interconnection lines.
Both CVD and PVD processes can be used to to deposit aluminum. PVD
aluminum has higher quality and lower resistivity. PVD is a more popular
method in microelectronic industry. Thermal evaporation, electron beam
evaporation, and plasma sputtering can be used for aluminum PVD. Magnetron
sputtering deposition is the most commonly used PVD process for aluminum
alloy deposition in advanced fabrication.
Aluminum CVD normally is a thermal CVD process wth an aluminum
organic compound such as dimethylaluminum hydride DMAH Al((CH3)2H)
with aluminum as the precursor.
Aluminum interdiffuses into silicon to form aluminum spikes. Aluminum
spikes can punctual through the doped drain/source junction causing shorting to
substrate silicon. The effect is called junction spiking as illustrated in Fig. 8.3.
This problem can be solved by adding 1% of silicon to aluminum to form alloy
instead of pure aluminum. Thermal annealing at 4000C forms Si-Al alloy at the
silicon-aluminum interface that helps to prevent aluminum silicon inter-
diffusion causing junction spike.
08 Metallization
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Figure 8.3: Illustration of junction spiking caused by aluminum diffusion
Metallic aluminum is a polycrystalline material, which consists of many small
monocrystalline grains. When electric current flows through an aluminum line,
a stream of electrons constantly bombards the grains. Some smaller grains start
to move down just like the rock at the bottom of stream moving down during
flood season. This effect is called electromigration. The illustration is shown in
Fig. 8.4.
Figure 8.4: Illustration of electromigration
Electromigration can cause serious problem fro aluminum lines. When some
grains begin to move due to elecron bombardment, they damage the metal line.
At some points, they cause higher current density at these points. This
aggravates the electron bombardment and causes more aluminum grain
08 Metallization
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migration. High current and high resistance would generate heat and eventually
cause breaking of aluminum line. Thus, electromigration can affect the
reliability of microelectronic devices.
Adding a small percentage of copper 0.5% wt to aluminum can
significantly improve the resistance of aluminum migration. This is because the
copper atom is large and it can hold aluminum grains preventing migration due
to electron bombardment.
8.3 Copper Metallization
Instead of depending on chemical reaction to produce reacting species to form
thin film like case of chemical vapor deposition, physical vapor deposition can
be used to deposit the film. PVD technique is generally more versatile than
CVD method because it allows deposition of almost any material.
Copper has lower resistivity (1.7µΩ-cm) than alumunum copper alloy (2.9
to 3.3 µΩ-cm). It also has higher electron migration resistance because copper
atoms are much heavier than aluminum and it has better reliability. Copper has
always been an attractive and recommended choice for the metal
interconnection in IC’s industry because it can reduce power comsmption and
increase the speed of the IC’s.
Copper does have problem of adhesion with silicon dioxide and high
diffusion rate in silicon and silicon dioxide. Copper difussion into silicon can
cause heavy metal contamination and lead to malfunction of the IC’s. Thus, a
barrier metal such as tantalum needs to be deposited before depositing copper.
Copper is very hard to dry etch because copper-halogen compound has very low
volatility. Copper also has issue of ansiotropicity due to lack of an effective dry
etch method. This is a hinderance for the use of copper as common interconnect
material for IC’s fabrication.
8.4 Tantalum Deposition
Tantalum and tantalum nitride can be used to prevent copper from diffusing into
silicon substrate and causing device damage. Tantalum barrier layer is about a
few hundred angstroms thick as the copper barrier. It is a better barrier material
for copper than other known barrier materials such as titanium and titanium
nitride. It is normally deposited with sputtering process.
08 Metallization
- 199 -
8.5 Characteristics of Metal Thin Film
Conducting film usually has polycrystalline structure. The conductivity and
reflectivity of a metal are related to the grain size. Normally larger grain size
has higher conductivity and lower reflectivity. For higher temperature
deposition, normally it has higher mobility to deposit atoms on the substrate
surface and formed large grain in the deposited film.
In the sub-section, we shall discuss some characteristics of metal film that
cover the thickness of the film, the uniformity, the stress, the reflectivity, and
the RC constant of the film.
