2003 Fiscal Year Final Research Report Summary
Void Formation Mechanisms in Cu Interconnect for Ultra Fast ULSI Application
| Project/Area Number |
13450281
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (B)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
Structural/Functional materials
|
|---|
| Research Institution | Tohoku University |
|---|
Principal Investigator |
KOIKE Junichi Tohoku University, Graduate School of Environmental Studies, Assoc. Prof, 大学院・環境科学研究科, 助教授 (10261588)
|
|---|
| Project Period (FY) |
2001 – 2003
|
| Keywords | Cu / Interconnect / Void / Thermal stress / ULSI / Reliability / Anisotropy |
|---|
| Research Abstract |
Cu thin films have been used for an interconnect material for advanced semiconductor devices. Void formation during thermal processing has been known to cause interconnect failure. This work has focused on understanding the void formation mechanism in Cu/Ta/SiO_2/Si multilayer samples. SEM and TEM observation indicated that voids were formed in a strongly <111> textured film but not in a ramdom texture film. It was also found that the voids were formed at corners of twins and at intersections between twins with other twins or with grain boundaries. In order to understand the role of twins, stress distribution was simulated using a three dimensional finite element method (FEM) computer code. Localized crystallographic information of actual samples was analyzed with electron diffraction and was, incorporated in the FEM simulation. The results indicated that a large elastic anisotropy of Cu gave rise to stress concentration at twin corners and intersections that acted as a driving force for void formation. Orientation analysis of twin planes indicated that the <111> texture film contained incoherent {322} twins.having a high energy, while the random textured film contained coherent {111} twins having a low energy. The former twin of the {322} type was found to be subject voiding. under stress concentration. When the film thickness and the initial texture are controlled, <100> oriented giant grains could be formed. Since the twins were absent in this film, no void was formed during thermal processing In damascene lines, slit-like voids were formed at the shoulder of the trench opening. Stress simulation indicated that shear stress concentration caused the void formation by partial delamination at the Cu/Ta interface. These results suggested that the improvement of adhesion strength at the Cu/Ta interface is important for the device reliability.
|
