Metal Residue Between BL and VSS-Line III

Metal Residue Between BL and VSS-Line III

Material Name: Silicon
Record No.: 114
Primary Chemical Element in Material: Si
Sample Type: Wafer
Uses: Etching
Etchant Name: None
Etching Method: Dry etching
Etchant (Electrolyte) Composition: No data
Procedure (Condition): No data
Note: The device is 0.15 µm process technology, 7-level metal (4-7 layers are dummy layers) design 2Mb synchronous SRAM with a single column failure. The device presents high IDD leakage of 700~900 µA under 1.5V constant voltage.
After several attempts, neither front-side OBIRCH nor front-side photoemisison microscope could isolated the fault site due to dense metal layers. As a result, liquid crystal analysis (LCA), which is a very traditional technique, under specific range of voltage bias was attempted to overcome this difficulty (Fig 1, 2). The attached laser cutter also provides an advantage to in-situ mark the fault site.
Reference: Cheng-Piao Lin, Cheng-Chun Ting, Chin-Hsin Tang, Cheng-Hsu Wu, Chih-Ming Kuo, Yung-Sheng Huang, Application of Various Fault Localization Techniques to Different Types of 6T-SRAM column Failures, ISTFA 2002, Proceedings of the 28th International Symposium for Testing and Failure Analysis, 3-7 November 2002, Phoenix Civic Center, Phoenix, Arizona, pp. 259-265.

Figure 1: Image of LCA hot spot and in-situ laser mark.

Figure 2: SEM image of LCA located metal residue between BL node and VSS-line.