Electromigration Study of SnAg 3.8 Cu 0.7 Solder Using Blech Structure 年

Electromigration Study of SnAg 3.8 Cu 0.7 Solder Using Blech Structure Student : Yung-Chang Hsu AdvisorDr. Chih Chen College of Engineering Industrial Technology R & D Master Program On Semiconductor Materials & Processes National Chiao Tung University ABSTRACT Critical length of lead-free solder has not been measure because it is very difficult to prepare short solder stripe. In this study, By employing focus ion beam, solder stripes of various lengths, including 5, 10, 15, 20, 30, 100, and 200 µm, can be fabricated. Length dependent electromigration behavior was observed, which implies that there may be back stress under current stressing. We can determine the critical length under testing condition under 2~10 4 A/cm 2 at 100-150, the critical product is 20~30 A/cm and critical length is 10~15m II

III

SnAg 3.8 Cu 0.7 Critical product SnAg 3.8 Cu 0.7 SnAg 3.8 Cu 0.7 References IV

µm µm µm µm µm V

Blech like s structure stripe 6.6 x 10 4 A/cm 2 FIBstripe strpie µm stripe FIBstripe 4-23 stripe 4-24 Blech structure 4-25 Blech structure 4-26 Blech structure stripe SEM EPMA 4-27 Blech structure stripe SEM EPMA 4-28 Blech structure stripe SEM EPMA 4-29 Blech structure stripe SEM EPMA 4-30 Blech structure stripe SEM EPMA 4-31 Temperature Dependence of yield stress for various alloys VI

critical product critical product VII

論路年路路來路不聯來路路易裂來若路不路連路數路連 1

不 3

不流度金流金不流金離例離力量流度流度不不流度流流度 4

什狀列流料更來說兩金料度良年立理料料量令令不金類令來量粒粒洞洞累良年來金金異料金金度良 5

金料金金了連金易裂金金金 6

1.4 臨度來度來流流度來度參數例度 drift velocity 流度 threshold current density, activation energy, 率數 product of diffusivity and effective charge number (DZ*) 參數量來臨度 critical length of electromigration 臨度度不力 back stress[5] 7

理論金料年路度金量率來年率參數流率流流流流度流度度度路流度度 8

理流度 10

力量流力兩力量力 [8] 兩理論金量來不量量 ' P = m0 V = m0v m0v 量度量來 ( m V ) 11 1 E h k dp x d = 0 dt dt dp x dt = 1 4π E E ' ' ' ( m0 / h) f ( k) [ 1 f ( k )] W ( k k ) dk dk ' 2, 3 k k 狀狀率句說率數 dp x = dt 1 4π E ' ' E ' ' ( m ) ( )[ ( ) ( ) ] ( ) ( [ ( )] ( ) ) 0 / h f k 1 f k W k, k' dksk m0 / h f k 1 f k W k, k dksk k' 3 ' k

理 dp x dt 2 E ( m ) { f ( k[ f ( k ' )] W ( k k ' ) f ( k ' )[ f ( k) ] W ( k ' 0 / h 1. 1 k )} 1 =, dk ' dk 3 4π k f ( k) f ( k) 0 3 τ d = { f ( k) [ f ( k' )] W ( k, k' ) f ( k' )[ 1 f ( k) ] W ( k', k) } 1 dk' / 4π 裡數 dp dt x 1 E = ( m0 / h) f ( k) dk 4π 3 τ d k E k 0 = f ( k) τ m d h 3 dk / 4π 流度量 j x = e f ( k) E 3 dk / 4π h k E 裡 h k dp dt j m x x 0 = eτ d 量 F = x dp dtn d jxm0 eτ N d d 裡度率 * m = ne τ ρ d 2 d 裡量參度 Fx nej m x 0 = ρ d Nd m * 律 j x = ε x ρ 12

ne ε x m0 Fx = ρ d N d ρ m * N ρ d m0 = eε x z N ρ m * d 裡離度離數離數 F x 1 N ρ d m0 = eε x z 2 N ρ m * d 流金離金離力力力 F driving = F + F field el wind 1 N 2 N ρ m ρ m 0 = eε x z eε x z * e ( Z + Z ) = ε * = z eε x x el wd d d 13

