Boron-doped Single-crystal Silicon Research Articles

Effects of deep subsurface damages on surface nanostructure formation in laser recovery of grinded single-crystal silicon wafers

A nanosecond pulsed Nd:YVO4 laser was irradiated on a boron-doped single-crystal silicon wafer after rough and fine grinding processes to recover the grinding-induced subsurface damages. The surface topography of samples was investigated by using a white-light interferometer, a scanning electron microscope, and an atomic force microscope; while the crystallinity was analyzed by a laser micro-Raman spectrometer. It was found that surface nanostructures were generated by the Mullins-Sekerka instability, which remained on the surface under recoil pressure and surface tension. The rough grinding-induced deep subsurface damages influenced the interface instability between liquid and solid silicon during recrystallization process. By increasing pulse width and decreasing laser peak irradiance, the subsurface damage was recovered and a flat surface with surface roughness of ~1 nm Sa was obtained. This study reveals important correlations among grinding-induced latent subsurface defects, laser peak irradiance and nanoscale surface topography formation in laser recovery, which contributes to high quality silicon wafer manufacturing.

Laser recovery of grinding-induced subsurface damage in the edge and notch of a single-crystal silicon wafer

The edges and notches of silicon wafers are usually machined by diamond grinding, and the grinding-induced subsurface damage causes wafer breakage and particle contamination problems. However, the edge and notch surfaces have large curvature and sharp corners, thus it is difficult to be finished by chemo-mechanical polishing. In this study, a nanosecond pulsed Nd:YAG laser was used to irradiate the edge and notch of a boron-doped single-crystal silicon wafer to recover the grinding-induced subsurface damage. The reflection loss and the change of laser fluence when irradiating a curved surface were considered, and the damage recovery behavior was investigated. The surface roughness, crystallinity, and hardness of the laser recovered region were measured by using white light interferometry, laser micro-Raman spectroscopy, and nanoindentation, respectively. The results showed that after laser irradiation the damaged region was recovered to a single-crystal structure with nanometric surface roughness, and the surface hardness was also improved. This study demonstrates that laser recovery is a promising post-grinding process for improving the surface integrity of the edge and notch of silicon wafers.

Characterization of recrystallized depth and dopant distribution in laser recovery of grinding damage in single-crystal silicon

A nanosecond pulsed Nd:YAG laser was irradiated on a boron-doped single-crystal silicon wafer with a diamond grinding finish to recover the grinding-induced subsurface damage. In order to visualize and measure the depth of the laser melted/recrystallized layer, small-angle beveled polishing was performed in pure water followed by KOH etching. It enabled the direct observation of the recrystallized region using a differential interference microscope and the measurement of its depth using a white light interferometer. Crystallinity analysis of the recrystallized region was carried out by using laser micro-Raman spectroscopy, and the dopant concentration profile was characterized by using radio frequency glow discharge optical emission spectrometry (rf-GD-OES). The results showed that the crystallinity and boron distribution in the recrystallized region changed after laser recovery. The dopant concentration becomes higher at the boundary of the recrystallized region and the bulk. This study demonstrates the possibility of boron concentration control by using suitable laser parameters.

Absolute standard of diffusion length and lifetime of minority charge carriers in single-crystal silicon

A substantial difference in electron recombination cross sections on Fe-B complexes (σ1) and on activated iron ions (σ2) in boron-doped single-crystal silicon is used to independently determine the lifetime of electrons in the standard T st using the surface photo-emf method. Pairs of values of the lifetime T 1 and T 2 before and after the decomposition of the Fe-B complexes were measured for each of 600 ingots at arbitrary diffusion length L cal for the calibrating specimen and were placed on the plane (T 1, T 2). At the boundary of the region filled with the points, ingots are presented that are only contaminated with iron ions, so that T 2/T 1 = σ1/σ2. The true values of L st and T st of the calibrating specimen and the ratio σ1/σ2 = 12.5 ± 0.5 are determined by selecting a new value of the diffusion length for the calibrating specimen, which straightens the boundary of the region filled with the points after the recalculation of the values of T 1 and T 2.

Effect of Selected Ionic Inorganic Surface Contaminants on Thermal Oxidation of p-Type Polished Silicon Wafers

The influence of substrate surface contamination, by selected inorganic ions, on the growth rate of thermal oxide on boron-doped single-crystal silicon wafers in dry oxygen at elevated temperatures is described. Of the contaminating species evaluated, only alkali metal cations and inorganic anions had any influence. Transition metal cations, common contaminants monitored in the manufacture of semiconductor devices from silicon wafers, had no affect on oxide growth rate. Increases in oxide growth rate, up to approximately twice that observed on an uncontaminated reference wafer, were noted for both alkali metal cations and inorganic anions. None of the contaminating species reduced the oxide growth rate. The dependence of oxide growth rate upon surface concentration was observed to be linear for inorganic anions and parabolic for alkali metal cations. The presence of extrinsic gettering on the wafer back surface was found to suppress, to a limited extent, the effect of contamination by only at higher surface concentrations. © 2003 The Electrochemical Society. All rights reserved.

Application of elastic mid-infrared light scattering to the investigation of internal gettering in Czochralski-grown silicon

The influence of the internal gettering process on the large-scale defects in Czochralski-grown boron-doped single-crystal silicon is investigated by low-angle mid-infrared light scattering. The large-scale defects in the as-grown material and crystals subjected to the internal gettering procedure are classified. The applicability of low-angle light scattering in laboratory investigations and in the industrial inspection of the operations in an internal gettering production cycle is demonstrated.

