Dopant Profile Measurement Research Articles

Combining dynamic modelling codes with medium energy ion scattering measurements to characterise plasma doping

Plasma doping ion implantation (PLAD) is becoming increasingly important in the manufacture of advanced semiconductor device structures but a fundamental understanding of PLAD is complicated. A model of PLAD into planar substrates has been constructed using the one dimensional computer code TRIDYN to predict collision cascades and hence substrate compositional changes during implantation. Medium Energy Ion Scattering (MEIS) measurements of dopant profiles in PLAD processed samples were used to calibrate the input ion and neutral fluxes to the model. Rules could then be proposed for how post implant profiles should be modified by a cleaning step. This learning was applied to a three dimensional TRI3DYN based model for PLAD implants into FinFET like structures. Comparison of the model to dopant profile measurements made by time of flight (TOF)-MEIS revealed the angular distributions of neutral species and doping mechanisms acting in three dimensional structures.

Precise Comparison of Two-dimensional Dopant Profiles Measured by Low-voltage Scanning Electron Microscopy and Electron Holography Techniques

Detailed comparison of low-voltage scanning electron microscopy and electron holography techniques for two-dimensional (2D) dopant profiling was carried out with using the same multilayered p-n junction specimen. The dopant profiles obtained from two methods are in good agreement with each other. It demonstrates that reliability of dopant profile measurement can be increased through precise comparison of 2D profiles obtained from various microscopic techniques.

Nanoscale Non-Destructive Semiconductor Dopant Characterization and Failure Analysis

The non-destructive semiconductor dopant characterization and failure analysis has been an important and elusive measurement challenge to date. We have employed the vector network analyzer (VNA) as the measurement engine to address the nano scale electronic characterization challenge. The VNA architecture as it exists today has the ability to measure impedances close to the analyzer's own characteristic impedance (i.e., 50 ohms) with good precision up to 100GHz stimulus frequency. However, the measurement precision and resolution provided by a VNA drop by two orders of magnitude as impedance deviates from 50 ohms. We propose a solution that remedies the lack of measurement precision and resolution for large and small impedances when measured by a VNA. Agilent has developed a new scanning microwave microscope (SMM) mode that utilizes a half-wavelength resonator in conjunction with a diplexer connected to a VNA to perform very sensitive capacitance measurements at the tip of a conductive atomic force microscope (AFM). These measurements are achieved via transformation of the high impedance (i.e., the very small capacitance between the AFM tip/sample to the ground) to 50 ohms (i.e., the measurement system's characteristic impedance) using a half-wavelength resonator and diplexer. We also designed a Dopant Profile Measurement Module as a measurement accessory to the SMM system. This module in conjunction with the VNA /SMM enables the non-destructive semiconductor dopant characterization and failure analysis.

Electron holography study for two-dimensional dopant profile measurement with specimens prepared by backside ion milling

The visualization of two-dimensional dopant profiles and the quantitative analysis of the built-in potential across the p-n junction, DeltaV(p-n), by electron holography were carried out with specimens prepared from the backside ion milling method combined with the focused ion beam technique. It was possible to obtain dopant profiling of the large field of view with low surface damage and gradually changed thickness. From the quantitative analysis using the phase information of electron holography and the thickness information of electron energy-loss spectroscopy, DeltaV(p-n) was estimated to be about 0.78 V assuming that the thickness of the dead layer on both surfaces is 50 nm, which is to show the difference of within 12% from the calculated value. It demonstrates that the backside ion milling method is a very promising specimen preparation technique for the reliable and quantitative analysis of dopant profiling with electron holography.

Nondestructive dopant profile measurement and its quantitative analysis using the nanocapacitance–voltage method

We propose a new method that can quantitatively extract the dopant profile in a nondestructive manner using scanning capacitance microscopy (SCM) or a nanocapacitance–voltage (nano-C–V) system. The method is based on a nanotip capacitor model, and not the common parallel-plate capacitor model. For the first time, we have physically analyzed a nanotip capacitor by considering the interaction between the air and a semiconductor and have calculated the full C–V curves and the rate of capacitance change with bias (dC/dV). We calculated the local dC/dV curve that was matched to the experimental dC/dV data. This quasi-three-dimensional modeling illustrates that the C–V characteristics derived from the nanotip model are different from those of a conventional parallel-plate method. We found that the increase in capacitance in the inversion region (characterized by a double peak in the dC/dV curve) is due to the quasispherical characteristics of the depleted layer generated by the nanotip located in the air. These results enable the quantification of dopant profiles in a step-by-step process using a one-dimensional inversion algorithm, and their subsequent comparison with a secondary ion mass spectroscopy profile.

