Overview of Phase Modulation Technology

Performance

Ten measurements on NIST 100 nm were performed at an angle of incidence of 70°, using an integration time of 200 ms/point across the spectral range 190-2100 nm. A single layer model of SiO2 on c-Si was used. The optical constants of the SiO2 were determined using the classical Lorentz oscillator dispersion formula.

Results provide an excellent repeatability over the whole spectral range showing:

  • an average thickness value of 973.23 ± 0.11 Å,
  • an average refractive index value of 1.4627 ± 0.00006.

According to the definition above the UVISEL features an accuracy of:

  • 0.23 Å for the thickness,
  • 0.002 for the refractive index.

Repeatability versus integration time

For usual applications an integration time of 100ms 200ms per point is generally used.

Experimental conditions:

  • Number of measurements: 10 at 2.75 eV (450 nm)
  • Sample: thermal oxide (~840Å) on Si
  • Integration time: ranges between 1000 and 1 ms

Time
(ms)

 

1000

 

500

 

200

 

100

 

50

Ψ (%)

 

0.02

 

0.03

 

0.05

 

0.05

 

0.07

Δ (%)

 

0.01

 

0.02

 

0.03

 

0.04

 

0.06


Time
(ms)

 

20

 

10

 

5

 

2

 

1

Ψ (%)

 

0.14

 

0.23

 

0.32

 

0.61

 

0.86

Δ (%)

 

0.10

 

0.16

 

0.20

 

0.25

 

0.41

Conclusion

Spectroscopic ellipsometry based on photoelastic modulation delivers very high accuracy and repeatability. Owing to this technology the UVISEL allows the unique combination of high performance and experimental versatility to meet advanced customers needs and application capabilities.