金属硅化物阻挡层刻蚀对一次性编程单元数据保持性能的影响

The Effect of Salicide Block Etch on the OTP Data Retention

在0.18μm通用平台上加入一次性编程单元(OTP)后组成的衍生工艺被广泛应用于微控制单元(MCU)设计,由于OTP的尺寸非常小,为了使OTP拥有良好的数据保持(Data Retention)能力,SAB模组工艺非常关键,尤其是SAB刻蚀工艺,不能再采用同标准0.18μm工艺平台一样的单一刻蚀方法,必须采用以干法刻蚀为主、湿法刻蚀为副,干、湿相结合的方式进行刻蚀。因OTP的数据保持性能与干法刻蚀后有源区表面剩余SAB的量有关,所以SAB干法刻蚀非常关键。实验表明,只要干法刻蚀后有源区表面剩余SAB厚度控制在180 A,工艺窗口±50 A,OTP Cell有源区表面可免遭不可逆的等离子体损伤,而剩下的SAB也能通过湿法刻蚀去除干净且有较大的工艺窗口。OTP因此具备较好的数据保持性能,晶圆由此实现高良率。

The 0.18μm based One Time Program(OTP) process is widely used for Micro Controller Unit(MCU) design. Due to the much more tightened design rule of OTP cell compared to the 0.18μm platform, Salicide Block(SAB) Module, especially the SAB etch process, is very critical to obtain a good OTP data retention. In this paper, the effect of SAB etch on the OTP data retention was discussed. Compared to the pure wet etch used by the 0.18μm platform, SAB etch here will use a combination of dry and wet etch instead due to the much thicker SAB. The dry etch plays the main role of SAB etch. It is observed the remaining SAB oxide on Active surface after dry etch is correlated to the data retention performance. The less the remaining SAB oxide, the more the tendency of Active surface to be damaged by plasma,the more the remaining SAB oxide, on the other hand, the harder the oxide to be removed completely by the subsequent wet etch, as a result, the Salicide cannot be properly formed. It is shown that the remaining SAB oxide thickness on the Active surface was controlled to 180 A, with the Spec. of +/-50 A, an excellent OPT data retention is obtained and thus the high Chip Probing(CP) yield.