Adhesion
Copper Interconnects in Microelectronics
University of Minnesota – Twin Cities
MatS 4221W
Lab Group 2
Timothy S. Marass
Loc Nguyen
Peter Sylvestre
Ethan Taylor
Date(s) of Laboratory: November 20 & Decmber 4, 2007
Date of Report: December 12, 2007
Adhesion – MatS 4221W – Dec. 12, 2007
I.
Executive Summary
This experiment investigated…
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Table of Contents
Executive Summary ............................................................................................................... 2
Introduction ............................................................................................................................ 4
Methods .................................................................................................................................. 5
Results .................................................................................................................................... 7
Discussion ............................................................................................................................ 16
Conclusions .......................................................................................................................... 17
References ............................................................................................................................ 18
Appendix A: Data................................................................................................................. 19
Appendix B: Sample Calculations ....................................................................................... 20
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II.
Introduction
Periods of time have been named for, and often defined by, various technological
advances. By the same convention, if 2000 to 700 B.C is known as the Bronze Age1 because of
the appearance of bronze tools and weapons, then surely the last 100 years could be
characterized as the beginning of the Silicon Age. The microelectronics industry is rapidly
enlarging due to the ever-present demand for smaller, more powerful electronic devices with
extended battery lives. Most integrated circuits use aluminum for interconnects; however, there
are issues with miniaturizing aluminum connections because of electro-migration and stressmigration issues2. Aubel et. al. found that “Copper shows a much higher electromigration
resistance compared to aluminum3.” Copper can diffuse through the silicon wafers it is
deposited on, resulting in short circuits, and poorly adheres to the silicon wafers. To combat
these problems with copper, it has been theorized4 that an intermediate layer of Ti between the
Cu and silicon wafer could form a diffusion barrier and increase the overall adhesion of the
system.
In this lab, three samples will be analyzed to determine if the adhesion issues can be
resolved by depositing a layer of Ti. These three samples include: A: 3um, Ti, Cu on a Si wafer;
B: bare Si wafer; and C: 200nm, Ti, Cu on a Si wafer.
1
www.le.ac.uk/archaeology/ulas/birstall.html
Lab 6 Handout.
3
http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel5/7298/28198/01261738.pdf
4
Lab 6 Handout.
2
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III.
Methods
The first experiment was performed using micro-indenters. The three samples were
mounted onto a mounting platform shown below.
Figure 1. Sample on testing platform. A: 3um, Ti, Cu on a Si wafer; B: bare Si wafer; and C: 200nm, Ti, Cu
on a Si wafer. Location of indentation marked with arrows per sample.
Tribo-indentor and Vickers indenters were used to produce indentation blisters which will later
be analyze to determine the adhesion properties of the film. The initial process was preparing
and determining a clean area on the film for indentation via Video Enhanced Microscope
(VEM). Areas were then marked with sharpie marker; Figure 1 showed the circled marked area.
Sample C was chosen for the first Tribo-indentation test then sample A and B. Two
experimental tests were done for sample C and A, and one test for sample B; sample C was
performed with 100nm and 20nm indentation depth, sample A with 1000nm and 2000, and
sample B with 1000nm depth. VEM images were then taken of the indentation blister.
Vicker hardness was then performed on sample A and C using NanoXp indenter. Four
experiments were taken for sample A and six for sample C with various load setting. Relative
indentation locations are shown in Figure 2 below.
Figure 2. Vicker hardness indentation number and location for sample A and C.
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Indentation areas were then imaged via VEM. Profile scan of the indentation blisters using
profilometer were then taken for sample A with 2 blisters in the same scan path. The second
profile scan was from a third indentation blister for sample A. Sample B and C were then
scanned using the profilometer.
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IV.
Results
Initial VEM images revealed possible film buckling prior to indentation for sample C
with the 200nm film on Si wafer shown in Figure 3.
(a)
(b)
(c)
(d)
Figure 3. VEM images of 200nm copper film. (a) 2.5x Possible Blister: shows location of blister shown in 1.d. in
respect to sample; arrow denotes blister location. (b) 50x Prior indentation on film. (c) 50x Possible Blister: shows
5um difference between blister surface and film background. (d) 50x Possible Blister: image showing 3um
difference between blister surface and film background.
Figure 4 showed indentation marks and indentation blisters for the 6 indentation experiments.
Table 1 contains the load for each indentation mark as well as the calculated hardness value; data
for indentation 1 and 2 was not recorded.
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(a)
(b)
(c)
(d)
(e)
(f)
Figure 4. Indents made on 200nm film sample C. (a) Indent 1. (b) Indent 2. (c) Indent 3. (d) Indent 4. (e) Indent 5.
Surface height = 0.004mm, maximum indent depth = 0.003mm, overall change (indentation depth) = 0.001mm. (f)
Indent 6. Surface height = 0.004mm, maximum indent depth = 0.003mm, overall change (indentation depth) =
0.001mm.
Table 1. Sample C, 0.2um of Cu. Hardness Measurements.
Position Load,P[mN]
D1[um]
D2[um]
HV
3
2942
22.1
25.7
973.9
4
490.3
12.8
12
603
5
490.3
11.9
12.7
617.8
6
980.7
15.4
15.9
757.1
Note: No data was taken from positions 1 and 2.
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Figure 5 showed VEM images of indentation mark and blister for sample A with 3um film and
Table 2 contains load value and hardness that correspond to each indentation.
