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Sub Surface Cu Voids

Material Name: Copper
Record No.: 110
Primary Chemical Element in Material: Cu
Sample Type: Layer
Uses: Etching
Etchant Name: None
Etching Method: Dry etching
Etchant (Electrolyte) Composition: No data
Procedure (Condition): No data
Note: Copper voiding is major headache in the megafab production of IC's. Copper can form as many as four different types of voids, necessitating constant vigilance and tight process control. FIB sectioning of void test structures is a destructive but effective method to monitor process induced voids. See Figures (14-16) below. Sub surface Cu voiding is particularly hard to detect because it neither visible to "top view" KLA-like inspections and rarely results in a full electrical opens. Thus slower and destructive techniques are required to monitor the process. Passive FIB voltage contrast is especially helpful with well-designed test structures.
Reference: Bryan Tracy, Materials Analysis and Process Monitoring in MegaFabs, ISTFA 2002, Proceedings of the 28th International Symposium for Testing and Failure Analysis, 3-7 November 2002, Phoenix Civic Center, Phoenix, Arizona, pp. 69-75.


Figure 1: SEM of a M2/M1 via void test structure.


Figure 2: Bulk and via sidewall voids.


Figure 3: Cap interface voids.