Technology News
10/01/2003
Tungsten emitters modify Planck's law
Researchers at Sandia National Laboratories, Albuquerque, NM, have shown that tungsten lattice filaments when heated emit remarkably more energy in the near-infrared range than solid tungsten filaments. Currently, the output is keyed to the 1.5–2µm IR range, but has a "tail" into the visible spectrum.
This output offers the possibility of a superior energy source for hybrid electric cars, electric equipment on boats, and industrial waste-heat driven electrical generators. The lattices' energy emissions put more energy into wavelengths used by photovoltaic cells used to run engines. The work has been granted two patents with a third pending.
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For example, a photonic lattice absorbing energies from a power plant generator's excess heat could release it at higher frequencies readily absorbable by photovoltaic cells that power electricity-driven engines. While such systems exist, their efficiencies are low because receivers cannot absorb incoming energies across the spectrum of IR radiation generated as unwanted heat, but only from limited bands.
In effect, the new lattice could serve as a funnel, forcing heat radiation into predetermined frequency bands. When placed between a solar, dynamo, or fire generator and receiver, it is envisioned that the lattice can be engineered to absorb energies, become thermally excited, and release them in only a few frequency bands.
The lattices are photonic crystals because of the crystalline regularity of the spacing of their components. As previously reported in Solid State Technology ("Curious-looking device bends light with little loss," Technology News, Jan. 2001), initially the interest in these crystals was in their ability to bend specific frequencies of light without loss of energy, related to the dimensions of the crystal's channels. The current work uses the channels not to bend light, but to permit input energy to exit only in the desired frequency bands.
The submicron-sized lattices (i.e., stacks of 0.5µm dia. "miniature logs" separated by 1.5µm) can be inexpensively mass-produced using semiconductor fabrication technologies. In the work at Sandia Labs, the filaments are jury-rigged onto the screw-in bases and filament supports from common light bulbs.
Sandia researcher Shawn Lin, says, "The output achieved exceeds Planck's law of blackbody cavity radiation [which predicts maximum emissions expected at any wavelength from ideal solids] four to ten times at the near-IR." In terms of electrical output, with the lattice heated to 1250°C in a vacuum (i.e., the typical operating temperature of a thermal photovoltaic generator), a conversion efficiency of 34% was calculated, three times the 11% performance of an ideal blackbody radiator.
"Electrical power density was calculated to be ~14W/cm2, rather than 3W/cm2 expected from an ideal blackbody radiator. In addition, no deterioration of the tungsten lattice was observed, although long-term tests have yet to be run," he says.
Lin says his group's work modifies Planck's law by demonstrating the creation of a new class of emitters.
"A photonic lattice apparently subjects energies passing through its links and cavities to more complex photon-tungsten interactions than Planck dreamed of when he derived his system that successfully predicted output energies of simple heated solids," said Lin. A lattice's output is larger than a solid's only in the frequency bands the lattice's inner dimensions permit energy to emerge in.
"If our results can be extended to the visible spectrum, ramifications of this work may help form the next generation of lighting after the currently more mature LED technology," says Lin.
APC and e-Diagnostics with SECS
As a subcontractor to a NIST project, Cimetrix, Salt Lake City, UT, has signed on to enable connectivity that will help shake out new equipment data acquisition (EDA) standards. Dating from late 2001, NIST "e-Manufacturing Security Framework to Improve Semiconductor Manufacturing Productivity" project is a joint venture with Advanced Micro Devices (AMD), ILS Technology, and Oceana Sensor Technologies. The Semi EDA standards efforts target enabling rich, secure, standard format data for e-Manufacturing.
The contribution from Cimetrix is CIMPortal, the ability to take data from a SECS wafer fab tool and separate MES and e-Diagnostics data. This enables the use of older SECS-based software interconnects.
David Faulker, executive VP at Cimetrix, says, "This will let us look at the financial benefits and the effectiveness of new EDA standards. Then, the JV participants will go back to the EDA standards committee with recommendations.
SECS and GEM on existing tools (i.e., 200mm fabs) was done when data throughput and multihosts were not a consideration. "CIMPortal allows us to work with these existing interfaces, typically the only connection that comes off a tool, and hook into some of the neat stuff, pumping a massive amount of data to the host level, one stream to the MES and the other to data robust systems that are needed to drive APC and e-Diagnostics," says Faulkner. "It is the only way to get APC and e-Diagnostics going with SECS tools. The trick is dividing out the right data, and reformatting it into Semi-standard SOAP/XML-based data without any software changes to existing equipment."
CIMPortal passes this data to ILS Technology's e-Centre, which then persists, filters, and securely delivers tool data to users internal and external to the fab.
Cimetrix's capability will be installed in an AMD fab by mid-August and is expected to enable unparalleled access to critical data directly from equipment-to-equipment engineering control applications without having to wait for each equipment supplier to update their software.
Michael Feaster, VP of software engineering at Cimetrix, says, "A key goal of CIMPortal is for manufacturers to avoid any changes to existing equipment interface software, which are costly to both the IC maker and equipment supplier." CIMPortal operates on Windows servers connected to multiple pieces of equipment at various locations throughout a fab; it is being tested with both SECS-I and HSMS protocols and has the ability to convert from one to the other.
An ALD with CVD throughput?
What do you do when you have two conflicting requirements in ALD processing — throughput and maintainability — but only one process knob: residence time (the time that a flowing gas spends inside the chamber)? You develop a second process knob, of course.
Conventional ALD uses a constant residence time of about 10–40 msec throughout the process. Sundew Technologies uses a different gas routing apparatus and method compared to conventional ALD that allows a short residence time in the range of 0.5–4 msec when chemicals are moving into and out of the process chamber, and long residence times >200 msec when chemicals are interacting with the wafer.
The technique is called synchronously modulated flow draw-ALD and the company says it has achieved a deposition rate >11nm/min for a 450 msec cycle time and is capable of going for more than 45,000 wafers with 50Å thick films (see figure).
Ofer Sneh, company president and director of technology, describes the method as a way to de-couple precursor dose (exposure) optimization from the speed at which the precursor is flushed out of the process chamber. "The flow of chemicals into the process chamber during the dose time can be choked down to a very low flow, about 10sccm or less," explains Sneh. "We're not bound to one flow rate throughout the process."
 Mini-marathon data as a function of accumulated maintenance load (units: equivalent number of wafers) with 50Å thick film/wafer. |
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The process technology specifically addresses the trade-off required to make ALD cost-effective. Very slow flow ensures that the chemicals react with the wafer.
"If you let a high flow of ALD precursor chemicals enter the chamber, you are using only a small part of the chemical dose, and the chemicals that you waste turn into maintenance-intensive build-up of loose film on the chamber walls," explains Sneh.
Hence the use of a second process knob — the draw out of the process chamber — to be able to switch flows at the ALD process rate. "Since conventional ALD uses constant flow, the flow rate at the dose step has to be much higher than necessary in order to match the need to quickly rid the chamber of residual chemicals before a new precursor is introduced," said Sneh.
While the company currently is in start-up mode, Sneh notes that its technology is being evaluated by several major chip manufacturers. "Results so far have produced a keen interest in commercializing the technology," says Sneh, who anticipates that it could be a replacement for HDP currently used for STI applications.