Growth kinetics and compositional analysis of silicon rich a-SiNx:H film: A soft X-ray reflectivity study

In this study, optical index profile derived over extended energy region of soft x-ray regime combined with soft x-ray reflectivity technique has been utilized to obtain depth graded compositional details and growth kinetics. This method has been applied near the Si L_2,3 edge for non destructive characterization of Si-rich silicon nitride (SRSN ) film to reveal buried Si-rich interfacial layer. Further, the combined study of soft x-ray reflectivity and optical density obtained from the reflectivity fitting at various photon energies provide a qualitative estimation of the film composition and its growth. The new method suggested in this work might be capable in improving the understanding of growth kinetics in other materials also.

Optical density profiles across the depth of SRSN film as derived from SXR fit. Appl. Phys. Let. 97 (2010) In press.

Optical properties of Indium Phosphide in 50-200Å; wavelength region using reflectivity technique

The optical constants of Indium Phosphide (InP) in the soft x-ray region of 50-200Å are determined from the angle dependent reflectivity measurements. The derived optical constants are compared with tabulated values of Henke et al. Experimental values of δ and β are in close agreement with the tabulated values in lower wavelength region of 50-120Å. The experimental value indicates an edge shift of 0.4Å towards lower wavelength side from the phosphorous L-edge value of 92Å. However, above 120Å region where Indium N₂ edge falls at 160.7Å there is huge difference between experimental and tabulated values are observed. Both delta and beta values are significantly higher. In contrary to tabulated values of β/δ ratio which is more than one above 140Å region, the experimental measured ratio is found to be less than one. This study presents first reported experimental values of optical constants for InP in this wavelength range.

Fig.: Measured optical constants of InP material in 50-200 Å wavelength region [Appl. Opt. 49, 5378 (2010).]

Study of polished zinc sulphide surface

Resonant soft x-ray reflectivity measurements at and near the L absorption edge of sulphur have been performed on mechanically polished zinc sulphide using reflectivity beamline. A sulphur rich surface (∼15nm thick) consisting of two layers with gradient electron density distribution was uniquely determined. As compared to bulk ZnS, the top layer has ∼30–50% less electron density whereas, the intermediate layer has ∼10–18% less electron density. Conventional hard X-ray reflectivity measurement at Cu Kα wavelength also indicates low electron density (sulphur rich) surface of ZnS but the technique was found insensitive for unique determination of electron density distribution. Optical constants of ZnS in the soft x-ray region (100–250 eV) have been reported for the first time and were in good agreement with the theoretically reported values.

Fig.: The figure shows that the soft x-ray reflectivity near Sulphur L- edge gives a significant contrast corresponding to change in surface density in ZnS sample [Applied Surface Science 257 (2010) 210].

Probing porosity at buried interfaces using soft x-ray resonant reflectivity

The optical constants of electron beam evaporated boron carbide are measured near boron K-absorption edge. Near the edge, the dispersion part of refractive index shows a sign reversal. Simulated reflectivity profiles near the absorption edge of boron are used to show the utility of soft x-ray resonant reflectivity as a sensitive tool for probing selected buried interfaces. This is due to high and tunable scattering contrast. The simulated resonant reflectivity profiles are sensitive to porosity and position of the porous layer containing the resonating atom. This is experimentally demonstrated through soft x-ray resonant reflectivity measurements of B₄C-on-Fe bilayer structure

Fig.: Soft x-ray reflectivity profiles of B4C-on-Fe bilayer film near boron K-absorption edge. [J.Appl.Phys. 107, 023529 (2010)].

Publications 2011

1. “Study of micro roughness parameters and growth characteristics of NbC/Si multilayer using layer by layer power spectral density analysis”
   Mohammed H. Modi, G. S. Lodha, M. Thomasset, and Mourad Idir
   AIP Proceeding 1349, 715, (2011).
   
