Advantages of Using Hot Deionized Water

• Improves removal of chemical residue and particles
• Reduces DI water consumption up to 70%
• Reduces usage and discharge of hazardous chemicals
• Reduces bacterial contamination
• Improves process yields
• Uniform process temperature control
• Reduces thermal shock
• Eliminates heat-up time where chemical mixes are primarily DI water

HOT DI WATER IS MUCH BETTER THAN COLD DI WATER

Cleaning processes that use sulfuric acid (i.e. prediffusion clean and resist stripping) leave residual chemical particles that can affect yields and throughput. Particulates can be produced in as little as 48 hours via the migration and nucleation of the H4SO4 molecules. Additional process steps that have been taken to address this problem include:

• Chemical cleaning (i.e., hydrofluoric [HF] rinses and RCA cleans)
• Multiple DI water rinses (cold water)
• Mechanical agitation of the wafers in a cold DI bath

These additional steps are undesirable because:

• HF and RCA clean processes generate additional hazardous chemical waste
• Multiple cold DI water rinses waste costly DI water
• Mechanically agitating the wafers adds energy to cold water rinses through the use of robotics which requires high maintenance

REDUCE THE NUMBER OF PROCESS STEPS NEEDED (OR ELIMINATE THEM ENTIRELY), YET STILL ACHIEVE YOUR GOAL OF CLEANER WAFERS

When heated, ultrapure DI water is much more aggressive and therefore more effective than cold DI water in rinsing applications. Prediffusion cleaning chemicals and photo-resist from wafers are more soluble in Hot DI water and therefore more easily removed. The Lufran ® UP Series features an all fluoropolymer, PVDF and red silicone fluid path which provides instantaneous heating of water while avoiding any potential contact of the process water with metal components. The H2OT SHOT quartz series heater utilizes all type 214 quartz and PFA wetted parts for ultra clean performance. One Process Technology/Lufran® customer reported, "The total ionic concentration as measured by ultratrace ion chromatography consistently demonstrated no increase in any ionic species. No ions or metal were detected in either the UPW feed or the HUPW system product". Wafer yields are increased because the process environment is not contaminated with metal ions or other impurities.

REDUCE DI WATER CONSUMPTION OF UP TO 70% AND REDUCE USAGE OF HAZARDOUS CHEMICALS

The molecules in heated DI water possess a higher level of energy than cold water molecules. When transferred to the wafer surface the high translational energy of the water molecules quickly dissolves and dilutes process chemicals off the wafers. This results in dramatically reducing the amount of water needed to effectively rinse the wafers. One customer wrote, "A hot DI rinse at post H2SO4 locations reduces the average SRD TPT (Spin Rinse Dryer, Total Process Time) needed after standard rinse cycles from 9 min. to 30 sec." In addition, using heated DI water rinsing avoids the need to use hazardous chemicals, i.e., HF and RCA cleans.

REDUCE BACTERIAL CONTAMINATION AND IMPROVE PROCESS YIELDS

Wet process stations provide an excellent environment for the growth of bacteria. Usual causes are low or intermittent flow of DI water, airborne bacteria and cross contamination from filters. Lufran ® DI Water Heaters reduce bacterial growth throughout the point-of-use water distribution system. By heating your DI water to 90°C, it is possible to sanitize internal plumbing without resorting to the disassembly of the station components or by using potentially hazardous chemicals. Furthermore, downtime is eliminated, as are associated labor costs that would be required for sanitizing via the use of chemicals. By reducing bacteria contamination, production yields can be improved.

ENSURE CONSTANT DI WATER TEMPERATURE

DI water temperatures can vary by as much as 10°C depending on the location and season. This undesired variability in water and process temperatures can be avoided by heating the water to a constant temperature with the UP Series DI Water Heater. Temperature and humidity in cleanrooms are maintained at great expense. Eliminating temperature variations in DI water is extremely important, since DI water will come in direct contact with the wafers throughout numerous processing steps.

REDUCE THERMAL SHOCK

Many strip, etch and develop processes are operated at elevated temperatures. RCA cleaning and silicon nitride etch processes are commonly heated to 45, 140 and 185°C respectively. Transferring wafers from a hot acid environment to a cold 23°C DI water rinse could result in thermal shock and damage the wafers. Heating your DI water can eliminate potential risks associated with thermal shock. INCREASE PRODUCTION THROUGHPUT Heating DI water will result in increased throughput for virtually any process. For example, by utilizing hot DI water, cleaning times in wafer boat and box cleaning equipment can be reduced by as much as 60%. Rinse times for wafers that have been processed in barrel reactors can be reduced by as much as 80%. By heating the hot DI water it effectively removes fluoropolymer contamination from the wafer surfaces.