|
Melting defects could lead to smaller, more powerful microchips
May 05, 2008As microchips shrink, even tiny defects in the lines, dots and other shapes etched on them become major barriers to performance. Princeton engineers have now found a way to literally melt away such defects, using a process that could dramatically improve chip quality without increasing fabrication cost.
The method, published in the May 4 issue of Nature Nanotechnology, enables more precise shaping of microchip components than what is possible with current technology. More precise component shapes could help manufacturers build smaller and better microchips, the key to more powerful computers and other devices.
"We are able to achieve a precision and improvement far beyond what was previously thought achievable," said electrical engineer Stephen Chou, the Joseph C. Elgin Professor of Engineering, who developed the method along with graduate student Qiangfei Xia. Chou's lab has previously pioneered a number of innovative chip making techniques, including a revolutionary method for making nanometer-scale patterns using imprinting.
Microchips work best when the structures fabricated on them are straight, thin and tall. Rough edges and other defects can degrade or even ruin chip performance in most applications. In integrated circuits, for instance, such flaws could cause current to leak and voltage to fluctuate. In optic devices, they could interfere with the transmission of light. In biological devices, they could impede the flow of DNA and other biomaterials.
"These chip defects pose serious roadblocks to future advances in many industries," Chou said.
To deal with this problem, researchers try to improve the process used to make the microchips. However, Chou said such an approach works only to a point; eventually chip makers will run up against fundamental physical limits of current manufacturing techniques. In particular, the electrons and photons that are used like chisels to carve out the microscopic features on a chip always have some random behavior. This effect becomes pronounced at very small scales and limits the accuracy of component shapes.
"What we propose instead is a paradigm shift: Rather than struggle to improve fabrication methods, we could simply fix the defects after fabrication," said Chou. "And fixing the defects could be automatic -- a process of self-perfection."
Chou's method, termed Self-Perfection by Liquefaction (SPEL), achieves this by melting the structures on a chip momentarily, and guiding the resulting flow of liquid so that it re-solidifies into the desired shapes. This is possible because natural forces acting on the molten structures, such as surface tension -- the force that allows some insects to walk on water -- smooth the structures into geometrically more accurate shapes. Lines, for instance, become straighter, and dots become rounder.
Simple melting by direct heating has previously been shown to smooth out the defects in plastic structures. This process can't be applied to a microchip, for two reasons. First, the key structures on a chip are not made of plastic, which melts at temperatures close to the boiling point of water, but from semiconductors and metals, which have much higher melting points. Heating the chip to such temperatures would melt not just the structures, but nearly everything else on the chip. Secondly, the melting process would widen the structures and round off their top and side surfaces, all of which would be detrimental to the chip.
Chou's team overcame the first obstacle by using a light pulse from so-called excimer laser, similar to those used in laser eye surgery, because it heats only a very thin surface layer of a material and causes no damage to the structures underneath. The researchers carefully designed the pulse so that it would melt only semiconductor and metal structures, and not damage other parts of the chip. The structures need to be melted for only a fraction of a millionth of a second, because molten metal and semiconductors can flow as easily as water and have high surface tension, which allows them to change shapes very quickly.
To overcome the second obstacle, Chou's team placed a plate on top of the melting structures to guide the flow of liquid. The plate prevents a molten structure from widening, and keeps its top flat and sides vertical, Chou said. In one experiment, it made the edges of 70 nanometer-wide chromium lines more than five times smoother. The resulting line smoothness was far more precise than what semiconductor researchers believe to be attainable with existing technology.
The conventional approach to fixing chip defects is to measure the exact shape of each defect, and provide a correction precisely tailored to it -- a slow and expensive process, Chou said. In contrast, Chou's guided melting process fixes all defects on a chip in a single quick and inexpensive step. "Regardless of the shape of each defect, it always gets fixed precisely and with no need for individual shape measurement or tailored correction," Chou said.
One of the big surprises from this work is observed when the guiding plate is placed not in direct contact with the molten structures, but at a distance above it. In this situation, the liquid material from the structures rises up and reaches the plate by itself, causing line structures to become taller and narrower -- both highly desirable outcomes from a chip design perspective.
"The authors demonstrate improved edge roughness and dramatically altered aspect ratios in nanoscale features," said Donald Tennant, director of operations at the NanoScale Science and Technology Facility at Cornell University. The techniques "may be a way forward when nanofabricators bump up against the limits of lithography and pattern transfer," he said.
Next, Chou's group plans to demonstrate this technique on large (8-inch) wafers. Several leading semiconductor manufacturers have expressed keen interest in the technique, Chou said.
Princeton University, Engineering School
Microchips work best when the structures fabricated on them are straight, thin and tall. Rough edges and other defects can degrade or even ruin chip performance in most applications. In integrated circuits, for instance, such flaws could cause current to leak and voltage to fluctuate. In optic devices, they could interfere with the transmission of light. In biological devices, they could impede the flow of DNA and other biomaterials.
"These chip defects pose serious roadblocks to future advances in many industries," Chou said.
To deal with this problem, researchers try to improve the process used to make the microchips. However, Chou said such an approach works only to a point; eventually chip makers will run up against fundamental physical limits of current manufacturing techniques. In particular, the electrons and photons that are used like chisels to carve out the microscopic features on a chip always have some random behavior. This effect becomes pronounced at very small scales and limits the accuracy of component shapes.
"What we propose instead is a paradigm shift: Rather than struggle to improve fabrication methods, we could simply fix the defects after fabrication," said Chou. "And fixing the defects could be automatic -- a process of self-perfection."
