Resolution Secondary Ion Mass Spectrometry Research Articles

Structural and electrical properties of p+n junctions in Si by low energy Ga+ implantation

Ultrashallow p+n junctions have been formed in silicon by low energy (5.5 keV) Ga+ implantation into n-type substrates. This avoids the use implantation of molecular species such as BF2+ or preamorphization with Ge+ or Si+, which degrade the integrity of p+n junctions in metastably strained SixGe1−x layers. High resolution secondary ion mass spectroscopy measurements indicate an implant peak at less than 10 nm, except for postanneal temperatures above 800 °C, for which severe loss of profile control was observed. Electrical characteristics of the implanted junctions were determined from diode current–voltage measurements and Hall data. At low anneal temperatures, these showed good rectification behavior, with an ideality factor of 1.1±0.1 and a reverse bias leakage of ≈3 μA cm−2 in a relatively large junction area of 5×10−2 cm2. The electrical properties of the p+n junctions were found to be sensitive to implant dose, improving with increasing dose. At 580 °C, implant doses were achieved that were completely activated at levels above previously published Ga equilibrium solubility data. For temperatures of 800 °C, reverse annealing occurred, observed as a reduction in carrier concentration with increasing anneal time and severe profile broadening.

Synthesis and electron field emission of nanocrystalline diamond thin films grown from N2/CH4 microwave plasmas

Nanocrystalline diamond films have been synthesized by microwave plasma enhanced chemical vapor deposition using N2/CH4 as the reactant gas without additional H2. The nanocrystalline diamond phase has been identified by x-ray diffraction and transmission electron microscopy analyses. High resolution secondary ion mass spectroscopy has been employed to measure incorporated nitrogen concentrations up to 8×1020 atoms/cm3. Electron field emission measurements give an onset field as low as 3.2 V/μm. The effect of the incorporated nitrogen on the field emission characteristics of the nanocrystalline films is discussed.

Repeatability of Si concentration measurements in Si-doped GaN films

In high mass resolution secondary ion mass spectrometry Cs+ depth profile measurements of Si in GaN films, the secondary ion intensity ratio of Si-28 to the matrix Ga-69 signal has been observed to be poorly repeatable from measurement to measurement. In some cases the Ga-69 signals from adjacent areas showed different intensity levels even though the Si-28 intensities were similar. Variation of the Ga-69 matrix signal from run to run creates a large uncertainty in the determination of the Si concentration in a GaN film when a relative sensitivity factor is used. The changes in Ga-69 intensity from repeat measurements have been determined to be affected by the instrument vacuum condition, ion energy distribution, sample charging, and type of sample holder used in the measurement.

Transient phenomena and impurity relocation in SIMS depth profiling using oxygen bombardment: pursuing the physics to interpret the data

High detection sensitivity in bulk analysis or depth profiling by secondary ion mass spectrometry (SIMS) can only be achieved, for positively charged ions, if the nearsurface regions of the sputter eroded sample are fully oxidized. Using oxygen primary ions, a stationary oxidation state is established after some time of bombardment during which period the sputtering yield decreases and the ionization probability increases. The physical and chemical processes occurring during the transient period are reviewed with emphasis on the results for impurity analysis in silicon, i.e. the matrix material that has been studied most thoroughly in the past. The transient decrease in sputtering yield gives rise to a depth scale offset and an associated apparent shift of impurity profiles towards the surface. The effect is largest at normal beam incidence, ca. 1 nm /keV (O + 2 ), in which case silicon is fully oxidized. The transition depth, i.e. the depth sputtered before achieving a stable ion yield is about twice as large and increases as the impact angle is turned away from normal. The shift and the depth scale offset can be measured safely using thin (delta) layers of isotopically pure tracers, for example 30 Si in 28 Si. Boron delta layers can serve as secondary standards because this impurity behaves almost the same as the host silicon atoms. The profile shift observed with other common dopants may contain contributions due to unidirectional relocation, often driven by segregation away from the surface. At O + 2 energies below about 0.7 keV the transition depths fall below the thickness of typical native oxides, so that the transient changes in sputtering yield and ionization probability can disappear. The transient phenomena may be described by a simple sputtering-oxidation model that connects the depth scale offset to other observable parameters like the initial and final sputtering yield, the transition fluence and the oxide thickness.

