Non-intrusive mapping of subsurface defects in semiconductors

We have adapted differential interference contrast Nomarski microscopy in the transmission configuration to the problem of mapping subsurface defects in semiconductors. We have demonstrated the ability to rapidly measure the depth of the precipitate-free-zone in silicon with a reproducibility of ±1 m in whole Si wafers up to 200 nm in diameter, having an extrinsic doping concentration up to 7×10¹⁹ cm^–3 and a nominal, as received, back side roughness. Because our subsurface defect profiler is completely non-destructive, product wafers can be inspected at various stages of processing and immediately returned to the production line.     

Infrared reflection spectra in contactless nondestructive measurements of the electron density and mobility in indium phosphide

On the basis of numerical calculations and experimental studies we analyze the possibilities of measuring the electrophysical parameters of indium phosphide by means of infrared reflection spectra at wavelengths ranging from 5 to 200 m. We demonstrate that contactless nondestructive measurements of the electron density in the range 10¹⁶–10²⁰ cm^–3 can be made with a relative error not exceeding 15%, and of mobility with a relative error not exceeding 25%. A nomogram method is presented for rapid conversion of data from infrared reflection spectra into the parameters being measured.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 22–27, January, 1988.     

Crystallite misorientation analysis in semiconductor wafers and ELO samples by rocking curve imaging

Rocking curve imaging is based on measuring a series of Bragg-reflection digital topographs by monochromatic parallel-beam synchrotron radiation in order to quantify local crystal lattice rotations within a large surface area with high angular and high spatial resolution. In this paper we apply the method to map local lattice tilts in two distinct semiconductor sample types with lattice misorientations up to 0.5° and with spatial resolution from 30  down to 1 . We analyse the measured surface-tilt data volumes for samples with almost smoothly varying specific misoriented defect formation in GaAs wafers and for an inherent subsurface grain structure of epitaxial lateral overgrowth wings in GaN. Back-projected tilt maps and histograms provide both local and global characteristics of the microcrystallinity.     

Excimer laser-assisted chemical process for formation of hydrophobic surface of Si (001)

Silicon (Si) wettability is one of the important parameters in the development of Si-based biosensing and lab-on-chip devices. We report on UV laser induced hydrophobicity of Si (001) wafers immersed in methanol during the irradiation with an ArF excimer laser. The irradiation with 800 pulses of the laser operating at 65 mJ/cm² allowed to significantly increase the hydrophobicity of investigated samples as characterized by the static contact angle change from 77° to 103°. Owing to the irradiation with relatively low laser fluence, no measurable change in surface morphology of the irradiated samples has been observed with atomic force microscopy measurements. The nature of the hydrophobic surface of investigated samples is consistent with X-ray photoelectron spectroscopy analysis that indicates formation of Si–O–CH₃ bonds on the surface of the laser-irradiated material.     

Voltage reduction for photorefractive two-wave mixing in InP:Fe by optical gap control

We report a method to increase the photorefractive two-wave mixing gain coefficient in semiconductors by using additional incident laser radiation. Two auxiliary beams are used to optimize the spatial distribution of an applied electrical field via modulation of the photoconductivity of the sample. By applying a voltage of 3.5 kV on a 4.3 mm thick InP:Fe crystal we obtain a two-wave mixing gain of 9 cm^–1. This is about 50% larger than that obtained without auxiliary beams.     

Quasi-stationary states of the NRT nonlinear Schrödinger equation

With regards to the nonlinear Schrödinger equation recently advanced by Nobre, Rego-Monteiro, and Tsallis (NRT), based on Tsallis q$q$-thermo-statistical formalism, we investigate the existence and properties of its quasi-stationary solutions, which have the time and space dependences “separated” in a q$q$-deformed fashion. One recovers the normal factorization into purely spatial and purely temporal factors, corresponding to the standard, linear Schrödinger equation, when the deformation vanishes (q=1)$(q=1)$. We discuss various specific examples of exact, quasi-stationary solutions of the NRT equation. In particular, we obtain a quasi-stationary solution for the Moshinsky model, providing the first example of an exact solution of the NRT equation for a system of interacting particles.     

