Helium bubbles or cavities in silicon produced by implantation of helium ions have been the subject of attractive investigations, since their ability of trapping sites for detrimental metallic impurities was revealed [1] and further investigations have been reported. However, little information about dynamical behavior of bubbles and also dislocation loops inevitably introduced by implantation processing is available. Therefore, in the present study, in-situ irradiation and TEM observation is performed to reveal dynamical behavior of each helium bubble and dislocation loop.

Helium bubbles were introduced into (011) FZ-Si single crystals by irradiation with 5 - 10 keV He⁺ ions at temperatures ranging from room temperature to 620K and heated up stepwise to 1250K. Dynamical behavior of helium bubbles and dislocation loops during the temperature elevation was continuously monitored by TEM with a video recording system. Thermal desorption spectra (TDS) of helium from Si specimen was also measured by a quadru-pole mass spectrometer.

It is found that dislocation loops disappear at temperatures above about 950K and nano-sized helium bubbles start to move randomly above the temperature. The mean square of the bubble migration distance is proportional to the time, which allows us to yield the diffusion coefficient of helium bubbles according to the random walk theory. Bubble coalescence during the random motion was frequently observed and converted to stable larger bubbles. Correlation between the microstructure change and TDS is discussed.