Growth of fully doped Hg1−xCdxTe heterostructures using a novel iodine doping source to achieve improved device performance at elevated temperatures

Band gap engineered Hg1−xCdxTe (MCT) heterostructures should lead to detectors with improved electro-optic and radiometric performance at elevated operating temperatures. Growth of such structures was accomplished using metalorganic vapor phase epitaxy (MOVPE). Acceptor doping with arsenic (As), using phenylarsine (PhAsH2), demonstrated 100% activation and reproducible control over a wide range of concentrations (1 × 1015 to 3.5 × 1017 cm−3). Although vapor from elemental iodine showed the suitability of iodine as a donor in MC.T, problems arose while controlling low donor concentrations. Initial studies using ethyliodide (EtI) demonstrated that this source could be used successfully to dope MCT, yielding the properties required for stable heterostructure devices, i.e. ≈100% activation, no memory problems and low diffusion coefficient. Cryogenic alkyl cooling or very high dilution factors were required to achieve the concentrations needed for donor doping below ≈1016cm−3 due to the high vapor pressure of the alkyl. A study of an alternative organic iodide source, 2-methylpropyliodide (2 MePrI), which has a much lower vapor pressure, improved control of low donor concentrations. 2 MePrI demonstrated the same donor source suitability as EtI and was used to control iodine concentrations from ≈ 1 × 1015 to 5 × 1017cm−3. The iodine from both sources only incorporated during the CdTe cycles of the interdiffused multilayer process (IMP) in a similar manner to both elemental iodine and As from PhAsH2. High resolution secondary ion mass spectroscopy analysis showed that IMP scale modulations can still be identified after growth. The magnitude of these oscillations is consistent with a diffusion coefficient of≈7 × 10−16cm2s−1 for iodine in MC.T at 365°C. Extrinsically doped device heterostructures, grown using 2 MePrI, have been intended to operate at elevated temperatures either for long wavelength (8–12 smm) equilibrium operation at 145K or nonequilibrium operation at 190 and 295K in both the 3–5 µ and 8–12 µ wavelength ranges. Characterization of such device structures will be discussed. Linear arrays of mesa devices have been fabricated in these layers. Medium wave nonequilibrium device structures have demonstrated high quantum efficiencies and R0A = 37 Ωcm2 for λco = 4.9 µ at 190K.

Can carbon-implanted silicon be applied as wide-bandgap emitter?

We examine the formation of Si1-xCx (x = 0.04–0.2) by means of CFy (y = 0,1,3) implantation in p-type Si, for application as a wide-bandgap emitter in a Si heterojunc-tion bipolar transistor. Upon implantation with 2.5 × 1016 CF+/cm2 at 45 keV, and subsequently with 2.5 × 1016 C+/cm2 at 30 keV, an amorphous top layer is formed. Annealing at temperatures up to 900 °C leads to a layer consisting of nanocrystalline material. High resolution transmission electron microscopy and secondary ion mass spectrometry show that a well-defined nanocrystalline/crystalline interface is created at an anneal temperature of 550 °C. At higher temperatures lattice defects start to develop. Preliminary attempts to dope the material via phosphorus or arsenic implantation indicate that temperatures of at least 900 °C are required to activate a fraction of the implanted dopants. This, however, adversely affects the adlayer/substrate interface.

