Manufacturing Bits: Sept. 19

Ion implant lithography; new AFMs; wide-bandgap semis.


Ion implant lithography
At a recent conference, the University of California at Berkeley presented more details about its efforts to develop a multiple patterning method using tilted ion implantation (TII) technology.

TII is somewhat similar today’s self-aligned double patterning (SADP) processes in logic and memory. SADP and the follow-on technology, self-aligned quadruple (SAQP), enable chipmakers to extend lithographic scaling, but the technologies are expensive and time consuming.

SADP uses one lithography step and additional deposition and etch steps to define a spacer-like feature. In TII, though, ion implantation steps are inserted in a flow to create tiny features.

“TII can be used to pattern features as small as 10nm,” said Tsu-Jae King Liu, the TSMC Distinguished Professor in Microelectronics at the University of California at Berkeley. Liu presented details of the technology at the recent SPIE Photomask Technology + Extreme Ultraviolet Lithography 2017 conference.

The technology can be scaled down to 10nm half-pitch and beyond. The cost of TII double‐patterning is roughly 60% of the cost of SADP, according to researchers.

In a recent issue of Silicon Semiconductor, the University of California at Berkeley outlined the process steps for TII. The work was done in conjunction with Axcelis Technologies.

The first steps are similar to SADP. Initially, a mask layer is deposited on a substrate, followed by a mandrel layer and a resist, according to UC Berkeley. Then, like SADP, the structure is patterned and etched, which, in turn, forms tiny mandrels. Unlike SADP, though, an ion implantation process is then inserted in the TII flow.

The mandrel structure then undergoes a double implantation process. The implanter hits the mask layer with ions at a positive tilt angle at 15 degrees, according to researchers. Then, a second implant is implemented at a negative tilt angle. The implanted material is removed using etch.

The technology opens up new possibilities for chip designs. Generally, ion implantation is a mature and simple process. “TII improves low‐ and mid‐frequency line‐edge roughness,” Liu said.

New AFMs
The National Institute of Standards and Technology (NIST) has devised a new atomic force microscope (AFM) that can be used for chemical composition and thermal conductivity measurements at the nanoscale.

Used for metrology and other applications, AFMs utilize a tiny tip that looks at the surface of a structure at the angstrom level.

NIST, meanwhile, has devised a new AFM probe that weighs a trillionth of a gram and achieves a high temporal resolution. Researchers integrated the probe with an optical resonator. Then, they combined AFM with a technique called photothermal induced resonance (PTIR). PTIR uses infrared light to examine the composition of a material.

Illustration of a new atomic force microscope (Source: NIST)

The combo AFM-PTIR system can simultaneously measure the thermal conductivity and chemical composition of structures and materials. With the new AFM-PTIR system, researchers looked at a class of microcrystals or tiny pores called metal-organic frameworks (MOFs). The MOFs were heated by a light pulse. Researches then recorded how long it took for the MOF crystals to cool down and return to their original size.

In the experiment, the AFM-PTIR system can record a displacement as small as a trillionth of a meter, which occurs over 10 billionths of a second.

Wide-bandgap semis
The Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E) recently announced $30 million in funding for new 21 projects.

The projects are part of the agency’s so-called Creating Innovative and Reliable Circuits Using Inventive Topologies and Semiconductors (CIRCUITS) program. CIRCUITS project teams will accelerate the development of a new class of electric power converters.

The power converters will be based on wide-bandgap (WBG) semiconductor technology, using materials like silicon carbide (SiC) or gallium nitride (GaN). “Hardware built with WBG devices has the potential to be smaller, lighter, and much more energy-efficient, with applications across valuable sectors including transportation, information technology, the grid, and consumer electronics,” said ARPA-E Acting Director Eric Rohlfing. “Developments from CIRCUITS projects could one day lead to super-fast, compact electric vehicle chargers, more efficient ship propulsion systems, and lighter, aerodynamic aircraft that can carry more passengers with less fuel.”