   
2. “Effect of soft x-ray/VUV illumination on soft matter thin film”
   S. R. Naik, M. H. Modi, P. Pandit, G. S. Lodha, and A. Gupta
   AIP Proceeding 1349, 701, (2011).
   
   
3. “Si-rich a-SiNx:H thin film a prospective material for EUV lithography: An optical response near Si L2,3-edge”
   S.P. Singh, Mohammed H. Modi, and P. Srivastava
   AIP Proceeding 1349, 667, (2011).
   
   
4. “Qualitative estimation of Si-rich a-SiNx:H thin film composition by soft X-ray reflectivity analysis
   S. P. Singh, Mohammed H. Modi, and P. Srivastava”
   AIP Proceeding 1349, 665, (2011).
   
   
5. “Study of the optical response of Si-rich a-SiNx:H thin film near Si L2,3 -edge using soft x-ray reflectivity”
   S. P. Singh, Mohammed Hussein Modi and P Srivastava
   J. Phys. D: Appl. Phys. 44, 215501(2011) .
   
   
6. "Fabrication and evaluation of large area Mo/Si soft x-ray multilayer mirrors at Indus SR facilities"
   N. Pothana, M. Nayak, S Rai, G. S. Lodha, MH Modi, A Sagdev
   Review of Scientific Instruments (2011) Communicated .
   
   
7. “Optical response near the soft x-ray absorption edges and structural studies of low optical contrast system using soft x-ray resonant reflectivity"
   M. Nayak, G. S. Lodha
   Journal of Atomic, Molecular and Optical Physics (2011).
   
   
8. “Soft x ray study of Cd Arachidate Langmuir Blodgett Films
   S.R. Naik, Mohammed H. Modi, Pallavi Pandit, Ajay Gupta”
   J. Radiation Chemistry 2011 (Communicated) .
   
   

Publications 2010

1. Growth kinetics and compositional analysis of silicon rich a-SiNx:H film: A soft X-ray reflectivity study,
   S. P. Singh, Mohammed H. Modi and P. Srivastava,
   Appl. Phys. Lett. Vol. 97, 2010 (In Press)
   
   
2. Study of the optical response of Si-rich a-SiNX:H thin film near Si L2,3 -edge using soft X-ray reflectivity,
   S. P. Singh, Mohammed H. Modi and P. Srivastava ,
   Communicated 2010.
   
   
3. Optical Properties of InP in the 50-200Å wavelength region,
   N. Pothana, Mohammed H Modi, G.S. Lodha ,
   Applied Optics 49, 5378 (2010).
   
   
4. X-ray multilayer characterization using reflectivity beamline at Indus-1 ,
   Mohammed H. Modi , T.T. Prasad, M. Nayak, N. Pothana, A. Jaiswal, S.K. Rai and G.S. Lodha,
   AIP Proceeding 1234, 710, (2010).
   
   
5. Resonant soft x-ray reflectivity as a sensitive probe to investigate polished zinc sulphide surface,
   Pooja Gupta, A K Sinha, Mohammed H Modi, S M Gupta, P K Gupta, S K Deb ,
   Applied Surface Science 257, 210 (2010).
   
   
6. X-ray characterization of thin foil gold mirrors of a soft X-ray telescope for ASTROSAT Characterization of SXT mirrors by X-ray reflectivity,
   A. Sagdeo, S. K. Rai, G.S. Lodha1, K. P. Singh , N. Yadav, R. Dhawan, U. Tonpe, M. N. Vahi ,
   Experimental Astronomy, (2010)
   
   
7. Probing porosity at buried interfaces using soft x-ray resonant reflectivity ,
   M. Nayak, G. S. Lodha, T. T. Prasad, P. Nageswararao, and A. K. Sinha ,
   Journal of Applied Physics 107, 023529 (2010).
   
   
8. Polarization dependence in non-resonant photo-triple-ionization of CO2,
   R K Kushawaha, S Sunil Kumar, I A Prajapati, K P Subramanian and B Bapat,
   Journal of Physics B 42, 105201 (2009).