Acoustic emission monitoring during laser shock cleaning of silicon wafers

A laser shock cleaning is a new dry cleaning methodology for the effective removal of submicron sized particles from solid surfaces. This technique uses a plasma shock wave produced by laser-induced air breakdown, which has applied to remove nano-scale silica particles from silicon wafer surfaces in this work. In order to characterize the laser shock cleaning process, acoustic waves generated during the shock process are measured in real time by a wide-band microphone and analyzed in the change of process parameters such as laser power density and gas species. It was found that the acoustic intensity is closely correlated with the shock wave intensity. From acoustic analysis, it is seen that acoustic intensity became stronger as incident laser power density increased. In addition, Ar gas has been found to be more effective to enhance the acoustic intensity, which allows higher cleaning performance compared with air or N₂ gas.     

Acoustic emission at phase transition in vanadium sesquioxide single crystals

The metal-semiconductor phase transition in vanadium sesquioxide is investigated by the acoustic emission method. It is shown that the acoustic emission in single crystals of this compound is due to thermoelastic stresses arising in the crystal upon the phase transition. Transformation of the acoustic emission activity and an increase in the phase transition temperature are revealed in the temperature cycling of the sample. Observation of peaks of the acoustic emission activity at a temperature of 5–6 K above the critical temperature indicates that crystal nuclei of the monoclinic phase appear in the high-temperature (trigonal) phase of the crystal.     

Acoustic emission upon spontaneous polarization in triglycine sulfate single crystals

We report on the results of analysis of acoustic emission (AE) under thermal action on a triglycine sulfate (NH₂CH₂COOH)₃ ? H₂SO₄ crystal. The triglycine sulfate single crystals grown from solution and not subjected to mechanical treatment are heated to a temperature above the Curie point (T_C = 49°C). During natural cooling of the crystal, a transition from the paraelectric to ferroelectric phase is accompanied by intense AE. In the temperature range ～28–30°C, an anomalous drop of the mean-square voltage in the AE signal is observed against the background of monotonic accumulation of AE events.     

Secondary-phase behavior in silicon single crystals on annealing in an electric field

In the high-temperature annealing of a silicon single crystal with inclusions of secondary phase-Cu-Si or Al-Si- in a dc field, the inclusions are seen to migrate toward one of the electrodes. Aluminum-based inclusions move toward the negative electrode and copper-based inclusions toward the positive electrode. For each type of inclusion in the investigated temperature range (900–1100°C), the value of the relative-velocity of inclusion migration with respect to the initial area is given. The mechanism of migration is described.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 26–31, October, 1978.It remains to thank S. A. Derikova, V. V. Federenko, and S. P. Lavrenko for assistance in conducting the experiments.     

Acoustic fields detected by a laser interferometer in aluminum single crystals

Elastic fields in aluminum single crystals are studied using the laser interferometry technique. The measurements are conducted at a frequency of 10 MHz for the case of the wave propagation along the [001] and [111] axes and also for small deviations from the [111] axis. The energy distribution is measured in the transition region between the near and far fields. The energy of transverse elastic waves in the case of the propagation along the [111]-axis is distributed within a sector. The deviation of the propagation direction from this axis leads to radical changes in the energy distribution.     

Epitactic formation of forsterite on MgO single crystals during vacuum annealing

Specimens of {0 0 1} MgO, prepared for analysis in the transmission electron microscope (TEM), have been heated in situ in a conventional TEM in order to study the effect of different heat treatments on the surface of the MgO specimens. A previous study, using a similar in situ heat treatment of MgO, found that at elevated temperatures (∼500 K) a film of different structure and composition formed on the surface of the sample. The previous study concluded that the composition and structure corresponded to that of MgO₂. In the present study, similar results to those shown previously have been found. However, the interpretation of these results is quite different. The films are shown to be of a composition and crystal structure that is consistent with forsterite, Mg₂SiO₄. The films can form as a result of contamination during the high-temperature in situ annealing process.     

