Evolution Of Sheet Resistance Research Articles

Effects of Impurity Elements on Isothermal Grain Growth of Electroplated Copper

The grain growth of electroplated copper films implanted with individual impurity elements were studied with elements implanted separately. Sheet resistance evolution, focus ion beam imaging, and X-ray diffraction were used to characterize the grain growth along time at various annealing temperatures. While the incorporation of oxygen, sulfur, and chlorine impedes the grain growth, the oxygen has the weakest impact and chlorine has the strongest. Fully transformed films with coarse grains were obtained at temperatures up to 400 C. The presence of carbon resulted in a nucleation limited grain growth and the full transformation was not achieved until at 700 C. On the other hand, the presence of chlorine enhanced a preference of grain growth in [111] orientation. This study aims to provide a new perspective of improving grain structures of copper with engineered chemical additives.

Kinetics of Ni3Si2 formation in the Ni2Si–NiSi thin film reaction from in situ measurements

The kinetics of Ni3Si2 formation in the Ni2Si–NiSi thin film reaction were determined from simultaneous in situ x-ray diffraction (XRD) measurements, performed using a synchrotron source, and sheet resistance measurements. Samples consisted of 90nm Ni∕100nm polycrystalline-Si∕SiO2 stacks, of interest for fully silicided gate applications, on (100) Si. After initial formation of a Ni2Si∕NiSi bilayer, these films reacted to form Ni3Si2. The evolution of sheet resistance and of the intensity of XRD peaks were used to extract the fraction of Ni3Si2 formed during ramp and isothermal annealings. A Kissinger analysis was performed for ramp annealing with ramp rates of 1, 3, 5, 9, and 27°C∕s, obtaining the activation energy of Ni3Si2 formation, Ea=1.92±0.15eV. A Kolmogorov-Johnson-Mehl-Avrami analysis was performed for isothermal anneals, finding an Avrami exponent of 2.1±0.2, suggesting two-dimensional growth. This is consistent with a nucleation controlled process for Ni3Si2 formation, with nucleation sites at different positions in the thin film, and subsequent lateral two-dimensional propagation of the transformation front parallel to the film surface. Implications for Ni fully silicided gate applications are discussed.

Annealing characteristics of electrically isolated InGaAsP devices

The authors report on the effects of fluorine implants on the sheet resistivity of n-type InGaAsP layers grown lattice matched to InP by metal organic molecular beam epitaxy. Projected range matched fluorine ions are implanted at multiple energies and single MeV energy at room temperature (RT) and 77K in both cases. Hall and resistivity measurements are carried out for the van der Pauw samples and the evolution of sheet resistivity (Rs) as a function of annealing temperature was studied in both cases. Fluorine multienergy implantation at 77K produces higher as-implanted resistivity layers of ∼107Ω∕◻ compared to RT implants. It is further observed that RT and 77K implants recover to their preimplanted sheet resistivity values as soon as they are annealed at temperatures higher than 500°C. Substrate temperature and collision cascade density due to multiple energy implants are found to play an important role to optimize the isolation process.

Nickel-Based Germanosilicide of Heavily-Doped SiGe Films for Low Resistance and High-Temperature Stability

We have studied thermo-electrical properties for Ni-based germanosilicide to understand the influence of temperature on the evolution of sheet resistance and micro-structures of contacts on heavily-doped SiGe grown by reduced pressure chemical vapor deposition. After the deposition of Ni, Ni/Ti, Ni/Pt films on Si0.83Ge0.17 epi layer and subsequently annealing for silicide reaction, we analyzed sheet resistance, surface roughness and reaction interfaces using four point probe method, scanning probe micrograph and transmission electron microscope. Bi-layer metal structures of Ni/Ti and Ni/Pt were investigated to study feasible use for suppressing inappropriate reaction at interface. It is found that bi-layer structure with thin Pt interlayer presented promising properties for germanosilicide of n+-Si0.83Ge0.17 with low sheet resistance, smooth surface morphology and high temperature stability up to 800 oC.

Interlayer-Assisted Stability of Germanosilicide for Heavily-Doped n+-Si0.83Ge0.17 Grown by Reduced Pressure Chemical Vapor Deposition

Ni-based germanosilicide process of heavily doped n+- Si0.83Ge0.17 has been investigated to understand the influence of temperature and doping concentration on the evolution of sheet resistance and micro-structures. After annealing Ni film on various Si0.83Ge0.17 epi layers for silicide reaction, the evolution of sheet resistance and surface roughness was analyzed using x-ray diffraction, four pint probe, atomic force microscope, and transmission electron microscope. Especially, bi-layer metal structures were employed to resolve inappropriate degradation associated with heavy doping of phosphorous in Si0.83Ge0.17, from which crucial improvements in structural and electrical properties could be confirmed. Pt interlayer played an important role for uniform germanosilicide at the interface of metal and semiconductor, and resulted in low sheet resistance and relevant thermal stability.

