Spreading Resistance Probe Measurements Research Articles

Measuring doping profiles of silicon detectors with a custom-designed probe station

Silicon detectors are often used in High Energy Physics (HEP) experiments as tracking and vertexing devices. Many scientific institutes are equipped with setups able to electrically characterize those detectors e.g. for quality assurance reasons. Such probe stations can be easily extended to measure resistivities and doping profiles in the bulk material and in doped regions by using the Spreading Resistance Probe (SRP) technique. After an introduction to the method, this paper describes how an existing probe station, that has been used for electrical measurements on strip detectors, has been modified to perform SRP measurements. The presented results prove that the method is reliable and capable of characterizing doping regions as thin as one micron. Beside profiling implants, SRP measurements have the potential to deliver the basis for investigations of bulk material defects in heavily irradiated samples.

Dopant profiles in silicon created by MeV hydrogen implantation: Influence of annealing parameters

AbstractDopant profiles created by MeV proton implantation in float zone and Czochralski silicon are examined with spreading resistance probe measurements after annealing in the temperature range of 300–500 °C. For the description of the profile shape, two species are used, one being the implanted and mobile hydrogen and the other being an immobile irradiation induced point defect complex. The diffusion of the implanted hydrogen through the radiation damaged layer is found to be of great relevance for the resulting depth distribution of the hydrogen related donors. An effective diffusion coefficient is given for implantation into float zone silicon. Furthermore, the profile shape varies significantly with the annealing temperature. It is proposed that two donor species are generated which each exhibit a different thermal stability, and that these two species have individual depth distributions. Profiles created in Czochralski silicon seem to be additionally affected by an enhanced generation of oxygen thermal donor species. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Porous silicon as an internal reflector in thin epitaxial solar cells

AbstractThin film epitaxial silicon solar cells are considered a near future alternative to bulk silicon solar cells. However due to the limited thickness of the active layer they require efficient light trapping. Therefore we propose the development and implementation of such light confinement by means of a porous silicon (PS) intermediate reflector at the epi/substrate interface. The formation of the reflector is done by electrochemical etching of a highly doped Si substrate into a multilayer stack (Bragg‐optical reflector), and is followed by epitaxial deposition of the active layer. The implementation of the PS reflector however requires detailed analysis of many problematic issues, foremost the optical optimisation of the stack for internal reflection at the Si/PS/Si interface. Other topics include the pore rearrangement during high‐temperature CVD as well as the quality of the epitaxial layer grown on porous silicon. Another challenge is the resistance within the PS layers. For that purpose, SRP (Spreading Resistance Probe) and resistance measurements were performed to determine the conductive properties of rearranged PS. First cells with a 9‐layer porous silicon reflector gave a very promising efficiency of 13.5% which is 1.5% higher compared to cells without internal reflector. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Enhanced formation of oxygen-related thermal donors in Ge crystals exposed to hydrogen plasma

Enhanced thermal donor (TD) formation and oxygen diffusion in silicon exposed to hydrogen plasma are well known and have been widely studied. Similar phenomena are expected to occur in oxygen-rich Ge crystals as well, but they have not been studied in detail yet. In this work the effects of hydrogenation in H +-plasma on the TD formation in Ge are investigated. Both oxygen-rich and oxygen-lean Ge crystals of n- and p-type conductivity were used. The samples were treated in dc H +-plasma in the temperature range 200–350 °C for different durations. The TD depth profiles were obtained by spreading resistance probe measurements on the angle-lapped surfaces of the samples. In oxygen-rich Ge crystals an enhanced formation of TDs has been found to occur upon hydrogenation as well as upon subsequent annealing at 350 °C deeply in the bulk up to depth of about 1 mm. The depth distribution of the TDs formed in enhanced way depends on the hydrogenation procedure as well as on the conditions of the subsequent heat-treatments. A possibility of the deep p–n-junction formation by H +-plasma treatment of the oxygen-rich Ge crystals has been demonstrated. An enhancement factor of the TD formation is estimated and a comparison with similar phenomena in silicon has been carried out.

Suppression of hydrogen diffusion at the hydrogen-induced platelets in p-type Czochralski silicon

Hydrogen diffusion in p-type Czochralski silicon is investigated by combined Raman spectroscope, scanning electron microscope, and spreading resistance probe measurements. Exposure of silicon wafers to rf hydrogen plasma results in the formation of platelets. The increase of hydrogenation duration leads to the growth of the platelets and the reduction of the hydrogen diffusivity. The large platelets grow faster than the small ones. The growth of the platelets is based on the capture of hydrogen. The dependence of the hydrogen diffusivity upon the average size of the platelets suggests that the indiffusion of hydrogen is suppressed by the platelets.

