Solutions for a High-quality Analysis of Micro- and Nano-structures
in semi-conductor productions, manufacture of МEМS
and in various spheres of R&D
Xact for thinning with application of the adaptive ion milling technology;
EM3i for a preliminary preparation of samples with application of the cryo-cooled dry sawing technology.
Installation for thinning with application
of the adaptive ion milling technology
A specific feature of Xact is that it uses a "double-beam" concept, allowing us to watch in real time the thinning of a sample and to have a precision control of the process fig.1). The installation consists of the following main units: a vacuum camera with a loading lock; a precision manipulator; a visual observation system; a scanning electron microscope (SEM), which at the final stages of thinning also works as a transmission electron microscope (TEМ); sensors of the back-scattered, secondary and transmitted through a sample electrons; an ion gun with a xenon source and controllable energy, form and direction of a beam. As a whole, the concept of Xact system (fig.2) resembles a TEM device.
The monitoring system uses three kinds of detectors, which ensure a contrasting high-resolution image (STEM). Thanks to this during the thinning an operator can continuously observe a sample, measure its thickness in real time, and determine a stop point of the process with high accuracy.
The source of ions is duoplasmatron, which ensures emission of a huge number of ions from a small volume of gas (annual consumption of gas compressed under pressure of 6 bars is about 0.5 l). Application of a xenon source is explained by the fact that xenon does not interact with the processed material – its atoms are of a bigger size and weight, therefore they do not penetrate deeply into the structure of the thinned sample. Possibility of a flexible control of the beam energy ensures adjustment of the speed of thinning. Thus, if the beam energy is about 1 keV and the incidence angles are 3 – 4°, it is possible to remove separate atomic layers, achieving a reduction of the thickness of the damaged amorphous layer of the sample up to 1 – 2 nm.
At the initial stage of processing the thinning of a sample is done by the beams of relatively high energies – about 10 keV. When its thickness reaches about 100 nm, an electronic beam from REМ penetrates through a sample and reaches the detectors of the transmitted beams. At the stage of a "soft" processing the energy of a beam of ions of xenon decreases up to 1 keV, allowing us to obtain thickness of 30 nm with a minimal damage of the sample. During the thinning process the thickness and quality of the sample’s surface are controlled, and optimization of its profile is possible.
The employed technical solutions make possible to obtain samples with very good characteristics. For example, typical values for a semi-conductor sample prepared for a side-view of TEM are the following:
Thickness in the zone with the width of 3 microns – 18±4 nm with homogeneity of 10%;
Thickness in the zone with the width of 10 microns – 30±10 nm with homogeneity of 10%;
Thickness in the zone with the width of 30 microns – 100±30 nm with homogeneity of 10%.
The basic characteristics of Xact installation are presented in table 1. After selection of the modes for processing of a sample, its operation in an automatic mode is possible. The installation is equipped with an optical unit for an automatic calibration. As a whole, the sum total of the applied solutions has no analogues, which makes this system unique.
Installation for a preliminary preparation of a sample
EM3i installation (fig.4) is intended for a preliminary preparation of a sample by the method of a dry cryo-cooled disk sawing. It ensures fast automatic processing of materials and is a part of a complex solution of the sample preparation for SEM and TEМ (side view, plan view). Dry cryo-cooled sawing allows us to prepare samples from crystal and amorphous materials. At the outlet a sample is fixed on compatible holder, which facilitates operation with it at the subsequent stages (fig.5). Another feature of ЕМ3i is operation with plates up to 300 mm in size, at that the system allows us to carry out their optical inspection, to find and mark interesting areas. The basic characteristics of the installation are presented in table 2.
Typical process of a sample preparation
First, an operator loads a sample in ЕМ3i and specifies the target zone and the research type, for which it should be prepared. The installation makes all the operations in an automatic mode. At the outlet the operator receives the prepared sample on a compatible holder, ready to be loaded into Xact installation. After that the final stage of the preparation is carried out in a semi-automatic or automatic mode with a continuous real time control.
An important advantage of the system is a high degree of automation, therefore, dependence of the speed and quality of work on the human factor is minimal. For example, a high-quality sample with thickness of the investigated zone of 20 nm can be prepared approximately in one hour and a half. The basic stages of the process are shown in fig.6.
Xact and EM3i installations are parts of an integrated complex, allowing us to automate the process and to reduce the time for preparation of the investigated samples, considerably improving their quality. One can say for sure that the given solution is of great interest to the laboratories employing electron microscopy in their work. ■