Silicon Surface Damage Research Articles

Study of surface damage in silicon by irradiation with focused rubidium ions using a cold-atom ion source

Cold-atom ion sources have been developed and commercialized as alternative sources for focused ion beams (FIBs). So far, applications and related research have not been widely reported. In this paper, a prototype rubidium FIB is used to study the irradiation damage of 8.5 keV beam energy Rb+ ions on silicon to examine the suitability of rubidium for nanomachining applications. Transmission electron microscopy combined with energy dispersive x-ray spectroscopy is applied to silicon samples irradiated by different doses of rubidium ions. The experimental results show a duplex damage layer consisting of an outer layer of oxidation without Rb and an inner layer containing Rb mostly at the interface to the underlying Si substrate. The steady-state damage layer is measured to be 23.2(±0.3) nm thick with a rubidium staining level of 7(±1) atomic percentage.

Surface damage and metal-catalyzed chemical etching investigation of multicrystalline silicon by diamond wire sawing

Cutting silicon ingots into silicon wafer is a crucial step in solar cell production process. As a major cutting technique, diamond wire sawing (DWS) has already completely replaced the multi-wire slurry sawing (MWSS). In this work, the essential features of diamond wire cut multicrystalline silicon wafer, behavior of surface damage, formation mechanism, removal of damage layer, and influence of damage layer on making texture surface and performance of solar cells were investigated. Amorphous layer and defects layer are found on the surface of DWS wafer, which restricts the process of making texture. By using metal-catalyzed chemical etching (MCCE) method to make texture surface, the etching rate is faster without damage layer than with damage layer, and the reflectivity can be reduced from 19.08% to 14.79%. After removing the damage layer, the conversion efficiency of solar cell is 17.29%, which is 2.35% higher than that of the cell with the damage layer.

Surface passivation of silicon photonic devices with high surface-to-volume-ratio nanostructures

Recently, a high-speed and high-efficiency silicon photodiode (PD) was demonstrated by enabling light trapping micro/nanostructured holes. While attractive for light manipulation, these high surface-to-volume-ratio nanostructures, which are created by top-down dry etching processes, can also bring other challenges, such as creating silicon surface damage and crystalline defects. To reduce the dark current level and minimize surface recombination, successful passivation is a vital step to achieving the ultimate performance of the silicon PD based on photon-trapping structures. In this paper, we present and compare several effective silicon surface passivation schemes including plasma-enhanced chemical vapor deposited SiO2 and Si3N4, hydrofluoric acid (HF) treatment, thermal oxidation, and low ion energy dry etch. These passivation techniques can reduce the dark current by more than 4 orders of magnitude, bringing it down to the nanoampere level. Among these passivation schemes, HF treatment is relatively simple and cost effective, while other techniques may alter the light trapping characteristics of silicon PDs to some extent, thus affecting their external quantum efficiency. The passivation techniques discussed in this paper are CMOS compatible and can also be applied to other silicon photonic devices, such as photovoltaics.

Main properties of Al2O3 thin films deposited by magnetron sputtering of an Al2O3 ceramic target at different radio-frequency power and argon pressure and their passivation effect on p-type c-Si wafers

In this work, 50-nm thick Al2O3 thin films were deposited at room temperature by magnetron sputtering from an Al2O3 ceramic target at different RF power and argon pressure values. The sputtering technique could be preferred to conventional atomic layer deposition for an industrial application, owing to its simplicity, availability, and higher deposition rate. The resulting thin films were characterized by UV/Vis/NIR spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The deposited Al2O3 material was always highly transparent and amorphous in nature. It was found that the O/Al ratio is higher when the Al2O3 layer is deposited at lower RF power or higher argon pressure. Also, some argon incorporation into the films was observed at low deposition pressure. On the other hand, the performance of the previously characterized Al2O3 thin films in the passivation of 2.25-Ωcm p-type float zone c-Si wafer surfaces was evaluated by the quasi-steady-state photoconductance technique. The best effective carrier lifetime value at one-sun illumination, 0.34ms (corresponding to a surface recombination velocity of 41cm/s), was obtained with the 50-nm Al2O3 deposited at the higher argon pressure studied, 0.67Pa (5.0mTorr), with the lowest RF power studied, 150W (corresponding to a power density of 3.3W/cm2), and after an annealing process, in this case at 350°C for 20min with forming gas. It was assumed that the reduction of the surface passivation quality at higher RF power or lower argon pressure is a consequence of an increased surface damage, and, probably, to a decrease of the O/Al ratio of the Al2O3 passivation material. These assumptions were confirmed with the obtainment of a lifetime of 0.73ms (a surface recombination velocity equal to 19cm/s) with a simple experiment with Al2O3 deposited with progressively varied sputtering conditions started from minimal silicon surface damage conditions: 50W (corresponding to a power density of 1.1W/cm2) and 6.67Pa (50mTorr). Finally, comments about further improvement of the effective lifetime (up to 1.25ms, corresponding to a surface recombination velocity of 11cm/s) with preliminary experiments about the incorporation of an intrinsic hydrogenated amorphous silicon interlayer are included.

