Cw Laser Annealing Research Articles

Laser Polishing and Annealing Injection Mold Using Dual-Beam Laser System

One of the challenges regarding the application of laser polishing in injection mold manufacturing is to eliminate the tensile residual stress on a polished cavity surface without the extra expenses of an annealing vacuum furnace. This study aims to develop a fast laser annealing method using a dual-beam laser system by which a mold cavity can be laser-polished and then laser-annealed. Fourteen mold steel specimens were laser-polished by a dual-beam laser, resulting in a roughness reduction from the initial state, Sa 1.11 μm, to Sa 0.16 μm, a smoother surface finish. A numerical simulation of laser annealing using the current CW laser was implemented to optimize the laser annealing parameters to guide the experiment of CW laser annealing. XRD measurement results showed that the tensile residual stress dropped from an initial 638 MPa to 10 MPa in an annealing cycle time of 40 min at 750 °C; therefore, fatigue cracks or stress corrosion cracks (SCC) on the mold cavity will no longer occur. Confocal microscopy, X-ray diffraction, and scanning electron microscopy were used to obtain the microstructure and phase composition of the microstructures, demonstrate that laser polishing and laser annealing by a dual-beam laser is a fast and effortless technique which can be effectively employed in injection mold manufacturing.

9‐1: Fabrication of Lateral Crystal Si on Cu Bottom‐Gate Structure via Blue‐Laser Diode Annealing (BLDA)

We report that Si lateral crystal is fabricated on bottom gate cupper electrode with having no crack and ablation of the electrode by blue laser diode annealing (BLDA). In CW laser annealing, the long irradiation time and wide beam width induce some damage to glass substrate, electrode and membrane, so our research adopted a narrow beam size (33 μm × 8.25 μm) and fast scanning speed (over 500 mm/s) in order to reduce the amount of generated thermal in annealing. In our presentation, evaluation of Si crystals fabricated on Cu electrodes, cross‐section SEM results indicating no metal damage and relationship between laser irradiation time and the damage are discussed. Our BLDA system can realize high TFT mobility and which is composed of inexpensive beam heads, therefore it is expected to be applied to Mini LED back light and OLED etc.

CO 2 laser annealing on erbium-activated glass–ceramic waveguides for photonics

Silica-based sol–gel waveguides activated by Er 3+ ions are one of the most important materials for integrated optics devices. In this paper, we present an alternative method combining sol–gel route and CO 2 laser annealing for planar optical waveguides processing. The effects of pulsed and continuous CO 2 laser irradiation on the optical and spectroscopic properties of SiO 2–ZrO 2 and SiO 2–HfO 2 planar waveguides are evaluated and the thermal conventional annealing effects for these systems are reported for comparison. All the planar waveguides, doped with 0.5 and 5 mol% Er 3+, were prepared by sol–gel route using dip-coating deposition on v-SiO 2 substrates. An increase of the refractive index of approximately 0.04 at 1.5 μm has been observed on 70SiO 2–30HfO 2 planar waveguide after continuous CO 2 laser annealing. A similar refractive-index variation was detected in all SiO 2–ZrO 2 planar waveguides after CO 2 laser irradiation. We have observed, moreover, that continuous CO 2 laser annealing can lead to waveguides with a lower attenuation coefficient with respect to the attenuation coefficient measured for thermal annealed waveguides. Upon excitation at 514.5 nm continuous-wave laser light, on the irradiated sample, the shape is found to be almost independent on the time and irradiation power with CW laser annealing but a decrease of the FWHM of approximately 46–12 nm has been observed on planar waveguides after pulsed laser annealing. Before and after conventional thermal annealing, the 4 I 13 / 2 level decay curves present a single-exponential profile with a lifetime of 4.0 and 5.7 ms, respectively, but the lifetime increases up to 7.0 ms, after pulsed laser annealing treatment. X-ray diffraction and optical spectroscopy showed that after an adapted pulsed CO 2 laser annealing, the resulting materials showed a crystalline environment.

Laser-induced defect creation in 300 mm SOI-wafer analyzed by use of photoelastic imaging

Dopant profile engineering in advanced semiconductor devices needs advanced pulse heating regimes in the range of microsecond to millisecond. Laser annealing in the solid-phase recrystallization regime provides precise local temperature pulses with peak values of 1,300 °C and a mean duration between a nsec up to a few millisecond. Conventional CW-laser annealing by scanned laser beam is applied to anneal bulk and SOI-wafers. Beside of temperature gradient induced crystal defects this local heating caused a special nucleation and growth of local defect clusters in CZ-silicon. By using photoelastic, photoluminescence and photothermal methods, the specific impacts of defect evolution and cluster growth caused by heat pulses were studied by direct imaging of the mesoscopic stress fields of the crystal defects.

