Excimer refers to the bound excited upper state of a molecule that breaks apart when a photon is emitted. Resonance excites Excimer emission from its lamps with a proprietary RF power supply.Some of the UV emission wavelengths for various gas fill and window combinations are shown below.
Excimer Cleaning:Excimer systems use a UV cleaning process referred to as Dry Cleaning. This process destroys and removes organic compounds with minimum impact on the process stream. This is superior to wet cleaning as it does not produce toxic liquids. Excimer destruction of organic compounds takes place when contaminant molecules (e.g. photoresists, resins, human skin oils, cleaning solvent residues, silicone oils, soldering flux etc.) are broken down to simple non-toxic volatile molecular fragments by the action of vacuum ultraviolet light (pictured below).Terms to Know:Photo-oxidationrefers to the UV induced processes referenced above which result in the breakdown of organic compounds. Atomically cleanrefers to a surface condition in which the substrate has a contaminating film less than one molecule thick leaving the substrate directly exposed. Applications:Semiconductor and Related• Dry cleaning surface of silicon wafers and photo-resist films • Dry cleaning lithography masks • Post CMP dry cleaning • Surface conditioning of high K materials • UV dry cleaning of interlayer dielectric (SOG) • Optical chemical vapour deposition (CVD) • PMMA conditioning (resist smoothing) • Post dicing dry cleaning of tape residues • Pre-wire bonding dry cleaning • Dry cleaning of backside of lead frames Plasma Display Panels• Pre-photo-resist, Pre-sputtering dry cleaning • Dry cleaning before and after wet cleaning to improve yield • PDP phosphor evaluation systems using Excimer lamps and fiber optic UV delivery systems Environmental and Medical• Toxic waste (e.g. CFC's, PCB's, dioxin's, trichloroethylene) destruction in air/water streams by photo-oxidation • Non solvent cleaning: of mechanical parts • UV/Ozone sterilization of medical instruments and medical supplies • Cleaning glass boards, PDP Fluorescent light and LCD Other• Improvement for non-exposed part surface of photo-resist film • Soft-Ashing • Pre-treatment of disc surfaces, i.e., CD and DVD • Dry cleaning ball bearings for hard disk drives • Igniter and stabilizer for plasma etcher (Excimer used as an assist light) • Post-process treatment of CMP hardening of coatings and adhesives • Generation of amorphous material, such as amorphous silicon solar cell • Printing - textile printing, finishing, printed circuits • Reforming surfaces - ceramics, surface etching • Environmental CLEAN UPContact Angle Measurements:• A simple way to measure the cleaning of certain surfaces. • Surface tension of water droplets will depend on surface contamination. • The angle of contact of a water drop will decrease as the surface tension decreases due to removal of surface contamination (on a hydrophilic surfaces that wet easily) The images below show surface cleaning on a glass microscope slide with Excimer UV Start of Exposure (0 seconds) After 30 Seconds of Exposure• Using the contact angle method it can be seen that 172 nm Excimer light rapidly removes contamination from glass surfaces in 30 seconds or less. • The strong dependence on distance to the sample results from the large absorbance of O2 at 172 nm. This effect can be minimized by using a gas mixture with a smaller O2 fraction than air. Example Measurements:Mercury vs. Excimer on a Si surface Contact Angle Measurements (see figure below)• The Excimer Lamp takes 15 sec. to change the water contact angle from 50.9 deg. to 2.6 deg.• The Mercury Lamp takes 220 sec. at almost twice the power to change the contact angle from 60 deg. to 8 deg.• Excimer VUV cleaning is much faster than Mercury cleaning
Advantages of Excimer:• NON TOXIC - No toxic mercury vapour in lamp. • NO HF- and other acids, no toxic organic solvents result from lamp use. • PROCESS FRIENDLY- Cannot harm vacuum process with mercury vapour. • NO FLUIDS- Process does not require fluids with consequent de-sorption and contamination problems. • EMIT SINGLE PEAK -(wavelength) radiation with high output in UV or VUV (Vacuum ultraviolet) • CAN TARGET SPECIFIC CHEMICAL • LOW ENERGY CONSUMPTION- Can be greater than 10%. • BETTER THAN LASERS - Excimer lasers are typically only 1 to 3 % efficient. • COOL OPERATION - Low operating temperature (do not heat irradiated surface). • INSTANT START - Typically start in less than 1 millisecond. • MINIMUM DAMAGE-UV absorbed in 1 micron layer