Micro Sheet Resistance Probing (µRSP)

The advancement of the semiconductor industry has an enormous impact on our daily lives and society in general. Examples of semiconductor products are central processing units (CPUs), memory, imaging sensors in digital cameras and mobile phones - the list is inexhaustible. Major companies in this industry are Intel, IBM, AMD and NEC Toshiba etc.

Consumers worldwide demand faster and better computers and exciting electronic gadgets at a very competitive price. To fulfill this massive demand and enormous consumer market, the semiconductor industry has continuously reduced production costs and decreased the size of basic structures which are the building blocks of e.g. computer chips. The smallest width of structures inside the latest Xeon Intel processors is 45 nm. The depth of ultra-shallow junctions (USJ) of the next generation 32-nm technology is less than 20 nm. Characterizing the electrical properties (sheet resistance, mobility, active carrier density) of USJ and CIPT (resistance area product and tunnel magnetoresistance) wafers is critical for the development and quality control of next generation semiconductors.

Our vision is to develop novel metrology tools based on advanced silicon micromachining technology, which will enable the multibillion euro semiconductor industry to characterize USJ and CIPT structures in the near future.

Fig. 1: SEM images of µRSP. µRSP is a miniaturization of the well established four-point-probe metrology used for sheet resistance measurements. Left: top view, the cantilevers are about 25 µm long. Middle: front view. Right: zoom in of the front view.

Advanced metrology for characterization of magnetic tunnel junctions

Metrologies play a dominant role in the development of new materials and products. 
Among a group of materials that are particularly difficult to characterize is magnetic tunnel junctions (MTJ’s). These are multilayered structures of magnetic thin films separated by one or more dielectric tunnel barrier(s), which are only few angstroms thick. MTJ’s are widely used in hard disk read heads and magnetic random access memory (MRAM). 

In the past decade, the current-in-plane tunneling (CIPT) method has been employed as an increasingly important MTJ metrology and is today used in industry and research worldwide. The CIPT method extracts electrical material properties of MTJ’s using micro fabricated electrodes, the so-called micro 12-point probes (M12PP). The CIPT method extracts the resistance-area product (RA) and the tunnel magnetoresistance (TMR) of non-patterned MTJ samples. 

The measurement requirements depend on the specific structure of the MTJ samples, and in order to meet the present and future requirements for MTJ based products, improvements to measurement speed, dynamic range, precision, reliability and cost are all urgent challenges to be addressed in this project.
 
Fig 2. State of the art M12PP supplied by CAPRES A/S.

Fig. 3. L-shaped static contact micro four-point probes. Similar cantilever design will be tested in this project to determine their influence on CIPT measurement quality and probe lifetime.
Petersen D. H., et al. Static contact micro four-point probes with <11 nm positioning repeatability. Microelectronic Engineering 85 (2008) 1092–1095.

Micro Hall effect measurements for commercial use

In 2008 researchers at DTU Nanotech invented a method to measure charge carrier mobility using inline micro cantilever four point probes (µ4pp). Inline µ4pp is the core technology of Capres A/S (located at Scion DTU), who is the collaborational partner on the project. The aim is to further refine the technique for proper implementation into a semi-automatic measurement platform. The main focus is on how various sources of error affect the measurements, how to detect them and deal with them. This will ensure maximum reliability of the metrology as expected by the industry. Secondly precision and accuracy must be optimized to offer the best possible performance.

Fig. 4. The core principle of measuring the charge carrier mobility with an inline µ4pp is to break sample symmetry by measuring close to the sample edge. Only at the edge a Hall signal can be measured when the sample is placed in a magnetic field perpendicular to the edge. L-shaped cantilevers are used to minimize dynamic position errors.

 

People

   

Daniel Kjær   Henrik H. Henrichsen Dirch H. Petersen    Ole Hansen 
 

Partners

 


 

Student projects

Please contact Ole Hansen.
 

Funding

DTU Nanotech, Capres A/S, and The Danish National Advanced Technology Foundation

https://www.nanolab.dtu.dk/english/research/silicon-microtechnology/research/mrsp
19 JUNE 2019