A new manufacturing technology promises to scrub the chipmaking process and extend the life of Moore's law.
It�s the $140 billion semiconductor industry�s dirty not-so-little secret: Behind the clean rooms that churn out millions of chips every year, a filthy manufacturing process uses millions of pounds of noxious compounds, billions of gallons of water to wash them away, and a flood of toxins to dry it all out. The regimen is so poisonous that IBM and National Semiconductor recently have come under fire from environmental groups and employee lawsuits that allege clean-room jobs cause severe health problems, even death.
But where there�s a problem, there�s a technology waiting to solve it. A promising green chip-manufacturing process is emerging from the least likely of places — Los Alamos National Laboratory, the world�s premier weapons lab. Known as Scorr, or supercritical carbon dioxide resist remover, the process requires no water, few of the nasty chemicals used in traditional wafer cleansing, and no drying. Scorr could save billions of dollars, conserve water, and help semiconductors grow ever smaller. �This technology could transform the industry,� says Craig Taylor, leader of the Los Alamos team holding the Scorr patent.
IBM IS ON BOARD, INTEL IS A MAYBE
Photolithography — the method by which the pattern of circuits is imprinted on a wafer — sits at the heart of chip manufacturing. A photoreactive polymer, called photoresist, is applied to the wafer�s surface and exposed to light before the circuits are etched. A few steps later, excess photoresist is removed using various toxic compounds — sulfuric acid, hydrogen peroxide, methyl ethyl ketone — and rinsed away with water. (A fab can go through 6 million gallons a day.) If the wafers were left to air dry, the water would leave defect-causing residue, so they�re treated with another solvent, isopropyl alcohol. Put it all together, and chipmaking risks being flat-out carcinogenic.
The Scorr process works to replace these dangerous chemicals with supercritical carbon dioxide — CO² that�s been placed under extreme pressure to give it the solvency of a liquid and the mobility of a gas. It removes the resist in about half the time and leaves almost no residue. Of course, lawsuits and do-goodism aren�t enough to convince chipmakers to scrap their manufacturing process. But Scorr also has a cost advantage. The technology�s first licensee, SC Fluids, is selling its machines for roughly $2 million — about half the cost of conventional rinse-and-cleanse presses. IBM began a pilot program earlier this year in its East Fishkill, New York, factory and hopes to save millions of dollars on water and chemicals within a few years.
Big Blue is betting the process will also help the company extend Moore�s law. With some chip features a thousand times as narrow as a human hair, wet wafer-cleansing is approaching its limits. Water�s natural surface tension prevents it from penetrating supersmall spaces to remove residue. Supercritical carbon dioxide has no surface tension. Mixed with ecofriendly cosolvents like butylene carbonate or propylene carbonate, it forms a compound that can penetrate the tiny crevices water can�t. �There�s a real need for this process,� says Kenneth McCullough, who�s overseeing the IBM test.
It seems pristine, but making microchips is a filthy business.
Intel stands to benefit most from the Scorr technology. The semiconductor king will soon begin production at its first 300-millimeter chip factory in Rio Rancho, New Mexico. The fab already uses roughly 4.5 million gallons of water per day — in an area suffering from a drought-induced state of emergency. Intel�s Terrence McDermott says the company recognizes the problem and is exploring solutions. Scorr is on the list, along with new ways to recycle water and reduce the volume of chemicals used in manufacturing.
The stakes for Intel and the whole industry reach beyond good PR. Residents downwind of the Rio Rancho fab are complaining that noxious vapors have caused chronic headaches, skin rashes, sleeping disorders, and even one death from lung fibrosis. (Intel maintains that its emissions are at safe levels.) National Semi faces a worker-exposure class action, and more than 200 individual suits have been filed against IBM — some set for trial early next year.
At Los Alamos, the stakes are also high for Craig Taylor and colleague Kirk Hollis. �If this isn�t in full production in two years,� Hollis predicts, �we�ll be working somewhere else.�
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