Acoustic laser cleaning of silicon surfaces

We investigate the detachment of small particles from silicon surfaces by means of acoustic waves generated by laser-induced plasma formation at the back side of the sample. It is demonstrated that sufficiently high acoustic intensities can be reached to detach particles in the submicron regime. In order to study this “acoustic laser cleaning” in more detail, we have developed an interference technique which allows one to determine the elongation and acceleration of the surface with high temporal resolution, the basis for an analysis of the nanomechanical detachment process, which takes place on a temporal scale of nanoseconds. We find that the velocity of the detaching particles is significantly higher than the maximum velocity of the substrate surface. This indicates that not only inertial forces, but also elastic deformations of the particles, resulting from the acoustic pulse, play an important role for the cleaning process. PACS 81.65.Cf; 68.35.Np     

Calculated temperature distribution during laser annealing in silicon and cadmium telluride

By solving the time-dependent heat flow equation, the temperature reached by silicon and cadmium telluride surface layers under high power density ruby laser pulsed illumination, is calculated. The results are presented in directly useful figures allowing the determination of the surface temperature, its evolution towards the bulk as a function of time... In particular, it should be noticed that for a 25 ns half-power width, pulses of 0.8J/cm² are sufficient to melt the top of an amorphous silicon layer, this value becomes noticeably lower for cadmium telluride. Work performed while visiting the Centre de Recherches Nucléaires, Groupe PHASE, Strasbourg.     

Laser grown single crystals of silicon

Single crystal rods of silicon have been grown by laser-induced chemical vapor deposition (LCVD) using visible light. We believe these to be the first reported single crystals of any material grown by LCVD.     

Patterned laser annealing of silicon oxide films

UV-absorbing silicon monoxide (SiO _x , x≈1) thin films on fused silica substrates are irradiated by an ArF excimer laser (wavelength 193 nm) in the sub-ablation threshold regime. Multi-pulse irradiation of films with ∼200-nm thickness at a fluence of about 100 mJ/cm² leads to a significant increase of the UV transmission, indicating the oxidation of SiO _x to SiO₂. The quality of the obtained films after this laser annealing process depends on the oxygen content of the environment. Irradiation in air at atmospheric pressure leads to the formation of sub-micron-sized oxide particles on top of the film. Structured illumination is applied either to form areas of the film with changed transmission and refractive index, or for the formation of regular particle patterns with sub-micron periods. These processes can be utilized for the fabrication of phase masks or for various types of surface functionalization.     

Magnetoresonant hardening of silicon single crystals

JETP Letters - A microwave magnetic field crossed with a static field was found to exert a resonance effect on the dislocation mobility in single crystals of p-type silicon. The frequency of...     

Growth of polymer crystals during annealing

Observations by transmission electron microscopy are reported on the processes involved in polymer crystal growth during annealing. The observations suggest that crystal growth occurs by two processes. One process involves the melting of those regions of the crystals in which the melting point is lower than the annealing temperature. The polymer melt due to the melting process gradually becomes incorporated into the unmolten crystals, resulting in crystal growth. The alternative process is solid-state crystal growth by the migration of the amorphous region between crystallites.     

Effect of annealing on the electrical properties of nitrogen-doped silicon single crystals grown by crucibleless zone melting

The electrical properties of nitrogen-doped silicon single crystals of the n and p types grown by crucibleless zone melting and annealed at 680°C have been studied. It is shown that the annealing brings about the appearance, in the crystals, of nitrogen-containing centers, which form deep donor and acceptor levels in the band gap. The process is accompanied by an increase in the electrical resistivity; the increase is particularly substantial in the initially high-resistance single crystals. On the other hand, in slightly boron-doped single crystals of the n and p types, the conversion of the conduction type is observed. In a converted material of the n-type, the electron mobility is anomalously low, which demonstrates its high electrical spatial inhomogeneity. The energy of the deep acceptor level near E _c ? 0.35 eV introduced during annealing has been determined. The model explaining the phenomena observed is proposed.     