8.5.1 Thickness of Metal Film
The thickness measurement for metal thin film is quite different from that of
dielectric thin film. It is difficult to directly and precisely measure the thickness
of an opaque thin film such as aluminum, titanium, titanium nitride, and copper,
which usually needs to be performed on test wafer in a destructive way until the
introduction of the acoustic measurement method. The metal film needs to be
removed and its thickness either measured by scanning electron microscope
SEM or by measuring the step height with profilometer.
Energetic electron beam scans across the metal film creates secondary
electron emission from the metal sample. By measuring the intensity of the
secondary electron emission, the thickness can be known from the image of
secondary electron emission. It is also known that the different metal will have
different rate of emission of secondary electron. SEM method can also detect
void in the metal film.
Profilometer measurement can provide information pertaining the thickness
and uniformity for film thicker than 1,000o
A . A pattern of metal is required to
be deposited before it is being measured by stylus probe of profilometer as
shown in Fig. 8.5.
08 Metallization
- 200 -
(a)
(b)
Figure 8.5: (a) Schematic of stylus profilometer and (b) the profile of thickness
The metal pattern is done by depositing a layer of metal on silicon substrate. It
is then followed lithography process with a metal pattern mask to form a metal
pattern on the photoresist. After development and etch processes, the metallic
pattern is remained on silicon substrate. This metallic pattern is then measured
with profilometer to determine its thickness.
Ultrathin titanium nitride from 50 to 100o
A is almost transparent. Its
thickness can be measured with reflectospectrometer. The four-point probe is
also commonly used to indirectly monitor the metal film thickness by assuming
the resistivity of the metal film is constant throughout the wafer.
Acoustic method is a new technique used to measure the thickness of
opaque metal thin film with direct contact with the film. Thus, it is a useful
technique to measure the thickness of film and its uniformity. The basic
principle of acoustic measurement method is shown in Fig. 8.6. It consists of a
laser beam and a detector. A very short laser pulse of approximately 0.1ps is
shot to the surface of the thin film at a focus spot, which is about 10m by
10m, for 10 to 13s. This will heat up the spot by 5 to 100C. The thermal
expansion of the film will cause a sound wave to propagate in the film at the
speed of sound of that material. When the acoustic wave reaches the interface of
08 Metallization
- 201 -
different material, part of the wave will be reflected, while another part will
continue to propagate in the underneath material. The reflected wave sound
wave or echo can cause reflectivity changes when it reaches the thin film
surface. The reflected wave echoes back and forth in the film until it is damped
off. The time difference t between the peaks of reflectivity indicates the time
sound wave traveled back and forth in the thin film. If the speed of sound Vs in
the material is known, the film thickness can be calculated by equation (8.2).
2/tVd S (8.2)
The decay rate of the echo is related to the film density. This method can be
used to measure the thickness of each film in multi-layer device structure.
The result shown in Fig. 8.6(b) is the acoustic wave form for the thickness
of titanium nitride TiN film deposited on tetraethyl orthosilicate Si(OC2H5)4
TEOS silicon dioxide. Note that it is a process of forming silicon dioxide when
TEOS reacts with water. The time between two peaks of reflectivity is t =
25.8ps. The speed Vs of sound in TiN film is equal to 9,500m/s. Thus, the
thickness d of film is 122.5nm.
(a)
08 Metallization
- 202 -
(b)
Figure 8.6: (a) Schematic of acoustic method for thin film measurement and (b) the change
of reflectivity with time
8.5.2 Uniformity of Metal Film
The non-uniformity of the metal film can be measured by measuring the sheet
resistance and reflectivity at multiply locations on the wafer in the pattern
illustrated in Fig. 8.7.
(a) (b) (c)
Figure 8.7: The mapping pattern of wafer with (a) point measurement, (b) 9-point
measurement, and (c) 49-point measurement
The more measurement points are taken, the more precision can be achieved. In
the industry, 5-point and 9-point measurements are commonly used to save cost
and time. The 49-point and three sigma 3 standard deviations is the most
common defined criteria for qualification process of semiconductor industry.
