光刻返工引起的MIM电容失效机理和解决方案

MIM Capacitor Failure Mechanism and Solution by Lithography Rework

针对由金属-绝缘体-金属（MIM）电容金属层光刻返工引起的产品成品率下降10%的问题,开展了一系列工艺实验,分析了引起失效的机理并提出了改进措施。采用扫描电子显微镜对失效样品进行了分析和表征,发现失效样品的氮化硅介电层有空洞,而未经MIM光刻返工的样品均未发现介质层有异常。由于MIM金属层光刻返工时,经过等离子体去胶和EKC溶液清洗表面易对电容介质层造成损伤,引起极板间短路,进而影响器件性能。实验结果表明,采用有机显影溶剂去胶来取代等离子体去胶,可有效改善光刻返工引起的电介质层损伤。采用该方法返工两次以内的成品率均不受影响。同时发现MIM电容层上的钨塞孔链密度在一定程度上影响失效率,分析认为高孔链密度样品更易受到后续孔刻蚀工艺的强电场影响。

A series of process experiments were carried out to solve the problem of 10% product yield reduction caused by lithography rework of the metal-insulator-metal（ MIM） capacitor metal layer.The failure mechanism was analyzed and the improvement measures were proposed. The failure sample was analyzed and characterized by the scanning electron microscope. It was found that there was a pin hole on the silicon nitride dielectric layer of the failure sample,but no abnormality on the dielectric layer was found in the samples without MIM lithography rework. During the MIM metal layer lithography rework,the capacitor dielectric layer was easy to be damaged by the plasma strip and EKC solution cleaning of the surface,causing the short circuit between the plates,thus affecting the device performance.The experiments results show that the use of organic developer solvent instead of the plasma strip can effectively improve the dielectric layer damage induced by lithography rework. With this method,the yield is not affected within twice rework. Meanwhile,the density of the tungsten plug via chain on the MIM capacitor layer affects the failure rate to a certain extent. It is considered that high via chain density samples are more easily to be affected by the strong electric field of subsequent via etching process.