EM 388F Term Paper: Subcritical Cracking of Low-k Dielectrics

Abstract

With the scaling of VLSI, ultra low-k dielectrics with porosity are being introduced to reduce the capacitance coupling. But due to the weak bonding strengths, low-k dielectrics may fail by environmental-assisted subcritical cracking, fracture at stresses far below the loads required for catastrophic failure, causing reliability issues. In this term paper, several references are reviewed to investigate the mechanism of subcritical cracking at multiscale levels.

Various experimental techniques including four point bending (FPB) and double cantilever beam (DCB) were used to evaluate the relationship between crack velocity and energy release rate under environments with different relative humidity (RH), potential of hydrogen (PH), and temperature. It turned out that the graph of crack velocity versus energy release rate was mainly composed of three regions, reaction-controlled region, transport-controlled region, and critical fracture region. Additionally, there was a threshold energy release rate, below which no crack was observed.

In order to understand the physics behind the subcritical cracking, first principle calculations on strained silicate structure was used to investigate how bond strains enhanced the chemical reaction between Si-O bonds and the environments. It showed that by creating Lewis acid sites on silicon and Lewis base site on oxygen, the changes in either Si-O-Si or O-Si-O bond angles increased chemical reacitivity.

Reference

 1.       J. J. Vlassak, etc., Materials Science and Engineering A 391 (2005) 159-174.

2.       S. Y. Kook, etc., J. Appl. Phys., Vol 91, No. 3, (2002), 1293-1303.

3.       R. F. Cook, etc., Journal of the Electrochemical Society, 146(12) 4439-4448 (1999).

4.       T. A. Michalske, etc., J. Appl. Phys., Vol 56 (10) (1984), 2686-2693.

5.       M. Lane, Annu. Rev. Mater. Res. (2003), 33:29-54.

6.       Z. Suo, Comprehensive Structure Integrity, Volume 8 (2002).

7.       R. S. Smith, etc., Materials Resaerch Society Symposium Proceedings Volume 914 (2006) 83.