When equipment techs are tasked to clean Ion Implant Source Bushings the main goal is to remove the process by-product. Since the process by-product contains arsenic, phosphine and boron safety must be factored into the PM process.
Other Important Factors:
- Cleaning materials
- Cleaning chemistry
- Technician time
- Wear damage to the polymer coating
The Current Landscape
Current cleaning methods force equipment engineers to tradeoff equipment wear vs. cleaning time. The two cleaning procedures now extensively used are:
Material: Scotch-Brite and Cleanroom Wipers
Type of Solution: 3% or 31% H2O2
Amount of Labor: Medium
Safety: High Risk
Despite the best efforts of equipment engineers and the tool manufacturers, cleaning source bushings is most often carried out by with Scotch-Brite and 31% H2O2. The abrasive action of Scotch-Brite and the oxidizing nature of H2O2 speeds up the cleaning task but presents safety risks. 31% H2O2 creates an exothermic reaction which when combined with the phosphine by-product and high metallic Scotch-Brite content creates sparking, smoking and fire risks. For this reason, many Implant modules have opted for 3% H2O2 even though this extends the cleaning task for the technician.
The polymer coating is critical for the Implant source bushing to properly function. The abrasive materials incorporated into Scotch-Brite will scratch and damage the polymer coating. This is not ideal; a damaged Source Bushing will cause arcing during the Implant Process leading to expensive repairs, replacements and unscheduled equipment downtime. In addition to abrasive materials, Scotch-Brite has high metallic content which embeds itself into the polymer bushing which is another reason for post-pm arcing. This forces techs to spend a large amount of time and many cleanroom wipers to remove any metallic particles before running the tool.
Pictured: Arcing damage marks left on an Ion Implant Source Bushing (previously cleaned with Scotch-Brite and Cleanroom Wipers)
Material: High Volume of Cleanroom Wipers
Type of Solution: 31 % H2O2
Amount of Labor: High
Safety: Medium Risk
To address polymer coating damage and to avoid metal contaminants some implant modules in sub 14nm wafer fabs have eliminated Scotch-Brite from the PM procedure and instead relied on cleanroom wipers. Since cleanroom wipers have poor scrubbing performance, to remove the process by-product, a higher concentration of Hydrogen Peroxide is required. The poor cleaning efficiency of this method requires technicians to use a large quantity of wipers and is a long and grueling process.
Hydrogen peroxide itself is not flammable but can cause spontaneous combustion if mixed with solvents such as IPA and continued support of the combustion because it liberates oxygen as it decomposes. The use of 31% H2O2 vs. 3% H2O2, dramatically increases the risk of fire.
What is being done to improve the Cleaning Process?
Material: Sahara Sponge and Cleanroom Wipers
Type of Solution: 3% H2O2
Amount of Labor: Low
Safety: Ultra-Low Risk
Foamtec has developed the Sahara Sponge, a cleaning product to address the issues with current cleaning materials. The Sahara Sponge is a non-abrasive, 100% polyurethane foam sponge that is strong enough to quickly dislodge implant process residue from Ion Implant Source Bushings without damaging or scratching the polymer coating. Due to its construction and abrasion resistance, it will not deposit metallic adders, and will dramatically reduce particle shedding when compared with Scotch-Brite, reducing excessive wipe downs associated with the Scotch-Brite Method. Since only 3% H2O2 is required, fire and health hazards will dramatically decrease. The Sahara Sponge + MiraWIPE has been proven to be very efficient and safe for removing implant process by-product for Ion Implant Source Bushings.
*Sahara sponges should be changed when physical degradation is observed.
For More Information or to Request a Sample: