Ozone-Based Cleans Evaluated

The purpose of the study was to determine the removal efficiency of the ozonated cleans for different organic compounds. The efficiency of ozonated cleans for the removal of these organic compounds was studied in a controlled, reproducible, quantitative method. Exposure to a sealed ambient of organic compounds and wet chemical exposure were assessed. The removal efficiency depended on the type of organic species.

Sealed gas-phase ambient

Although dictyl phthalate (DOP) is present in the wafer box materials, DOP outgassing contamination on Si wafers stored in a sealed ambient for less than one week at room temperature was shown to be negligible. In addition, no significant differences were measured between intensity ratios obtained for contamination with stearic acid dissolved in water or in ethanol. The small and closed environment of the box prevented air exchange, implying that stearic acid coming from cleanroom processing materials is unlikely to contaminate wafers when stored in suitable closed wafer boxes. Experiments also showed that wafers were barely contaminated in a highly saturated environment of organic compounds at room and at elevated temperatures. Under the sealed conditions, adsorption did not appear to be dependent upon vapor pressure of the contaminants, assuming that the vapor pressure of a substance in solution is identical to its partial pressure. This is in contrast to wafers stored in cleanroom ambient with a constant, uncontrolled supply of organics via the laminar flow.

Wet bench

Contamination was removed in a wet bench setup operating with an ozone gas phase or an immersion-ozone process. TOF-SIMS results showed complete removal of all compounds. No significant difference in removal efficiency of organic contamination by immersion ozone and moist ozone was observed, except for 4-dodecylbenzenesulfonic acid. Removal of the acid seemed to be less effective with an immersion ozone process. Further experiments are needed to determine its cause.

Spray tool processing

Analysis revealed exceptional removal efficiency for all compounds under study, even for 4-dodecylbenzenesulfonic acid. The reaction of ozone with organic material on the surface was far more efficient when compared with the ozone process in a static wet bench tool (immersion as well as moist ozone processes). For all organic compounds, the researchers observed decreased intensities on the samples processed with the ozone clean, yielding even lower intensities than the reference cleaned samples. TOF-SIMS results showed no difference between contaminated and cleaned wafers.

Overall, ozone cleanings applied in a wet bench and spray-processing tool, as well as immersion-based ozone cleans, showed high removal efficiency for the organic compounds under study.

Company News
Air Products and Chemicals Inc. (Lehigh Valley, Pa.) completed its nitrogen trifluoride (NF₃) capacity expansion on time. The plant is now producing 1.35M lbs/yr of NF₃, with all products going directly to contracted semiconductor manufacturers in North America, Asia and Europe.

Daw Technologies Inc. (Salt Lake City) signed a letter of intent to form a joint-venture company to provide integrated cleanroom design, engineering, construction and manufacturing services in China. Joining Daw in the venture are the Eleventh Design and Research Institute; China West Investment; and Sichuan Provincial National Investment Management Corp.

Mattson Technology (Fremont, Calif.) received several orders for multiple 300 mm RTP, CVD, strip and wet processing equipment from a European-based semiconductor manufacturer. Shipping has begun and will continue through 2002.

Verteq Inc. (Santa Ana, Calif.) received a financial investment from Seki Technotron Corp. (Tokyo). Seki has been distributing Verteq's wafer-cleaning products in Japan for several years.

Olympus Optical Co. Ltd. (San Jose) received an order for multiple AL3100 optical defect and wafer inspection systems from a large Japanese semiconductor device manufacturer. The systems will include FOUP and open cassette configurations and advanced photographic equipment.