Engineering Materials and Processes phần 10 pptx

RBS spectra 3.7 MeV He+2, 7° tilt of the diffusion barriers before broken line and after solid line testing at 620°C for 30 minutes in flowing atmosphere N 2 -5% H 2 ambient [8] 7.3 Ele

Figure 7.4 RBS spectra (3.7 MeV He+2, 7° tilt) of the diffusion barriers before (broken line)

and after (solid line) testing at 620°C for 30 minutes in flowing atmosphere N 2 -5% H 2

ambient [8]

7.3 Electromigration Resistance

Electromigration (EM) resistance of Ag is the most critical interconnect reliability

concern that would determine its suitability for integrated circuit technology EM is

the drift of metal ions as a result of either collision between the conductor electrons

and/or the metal ions or high electrostatic field force when current is passed

through a metal conductor The direction of mass transport depends on the

direction of the net force When high current densities pass through the metal line,

voids or hillocks are formed at a point of ion flux divergence (Figure 7.5) Voids

and hillocks deform and grow until electrical failure is completed [10]

118 Silver Metallization

Figure 7.5 Schematic to illustrate metal conductor failure due to electromigration [17]

Ho and Huntington [11], Patil and Huntington [12] reported that Ag migrates toward the anode for the temperature range 670–877°C Klotsman et al [13] and Breitling and Hummel [14] however, found that Ag ion transport is toward the cathode, and is opposite to the direction of the electron wind Studies conducted by

Hummel et al showed that the dominating movement path is grain boundaries for

temperatures in the range of 225–280°C (activation energy of 0.95 eV) and surface for the temperature range 160–225°C (activation energy of 0.3 eV) [15]

In this study the influence of an encapsulation process on the electromigration resistance of Ag has been investigated The sample configurations used consisted

of bare Ag patterns and encapsulated Ag patterns Compared to bare Ag lines, TiN(O) encapsulated Ag lines exhibited much better electromigration resistance in terms of the time required for the formation of significant number of voids and hillocks

After the encapsulation process, the Ag surface is capped by a thin layer of TiN(O) The mobility of Ag atoms at the TiN(O)/Ag interface is substantially reduced Therefore the electromigration resistance is improved significantly By examination of the surface of the encapsulated Ag lines tested for a long time, almost no hillocks were observed This implies that the surface diffusion has been hindered substantially by the presence of the TiN(O) encapsulation Comparison of Tables 5.1 and 5.2 suggests that the encapsulation process improves the electromigration resistance of Ag metallization by at least one order of magnitude for the test structures and conditions used [16]

7.4 Future Trends

Ag metallization research has intensified significantly in recent years Research work has been conducted mainly in the US Increasing numbers of companies have already begun research and development (R&D) efforts in Ag-based metallization However in this highly competitive era the industrial research has been propriety Ag-based interconnects represents the future trend in the deep sub-micron regime

Ag is an attractive material for interconnect-metallization in future integrated circuits technologies due to its low bulk resistivity and high reliability against

electromigration Ag can be deposited by plating (electroless and electrolytic),

sputtering (physical vapor deposition (PVD)), laser induced reflow and chemical

vapor deposition (CVD) cluster tools, chemical mechanical polishing (CMP)

polishers and low temperature etchers

There are still many critical issues that remain to be resolved in the

development of Ag-based metallization For instance, to meet the throughput

requirement in device manufacturing, there is a need to demonstrate a Ag

deposition technique with a high deposition rate (>250 nm/min) at low substrate

temperatures without simultaneously sacrificing low resistivity, good step coverage

and complete via fill The adequate use of thin diffusion barriers in Ag-based

metallization will be critical for the 0.25 mm technology Other materials science

issues in Ag-based metallization need to be address: (1) microstructural control

(e.g grain size and texture); (2) contamination control (C, O and CI); (3) oxidation

and corrosion control; (4) prevention of Ag diffusion in metals and dielectric

materials; and (5) mechanical properties (e.g stress migration, adhesion

improvement) In addition, the development of Ag-based on-chip interconnects

technology will also lead to new advancements in electronic packaging technology

The implementation of Ag-based interconnects will represent the future trend in

the deep submicron regime

7.5 References

[1] S P Murarka, R J Guttman, A E Kaloyeros, W A Lanford, Thin Solid

Films 236, 257(1993)

[2] M E C Willemsen, A E T Kuiper, A H Reader, R Hokke,

J C Barbour, J Vac Sci Technol B 6, 53(1988)

[3] S Q Wang, I Raaijmakers, B J Burrow, S Suthar, K B Kim, J Appl

Phys 68, 176(1990)

[4] T L Alford, D Adams, T Laursen, B M Ullrich, Appl Phys Lett 68,

3251(1996)

[5] Y L Zou, T L Alford, D Adams, T Laursen, K N Tu, R Morton,

S S Lau, MRS Proc 427, 355(1996)

[6] J Li, J W Mayer, E G Colgan, J Appl Phys 70, 2820(1991)

[7] D Adams, T L Alford, N D Theodore, S W Russell, R L Spreitzer,

J W Mayer, Thin Solid Films 262, 199(1995)

[8] Y Wang, T L Alford, Appl Phys Lett 74(1), 32(1999)

[9] D Adams, Ph.D dissertation, Arizona State University, 1996

[10] M Mahadevan, R M Bradley, J M Bebierre, Europhys Lett 45,

80(1999)

[11] P S Ho, H B Huntington, J Phys Chem Solids 307, 1319(1966)

[12] H R Patil, H B Huntington, J Phys Chem Solids 31, 463(1970)

