Secondary electron imaging as a two-dimensional dopant profiling technique: Review and update

Venables, D.; Jain, Harsh; Collins, David C.

doi:10.1116/1.589811

Cited by 82 publications

(64 citation statements)

References 4 publications

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“…In addition, the height of the Schottky barrier will be a function of the dopant concentration; thus, the SE yield will vary accordingly. This is as observed by Venables et al 8 …”

Section: Metal-semiconductor Contactsupporting

confidence: 83%

“…If a region within this substrate is doped to produce features of p-type material, then it is possible to obtain, in the LVSEM mode, different SE brightness levels from these two regions giving a distinct contrast between them. Venables et al,8 in an attempt to quantify the SE contrast profiles, found a linear relationship between the observed SE intensity and the logarithm of the dopant concentration of boron-doped silicon in the range 4 ð 10 16 cm 3 to 3 ð 10 20 cm 3 , as shown in Fig. 1.…”

Section: Introductionmentioning

confidence: 87%

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Why is it possible to detect doped regions of semiconductors in low voltage SEM: a review and update

El-Gomati

Zaggout

Jayacody

et al. 2005

Surface & Interface Analysis

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There is an urgent need for fast, non-destructive and quantitative two-dimensional dopant profiling of modern and future ultra large-scale semiconductor devices. The low voltage scanning electron microscope (LVSEM) has emerged to satisfy this need, in part, whereby it is possible to detect different secondary electron yield values (brightness in the SEM signal) from the p-type to the n-type doped regions as well as different brightness levels from the same dopant type. The mechanism that gives rise to such a secondary electron (SE) contrast effect is not fully understood, however. A review of the different models that have been proposed to explain this SE contrast is given. We report on new experiments that support the proposal that this contrast is due to the establishment of metal-to-semiconductor surface contacts. Further experiments showing the effect of instrument parameters including the electron dose, the scan speeds and the electron beam energy on the SE contrast are also reported. Preliminary results on the dependence of the SE contrast on the existence of a surface structure featuring metal-oxide semiconductor (MOS) are also reported.

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“…In addition, the height of the Schottky barrier will be a function of the dopant concentration; thus, the SE yield will vary accordingly. This is as observed by Venables et al 8 …”

Section: Metal-semiconductor Contactsupporting

confidence: 83%

Section: Introductionmentioning

confidence: 87%

Why is it possible to detect doped regions of semiconductors in low voltage SEM: a review and update

El-Gomati

Zaggout

Jayacody

et al. 2005

Surface & Interface Analysis

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“…A resolution up to 1 nm is achievable (Elliott et al, 2002), and sensitivity to dopant concentrations ranging from 10 14 up to 10 20 dopants cm -3 can be obtained at a quantification accuracy of at least ± 3 % (Perovic et al, 1998;Venables et al, 1998;Elliott et al, 2002, Chee, 2009. As SE doping contrast is able to characterise dopants with high sensitivity over the required range and resolution, it is highly viable compared to a number of alternative techniques of limited range and resolution, are time-consuming, costly or destructive, or provide only 1-D measurements (e.g.…”

Section: Introductionmentioning

confidence: 99%

Dopant profiling based on scanning electron and helium ion microscopy

Chee

Boden

2016

Ultramicroscopy

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Highlights• Strong doping contrast from n-type regions in the SHIM without energy-filtering.• Sensitivity limits are established of the SHIM and SEM techniques.• We discuss the impact of SHIM imaging conditions on quantitative dopant profiling.• Doping contrast stems from different surface layer thicknesses in the SHIM and SEM.In this paper, we evaluate and compare doping contrast generated inside the scanning electron microscope (SEM) and scanning helium ion microscope (SHIM). Specialised energy-filtering techniques are often required to produce strong doping contrast to map donor distributions using the secondary electron (SE) signal in the SEM. However, strong doping contrast can be obtained from n-type regions in the SHIM, even without energy-filtering. This SHIM technique is more sensitive than the SEM to donor density changes above its sensitivity threshold, i.e. 10 16 or 10 17 donors cm -3 respectively on specimens with or without a p-n junction; its sensitivity limit is well above 2 × 10 17 acceptors cm -3 on specimens with or without a p-n junction. Good correlation is found between the widths and slopes of experimentally measured doping contrast profiles of thin p-layers and the calculated widths and slopes of the potential energy distributions across these layers, at a depth of 1 -3 nm and 5 -10 nm below the surface in the SHIM and the SEM respectively. This is consistent with the mean escape depth of SEs in Si being about 1.8 nm and 7 nm in the SHIM and SEM respectively, and we conclude that short escape depth, low energy SE signals are most suitable for donor profiling. Keywords: Doping contrast; Secondary electron energy filtering; Sensitivity limit; Electric potentials; Escape depth; p-n junction I. INTRODUCTIONThe future of the semiconductor industry depends critically on the ability to map dopants rapidly at high spatial resolution, and with high sensitivity. New spectroscopic techniques are in considerable demand to cope with the advent of next generation semiconductor devices having ultra-shallow junctions. Hence, dopant profiling at a resolution of sub-10 nm and detection sensitivity over a range of ~10 16 -10 20 dopants cm -3 are important requisites. Using an SEM, it is possible to provide a rapid and contactless technique for the two-dimensional mapping of electrically active dopant profiles based on SE doping contrast (Perovic et al., 1995;Turan et al., 1996;Castell et al., 1999;Elliott et al., 2002). Under standard imaging conditions, the p-type regions appear bright and the n-type regions appear dark, therefore doping contrast can be used to determine the position of electrical p-n junctions. The doping contrast mechanism is due to the built-in electric field across a p-n junction, modified by the effects of surface bandbending and external patch fields as the SEs are scattered by the surface electric potentials (Chee et al., 2011). Oatley et al. (1957) first studied SE doping contrast from p-n junctions where it was shown that reverse biasing enhances contrast by changing the electric ...

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“…This leads to a built-in potential such that the energy bands in the p-type region are shifted up relative to those in the n-type region, thus reducing E b , the energy required to escape to the detector. This effect has been used mainly to image doped regions in semiconductors [4][5][6][7][8][9] and the technique is often called "doping contrast". In addition, the electrostatic potential distribution of a cross-section of a p-n junction has been mapped by subtracting two images obtained at different bias voltages [10].…”

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confidence: 99%

Mapping the potential within a nanoscale undoped GaAs region using a scanning electron microscope

Kaestner

Schönjahn

Humphreys

2004

Applied Physics Letters

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Semiconductor dopant profiling using secondary electron imaging in a scanning electron microscope (SEM) has been developed in recent years. In this paper, we show that the mechanism behind it also allows mapping of the electric potential of undoped regions. By using an unbiased GaAs/AlGaAs heterostructure, this article demonstrates the direct observation of the electrostatic potential variation inside a 90nm wide undoped GaAs channel surrounded by ionized dopants. The secondary electron emission intensities are compared with two-dimensional numerical solutions of the electric potential.

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Secondary electron imaging as a two-dimensional dopant profiling technique: Review and update

Cited by 82 publications

References 4 publications

Why is it possible to detect doped regions of semiconductors in low voltage SEM: a review and update

Why is it possible to detect doped regions of semiconductors in low voltage SEM: a review and update

Dopant profiling based on scanning electron and helium ion microscopy

Mapping the potential within a nanoscale undoped GaAs region using a scanning electron microscope

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