Hydrogen diffusion at moderate temperatures in p-type Czochralski silicon

In plasma-hydrogenated p-type Czochralski silicon, rapid thermal donor (TD) formation is achieved, resulting from the catalytic support of hydrogen. The n-type counter doping by TD leads to a p-n junction formation. A simple method for the indirect determination of the diffusivity of hydrogen via applying the spreading resistance probe measurements is presented. Hydrogen diffusion in silicon during both plasma hydrogenation and post-hydrogenation annealing is investigated. The impact of the hydrogenation duration, annealing temperature, and resistivity of the silicon wafers on the hydrogen diffusion is discussed. Diffusivities of hydrogen are determined in the temperature range 270–450°C. The activation energy for the hydrogen diffusion is deduced to be 1.23eV. The diffusion of hydrogen is interpreted within the framework of a trap-limited diffusion mechanism. Oxygen and hydrogen are found to be the main traps.

Boron-enhanced diffusion in excimer laser annealed Si

The effect of excimer laser annealing (ELA) and rapid thermal annealing (RTA) on B redistribution in B-implanted Si has been studied by secondary ion mass spectrometry (SIMS) and spreading resistance probe (SRP). B has been implanted with an energy of 1 keV and a dose of 10 16 cm −2 forming a distribution with a width of 20–30 nm and a peak concentration of ∼5 × 10 21 cm −3. It has been found that ELA with 10 pulses of the energy density of 850 mJ/cm 2 results in a uniform B distribution over the ELA-molten region with an abrupt profile edge. SRP measurements demonstrate good activation of the implanted B after ELA, with the concentration of the activated fraction (∼10 21 cm −3) exceeding the solid solubility level. RTA (30 s at 1100 °C) of the as-implanted and ELA-treated samples leads to a diffusion of B with diffusivities exceeding the equilibrium one and the enhancement is similar for both of the samples. It is also found that RTA decreases the activated B in the ELA-treated sample to the solid solubility limit (2 × 10 20 cm −3). The similarity of the B diffusivity for the as-implanted and ELA-treated samples suggests that the enhancement of the B diffusivity is due to the so-called boron-enhanced diffusion (BED). Possible mechanisms of BED are discussed.

Excimer laser annealing of shallow As and B doped layers

Excimer laser annealing (ELA) of As-, B- and BF 2-implanted Si has been studied by secondary ion mass spectrometry (SIMS), spreading resistance probe (SRP) and transmission electron microscopy (TEM). The implantations have been performed in the energy range from 1 to 30 keV with doses of 10 15–10 16 cm −2. ELA has been carried out with the energy densities in the range of 600–1200 mJ/cm 2 and the number of laser pulses from 1 to 10. It is shown that ELA results in a more uniform dopant distribution over the doped region with a more abrupt profile edge as compared to those after rapid thermal annealing (RTA). Besides, in contrast to RTA, ELA demonstrates a highly confined annealing effect, where the distribution of dopants below the melting region is not affected. SRP measurements demonstrate almost complete activation of the implanted dopants after ELA, and TEM does not reveal extended defects in the ELA-treated samples. The depth of the doped layers, abruptness of the profiles and the total doping dose as a function of ELA energy density and number of laser pulses are investigated. Computer simulations of ELA show a good agreement with the experimental data.

Direct Electrical Characterization of Metal Induced Lateral Crystallization Regions by Spreading Resistance Probe Measurements

AbstractMaterial characterization of metal induced lateral crystallization (MILC) process of amorphous silicon (a-Si) has been performed by using the spreading resistance probe (SRP) measurements. It was found that carrier mobility in boron ion implanted layer, formed in MILC region, is up to 65 % in comparison with mobility in boron ion implanted layer, formed in single crystalline silicon. It was also observed in this work that prolongation of MILC process from 1 hour to 2 hours had induced the increasing of mobility from 24 cm2/Vs to 34 cm2/Vs.

Impact of probe penetration on the electrical characterization of sub-50 nm profiles

The spreading resistance probe (SRP) and four point probe (FPP) use, respectively, two or four metal probes with loads in the range of 5–100 g to obtain indispensable information on the electrical characteristics (sheet resistance, junction depth, activation degree, profile shape) of impurity depth profiles in silicon. Recently, however, it has been reported that FPP sheet values are becoming irreproducible and that SRP depth profiles can be significantly shallower than the corresponding secondary ion mass spectrometry dopant profiles for ultrashallow structures. In this work we analyze the impact of probe penetration on the accuracy of SRP and FPP measurements for a series of sub-50 nm profiles with different steepness and substrate level. The probe penetration has been measured by atomic force microscopy and ranged from 5 to 130 nm. The FPP sheet resistance errors of up to 300%, as found for the higher loads, can be correlated with the penetration of the probes through the electrical junction taking into account material removal effects. Experimental data and simulations indicate that SRP raw data are relatively insensitive to probe penetration for source/drain implantation and diffusion profiles. Dependent on the structure involved, however, the SRP depth scale must be corrected for an offset due to probe penetration.

