Pavel Bulkin

Metrology of replicated diffractive optics with Mueller polarimetry in conical diffraction

The feasibility of metrological characterization of the one-dimensional (1D) holographic gratings, used in the nanoimprint molding tool fabrication step, by spectroscopic Mueller polarimetry in conical diffraction is investigated. The studied samples correspond to two different steps of the replicated diffraction grating fabrication process. We characterized master gratings that consist of patterned resist layer on chromium-covered glass substrate and complementary (replica) gratings made of nickel. The profiles of the gratings obtained by fitting the experimental spectra of Mueller matrix coefficients taken at different azimuthal angles were confirmed by atomic force microscopy (AFM) measurements. The calculated profiles of corresponding master and replica gratings are found to be complementary. We conclude that the Mueller polarimetry, as a fast and non-contact optical characterization technique, can provide the basis for the metrology of the molding tool fabrication step in the nanoimprint technique.

Deposition of SiO2 in integrated distributed electron cyclotron resonance microwave reactor

Abstract The deposition of dielectrics onto large areas is mostly carried out in traditional capacitively coupled 13.56 MHz RF plasma enhanced chemical vapour deposition reactors. Integrated distributed microwave 2.45 GHz electron cyclotron resonance (IDECR) configuration may be a possible alternative, if its potential advantages are realised. In this work we report on the results of SiO 2 deposition obtained with the IDECR system. Thin films of silica were deposited from the mixtures of SiH 4 with O 2 at different process conditions. Growth rates of silica up to 10 A s −1 were obtained. Optical properties in UV-visible range were studied with spectroscopic phase-modulated ellipsometry. The first results suggest that films have high material quality and the deposition technique provides a broad process window. We study the influence of working pressure, power and gas composition on optical properties of SiO 2 .

Real time control of plasma deposited multilayers by multiwavelength ellipsometry

A robust direct method for real time control, by multiwavelength phase modulated ellipsometry (PME), of the growth of plasma deposited structures is presented here. Transparent multilayers consisting of SiO2 and SiNx alloys are investigated. This feedback control method is based on the comparison between the real time PME measurements and precomputed target trajectories. It can provide the high precision required to deposit high performance optical coatings. In particular an overall accuracy better than 1% is obtained on a fifteen layer quarter‐wave filter, designed at 670 nm. This real time procedure, which is not limited to transparent materials nor plasma processes, appears to be a useful tool for process control.

Plasma enhanced chemical vapour deposition of SiOxNy in an integrated distributed electron cyclotron resonance reactor

The deposition of silicon alloy thin films at room temperature is of increasing interest for various applications, such as functional, protective and optical coatings on polymers. In this work an integrated distributed electron cyclotron resonance (IDECR) high density plasma reactor is used for the deposition of SiOxNy thin films with variable optical properties. The reactor has planar geometry and is scalable for large area applications. Properties of material are analyzed with in situ UV–Visible ellipsometry, ex situ infrared transmission, RBS and ERDA measurements. Without substrate heating, dense, non-absorbing and low hydrogen content stoichiometric films of SiO2 and Si3N4 are grown from the mixture of SiH4, O2 and N2. Deposition rates are between 0.5 and 5 nm/s for Si3N4 and SiO2, respectively. By changing the nitrogen to oxygen gas flow ratio the refractive index (measured at 632.8 nm) can be smoothly and reproducibly tuned from 1.96 to 1.46. The correlation between material properties and plasma parameters indicates that the silane partial pressure influences the hydrogen incorporation into the silicon nitride films.

Matrix-distributed ECR-PECVD for high-rate deposition of silica for applications in integrated optics

We report on a novel high density ECR plasma deposition system based on matrix-distributed configuration specifically designed for large area applications. System is capable of depositing uniform high quality silica films with rate of up to 10 nm/s onto 300 mm wafers. Films are grown from silane and oxygen, while nitrogen is used for doping. Optical properties of the layers have been assessed by UV-visible ellipsometry while their chemical composition have been evaluated by ERDA and RBS techniques. FTIR spectroscopy was used to evaluate quality of the films for application in communications. Preliminary data show that films are perfectly stoichiometric and contain hydrogen in amount between 1 and 4 per cent, depending on experimental conditions. We have also deposited films doped with nitrogen doping and were able to control precisely refractive index of the material with simple gas flow regulation and in-situ kinetic ellipsometry measurements.

