Redistribution of dopant impurities in oxidizing ambients

The redistribution of dopant impurities in an oxidizing ambient is considered using a new series method. The results obtained are valid for a wide class of oxide growth functions including as special cases the parabolic and linear laws. More importantly, the method copes readily with the practically useful mixed linear-parabolic growth law. The solution retains the flexibility of the related Chen and Chen series and is applicable for a wide range of initial dopant profiles and for different boundary conditions at the oxide-semiconductor interface.As an example of the power of this new technique results are presented for the previously analytically unsolved problem of redistribution from an initial erfc profile, with a segregation type boundary condition, assuming a linear-parabolic growth law. The convergence difficulties of our general series solution have been surmounted by the use of the Euler transformation, providing solutions which are valid for realistic diffusion times. Our analysis permits a comparison with the earlier work of Guckel and Hall on the redistribution from a step profile.     

Redistribution of ion-implanted impurities in silicon during diffusion in oxidizing ambients

A closed form expression for the redistribution of ion-implanted impurities in silicon during diffusion in an oxidizing ambient is derived, based on a theoretical model proposed by Huang and Welliver. It is shown that the computed results for boron profiles agree very well with experimental data. The closed form solution requires considerably less computer execution time than the usual numerical solution.     

Two-dimensional semiconductor analysis using finite-element method

Two-dimensional simulation of semiconductor devices using a finite-element formulation is described. In the present analysis, Poisson's equation is solved by a finite-element method, based on the variational principle, and current continuity equations are solved by a method of weighted residuals. The advantage of this method is mentioned. In order to demonstrate the validity of this method, a bipolar n-p-n transistor is analyzed, considering the generation-recombination term. Not only voltage-current characteristic, but also junction capacitance and cutoff frequency are calculated. Then transistor behavior under inverse mode by using the n-type buried layer as a common emitter is discussed.     

Electronic interaction between impurities in the oxide film and the semiconductor substrate

Electronic interactions between impurities incorporated into the oxide film on silicon (or other semiconductors) and the semiconductor substrate are postulated. The impurities are presumed to change the Fermi level in the oxide, thus causing charge transfer between the oxide and the semiconductor surface. The anodic behavior ofN-type silicon contacting an electrolyte as a function of impurities incorporated into the oxide is suggested as experimental verification of this concept.     

Investigation of a new method for dopant characterization

In microelectronics, the size of the components is continuously decreasing and is now in deep submicron range. Therefore, the dimensions of the implant profile become a major issue. Indeed, a slight fluctuation of the profile could be the origin of detrimental effects of the final properties of the component, such as the increase of the leakage current for instance. The failure analysis at implant level makes it possible to solve problems which have occurred on the production line. It can explain bad properties of the component and consequently increase the reliability of the products manufactured. SCM (Scanning Capacitance Microscopy) and SSRM (Scanning Spreading Resistance Microscopy) are more and more used for dopant visualization. These techniques have some limitations for future devices, which are mainly the spatial resolution and the accessibility of the areas under investigation by the AFM electrical tip. The proposed approach combines chemical delineation and topographic AFM in order to take advantage of the accuracy of the topographic AFM profile measurement on implant delineated regions.     

Benchmarking semiconductor manufacturing performance using apairwise-comparison method

Benchmarking performance against competitors is an increasingly popular activity within the semiconductor industry. Owing to the high variability in manufacturing metrics, a simple monthly metric score is usually insufficient to accurately benchmark performance. However, in the rapidly changing semiconductor world, data which are one to two years old may be irrelevant to the current situation. We propose a simple ranking method based on a method of paired-comparisons for unbalanced data which gives a good ranking and is also reliable under fluctuations in the data. Using semiconductor manufacturing performance data from the Competitive Semiconductor Manufacturing Study at the University of California at Berkeley, we give an example of this method and compare its reliability and accuracy against other techniques through simulations     

Redistribution of deep selenium and sulfur impurities in silicon upon surface doping with phosphorus

The study is concerned with the effect of short-term high-temperature heating on Si:Se and Si:S samples, whose surface layers are doped with phosphorus to high concentrations. It is found that the resistivity of the wafers substantially increases deep in the bulk within up to ～10 μm. The experimental data suggest that this effect is due to enhanced diffusion of chalcogen in the presence of the phosphorus-doped surface region. The mechanism of the effect is the injection of nonequilibrium interstitial silicon atoms from the layer heavily doped with phosphorus to the bulk of the sample. This results in a shift of the equilibrium between the concentrations of substitutional and interstitial impurity atoms towards higher concentrations of interstitials and, as a consequence, towards the increase in the relative content of the fast-diffusing interstitial component of the impurity.     

Formation of Boron‐doped region using spin‐on dopant: investigation on the impact of metallic impurities

Investigation on the electrical properties of p⁺‐doped regions formed by spin‐on‐dopant (SOD) technique was achieved. Using this technique, boron‐diffused regions were formed on both p‐type and n‐type float zone wafers. Homogeneous sheet resistances were obtained for both types of wafers. Bulk properties were investigated by measuring effective carrier lifetime. An iron contamination was observed after the boron diffusion step and interstitial iron concentrations were deduced from lifetime measurements. More investigations proved that the iron was initially present within the SOD film. A phosphorus diffusion allows to remove this bulk contamination, leading to an improvement of effective lifetime values. Nevertheless, the corresponding emitter saturation current density was estimated on n‐type wafers and presented a high value. It is likely that this poor electrical quality is the consequence of a high iron concentration which remains in the diffused region. Some possibilities are suggested to avoid or to limit this contamination. Copyright © 2008 John Wiley & Sons, Ltd.     