Deep boron diffusion induced surface damage in silicon

This paper presents deep boron diffusion induced damages in silicon (100), (110) and (111) surfaces. The silicon (100) and (110) samples showed a broad hump at the higher angle (ω) side during x-ray Rocking curve measurement; whereas, the (111) sample shows an additional broad peak at higher angle side. All the diffused samples showed two distinct contours in reciprocal space mapping measurements. Due to the diffusion process, surface roughness of the silicon samples is found to be increased from 10nm to 110nm, 70nm and 30nm for the silicon (100), (110) and (111) samples respectively.

Frictional Characteristics of Sub-100-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> Borosilicate Glass Balls for Actuator Applications

The frictional characteristics of $\sim 62$ - $\mu \text{m}$ diameter borosilicate glass balls used as rolling elements for a miniature electromagnetic linear actuator were assessed. The glass balls were placed between two silicon plates of the actuator with linear bearing tracks fabricated in the shape of V-grooves on the silicon surface. Rolling friction experiments were conducted using the electromagnetic linear actuator as well as a tribotester. It was shown that the glass balls were effective in generating a low friction coefficient of $\sim 0.01$ over 11 million cycles under a load of 6.6 mN. For the durability test using the tribotester, a relatively high load of 245 mN was applied. In this case, evidence of silicon surface damage could be found. The feasibility of using Au as a solid lubricating film on the silicon surface was investigated. It was found that the friction coefficient and surface damage depended on the thickness of the film, which was varied from $7\sim 20$ nm. It was postulated that the low shear strength of Au aided in reducing the friction coefficient from $\sim 0.017$ to $\sim 0.013$ . With improved adhesion of the Au coating on silicon, the use of sub-100- $\mu \text{m}$ borosilicate glass balls as rolling elements for miniature actuators seems promising. [2015-0170]

Annealing recovery of nanoscale silicon surface damage caused by Ga focused ion beam

Abstracts In this paper, molecular dynamics method with the Tersoff–ZBL combined interatomic potential was adopted to study the dynamics of focused ion beam (FIB) milling and subsequent annealing. The Ga FIB induced damage and its recovery mechanism during subsequent annealing process were investigated in nanoscale time and space. To investigate the nanoscale damage during FIB milling with the ion energy of 0.5 keV, 1 keV and 2 keV, radial distribution function, bond length distribution, bond angle distribution, and common neighbour analysis (CNA) were calculated and analyzed under various ion doses. FIB irradiated silicon substrate with ion dose of 2 × 1014 ions/cm2 was annealed at various annealing temperatures from 1400 K to 2400 K. Molecular dynamics simulation illustrated that as a-Si region was surrounded by c-Si after implantation, the recrystallization lead to a c-Si regrowth processes both from bottom towards top surface and from periphery to centre. The damage area profiles by CNA represented a shortest recovery time of 2.0 ns at 2200 K. Both melting on the top surface and recrystallization at crystalline/amorphous interface have existed as annealing at 2400 K, which is near the melting point. Ga migrated together and moved towards the surface with the a-Si/c-Si interface.

Surface characteristics and damage of monocrystalline silicon induced by wire-EDM

Wire-EDM has recently shown itself as an alternative approach for slicing silicon and other semiconductor materials without the presence of significant chipping as normally found in the traditional machining processes. However, the intensive electrical spark between a wire electrode and silicon can cause damage to the cut surface and subsurface in micro and nano-scale aspects. This paper presents the influence of major process parameters on the cut surface characteristics and damage in the wire-EDMing of silicon. An n-type monocrystalline silicon wafer was cut under different spark energy densities, duty cycles and dielectric flushing rates. Poor cut surface quality and high amount of electrode material deposition were obtained when low spark energy density, small duty cycle and low dielectric flushing rate were applied. Moreover, the amorphous and defective crystal structures of silicon were apparent under the low spark energy condition. The interactions between the wire-EDMing parameters and cut surface characteristics drawn in this study could have significances for the further development of EDM technology towards the fine-scale and damage-free processing of semiconductor materials.