Specific properties of fine SnO2 powders connected with surface segregation.

The effect of surface segregation in Sb- and In-doped SnO2 fine-grained powders has been analyzed in comparison with single-crystalline samples. The kinetics and thermodynamics of the Sb and In segregation processes were studied as a function of annealing temperature by X-ray photoelectron spectroscopy (XPS) after annealing in an oxygen-containing atmosphere. Significant differences between diffusion and segregation were revealed for doped powders and single crystals, obviously because of simultaneous diffusion and particle-growth processes proceeding during annealing of powders. For doped single crystals the thermodynamic equilibrium is approached after 24 h annealing above 850 degrees C and at 1000 degrees C for Sb and In, respectively. Higher effective activation energies of diffusion are observed for doped powders and the thermodynamic equilibrium is not achieved under technologically relevant annealing conditions. On the basis of dopant profile measurements anomalies in the electrical resistivity at 300 degrees C of Sb-doped SnO2 powders annealed at 700 and 900 degrees C were attributed to an Sb-depleted zone formed beneath the segregated surface during the kinetic regime. To achieve optimum resistivity behavior for commercial application, inhomogeneous doping of powders must be avoided by appropriate preparation steps.

Computational investigation of the accuracy of constant-d C scanning capacitance microscopy for ultra-shallow doping profile characterization

Accurate prediction of very shallow junctions by TCAD tools presents a major challenge which requires process simulation models to be accurately tuned on the basis of two-dimensional (2D) dopant profile measurements. Scanning capacitance microscopy (SCM) provides 2D images with a spatial resolution in the 10 nm range, but the extraction of quantitative doping information from the raw experimental data requires a large reverse simulation effort. A methodology for an efficient 2D constant-d C operating mode SCM simulation is presented in this paper: although the simulation requires to calculate the local C– V characteristics for each measurement point, a very high computing speed has been achieved. The accuracy and the resolution of the constant-d C operating mode using direct inversion in presence of arbitrary doping profiles are discussed.

Dopant profile measurements in ion implanted 6H–SiC by scanning capacitance microscopy

Two-dimensional carrier profiles were determined in ion implanted 6H–SiC by scanning capacitance microscopy (SCM). The measurements were performed on cross-section using metal covered Si tips. The implantations were performed into a SiC substrate at a temperature of 500 °C (on both n and p-type material) with 200 keV N + and 300 keV Al + ions in the fluence range 1×10 14–2×10 15 cm −2 . Annealing processes were carried out at 1300 °C in argon flux. The defect profile before and after thermal processes were analysed with Rutherford backscattering spectroscopy and the residual defects were characterised by transmission electron microscopy. The integration of carrier profiles measured by SCM gives an electrical dopant activation of 10% for N implanted layer and of 4% electrical activation in Al implanted layer. The carrier profiles and the active fraction of implanted atoms are correlated to the concentration and structure of residual defects.

Quantitative two-dimensional profiling of 0.35 μm transistors with lightly doped drain structures

We report the first quantitative experimental two-dimensional (2D) dopant profile measurement of 0.35 μm transistors with lightly doped drain structures and its comparison with theoretical simulation. Experimentally, the 2D dopant profile is determined using dopant-selective etching followed by atomic force microscopy imaging. These results show excellent quantitative agreement with recent theoretical profile simulation for both n- and p-channel metal–oxide–semiconductor transistors.

Two-dimensional Dopant Profile Measurements by Scanning Capacitance Microscopy.

Two-dimensional dopant profiles of LSI device cross-sections are extracted below 100nm scale from SCM (Scanning Capacitance Microscopy) technique. Sample cross-sections are prepared with a glass polishing technique, followed by a final polishing step with a colloidal silica. Samples are also fabricated with FIB (Focused Ion Beam) to acquire SCM images on specific cross-sections of devices, which become effective for failure analysis. The phosphorus profiles of P-doped Si substrate and DRAM device are imaged within the range of 1×1016-2×1019 atoms/cm3 with the lateral resolution of 50-60nm. The chemical bonding states of glass-polished and ion-milled Si-surfaces are also examined by XPS (X-ray Photoelectron Spectroscopy). The influence of the surface bonding-states on SCM images is discussed.

