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Mechanics of thin film on wafer

Mechanics of thin film on wafer. R91943100 詹孫戎. Mechanics of thin film on wafer. Basic mechanics Axial stress， strainPoisson’s ratio Poisson’s ratio Shear stress，strain，modulus Stress-strain Thermal strain Mechanical properties of microelectronic material

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Mechanics of thin film on wafer

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  1. Mechanics of thin film on wafer R91943100 詹孫戎

  2. Mechanics of thin film on wafer • Basic mechanics • Axial stress， strainPoisson’s ratio • Poisson’s ratio • Shear stress，strain，modulus • Stress-strain • Thermal strain • Mechanical properties of microelectronic material • Effective Young’s modulus of composite layers • Substrate warpage • Biaxial stress in thin film on thick substrate • Mechanics of film-on-foil electronics • Failure resistance of amorphous silicon transistors • Mobility in thin-film under compressive strain • Reference

  3. Axial stress • Load P(Newton)： • Internal resultant normal force • Area A (m2)： • Cross-section area of the bar • Stressσ (N/m2；Pa)： • Average normal stress at any point on the cross-sectional area • σ ＞0 tensile • σ ＜0 compressive Source:Mechanics of materials by R.C.Hibbeler

  4. Axial strain • Strainε(dimensionless)： • Deformation changes in length • Average elongation／Original length • Yong’s modulus E (N/m2；Pa)：

  5. Poisson’s ratio • Poisson’s ratio ν： • Transverse strain／Longitudinal strain • ν= 0.5 → volume conserved Source:Mechanics of materials by R.C.Hibbeler

  6. Shear stress，strain，modulus • Shear stress τ (N/m2；Pa)： • V (Newton) ；internal result shear force • A (m2)：area at the section • Shear strain γ (rad) • Shear modulus G (N/m2；Pa)： Source:Mechanics of materials by R.C.Hibbeler

  7. Stress-strain • Low stress • Elastic • stress／strain = constant • σy = yield stress • Ultimate stress – material break • Si (brittle) ；ultimate stress ~ yield stree Source:UC Berkeley EE143,Lec 25

  8. Thermal strain • 1εth = ∫[αf(T) – αs(T)] dT ≒ (αf – αs)(TDep – Troom) Source:UC Berkeley EE143,Lec 25

  9. Mechanical properties of microelectronic material

  10. Effective Young’s modulus of composite layers • Stressing along x-direction • All layers takes the same strain • Ex = fAEA + fBEB • Material with lager E takes larger stress • Stressing along y-direction • All layers takes the same stress • Material with small E takes larger strain Source:UC Berkeley EE143,Lec 25

  11. Substrate warpage • Radius of curvature of warpage • Stoney’s equation • ts：substrate thickness • tf：film thickness • Es：Young’s modulus of substrate • υs：Posson’s ratio of subsrate Source:UC Berkeley EE143,Lec 25

  12. Biaxial stress in thin film on thick substrate • σz = 0 • No stress direction normal to substrate • Assume isotropic film • εx = εy = ε → σx = σy = σ Source:UC Berkeley EE143,Lec 25

  13. Mechanics of film-on-foil electronics • When sheet is bent • Top surface in tension • Bottom surface in compression • Neutral surface：one surface inside the sheet has no strain • Strain in top surface： • df：film thickness • ds：substrate thickness • Circuit sandwiched between substrate and encapsulation layer • Circuit in the neutral surface if Source:Z.Sue,E.Y.Ma,H.Gleskova, and S.Wagner, Appl.Phys.Lett.74,1177(1999)

  14. Mechanics of film-on-foil electronics • Film and substrate have different Young’s moduli • η = df／ds • χ = Yf／Ys • Two kids of substrate • Steel： Yf／Ys ≒100 • Plastic： Yf／Ys ≒1 Source:Z.Sue,E.Y.Ma,H.Gleskova, and S.Wagner,Appl.Phys.Lett.74,1177(1999)

  15. Failure resistance of amorphous silicon transistors • a-Si:H TFTs • 51-μm-thick polyimide • Both side coated 0.5-μm-thick SiNx • 100-nm-thick Ti／Cr layer electrode • 360nm gate SiNx • 100nm undoped a-Si:H • 180nm passivating SiNx • 50nm (n+) a-Si:H • 100nm Al for source-drain contact • Compliant substrate • Without SiNx back layer • Stiff substrate • With SiNx back layer Source:H.Gleskova,S.Wagner,and Z.Sue,Appl.Phys.Lett.75,3011(1999)

  16. Failure resistance of amorphous silicon transistors • TFT bent to a radius R • χ= Yf／Ys；η1= df1／ds； η2= df2／ds • Yf≒200GPa；Ys≒5GPa • TFT • Compressed by at least 2% without failing • Tensile 0.5% Source:H.Gleskova,S.Wagner,and Z.Sue, Appl.Phys.Lett.75,3011(1999)

  17. Failure resistance of amorphous silicon transistors Source:H.Gleskova,S.Wagner,and Z.Sue,Appl.Phys.Lett.75,3011(1999)

  18. Mobility in thin-film under compressive strain • Electronic mobility in amorphous silicon thin-film transistor under compressive strain Source:H.Gleskova,S.Wagner ,Appl.Phys.Lett.79,3347(2001)

  19. Reference • UC Berkeley EE143,Lec 25 • Mechanics of materials by R.C.Hibbeler • Z.Sue,E.Y.Ma,H.Gleskova,and S.Wagner,Appl.Phys.Lett.74,1177(1999) • H.Gleskova,S.Wagner,and Z.Sue,Appl.Phys.Lett.75,3011(1999) • H.Gleskova,S.Wagner ,Appl.Phys.Lett.79,3347(2001)

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