ESD Electric Corona Air Ionizer Emitter Tip Deposit Analysis
Have you ever wanted to predict cleanroom contamination levels before they become a problem for production? StaticTek provides sampling kits and service in the identification of elements and compounds present in deposits on the tip of air ionizers. Airborne Molecular Contamination (AMC) in the cleanroom air is attracted to and encapsulated by air ionizer tip deposits. Areas with higher than normal AMC deposit build up is clearly visible, emitter tip contamination grows at a much higher rate as a result of the air ionizer reaction with AMC. Analyzing this contamination is an early warning method to protect wafers, UV Optics, reticles and scanners. With the identification of ion emitter tip deposits comes the understanding of the elements involved, aiding in identification/control/elimination of the source of cleanroom contamination.
StaticTek provides evaluation support and ionizer emitter tip sample collection. Lab sampling kits and nanoanalysis of ion emitter tip compound is performed by a nationally recognized independent laboratory.
- Tip removal (for ceiling ionizers)
- Swabs (call to discuss proper method)
- Quadbars (call first to discuss)
- Scanning Electron Microscopy with Energy Dispersive X-Ray Spectroscopy (SEM-EDS) Used for main elemental ID, provides surface analysis
- Inductively Coupled Plasma Mass Spectrometry (ICP-MS) Used for quantitative results of entire tip deposit
The term airborne molecular contamination (AMC) refers to the presence of unwanted gas-phase contaminants in the cleanroom.
Due to the proximity of positive and negative emitter points and the high energy required to create air ions, electric corona discharge ionizers will react with excessive amounts of volatile Airborne Molecular Contamination (AMC) to form non-volatile SMC (Surface Molecular Contamination), which can collect over time on hot emitter points to form deposits that range from microns (µm) to several Millimeters (mm) in length. These ion emitter tip deposits are often dielectric insulators such as SiO2, formed from Si compounds in air that can lead to faults or imbalance in ionizer circuits. Ammonia may form ammonium salts like ammonium nitrate or sulfate. These deposits grow as a result from AMC reacting thermally with the tip and air or by other mechanisms. The ionizer tips form oxygen, the superoxide ion (O2-), the hydroxyl radical (OH), ozone (O3), nitrogen oxides, and H3O+(H2O)x clusters. HEPA and ULPA filters are used to remove particles in the air, however AMC molecules are volatile and hit the fibers in the filters, but then revolatilize and eventually are not retained for long. Then, AMC can pass into the particle-free cleanroom to possibly interact negatively with the air ionizers or other critical surfaces and form particles.
By analyzing these air ionization emitter tip deposits your company can learn a great deal about trace unwanted elements in the critical environments.
Tip Deposit Identification Methods:
Ionizer emitter tips with deposits are removed using a Ceiling Emitter Tip Sampling Kit. These ion emitter tip samples are sent to a specialized lab for analysis.
When an ionizer tip arrives for analysis, it is optically photographed and weighed to 1 µg. Scanning Electron Microscopy with Energy Dispersive X-Ray Spectroscopy (SEM-EDS) is used to make an elemental map of the intact tip residues using electron imaging as well as determine the elemental composition of the sample (except H, Boron). If the deposits are inhomogeneous, further analysis is needed since EDS detects to a few microns depth, and does not detect deeper, or far side elements in deposits that can be thousands of microns long. If the deposits are mainly SiO2, our trained chemist can safely use HF to etch and completely dissolve the SiO2 from the Si tip. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) can be used to identify 20 elements including Si, Sn and dopants like B, P, which may not be detected or accurately quantitated at low levels by one SEM-EDS analysis. By identifying and quantifying elements present in the deposits, it becomes possible to assess AMC-to-SMC risks quantitatively for trending. Higher refractory AMC levels are likely in areas with the largest deposits on the ionizer tips, and these compounds may also put UV optics at risk of photo deposition. SEM-EDS and ICP-MS can similarly be used to perform an elemental analysis for crush tubes used to collect tip deposits.
New problems with higher ionizer deposition rates that were not present before suggest a chemical leak, air handler failure, or other issues. Knowing the elements present greatly simplifies assessing what sampling method may be used next to help find and eliminate the source to reduce risks to wafers, UV optics, masks, scanners and air ionizers. Balazs can provide separate methods for analysis when needed, such as GC-MS, Ion Chromatography, and FTIR for air or witness wafers to further diagnose AMC, SMC and ionizer issues.
If you have deposits on your ionizer tips, especially if >1 mm white deposits in one month, or green or blue deposits that might indicate a corrosion issue, please contact us. Fabs with 193 nm ArF scanners might require better control, and longer wavelengths might be more tolerant of deposits. EUV pellicle–free masks might have new requirements.
- Call 503-304-9633 or send an email to request an Ionizer Emitter Tip Sampling Kit. Include your contact information, type and quantity of ionizer emitter tips along with your company shipping address.
- We will send a price quote for ionizer deposit evaluation service and request for purchase order.
- We will send you the ion emitter deposit sample kit with sample collection and return instructions.
- The ion emitter deposit chemical makeup analytical results will be provided, along with the data collected, a detailed report of findings, recommendations of issues to address and customer support follow up.