Modeling Silicon Implantation Damage and Transient Enhanced Diffusion Effects for Silicon Technology Development

ABSTRACTDespite more than 20 years of effort, detailed understanding of defect-coupled dopant diffusion in silicon still falls short of what is practically required to support state-of-the-art silicon technology development. The challenge for modeling in industry is to combine the best of our physical understanding with measurements of dopant profiles for technology-relevant conditions to provide models which are as predictive and efficient as possible. This paper presents experimental results which provide insight into damage generation and annealing processes and discusses practical modeling approaches to support technology development despite our incomplete understanding of the physical processes involved.

Scanning probe microscopy for 2-D semiconductor dopant profiling and device failure analysis

We have extended the capabilities of an atomic force microscope (AFM) with double heterodyne force detection, to include both electrostatic force microscopy (EFM) and scanning differential capacitance microscopy (SdCM). Samples measured with this tool are imaged simultaneously in each of these three modes. Inhomogeneities in surface topography (AFM), surface work function (EFM) and sub-surface charge (SdCM) are thus detected at once. We work in non-contact mode in order to interact non-destructively with our samples, with resultant lateral spatial resolution of 25–50 nm. Variations in surface topography of less than 1 nm, and surface potential variations as small as 1 mV, are imaged easily. We have applied the techniques based on this tool to microfabricated materials and device structures. In particular, we have studied the metal-oxide-silicon field-effect transistor (MOSFET) structure, of importance to microelectronic science and engineering. Following a brief description of our detection system, this work will describe our measurements of dopant profiles related to this structure. It will also demonstrate our ground-breaking application of scanned probe techniques to the analysis of other materials defects, and of device failure, in these structures. The work will conclude with a quantitative discussion of the three most limiting factors for our techniques: parasitic capacitance; convolved signals; and large-signal behavior of the cantilever.

Quantitative two-dimensional dopant profile measurement and inverse modeling by scanning capacitance microscopy

Quantitative dopant profile measurements are performed on a nanometer scale by scanning capacitance microscopy (SCM). An atomic force microscope is used to position a nanometer scale tip at a semiconductor surface, and local capacitance change is measured as a function of sample bias. A new feedback method has been demonstrated in which the magnitude of the ac bias voltage applied to the sample is adjusted to maintain a constant capacitance change as the tip is scanned across the sample surface. A quasi-1D model is used to extract dopant density profiles from the SCM measurements. The inverted SCM dopant profiles are compared with profiles obtained by process simulation and secondary ion mass spectroscopy measurement. Good agreement was found between the SCM measured profile and the lateral profile predicted by SUPREM 4 over the concentration range from 1017 to 1020 cm−3.

Measurement of two-dimensional doping profiles

This paper presents a brief review of methods for the measurement of two-dimensional doping profiles. The main focus is on methods that have been actually been used to measure 2D profiles with acceptable accuracy and sensitivity. A comprehensive historical review is beyond the scope of this paper, and for this the reader is referred to an earlier paper which exhaustively cites work in the 2D dopant-profile measurement area.

Doping studies using thermal beams in chemical-beam epitaxy

The use of chemical-beam expitaxy instead of chemical vapor deposition allows the incorporation of thermal atomic beams for doping. Dopant profile measurements by a differential capacitance-voltage technique and secondary ion mass spectroscopy technique show that there is no surface segregation with Si dopants in InP at all growth temperatures (<600 °C). On the other hand, Sn and to a lesser extent Be show surface segregation which can be reduced by growing the InP at a lower temperature (<550 °C). From this study, it is seen that Si should be preferred as the n-type dopant in producing InP/InGaAs high electron mobility transistors.

MeV Helium Microbeam Analysis: Applications to Semiconductor Structures

ABSTRACTWe have employed an MeV He+ microbeam for the analysis of micron-scale semiconductor structures. The analysis combines a unique beam scanning and mapping capability with powerful ion beam techniques such as particleinduced x-ray emission, Rutherford backscattering and ion channeling. These analysis capabilities are applied to the measurement of dopant profiles in polycrystalline resistors, identification of micro-alloying in metal-GaAs contacts and damage/atom location in individual polycrystalline silicon grains. The latter application utilises the newly-developed technique of channeling contrast microscopy.