Activation, Diffusion and Defect Analysis of a Spike Anneal Thermal Cycle

ABSTRACTIn this paper, the evolution of sheet resistance, junction depth and defects during the whole thermal cycle of a typical spike anneal with a peak temperature of 1050°C was investigated in detail. To this purpose, spike anneals were performed at peak temperatures ranging from 800°C up to 1050°C in temperature steps of 50°C. These experiments were done both on B+ (500 eV, 1.1015 cm−2) and BF2+ (2.2 keV, 1.1015 cm−2) implanted wafers. It is found that for temperatures below 850°C BF2+ implanted wafers exhibit a much better electrical activation, resulting in a lower sheet resistance, than B+ implanted ones, due to the amorphisation process occurring during the BF2+ implant and the subsequent solid phase epitaxial growth. In this low temperature regime, boron clustering takes place very rapidly in B+ implanted wafers, as confirmed by both SIMS and TEM analysis. In particular, “large” clusters, i.e. with diameter above the TEM detection limit (∼2 nm), undergo a classical Ostwald ripening process (increase in size, decrease in density). SRP measurements indicate that boron activation in this low temperature regime is not related to cluster dissolution. On the other hand, after the initial solid phase epitaxial regrowth, BF2+ implanted wafers exhibit a slight increase in sheet resistance, due to boron clustering induced by the dissolution of end of range defects. Finally, it is found that at higher spike anneal temperatures (above 850°C), both B+ and BF2+ implanted wafers exhibit a similar behaviour, with a progressive decrease in sheet resistance due to boron cluster dissolution and dopant diffusion.

Implant isolation of ZnO

We study ion-irradiation-induced electrical isolation in n-type single-crystal ZnO epilayers. Emphasis is given to improving the thermal stability of isolation and obtaining a better understanding of the isolation mechanism. Results show that an increase in the dose of 2 MeV O16 ions (up to ∼2 orders of magnitude above the threshold isolation dose) and irradiation temperature (up to 350 °C) has a relatively minor effect on the thermal stability of electrical isolation, which is limited to temperatures of ∼300–400 °C. An analysis of the temperature dependence of sheet resistance suggests that effective levels associated with irradiation-produced defects are rather shallow (<50 meV). For the case of implantation with keV Cr, Fe, or Ni ions, the evolution of sheet resistance with annealing temperature is consistent with defect-induced isolation, with a relatively minor effect of Cr, Fe, or Ni impurities on the thermal stability of isolation. Results also reveal a negligible ion-beam flux effect in the case of irradiation with 2 MeV O16 ions, supporting high diffusivity of ion-beam-generated defects during ion irradiation and a very fast stabilization of collision cascade processes in ZnO. Based on these results, the mechanism for electrical isolation in ZnO by ion bombardment is discussed.

Annealing characteristics of the implant-isolated n-type GaAs layers: Effects of ion species and implant temperature

The evolution of sheet resistivity with the annealing temperature for implant-isolated n-type GaAs layers has been studied for a variety of ion species. Annealing characteristics of the isolated n-type GaAs layers implanted with different ions at RT, 100 or 200 °C were compared for each implant temperature. For the doses and energies used in this work, it is observed that protons and helium ions exhibit a pronounced enhanced dynamic annealing and offer excellent persistence of isolation to higher annealing temperatures for elevated temperature implantations. The actual carrier removal phenomenon in case of nitrogen and oxygen ions is thought to be a product of both damage related and chemically introduced isolation, which requires the implanted specie itself to be active as a trap centre. For hot implants, different trap structures are formed which in turn provide better resistivity values around these temperatures though the critical temperature may shift still higher, exhibiting persistence to thermal processes especially for light ion irradiation cases. The data presented in this work has ramifications for device engineers.

Implant isolation of ZnO epitaxial layers

ABSTRACTThe formation of highly resistive films of single-crystal ZnO as a result of irradiation with MeV Li, O, and Si ions is demonstrated. Results show that the ion doses necessary for electrical isolation close-to-inversely depend on the number of ion-beam-generated atomic displacements. Results show that an increase in the dose of 2 MeV O ions (up to ∼ 2 orders of magnitude above the threshold isolation dose) and irradiation temperature (up to 350 °C) has a relatively minor effect on the thermal stability of electrical isolation, which is limited to temperatures of ∼ 300 — 400 °C. For the case of multiple-energy implantation with keV Cr, Fe, or Ni ions, the evolution of sheet resistance with annealing temperature is consistent with defect-induced isolation, with a relatively minor effect of Cr, Fe, or Ni impurities on the thermal stability of isolation. Based on these results, the mechanism for electrical isolation in ZnO by ion bombardment is discussed.

