New application of variable‐pressure/environmental microscopy to semiconductor inspection and metrology

Postek, Michael T.; Vladár, András

doi:10.1002/sca.4950260103

Cited by 14 publications

(11 citation statements)

References 16 publications

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“…This charge build-up results in a decrease in signal collection because of the secondary electrons are re-attracted back to the sample by the charge and are lost to signal collection.Figure 4(right) shows the charge being mitigated by the electron flood gun resulting in images of the photomask comparable to those obtained from the VP-SEM[4].At smaller field of view (higher magnification) the HIM image of the photomask samples is comparable to that obtained from the variable pressure SEM.…”

supporting

confidence: 69%

“…Third, a variable pressure scanning electron microscope (VPSEM) can be employed. [4] VPSEM has demonstrated excellent resolution of mask details with little or no disturbing charge build-up. Controlling the pressure in the VPSEM allows for the neutralization of the charge induced by the electron beam through gas ionization that takes place in proximity to the electron beam interaction region.…”

Section: Chromium-on-quartz Photomasksmentioning

confidence: 95%

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The potentials of helium ion microscopy for semiconductor process metrology

Postek

Vladár

2008

SPIE Proceedings

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Semiconductor manufacturing is always looking for more effective ways to monitor and control the manufacturing process. Helium Ion Microscopy (HIM) presents a new approach to process monitoring which has several potential advantages over the traditional scanning electron microscope (SEM) currently in use in semiconductor research and manufacturing facilities across the world. Due to the very high source brightness, and the shorter wavelength of the helium ions, it is theoretically possible to focus the ion beam into a smaller probe size relative to that of an electron beam of an SEM. Hence, resolution 2 to 4 times that of comparable SEMs is theoretically possible. In an SEM, an electron beam interacts with the sample and an array of signals are generated, collected and imaged. This interaction zone may be quite large depending upon the accelerating voltage and materials involved. Conversely, the helium ion beam interacts with the sample, but it does not have as large an excitation volume and thus, the image collected is more surface sensitive and can potentially provide sharp images on a wide range of materials. Compared to an SEM, the secondary electron yield is quite high -allowing for imaging at extremely low beam currents and the relatively low mass of the helium ion, in contrast to other ion sources such as gallium potentially results in minimal damage to the sample. This presentation will report on some of the preliminary work being done on the HIM as a research and measurement tool for semiconductor process metrology being done at NIST.

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confidence: 69%

Section: Chromium-on-quartz Photomasksmentioning

confidence: 95%

The potentials of helium ion microscopy for semiconductor process metrology

Postek

Vladár

2008

SPIE Proceedings

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“…In the high vacuum environments of conventional SEM and focused ion beam ͑FIB͒ tools, photomask imaging, metrology, and repair are inhibited by severe charging. 3 The low vacuum SE images in Fig. 2 do not show charging artifacts.…”

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confidence: 89%

Secondary electron imaging of nonconductors with nanometer resolution

Toth¹,

Knowles

Thiel³

2006

Applied Physics Letters

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The resolution of secondary electron (SE) images in scanning electron microscopy (SEM) is limited by the SE diffusion length. However, most materials are poor electrical conductors and in practice, resolution and image information content are often limited by charging. We demonstrate how charging can be eliminated as the resolution-limiting factor using a gaseous SE detector for magnetic immersion electron lenses. Charging is stabilized by ions produced in a magnetic field-assisted gas ionization cascade. The charge control self-regulation process does not quench the SE imaging signal, thereby enabling high resolution image contrast mechanisms that are suppressed in high vacuum SEM.

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“…4,5 Widespread acceptance of the technique is hindered because the image formation process is considerably more complicated than in high-vacuum scanning electron microscopes (SEMs). Interactions between electrons and gas molecules, as well as the behavior of positive gaseous ions, all influence the appearance and information content of secondary electron (SE) images.…”

Section: Modeling Of Imaging Processes In the Low-vacuum Semmentioning

confidence: 99%

Modeling of imaging processes in the low‐vacuum SEM

Thiel

2005

Surface & Interface Analysis

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The presence of a gas in the specimen chamber of low-vacuum scanning electron microscopes (SEMs) gives rise to a number of interactions that are not found in their high-vacuum counterparts. Many of these interactions are integral to the specimen charge neutralizing capabilities of these instruments. However, these interactions, and the electronic charge state of the specimen, give rise to a number of processes that influence, and sometimes even dominate, secondary electron contrast. As many of the processes are stochastic in nature, and depend on discrete interactions between electrons, gaseous ions, neutral molecules, and the specimen surface, modeling can offer important insights for contrast interpretation. This paper discusses these interactions and the mechanisms through which contrast is influenced. Copyright MODELING OF IMAGING PROCESSES IN THE LOW-VACUUM SEMLow-vacuum scanning electron microscopy is emerging as a powerful new technique for the study of poorly conducting materials and other difficult samples.1 -3 Because of these attributes, it is also being considered as a candidate for the next generation of sub-10 nm critical dimension metrology tools for the semiconductor manufacturing industry. 4,5 Widespread acceptance of the technique is hindered because the image formation process is considerably more complicated than in high-vacuum scanning electron microscopes (SEMs). Interactions between electrons and gas molecules, as well as the behavior of positive gaseous ions, all influence the appearance and information content of secondary electron (SE) images. Furthermore, SE images obtained from dielectric materials appear to contain more information than their high-vacuum counterparts, related to the local dielectric properties of the material. 3,6 Considerable work needs to be done before it will be possible to make routine interpretations of the SE contrast. Many of the processes that influence the information content of SE images have complicated nonlinear interdependencies, which make simple analytic descriptions unlikely. The situation is exacerbated by the commercial introduction of detectors with increasingly complicated physical and electromagnetic field geometries. However, since many of the processes are stochastic in nature, computer modeling can offer insights. The processes that contribute to image formation can be divided into three categories: cascade amplification/ion production, intrinsic SE emission from dielectrics, and modulation of SE emissions by the gaseous ions. Most commercial low-vacuum SEMs use some degree of gas cascade amplification to amplify the secondary electron emission current, regardless of the form of the signal that is actually measured. Another critical function of the cascade is to produce a flux of positive ions sufficient to stabilize electronic charging of insulating samples. In its simplest form, the gas cascade is manipulated by placing a positively biased anode (typically a few hundred volts positive) in the vicinity of the specimen. Secondary electrons ...

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New application of variable‐pressure/environmental microscopy to semiconductor inspection and metrology

Cited by 14 publications

References 16 publications

The potentials of helium ion microscopy for semiconductor process metrology

The potentials of helium ion microscopy for semiconductor process metrology

Secondary electron imaging of nonconductors with nanometer resolution

Modeling of imaging processes in the low‐vacuum SEM

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