Analytical was founded in 1981 and is presently situated in a
2,130m2 manufacturing plant in Warrington, England with a staff of
over 50. As a privately owned company our reputation is built on creating close
and positive relationships with our clients. Many of these customers are working
at the forefront of new technology - in the fields of plasma research, surface
science, vacuum processing and gas analysis. To maintain this reputation Hiden
Analytical have, over the years, established exceptional levels of technical
expertise in these areas within our company.
Coated glass plays a major energy conservation role in modern buildings;
because of this the glass coating industry has grown enormously in recent years.
Typical low emissivity glass comprises a thin silver layer sandwiched between
other metals and dielectrics. The extreme sensitivity of SIMS means
that it can play a crucial role in determining the composition and failure
mechanisms of this material.
The requirement for energy efficient buildings has led to the development of
glass coatings capable of reflecting heat (infrared radiation) whilst passing
visible light with little degradation of color or perceived clarity. In
addition, the coatings provide an opportunity to add color to the exterior of a
glass clad building, resulting in exciting architectural possibilities.
The active part of most low emissivity (low-e) glass is a thin layer of
sputter deposited metallic silver, typically only 10 nm thick. This is protected
by other metallic and dielectric layers, giving a layer stack of around 100nm
thick. Nonuniformities in thickness or composition lead to obvious optical
variation and degrade performance.
In-situ failure of the layers can be extremely expensive, especially if a
large building has to be reglazed, or many production units are affected.
Failure may be caused by inappropriate use of chemicals, incorrect handling, or
a manufacturing defect. Secondary ion mass spectrometry (SIMS)
provides a rapid and cost effective analysis tool either for production control
or failure analysis.
is able to evaluate layer composition and detect contaminants such as chlorine
and sulfur that can directly attack and darken the silver layer.
Secondary Ion Mass Spectrometry uses a focused, monoenergetic, chemically
pure ion beam of typically 1- 10 keV to sputter erode the surface under
analysis. Ionized secondary particles are then analysed and detected in the mass
spectrometer. At very low ion beam currents analysis is confined to the top few
monolayers – excellent for detection of surface contamination. As the ion beam
dose is increased and sputtering becomes more aggressive, subsequently deeper
layers are exposed and concentration as function of depth can be determined.
Generally SIMS depth profiles are presented with logarithmic
concentration scales owing to the extreme dynamic range that can be achieved,
ranging from ppb to bulk in the same analysis.
A flood of low energy electrons is used during analysis of insulating
samples, such as glass, to prevent the buildup of surface charge.
The analysis presented here was made using the Hiden SIMS
workstation, a complete and highly flexible quadrupole SIMS
instrument equipped with the IG20 gas
ion gun and MAXIM SIMS analyzer. The component parts are also available
separately enabling high performance SIMS to be
configured on a customers existing instrument (such as XPS or Auger), or
optimizing the analysis for a particular part of the process flow.
Depth Profile Analysis
The SIMS depth profile shown below was collected using 5keV Ar
ions focused to an 80ìm spot and rastered over an area of 400 x 550ìm. Positive
secondary ions were collected and a 500eV electron flood was employed to prevent
SIMS depth profile of a low-e glass sample
The SIMS depth profile agrees well with the design specification
Beginning at the exposed surface, the first layer is extremely thin and is
partly consumed by the pre-equilibrium region at the start of the analysis.
However, zinc and tin signals are clearly present at the very surface. There is
a high silicon signal (rising to a level almost of that in the glass substrate)
suggesting that a thin SiO2 layer may exist in the vicinity of the ZnSnOx.
The silicon nitride layer is characterised by a uniform concentration of
silicon, however, this layer also contains aluminium, estimated to be ~7%
Optical image of sample during analysis as seen by instrument
Beneath the SiN layer lies a similar thickness of AlN. Interestingly,
throughout this layer the Cr signal is rising, albeit from three orders of
magnitude below the eventual peak. SIMS is
perfectly suited to the investigation of this type of low concentration feature
and for the analysis presented here it was necessary to significantly reduce the
sensitivity to ensure that the peak of the Cr signal did not saturate the
The region below the AlN contains the thin silver layer and its associated
thin protective barrier layers containing Zn, Al, O Ni and Cr. The design
thickness of the NiCrOx layer is only 1 nm and there has been some mixing of
this into the silver layer during analysis.
Immediately below the silver, the thin Zn and ZnSnO layers are visible,
before the final AlN layer and the glass substrate.
In conclusion, the Hiden SIMS Workstation is easily able to perform sensitive
depth profile analysis on glass coatings, revealing layers of only a few
nanometers thick and simultaneously observing low concentrations.
Source: Hiden Analytical
For more information on this source please visit Hiden