Bent-beam strain sensors

We examine a new class of sensitive and compact passive strain sensors that utilize a pair of narrow bent beams with an apex at their mid-points. The narrow beams amplify and transform deformations caused by residual stress into opposing displacements of the apices, where vernier scales are positioned to quantify the deformation. An analytical method to correlate vernier readings to residual stress is outlined, and its results are corroborated by finite-element modeling. It is shown that tensile and compressive residual stress levels below 10 MPa, corresponding to strains below 6/spl times/10/sup -5/ can be measured in a 1.5-/spl mu/m-thick layer of polysilicon using a pair of beams that are 2 /spl mu/m wide, 200 /spl mu/m long, and bent 0.05 radians (2.86/spl deg/) to the long axis of the device. Experimental data is presented from bent-beam strain sensors that were fabricated from boron-doped single crystal silicon using the dissolved wafer process and from polycrystalline silicon using surface micromachining. Measurements from these devices agree well with those obtained by other methods.

Effect of Boron Doping on the C49 TO C54 Phase Transformation in Ti/Si (100) Bilayers

AbstractWe have demonstrated that the formation of C54 TiSi2 on Boron-doped single crystal silicon substrates, under RTA annealing conditions in a Nitrogen ambient, leads to a thicker TiN capping surface layer, thinner silicide layer, higher C49 to C54 transformation temperature and greater interface roughness compared to C54 TiSi 2 formation on undoped single crystal silicon substrates. Titanium films 32 nm thick were deposited on undoped and boron-doped single crystal silicon substrates. The films were annealed at 3 /C/isn nitrogen to final quenching temperatures between 500 °C and 900 TC. Ex-situ four point probe sheet resistance, cross sectional transmission electron microscopy (XTEM), high resolution transmission electron microscopy (HRTEM) and x-ray diffraction (XRD) were used to analyze the resulting TiN on TiSi2 bilayer. The C49 to C54 transformation occurs circa 760 TC and 810 TC for the undoped and boron-doped cases respectively. HRTEM observations reveal a thick 20 nm TIN layer on the C54 TiSi2 film in the boron-doped case but only fine dispersed TiN particles embedded on the top of the silicide in the undoped case. It was observed that the resultant silicide in the boron-doped case was thinner and the TiSi2 /Si(100) interface is rougher. XRD and TEM analysis show that in the boron doped case, there is a preferred C54 (040) orientation compared to a random orientation for the undoped case.

Aging phenomena in heavily doped (p +) micromachined silicon cantilever beams

Micromachined (100) silicon cantilever beams with and without coating materials have been excited to study their aging process. The center frequency and the full width at half amplitude (FWHA) of the spectra are obtained as a function of time to study internal friction. The dynamic Young's modulus is determined from the resonance frequency of the cantilever beams. In uncoated silicon cantilever beams, the dynamic Young's modulus increases as a function of aging from 129 to 136 GPa in 2 × 10 9 cycles. The Young's modulus in these heavily boron-doped beams is smaller than the Young's modulus in silicon with low doping. In coated cantilever beams, the effective dynamic Young's modulus decreases as function of aging and the amount of this change depends on the coating material, being largest in the Al/Si system. In all the cantilever beams the FWHA increases as a function of time, indicating that the amount of energy dissipated internally increases as the cantilevers age. Also, the observed FWHA values of the resonances in these systems are too large to be caused by thermoelastic effects; microcracks are probably generated as the beams age. This is the first study of aging in micromachined p + heavily boron-doped single-crystal silicon.

Low temperature mechanical properties of boron-doped silicon.

The audio-frequency mechanical properties of oscillators fabricated from boron-doped single-crystal silicon were measured as a function of temperature. The mechanical properties (${\mathit{Q}}^{\mathrm{\ensuremath{-}}1}$ and period) are dominated by the boron impurities and cannot be attributed to glassy defects. We also found the higher strain mechanical response of these crystals to be nonlinear below 0.3 K. The strength of this nonlinearity is related to the boron concentration.

Physical and electrical characterization of in situ boron-doped single-crystal silicon films grown at 450°C using remote plasma-enhanced chemical vapor deposition

The ability to deposit boron-doped homoepitaxial silicon films at very low temperatures (450°C) using remote plasma-enhanced chemical vapor deposition (RPCVD) has been investigated. The boron incorporation efficiency is found to be between 0.2 and 0.4. 100% electrical activation is obtained for an epitaxial silicon film with boron doping of 1 x 10 19 cm −3 deposited at 450°C. The current-voltage characteristics for mesa diodes fabricated on these in situ boron-doped films where the maximum temperature during the entire fabrication process was kept below 450°C indicate an ideality factor of 1.2 and reverse bias leakage current of 320 nA cm −2. Addition of diborane is found to result in the genaration of defects which require increased deposition temperatures compared with undoped films to maintain excellent crystalline quality.

Internal friction measurements in Boron-doped single-crystal silicon

Internal friction measurements, Q −1, of a boron-doped single crystal of silicon at a frequency ω = 2 π × 29.2 kHz showed: (1) results in agreement with the Akhieser mechanism above 100 K; and (2) Q -1 ∝ ω T −1 at temperatures below 10 K.