08 Metallization
- 203 -
8.5.3 Stress of Metal Film
Stress is caused by material mismatch between the film and the substrate. There
are two type stresses namely compressive and tensile types. If stress is too high
irrespective of the types, it can cause serious problem such as hillock and crack
as shown in Fig. 8.8.
(i) Hillock caused by compressive force (ii) Crack caused by tensile
Figure 8.8: Hillock and crack caused by high stress
There are two type stresses, which are intrinsic stress and thermal stress.
Intrinsic stress is caused by film density. It is determined by ion bombardment
in the plasma sputtering deposition process. When the atoms on the wafer
surface are bombarded by the energetic ions from the plasma with much force,
they are squeezed densely together while forming the film. This type of film
would expand but it is being compressed by the substrate and this type of stress
is the compressive type. Higher deposition temperature increases the mobility of
the atoms, which in turn increases the film density and causes less tensile stress.
Intrinsic stress is also related with wafer temperature change and different
thermal expansion coefficient of the thin film and substrate. The thermal
expansion coefficient of aluminum is 23.6x10-6
k-1
and thermal expansion
coefficient of silicon is 2.6x10-6
k-1
. When an aluminum film is deposited at high
temperature of 2500C on silicon substrate at high temperature, upon cooling
down aluminum shrinks more than silicon. This would result tensile stress on
aluminum thin film by the silicon substrate.
Stress can be measured from the change in curvature of wafer before and
after thin film process. The normal procedure for metal thin film stress
measurement is: first measurement of curvature of wafer, deposition of metal
thin film with known thickness, and second curvature measurement.
8.5.4 Reflectivity of Metal Film
Reflectivity is an important property of metal thin film. For stable metallization
process, the reflectivity of the deposited film should be constant. The change of
reflectivity is an indication of process drift. Reflectivity is a function of the film
08 Metallization
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grain size and surface smoothness. Normally the larger grain size means lower
reflectivity. The smoother the metal surface, the higher will be the reflectivity.
Reflectivity is important to photolithography process because it can cause a
standing wave effect due to interference between incoming light and reflected
light causing wavy grooved on the sidewall of the photoresist stack from
periodic overexposure and underexposure. Anti-reflectant is normally coated to
prevent this effect during pattern process especially the aluminum patterning
that has very high reflectivity (180 to 200% relative to silicon). You may recall
what has been discussed pertaining to this issue in lithography class.
8.5.5 Sheet Resistance and Capacitance of Metal Film
Sheet resistance s is one of the most important characteristics of the conducting
material especially the conducting film. It is commonly used to monitor the
process of metal film deposition. For film with known conductivity, the sheet
resistance measurement is widely used to determine the thickness of the film.
The metal line resistance as shown in Fig. 8.9 is defined by equation (8.3).
Wt
LR (8.3)
where is the interconnect resistivity. L, W, and t are the interconnect length,
width, and height respectively. Resistivity is related with the film material,
grain size, and structure. For metal film with larger grain size, the lower will be
the resistivity.
The sheet resistance s is then defined as
t
s
(8.4)
Thus, from equation (8.3), the resistance R of metal line is equal to
W
LR s (8.5)
where W
Lis the number of square. For a known fabrication technology, the
thickness H of metal line is fixed. This, the resistance R of the metal line is
08 Metallization
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simply equal to the sheet resistance s of the metal material multiplied by the
number square of the metal line.
Figure 8.9: Metal film line
A four point probe as shown in Fig. 8.10 is the most common tool used to
measure the resistivity and sheet resistance of the metal film. A current I is
forced between two pin P1 and P4. The voltage V between pin P2 and P3 is
measured.
Figure 8.10: Four point probe
The metal tip of probe is usually made from tungsten. It is assumed to be
infinitesimal and the metal film is semi-infinite in lateral dimension. For the
sample that has thickness t >> S then the spherical protrusion of current
emanating from the outer probe tips has the differential resistance shown in
equation (8.6).
2x2
xR
(8.6)
08 Metallization
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The resistance between probe 1 and probe 2 is the integration of equation (8.6)
for limit X1 to X2, which is s. It yields equation (8.7).