On the understanding of the microscopic origin of the properties of diluted magnetic semiconductors by atom probe tomography

Spintronics, in which both the spin and charge of electrons are used for logic and memory operations, promises to revolutionize the current information technology. Just as silicon supports microelectronics, diluted magnetic semiconductors (DMSs) will be the platform of spintronics. Ideal DMSs should maintain ferromagnetic and semiconducting properties at operating temperatures to realize the spintronic functions. Although many high-temperature Curie temperature DMSs have been reported, the origin of ferromagnetism remains controversial. Currently, this is a major obstacle to the development of spintronic devices. The solution to this problem depends on a more complete understanding of DMS microstructure, especially the distribution of doped magnetic ions at atomic resolution and any defects introduced. Therefore, an analysis technique is required, possessing both high spatial and elemental resolutions, which is beyond the capability of conventional techniques, such as electron microscopy. However, atom probe tomography (APT), which recently has been successfully applied to nanoscale characterization of structural materials, has the potential to provide the unique combination of near atomic spatial and elemental resolutions needed for such an investigation.     

CMOS 1/f noise: n-channel versus p-channel

This note reports on the noise of CMOS devices. It is shown experimentally that a weak boron threshold implant (10¹² cm^–3) can influence the 1/f noise levels. For wafers with threshold adjustment the p-channel noise decreases whilst the n-channel noise increases. The changes in the n/p noise ratio with/without threshold implantation are predicted using a simple model in conjunction with carrier profile simulations.     

Rapid dislocation‐density mapping of as‐cut crystalline silicon wafers

Rapid quantification of structural defects, especially dislocations, is desired for characterization of semiconductor materials. Herein, we outline and validate a low‐cost approach for dislocation‐density quantification in silicon, involving a high‐resolution commercial dark‐field imaging device, a flatbed scanner. This method requires minimal surface preparation and can be performed on as‐cut 15.6 × 15.6 cm²wafers in less than 5 minutes. The method has been tested at a spatial resolution down to 250 µm. At 1 mm resolution, the average root mean square of the normalized error was 0.39.

     

Computer controlled diode laser spectrometer with a helium evaporation cryostat and spectroscopy of thev 3 vibration of NCO

A computer-controlled diode laser spectrometer for the 1200 to 2500 cm^–1 spectral region is described. The spectrometer has been applied to high resolution spectroscopy of the NCO radical at 5.2 m. The lead-salt diode lasers are cooled to their operating temperature with a temperature adjustable helium evaporation cryostat. Computer-controlled tuning procedures for the frequency tuning of the diode lasers have been developed; they are independent of tables describing the tuning characteristics of the diode lasers. 41 lines of the antisymmetric stretching-vibrationv ₃ of the linear NCO radical have been observed. We were able to detect vibration-rotation transitions in both² _1/2 and² _3/2 fine structure sublevels. These measurements led to the precise determination of additional molecular constants.     

Control of radiation spatial coherence under synchronous amplification in crystalline LiF:F 2 − amplifier

A technique of spatial coherence control, based on the synchronous amplification of a radiation in LiF crystals with F ₂ ^? color centers, is demonstrated. Spatial radiation distributions of stimulated Raman scattering (SRS) in oxide crystals were investigated under picosecond laser excitation. Low spatial radiation coherence was revealed for both the transient and quasi-stationary SRS. Spatially incoherent SRS was transformed to spatially coherent radiation as a result of phase—locked picosecond synchronous laser pumping of nonlinear Raman and LiF: F ₂ ^? crystals and the Stokes radiation amplification in the color center crystal.     

Impact ionization rate in direct gap semiconductors

In the framework of the 14-band k ? p model, the intensity of the impact ionization processes in direct gap semiconductors is studied and explicit expressions for the impact ionization rate are obtained. It is shown that the rate of the process near the threshold energy is determined by the sum of the isotropic and strongly anisotropic contributions. The former contribution is proportional to the cube of the distance from the threshold, whereas the latter is a quadratic one arising only because of the coupling with remote bands. The comparison of these contributions under averaging over the nondegenerate isotropic distribution of nonequilibrium electrons characterized by some effective temperature T* demonstrates that the cubic contribution rather than the commonly used quadratic one is dominant in the direct gap semiconductors with E _g<1?1.5 eV up to T* = 300 K. This should be taken into account in the calculations of the operating characteristics of the devices based on the avalanche multiplication of charge carriers.     