Electrical isolation of p-type GaAsN epitaxial layers by ion irradiation

ABSTRACTThe evolution of sheet resistance (Rs) of p-type conductive GaAs(1-x)Nx epilayers (x = 0.6%, 1.4%, and 2.3%) exposed to MeV 1H+, 7Li+, 12C+, and 16O+ ions and the stability of the formed electrical isolation during post-irradiation annealing were investigated. Results show that the threshold dose (Dth) to convert a conductive layer to highly resistive one close-to-linearly depends on original free carrier concentration and inversely depends on the number of irradiation-generated atomic displacements, and is independent of the nitrogen content in GaAsN layers. Increasing beam flux of 12C+ results in a lower Dth, whereas 1H+ beam flux does not affect it, showing the influence of collision cascade density. Results also show that irrespectively of the ion mass, the stability of electrical isolation formed in GaAsN is dependent on the ratio of the concentration of irradiation-created carrier traps to Dth. The electrical isolation can be preserved up to 550°C when the accumulated dose (D) is greater than 3.3 Dth.

Implant isolation in GaAs device technology: Effect of substrate temperature

Protons (H 2 +), boron (B +) and oxygen (O +) ions were used to isolate n-type GaAs layers at RT, 100 and 200 °C. Prior to the carrier removal implants, the n-type region was formed using keV multiple-energy implants of 29 Si + ions. 0.5–2 MeV isolation implants were performed at fluences around 1–3×10 14 cm −2 to create an almost uniform damage profile over ∼0.5 μm. This procedure placed the heavily damaged region associated with the end of the H 2 + , B + or O + ions range well into the semi-insulating GaAs substrate. The evolution of sheet resistivity ( R s) as a function of annealing temperature was studied in all cases. It is observed that the RT implants recover quicker to their pre-implanted sheet resistivity values for proton- and boron-isolated GaAs layers. In both cases, the thermal stability is improved as the implant temperature is increased which is due to the formation of thermally stable defects during implantation. The effect of enhanced dynamic annealing is also investigated which introduces higher as-implanted resistivity values for proton-implanted samples maintained at 100 or 200 °C during implantation. No such improvement in thermal stability due to hot implants, or any noticeable effect of dynamic annealing is found in oxygen-implants at either RT or elevated substrate temperatures. Compensation introduced in this case is a product of both damage related centres and oxygen itself.

Reversible changes in doping of InGaAlN alloys induced by ion implantation or hydrogenation

Carrier concentrations in doped InN, In0.37Ga0.63N, and In0.75Al0.25N layers are reduced by both F+ ion implantation to produce resistive material for device isolation, and by exposure to a hydrogen plasma. In the former case, post-implant annealing at 450–500 °C produces sheet resistances ≳106 Ω/⧠ in initially n+ (7×1018–3×1019 cm−3) ternary layers and values of ∼5×103 Ω/⧠ in initially degenerately doped (4×1020 cm−3) InN. The evolution of sheet resistance with post-implant annealing temperature is consistent with the introduction of deep acceptor states by the ion bombardment, and the subsequent removal of these states at temperatures ≲500 °C where the initial carrier concentrations are restored. Hydrogenation of the nitrides at 200 °C reduces the n-type doping levels by 1–2 orders of magnitude and suggests that unintentional carrier passivation occurring during cool down after epitaxial growth may play a role in determining the apparent doping efficiency in these materials.

Effects of Ion-Irradiation and Hydrogenation on the Doping of InGaAIN Alloys

AbstractCarrier concentrations in doped InN, In0.37 Ga0.63 N and In0.75 Al0.25 N layers are reduced by both F+ ion implantation to produce resistive material for device isolation, and by exposure to a hydrogen plasma. In the former case, post-implant annealing at 450–500°C produces sheet resistances > 106 Ω/ℹ in initially n+ (7 x 1018 − 3 x 1019 cm−3) ternary layers and values of ∼5 x 103 Ω/ℹ in initially degenerately-doped (4 x 1020 cm−3) InN. The evolution of sheet resistance with post-implant annealing temperature is consistent with the introduction of deep acceptor states by the ion bombardment, and the subsequent removal of these states at temperatures −500°C where the initial carrier concentrations are restored. Hydrogenation of the nitrides at 200°C reduces the n-type doping levels by 1-2 orders of magnitude and suggests that unintentional carrier passivation occurring during cool down after epitaxial growth may play a role in determining the apparent doping efficiency in these materials.