Deane Chandler-Horowitz

Sub-bandgap defect states in polycrystalline hafnium oxide and their suppression by admixture of silicon

The crystallinity of atomic layer deposition hafnium oxide was found to be thickness dependent, with the thinnest films being amorphous and thick films being at least partially crystalline. Hafnium oxide films fabricated by metalorganic chemical vapor deposition are mostly monoclinic. Formation of hafnium silicate by admixture of 20% Si prevents crystallization. Electronic defects are reflected by an absorption feature 0.2–0.3 eV below the optical bandgap. These defects arise in polycrystalline, but not in amorphous, hafnium-based oxides.

Determination of the optical constants of ZnSe films by spectroscopic ellipsometry

Spectroscopic ellipsometry was used to determine the real and imaginary parts of the dielectric function of ZnSe thin films grown on (001) GaAs substrates by molecular‐beam epitaxy, for energies between 1.5 and 5.0 eV. A sum of harmonic oscillators is used to fit the dielectric function in order to determine the values of the threshold energies at the critical points. The fundamental energy gap was determined to be at 2.68 eV. The E0+Δ0 and E1 points were found to be equal to 3.126 and 4.75 eV, respectively. Below the fundamental absorption edge, a Sellmeir‐type function was used to represent the refractive index. At the critical points, E0 and E0+Δ0, the fitting was improved by using an explicit function combining the contributions of these two points to the dielectric function.

Spectroscopic ellipsometry determination of the properties of the thin underlying strained Si layer and the roughness at SiO2/Si interface

The existence of both the strain and microroughness at the interface of thermally grown SiO2 films on Si was ascertained unambiguously for the first time by high accuracy spectroscopic ellipsometry. The dielectric function of the interface was determined by a comprehensive data analysis procedure. By carefully examining the dielectric function obtained by our model, the strain was seen to cause a red shift of 0.042 eV of the interband critical point E1 compared with the bulk silicon value. The thickness of the interface region was found to be 2.2 nm of which a significant part is due to the strain.

High-accuracy, midinfrared (450cm−1⩽ω⩽4000cm−1) refractive index values of silicon

The real and imaginary parts of the refractive index, n(ω) and k(ω), of silicon were measured as a function of photon frequency ω using Fourier transform infrared (FTIR) transmission spectral data. An accurate mechanical measurement of the wafer’s thickness, t, was required, and two FTIR spectra were used: one of high resolution (Δω=0.1to0.5cm−1) yielding a typical channel spectrum (Fabry–Perot fringes) dependent mainly on t and n(ω), and one of low resolution (Δω=4.0cm−1) yielding an absorption spectrum dependent mainly on t and k(ω). A procedure was developed to first get initial estimates for n(ω) for the high-resolution spectrum and then calculate k(ω) from the faster low-resolution spectrum with minimal measurement drift. Then both initial n and final k values were used together as starting point data for a fit to the high-resolution spectrum. A previously derived transmission formula for a convergent incident beam was used for the fit. The accuracy of n(ω) determined using this procedure is mostly d...

The relationship between local order, long range order, and sub-band-gap defects in hafnium oxide and hafnium silicate films

We have measured x-ray absorption spectra (XAS) at the oxygen K edge for hafnium oxide (HfO2) films grown by chemical vapor deposition (CVD) and atomic layer deposition (ALD), as well as for hafnium silicate (HfSiO) films grown by CVD. The XAS results are compared to x-ray diffraction (XRD) and spectroscopic ellipsometry (SE) data from the same films. Features characteristic of crystalline HfO2 are observed in the XAS spectra from all CVD-grown HfO2 films, even for a thickness of 5 nm where XRD is not sensitive. XAS and XRD spectra from the ALD-grown HfO2 films exhibit the signature of crystallinity only for films that are 20 nm or thicker. These characteristic XAS features are absent in all HfSiO films measured, which is consistent with their being amorphous. The appearance of these peaks in XAS and XRD is correlated with sub-band-gap absorption in the SE spectra, which appears to be intrinsic to crystalline HfO2 in the monoclinic phase.