Deposition of microcrystalline silicon in an integrated distributed electron cyclotron resonance PECVD reactor

Abstract The deposition of μc-Si in a low pressure high density plasma reactor is studied. Films were deposited either from pure silane or from the mixture of SiH4 and H2 onto glass substrates and deposition kinetics followed with kinetic phase modulated ellipsometry Growth rates of up to 0.8 nm/s were achieved with good quality material. Crystalline fraction shows a strong dependence on process pressure and exceeds 80% for samples grown at optimal conditions. It is found that hydrogen dilution is not needed for integrated distributed electron cyclotron resonance (IDECR) discharge to produce crystallized material. The grain size measured with X-ray diffraction was found to be between 10 and 15 nm and of single (111) orientation. Both ellipsometric data and Raman analysis show a strong dependence of crystallinity or hydrogen residence time in the reactor.

In situ infrared ellipsometry study of plasma processing of metallic surfaces

Abstract Aluminium and stainless-steel surfaces were processed using H2 plasma in an Integrated Distributed Electron Cyclotron Resonance reactor. H2 plasma treatment was monitored by in situ infrared (IR) ellipsometry in the range 2800–3050 cm−1 and correlated with ex situ AES depth profiling measurements. The removal of hydrocarbon surface contamination was first demonstrated. Real-time monitoring was also performed during treatment. The evolution of the ellipsometrical angle Δ at fixed wavelength, out of any vibration range, reveals a reduction of the native oxide layer. On Al, Δ shifts are attributed to the reduction of the external hydroxylated and porous oxide phase, the dense Al2O3 passivating layer remaining unchanged. In contrast, stainless-steel oxide is found less stable than Al2O3 and its reduction is almost complete (thickness estimated to be 1.1 ± 0.2 nm) using the same plasma conditions. As a consequence, the adhesion of SiO2 thin films to stainless-steel substrate is found to be enhanced after H2 plasma treatment. The enhancement is attributed to an increase in the substrate surface energy due simultaneously to cleaning and to native oxide reduction, which leads to stronger interactions with SiO2. In conclusion, IR ellipsometry appears a very promising in situ technique to probe plasma processing of surfaces.

Deposition of conventional and gradient optical coatings by ECR plasma-enhanced chemical vapor deposition

The computer-controlled electron cyclotron resonance plasma enhanced chemical vapor deposition of SiOxNy was used for the manufacturing of optical interference coatings with inhomogeneous and traditional multilayer refractive index profiles. Such complex structures as triple-band rugate optical interference filters and graded refractive index antireflection coatings were grown. The design of coatings was performed using measured optical constants of the SiOxNy-system.

Direct numerical inversion method for kinetic ellipsometric data. II. Implementation and experimental verification

A direct numerical inversion method is applied to the monitoring of thin-film growth. Several improvements of the method, including a correction for weakly absorbing materials, are presented. The method has been successfully applied to the inversion of the growth of constant-refractive-index layers andused for the process calibration of plasma-enhanced chemical vapor deposition of silicon oxynitrides. The validity of this calibration has been successfully tested on a linear index gradient and quintic matching layer between a polycarbonate substrate and a scratch-resistant coating.

Optical thin films deposition by MDECR-PECVD

We designed and built Matrix Distributed ECR (MDECR) PECVD reactor dedicated for dielectric filters deposition and equipped it with multiple sensors for process control. Planar matrix geometry of plasma source is based on electron cyclotron resonance effect at 2.45 GHz microwave frequency and provides scalability of the deposition on large area substrates. High (up to 5 nm/sec) deposition rate obtained due to high dissociation efficiency and careful design of the gas injection system. Optical emission spectroscopy, quadrupole mass-spectrometry and spectroscopic and multi-channel kinetic ellipsometry are installed for in-situ studies and control of the film deposition. We performed studies of the nature of high-density plasma discharge in silane, oxygen and nitrogen mixture and correlated its properties with optical and physical properties of deposited materials. To demonstrate the capabilities, a wide band gradient index antireflection coating on glass was realized by deposition of SiOxNy alloy thin films. The predefined variation of an index in a profile is obtained by changing the flows of precursors. Real-time control is performed with multi-channel kinetic ellipsometry.