AIN中光学特性检测方案(椭偏仪)

Application NoteMM-16Spectroscopic EllipsometrySE03 Spectroscopic Ellipsometry Semiconductor LCM Optical properties of AIN characterized byMM-16 Spectroscopic Ellipsometer Celine Eypert - Application Scientist - Thin Film Division AIN has been identified as a promising material for a wide range of electronic， optoelectronic andacoustic applications， due to its chemical， mechanical and thermal stability， wide direct bandgap(6.2eV)， high thermal conductivity， high sound velocity， and high electron drift velocity. Furthermore，AIN is interesting because it can be alloyed with GaN over the whole composition range and multi-ayers find roles in optical lasers such as bllue lasers. AlN can be also used as a substrate for growthot optoelectronic devices emitting at wavelengths ranging trom blue to deep UV. _pitaxial growth and reactive magnetron sputtering techniqueshave been routinely used to grow I-Nitride compounds， andaccurate measurement ot the tilm thickness and thickness uni-tormity is an essential step for the process and production con-trol of these materials. To perform this work non -destructivecharacterization methods such as ellipsometry are used for in-situ monitoring of thickness and refractive index of the growingfilm. Spectroscopic ellipsometric information is vital for this de-termination as a single wavelength is inadequate for the charac-terization of multilayered films. n this note， spectroscopic ellipsometry (SE) was used to deter-mine optical properties of thick and thin AlN films. AlN characterization： Spectroscopic Ellipsometry was performed using the HORIBAJobin Yvon MM-16 instrument across the wavelength range of430-850nm. The MM-16 uses liquid crystal modulators to detect the polari-sation state of the retlected light beam. Two liquid crystal mod-ulators are used as the polarization state generator on the inputarm ot the ellipsometry，and two further modulators are used asthe polarization state analyzer on the output arm of the ellipsom-eter. This arrangement provides a full picture of the polarisationstate of the sample， and as a result enhances the accuracy andprecision of the measured ellipsometric angles W and A. TheMM-16 also provides all 16 coefficients of the Mueller Matrix al-lowing simple access to anisotropic modelling functions. Experimental data were collected at an angle of incidence of70° and the data acquisition time was 30s. Thick Film： The following structure has been used to model this sample. Theintroduction of a thick surface layer improves the goodness ofthe fit parameter (x²=500→x²=160). This surface layer isdescribed using the Bruggeman Effective Medium Approxima-tion with anisotropic mixing. The MM-16 provides as a standardfeature the full Mueller Matrix， and a feature of the Mueller Ma-trix is that the off-diagonal elements are not equal to 0 when thesample exhibits anisotropic behaviour and especially when the measurement is done in a random position (that is away fromthe direction of the optical axis and at rotation of 90° from thisoptical axis， and when the optical axis is not orthogonal to theplane). Several tests were carried out， and we found that the AlN layerwas anisotropic with its axis orthogonal to the sample plane(x²=160→x²=48). For the work performed here there is anuniaxial anisotropic material with its optical axis orthogonal tothe sample plane， and when the measurement is made in theoptical axis direction or rotated at 90° the off-diagonal elementsbecome equal to 0. The ability to measure this condition simpli-fies modelling of the sample. The optical properties of aluminium nitride have been deter-mined using the Lorentz Oscillator： The MM-16 enables the characterization of inhomogeneousilms with high accuracy. For example， the following exampleuses a three-layer model to tit the experimental data perfectly. Thin film The following structure has been used to model this sample.Once again， the model shows that the AlN material has anoverlayer present. Conclusion The feasibility of using the MM-16 SE in measuring thicknessand refractive index of AlN thin and thick films has been dem-onstrated. Non destructive measurement of thickness was suc-cessfully applied to films as thick as 3um deposited on Si. Themulti-layer models with a surface layer with void and the s1inm6pslsedispersion gave useful information about surface roughness，film density and oxygen contamination. USA： +1-732 494 8660 France：+33 (0)1 64 54 1300 Japan： +81 (0)3 3861 8231 Germany：+49 (0)89 462317-0 UK： +44 (0) 20 8204 8142 Italy： +39 02 57603050+86 (0)10 6849 2216 Other Countries： +33 (0)1 64 54 1300 HORIBAExplore the future Find us at www.jobinyvon.com or telephone：(All HORIBA Jobin Yvon companies were formerly known as Jobin Yvon)HORIBAExplore the future The feasibility of using the MM-16 SE in measuring thickness and refractive index of AlN thin and thick films has been demonstrated. Non destructive measurement of thickness was successfully applied to films as thick as 3µm deposited on Si. The multi-layer models with a surface layer with void and the simple dispersion gave useful information about surface roughness, film density and oxygen contamination.