Nanosecond optical transmission studies of laser annealing in ion-implanted silicon-on-sapphire

Time-resolved optical transmission has been studied using 633 and 514 nm CW probes on ion-implantation-amorphized silicon-on-sapphire during annealing by a 10 nsec, ⊥ J/cm² pulse at either 532 nm or 485 nm. As recrystallization sets in the transmitted signal at 514 nm rises by ⊥ 10³ in ⊥ 60 nsec and provides a measure of regrowth velocity. Beyond 200 nsec the much slower transmission rise is used to provide an estimate of the Si cooling rate. The difference in transmission observed between initially crystalline and initially amorphous Si provide an estimate of the latent heat of recrystallization of the amorphous phase.     

Time-resolved defect production and annealing during electron-beam processing of silicon

In (100)p-Si radiation damage was produced by implanting B⁺ ions with an energy of 80keV, 90keV and 1.6MeV. The specimens were annealed by scanned electronbeam irradiation (20keV, 1–2mAcm^–2). The formation, evolution and annihilation of defects during the irradiation process were investigated by employing DLTS and RBS measuring techniques. The results show a minimum of defect concentration and an efficiency of the electrical activation of B higher than 80% at an annealing time of 4.5 s. For irradiation times longer than 5 s it becomes evident, that the crystal surface acts as source of defects and contributes to an increase in defect concentration.     

用模拟退火算法研究非晶硅薄膜的光学性质

在玻璃衬底上采用等离子体增强的化学气相沉积(PECVD)法制备了非晶硅薄膜(A-Si:H)。用紫外-可见-近红外分光光度计测出了其透射光谱。采用模拟退火算法研究了透射光谱,得出了薄膜的厚度、折射率和吸收系数随波长变化的关系式、光学带隙等光学常数,并对该方法的优缺点进行了讨论。     

Neodimium laser pulse annealing and decomposition of ion-implanted GaAs

Summary The amorphous-to-single crystal transition induced by high-power Nd laser pulse has been studied in ion-implanted GaAs by taking advantage of the high-absorption coefficient of amorphous material. A threshold energy density of about 0.8 J/cm² has been measured for both 50 keV Te⁺ and 100 Ar⁺ implants. Channelling effect and X-ray photoelectron spectroscopy techniques indicate that no appreciable As loss occurs in a narrow energy density window just above threshold. High-energy densities cause instead As loss from the near surface region. Visiting scientist on the basis of I.N.F.N. Academia Sinica cultural exchange plan.     

Time-resolved transmission study of fused silica during laser-induced backside dry etching

Laser-induced backside dry etching (LIBDE) is a promising technique for micro- and nanomachining of transparent materials. Although several experiments have already proved the suitability and effectiveness of the technique, there are several open questions concerning the etching mechanism and the concomitant processes. In this paper time-resolved light transmission investigations of etching process of fused silica are presented. 125 nm thick silver coating was irradiated through the carrying 1 mm thick fused silica plate by single pulses of a nanosecond KrF excimer laser. The applied fluences were 0.38, 0.71 and 1 J/cm². During the etching process the irradiated spots were illuminated by an electronically delayed nitrogen laser pumped dye laser. The delay between the pump and probe pulses was varied in the range of 0 ns and 20 μs. It was found that the transmitted probe beam intensity strongly depends on the applied delays and fluences. Scanning electron microscopy and energy dispersive X-ray spectrometry of the etched surface showed the existence of silver droplets and fragments on the illuminated surfaces and silver atoms built into the treated surface layer influencing the transmission behavior of the studied samples.     

Investigations of the electron structure of ion-implanted amorphous germanium

Ge amorphised by Sb⁺ implantation has been investigated by means of UV photoemission. Our results differ significantly from earlier data on amorphous Ge. It is suggested that this implantation produces a new kind of amorphous state, characterized by modified local atomic arrangement.     

