Measuring film thickness using Opti-Probe

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Measuring film thickness using Opti-Probe

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 The wavelength of the light

Brewster’s angle 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.

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.

BPR optics diagram

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.

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

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

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.

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

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

We obtain following values:
Film n1 r2 Cos(r2) Oxide 1.5 37 0.80 11574A Nitride 2 27 0.89 15340A PolySi 4 13 0.97 33751A ~ n1*8000A for once full cycle in profile Thickness = m*ni*8000A; m=# of cycle in profile