金量 14

力年利流 [9]- [12] 率若度臨度不若臨流度率零力力更 Nabarro-Herring mode 度度流流 J = J chem + J em C D D dσω + Jσ = D + C Z * eρj C KT KT KT dx 力流若度度流力力 J = C D KT D dσω Z * eσj C KT dx 若臨度 X crit σω = Z * e ρ j 不 j X σω σω = j X crit = (critical product Z * eρ Z * eρ 16

流利來狀 The inductively coupled plasma-reactive ion etching (ICP-RIE) 來度 α-stepper and Atomic Force Microscopy (AFM) 來量 SiO 2 金了漏流利 Å 利 ÅÅ 利來來 FeCl 3 +D.I.1200 來利 Eutectic SnAgCu 金 Blech-like 利切度 17

3.1µm Si Si 3.1 µm 1200Å SiO 2 SiO 2 SiO 2 Si 1500Å Ti SiO 2 Cu Cu Ti Ti SiO 2 SiO 2 Si 4000Å Cu Ti SiO 2 18

SiO 2 SiO 2 370µ Si Cu Ti SiO 2 SiO 2 SiO 2 Si SnAgCu IMC Cu Ti SiO 2 polish Si Cut by FIB 19

Pad Short solder stripe Pad 流 20

流度度力度率聯流度力 21

立 0 22

µ 率 23

1. CCD camera 2. Probe 3. Sample 4. Optical lens 5. Current source 6. hot plate 24

= Z FEM * eξ Ωdσ F = Backstress dx When F EM = F backstress e - σω Lc = * Z ejρ 力 25

了流立數利流理數說數利不數數 26

Scanning Electron Microscopy 力 (AFM Atomic Force Microscopy) 量 (EDS Energy Dispersive Spectrometer) (Infrared scope IR) (Electron Probe X-Ray Microanalyzer EPMA) ANSYS LabVIEW 27

論度量落度利來不度不度度不流度切度度 µm 零 Ag 3 Sn 金 0.2µmCu 6 Sn 5 金度 µm 度流流 42.9%IMC53.1%4% 利 (Infrared scope IR) 來量度 4-410IR 量度 4-5~4-10 流度不度 R 量流度不流度兩 silicon substrate 良狀 28

5m 15m 30m 10m 20m 29

Cross-section SEM image on tilt 52 E-SnAg 3.8 Cu 0.7 The average thickness of Cu 6 Sn 5 is 1.3µm Ag 3 Sn IMC Ti 流流度流例 SnAg 3.8 Cu 0.7 0.01 10 4 42.874% Cu 6 Sn 5 0.012 10 4 53.082% Ti 0.0009 10 4 4.044% 流例 30

量流度量 31

流度 µm 量流度 µm 量 32

流度 µm 量流度 µm 量 33

流度 µm 量不流度 34

SnAg 3.8 Cu 0.7 Critical product 量利來量 critical product 理論年利流度 SnAg 3.8 Cu 0.7 Critical product280a/c SnAg 3.8 Cu 0.7 Critical product60a/c 兩理論率量度流度 µm 都洞 Critical product2030(a/cm) 理論 Blech 利 Blech structurecritical product 2-1Blech structure 度行流度利 Blech structure 狀 µm 都 ANSYS 來 stripeblech like s structure stripe 流 35

(a) 0hr 5um 15um 30um 10um 20um (b) 940hrs e - void 36

(a) 0hr (b) 273hrs e - Void 30um 37

(a) 0hr (b) 200hr e - void 15um 20um 30um 38

(a) 0hr (b) 300hrs e - void Blech like s structure stripe 39

SnAg 3.8 Cu 0.7 流度 ANSYSBlech structure 流流流度 6.6 x 10 4 A/cm 流流 stripe 流度 4-16Blech structure 流度 contact windoeffect 流度離便 4-17 流度流 stripe current crowding effect[14 落流度流流度 10 5 A/cm 2 見 three element 流度 elementcurrent crowding effec 不 contact resistance 不 contact resistanc 利度 Deposition 理論不若 contact window 流度不 [15 切 strip 切 stripecontact window 流度不 µmstripe 流度不不 µm stripe 流度 90FIB 切 stripe 不 µm 流度 current crowding effec 切 Blech structure 流度切 blech structure 流度易 40

