Surface passivation in n-type silicon and its application in silicon drift detector*

Based on the surface passivation of n-type silicon in a silicon drift detector (SDD), we propose a new passivation structure of SiO 2 /Al 2 O 3 /SiO 2 passivation stacks. Since the SiO 2 formed by the nitric-acid-oxidation-of-silicon (NAOS) method has good compactness and simple process, the first layer film is formed by the NAOS method. The Al 2 O 3 film is also introduced into the passivation stacks owing to exceptional advantages such as good interface characteristic and simple process. In addition, for requirements of thickness and deposition temperature, the third layer of the SiO 2 film is deposited by plasma enhanced chemical vapor deposition (PECVD). The deposition of the SiO 2 film by PECVD is a low-temperature process and has a high deposition rate, which causes little damage to the device and makes the SiO 2 film very suitable for serving as the third passivation layer. The passivation approach of stacks can saturate dangling bonds at the interface between stacks and the silicon substrate, and provide positive charge to optimize the field passivation of the n-type substrate. The passivation method ultimately achieves a good combination of chemical and field passivations. Experimental results show that with the passivation structure of SiO 2 /Al 2 O 3 /SiO 2 , the final minority carrier lifetime reaches 5223 μs at injection of 5×10 15 cm −3 . When it is applied to the passivation of SDD, the leakage current is reduced to the order of nA.