Microwaves are radio or electromagnetic waves in the frequency band from 300 Mhz to 300 GHz. Typically, most applications fall within 40 GHz, and electro heating applications use a limited frequency band, the so called Industrial, Scientific and Medical (ISM) radio bands, reserved intentionally for uses other than communications: among these the most common frequencies are 915 MHz 2.45 GHz and 5.80 GHz.
Microwave applications include coating, etching, stripping, cleaning, surface modification in semiconductor and thin-film applications; vacuum heating, vacuum drying, pre-cooking, pasteurizing and sterilizing in food processes; curing, gas recombination, synthesis for chemical and pharmaceutical industries and diathermy, the treatment of biological tissues in medical application.
Remote microwave plasma disassociates a wide range of semiconductor process gases to their atomic form. Applications include hydrogen for native oxide etch, fluorine for silicon etch, oxygen and nitrogen for oxidation and nitration to increase the dielectric constant of gate oxides. Atomic oxygen is widely used for high-rate, damage-free photoresist removal, and atomic fluorine effectively eliminates hard photoresist. Water vapor plasma successfully removes residue and aids post-metal etch passivation. With high selectivity and minimal dielectric damage, microwave plasma strip processes meet the cleanliness and residue removal requirements of fine device architectures, high aspect ratios and new low-k materials. An ion-depleted downstream microwave plasma has proven superior for achieving a pure dry chemical process and in dual-damascene low-k processes.
In remote microwave plasma subsystems, the plasma discharge is used to dissociate process gases and produce active atoms (radicals) upstream of the process chamber. Remote microwave plasma subsystems produce a low content of energetic ions. Therefore, the flow of radicals generated in the microwave plasma source can be used for damage-free wafer processing.
Microwave is a fast and efficient method of heating materials that are difficult to heat by convection or infrared methods, and unlike other types of heating, microwaves penetrate all parts of the material concurrently, so they heat uniformly. Microwave technology is used in numerous applications including: