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Measuring film thickness using Opti-Probe Weilan Ladeau 3/01/03.

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Presentation on theme: "Measuring film thickness using Opti-Probe Weilan Ladeau 3/01/03."— Presentation transcript:

1 Measuring film thickness using Opti-Probe Weilan Ladeau 3/01/03

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

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

4 Brewster’s angle Brewster's angle is the angle of incidence for which the reflected intensity is 0 for the p-polarized rays. Brewster's angle 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. 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. 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. 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. BPR can be used to measure thickness, n of a film.

6 BPR optics diagram

7 Diode laser and Lens Single wavelength (6750 A) Single wavelength (6750 A) Using two objective lens (5X and 80X) Using two objective lens (5X and 80X) Forms a column of light before entering lens Forms a column of light before entering lens Cone shaped upon exit Cone shaped upon exit The angle of incidence of a ray is related to its distance to the center of the beam. 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. Light collected by a linear diode. Diodes mm apart Diodes mm apart Each diode measures the light intensity resulting form interference pairs of ray #1 & ray #2 Each diode measures the light intensity resulting form interference pairs of ray #1 & ray #2

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

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

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

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

13 We obtain following values: ~ n1*8000A for once full cycle in profile ~ n1*8000A for once full cycle in profile Thickness = m*ni*8000A; m=# of cycle in profile Thickness = m*ni*8000A; m=# of cycle in profile Filmn1r2Cos(r2) Oxide A Nitride A PolySi A


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