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Product Briefing Outline: Entegris has introduced its ‘LiquidLens' ultrapure water (UPW) purification system that is designed specifically for 193nm ArF immersion lithography systems. The sub-system combines advanced technology and process expertise from both Entegris and the former Mykrolis as a result of their merger in August 2005 to tackle high-purity issues associated with the needs of immersion lithography.

Problem: Immersion is the newest lithography technique for printing 45nm or smaller features on semiconductor wafers, using ultra pure water between the optical lens and the wafer. The UPW lens is utilized to significantly improve image resolution. The water must be extremely pure as the smallest impurity can damage image resolution, react with the photoresist. Ensuring ultrapure, consistent water quality also preserves optic's life by controlling contaminants at the point of use such as dissolved gases, micro bubbles and particles.

Solution: Important factors in designing an ultrapure water system for immersion lithography is the selection of high purity, inert construction materials and the integration of purification techniques in an optimal sequence.  It is important to deliver a stable DI flow precisely/repeatedly to the illuminated area to prevent any bubble attachment on the wafer or the lens during the filling process. The current flow rate control required is in the range from 0.4 to 3 LPM at steady state with slower flow rate at initial fill, to ensure complete filling under the lens, followed by a faster rate during scanning to ensure byproduct removal and meniscus integrity during stage movement. The contaminants to be removed from the UPW system include dissolved gases and bubbles, particles, total oxidizable carbon (TOC) and non-volatile residue (NVR), and ionic and organic extractables that are added from the process materials and piping components. Temperature control is also very important to ensure constant optical properties (refractive index) and to ensure constant physical properties (e.g. density, surface tension and gas solubility). A ‘pHasor' II membrane contactor ensures the process water is free of bubbles by delivering high dissolved gas concentrations with a low pressure drop over the fluid path. Two UV lamps break down TOC levels in the water while an ion exchange purifier removes the organics, ensuring a high purity fluid stream. These elements are linked to an advanced process control unit that monitors critical parameters, providing 48-hour rolling trend data with configurable warning and error alarms.

Applications: 193nm ArF immersion lithography systems.

Platform: Incorporates a ‘Durapore' 0.02 µm filter in a ‘Chemlock housing'. The high zeta potential PVDF membrane filter is ideally suited for water applications and the Chemlock housing preserves space while reducing cost of ownership, according to the company. LiquidLens UPW purification systems are built to customer specifications and individually quoted.

Availability: July 2006 onwards