2
1
X
X
2x2
dxR =
s4
(8.7)
Owing to superposition of current at the outer two probes, the resistance R is
equation V/2I. Thus, the resistivity is equal to
I
Vs2 (8.8)
After adding thickness correction factor a, equation (8.8) is equal to
I
Vsa2 (8.9)
Based on the correction factor a versus t/s plot shown in Fig. 8.11, the thickness
correction factor a is expressed as follows.
s
t721.0a (8.10)
for t/s < 0.5 and it is equal to
9.1)s/t(
52632.01
1a
for t/s > 0.5. Substitute equation
(8.10) into equation (8.9), the resistivity is equal to
I
V
s
ts721.0x2 =
I
Vt721.0x2 (8.11)
Indeed 0.721 is equal 2ln2
1. Thus, equation (8.11) is equal to
tI
V
2ln
(8.12)
The sheet resistance s is t
s
, which is
08 Metallization
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I
V
2lns (8.13)
Figure 8.11: Correcton factor versus t/s plot
For a thin film whereby the thickness much smaller than S (t<<S), the resistance
R can be calculate using current rings instead of spherical current. Thus, the
resistance R is equal to
2
1
X
Xxt2
dxR
2
1
S
Sxt2
dx2ln
t2
(8.14)
The sheet resistance s is equal to
I2
V
2ln
2
2ln
R2s
I
V
2ln (8.15)
This equation is also same as equation (8.13). It is true for semi-infinite thin
film whereby the the size of the sample is large compared to the probe spacing
so that edge effects could be ignored. However, if the sheet resistance s
08 Metallization
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measurement will to be made on a test area on the wafer where the test area
with typical dimensions 2.9mm by 5.8mm not larger than the probe spacing of
0.63mm, in order to get accurate measurement, one needs to correct for the edge
effects.
A metallic line structure shown in Fig. 8.12, the RC time delay of a signal
propagating along this structure is first order obtained by treating it as a
distributed, un-terminated transmission line. For such a system, the time delay tL
is approximately equal to 0.89RC. R is the line resistance and C is the total
capacitances associated with the line. A more accurate analysis would include
such elements as the load capacitance, driver resistance, and line inductance.
The total capacitance associated with the line is
S
0ox
ox
0oxL
tLK
d
WLKC (8.16)
where dox and Kox are the oxide thickness and its dielectric constant respectively,
and 0 is the permittivity in free space. The first term of equation (8.16) is the
line to substrate capacitance and the second term is the coupling capacitance Cl
between adjacent lines. This is true only if all lines are surrounded by oxide.
The total RC delay associated with the metal interconnecting line is
Sox
2
0oxlLWL
1
td
1LKK89.0t (8.17)
where Kl is added empirically to account for fringing electric fields and other
interconnecting line above or below multi-layer system. Kl is often taken as
approximately equal to 2.
08 Metallization
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Figure 8.12: Interconnect metallic structure for RC analysis
As the technology progresses, the minimum feature size Fmin of the device is
getting smaller. The values of Ls and W may be larger than the minimum
feature size for some interconnect levels. Both dox and t also shrink as Fmin
shrinks. Ideally the aspect ratio of t/W should be kept constant. In the earlier
analysis by Saraswat and Mohammadi, it was assumed that dox and t equal to
0.35Fmin and 0.25Fmin respectively. However, these thicknesses have not
decreased as quickly as in recent years especially the global interconnects. To
keep the analysis simple, one assumes that dox, t, Ls, and W are all equal to
minimum feature size Fmin. Equation (8.16) becomes equation (8.18) after taking
the value of the coupling capacitance Cl between adjacent lines equal to 2. Thus,
the RC delay tL is equal to
2
min
2
0oxLF
LK56.3t (8.18)
For local interconnection, L is usually shrinks as Fmin shrinks. Therefore, the net
result is that the RC time delay for local interconnection stays approximately
constant according to scaling scheme. However, for global interconnection, the
length usually increases rather than shrinking. This is because integrated circuit
area of each new technology usually keeps increasing forcing the global
interconnection to increase in length. The average length of the longest global
interconnection in a circuit can be approximated by equation (8.19).