Excitonic transitions in β-FeSi2 epitaxial films and single crystals

Photoreflectance spectra were obtained from an epitaxial film and a bulk single crystal of β-FeSi2 at low temperatures (T⩽180 K). A model based on the results of low-temperature absorption [M. Rebien et al., Appl. Phys. Lett. 74, 970 (1999)] was used to describe the main features of the spectra. In agreement with the absorption results, transitions corresponding to the ground state and first excited state of the free exciton were observed in both the epitaxial film and single crystal. However, additional subband gap features are revealed in the photoreflectance spectra of the thin film. It is suggested that these may be related to impurity transitions or an impurity transition plus a bound exciton resonance. From the analysis of the spectra taken on the thin film, over a temperature range of 12–180 K, we extract a free exciton binding energy of (0.009±0.002) eV and a direct energy gap at T=0 K of (0.934±0.002) eV.

Nondestructive characterization of oxygen‐ion‐implanted silicon‐ on‐insulator using multiple‐angle ellipsometry

Silicon‐on‐insulator formed by high‐dose and high‐energy oxygen ion implantation in silicon, called SIMOX (separation by implanted oxygen), has been characterized nondestructively by multiple‐angle ellipsometry using a He–Ne laser at 632.8 nm. A multilayered model exhibiting two interlayers, one between the top silicon layer and the buried oxide layer and the other between the buried oxide and the substrate silicon, offers a simple representation of SIMOX. The difference between low‐temperature furnace anneal (1150 °C) and an additional high‐temperature rapid thermal anneal (1150+1350 °C) on as‐implanted wafers is shown by the better agreement between the theoretical model and the experimental results for the high‐temperature annealed SIMOX sample.

Ellipsometric Accuracy And The Principal Angle Of Incidence

The effects of improving the accuracy of the angle of incidence on the ellipsometric determination of thickness and refractive index of oxide and nitride films on a silicon substrate are analyzed. It is found that the accuracy of a determination of a films parameters, thickness and refractive index, depends as much or more on the accuracy of the angle of incidence measurement as on the accuracy of the measurement of the ellipsometric angles Δ and ψ. If measurements of Δ and ψ are made close to the principal angle of incidence, the accuracy of the determined film parameters can be improved by measuring the incident angle to an accuracy better than Δ and ψ. This is especially true for thin films of oxide less than a few tens of nanometers. Because of the higher refractive index of silicon nitride relative to silicon dioxide, a nitride films thickness can be determined more accurately than an oxide films thickness. Therefore, silicon nitride may make a good candidate film for a standard thickness sample.

Film Thickness And Refractive Index Standard Reference Material Calibrated By Ellipsometry And Profilometry

A Standard Reference Material (SRM) has been designed and fabricated and will be certified for thickness and refractive index using a highly accurate ellipsometer. The SRM consists of a three-inch diameter silicon wafer with a silicon dioxide film of uniform thickness. The design and preparation of the SRM are discussed and the ellipsometric measurement results and their comparisons with stylus profilometry are presented, along with the precision of the measurements. The ellipsometric accuracy depends upon the wafer oxide film, the model that represents the film-interface-substrate system, and the methods used to make the measurements. When the optical thickness, as determined by the ellipsometer, is compared with the mechanical thickness, as determined by the stylus profilometer, both the correct sample preparation and correct model are important in order to obtain high accuracy. This SRM will be available initially in three nominal oxide film thicknesses of 50, 100, and 200 nm. The SRM can be used to calibrate many different optical and mechanical thickness monitoring instruments as well as ellipsometers for which it was specifically designed.

An Ellipsometry System For High Accuracy Metrology Of Thin Films

A computer-controlled spectroscopic ellipsometer of high accuracy has been designed and constructed. A theta-two-theta goniometer unit and optical rail system allows various ellipsometric methods to be used to measure the parameters A and 4). Three important methods under study for accuracy, precision, and speed of measurement are the conventional null method, the rotating analyzer method, and the principal angle method. All the goniometer angles, including the angle of incidence, can be measured to an accuracy of 0.001 deg. The present light sources are two lasers with fixed wavelengths, 632.8 nm and 441.6 nm, in addition to a monochromator that can be used to scan the wavelength range from 190 to 2600 nm. A unique sample alignment system which utilizes two quadrant detectors has been developed and a simple but very effective nulling scheme is used. This instrument is primarily used for the metrology of semiconductor materials and for the calibration of reference standards for thin film thickness and refractive index.