Page 41 - Semiconductor Manufacturing Handbook

Geng(SMH)_CH04.qxd 04/04/2005 19:36 Page 4.4

COPPER, LOW-k DIELECTRICS, AND THEIR RELIABILITY

4.4 SEMICONDUCTOR FUNDAMENTALS AND BASIC MATERIALS

Temperature (°C)
1400 1300 1200 1100 1000 900
10 −3
Cu
10 −4
Li
Au(I)
10 −5
He
10 −6 Au(I-S) K
Fe
H Na
S
10 −7
Ni Zn
Au(I-S)
Ag +VI
−8
Diffusivity (cm 2 /s) 10 −9 O C
10

−10
10
Al
10 −11 Bi Ga

As B
10 −12
Sn
In.Ti
10 −13

Sn Ge P
10 −14
Sn
10 −15
0.6 0.7 0.8
1000/T (1/K)
FIGURE 4.4 Diffusivity of various impurities in silicon as a function of temperature. 4

physical and chemical stability. It should adhere well to both copper and the dielectric. Its deposi-
tion should be highly conformal so that adequate coverage is achieved in high aspect ratio structures.
Figure 4.5 lists the attributes of a good liner and compares different materials as potential liner can-
didates. 10
Missing liners is one of the major reliability concerns with copper metallization. It can lead to
pinhole defects in via/line structures and thus potential electromigration and stress voiding problems.
It can cause copper to leak out and short to adjacent metal structures during TDDB stress. High resis-
tivity is one of the serious drawbacks of liners that add to the line resistance by usurping copper
cross-section area. To keep the line resistivity low and maintain copper’s advantage, thickness should
also be minimized without compromising the liner’s functionality.
Electroplating is currently the preferred method of depositing thick copper films in dual-damascene
architecture. This process requires the presence of a copper seed layer that serves as the cathode on

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2004 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.