08 Metallization
- 210 -
2
ALmax (8.159)
where A is the area of integrated circuit. Replacing inductance L of equation
(8.19) with equation (8.4) will yield equation (8.20).
2
min
0oxLF
AK56.3t (8.20)
Exercises
8.1. State the reason why void in a contact via is not acceptable.
8.2. Calculate the time constant for a l.0cm long doped polysilicon
interconnection line on 1.0m thick silicon dioxide. The polysilicon has a
thickness of 5,000o
A and resistivity of 1,000-cm.
8.3. State a method to reduce aluminum diffusion into silicon substrate.
8.4. State a method to reduce electro-migration of aluminum.
8.5. Calculate the interconnect delay time for aluminum with resistivity
3.0x10-6cm, silicon dioxide dielectric constant 3.9, IC area 100mm
2,
and aluminum feature size of 0.35m.
8.6. State the reason why the photograph of scanning electron microscope
SEM is always black and white in color.
8.7. The change of reflectivity versus time of the copper metallic film
measured with acoustic method is shown below. Calculate the average
thickness of the copper film if the speed of sound in copper is 4,710ms-1
.
08 Metallization
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8.8. Three metal conducting lines of the integrated circuit are deposited with
same type of metal film with the length and wide illustrated in figure
below. Calculate the resistance of metal 1 and the resistance of metal 2
and 3 in terms of the resistance of metal 1.
8.9. Why silicon oxide film has compression stress at room temperature?
8.10. A four point probe used to measure the sheet resistance n-type silicon has
forcing current of 0.4mA and measured voltage of 10mV. Find the sheet
resistance of n-type silicon.
08 Metallization
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Bibliography
1. JD Pummer, MD Del, and Peter Griffin, “Silicon VLSI Technology”
Fundamentals, Practices, and Modeling”, Prentice Hall, 2000.
2. Hong Xiao, “Introduction to Semiconductor Manufacturing Technology”,
Pearson Prentice Hall, 2001.
3. Debaprasad Das, “VLSI Design”, Oxford University Press, 2011.
Index
- 213 -
A
Acoustic method ................................................ 200 Aluminum ........................... 193, 194, 196, 197, 203
B
Borophosphosilicate glass ................................. 194
C
Chemical mechanical polishing .......................... 194 Copper ....................................................... 193, 198 Coupling capacitance ................................. 208, 209
D
Dimethylaluminum hydride ............................... 196
E
Electromigration ........................................ 193, 197
F
Fluorosilicate glass ............................................. 194 Four point probe ................................................ 205 FSG ........................................See Fluoroslicate glass
H
Hillock ................................................................ 203
I
Inductance ......................................................... 208 Intrinsic stress .................................................... 203
J
Junction spiking ................................................. 196
L
Lithography ................................................ 200, 204
M
Metallization ...................................................... 193
Mohammadi....................................................... 209
P
Phosphorosilicate glass ...................................... 194 Photoresist ......................................................... 200 Physical vapor deposition .......................... 193, 198 Profilometer ....................................................... 199 PSG ............................... See Phosphorosilicate glass
R
RC time constant ................................................ 208 Reflectivity ................................. 201, 202, 203, 204 Reflectospectrometer ........................................ 200 Resistivity ........................................... 196, 204, 206
S
Saraswat ............................................................. 209 Scanning electron microscope ........................... 199 SEM ................... See Scanning electron microscope Sheet resistance ................. 194, 202, 204, 205, 207 Silicon dioxide .................................................... 201
T
Tantalum ............................................................ 198 Tantalum nitride ................................................ 198 TEOS .............................. See Tetraethyl othosilicate Tetraethyl orthosilicate ...................................... 201 Thermal expansion coefficient ........................... 203 Thermal stress .................................................... 203 Thickness correction factor ................................ 206 Time constant .................................................... 195 Titanium nitride ................................. 194, 200, 201 Tungsten .................................................... 194, 205
U
Undoped silicate glass........................................ 194 USG ................................ See Undoped silicate glass