Fabrication of black silicon via reactive ion etching through Cu micromask

Black silicon was fabricated on a pyramid silicon surface via reactive ion etching (RIE) through a Cu micromask formed by a sputtering and annealing process. This adopted RIE technique does not rely on oxygen gas avoiding the silicon surface damage from oxygen plasma. Scanning electron microscopy and an UV–vis-NIR spectrophotometer were used to characterise the morphology and optical reflectance of the prepared samples with porous structures on a pyramid. The results show that the homogeneity of the Cu micromask controlled by the annealing condition determines the reflectance of the textured silicon wafer. A lowest reflectance of 6.2% appears in the samples with sputtered Cu thin film annealed at a temperature of 500°C for 10 min. This work may provide a choice to fabricate black silicon with an excellent light confinement structure, which will have potential application for the improvement of efficiency of silicon solar cells.

Surface Damage of Silicon after Swift Heavy Ion Irradiation

In order to answer the long-standing question, if silicon surfaces can be damaged by swift heavy ions, a set-up to study ion-irradiation damage of reactive surfaces is presented. This set-up allows for the first time to avoid oxidization of the silicone surface during the experimental study. Scanning tunneling microscopy as well as low-energy electron diffraction was used to study the surfaces before and after irradiation. Silicon surfaces were prepared by flash-heating before irradiation with swift heavy ions (Xenon at 0.9 MeV/u). The targets stayed in ultra-high vacuum during preparation, irradiation and surface imaging. No surface damage was detected, at normal as well as at grazing incidence angle.

Surface damage in silicon co-implanted with He and H ions: Effect of H implant energy

Cz n-type Si (100) wafers were singly or sequentially implanted with 160keV He ions at a fluence of 5×1016/cm2 and H ions at a fluence of 1×1016/cm2 with different energies of 40, 110 and 160keV, respectively. Surface damage, defect microstructures as well as H diffusion have been studied. Our results clearly show that depending on H energy, sequential implantation of He and H into Si could induce a series of surface features upon annealing. Localized surface exfoliation with thickness corresponding to H ion range is observed in He and 40 keV H ion co-implanted Si after annealing at temperatures of 600°C and above, while large area exfoliation appears on the 110keV H co-implanted Si surface at a depth close to the He ion range upon high temperature annealing. However, no clear surface damage is found on the post 160keV H implanted and annealed Si. Results from transmission electron microscopy observations reveal that the post H ion implantation at different energies plays quite different role in thermal growth of He-induced micro-defects. The observed surface phenomena have been interpreted based on the defect creation, its evolution as well as H diffusion.

Molecular dynamics simulation of nanoindentaiton on ion-induced damage of silicon surface

Nanoindentation on ion-induced damage of silicon surface was performed using molecular dynamics. The simulation revealed interaction between a ion-induced damage substrate and a indentation. Two types of silicon substrates are used. One is silicon crystal, and another is amorphous silicon which damaged by argon ion bombardment. The initial velocity of the ion bombardment was 3.807×105 m/sec at 30 keV. The computation volume (8.00 nm × 8.00 nm × 17.24 nm) consisted of 57600 Si atoms with Si (100) surface. Each silicon substrate was pressed by the indentation and the force acting on the indentation head were investigated. The force of the ion-induced substrate is smaller than that of the crystalline substrate. Consequently, it turned out that the internal structure of silicon with ion-induced damage can be examined by the force distribution of the indentation.

Patterning of ALD HfO2 Layers on Silicon

A patterning technology for very thin layers of HfO2 layers grown by atomic layer deposition is proposed and evaluated in the case of patterning on silicon. This technology makes use of atomic layer deposited Al2O3 as a buffer layer, thus preventing silicon surface damage during HfO2 dry etching. The final surface roughness of silicon and of the patterned HfO2 layer as measured by AFM indicates that the proposed technology successfully leaves the silicon surface undamaged. The effects of photomasks overlapping have also been evaluated, which have lead to some design rules and buffer layer thickness requirements.

The early stages of silicon surface damage induced by pulsed CO2 laser radiation: an AFM study

The early stages of the surface microstructural modification of silicon, induced by single pulses of CO2 laser irradiation (λ=10.6μm), have been studied, in both vacuum and air, by contact mode AFM. The laser pulse was found to be absorbed at the front surface of the sample, facing the laser; this was shown to be due to the presence of native oxide, which absorbs at this wavelength. We found that this absorption of energy caused the stress-induced formation of vertically oriented, square-shaped fragments, 400–700nm in length, often with short branches, that form a wall around the impact site; they oriented toward the plane of the sample with distance from the impact site, aligning more in the electric field direction of the pulse. In addition, electrically charged, branched fragments were redeposited at the outer extremities of the pulse site.

