Potential and Lim its of Texture Measurem ent Techniques for I nlaid Copper Process Optim ization Holm Geisler, Inka Zienert, Hartmut Prinz, Moritz-Andreas Meyer, Ehrenfried Zschech AMD Saxony LLC & Co. KG, Dresden, Germany
Outline • Microstructure characterization of inlaid copper interconnects • Texture measurement techniques – X-ray micro-diffraction – OIM: EBSD & ACT • Application – Microstructure monitoring – ECD-filled inlaid structures with new ILDs, capping layers and barrier layers – Texture and stress – Orientation stereology, grain size, grain boundary distribution – Texture in ECD-filled via chains – Texture of barrier and seed layers before ECD filling • Summary 03/ 26/ 03 ICCM, March 24 - 28, 2003, Austin, Texas Holm Geisler 2
Microstructure characterization of inlaid copper interconnects • Aluminum vs. inlaid copper: What is different ? • Texture, EM & defects • Microstructure characterization: general concept • Orientation distribution function (ODF) • Quantification 03/ 26/ 03 ICCM, March 24 - 28, 2003, Austin, Texas Holm Geisler 3
Texture Al vs. inlaid Cu Al I nlaid Cu Al I nlaid Cu { 111} { 111} { 511} twins { 111} + sidewalls + twins + engaged 03/ 26/ 03 ICCM, March 24 - 28, 2003, Austin, Texas Holm Geisler 4
What is different ? Inlaid Copper Interconnects Aluminum Interconnects Twins + Sidewall Bamboo + Columnar ???? Optimum EM Behaviour Large Anisotropy Small Anisotropy E 〈 111 〉 = 1 9 1 GPa E 〈 100 〉 = 6 6 .7 GPa Electroplating Vapour Deposition Cu CMP Metal etch .... .... 03/ 26/ 03 ICCM, March 24 - 28, 2003, Austin, Texas Holm Geisler 5
Texture, EM & defects Electromigration: Prevent grain boundaries along the trench direction! = Fast diffusion pathways j � Top view v > v void Sidewall-oriented grains? High-angle grain boundary? 03/ 26/ 03 ICCM, March 24 - 28, 2003, Austin, Texas Holm Geisler 6
Microstructure Characterization: General Concept • Microstructure Function: i ( x ) phase = G ( x ) g ( x ) orientatio ns D ( x ) defects, lattice strain g(x) • Orientation Distribution Function: K B dV / V g = = ϕ Φ ϕ f ( g ) f ( , , ). x 1 2 dg dg x 3 g V x 2 H.J. Bunge K A x 1 (1999, 2001) 03/ 26/ 03 ICCM, March 24 - 28, 2003, Austin, Texas Holm Geisler 7
Quantification: ODF approximation ( hkl) pole figure, P( χ , φ ) OD, f( φ 1 , Φ , φ 2 ) Euler angles ϕ 1 , Φ , ϕ 2 (111)+ (200)+ (220) e.g., ADC χ φ P ( , ) χ π 2 1 ∫ χ φ = φ Φ φ P hkl ( , ) f ( , , ) dg ( ) 1 2 π 2 0 dV / V g = = ϕ Φ ϕ f ( g ) f ( , , ). K A : sample coordinates 1 2 dg φ K B : cryst. coord. system [ K. Helming, http: / / www.texture.de/ ] 03/ 26/ 03 ICCM, March 24 - 28, 2003, Austin, Texas Holm Geisler 8
Evaluation of pole figures • Computational algorithms for OD analysis – Harmonic Methods: computation in Fourier space – Discrete (Direct) Methods: computation in orientation space: = ∑ N 1 χ φ χ φ ⇐ φ Φ φ K. Pawlik et al. P ( , ) f [( , ) ( , , ) ] h 1 2 i N (1991) = i 1 U.F. Kocks et al. • Commercial software: LaboTex (1998) – based on ADC (Arbitrarily Defined Cells) – direct method, good for sharp textures – quantification of • fibers • engaged fibers • tw ins – uncertainty in determination of random texture component (background, low signal-to-noise ratio) 03/ 26/ 03 ICCM, March 24 - 28, 2003, Austin, Texas Holm Geisler 9
Texture measurement techniques • Overview • X-ray micro-diffraction • OIM (Orientation Imaging Microscopy) – EBSD: Electron Backscatter Diffraction – ACT: Automated Crystallography for the TEM 03/ 26/ 03 ICCM, March 24 - 28, 2003, Austin, Texas Holm Geisler 10
Texture measurement techniques for inlaid Cu interconnects: Overview • Single Inlaid ACT EBSD • Dual Inlaid EBSD ? µ-XRD ? • Seed • Barrier ACT nano- cryst. µ-XRD EBSD 03/ 26/ 03 ICCM, March 24 - 28, 2003, Austin, Texas Holm Geisler 11
Techniques: comparison � Classical Texture, ODF: f ( g ) = f ( ϕ 1 , Φ , ϕ 2 ) • µ-XRD � Phase: i � Strain (Stress): D s � Orientation Stereology: g ( x ) • OIM � Grain Size � Grain-boundary distribution 03/ 26/ 03 ICCM, March 24 - 28, 2003, Austin, Texas Holm Geisler 12