7.3: Giant‐grain Poly‐Si by CW Laser Annealing of a‐Si with Cylindrical Microlens Array

AbstractWe have developed a super large grain poly‐Si on glass by CW laser crystallization using cylindrical microlens array. A giant‐grain poly‐Si with average grain size of 15 μm × 15 μm was achieved. The n‐channel TFT using the poly‐Si exhibited the field‐effect mobility, on/off current ratio, threshold voltage and gate voltage swing of 470 cm2/Vs, ∼108, 0.1 V and 0.4 V/dec., respectively. On the other hand, the p‐channel TFT exhibited 192 cm2/Vs, ∼108, −2.2 V and 0.5 V/dec., respectively. A single crystalline Si on glass can be achieved with this technique.

Quantum confinement effects in silicon nanocrystals produced by laser-induced etching and cw laser annealing

A comparative study of quantum confinement of electrons and phonons in silicon nanocrystals produced by laser-induced etching on a silicon (Si) substrate and continuous wave (cw) laser-induced crystallization in a-Si:H film on a quartz substrate is presented here. Raman line shapes of optical phonons confined in Si nanocrystals were utilized using a phenomenological phonon-confinement model. It is appropriately modified by incorporating a Gaussian distribution of sizes for two-dimensional (columnar) and three-dimensional (spherical) confinement parameters for laser-induced etching and cw laser-induced crystallization processes, respectively. The calculated mean crystallite sizes were in consonance with those calculated from the bond-polarizability model. Confinement effects were found to be more prominent in Si nanocrystals prepared by laser-induced crystallization in comparison to laser-etched Si. Photoluminescence spectra of both the samples were also utilized to study the dimensionality aspect of nanocrystals.

Clustering in carbon implanted, laser annealed, fused quartz

Buried graphitic clusters of an average size up to 37 Å have been realised in fused quartz using a combination of keV C ion implantation and CW laser annealing. The annealing dynamics of these clusters has been studied by confocal laser microRaman spectroscopy. Detailed analysis of the Raman parameters suggests that, in spite of the presence of ‘free’ Si and O atoms displaced by the implantation process, the carbon undergoes CC bonding exclusively. Comparison with annealing studies of disordered pure carbon systems indicates that the SiO 2 matrix behaves as an inert material, merely holding the C in place while the graphitic bonding and clustering progresses.

Structural relaxation of amorphous silicon during thermal and CW laser annealing

Different amorphous silicon thin films were prepared by high energy ion bombardment of crystalline silicon (a-Si) and by magnetron sputtering deposition (a-Si:H and a-Si 1− x C x :H). All samples were laser annealed and a-Si sample was thermally annealed. Structural changes were monitored by bandwidth and position of transverse optical (TO)-like vibrational band in Raman spectrum of amorphous silicon. They were compared with changes of broad background signal, recently interpreted as `boson peak'. Correlation of structural and boson peak changes was explained by a fractal model.

Comparison of structural changes in amorphous silicon induced by thermal and cw laser annealing

Thermal and photo-induced annealing was performed on different samples of amorphous silicon. The structural changes were monitored by Raman spectroscopy by means of the frequency shift and change in width of the TO-like phonon band of a-Si. While thermal annealing leads to the expected increase of structural order with temperature, photo-induced annealing shows anomalous behaviour: an increase of disorder with light soaking. This effect is discussed in terms of structural rearrangements of atoms caused by photo-induced electronic transitions.

Laser-induced modification of the critical current in Y-Ba-Cu-O step-edge Josephson junctions

Transport properties of YBa2Cu3O7−x (YBCO) step-edge weak links were measured in the absence and presence of the magnetic fieldB, both before and after the cw-laser annealing. Depending on the laser power density, either an increase (up to 75%) or decrease (up to 100%) of the junction critical currentIc was observed. TheIc(B) characteristics of the laser-treated junctions exhibited about 10% variations of theIc(B) periodicity, indicating permanent changes in the junction barrier and/or adjacent YBCO electrodes.

Raman study of cw laser-induced crystallization of a-Si:H films on quartz and sapphire substrates

A Raman-scattering study of amorphous-to-crystalline transition in a-Si:H films on quartz and sapphire substrates induced by cw laser annealing is reported. The threshold power density for crystallization is much greater for a-Si:H films on sapphire than on quartz substrates. It is determined that crystallization occurs in a-Si:H films on quartz substrates due to a bulk-induced solid phase process. Crystallization in a-Si:H films on sapphire substrates is due to liquid phase epitaxy. It was found that annealing with laser powers significantly greater than the threshold powers causes substantial stresses at the interface.

Combined CW laser and furnace annealing of amorphous Si and Ge in contact with some metals

Abstract Amorphous Si and Ge, subject to mechanical contact with Au, Cu and Ni, have been crystallized under external excitation produced by a CW Ar laser combined with furnace annealing. Compared to simple thermal annealing, a lowering of the crystallization temperature and an increase of the diffusion rate of the metallic components have been observed. By TEM we identified some metastable phases of metal-semiconductor compounds.

