New photoresist removal system touts low particulate and environmental safety
By Lisa A. Karter
Fremont, CA –Test results from a new photoresist removal system developed by Legacy Systems indicate low particulate on wafers, low water cosumption, low ionic contamination and en vi ronmental safety.
Legacy`s new pro cess, dubbed Cold-strip, eliminates and minimizes the use of harsh chemicals from semiconductor fabs. During the four years that Legacy took to develop the technology, Coldstrip was moved from pilot testing into commercial manufacture. According to Legacy, sulfuric acid, hydrogen peroxide, nitric acid and isopropyl alcohol are reduced or eliminated in lieu of 12 gallons of water and oxygen required for Coldstrip. The technology has garnered Legacy a patent and the 1997 Presidential Green Chemistry Challenge Award.
Legacy is betting on the in- dustry moving away for sulfuric acid chemistry and into a safer process, such as Coldstrip. “The semiconductor industry is very conservative, it will take three to five years to change the industry,” says Legacy Systems President and Founder Robert R. Matthews. “Many companies take 12 to 18 months to convert from high temperature sulfuric processes and each company must be converted one at a time. You`re asking people in the process field to change their process to one they didn`t know really existed. When you`re used to working with sovents, ashers, and high temperature chem istries, there is a plethora of information you can always fall back on. The new process chemistry educates process engineers with respect to fundamental chemistry. We teach you how to look at this in terms of the carbon-carbon double bonds.”
The new process starts with submicron temperature de-ionized (DI) water into which the wafers are introduced. An ozone generator is activated and delivers ozone to the diffuser in the bottom of the tank. Since ozone has higher liquid adsorption rates in colder temperatures, highly ozonated DI water is generated upon introduction of the gas. The ozone reacts on contact with the organic material on the silicon wafer surface. In addition, the tank can then be run in either continuous trickle over-flow mode or in a stagnant batch processing application.
Process equipment required for Coldstrip includes an in-situ generation tank with the diffuser, ozone generator, chiller unit, circulation pump, and ozone premix chamber. Water from the process tank is recirculated via an overflow weir to the chiller. Water from the chiller enters the process tank under the product, absorbs ozone from the diffuser and rises through the wafer stack where it overflows the weir and returns to the chiller. The purpose of the recirculation is not to filter the water but to maintain the subambient water temperature.
The ozone generator then converts oxygen to ozone and the ozone is diffused into the chilled water in the process tank directly under the product. Ozone attacks the carbon-carbon double bonds of the resist converting the molecules to carbon dioxide, carbon monoxide, oxygen, and water.
Legacy has licensed the technology to SubMicron Systems (Allentown, PA). Their agreement covers patented material and know-how data for the manufacturing of new wet stations using Legacy`s technology.
For more information, contact Legacy Systems, Inc., Fremont, CA, (510) 651-2312, fax (510) 651-9444.