Environmentally stable chemically amplified resist

The dissolution characteristics and the free volume of the chemically amplified resists were studied for the improvement of their environmental stability. In the case of the environmentally unstable t-Boc type resist, we have found that the resist film after 1 hour PED under the 10 ppb NH 3 atmosphere showed the decrease of dissolution rates with increasing exposure energies. This fact suggests that it is important to select an appropriate combination of a photoacid generator (PAG) which generates a weak acid and a protecting group which can be easily deprotected under the weak acidity condition. As an example for the resist which deprotection activation energy was small, we examined the development behavior of acetal type resists. Among acetal type resists there are differences for the airborne contamination stability. These differences are caused by the kind of PAGs or solvents. Using the measured results, CD changes and pattern profiles were calculated by photolithography simulator 'PROLITH/2'. It was able to explain the real behavior of the resists. As for the kinds of resist solvents, some structural changes in the resist film may occur by the resist solvent. Especially, the free volume in the resist film correlates to the amount of airborne basic contamination. To estimate the free volume in the resist film, we applied a new technique which was called a 'positron annihilation.' We observed that the free volume in the resist film depended on kinds of solvents. Using these experimental results, a resist which had good PED stability was developed. This resist resolved 0.20 micrometer lines and spaces pattern with good profile using KrF excimer laser stepper and it had also excellent stability for airborne basic contamination and substrate influences.