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11 00 Dhr Dijkstra
11 00 Dhr Dijkstra
11 00 Dhr Dijkstra
11 00 Dhr Dijkstra
11 00 Dhr Dijkstra
11 00 Dhr Dijkstra
11 00 Dhr Dijkstra
11 00 Dhr Dijkstra
11 00 Dhr Dijkstra
11 00 Dhr Dijkstra
11 00 Dhr Dijkstra
11 00 Dhr Dijkstra
11 00 Dhr Dijkstra
11 00 Dhr Dijkstra
11 00 Dhr Dijkstra
11 00 Dhr Dijkstra
11 00 Dhr Dijkstra
11 00 Dhr Dijkstra
11 00 Dhr Dijkstra
11 00 Dhr Dijkstra
11 00 Dhr Dijkstra
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11 00 Dhr Dijkstra

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  • 1. Overlay als gevolg van ‘wafer heating’ in wafer steppers March 2010 Willem Dijkstra
  • 2. Company profile MECAL BV Location: Enschede, Veldhoven, Groningen Consultancy & product development # employees: 90 Customers: ASML, Zeiss, Océ, Philips, ICOS, Nedinsco, BESI Click to edit Master title style 2
  • 3. MECAL Semiconductor industry Simulation Product development Turn-key solutions Optronics and Vision (mainly Veldhoven) Wind energy Product development Turn-key solutions (mainly Enschede) Click to edit Master title style 3
  • 4. Competencies semiconductor industry • Statics ⇒ stress, stiffness, tolerances, deformation, force path • Dynamics ⇒ vibration, damping, mass, stick-slip, mode shapes, eigen frequencies • Kinematics ⇒ DOF, rigid body systems, acceleration, inertia, set point, friction • Thermal ⇒ conductivity, convection, radiation, thermo-mechanics • Fluid dynamics ⇒ Air-bearing stiffness and loads, low vacuum, contaminations, flow induced vibrations Click to edit Master title style 4
  • 5. Analysis At MECAL: FEM simulation is problem identification a tool, not the goal FEM simulation hand calculations understanding the physics = validation measurements design optimization output: performance parameters design improvement Click to edit Master title style 5
  • 6. Lithographic process problem identification Production of chips: lithographic process For 175 wafers/hour: huge power required heat Dissipated heat can lead to errors in chips: Process chips: features of O(45 nm) Total allowable error: O(15 nm) Specific allowable error: O(1 nm) Click to edit Master title style 6
  • 7. Exposure problem identification reticle interfero- meter mirror lens interfero- meter wafer table Click to edit Master title style chuck 7
  • 8. Heat dissipation problem identification first field Wafer is divided in fields Fields are exposed one after another Several exposures 95% of light is transformed to heat and absorbed in wafer Heat transfer to table Chuck: very low conductivity last field Click to edit Master title style 8
  • 9. Deformations problem identification Wafer + table deform due to thermal expansion overlay Wafer pressed onto chuck Chuck deforms Positioning is affected Questions: o Wafer deformations? o Design improvements? Keep in mind: mirrors, needed for positioning, are also deformed Click to edit Master title style 9
  • 10. Outline model problem identification Input Power Heat dissipation Temperature profile changing with time Deformation chuck Overlay at wafer Output Click to edit Master title style Long path between input and output! 10
  • 11. Finite Element Model FEM simulation Boundary conditions Heat load at wafer surface in [mJ/cm2] air shower Convection to environment [22 oC] (air shower at wafer) Chuck statically fixed no reaction forces Vacuum pressure to push wafer + table onto chuck Click to edit Master title style 11
  • 12. Thermal results FEM simulation Temperatures after exposure first field Wafer 0 0.098 0.196 Table 0 0.293 0.029 0.391 0.059 0.489 0.088 0.587 Chuck 0 0.118 0.685 0.002 0.147 0.782 0.004 0.176 0.880 0.006 0.206 0.008 0.235 0.010 0.265 Click to edit Master title style 0.012 0.015 0.017 0.019 12
  • 13. Thermal results FEM simulation Temperatures after exposure last field Wafer 0.017 0.126 0.236 Table 0.345 0.018 0.454 0.066 0.563 0.114 0.672 0.162 0.782 Chuck 0 0.210 0.891 0.012 0.258 1.000 0.025 0.306 0.037 0.354 0.049 0.402 0.062 0.450 Click to edit Master title style 0.074 0.086 0.098 0.111 13
  • 14. Mechanical results FEM simulation Deformations after exposure first field z-dir -0.019 -0.008 0.003 y-dir 0.014 -0.047 0.025 z y -0.031 0.036 -0.015 0.047 0.001 0.058 x-dir x -0.049 0.017 0.069 -0.034 0.033 0.080 -0.019 0.049 -0.004 0.066 0.011 0.082 0.026 0.098 Click to edit Master title style 0.041 0.056 0.071 0.086 14
  • 15. Mechanical results FEM simulation Deformations after exposure last field z-dir -0.306 -0.162 -0.017 y-dir 0.129 -0.285 0.275 z y -0.236 0.419 -0.187 0.565 -0.139 0.709 x-dir x -0.250 -0.090 0.853 -0.196 -0.042 1.000 -0.140 0.007 -0.084 0.055 -0.029 0.104 0.027 0.153 Click to edit Master title style 0.082 0.137 0.193 0.248 15
  • 16. Output: performance parameters Performance parameters 100 Displacement plots For each field, displacements are 50 plotted directly after exposure of die 0 Correction for chuck deformations −50 −100 Overlay = O(1 nm)? −150 −100 −50 0 50 100 150 Click to edit Master title style 16
  • 17. Validation Validation model measurements ux Difference in row number row number amplitude: model measurements ux: 32% uy: 12% uy Click to edit Master title style row number row number Row averaged displacements 17
  • 18. Validation Validation model measurements 0 5 0 5 0 5 0 5 0 25 −20 −15 −10 −5 0 5 10 15 20 25 Exposure of one die in the center of the wafer Click to edit Master title magnitude: 14% Difference in style 18
  • 19. Materials Design improvement Current materials: - wafer: silicium: high conductivity, high CTE - table: glass/ceramics: low conductivity, low CTE Conductivity low / high ΔT high / low Expansion = CTE * ΔT ΔT CTE expansion wafer high high high2 table high low low Click + table high wafer to edit Master title style low FEM? 19
  • 20. Materials Design improvement Other materials: - wafer: silicium: high conductivity, high CTE - table: material X : high conductivity, high CTE - water cooling in table best material: machine dependent ΔT CTE expansion wafer low high moderate table low high moderate Click + table low wafer to edit Master title style high FEM? 20
  • 21. Conclusions FEM model to predict overlay caused by wafer heating Good agreement with measurements Model can be used for design improvements: - add water cooling - materials - feed forward corrections Click to edit Master title style 21

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