The BRR™, a truly integrated SEM/SPM System

Binnig, Rohrer, Ruska united. Not only in the Nobel Prize

In 2011 two of the most important innovations to the field of microscopy will celebrate their anniversary. When Ernst Ruska focused the first time an electron beam in 1931 the base stone for the scanning electron microscopy was laid. Only two years later Ruska finally succeeded to reach a magnification of 12.000 times with his self constructed first electron microscope. This magnification lies way beyond the abilities of the light microscope the highest resolving technique at that times. The effect of electron tunneling between a sharp probe and a surface was discovered by Gerd Binnig and Heinrich Rohrer in 1981. One year later Binnig and Rohrer combined the tunneling effect between Probe and sample with a scanning motion. The invention of the scanning tunneling microscope marks the start for all the diverse scanning probe microscopic methods known today. All three pioneers and their revolutionary ideas were honored in 1986 with the Nobel prize in physics.

DME took the challenge to combine the highest resolving microscopic techniques in a single system in a totally integrated way. The resulting system gives researches a tool in hand to address questions in experiments which could never performed before. In memory and honor to the inventors of the combined microscopic techniques Binnig, Rohrer and Ruska this system should carry their initials, BRR, as its name. The logo on the left unites the initials of the inventors and a symbolic display of the two techniques. The initials of Binnig and Rohrer are connected by a SPM sensor (cantilever) as a symbol of all SPM techniques. The second R, for Ruska, is partly formed by a wave. This symbol stays for the accelerated electrons which are used in th scanning electron microscope. The displaced "e" represents the secondary electrons which are used to generate the image in an SEM.

Why build a combined SEM/AFM?

A combined SEM/AFM has a number of advantages in comparison to the two systems as standalone. Have a look at our article SEM and AFM, a natural combination.

Hardware Integration

Our approach to realize a combined SEM/SPM system bases on the integration of a vacuum compatible SPM into existing SEM systems. This combination was selected to reach highest performance and usability of the system. Another benefit of this strategy is that existing SEM systems can be upgraded to a combined SEM/SPM system. In both cases the SEM will be not limited in its function so that combined SEM/SPM measurements are possible.

The SPM for integrations designed as a sample scanner. This design enables to align the electron beam and the SPM tip with the highest precision, because the beam and tip are not moved against each other. Even during SPM scanning. This enables unknown possibilities of combined measurements. Additionally highest performance in terms of resolution and frame rate can be achieved by this setup. The scan unit itself is the next developmental step of our STM scanner, known for highest stability and reliance in the last decades. With a scan volume of 9 µm x 9 µm x 1 µm and a possible sample size of 10 mm the design claim for high resolution is clearly visible. electronic components like the laser diode the detector and preamplifier are located inside the vacuum chamber in hermetically encapsulated compartments. The alignment of the laser path and also the exchange of the cantilever and the sample can be performed without breaking the vacuum. The positioning of the SPM in respect to the SEM and positioning the SPM tip to the area of interest can be realized remote controlled. With a small number of changes to the SPM a UHV compatible version is available.

The first version of the BRR™ will be realized as a integration of the DME developed SPM in a ZEISS AURIGA System. In this system SEM, FIB and SPM will be united and can be performed in combined measurements. The SPM is mounted to a special designed stage which enables vertical and rotational movement. This stage is part of the main door of the AFM (see figure on the left). In this setup the SPM tip can be aligned with the FIB e-beam cross point and rotated around it in an angle of about 75°. This enables the operator to either align the e-beam or the FIB perpendicular to the sample surface. The rotation of the whole SPM opens the possibility to work with commercially available Si and SiN SPM probes because it is possible to observe the tip with the SEM from a sidewards angle (see Fig on the right side). With a free field of view for the SEM the SPM the tip can be positioned to the area of interest under total observation by SEM with nm precision. From a view position perpendicular to the sample the view on SPM tip is blocked by the cantilever itself. The SPM the tip can be positioned to the area of interest under total observation by SEM.

Software Integration

The grade of functionality of highly complex scientific instruments, like the BRR™, depends to a large part on the operating software. To achieve the seamless integration of the to methods a single software user interface is a must. The open design of our SPM Software ScanTool enables us to integrate a self designed SEM operating software. So the operator is able to control both systems from one and the same software without clicking through a labyrinth of tabs and windows. The view on all settings and image data of both methods is unblocked and accessible. The software is designed for highest work flow and throughput. In the same time program functions like the DME Automator gives access to all functions of the BRR™ system, so that user designed advanced measurement routines can be designed and performed. So it is possible to create measurement automatically running measurement routines for the acquisition of comparable data from different regions of the sample. Image data from SEM and SPM are analyzed in the ScanTool software. Standard analyzing tools are available, more advanced or specialized analysis procedures can be self implemented or implemented by us om customer demand by the use of the "DME Automator" or "DME Image Calculator".

Application

The BRR™ opens totally new possibilities for the investigation of surfaces and nano structured devices. Both methods equalizes their lags in this combination and the benefits add up and gain a tremendous amount of possibilities. SEM images can be overlaid with 3D surface plots from the SEM wile the fast, high resolving imaging possibilities allow positioning of the SPM tip with an incredible precision The SPM is able to perform standard modes like AC, DC, LFM and PDM mode, electrical modes like EFM, KPFM, SCM, SSRM and STM. Different modulator-detector role-allocations between SEM and SPM create the ability to widen the possibility of application different modes and even enable to create totally new measuring modes. As an example the e-beam could be used to induce current in the sample surface (electron beam induced current). The propagation of the electrons through in the sample could be imaged by the SPM tip.