Heterodyne Reflectometry for Angstroms-thick thick Thin Films

Transcription

1 1 Heterodyne Reflectometry for Angstroms-thick thick Thin Films Arun Aiyer, Ken Harvey, Andy Kueny, Mark Meloni Verity Instruments Inc, Carrollton, TX Ajith Varghese, Jonathan VanBuskirk, Malcolm Bevan Texas Instruments, Richardson, TX AEC /APC Symposium September 2005

2 Outline! Classical Heterodyne Interferometer (HI)! Adapting HI for Reflectometry! Heterodyne Reflectometer (HR) Results! Difference between HR and Ellipsometer! Advantages AEC/APC Symposium Slide 2

3 Classical Heterodyne Interferometer Detector Pol. mixer s-polarized at freq. ω p-polarized at freq. ω+ ω Laser λ/4 plate Target d λ/4 plate S = A + B cos ( ωt+φ) φ = ω. t = 4π.n.d/λ Reference t AEC/APC Symposium Slide 3

4 Heterodyne Reflectometer (HR) Split Frequency Laser; e.g., Zeeman Split or AOM He-Ne s-polarized at freq. ω p-polarized at freq. ω+ ω I ref M BS I het Polarization Mixer Employs single wavelength at fixed incidence angle Dynamic range >0-1000Å. Extendable by switching λ Current theoretical resolution of ~ 0.5Å Roadmap in place to improve resolution to 0.05Å Unlike ellipsometry HR measures thickness directly AEC/APC Symposium Slide 4

5 Computed HR Signal d f 2δ λ = 4π n 2 sin 2 α 2δ= ω. t AEC/APC Symposium Slide 5

6 Physics of Heterodyne Reflectometer ω, ω+δω α - s ω - s, - p ω, ω+δω ρ d f When α is Brewster s angle, only s- polarization (ω) is reflected from top surface and p- polarization is transmitted into the film and reflected by the substrate. Interference between this s- pol. and p- pol (ω+δω) reflected by the interface will generate a beat frequency at ω. Reff Κ cos( ωt + 2 δ ) AEC/APC Symposium Slide 6 2π d f n sin δ = λ 2 2 α

7 Measured HR Signal d sample = d ox 2 2 n sin 2 ox α + δ λ 4π n sin α 2 2 sample AEC/APC Symposium Slide 7

8 HR Data vs. Ellipsometer Data. Sub 100Å films High-k HfSiO Thickness: Comparing HR data to UTD Data Thickness in Angstroms UTD Data Å 20 HR Data Å Sample # Ellipsometry data provided by Univ. of Texas, Dallas ~ 30 31Å First proof of HR measurement ability AEC/APC Symposium Slide 8

9 HR Measurement vs. Ellipsometer Measurement sub 10Å films HR and UTD ellipsometer measurements of ultra thin oxide films Thickness in Angstroms A Oxide 7A Oxide Sites Ellipsometer HR UTD and Verity measured different samples taken from the same wafer AEC/APC Symposium Slide 9

10 HR measurements of SiO 2 and SiON Films Description HR Ellipsmtr XPS Å Å Å 12A oxide A oxide PNO.C PNO.C HR vs. Ellipsometer Measurement Ellipsometer Results in Angstroms HR Results in Angstroms AEC/APC Symposium Slide 10

11 HR Repeatability Study Repeatability Over Three Hour Period 17 Thickness in Angstroms Thickness in A Time With Current resolution, static repeatability (1σ) better than 0.02% AEC/APC Symposium Slide 11

12 HR vs. Ellipsometer HR Uses single λ source at fixed angle Ellipsometer Uses single λ source at fixed angle Measures phase shift 2δ Measures ψ and d to measured 2δ 2δ λ d f 2 2 4π n sin α Error in incidence angle has minimal impact on thickness accuracy 0.05Å for 10Å for 1 0 error d extracted from thin film model using ψ and i2δ i2δ r1p + r2pe i 1+ rre 1s 2s tanψ e = i2δ i2 1 r1pr2pe δ + r1s + r2se Sensitivity of is critically dependent on incidence angle Uses no moving optical components Larger MTBF Mechanically or electro-optically active components used e.g., rotating compensator, piezo modulator etc. IM solution possible IM solution possible AEC/APC Symposium Slide 12

13 Potential Advantages " Uses single non-actinic wavelength at fixed incidence angle - Mitigates photo contamination issues " Current measurement resolution of ~ 0.5Å - Working to improve resolution to ~ 0.05Å - Static repeatability (σ) better than 0.02% " Application: Gate dielectrics, metal films " Can be integrated with process tool " Potential exists for retrofitting existing process tool AEC/APC Symposium Slide 13

14 Acknowledgement " Prof. Bob Wallace of UT, Dallas for providing thin film samples of Oxide and HfSiO for providing ellipsometry data AEC/APC Symposium Slide 14