D. A. Pryakhin

Optical monitoring of technological parameters in metal-organic vapor-phase epitaxy

The possibility of applying low-coherent tandem interferometry to optical monitoring of the temperature of a semiconductor substrate and the thickness of a deposited layer in metal-organic vapor-phase epitaxy (MOVPE) is demonstrated for the first time. The absolute accuracy in the temperature measurements of Si, GaAs, and sapphire substrates under MOVPE conditions is limited by the calibration accuracy and is ±1°C. The accuracy in the measurement of the deposited layer thickness is 2 nm. A considerable (10–100°C) deviation of the temperature measured by a thermocouple placed inside a susceptor from the actual substrate temperature is found. A significant temperature gradient along the susceptor depending on the gas flow rate and other factors is revealed. It is shown that, owing to the high heating efficiency of sapphire substrates, there is no need to coat their reverse with absorbing layers upon heating up to 300°C or in the presence of hydrogen pressure of higher than 100 mbar.

Optical monitoring of substrate temperature and etching speed of multilayered structures during plasmochemical etching

Using weakly coherent tandem interferometry, the possibility of simultaneous temperature and film thickness measurements in plasmochemical etching processes of silicon on insulator structure is demonstrated. It is shown that changes of the structure’s total optical thickness related to temperature variation can be separated from a change of the physical film thickness. For that purpose we have to take in account changes of zeros interference peak amplitude caused by changes of the interferentional conditions inside the film when its thickness is changing. Temperature measurement precision is ±1°C. Thickness measurement precision is ±10 nm. The results of process monitoring closely correlate with the results of a stair’s profile obtained with a profilometer.

Fabrication of nanocrystalline silicon layers by plasma enhanced chemical vapor deposition from silicon tetrafluoride

The data on fabrication of silicon layers on various substrates by plasma enhanced chemical vapor deposition from the (silicon tetrafluoride)-hydrogen system are reported. The emission spectra of the plasma in the system are recorded. The samples were studied by the X-ray diffraction and secondary ion mass spectrometry techniques. The morphologic properties of the surface are examined, and the Raman spectra, the transmittance spectra in the infrared region, and photoluminescence spectra are recorded. The phase composition of the layers corresponds to nanocrystalline silicon, in which the dimensions of coherent-scattering grains vary with the conditions of the preparation process in the range from 3 to 9 nm. The layers exhibit intense photoluminescence at room temperature.

Qualitative sims analysis of28,29,30Si isotope concentration in silicon using a Tof.Sims-5 Setup

The possibility of quantitative SIMS determination of28-30Si isotope concentrations in silicon samples using a TOF.SIMS-5 spectrometer is shown. Th e isotope composition of a large number of Si samples, namely epitaxial Si layers with a natural isotope ratio, amorphous Si films depleted of28Si isotope (deposited on natural Si substrates), and samples enriched with 28Si isotope (manufactured by VITCON) is investigated. Substantial variations in the 29Si/30Si isotope ratio (from 1.51 for the natural content up to 25 in the case of limiting enrichment with 28Si isotope) are revealed.

Effect of B atoms on the properties of InAs quantum dots in the GaAs matrix

The effect of B dopants on the properties of InAs quantum dots is studied experimentally. It is shown that the incorporation of B atoms decreases the integral amount of InAs that is needed to form islands according to the Stransky-Krastanov mechanism and leads to an increase in the density of dots. At the same time, it is discovered that the sensitivity of InAs quantum dots to annealing increases, which leads to the degradation of the optical properties of these quantum dots during growth of covering layers.

MEMS Tunneling Sensor Without the Feedback Loop

A possibility of fabrication of a microelectromechanical tunneling sensor without a feedback loop is demonstrated. The tunneling gap of less than 10 nm shows a long-term stability at room conditions. The sensor can be used for construction of an accelerometer in which the linear acceleration causes mutual displacements of mobile microelectrodes. Acceleration can be detected due to a strong dependence of the tunneling current on interelectrode gap. The sensor is fabricated on a silicon-on-insulator (SoI) wafer in the planar technology. Experiments have shown the accelerometer resolution to be 2.221 g/Hz1/2 at frequencies up to 3.17 kHz. The frequency of the first mechanical vibration mode of the sensor was estimated at a few MHz. By lowering this frequency through an increase in the proof mass, it is possible to largely upgrade the resolution of the accelerometer.

Production of nanocrystalline silicon layers using the plasma enhanced chemical vapor deposition from the gas phase of silicon tetrafluoride

The production of silicon layers using plasma enhanced chemical vapor deposition in the mixture of silicon tetrafluoride and hydrogen is reported. The samples have been analyzed by X-ray diffraction, Raman spectroscopy, and secondary ion mass spectrometry. The phase composition of the layers is nanocrystalline silicon with the crystalline-domain sizes from 3 to 9 nm in dependence of the conditions of the process. The samples are characterized by intense photoluminescence at room temperature.

MOVPE of structures with aluminum nanocluster layers in a GaAs matrix

Metalorganic vapor phase epitaxy (MOVPE) was used to grow semiconductor structures comprising a GaAs single crystal matrix with incorporated layers of aluminum nanoclusters (Al-NCs). A new regime of GaAs overgrowth on Al-NC layers is proposed, which ensures planarization of the semiconductor layer surface at a thickness comparable with the height of Al-NCs.

Evidence of impurity assisted tunneling in SiGe/Si heterostructures

The investigation of vertical transport in delta-doped SiGe/Si heterostructures has been presented. The asymmetrical triple barrier structure was grown by MBE technique. The delta layer of boron impurity was placed into the center of narrower quantum well. The growth procedure was followed by conventional processing including photolithography and plasma etching and magnetron sputtering. SIMS and X-rays diagnostics have been used to control the desired structure. The conductance of the structure has been measured at liquid helium temperature and analyzed. All pronounced resonances have been identified. The resonant feature near 60 mV has to be attributed to impurity-assisted tunneling that is supported by calculation of binding energy of the acceptor in the narrower quantum well.

Fiber-optic equipment for monitoring technological processes

The results on the development and implementation of optical systems for monitoring technological processes are presented. The developed equipment is based on the principles of tandem low-coherence interferometry. The equipment allows contactless remote monitoring of the optical thickness of transparent layered objects with nanometer resolution immediately during technological processes. One of the versions of the equipment intended to control the sheet glass thickness is successfully implemented in industry. The second version intended for monitoring semiconductor nanostructure fabrication is successfully applied to control the growth processes under condition of metal-organic vapor-phase epitaxy and the plasma-chemical etching processes.