Probed volume • Beam diameter between 50µm and several 100µm γ • X-rays � „Bulk“ information, penetration of ILD X-rays: ILD Penetration depth Met n+ 1 > > µm Via n Compared with EBSD: Met n ≤ tens of nm 03/ 26/ 03 ICCM, March 24 - 28, 2003, Austin, Texas Holm Geisler 13
Statistics { 1 1 1 } pole figures • X-ray m icro-diffraction RD – Beam diameter d = 100µm � A = π r 2 = 7854 µm 2 X-ray – Test pattern: parallel trenches, w = 180nm, p = 360nm TD – Assumption: mean grain diameter = w (one grain extends over the whole line width and depth) – n = ( L / w ) / (2 Lw ) = 1 / (2 w 2 ) L : length of the line EBSD – n ∼ 15 grains / µm 2 – N = n A ∼ 118000 grains • EBSD – A = 3µm x 10µm = 30 µm 2 – N = n A ∼ 450 grains 03/ 26/ 03 ICCM, March 24 - 28, 2003, Austin, Texas Holm Geisler 14
X-ray X-ray micro-diffraction • Arrays of ECD-filled inlaid copper lines • Arrays of ECD-filled inlaid line segments • Arrays of ECD-filled vias (?) • Process monitoring • In-line application 03/ 26/ 03 ICCM, March 24 - 28, 2003, Austin, Texas Holm Geisler 15
Texture and stress measurements at inlaid test structures using X-ray micro-diffraction Huber goniometer Bruker AXS D8 micro-diffraction tool with ¼ Eulerian cradle, PolyCap and area detector (GADDS) Video + laser for accurate height adjustment • Tool perform ance: • large detector area with high detector sensitivity (80% quantum efficiency) • small area beam focus with high intensity • Test structures: • blanket or structured thin film samples from 120 x 120 µm 2 up to 10 x 10 mm 2 03/ 26/ 03 ICCM, March 24 - 28, 2003, Austin, Texas Holm Geisler 16
X-ray micro-diffraction on arrays of inlaid Cu lines or Narrow inlaid Wide inlaid Cu lines Cu lines Inlaid structure Copper lines SiN, SiCN > 120µm Barrier Si(F)O, X-ray beam Metal 1 SiCOH 80µm Ø Silicon Video camera + laser beam � alignment 03/ 26/ 03 ICCM, March 24 - 28, 2003, Austin, Texas Holm Geisler 17
X-ray µ-diffraction on arrays of Cu lines and line segments � geometry effects Narrow Cu lines and line segments – width = 180nm 10µm x 10µm 10µm x 10µm 10µm x 10µm 4.3µm x 4.3µm 10µm x 10µm X-ray beam ~ 8 0 - 1 0 0 µm Ø { 111} { 111} { 111} { 111} ....... I t should w ork on dense via good good poor bad arrays 03/ 26/ 03 ICCM, March 24 - 28, 2003, Austin, Texas Holm Geisler 18
X-ray microstructure monitoring: Arrays of inlaid copper lines { 111} - narrow copper lines (180nm) RD • ILD = Si(F)O • SiN etch stop TD • Metal 1 • sharp { 111} fiber • engaged component { 111} - wide copper lines (1.8µm) • { 511} twins • sidewall-oriented grains negligible • Stability of process of record RD Week TD 03/ 26/ 03 ICCM, March 24 - 28, 2003, Austin, Texas Holm Geisler 19
Texture components in Cu lines {111} Blanked Trenches {110} {112} Cu SiO 2 {111} {111} Si (-110) (-1-12) Sketch of (111) (0-11) Pole Figure Sym m etry equivalent, 7 0 .5 ° Engaged ( 1 1 1 ) lattice ( 1 1 1 ) planes Fiber Texture Sym m etry equivalent, 7 0 .5 ° 03/ 26/ 03 ICCM, March 24 - 28, 2003, Austin, Texas Holm Geisler 20
Texture Components in copper lines Tilted sidewalls {111} {111} {111} {111} (-110) (0-11) (-1-12) (-211) {111} {111} {111} (-110) (-211) Sketch of (-1-12) { 1 1 1 } pole figure (0-11) 03/ 26/ 03 ICCM, March 24 - 28, 2003, Austin, Texas Holm Geisler 21
Texture Components in copper lines {111} {111} Superposition sidewall + fiber 03/ 26/ 03 ICCM, March 24 - 28, 2003, Austin, Texas Holm Geisler 22
1 st generation twins { 5 1 1 } : 1 st generation tw ins { 1 1 1 } pole figure Additional circles @ 38.9°, 56.2° and 70.5° in { 111} pole figure { 511} { 111} Twin { 111} center peak 03/ 26/ 03 ICCM, March 24 - 28, 2003, Austin, Texas Holm Geisler 23
2 nd generation twins { 5 7 1 3 } : 2 nd generation tw ins { 1 1 1 } pole figure Additional circles @ 22.19°, 56.25° and 65.95° in { 111} pole figure { 5 7 13} { 111} Twin { 111} centre peak 03/ 26/ 03 ICCM, March 24 - 28, 2003, Austin, Texas Holm Geisler 24
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