Characterization of B and Sb delta-doping profiles in Si and Si1−xGex alloys grown by molecular-beam epitaxy

Boron and antimony deltalike doping spikes in Si and Si1−xGex layers with x=0 to x=0.25 deposited by molecular-beam epitaxy (MBE) have been investigated as candidates for p and n delta- doping MBE technology. They were characterized by high depth resolution secondary ion mass spectrometry (IMS) measureements using oxygen and cesium primary ion beams in the energy range from 2 to 12 keV and by high depth resolution spreading resistance measurements. Deltalike doping profiles with a full width at half-maximum of less than 2.7 and 3 nm have been measured by SIMS for Sb and B, respectively, with corresponding upward slopes of 0.4 and 1 nm. For Si1−xGex growth segregation effects, the electrical activity of B decreases with increasing Ge content, and the steepness of the B spikes increases. The behavior of B spikes during annealing is investigated.

Secondary ion mass spectroscopy ultrashallow depth profiling for Si/Si1−xGex/Si heterojunction bipolar transistors

Starting from a theoretical dopant and composition profile of a Si/Si1−xGex/Si heterojunction bipolar transistor (HBT), the requirements for high depth resolution secondary ion mass spectroscopy (SIMS) measurements are discussed. To characterize the boron out-diffusion from the Si1−xGex base, which can crucially degrade the transit frequency fT, a depth resolution of better than about 3 nm is necessary. SIMS measurements have been performed using low energy oxygen primary beams at normal incidence to characterize sharp B profiles in Si and Si1−xGex layers. Graded Ge concentrations have been measured quantitatively using cesium primary beams and MCs+ secondary ion detection. It is shown that in the limit of low energy primary beams, the leading edges of the SIMS profiles with upslopes of 1–2 nm/decade show sufficient resolution for many of the HBT applications. For better characterization of effects which are located on the trailing edge of the profile, deconvolution procedures are necessary.

Oxidation mechanisms of β-NiAl + Zr determined by SIMS

The oxidation mechanisms of single crystal Zr-doped β-NiAl from 800 to 1200 °C were determined using primarily secondary ion mass spectrometry (SIMS) imaging and depth profiling. High spatial resolution SIMS imaging provides a means for critically assessing the effects of diffusion through the boundaries of the various morphologies of α-Al 2O 3 scales that form on β-NiAl. Transient oxidation occurs by outward Al diffusion through transition Al 2O 3 scales, θ-Al 2O 3 in this case, for temperatures from 800 to 1100 °C. Steady-state oxidation occurs by counter-diffusion of oxygen inward and both Al and Zr outward through boundaries in the α-Al 2O 3 ridge morphology.

A newly developed chemical bevelling technique used for depth independent high depth resolution SIMS analysis

A newly developed chemical bevelling technique has been used to produce bevelled samples for secondary ion mass spectrometry (SIMS) studies. A linear bevel with an abrupt surface/bevel interface was produced for the first time in chemical bevelling by adding a layer of oil on top of NH 4OH H 2O 2 etching solution. A series of bevel magnifications ranging from 5 × 10 2to 6 × 10 3 were obtained by changing the concentration of the etching solution. Al ion implanted GaAs and Al 0.3Ga 0.7As GaAs multi- quantum well samples were chemically bevelled and investigated using SIMS linescan profiling. A typical Al implant linescan profile was obtained and its accuracy was comparable to that achieved by depth profiling. Results from Al 0.3Ga 0.7As GaAs MQWs showed a high depth resolution of 3.1 nm retainable through the structure to at least 1.6 μm beneath the original surface. The relationship between depth resolution and the ion beam energy was studied.