Modeling of polysilicon diffusion sources during rapid optical annealing

A new model for polysilicon diffusion sources is presented. It considers the following effects: 1) dopant diffusion in grains, in grain boundaries and in the single-crystal silicon substrate, 2) dynamic dopant segregation between grain and grain boundary phases and between the phases of polysilicon and the single-crystal silicon substrate, 3) dynamic dopant activation or clustering in grains and in the single-crystal silicon substrate, 4) dynamic grain growth depending on local grain size and local electron density. These mechanisms with completely different time scales are modeled simultaneously. For the first time this allows the analysis of furnace and rapid optical annealing processes with arbitrary grain growth kinetics even during epitaxial realignment. The advanced model for segregation allows for the effect that dopants in grain boundaries and active dopants in grains as well as in the single-crystal silicon substrate find only a limited number of sites which can be occupied. These limitations are necessary to explain the dopant distributions in polysilicon and in the single-crystal silicon substrate. For the first time the coupling between the concentration of active dopants in grains, between the concentration of dopants in grain boundaries and between the local grain size is shown during doping enhanced grain growth.     

Periodic variations of plasma optical emission during repetitive pulsed-laser irradiation of aluminum in ambient air

Optical emission from plasma produced in ambient air by focusing a Nd:YAG laser beam on an aluminum surface was spectrally analysed. A periodic behaviour was observed in spectral line intensities associated with series of laser pulses. Based on simultaneous measurements of diffuse surface reflectivity and complementary measurements in other gases (He, O₂, N₂), this behaviour is ascribed to a competition between thermally-assisted surface oxidation and nitridation, and laser ablation. PACS 52.38.Mf; 52.50.Jm; 81.65; 78.68.+m; 52.70.Kz     

Shape of an amorphous metallic ribbon during annealing: A kinetic study

We have measured the curvature of an amorphous metallic ribbon (alloy Fe_72.5 Cr_6.5 P_13.2 C_7.8) as a function of time for several annealing temperatures. The change in curvature is due to different structural relaxations of the two sides of the ribbon. The data lead to a rather narrow distribution of activation energies, centered around E_eff ∼ 1.0 eV and to a limit frequency in the range 3.10³–3.10⁵ Hz, which is discussed at the light of previous magnetic studies.     

Preparation of ion-implanted silicon for transmission electron microscopy

This paper deals with the preparation technique of thin foils (below 5000 Å) for the transmission electron microscopy from silicon implanted by N⁺ ions. Mechanical and chemical thinning and anodic oxidation techniques are discussed and selective etching of the surface of silicon for the purposes of the replica technique is noted. Compositions of etching solutions and other experimental parameters are mentioned. The results are demonstrated on electron micrographs showing the radiation damage due to ion implantation in silicon.     

Time-resolved measurements of picosecond optical breakdown

Picosecond optical breakdown was investigated in order to assess its potential for performing highly localized incisions for laser surgery. Measurements of breakdown were performed using single 40-ps Nd: YAG laser pulses in distilled water. Novel optical pump-probe techniques were developed to characterize the transient spatial and temporal dynamics of the plasma, shock wave, and cavitation phenomena which are associated with the breakdown. The maximum cavity radius and the shock wave zone are shown to scale as the cube root of the pump pulse energy over almost three orders of magnitude. For pulse energies close to the threshold energy of 8 J, the shock range was 100–200 m and the cavity radius was 140 m. Complementary experiments were performed with 10-ns pulse durations. Since picosecond pulses have high peak intensities with low pulse energies, a significant enhancement in localizability may be achieved. The implications for ophthalmic microsurgery are discussed.     

Dynamics of gold clusters on amorphous carbon films induced by annealing in a transmission electron microscope

The change of the size distribution of Au clusters induced by annealing was studied in situ by transmission electron microscopy. Starting from statistically distributed Au clusters on a thin amorphous carbon film, “islands” are formed within a few months storage at room temperature, which consist of Au clusters with sizes <4 nm embedded in a thin Au film. These islands cover originally areas with sizes around 25 × 70 nm². If the temperature is increased in the transmission electron microscope two different processes can be clearly distinguished that lead to the coarsening of the cluster size distribution: cluster coalescence and (contactless) Ostwald ripening. The degree and rate of the coarsening are found to depend on the underlying surface (Au film or amorphous carbon) and the exposure to the high-flux high-energy electron beam, which can be estimated to lead to high-temperature excursions in a cluster on a 10⁻¹² s time scale. The experimental findings are confirmed by Monte-Carlo simulations using the many-body Gupta potentials in order to calculate the Au/Au interaction. Moreover, the results of MC simulations suggest an electron-beam induced formation of a “quasi-two-dimensional gas” of small highly mobile Au species on the Au film, which promotes Ostwald ripening.     

