S i LK * Semiconductor Dielectric S E M I C O N D U C T O R F A B M A T E R I A LS S E M I C O N D U C T O R F A B M A T E R I A LS Ultra-Low k Spin-on Polymer; Benefits, Challenges and Solutions for Damascene Integration Don Frye Semiconductor Fab Materials Dow Chemical Co. [email protected]
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SiLK *
Semiconductor Dielectric
S E M I C O N D U C T O R F A B M A T E R I A LS S E M I C O N D U C T O R F A B M A T E R I A LS
Ultra-Low k Spin-on Polymer;Benefits, Challenges and Solutions for
S E M I C O N D U C T O R F A B M A T E R I A LS S E M I C O N D U C T O R F A B M A T E R I A LS
Acknowledgements
J. Hsu, S. Cummings, K. Foster, K. Itchhaporia, M. Mills, C. Mohler, A. Oshima, J.G. Song, J. Waeterloos, R. Woods
Ensemble* Dielectric Solutions Development Team
porous SiLK* Dielectric Development Team
SiLK* Semiconductor Dielectric Development Team
SFM Application Lab Team
* Trademark of The Dow Chemical Company
SiLK *
Semiconductor Dielectric
S E M I C O N D U C T O R F A B M A T E R I A LS S E M I C O N D U C T O R F A B M A T E R I A LS
ITRS 2001 - Dielectric needsYear of Production 2001 2004 2007 2010DRAM 1/2 PITCH (nm) 130 90 65 45Interlevel metal insulator - effective dielectric constant (k)
3.0 - 3.6 2.6 - 3.1 2.3 - 2.7 2.1 - 2.4
Interlevel metal insulator (minimum expected) - bulk dielectric constant (k)
< 2.7 < 2.4 <2.1 < 1.9
• K-effective is the goal ! ⇒ ILD material selection and integration choice is open
• Most companies will use the same low k ILD material for 2 technology generations but achieve a lower k-effective with a different integration scheme for the second generation. •Different low k materials can potentially leapfrog each other atsuccessive technology generations
SiLK *
Semiconductor Dielectric
S E M I C O N D U C T O R F A B M A T E R I A LS S E M I C O N D U C T O R F A B M A T E R I A LS
Low k Spin-on Polymers
Benzocyclobutene k = 2.7
Fluorinated Polyimide k = 2.5 - 2.9 *
Perfluorocyclobutane k = 2.4
Polyarylene k = 2.8
Polybenzoxazole k = 2.6 - 2.9 *
Polynorbornene k = 2.5
Polyphenylene k = 2.6
* anisotropic materials exist in these polymer families
SiLK *
Semiconductor Dielectric
S E M I C O N D U C T O R F A B M A T E R I A LS S E M I C O N D U C T O R F A B M A T E R I A LS
S E M I C O N D U C T O R F A B M A T E R I A LS S E M I C O N D U C T O R F A B M A T E R I A LS
Low k Spin-on Polymer Material Property Benefits
Initial Cu+ Drift Rates
105
106
107
108
109
1010
1011
1012
1013
1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8
300 250 200 150 100°C350
1000/Temperature (1/K)
Initi
al C
u+ Drif
t Rat
e (io
ns/c
m2 s)
PECVDoxynitride
(1.39 eV)
BCB (1.20 eV )
FPI (0.85 eV)
PAE (1.01 eV)
0.8 MV/cm
1.0 MV/cm
depositedoxide
(0.99 eV)
Ref: Loke et al., “Copper Drift in Low-K Polymer Dielectrics for ULSI Metallization,” presented at the 1998 Symposium on VLSI Technology (Honolulu, HI), June 9, 1998.