Planar sulfur-doped silicon detectors for high-speed infrared thermography

Planar extrinsic sulfur-doped silicon detectors for infrared (IR) semiconductor-discharge gap image converters intended for use in high-speed thermography of remote objects have been developed. The detectors were fabricated by high-temperature diffusion of sulfur into silicon wafers from the vapor phase. The dependence of doping efficiency on the sulfur vapor pressure in the course of diffusion was analyzed. The detector fabrication technology was optimized to meet the specific requirements for their operation in the microdischarge devices considered. The detectors were tested in a laboratory setup comprising a blackbody source of IR light, an image converter, and a pulsed CCD camera for recording the converted images. The converter equipped with the detector can provide imaging of objects heated to a temperature, T_min ≈ 200 °C, with a temporal resolution on the order of 10^?6 s and spatial resolution of about 5 lines/mm.     

Hadronic vacuum polarization contribution to the Lamb shift in muonic hydrogen

We report on the accuracy of the measurement of the total cross section of the process e⁺e^– ZH and of the Higgs boson mass that would be achieved in a linear collider operating at a centre-of-mass energy of 350 GeV, assuming an integrated luminosity of 500 fb^–1. For that we have exploited the recoil mass off the Z using its leptonic decays into electron and muon pairs. The Higgs mass is determined with 150 MeV accuracy, the recoil mass resolution is about 1.5 GeV and the cross section is obtained with a statistical error of 3%.     

Changes produced in the electrical resistivity of ErH2 thin films when converted to ErH3 due to hydrogen treatment

The resistivity of thin films (80–200 Å) of ErH₂ increases sharply when heated for 2 h at 300 °C in vacuum in the presence of hydrogen gas at 10^–2 Torr. This confirms that the films, originally metallic conductor, have become converted to semiconducting ErH₃ which is in conformity with the structural studies. The negative values of TCR also indicate the semiconducting nature of the hydrogen treated films. Activation energies of the films have been evaluated.     

Effects of self-focusing on the selfdistortion of amplitude modulated microwaves in non-parabolic semiconductors

Omitting the dispersion of side bands, the self-distortion of an amplitude-modulated e.m. signal due to non-linear polarizability in nonparabolic semiconductors has been investigated. The distortion is basically due to self-focusing of the electromagnetic wave and is different from the resistive (absorption) type demodulation.In n-InSb and at average powers of 1 W the index of modulation is found to increase four times at a modulation frequency R~10⁸ s^–1.     

Wafer and epilayer improvement for integrated optics devices on InP: the ESPRIT project 2518

Ga _x In_1–x As _y P_1–y alloys lattice matched to InP substrates are currently used to fabricate optoelectronic and integrated optics devices. To achieve devices with high performances and high fabrication yield, the uniformity and reproducibility of the Ga _x In_1–x As _y P_1–y epitaxial layers (composition, thickness, doping, etc.) have become key parameters. These problems have been addressed in the frame of ESPRIT project 2518 and are presented in this paper. Several aspects have been considered starting from the optimization of InP substrates, the MOVPE growth of uniform GalnAsP layers, the material characterization to the validation of material uniformity on passive optical waveguides. Both scanning photoluminescence analysis and waveguide losses measurements performed on 2 inch wafers with a high lateral resolution have shown that high quality uniform GalnAsP layers can be obtained reproducibly on 2 InP substrates using a commercially available LP-MOCVD growth process. In particular, more than 60% of 36 mm long, 3m wide and 100m spaced rib waveguides exhibit losses below 0.8dBcm^–1.     

Optical imaging of microroughness on polished silicon wafers

The microscopic surface morphology of device quality polished silicon wafers has been imaged using laser scanning optical microscopy (SOM) in differential phase contrast (DPC) mode. The SOM-DPC technique has subnanometre vertical sensitivity and submicron lateral resolution. Surface texture was observed on all wafers examined. This was found to depend mainly on the originating wafer supplier and year of manufacture, rather than on any characteristic of the silicon material itself, and was assigned to silicon surface roughness. The amplitude of the directional 1–10 m wide polishing features observed on many of the as-received wafers was estimated to be in the region of 1–2 nm. An additional isotropic submicron-scale roughness (incompletely resolved optically) was present in all cases. Atomic misorientation steps were also observed on specially-prepared wafers.     

Sampling of free-space magnetic pulses

We report free-space detection of magnetic pulses via the Faraday effect with shot-noise limited detection. This allows a 10^–8 T / Hz magnetic field resolution. The orthogonal propagation of the optical probe beam and the THz waves demonstrate a 1.3 ps risetime with a 400 GHz frequency bandwidth. The temporal and frequency responses of several crystals are reported with a theoretical response function analysis presented. The dispersion of the magnetic pulse into the sensor crystal is illustrated with a theoretical simulation for comparison. We also contrast the properties of electro-optic sampling with this magneto-optic sampling technique.