Snapback应力引起的90nm NMOSFET’s栅氧化层损伤研究

Investigation of snapback stress induced gate oxide defect for NMOSFET's in 90nm technology

实验结果发现突发击穿(snapback),偏置下雪崩热空穴注入NMOSFET栅氧化层,产生界面态,同时空穴会陷落在氧化层中.由于栅氧化层很薄,陷落的空穴会与隧穿入氧化层中的电子复合形成大量中性电子陷阱,使得栅隧穿电流不断增大.这些氧化层电子陷阱俘获电子后带负电,引起阈值电压增大、亚阈值电流减小.关态漏泄漏电流的退化分两个阶段:第一阶段亚阈值电流是主要成分,第二阶段栅电流是主要成分.在预加热电子(HE)应力后,HE产生的界面陷阱在snapback应力期间可以屏蔽雪崩热空穴注入栅氧化层,使器件snapback开态和关态特性退化变小.

The experiment result shows that the holes generated by avalanche can be injected into gate oxide of a NMOSFET biased into snapback, and then both hole trapping and interface state generation can be found. These trapped holes may recombine with electroas tunneling into gate oxide due to the ultrathin gate oxide, and then many neutral electron traps would be generated and the gate oxide current would be increased. The threshold voltage would increase and the sub-threshold current would decrease when the injected electrons are trapped by the electron traps. The degradation of drain leakage current can be divided into two phases. Sub-threshold current is predominant in the first phase, while in the second phase gate current is predominant. After pre-HE stress, the generated interface states can reduce the number of holes being injected into gate oxide generated by avalanche process during snapback stress, which causes the MOSFET snapback degradation to decrease in on-state and off-state modes.