SiLK (0.97)
• Low k Spin-on Polymers have Cu drift rates approaching SiN and are more then 104 times lower then oxide or oxide based (OSG) ILD materials
SiLK *
Semiconductor Dielectric
S E M I C O N D U C T O R F A B M A T E R I A LS S E M I C O N D U C T O R F A B M A T E R I A LS
Low k Spin-on Polymer Material Property Challenges
• Modulus and hardness will decrease for all materials when voids (air) is introduced•At k<2.6, all ILD materials will have a modulus significantly less then the metal conductor (Cu)
S E M I C O N D U C T O R F A B M A T E R I A LS S E M I C O N D U C T O R F A B M A T E R I A LS
Low k Spin-on Polymer Material Property SolutionsFracture Toughness
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
Dielectric Constant
Toug
hnes
s, M
Pa-m
^1/2
OxideSiLK*
Aerogels
OSG
HSQ
OSG
SiO2
SiLK
PorousSiLK*
IncreasingCMP & Packaging
concerns
• Toughness determines CMP survivability not hardness or modulus for polymers. •Polymers have almost the same toughness as oxide and are significantly tougher then OSG materials at equivalent k values
SiLK *
Semiconductor Dielectric
S E M I C O N D U C T O R F A B M A T E R I A LS S E M I C O N D U C T O R F A B M A T E R I A LS
• Extendible K-effective roadmap• Leveraged development knowledge through multiple technology generations• Multiple Low k strategy entry points
SiLK *
Semiconductor Dielectric
S E M I C O N D U C T O R F A B M A T E R I A LS S E M I C O N D U C T O R F A B M A T E R I A LS
Low k Spin-on Polymer Integration ModulesChallengeAvailability of integrated all spin-on dielectric stackDielectric Dep.
Lithography
Etch SolutionAll dielectric layers deposited sequentially with a single final cure per interconnect layer !
Clean
Metal Barrier
CMP
Packaging
Reliability
Extendibility
SiLK *
Semiconductor Dielectric
S E M I C O N D U C T O R F A B M A T E R I A LS S E M I C O N D U C T O R F A B M A T E R I A LS
Low k Spin-on Polymer Integration Modules
Dielectric Dep.
Lithography
Etch
ChallengeCompatibility with 248nm, 193nm, … photoresistSolutionMost low k spin-on polymer materials do not contain any amine (NH) structures nor are they prone to amine absorption during etch and clean processing !
Clean
Metal Barrier
CMP
Packaging
Reliability
Extendibility
SiLK *
Semiconductor Dielectric
S E M I C O N D U C T O R F A B M A T E R I A LS S E M I C O N D U C T O R F A B M A T E R I A LS
Low k Spin-on Polymer Integration Modules
Dielectric Dep.
Lithography
Etch
StandardAsh
Process• Bottom hardmask protects polymer during ash•Top hardmask is removed during CMP to lower k-effective
ChallengeAvailability of a photoresist rework process
SolutionDual Hard mask integration scheme !Clean
Metal Barrier
CMP
Packaging
Reliability
Extendibility
SiLK *
Semiconductor Dielectric
S E M I C O N D U C T O R F A B M A T E R I A LS S E M I C O N D U C T O R F A B M A T E R I A LS
Low k Spin-on Polymer Integration Modules
• Both “timed etch” and “buried etch stop”integration schemes have been demonstrated
ChallengeEtch of high aspect structures in damascene integrationDielectric Dep.
Lithography SolutionDual Hard mask materials offer an etch selectivity of greater then 20:1 !
Etch
Clean
Metal Barrier
CMP
Packaging
Reliability
Extendibility
Courtesy of Tokyo Electron, Ltd.
SiLK *
Semiconductor Dielectric
S E M I C O N D U C T O R F A B M A T E R I A LS S E M I C O N D U C T O R F A B M A T E R I A LS
Before wet clean processing After wet clean processing
Depending on the etch chemistryDepending on the etch chemistryPost etch clean removes this material prior to Post etch clean removes this material prior to metallizationmetallizationCleaning similar to dense SiLKCleaning similar to dense SiLK
Lithography
Etch
Clean
Metal Barrier
CMP
Packaging
Reliability
Extendibility
Porous SiLKDielectric Dep.
SiLK *
Semiconductor Dielectric
S E M I C O N D U C T O R F A B M A T E R I A LS S E M I C O N D U C T O R F A B M A T E R I A LS
Low-k Materials in CMPMinimum Toughness/Adhesion Threshold to survive CMP
Dielectric Dep.