Surface segregation of boron atoms in Si and strained Si1−xGex layers during MBE growth: experiment and simulation

Boron segregation from submonolayer interfacial B deposition during molecular beam epitaxy (MBE) growth of Si1−xGex and Si layers in the temperature range 350–800 °C has been investigated by high resolution secondary ion mass spectroscopy and modeled by an atomistic description as a function of growth temperature and alloy composition.In the case of Si-MBE, beginning at 550 °C segregation-induced profile broadening occurs and at 600 C kinks appear in the boron profiles developing into shoulders for higher growth temperatures. At temperatures above 700 °C at the shoulder a concentration of (1–2) × 1019 cm−3 was found. For Si1−xGex growth the segregation is significantly reduced and a decay length of 0.6-0.8 nm can be obtained in the range 350–450 °C.From a fit of the B-profile between 450 °C and 600 °C we obtained a kinetic barrier for a jump to the surface state of approximately 2.1 eV and a Gibbsian heat of segregation of 0.44 eV in the case of Si-MBE. The transition temperature from strong surface segregation to kinetically limited segregation yields 640 °C. In the case of Si1−xGex growth the activation energy for segregation increases up to 4.5 eV for germanium, comparable with that of bulk diffusion.

Reactions at the matrix/reinforcement interface in aluminum alloy matrix composites

In this paper, the nature of interface reactions between F332 aluminum alloy matrix and alumina and alumina-silica-based reinforcement fibers in squeeze cast metal matrix composites (MMCs) is examined. The long range goal of the study is to evaluate Fiberfrax ® fiber as a low cost alternative to Saffil fibers for reinforcement of squeeze cast metal matrix composites, such as those used in diesel engine pistons. The fiber-matrix interface chemistry is investigated using high spatial resolution secondary ion mass spectrometry (SIMS). It is found that reactions occur during fabrication of the composites between the silica binder, which is used in both types of fiber preforms, and the liquid aluminum alloy. In the “as-cast” and T5 heat treated condition, Mg from the alloy matrix reacts with the silica binder to form MgO and elemental Si. The extent of the reaction during T5 heat treatment is independent of the fiber composition because the reactions are limited to the silica binder that coats the fibers. T5 heat treated Fiberfrax ® and Saffil-fiber-reinforced materials provide comparable tensile and fatigue strength up to 400 °C. During T6 heat treatment and prolonged treatment at 400 °C the silica binder reacts completely with Mg to form MgAl 2O 4 spinel; the fibers react strongly with the matrix as well. Possible mechanisms for these reactions are discussed.

Improvement of depth resolution in secondary ion mass spectrometry depth profiling of silicided poly contacts

Performing secondary ion mass spectrometry (SIMS) depth profiles with high depth resolution, <10 nm, through silicided polysilicon contacts is made difficult by the inherent roughness of the silicide/poly interface. This interface roughness results in a loss in depth resolution and leads to the subsequent broadening of the dopant profile under the silicide. In some instances, where the junction is less than 100 nm, it is not possible to obtain an accurate and reliable depth profile of the dopant in the poly or the substrate Si. In this article, the practical application of polishing techniques for planarization and subsequent high depth resolution SIMS analyses are presented. This article will focus on the application of this technique to silicided poly contacts over diffusion areas.

Observations on interfacial segregation and precipitation of arsenic-doped polycrystalline silicon on silicon (100) substrate

The interface structural evolution of arsenic-doped polycrystalline silicon thin films on a silicon (100) single crystal substrate was studied by cross-sectional high resolution transmission electron microscopy and secondary ion mass spectrometry. Native silicon dioxide thin film was observed to agglomerate into discrete oxide particles along with stable arsenic-oxygen compound precipitates. Arsenic influence upon the interfacial evolution is discussed.

Recent advances in application of focused ion beam technology

Focused ion beam (FIB) technology has seen application in a wide variety of disciplines including microelectronic and optoelectronic device fabrication, modification, lithographic mask repair, and materials analysis. Ongoing technological advances in these fields as well as increasing utilization of FIB within them has naturally led to new and novel application of focused ion beams. Recent advances in FIB applications include selective and enhanced material removal in microelectronic devices, three-dimensional patterning capabilities, and coupling with high resolution scanning electron microscopy and secondary ion mass spectrometry. This manuscript will provide background to application of focused ion beams and specific examples of new applications areas.

