Low-k dielectric family introduced by SBA Materials
Since Intel's Bohr published his seminal paper on interconnect scaling in 1995, the IC community has been searching for a manufacturable low-k dielectric which could scale to below k=2.0. The ITRS requirements for low-k have been continually relaxed due to the difficulty in achieving an electrically reliable, manufacturable process with either spin-on organic or inorganic dielectrics or C-doped CVD materials. Chemical and equipment companies, and the IDMs and foundries, have spent hundreds of millions of dollars trying to find this "holy grail." Technical articles over the last decade have documented issues such as CTE and fracture toughness that have arisen when trying to integrate highly porous low-k dielectrics.
The most recent ITRS roadmap (2009) indicates that low-k introduction to manufacturing has followed this timeline:
Now, as dense carbon-doped oxides k=2.8) attempt to evolve into porous carbon-doped oxides with "ultralow" k<2.5 (ULK), there have been widely reported problems in manufacture, test, assembly, and packaging of these fragile chips. Most fabs and foundries have reported that they are struggling to see their way to a manufacturable k<2.5 solution. In fact the 2009 ITRS roadmap points to a "red brick wall" when attempting to go past keff=2.5.
Several years ago, SBA Materials CTO Mark Philips and his team started developing "block polymer templated inorganic oxides" (US Patent #6,592,764) which self-assemble into materials with controlled structure and physical properties. These spin-on dielectrics (SBAM uLK) combine an amphiphilic block copolymer (structure-directing template) with silicon alkoxide esters. The block copolymer and silicate esters are self-assembled and the silicon compounds are polymerized to form mesoscopically structured silicon composites. The template is then removed (thermal, UV and/or e-beam) leaving a porous alkylated silicon dioxide low-k dielectric.
Properties of three grades of the new dielectrics are shown in the above table.
Microindent photos of uLK 124 show a clean ductile indent vs. many of the low-k materials currently available which show brittle fracture during such testing.
The uLK materials can be integrated into existing fab lines using equipment and process flows already in place, according to the company. While spin-on materials would be a change for IC fabs that currently use CVD ILD dielectrics, CTO Phillips insists that this has not been a problem with current customers since spin coating is a well-known technique for materials deposition.
SBA has agreements in place with Asian chemical producers to manufacture, bottle, and supply under their label, to ensure quantity and IC grade quality that a start-up would not be trusted to deliver, reveals SBA CEO Bill Cook. While the company reports that their uLK materials "...are in advanced qualification at three of the top 10 IC fabs in the world," they are not ready to reveal exactly who yet, because of secrecy agreements that are in place. It is thought that all three of the lead customers are in Asia.
The company is currently working with IMEC, and work on their first SBAM uLK processing paper was to be jointly presented at the Advanced Metallization Conference in Albany, NY in early October. — Dr. Philip Garrou, contributing editor