[13] S M Klotsman, A N Timofeyev, I S Trakhtenberg, Phys Metal

Metallogr 14, 140(1962)

[14] H.M Breitling, R E Hummel, J Phys Chem Solids 33, 845(1972)

120 Silver Metallization

[15] R E Hummel, H J Geier, Thin Solid Films 25, 335(1975) [16] Y Zeng, L H Chen, Y L Zou, P A Nguyen, J D Hensen,

T L Alford, Mater Lett 45, 157(2000)

[17] D Adams, T L Alford, Materials Science and Engineering R 40, 207(2003)

Index

Adhesion analysis, 54

tape test, 55

scratch test, 54

Ag on Pa-n, 51

compositional changes, 51

sheet resistance variation, 52

Ag on SiO 2 , 70

Ag(Ti) alloys, 20

Ag/barrier/silicide/silicon, 105

Ag/Ti-O-N/CoSi 2 /Si, 105

Ag/Ti-O-N/NiSi/Si, 105

Agglomeration, 2, 43–48, 69–73

Al(Cu), 75

Aluminum oxide, 59, 62, 84, 86, 93, 97

Aluminum properties, 5

bulk resistivity, 5

thin film resistivity, 5

diffusivity in Si, 5

self-diffusivity, 5

electromigration, 5

Young's modulus, 5

TCR, 5

mean free path of electron, 5

melting point, 5

thermal conductivity, 5

Ag sheet resistance, 36, 37

Amorphous-to-crystalline transition, 40

Annealing ambients, 57

argon ambient, 59

He-H ambient, 62

ammonia ambient, 63, 93

Annealing temperatures, 46 Auger depth profiles, 61 AES spectrum, 76 Bragg’s Law, 12 Bulk resistivity, 5 Cobalt silicide, 104 CoSi 2, 104 Composition of Ta-N, 31 Copper metallization, 4 Copper properties, 5 bulk resistivity, 5 thin film resistivity, 5 diffusivity in Si, 5 self-diffusivity, 5 electromigration, 5 Young's modulus, 5 TCR, 5

mean free path of electron, 5 melting point, 5

thermal conductivity, 5 Corrosion, 2, 22

encapsulated silver films, 22

H 2 S ambient, 29 Cu(Ti) alloys, 21 Copper (Cu), 5 Current density, 76 Dealloying kinetics, 18 Depth scale, 10

122 Index

Diffusion barriers, 15, 34

Diffusivity

in Si, 5

in SiO 2 , 1

Electromigration, 1, 5, 75, 76, 78–81

Electronegativity, 102

Encapsulation, 80, 81, 83

Energy resolution, 8

Failure mechanisms, 109

TiN(O)-encapsulated Ag lines, 80

electromigration resistance, 1, 75, 76

Formation of voids, 45

Four-point-probe, 49, 50, 52

van der Pauw, 70

Gold, 98, 101

H 2 S ambient, 24

Heat of formation, 93

Hillocks, 69, 75–81, 117, 118

Hole formation, 69

Hydrogen sulfide, 24

H 2 S ambient, 24, 25, 28, 29

Identification of phases, 39

Impurity scattering factor, 46

Interfacial energy barrier, 94

Ion resonances, 11

Joule heating, 78, 80

Kinematic factor, 8

Kinetics in Ag/Al bilayer systems, 83, 97

reaction kinetics, 83

outdiffusion of Al through Ag, 83

Kinetics of oxide, 89, 93

growth kinetics, 89

Law of Reflectivity, 12

Mass transport, 43 Melting point, 5 Nitridation, 20, 28 Nitrogen, 41

N 2 flow, 30, 34–40 interstitial nitrogen, 40 Onset temperature, 70–73 Outdiffusion of Al, 60, 62, 67 Oxide surface layer, 84, 89, 93, 95 Parylene, 48, 49

Pa-n, 48, 49

dielectric, 48, 49 reliability issues, 549 phase change, 50 Polyimides, 2, 548 Recoil energy, 8 Refractory metal nitrides, 15 Resistivity, 5, 17, 34, 39 Resonances, 11 RUMP, 17, 18 Rutherford backscattering spectrometry (RBS), 8

Scattering cross section, 9 Scattering kinematics, 8 Self-diffusivity, 5 Self-encapsulation, 15 Silicide, 40

Silver, 1, 5

Ag, 1, 2, 5, 29, 79 Silver properties, 5 bulk resistivity, 5 thin film resistivity, 5 diffusivity in Si, 5 self-diffusivity, 5 electromigration, 5 Young's modulus, 5 TCR, 5

mean free path of electron, 5

melting point, 5

thermal conductivity, 5

Silver-aluminum films, 46

Silver sulfide, 25

Stress, 67, 69

compressive stresses, 67, 69

thermal stresses, 67, 69

thermal expansion coefficients, 67

Surface energies, 67

Surface oxide layer, 102

Surface peak Al, 98

Tantalum nitride, 30

Ta-N films, 30, 39, 41

Ta-N diffusion barriers, 30, 34, 36

Ta-silicide, 40, 41

Test structures, 79

Thermal conductivity, 5 Thermal stability, 4, 43 Thermodynamic data, 93 Gibbs free energy, 93 enthalpy, 95 Thin film characterization, 7 Thin film resistivity, 5 TiN encapsulation, 24 TiN(O), 18, 117 Titanium nitride, 16, 113, 114 Titanium nitride self-encapsulation, 16 Transport of aluminum, 91

X-ray diffractometry, 12 XRD, 13, 30, 33, 37–41, 44, 46–50, 52