THE prospect of computer chips ten times more powerful yet one-tenth the size of today's has taken a large step forward with the development of the Ultra Clean Ion Beam Sputter Deposition System, the result of a collaboration between Livermore's Laser Programs and Veeco Instruments Inc. of Plainview, New York. The collaborating team received a 1997 R&D 100 Award for their successful development.|
The new machine, called the LDD-IBSD 350, deposits extremely thin single and multilayer film coatings with angstrom accuracy onto substrates of silicon and other materials. These films are used in creating advanced computer chips, hard disk drives, and the master patterns for extreme ultraviolet (EUV) lithography. The machine significantly advances the state of the art by drastically lowering the number of thin-film defects it deposits by a factor of 100,000 over existing equipment. Precise application of thin films is critical to the $120-billion semiconductor manufacturing industry and the $100-billion magnetic recording industry.
Compact but More Powerful
By vastly reducing the number of defects in thin films, the machine also eliminates one of the most significant obstacles to the realization of EUVL for the next generation of computer chips. EUVL will allow chip makers to work with wavelengths much shorter than today's deep ultraviolet light-based technology, reducing line widths (and feature sizes) to below a tenth of a micrometer (a millionth of a meter).
"The microchip industry now uses photolithography that employs wavelengths of light in the deep UV region [250 nanometers, or billionths of a meter]," explained Richard Levesque, Laser Programs engineer and award recipient. "To make chips more powerful and compact, we need to decrease the wavelength by using the extreme ultraviolet region of the electromagnetic spectrum [13.4 nanometers]."
Because conventional lenses and accompanying optical systems do not transmit EUV light, semiconductor researchers have turned to reflective multilayer-coated optical systems that are designed to operate at a new standard of 13 nanometers.
By using EUVL, manufacturers should be able to produce considerably more powerful chips yet shrink them to one-tenth their current size. Indeed, it is expected that the forthcoming technology will produce single chips containing 100 million transistors, truly the long-awaited "computer system on a chip."
A critical problem remained, however, with the thin-film coatings used in the reflective mask (the master pattern used to "print" the semiconductor circuits onto silicon wafers or chips). Livermore team member and Advanced Microtechnology Program leader Don Kania calls masks the "Achilles' heel of all advanced lithography systems." In the case of EUVL, if the reflective mask coatings have even extremely small defects, they would be replicated, or printed, in the lithography process onto the computer chips being manufactured, thereby destroying the chips' complex circuitry.
The conventional approach for making masks, known as magnetron sputtering, produces about 10,000 defects in a square centimeter, far too many for successful EUVL. What's more, there are no viable techniques for repair or replacement of defective regions of multilayer coatings. As a result, development of EUVL technology has been contingent in part upon a "defect-free" multilayer deposition process. The development of the IBSD-350 process for film coating, with its remarkably low defect density, effectively solves this long-standing problem.
For EUVL applications, the machine produces precise, uniform, high-reflective masks with 81 alternating layers of molybdenum and silicon, each 3 to 4 nanometers thick, on 150-millimeter-diameter silicon wafers. Having excellent control of the thickness of the 81 layers in the multilayer is paramount to the optical performance of the mask. In depositing the layers, the machine directs a beam of ions at molybdenum or silicon targets. The ions physically collide with the target, forming a vapor, which is then precisely deposited on the substrate with a defect density of less than 0.1 per square centimeter.
The machine's defect density represents a 100,000-fold improvement over typical defect levels for multilayers produced in conventional physical deposition processes. It also represents a sixfold improvement over the goal of the 1998 Semiconductor Industry Association (SIA) for particle contamination of bare silicon wafers and meets the SIA goal for process-induced contamination for the year 2004.
The development of the machine culminated 16 months of high-risk, high-payoff effort that combined the ion-sputtering technology expertise of Veeco with Livermore expertise in high-vacuum technology, opto-electronics, micro-electronics, and x-ray diagnostics built up over the past two decades from research in defense and laser fusion.
In particular, Laser Programs' Advanced Microtechnology Program was a natural partner for Veeco because of the members' strong expertise in processes for fabricating the microstructures used as targets and diagnostic equipment in Livermore inertial confinement fusion experiments. Over the past few years, the program has been working on the challenges posed by EUVL.
The Livermore team consisted of physicist Steve Vernon, mechanical engineer Levesque, and materials scientists Patrick Kearney and Kania. According to Levesque, "Our counterparts at Veeco had a real willingness to work with us, share their expertise, and also were receptive to Livermore ideas."
The Veeco-Livermore development team achieved the new process by integrating a breakthrough film-deposition module to a state-of-the-art wafer handling system, advanced vacuum technology, automated substrate handling, and mechanical systems. The machine permits flexibility in the type and number of thin-film-deposition processes that can be implemented by the end user.
Coatings for the Future
While the new technology helps to open the door to EUVL, its flexibility, uniformity of film deposition, and stable deposition rate make the machine a strong candidate for conventional processes used in current semiconductor production of a broad class of thin-film coatings where low defect density is a strong concern. Such coatings can be virtually any material or combination of materials including metals, semiconductors, and insulators. Near-term applications also include the fabrication of very low defect-density films for ultrahigh-density, multilayered magnetoresistive heads for the magnetic recording industry.