TABLE OF CONTENTS The process of voltage breakdown in SiO 2 has been studied extensively and is fairly well understood at this time. It is due to hot electron (>2 eV above the bottom of the oxide conduction band) generation of interface defects that are trapping sites and is defect mediated.68 At a given field strength across the insulator there is a critical interface charge above which breakdown occurs. Some of this charge has its origin in defects already present before voltage stressing. Thus, proper processing may enhance the resistance of a SiO 2 film to voltage breakdown. In particular it has been suggested that reduction of the number of oxygen vacancies near the interfaces, which it is believed can be done by intentional oxygen annealing or via nitridation schemes using ammonia (NH 3),69 will accomplish this objective. Also, minimizing hydrogen incorporation and hydrogen motion in the oxide layer through the blocking action of oxynitride barriers created by some of these nitridation schemes would also reduce trap creation effects and increase device lifetime, particularly at high fields.70 If possible, lowering the operating temperatures of devices below 200 K should also reduce defect generation and increase charge to breakdown.71
What are the nature of the defects that act to trap charge and lower breakdown voltage? The dangling bond is the primary defect. But, there are different dangling bond defects. One is the E' center illustrated in Figure 1.20, which consists of unpaired electrons in sp
