Metal Residue Between BL and VSS-Line II

Metal Residue Between BL and VSS-Line II

Material Name: Silicon
Record No.: 113
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 0.18 µm process technology, 6-level metal (4-6 layers are dummy layers) design 2Mb synchronous SRAM with a single column failure. The device presents high IDD leakage of 700~800 µA under 2.0V constant voltage.
Experiment shows that OBIRCH cannot find the fault site from front-side since dummy metal layers block the laser from the metal layers below. Nikawa Et al. reported in 1993 that the minimum temperature could be detected by Hamamatsu Photonics (emission system) was estimated to be about 180°C. It is considered to be thermal radiation. Therefore, the temperature of metallic short type of defect, which provided leak path, may have the possibility to reach closely 180°C or higher. To gain the advantage of front-side analysis, Hamamatsu photo emission microscope (Phemos 200, a dedicated emission system) was tried to localize fault site even though it is not expecting to detect metallic short type of defect.
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: Front-side photoemission image.

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