(a)
(b)
(c)
(d)
Figure 5. Indents made on 3um-film sample A. (a) Indent 1. (b) Indent 2. (c) Indent 3. (d) Indent 4.
Table 2. Sample A, 3um of Cu. Hardness Measurements.
Position Load,P[mN]
D1[um]
D2[um]
HV
1
490.3
22.4
26.1
157.6
2
980.7
29.3
32.4
192.9
3
2942
39.5
41.4
340
4
9807
60.1
55.9
551.2
(a)
(b)
(c)
Figure 6. NanoXP indentation groups. (a) Overall view of Groups 1 (left) and 2 (right). (b) Group 1 indentations.
(c) Group 2 indentations.
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Figure 7 showed VEM images of spontanious blisters for sample A that was not related to
indentation.
(a)
(b)
(c)
(d)
€
(f)
Figure 7. Sample A observed blisters. (a) Sample A, Blister 1. (b) Sample A, Blister 1 sample location. (c) Sample
A, Blister 2. (d) Sample A, Blister 2 sample location. (e) Sample A, Blister 3. (f) Sample A, Blister 3 sample
location.
Table 3 and 4 are result form nanoxp indentation data which contains modulus from unload and
hardness from unload for sample A.
Table 1. Sample A, 3um, Ti, Cu Material Properties. Trial 1.
Modulus From Unload Hardness From Unload
(GPa)
(GPa)
Test
1
148
2.59
2
139
2.57
3
154
2.70
4
145
2.71
Mean
147
2.64
St. Dev.
5.9
0.072
Table 2. Sample A, 3um, Ti, Cu Material Properties. Trial 2.
Modulus From Unload Hardness From Unload
GPa
GPa
Test
1
158
3.22
2
156
3.23
3
158
3.23
4
165
3.33
Mean
159
3.25
Std. Dev.
4.0
0.053
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Table 5 and 6 are result from nanoxp indentation data which contains modulus from unload and
hardness from unload for sample C.
Table 3. Sample C, 200nm, Ti, Cu Material Properties. Trial 1.
Modulus From Unload Hardness From Unload
GPa
GPa
Test
1
92
2.92
2
95
3.41
3
90
3.39
4
73
2.54
Mean
87
3.07
Std. Dev.
10.1
0.419
Table 4. Sample C, 200nm, Ti, Cu Material Properties. Trial 2.
Modulus From Unload Hardness From Unload
GPa
GPa
Test
1
23
1.72
2
47
1.78
3
78
1.22
4
0
****
Mean
49
1.57
Std. Dev.
27.9
0.31
Table 7 showed result from nanoxp indentation data which contains modulus from unload and
hardness from unload for sample B.
Table 5. Silicon (Si) Sample Material Properties.
Modulus From Unload Hardness From Unload
GPa
GPa
Test
1
179
13.04
2
197
12.28
3
186
12.63
4
195
12.38
Mean
189
12.58
Std. Dev.
8.3
0.34
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Figure 8 and 9 showed graph of depth versus hardness and depth versus modulus for sample A
with 3um film thickness from trial 1 and 2 respectively.
Figure 8. Hardness and Modulus Load/Unload Curves. Sample A, 3um, Ti, Cu. Trial 1.
Figure 9. Hardness and Modulus Load/Unload Curves. Sample A, 3um, Ti, Cu. Trial 2.
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Figure 10 and 11 showed graph of depth versus hardness and depth versus modulus for sample C
with 200nm film thickness from trial 1 and 2.
Figure 10. Hardness and Modulus Load/Unload Curves. Sample C, 200nm, Ti, Cu Material Properties. Trial 1.
Figure 11. Hardness and Modulus Load/Unload Curves. Sample C, 200nm, Ti, Cu Material Properties. Trial 2.
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Figure 12 showed graph of depth versus hardness and depth versus modulus for sample B of
silicon without and film.
Figure 12. Hardness and Modulus Load/Unload Curves. Silicon (Si) Sample.
a)
b)
c)
Figure 13. NanoXP indentation using conical tip. a) Sample A with 4um displacement. b) Sample C with a
1um displacement. c) Sample C single indentation.
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Table 6 and 7 present more data for sample A using NanoXP indenter. Figure 13a showed VEM
image of conical indentation using NanoXP; indentations are 4um apart.
Table 6. NanoXP data for sample A (3um film) with a 4um displacement between trial 1.
Test
Modulus From Unload Hardness From Unload
GPa
GPa
1
278.438
17.378
Table 7. NanoXP data for sample A(3um film) with a 5um displacement between trial 1 and 2.
Test
Modulus From Unload Hardness From Unload
GPa
GPa
1
275.599
15.601
2
291.314
17.979
Mean
283.456
16.79
Std. Dev.
11.112
1.682
% COV
3.92
10.02
Table 8 and 9 showed more data for sample C from NanoXP indenter. Figure 13b and c, showed
VEM image of conical indentation using NanoXP; indentations are 1um apart.
Table 8. NanoXP data for sample C(200nm film) with a 1um displacement between trial 1 and 2.
Test
Modulus From Unload Hardness From Unload
GPa
GPa
1
198.779
36.707
2
200.092
36.962
Mean
199.436
36.835
Std. Dev.
0.929
0.181
% COV
0.47
0.49
Table 9. NanoXP data for sample C(200nm film).
Test
Modulus From Unload Hardness From Unload
GPa
GPa
1
190.211
42.756
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V.
Discussion
A
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VI. Conclusions
Experimental data showed…
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VII. References
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VIII. Appendix A: Data
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IX. Appendix B: Sample Calculations
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