The current semiconductor resist process requires a clean atmosphere for 193-nm immersion exposure. Processing
involving such small dimensions and short wavelengths requires an atmosphere with extremely low concentrations of
various amines, as well as ammonia. This clean space is secured by using an ion-exchange type chemical filter. In
addition, a variety of organic contaminants cannot be ignored. For example, in the exposure process, siloxane and other
low molecular weight compounds are transformed into high molecular weight compounds by short-wavelength light, and
cause lens fogging. To deal with these organic compounds, an activated carbon filter has been used.
This paper establishes an optimized design theory for an ion exchange filter based on the molecular diameters of
targeted amines by examining the adsorption of various types of amines by ion-exchange resin.
We verified the adsorption behavior of a chemical filter by considering the actual environment around the wafer, and
established a clean environment by using adsorption theory for various types of contaminants.
The current semiconductor lithography process is in the high volume production phase of 193nm high NA (Numerical
Aperture) exposure, and further reaching the high volume production phase with 193nm immersion exposure
lithography. As a result of miniaturization of the devices, it has becomes necessary to reduce the concentration of basic
compounds (such as ammonia, amines, and N-methyl-2-pyrrolidone (NMP), which are used to insolubilize the chemical
amplified resist in developing process, in the environment surrounding the wafer. For this purpose, chemical filters are
used. In the clean room, in addition to these basic gases, there exist various organic compounds and the effects of organic
compounds on the chemical filter cannot be ignored. This paper reports the results of basic research on the adsorption
behavior of physical adsorption under the presence of the above-mentioned basic compounds and ion exchange reaction.
Then the adsorption behavior of activated carbon chemical filter impregnated with acidic chemicals and strongly acidic
cation exchange chemical filter for basic compounds was studied in the coexistence of organic components. The
performance of impregnated activated carbon chemical filter deteriorates due to the coexisting organic compounds
because removal of NMP is based on the physical adsorption mechanism. On the other hand, the performance to remove
ammonia and NMP of strongly acidic cation exchange chemical filter is not affected by organic compounds because the
filter exchanges ions with weakly basic compounds. The strongly acidic cation exchange chemical filter can provide
desired performance for basic compounds under an actual clean room environment.
While the current standard for NA (Numerical Aperture) for the semiconductor resist process is 193 nm High NA, use of the 193 nm immersion exposure process is growing and almost ready for application in mass production. With the growing trend toward the use of finer line processes in the manufacture of semiconductor devices, the need for cleanliness of the ambient atmosphere surrounding the silicon wafer has also been increasing. In addition to ammonia, that has hitherto been the main target for elimination, the concentration of other chemicals, such as amines and N-methyl-2-pyrrolidone (NMP), need to be kept sufficiently low for the new processes. Therefore, the role of chemical filters has become an essential one. We conducted a study on the dependency of chemical filters on the molecular diffusivity of target gas species, and, based on this data, developed a filter that eliminates amines. The filter has a honeycomb structure with a wide gas-contacting area, and consists of an ion-exchange resin that has received special treatment. The filter has a greatly improved gas capture efficiency (>99.8% for ammonia, >98% for triethylamine and NMP) and a very large adsorption capacity, which enables a 50% reduction of the filter volume compared with currently available chemical filters.