流度度 10 8 A/cm Blech structure(10 10 A/cm ) viod 流度論 41

流度 6.6 x 10 4 A/cm 2 65000 Current density (A/cm 2 ) 62500 60000 57500 55000 52500 50000 47500 45000 Contact window about 10µm -200-150 -100-50 0 50 100 150 200 Location (µm) 流度 42

Solder layer IMC layer Ti layer 流度 43

(b) (a) (c) (b) 60000 40000 (c) top element 20000 middle element bottom element average 0-188 -186-184 -182-180 Position (µm) 流度流 Current density (A/cm 2 ) 44

(a) (b) (c) FIB 切 stripe 45

100000 (a) Current density (A/cm 2 ) 80000 60000 40000 20000 0-200 -150-100 -50 0 50 100 150 200 Location (µm) 80000 Current density (A/cm 2 ) 70000 60000 25um (b) 50000-100 -90-80 -70-60 -50 Location (µm) strpie 流度 µm stripe 46

5 µm 10 µm 15 µm FIB 切 stripe 47

(µ current density/ calculation value) Current density (A/cm 2 ) 66000 64000 62000 60000 58000 56000 54000 52000 不度流度 0 10 20 30 40 50 Stripe length (µm) 4-23 stripe 度流度 48

(a) (b) 4-24 Blech structure 流度 49

4-25 Blech structure 流度 50

SnAg 3.8 Cu 0.7 了 SnAg 3.8 Cu 0.7 利 EPMA 來 mapping 4-26~30 4-26~30 EPMA Ag 3 Sn µm Ag 3 Sn 數 Cu 6 Sn 5 EPMA E-beam 度度若 Cu Ni 易 51

(a) e - (b) (c) (d) (e) (f) (g) (h) 4-26 Blech structure stripe SEM EPMA (a)5µm stripe SEM(b)Sn-map(c)Ag-map(d)Cu-map (e) 5µm stripe SEM(f)Sn-map(g)Ag-map(h)Cu-map 52

a b c d e f g h 4-27 Blech structure stripe SEM EPMA (a)10µm stripe SEM(b)Sn-map(c)Ag-map(d)Cu-map (e)10µm stripe SEM(f)Sn-map(g)Ag-map(h)Cu-map 53

a b c d e f g h 4-28 Blech structure stripe SEM EPMA (a)15µm stripe SEM(b)Sn-map(c)Ag-map(d)Cu-map (e)15µm stripe SEM(f)Sn-map(g)Ag-map(h)Cu-map 54

a b c d e f g h 4-29 Blech structure stripe SEM EPMA (a)20µm stripe SEM(b)Sn-map(c)Ag-map(d)Cu-map (e)20µm stripe SEM(f)Sn-map(g)Ag-map(h)Cu-map 55

a b c d e f g h 4-30 Blech structure stripe SEM EPMA (a)20µm stripe-2 SEM(b)Sn-map(c)Ag-map(d)Cu-map (e)20µm stripe-2 SEM(f)Sn-map(g)Ag-map(h)Cu-map 56

critical product 論 SnAg 3.8 Cu 0.7 critical produc150 10 4 A/cm 2 流度 20~30A/c 理論金兩不不度說兩不理論度不度不更來論不度流度 critical produc 57

金 critical product 理論量 j x c_snagcu * = 22.4A/ CM σω = Z eρ critical product 58

John H. L. Pang, B.S. Xiong and F.X. Che[16] 4-31 Temperature Dependence of yield stress for various alloys Dr. M. Warwick[17] 59

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