Good news for the semiconductor industry, the consumer and the environment

October 31, 2003
| By: Aubrey Bloom

Texas A&M University professor, Dr. Yue Kuo, is disrupting the semiconductor industry. The Texas A&M University System was recently issued a patent for Kuo's alternative to chemical mechanical polishing (CMP), the conventional process used in manufacturing microchips with copper. The new method, which is simpler, uses existing equipment and is more environmentally sound, could save manufacturers millions while producing faster microchips. The semiconductor industry is moving towards copper instead of aluminum for the tiny lines that connect the millions of transistors in each microchip. Copper is a much better conductor, and the speed of the current generation Pentium chips is about at the limit of what can be reached using aluminum interconnection. Aluminum offers too much resistance, which can delay or distort the signal from the transistors. Additionally, copper is a stronger metal and will last longer and result in more reliable chips than those containing aluminum. "Copper is starting to be used for newer generations. For future generations there is no choice," explained Kuo, Dow Professor of Chemical Engineering. Kuo is also a professor of electrical engineering and materials science and engineering, and a researcher with the Texas Engineering Experiment Station. However, significant problems exist in manufacturing chips with copper connecting lines compared with aluminum lines. Aluminum lines are etched on microchips using a plasma reaction, a process known as dry etching. The process etches the metal on the chips in a particular pattern, which is unique to the function of the chip. The aluminum is removed in-situ by vaporization. To use the same method with copper, the temperature would have to be raised to 400 degrees Celsius to vaporize the etched copper. As Kuo noted, this is not a practical option. "We know this has been the bottleneck for 50 years," said Kuo. With no feasible way to vaporize the copper, the industry developed a work-around, a process of engraving a pattern into the silicon oxide layer, electroplating copper onto the chip and then grinding away the excess using a technique called chemical mechanical polishing (CMP). "This method is tedious, and it has a lot of problems," said Kuo. Among the problems is the endpoint control of the polishing, which intensifies as chip geometry is taken to less than 100 nanometers. Additionally, CMP uses very harsh chemicals that can have serious environmental concerns if not handled properly. Kuo's newly patented method is an alternative to CMP. Kuo has demonstrated that copper reacts with various plasmas to form copper compounds that are totally soluble in weak aqueous solutions. They can be washed away at room temperature, eliminating the need for either expensive CMP grinding equipment and hazardous chemicals or metal vaporization. "They've been looking for the wrong thing. Everyone thinks of vaporizing the copper reaction product," said Kuo. Kuo also has developed a method of dry-etching a copper surface using a photo resist mask, eliminating the need for the engraving and electroplating equipment. It can be used with existing aluminum plasma etching equipment. The technology is also ideal for other large-scale electronics, such as plat panel displays, which have the same type of limitations as microchips and need copper connections. A additional patent is pending on this alternative method. "Some people call this a disruptive technology," said Kuo, explaining that some companies don't want to hear that there is a simple, inexpensive alternative to the complicated equipment in which they've just invested. Kuo said both methods are proven and tested. They have been successfully repeated many times under different circumstances in the Thin Film Nano and Microelectronics Research Laboratory <http://yuekuo.tamu.edu/Lab.htm> at Texas A&M. "We wanted to make sure it doesn't only work once. It's very repeatable under many conditions," said Kuo. Kuo said the issued patent is a testament to the validity of the new technology, which could have a major impact on the industry. "This could be very big," said Kuo. U.S. Patent No. 6,613,667, "Forming an interconnect of a semiconductor device," issued on Sept. 2, 2003. An additional patent is pending for the copper dry etching method. The A&M System Technology Licensing Office is currently seeking one or more industrial partners to facilitate commercialization of the procedures. For more information about licensing this technology, please contact Page Heller at <mailto:p-heller@tamu.edu> p-heller@tamu.edu or 979-847-8682. Please reference TAMUS Project # 1746 <http://tlo.tamu.edu/tlo/documents/INDR/1746.pdf> .

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