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New Method for Metrology with sub-10 nm Lithrography

New Method for Metrology with sub-10 nm Lithrography
by Daniel Nenni on 05-06-2014 at 6:00 pm

NewPath Research will describe their new method for nanoscale carrier profiling in semiconductors on May 19[SUP]th[/SUP] at the Annual SEMI Advanced Semiconductor Manufacturing Conference (ASMC) in Saratoga Springs, NY. This new method is intended to fill the gap that has been addressed in the Roadmaps for the semiconductor industry by providing metrology tools that have sufficiently fine resolution for use with the new sub-10 nm lithography.

In the new method, a mode-locked ultrafast laser is focused on the tunneling junction of a scanning tunneling microscope (STM) to generate a periodic sequence of femtosecond pulses of electrons that is superimposed on the DC tunneling current. In the frequency domain the sequence of electron pulses is equivalent to hundreds of microwave harmonics at integer multiples of the pulse repetition frequency of the laser. These harmonics set the present state-of-the-art for a narrow linewidth microwave source, thus enabling hyperspectral measurements to be made with exceptionally low noise. The electromagnetic field and photon processes within each laser pulse cause each electron pulse by optical rectification, but all subsequent photon and phonon processes decay during the time between consecutive laser pulses so they have no direct effect on the measured microwave harmonics. Each electron pulse forms a nanoscale spot of electrical charge at the surface of the semiconductor sample in the STM, and hyperspectral measurements of the microwave power are made to determine the spreading impedance as the charge moves from this spot, in order to calculate the concentration of carriers in the semiconductor.

The new method may be understood by relating it to the present state-of-the-art means of Scanning Spreading Resistance Microscopy (SSRM). In SSRM nanometer-size probes made of electrically conductive diamond are pressed into the surface of a semiconductor and the spreading resistance is measured in order to calculate the carrier concentration. However, our new method is non-destructive, and has the potential of making rapid seamless measurements across large areas of the semiconductor. Furthermore, instead of using fixed probes having a specific size, the spot may be adjusted from 0.1 nm to 1 nm in radius by varying the tip-sample separation in order to provide 3-D characterization of the sample.


Prototype Scanning Tunneling Microscope head.

The figure shows a prototype STM head developed to provide efficient and quantitative coupling of microwave harmonics from the tunneling junction. It is unique in that all DC and high-frequency sources and measurement apparatus are connected at one end of a section of miniature semi-rigid coaxial cable while all connections to the tip and sample are made in an electrically-small loop at the opposite end.

The new method was developed at NewPath Research L.L.C. in collaboration with Los Alamos National Laboratory and the University of Utah, with one patent (U.S. 8,601,607) issued and several others pending.

Celebrating 25 years of manufacturing excellence, the SEMI Advanced Semiconductor Manufacturing Conference continues to fill a critical need in our industry. Join conference co-chairs Israel Ne’eman, Applied Materials and Oliver Patterson, IBM Microelectronics, and industry professionals from around the globe during 3 days of networking, learning and knowledge-sharing on new and best-method semiconductor manufacturing practices and concepts. Beginning May 18, with a welcome reception, ASMC 2014 features over 90 technical presentations, keynotes and tutorials and networking opportunities over the following days.

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