Lithography
0
0.1
0.2
0.3
0.4
0.5
SiLK
TM
PQ-6
00
CVD
SOG
E
SOG
D
SOG
A
SOG
B
SOG
C
KC
(MPa
-m1/
2 )
Not Debonding Debonding
CMP Test Results*
Ohta et. al., JAPS Sept. 2000
Etch
Clean
Metal Barrier
CMP
Packaging
Reliability
Extendibility
SiLK *
Semiconductor Dielectric
S E M I C O N D U C T O R F A B M A T E R I A LS S E M I C O N D U C T O R F A B M A T E R I A LS
5
7
9
11
13
15
17
19
21
23
25
27
36 38 40 42 44 46 48
Ultrasonic Power(Arb. Units)B
ond
Forc
e (A
rb. U
nits
)
Cu/SiO2
Cu/Low-k• Higher Bond force is
necessary to ensure intimate contact between the wire and bond pad.
Dielectric Dep.
Lithography
Etch
Clean
Metal Barrier
CMP
Packaging
Reliability
Extendibility
• Inter metallic coverage and ball shear value was observed slightly less due to less efficient energy transfer to the wire/pad interface.
• With careful optimization of bond process parameter or wire bond pad design, good bond with tensile failure on the bond wire at the neck during wire pull can be achieved
V.Kripesh et.al., Institute of Microelectronics, ECTC 2002, May 28th -31st, San Diego, US
SiLK *
Semiconductor Dielectric
S E M I C O N D U C T O R F A B M A T E R I A LS S E M I C O N D U C T O R F A B M A T E R I A LS
S E M I C O N D U C T O R F A B M A T E R I A LS S E M I C O N D U C T O R F A B M A T E R I A LS
Low k Spin-on Polymer ExtendibilitySiLK V7 V8 Porous
SiLKK 2.65 2.35 2.20 2.10
Davg(nm) NA 25 16 < 10
Modulus(GPa @ 1 um) 3.6 2.8 2.7 2.8
Hardness(GPa @ 1 um) 0.27 0.17 0.16 0.15
CTE 62 62 62 ~ 62Toughness /
Adhesion(Mpa-m0.5)
> 0.35 > 0.35 > 0.35 > 0.35
ProcessTemperature
(oC)400 – 450 430 430 400
Chemistry SiLK SiLK SiLK SiLK
• Extendible material that leverages processing knowledge
Dielectric Dep.
Lithography
Etch
Clean
Metal Barrier
CMP
Packaging
Reliability
Extendibility
SiLK *
Semiconductor Dielectric
S E M I C O N D U C T O R F A B M A T E R I A LS S E M I C O N D U C T O R F A B M A T E R I A LS
Low k Spin-on Polymer Extendibility
0.0
0.3
0.5
0.8
1.0
0 5 10 15Diameter (nm)
Nor
mal
ized
Fra
ctio
n 8.2 nm mean diameter
0.99
0.992
0.994
0.996
0.998
1
16.0 16.5 17.0 17.5 18.0 18.5
0.6% > 2X Mean Size
Log-Normal Distributions for Porous SiLKTm
0.00E+00
5.00E-03
1.00E-02
1.50E-02
2.00E-02
2.50E-02
0 100 200 300
r (Å)
f(r) (
norm
aliz
ed)
V(9A)V9(B)V8
Dielectric Dep.
Lithography
Etch
Clean
Metal Barrier
CMP
Packaging
Reliability
Extendibility
• Continual reduction in pore size (closed) and pore size distribution•Good barrier metal integrity
SiLK *
Semiconductor Dielectric
S E M I C O N D U C T O R F A B M A T E R I A LS S E M I C O N D U C T O R F A B M A T E R I A LS
Pore Size Impact on Yield
Yield increase with decreasing pore size
Measurement ofleakage current
25 m meander line required to observe electrical differences (5025 m meander line required to observe electrical differences (50m effective length)m effective length)
SiLK *
Semiconductor Dielectric
S E M I C O N D U C T O R F A B M A T E R I A LS S E M I C O N D U C T O R F A B M A T E R I A LS
SummaryChallenges for Low k Spin-on Polymers
Polymer mechanical properties are not like oxide and will require different integration and design mindset
Benefits of Low k Spin-on Polymers (SiLK)Chemistry is unchanged since the mid 1990’s
Compatible with all existing process modules and tools
Extendible versions, lower dielectric constant (k=2.1), are already available
Existing materials meet ITRS targets for k and k-effective through 45nm technology
Have passed full reliability qualification at 130nm and 90nm