Porous silicon patterned by hydrogen ion implantation

This work presents some results on a new combination of process techniques in order to obtain patterning for porous silicon (PS) formation over silicon wafers aiming at integrated optical applications. Patterning is obtained by blocking PS formation on selective areas with a high resistivity buried layer as mask. This high resistivity layer is formed by hydrogen ion implantation and adequate annealing. Spreading resistance probe measurements showed a higher resistivity than 1E5 Ω cm for ion implanted layer. Structures obtained are examined by optical and scanning electron microscopy. Optical properties of PS are characterised by Raman spectroscopy. The results show the feasibility of the proposed process sequence and the preservation of PS optical properties.

Influence of the substrate doping level on spreading resistance profiling

A study has been performed of spreading resistance probe measurements on a series of 200-nm-deep boron implants into p-type substrates with varying doping levels ranging from 3×1014 up to 4×1017/cm3. All implants were performed under the same conditions and with the same dose. However, routinely generated spreading resistance carrier profiles from different sites consistently indicate abnormally high doses and shoulder peak artifacts at the back side of the implant profile for the more highly doped substrates. It is proposed that these artifacts can be related to pressure-enhanced carrier spilling effects underneath the probes. When performing a Laplace-based correction and hence neglecting any carrier spilling effects, the correction factor scheme reacts upon the position of the on-bevel junction position instead of on the vertical junction position which can be considerably deeper in the presence of pressure-enhanced spilling. The observed artifacts can be reduced within Laplace calculations by allowing for more barrier resistance and consequently a larger contact radius.

Depth Profiles for Hydrogen‐Enhanced Thermal Donor Formation in Silicon: Spreading Resistance Probe Measurements

Hydrogen enhancement of formation rates for oxygen‐related thermal donors in Si has been investigated for dependence on: the source of hydrogen, hydrogen isotope, and exposure time and temperature. Hydrogen injection efficiency is an important variable and depth profiles are dependent upon the surface preparation of samples exposed in an electron cyclotron resonance plasma where ion energies are ≤35 eV. Formation rates up to at 400°C have been observed. A sublinear dependence of the donor formation rate on beam current under 50 keV ion implantation is interpreted as a competition between oxygen‐hydrogen and hydrogen‐hydrogen interactions. Dependence on isotope mass and on exposure time in the plasma indicates hydrogen is the diffusing species that determines the penetration depth for the enhanced donor formation. Peculiar box‐like depth profiles and high formation rates near the advancing front produced in RF plasma exposures are suggestive of hydrogen accumulation near the advancing front. The temperature dependence for the penetration depth gives an activation energy of . This energy is attributed to trap‐limited diffusion wherein hydrogen lowers the energy barrier for the oxygen motion necessary to form thermal donors.

Enhancement of gold solubility in silicon wafers

Edge-defined film-fed grown silicon wafers with a thin Au film deposited on one side were annealed at 950 °C for various times. Spreading resistance probe measurements showed that at the wafer free surface the Au concentration was higher than the Au solubility in silicon found at the Au source side. Scanning electron microscopy, transmission electron microscopy, and energy-dispersive spectroscopy investigations revealed Au particles of nanometer size at the wafer free surface. The enhancement of the Au solubility at the wafer free surface is attributed to the existence of these small Au particles.

Hydrogen-accelerated thermal donor formation in Czochralski silicon

Acceleration of thermal donor formation at 400 °C in Czochralski Si by a hydrogen plasma has been observed using low-temperature infrared absorption and spreading resistance probe measurements. The accelerated formation in as-grown Si is attributed to hydrogen diffusion and catalyzed conversion of electrically inactive nuclei to thermal donors. When the nuclei concentration is small such as in rapid thermal annealed Si, hydrogen interaction at SiO bonds is suggested as the rate-limiting step in thermal donor formation.

The annealing of MeV energy boron ions implanted into silicon

P + -Type buried layers of boron in silicon samples have been made by implanting boron ions of 1–3 MeV energy at doses of 1 × 10 13 −5 × 10 15 cm −2. Different annealing conditions have been investigated mainly through automatic spreading resistance probe measurements, MOS structure C-V electrical properties measurements and TEM and TED observations. It is found that not only good implanted buried layers but also good top crystalline layers were formed, and the annealing of the deep implanted layers is effective by making use of the enhanced annealing effect of double implantation. This discovery of enhanced annealing of double implantation is very useful for new applications of high energy ion implantation.

Anomalies of antimony distribution within thin N/N + epitaxial layers of silicon

This paper deals with the distribution of antimony within thin silicon epitaxial layers obtained by pyrolysis of monosilane without any intentionally added dopants. The results of spreading resistance probe measurements revealed some anomalies in the antimony concentration profile within the layers. The nature of these anomalies is discussed.

Effect of the Surface Quality on the Spreading Resistance Probe Measurements

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