激光退火在背照式CCD图像传感器中的应用研究

Applications of Laser Annealing in Backside-illuminated CCD Image Sensor

摘要:

激光退火是消除背照式电荷耦合器件(CCD)图像传感器背面势阱的重要工艺。文章研究了激光退火工艺中不同的激光波长、能量密度、光斑交叠率对掺杂杂质激活效率、器件表面形貌、成像质量及紫外量子效率的影响。研究结果表明,在浅结注入的情况下,355nm波长激光激活效率要优于532nm激光,但是355nm激光比532nm激光更易在较低能量密度时使硅片出现龟裂现象。采用2J/cm²能量密度、50%~65%交叠率,355nm激光能有效激活离子注入的硼离子,背照式CCD图像传感器成像均匀性好,紫外量子效率明显提升。

Abstract:

Laser annealing is an important process of eliminating the backside well of the backside-illuminated charge-coupled devices (CCD) image sensors. The influences of different laser wavelengths, energy densities, overlap rate of laser spots on doping activation rate, device surface morphology, imaging quality and ultraviolet (UV) quantum efficiency of CCD were investigated. The results show that, the doping activation rate of 355nm laser is higher than that of 532nm laser at shallow junction implantation. However, the presence of wafer crack is easier to appear at low energy density when using 355nm laser. By adopting energy density of 2J/cm² and 50%~65% cross rate of 355nm laser, the boron doping is efficiently activated, the imaging uniformity of backside-illuminated CCD is achieved, and the UV quantum efficiency of CCD is significantly improved.