Positron annihilation is a non-destructive technique for investigating vacancy-type defects in condensed matter. When a
positron is implanted into a sample, it annihilates with an electron and emits two 511-keV γ quanta. From measurements
of Doppler broadening spectra of the annihilation radiation and positron lifetimes, one can detect point defects such as
monovacancies, vacancy clusters, and vacancy-impurity complexes. The regions sampled can range from the surface to a
depth on the order of microns. In the present study, we have used the positron annihilation technique to study
relationship between the impurity doping and vacancies in GaN. Defects in ion-implanted GaN and their annealing
properties were studied. The defects introduced by the implantation were identified as divacancies, and the defect
reaction during isochronal annealing were found to depend on ion spices. A relationship between intra-4f transitions of
Er and vacancies was studied. A correlation between the defect concentration and the PL intensity was observed. We will
demonstrate that the positron annihilation technique is sensitive to vacancy-type defects in GaN, and it can contribute to
the development of optical and electronic devices based such materials.
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<SUB>3</SUB> 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.