A Comparison of Different Techniques for the Rapid Thermal Annealing of Ion Implants in Silicon

ABSTRACTIn this paper, a comparative study is presented of different techniques used for the annealing of arsenic ion implants in silicon. The used techniques are: lamp annealing using a bank of tungsten-halogen lamps, CW laser annealing and conventional furnace annealing. The annealing quality of the implanted layers is evaluated in terms of dopant activation, dopant diffusion and final extended defect states. The furnace annealing combines a good electrical dopant activation with nearly complete annihilation of the a/c dislocation loops, but substantial diffusion of the dopant profile is measured. Laser annealing gives good electrical activation with very low diffusion, but fails in removing end-of-range extended defects. Furthermore, latent electrical active defects of a donor-type are created. The tungsten halogen lamp annealing gives comparable activation and the diffusion is still lower than can be resolved by SIMS measurements, while growth and annihilation of the a/c dislocation loops is present but not yet completed. These experiments are in agreement with theoretical comparison of the different annealing techniques based on the effective (T,t) coordinates of each technique, which favours RTA processes in the high temperature - “seconds” -time range.

Optical Feedback During CW Laser Annealing of Silicon Detected by SEM-EBIC

Optical Feedback During CW Laser Annealing of Silicon Detected by SEM-EBIC

Activation of polysilicon connections by selective CW laser annealing

A new self-aligned procedure has been developed to connect polysilicon links on chip by using a CW argon laser. A silicon nitride mask serves as a diffusion barrier over part of the link during doping of the polysilicon, and later as an antireflection coating to couple the maximum amount of light into the undoped region during laser scanning. The laser melts this region only and dopant atoms rapidly diffuse in from the neighboring parts of the link. For the optimum mask length, 100 percent of the links were open circuits ( >15 MΩ) before irradiation, while the sheet resistivity was reduced to 12 Ω after processing.

Transient‐Enhanced Diffusion during Furnace and Rapid Thermal Annealing of Ion‐Implanted Silicon

A transient‐enhanced diffusion has been observed during the furnace or rapid thermal annealing of ion‐implanted silicon. We have studied this transient in detail and show that, for doses of Group V dopants sufficient to amorphize the silicon, it arises from the trapping of interstitials by dopant atoms during implantation. These are retained during solid‐phase‐epitaxial (SPE) growth, but can be released by additional thermal processing to cause the observed transient and the formation of a band of extended defects. We have measured the enhanced diffusion coefficients and the duration of the transient for Sb‐implanted Si by careful furnace annealing experiments. We obtain general expressions which predict the effects of the transient during any thermal processing based on SPE growth (furnace, CW laser, or rapid thermal annealing). We show that there is no analogous mechanism of vacancy trapping by Group III elements.

A comparative study of laser and furnace annealing of P + implanted CdTe

We have undertaken a comparative study of CW argon ion laser and furnace annealing of P + implanted CdTe. SIMS measurements indicate that laser annealing can produce a noticeable broadening of the impurity profile when increasing the number of annealing pulses. Using a numerical simulation of the diffusion broadening of implanted impurity profiles, we have established that the diffusion coefficient are higher under laser annealing by orders of magnitude compared to furnace annealing ( D LA = 8.94 × 10 -10 cm 2 s -1 at 550°C, D FA = 4.95×10 -15 cm 2 s -1 at 500°C). This result raises the question of photostimulation of impurity diffusion. The electrical activity of the implanted P was estimated from capacitance measurements which give the degree of compensation achieved in n-type In doped material. A maximum acceptor concentration of about (1.6-1.7)×10 17 cm -3 was deduced for both laser and furnace annealed samples. Luminescence spectra of all the samples show the DA band corresponding to the phosphorus acceptor on the Te site. We found that the intensity of the exciton lines exhibited by the laser treated samples is strongest that that observed in the furnace annealed sample. This demonstrates that CW laser annealing is able to remove implantation damage in a better way that furnace annealing.

High-speed ellipsometry of arsenic-implanted Si during cw laser annealing

Ellipsometric study of solid phase epitaxial growth during cw Ar-ion laser annealing in arsenic-implanted Si is reported for the first time. Use of a high-speed microscopic ellipsometer has made it possible to measure growth rates and growth temperature under laser irradiation.

Time-resolved and space-resolved Si lattice-temperature measurements during cw laser annealing of Si on sapphire

We have developed an optical technique for in situ measurement of temporal change and spacial profile of Si lattice temperature during cw laser annealing. This technique utilizes time-dependent optical interference in Si films on insulator. By using a microscope for focusing a laser probe beam to 2.0 μm, time-resolved and space-resolved Si lattice-temperatures were measured below the melting point (1412 °C) on a time scale of 10−4–100 s during cw laser annealing of Si on sapphire.

Substitutional nitrogen impurities in pulsed-laser annealed silicon

Single-crystal Si samples with nitrogen (N) impurities (Si:N) and with N and phosphorus (P) impurities (Si:N:P) have been investigated by electron spin resonance measurements. It was found that substitutional N impurities Ns cannot be incorporated into Si by cw laser annealing of N ion-implanted Si or by N doping during crystal growth; however, Ns is incorporated into Si by pulsed-laser annealing (PLA) of N ion-implanted Si. The spin density of Ns decreases with doping of P shallow donors into PLA Si:N and increases by introduction of slight point defects in PLA Si:N:P. These results suggest that Ns with a negative charge are formed in PLA Si: N:P system.