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Measuring film thickness using Opti-Probe

Measuring film thickness using Opti-Probe. Weilan Ladeau 3/01/03. Opti-Probe Theory. Reflection and Refraction Intensities Polarizations Phase delay Brewster’s angle tan (ib)= ni/no. Phase delay. The length 2d of the extra travel The velocity of light propagation in the film

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Measuring film thickness using Opti-Probe

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  1. Measuring film thicknessusing Opti-Probe Weilan Ladeau 3/01/03

  2. Opti-Probe Theory • Reflection and Refraction Intensities • Polarizations • Phase delay • Brewster’s angle tan (ib)= ni/no

  3. Phase delay • The length 2d of the extra travel • The velocity of light propagation in the film • The wavelength of the light

  4. Brewster’s angle • Brewster'sangle is the angle of incidence for which the reflected intensity is 0 for the p-polarized rays. • Provides information on the index, n1 of the film.

  5. BPR ( Beam Profile Reflect meter) • Measures reflectivity as a function of angle of incidence on the wafer. • The intensity of reflected light is the square of the total amplitude of waves. • BPR can be used to measure thickness, n of a film.

  6. BPR optics diagram

  7. Diode laser and Lens • Single wavelength (6750 A) • Using two objective lens (5X and 80X) • Forms a column of light before entering lens • Cone shaped upon exit • The angle of incidence of a ray is related to its distance to the center of the beam.

  8. Diode laser and Lens • Light collected by a linear diode. • Diodes 0.025 mm apart • Each diode measures the light intensity resulting form interference pairs of ray #1 & ray #2

  9. Profile • Response of the array results • Profile symmetrical • Software folds profile and takes average

  10. S & P Polarizations • Rays on XZ and YZ planes are linearly polarized. • Rays on other planes elliptically polarized • Easier to calculate rays on two planes.

  11. S & P Polarizations • P-polarized rays collected on B-array aligned // to X direction • S-polarized rays collected on A-array aligned // to Y direction • Profiles complement each other giving us more information

  12. Thickness Estimation • Know n1 of film • Count # of cycles in A profile • Maximum in reflectivity occurs:

  13. We obtain following values: • ~ n1*8000A for once full cycle in profile • Thickness = m*ni*8000A; m=# of cycle in profile

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