Slow structural transitions of hydrogen in hydrogenated amorphous silicon during low temperature annealing

A slow decrease in the number of Si-H bonds in B-doped a-Si:H during annealing at 220°C has been observed. It is shown that during annealing hydrogen is transferred irreversibly from a bonded state into molecular H₂ trapped in the samples. This has important implications for the determination of H-diffusion coefficient by SIMS or ERDA.     

退火对含氮氟非晶碳膜结构及光学带隙的影响

采用射频等离子体增强化学气相沉积法,在不同条件下制备了含氮氟非晶碳膜,着重考察了退火温度对膜结构和光学带隙的影响. 研究发现：在350℃时,膜仍很稳定,当退火温度达到400℃时,其内各化学键的相对含量发生很大的改变. 膜的光学带隙随着退火温度的升高而增大,红外和拉曼光谱分析显示其原因是：退火使得膜内F的相对浓度降低,sp²相对含量升高,导致σ-σ^*带边态密度降低. 关键词： 含氮氟非晶碳膜 退火 光学带隙     

Reduction of the annealing temperature of radiation-induced defects in ion-implanted MOS structures

Si-SiO₂ structures irradiated with 11-MeV electrons for 10 s and then implanted with B⁺ ions with an energy of 10 keV at a dose of 1.0×10¹² cm^-2 through the oxide were annealed at different temperatures. MOS capacitors including such oxide layers were studied by quasi-static C/V and thermally stimulated current (TSC) methods. A comparison of the radiation defect annealing of double-treated (electron-irradiated and ion-implanted) samples and of implanted-only samples was carried out. It is shown that a preceding low-dose high-energy electron irradiation of the samples leads to a lowering of the annealing temperature of radiation defects introduced by ion implantation. After annealing at 500 °C for 15 min, no TSC spectra for the double-treated samples were observed. The spectra of the other samples (which were not previously irradiated) showed that after the same thermal treatment only some of the radiation defects introduced by ion implantation are annealed. The difference between the annealed interface state density of previously electron-irradiated and current MOS structures is also demonstrated. A possible explanation of the results is proposed . PACS 61.82.Fk; 85.40.Ry; 61.80.Fe     

Ultrashort laser-pulse annealing of hydrogenated amorphous silicon

Crystallization of hydrogenated amorphous silicon (a-SI:H) has been initiated using ultrashort laser-pulse train annealing. Optical microscopy, infrared absorption, Raman spectroscopy and photoluminescence measurements show that in our experiment the crystallized layer is localized on the surface and is non-epitaxial. The depth of the crystalline layer and its surface morphology are discussed. A sharp luminescence band at 0.970 eV with fine structure is found after laser annealing and is identified as a recombination center similar to irradiation induced defects in crystalline Si.     

Effects of annealing on ion-implanted Si for interdigitated back contact solar cell

Effects of annealing on the properties of P- and B-implanted Si for interdigitated back contact (IBC) solar cells were investigated with annealing temperature of from 950 to 1050 °C. P-implanted samples annealed at 950 °C were enough to activate dopants and recover the damage by implantation. As the annealing temperature was increased, the diode properties of P-implanted samples were degraded, while that of B-implanted samples were improved. However, in order to activate an implanted B ion, B-implanted samples needed an annealing of above 1000 °C. The implied V_oc of lifetime samples by quasi-steady-state photoconductance decay followed the trend of diode properties on annealing temperature. Finally, IBC cell was fabricated with a two-step annealing at 1050 °C for B of the emitter and 950 °C for P of the front and back surface fields. The IBC cell had V_oc of 618 mV, J_sc of 35.1 mA/cm², FF of 78.8%, and the efficiency of 17.1% without surface texturing.