Nd: YAG laser annealing of gallium-implanted silicon

A Q-switched Nd: YAG laser with a pulse duration of 20 ns was used to investigate effects of laser annealing in gallium implanted silicon. Rutherford backscattering and Hall-effect measurements were performed to evaluate the annealed layer. Differential Hall-effect measurements were carried out to obtain carrier concentration profiles after annealing. It was found that a maximum sheet carrier concentration of 8×10¹⁵ cm⁻² can be obtained for a gallium implantation of 10¹⁶ cm⁻² by laser annealing with an energy density of more than 1.0 J cm⁻². Although the peak carrier concentration was found to be 8.0×10²⁰ cm⁻³, the annealed layer showed polycrystalline structures even after annealing with an energy density up to 4J cm⁻². The annealing took place in the solid phase in this energy density range.     

Free-running ruby laser annealing of boron implanted silicon

An analytical treatment of the thermal phenomena during free-running ruby laser annealing of boron implanted silicon is presented. The heat equation was solved for a simplified shape of the pulse train consisting of a uniform succession of triangular spikes, identical in energy. During one spike the optical and thermal parameters of the sample were taken constant, but for each new spike, new values of these parameters were calculated taking into account their temperature dependence. Such a model predicts the melting of the top surface before the laser pulse has ended, for energy densities higher than 9×10⁴ J/m². RHEED confirms the presence of recristallization at about the same value of the laser-pulse energy densities.     

Domain structure of silicon iron single crystals

The model of a new domain structure arising after the magnetization of silicon iron single crystals in planes of the (110) type at an angle of 0°<Θ<-55° to the axis of easy magnetization is considered. Using this model the angular dependence of the domain-structure characteristics is established; it agrees closely with direct observations. On magnetizing a single crystal in the angular range 55° <Θ≤ 90° to the easy axis, layers with a uniform resultant magnetization parallel to the [001] direction are formed.     

Band-edge emission in CuI single crystals

The photoluminescence spectra of CuI single crystals have been studied at T = 4.2 K and at various excitation levels. The emission band of donor-acceptor pairs (DAP) with a maximum at about 4200 Å has been shown to possess a complex structure. Theoretical analyses and exciton spectroscopy data make it possible to calculate the ionization energies for the donors and acceptors participating in the formation of DAP, which are equal to E_D = = 0.045?0.065 eV and E_A = 0.155?0.170 eV, respectively. The fine structure of emission due to the annihilation of excitons bound on acceptor pairs (band maximum 4075 Å) has been detected and calculated. The energy of the longitudinal optical phonon participating in the exciton-phonon interaction (LO ? 18.7 meV) has been determined.     

Thermal emission of macroporous silicon chirped photonic crystals

In this Letter we report on the thermal properties of macroporous silicon photonic crystals with the unit cell gradually varied along the pore axis. We show experimentally that arbitrarily large omnidirectional total-reflectance bands can be produced with such structures. We also demonstrate that those bands can be effectively used to reduce thermal radiation in large spectral bands.     

Pulsed electron beam annealing and furnace annealing of Cu-implanted Al single crystals

A comparison has been performed of the effects of pulsed electron beam annealing (PEBA) and furnace annealing on the distribution and lattice site occupation of Cu implanted into Al single crystals. Both parameters have been determined by Rutherford backscattering and channeling measurements with 2 MeV He⁺ ions. With furnace annealing at 300°C the Cu diffusion into the bulk was determined by the release process from the implanted layer, while for PEBA a redistribution of the copper was observed for pulses with deposited energy densities above the threshold for melting. A supersaturated solid solution with 95% (2.1 at.%) of the impurity atoms on substitutional sites was formed by the electron beam treatment. After thermal annealing only little improvement of the lattice site occupation was observed with 66% of the impurities atoms on lattice sites, however with slight displacements from the perfect positions.     

Blue emission in Ti-sapphire laser crystals

The time resolved emission spectrum of the blue band of Ti:sapphire laser crystal has been investigated as a function of temperature (range 10–290 K) and UV (266 nm) laser excitation intensity. Two blue emission bands, centred at 420 nm and 460 nm, have been detected. The 420 nm band is attributed to Ti⁴⁺ centres whereas the 460 nm one is proposed to be due to Ti³⁺ ions. The evolution of the emission spectrum vs the UV excitation intensity has shown that the concentration of Ti⁴⁺ centres is increased under UV irradiation at the cost of the centres responsible for the 460 nm band.