High Mass Resolution Plasma Desorption and Secondary Ion Mass Spectrometry of Neutral Nickel Thiolate Complexes. Crystal Structure of [Ni6(SC3H7)12

The use of mass spectrometry for the analysis of transition metal complexes is demonstrated by combined high resolution Plasma Desorption Mass Spectrometry (PDMS) and Secondary Ion Mass Spectrometry (SIMS) investigations of the neutral nickel thiolate complexes [Ni4(SC3H7)8] (1), [Ni4(SC6H11)8] (2), [Ni8(SCH2COOEt)16] (3) and [Ni6(SC3H7)12] (4). The positive spectra are dominated by three kinds of SI-species: (a) molecular ions, (b) fragment ions and (c) molecular ions with one or more substrate atoms attached. The negative spectra show mainly nickel sulfur cluster ions of the composition (NixSy)-. In contrast to many Fast Atom Bombardment (FAB) spectra of neutral metal complexes, SIMS and PDMS spectra provide molecular weight as well as fragment ion information. Both techniques are most powerful tools for the investigation of coordination compounds because the samples are easy to prepare and the spectra are independent of matrix conditions. Additionally crystallographic studies have been carried out for 4. The hexanuclear complex 4 with square planar Ni-S coordination sites crystallizes in the trigonal space group R 3̅ with Z = 3 and α = 18.537(5), c = 13.966(3) Å.

Ge/Pd and Si/Pd/Ge/Pd Non-Alloyed Ohmic Contacts to InP Examined by Backside Secondary Ion Mass Spectrometry

ABSTRACTHigh resolution SIMS (secondary ion mass spectrometry) depth profiles of Ge/Pd and Si/Pd/Ge/Pd non-alloyed ohmic contacts on InP are obtained by sputter-etching from the back (semiconductor) side. The samples contain an InGaAs etch stop layer, to allow chemical thinning, and InGaAsP marker layers, which allow alignment and calibration of the depth profiles. Detailed comparisons are made to corresponding contacts on GaAs, processed and analyzed under similar conditions. The importance of interfacial alloy formation, semiconductor regrowth, and dopant incorporation are highlighted.

Sharp phosphorus spikes in silicon grown by fast gas-switching chemical vapor deposition at reduced and atmospheric pressure

Sharp phosphorus doping spikes in silicon were grown by fast-gas-switching chemical vapor deposition at temperatures between 800 and 850 °C using disilane and phosphine in 0.03, 0.1, and 1 atm hydrogen carrier gas. The phosphine doping gas was added while growing silicon at a rate of 0.15–0.5 nm/s. High depth resolution secondary ion mass spectrometry measurements have revealed sharp and high concentration dopant profiles. Peak phosphorus concentrations up to 7×1019 cm−3 and a full width at half maximum of 7 nm were obtained. Electrical measurements show that at these concentrations about 40% of the dopant atoms is electrically active in structures grown at 1 atm. Formation of doping tails is shown to be suppressed at atmospheric hydrogen pressure.

Improved resolution SIMS analysis of annealed Pt/Zn/Pt/ZrB 2/Au ohmic contacts to p-InGaAs on InP substrates using back-surface profiling

A secondary ion mass spectrometry (SIMS) investigation has been carried out on alloyed, Pt/Zn/Pt/ZrB 2/Au, ohmic contacts to p-InGaAs, on InP(001) substrates, in order to determine metal penetration depths into the semiconductor. The resolution obtained using front-surface and back-surface SIMS profiling has been compared. It has been demonstrated that front-surface profiles suffer reduced resolution as a result of surface roughness and sputter-induced roughening by the ion beam. Improved-resolution, back-surface SIMS profiles, supported by transmission electron microscopy, show negligible penetration of Au, Pt or Zn into the InGaAs, within the limits of obtainable depth resolution. However, some P diffusion from the InP into the InGaAs is indicated.

High mass resolution secondary ion mass spectrometry via simultaneous detection with a charge-coupled device

High mass resolution secondary ion mass spectrometry via simultaneous detection with a charge-coupled device