Drag current for ionization of impurities by an electromagnetic wave in a semiconductor superlattice

The drag current for ionization of a shallow impurity by a strong electromagnetic wave in a semiconductor superlattice is found. It is shown that at low temperatures, when it is possible to ignore the equilibrium carrier density, the dependence of the drag current on the intensity of the electromagnetic wave is nonlinear and it oscillates with growth of the intensity of the electromagnetic field. These oscillations are a consequence of the many-photon character of absorption of the electromagnetic wave by the impurities and also of nonparabolicity of the energy spectrum of the superlattice. A comparison is made of the contributions to the drag current from the anisotropic part of the impurity ionization probability and from its isotropic part, with allowance for modification of the distribution function by the electromagnetic wave. It is found that for (Δ is the width of the conduction miniband) the main contribution to the drag current comes from the isotropic part of the ionization probability. Fiz. Tekh. Poluprovodn. 33, 1443–1446 (December 1999)     

Low frequency noise measurements as a tool to analyze deep-level impurities in semiconductor devices

An analysis method to extract the pertinent trap parameters of impurities, i.e. energy level, trap density, spin degeneracy and capture cross section, from low-frequency noise measurements is discussed. This method, which is based on the model of traps interacting independently with the conduction band, is applied to generation recombination noise spectra measured on planar n⁺-n-n⁺ Si resistors as a function of temperature, and the trap parameters are obtained. Since the analysis method makes use of some assumptions, its validity is verified by using obtained trap parameters as input for an exact multilevel computer simulation program. This program generates zero-frequency plateau levels and characteristic times in good agreement with the measured data, indicating that the assumptions were warranted. In addition, an alternative explanation of the noise data in terms of a double-donor model is studied. However, no conclusive evidence was found in favor of either one of the two models since both models explained the experimental findings within the experimental errors.     

Statistical fluctuations of dopant impurities in ion-implanted bipolar transistor structures and the minimum device dimensions for vlsi system reliability

The minimum dimensions of bipolar transistors with ion implanted impurity profiles for predictable device and system behavior is calculated on the basis of limitations arising from the random positions of the implanted impurities. Doubly-stochastic effects arising from uncertainty in exact implantation parameters are included, and are shown to be of first order importance in the specification of minimum size for a given chip yield. For example, a ± 10% uncertainty in the standard deviation of one of the implants has been found to increase the minimum dimension by approximately a factor of 4. For a chip yield of 99% against this limitation, the minimum emitter size is of the order of 1 ? L ? 5 μm when a straight-forward scaling theory is applied to dimensions and impurity concentrations from present device designs and a parity check on a bit word is applied.     

Beam expanding fiber using thermal diffusion of the dopant

A beam-expanding fiber (BEF) for embedding optical devices has been fabricated by utilizing thermally induced Ge diffusion in silica single-mode fibers (SMFs). The preparation of fiber samples and their heat treatment is described, and the effect of heat on Ge dopant distribution and diffusion is discussed. Modal-intensity distributions were studied and found to confirm the broadening of the modal field distribution after heat treatment of the fiber. Localized heat treatment to obtain BEFs is considered, and device characteristics are discussed. The BEF can arbitrarily change the spot size of a propagating mode without changing the normalized frequency     

Photodisplacement microscopy using a semiconductor laser

A photodisplacement microscope has been realised, using a modulated semiconductor laser as the heating source and a phase sensitive HeNe laser probe for detection. Experimental results indicate that the instrument can have a wide range of applicability, including problems in nondestructive examination.     

A method for modulation of the charge-carrier mobility in a semiconductor

A new method for modulating the mobility of the majority and minority charge carriers in silicon was studied. It is shown that, under the effect of local avalanche breakdown of a p-n junction, the charge-carrier mobility in the bulk of the semiconductor increases or decreases, depending on the orientation of the p-n junction subjected to breakdown in relation to the direction of motion of the charge carriers.     

Two-dimensional dopant profiling in semiconductor devices by electron holography and chemical etching delineation techniques with the same specimen

The electron holography and chemical etching delineation techniques were successfully employed to assess two-dimensional (2D) dopant profiles in semiconductor devices. The results obtained from both techniques with the same specimen were precisely compared and discussed in order to evaluate the performance limits of these techniques. It was demonstrated that both techniques are very effective in obtaining reliable 2D dopant profiles in nanodevice.     

Model conversions of uncertain linear systems using a scaling and squaring geometric series method

This paper proposes a scaling and squaring geometric series method along with the inverse-geometric series method for finding discrete-time (continuous-time) structured uncertain linear models from continuous-time (discrete-time) structured uncertain linear systems. The above methods allow the use of well-developed theorems and algorithms in the discrete-time (continuous-time) domain to indirectly solve the continuous-time (discretetime) domain problems. Moreover, these methods enhance the flexibility in modeling and control of a hybrid composite system. It has been shown that the commonly used bilinear approximation model is a specific class of the proposed geometric series model.     

Volterra series analysis of semiconductor laser diode

Theoretical models for laser nonlinearities are analyzed. Volterra transfer function G/sub n/ are calculated from the laser rate equations using an output-to-input approach. Nonlinear models for second-harmonic, third-harmonic, and two-tone third-order intermodulation distortions are calculated from G/sub n/. The transfer function-based models are simplified and a new equation for intermodulation distortion is developed. Comparisons with previous results are presented. It is suggested that this analytical technique offers a valuable tool for the performance analysis of future broadband optical communication systems.<>