Bulk Homogeneous Uniaxial Stress Arising from Surface Damage of Crystalline Silicon and Germanium

Abrasion of two opposing surfaces of either crystalline Si or Ge produces a compressive, homogeneous, uniaxial stress extending throughout the bulk perpendicular to the surfaces. This is concluded by analyzing the splittings, intensities, and polarizations of the sharp Lyman absorption lines of bulk shallow impurities in the abraded materials. This effect so far has been observed for samples of thickness, t, from 0.4 to 5 mm for Si ground with water slurries of SiC or alumina with optical faces coplanar with {100} and {111} planes while {100}, {110}, {111}, and {112} planes of Ge have been abraded with SiC in water and examined over the range 0.8 ≤ t ≤ 3.0 mm. For both materials, the internal stress is found to be inversely proportional to t. Controlled etching indicates the damaged layers producing the bulk stress to be < 0.5 μm thick.

Characterization of Si(1 1 1) crystals implanted with Sb + ions and annealed by rapid thermal processing

Monocrystalline Si(1 1 1) targets are implanted (at room temperature) with antimony ions at 120 keV energy to 5×10 14 or 5×10 15 Sb + cm −2 dose. The samples are heat treated by means of rapid thermal processing (RTP) at 1000 °C during 60 s, under nitrogen atmosphere. In this work, we report the measured evolution of the silicon surface damage and the radiation damage recovery in relation to antimony dose and RTP processing. We also study the behavior of antimony dopant into Si(1 1 1) specimens. The investigation is carried out by He + Rutherford backscattering spectrometry (RBS; operating at 1.57 MeV energy in both random and channeling modes), X-ray diffraction (XRD) and atomic force microscopy (AFM) techniques. It is shown that a good surface damage recovery is obtained for all the annealed samples. However, after RTP, a significant loss of antimony has occurred for the specimens which are implanted with 5×10 15 Sb + cm −2 dose. This suggests an antimony out-diffusion. Finally, a good morphological characterization of the specimens is provided by AFM.

Bulk stress due to surface damage of crystalline silicon and germanium

It is found that abrading two opposing surfaces of either crystalline Si or Ge samples results in homogeneous, uniaxial stress throughout the bulk perpendicular to the damaged surfaces. The latter are chosen to coincide with simple crystallographic planes. This conclusion is reached by analyzing the splittings, intensities, and polarizations of the absorption lines of the Lyman series of bulk shallow impurities in the abraded semiconductors. This effect has been observed for samples which range in thickness, t, from 1 to 3 mm, the internal stress being proportional to t−1.

Comparative study of ion implantation caused anomalous surface damage in silicon studied by spectroscopic ellipsometry and Rutherford backscattering spectrometry

Damage created by ion implantation of 150 keV Ne + and 800 keV Ar + ions in single-crystalline silicon was characterized using Spectroscopic Ellipsometry (SE) and Rutherford Backscattering Spectrometry (RBS) in combination with channeling. Results from both methods unambiguously show the presence of a heavily damaged thin layer at the surface that is not predicted by TRIM calculations. The amorphization rate at the surface was found to be proportional to the nuclear energy deposition at the surface. It is demonstrated that SE cross-checked with RBS could be used for quantitative and accurate evaluation of the thickness of the damaged surface layer. The formation of this thin amorphous layer could be attributed to the redistribution of Si interstitials produced by the implantation process from the buried damaged region towards the surface and to a subsequent segregation process (W. Fukarek et al., Nucl. Instr. and Meth. B 127/128 (1997) 879).

単結晶シリコン超精密切削面の微視的構造

Diamond-turned single-crystal silicon surfaces and formed chips were studied by transmission electron microscope (TEM) method. The crystallographic structure of ductile-regime turned surfaces consisted of amorphous material forming a thin surface layer with underlying dislocations generated by the {111} <110> slip systems. Continuous chips were also converted into amorphous material by turning. As depth of cut increased, microcracks were partially formed through the accumulation of excessive dislocations, and consequently brittle fractures occurred. Under these conditions, no continuous chips were obtained. The chips were fragmented and polycrystalline, and contained many crystal defects. At a greater depth of cut, where the material removal mechanism was governed by brittle fracture, the turned surfaces were covered with microcracks, and few dislocations were observed in the damaged layer. Even though the continuous chips had been obtained using a diamond tool with a sharp cutting edge, their structure remained that of single crystal. TEM observations revealed that amorphization and {111} <110> slip deformation are essential in realizing ductile-regime turning of single-crystal silicon.

Local strain in interface: Origin of grain tilting in diamond (001)/silicon (001) heteroepitaxy

Diamond grain tilting, one of the central problems of diamond heteroepitaxy on silicon (001) surface, has been studied by means of atomic-force and high-resolution electron microscopic observations, and by theoretical simulation using the molecular-orbital method. It is shown that, due to interface mismatch-induced local lattice strain and three-dimensional stacking, diamond nucleation in small areas results naturally in grain tilting. For more perfect heteroepitaxy, nucleation with reduced silicon surface damage and over relatively large lateral domains is required.