Chou's method, termed Self-Perfection by Liquefaction (SPEL), achieves this by melting the structures on a chip momentarily, and guiding the resulting flow of liquid so that it re-solidifies into the desired shapes. This is possible because natural forces acting on the molten structures, such as surface tension -- the force that allows some insects to walk on water -- smooth the structures into geometrically more accurate shapes. Lines, for instance, become straighter, and dots become rounder.
Simple melting by direct heating has previously been shown to smooth out the defects in plastic structures. This process can't be applied to a microchip, for two reasons. First, the key structures on a chip are not made of plastic, which melts at temperatures close to the boiling point of water, but from semiconductors and metals, which have much higher melting points. Heating the chip to such temperatures would melt not just the structures, but nearly everything else on the chip. Secondly, the melting process would widen the structures and round off their top and side surfaces, all of which would be detrimental to the chip.
Chou's team overcame the first obstacle by using a light pulse from so-called excimer laser, similar to those used in laser eye surgery, because it heats only a very thin surface layer of a material and causes no damage to the structures underneath. The researchers carefully designed the pulse so that it would melt only semiconductor and metal structures, and not damage other parts of the chip. The structures need to be melted for only a fraction of a millionth of a second, because molten metal and semiconductors can flow as easily as water and have high surface tension, which allows them to change shapes very quickly.
To overcome the second obstacle, Chou's team placed a plate on top of the melting structures to guide the flow of liquid. The plate prevents a molten structure from widening, and keeps its top flat and sides vertical, Chou said. In one experiment, it made the edges of 70 nanometer-wide chromium lines more than five times smoother. The resulting line smoothness was far more precise than what semiconductor researchers believe to be attainable with existing technology.
The conventional approach to fixing chip defects is to measure the exact shape of each defect, and provide a correction precisely tailored to it -- a slow and expensive process, Chou said. In contrast, Chou's guided melting process fixes all defects on a chip in a single quick and inexpensive step. "Regardless of the shape of each defect, it always gets fixed precisely and with no need for individual shape measurement or tailored correction," Chou said.
One of the big surprises from this work is observed when the guiding plate is placed not in direct contact with the molten structures, but at a distance above it. In this situation, the liquid material from the structures rises up and reaches the plate by itself, causing line structures to become taller and narrower -- both highly desirable outcomes from a chip design perspective.
"The authors demonstrate improved edge roughness and dramatically altered aspect ratios in nanoscale features," said Donald Tennant, director of operations at the NanoScale Science and Technology Facility at Cornell University. The techniques "may be a way forward when nanofabricators bump up against the limits of lithography and pattern transfer," he said.
Next, Chou's group plans to demonstrate this technique on large (8-inch) wafers. Several leading semiconductor manufacturers have expressed keen interest in the technique, Chou said.
Princeton University, Engineering School
Defects News and Current Defects Events RSSScientists demonstrate means of reducing Alzheimer's-like plaques in fly brain
Neuroscientists at Cold Spring Harbor Laboratory (CSHL) are part of a collaboration that has succeeded in demonstrating that overexpression of an enzyme in the brain can reduce telltale deposits causally linked with Alzheimer's disease.
Vitamin A pushes breast cancer to form blood vessel cells
Researchers at Georgetown University Medical Center have discovered that vitamin A, when applied to breast cancer cells, turns on genes that can push stem cells embedded in a tumor to morph into endothelial cells. These cells can then build blood vessels to link up to the body's blood supply, promoting further tumor growth.
Researchers crack final part of the immune system code
A group of researchers at the Technical University of Denmark and the University of Copenhagen have developed models of neural networks that make it possible to simulate how the body protects itself from disease and predict the immune system's access codes.
Mayo Clinic spearheads research to discover unsuspected gene for atrial fibrillation
Mayo Clinic researchers have found a gene mutation linked to one family's hereditary form of atrial fibrillation. Researchers hope this discovery will lead to better understanding of the disease and, eventually, better ways to predict, prevent and treat the heart rhythm problem.
Pitt-led Research Provides Insight Into Development of Common Congenital Circulatory Defects
University of Pittsburgh-led researchers could provide new insight into how two common congenital circulatory problems-aortic arch deformity and arteriovenous malformations (AVMs)-develop in humans, as reported in the June 15 edition of Developmental Biology.
Researchers reveal types of genes necessary for brain development
Researchers from Harvard Medical School and Brandeis University have successfully completed a full-genome RNAi screen in neurons, showing what types of genes are necessary for brain development. Details of the screen and its novel methodology are published July 4th in the open-access journal PLoS Genetics.
Mother's vitamin D status during pregnancy will affect her baby's dental health
Low maternal vitamin D levels during pregnancy may affect primary tooth calcification, leading to enamel defects, which are a risk factor for early-childhood tooth decay.
'Hibernation-on-demand' drug significantly improves survival after extreme blood loss
For the first time, researchers have demonstrated that the administration of minute amounts of inhaled or intravenous hydrogen sulfide, or H2S - the molecule that gives rotten eggs their sulfurous stench - significantly improves survival from extreme blood loss in rats.
Researchers coat titanium with polymer to improve integration of joint replacements
Research at the Georgia Institute of Technology shows that coating a titanium implant with a new biologically inspired material enhances tissue healing, improves bone growth around the implant and strengthens the attachment and integration of the implant to the bone.
Resuscitation technique after brain injury may do more harm than good
The current standard practice of giving infants and children 100 percent oxygen to prevent brain damage caused by oxygen deprivation may actually inflict additional harm, researchers at UT Southwestern Medical Center have found.
More Defects News Articles
| © 2008 BrightSurf.com |