Bei VLSI_Design conference__________.ppt

VLSI Design

1. VLSI Design & Embedded Systems Conference
January 2015
Bengaluru, India
Diagnostic Tests for Pre-Bond
TSV Defects
Bei Zhang
Vishwani Agrawal

2. Purpose of Pre-bond TSV Test
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Defects arise in TSV manufacturing. Pre-
bond TSV test helps identify defective dies
early in the process.
Pre-bond TSV test provides known good die
(KGD) information for die-on-die or die-on-
wafer or wafer-on-wafer fabrication process.

3. Outline
•3D IC Structure and TSV Models
•Pre-bond TSV Probing technique
•Test Session Generation
•Experimental Results
•Conclusion
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4. 4
TSV-based 3D IC Structure
3D face-to-back stacked IC:

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5. RC Models of Defective
TSVs After Wafer Thinning
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Resistance-defective TSVCapacitance-defective TSV
S
u
b
s
t
r
a
t
e
InsulatorRTSV1
CTSV2
RTSV2
CTSV1
Rvoid
S
u
b
s
t
r
a
t
e
Insulator
CTSV
RTSV
Rleak
B. Noia and K. Chakrabarty, Design-for-Test and Test Optimization Techniques for
TSV-based 3D Stacked ICs. Springer, 2014.

6. Illustration of Pre-bond
TSV Probing on the Substrate Side
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GSF: Gated scan flip-flop

7. Circuit Model of Pre-bond
TSV Test
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Circuit Model of Pre-bond
TSV Test

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Circuit Model of Pre-bond
TSV Test

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Circuit Model of Pre-bond
TSV Test

11. Capacitor Charging Time Through
Parallel TSVs
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Number of
TSVs charging
in parallel (q)
Capacitor
charging time
t(q) (μs)
1 0.80
2 0.53
3 0.42
4 0.38
S. K. Roy, S. Chatterjee, C. Giri, and H. Rahaman, “Faulty TSVs Identification and
Recovery in 3D Stacked ICs During Pre-bond Testing,” Proc. International 3D
Systems Integration Conference, 2013, pp. 1–6.

12. Two Important Observations
1) Any faulty TSV within a parallel test will cause
the test to fail but we cannot tell which TSV(s)
is (are) faulty.
2) A good parallel test implies that all TSVs
within the parallel test are fault-free.
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13. Terminology
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TSV network TSVs simultaneously contacted by probe.
Test session (S
i
)TSVs grouped for parallel charging of capacitor.
Maximum number
of faulty TSVs in
network (m)
m is the number of redundant TSVs within the
TSV network.
Session size (q) q is the number of active TSVs within a session.
Resolution (r) r is an upper bound on session size.
Test time of a
session (t(q))
Charging time of C
charge
, related to session size.
Fault map (ρ) Fault map represents positions of defective
TSVs within the TSV network.

14. Test Session Generation
Motivation
Compared to individual TSV test, large test
time saving is possible if we test TSVs in
parallel without losing the capability of
identifying up to m faulty TSVs, while
guaranteeing that the size of each test session
does not exceed the resolution constraint r.
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15. Test Session Generation
Problem Statement
Given:
Test times t(q) for different session sizes q
(q[1, r]), and
∈
Maximum number (m) of faulty TSVs in a
network of T TSVs.
Determine: A set of test sessions of size less than
r, such that up to m faulty TSVs are uniquely
identified and the total test time is minimized.
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16. Test Session Generation
Sufficient condition
If each TSV
i is included in m + 1 sessions (say,
S
1, S
2, · · · , S
m+1) and the intersection of a pair
of these m + 1 sessions contains only TSV
i, i.e.,
S
i ∩ S
j = TSV
i for i ≠ j [1,
∈
m + 1], then up to
m faulty TSVs within the network can be
uniquely identi
fied. These
m + 1 sessions are
called unique test sessions for TSV
i .
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B. Noia and K. Chakrabarty, “Identification of Defective TSVs in Pre-Bond
Testing of 3D ICs,” Proc. 20th Asian Test Symposium (ATS), 2011, pp. 187–
194.

17. A Previous Heuristic Method
To pinpoint 1 faulty TSV in a 6-TSV
network
with resolution constraint r = 4, the
heuristic-based sessions are
{1,2,3,4}, {1,5,6}, {2,5}, {3,6}, {4}.
Careful examination shows:
•Each TSV resides in two unique test
sessions!
•The heuristic sessions reduce the total test
time compared to individual TSV testing.
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B. Noia and K. Chakrabarty, “Identification of Defective TSVs in Pre-Bond
Testing of 3D ICs,” Proc. 20th Asian Test Symposium (ATS), 2011, pp. 187–194.

18. Limitation of the
Heuristic Method
Sessions {1,2,3,4}, {1,5,6}, {2,5}, {3,6}, {4} are not optimal.
The optimal set of sessions are
{1,2,3}, {1,4,5}, {2,4,6}, {3,5,6}
 As we can see every TSV still resides in 2
unique sessions, but the total test time is
further reduced by 36.8%!
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19. ILP based Session Generation
Three general constraints for ILP model (ILP
model 1):
C1. Each TSV should be included in at least m + 1
test sessions.
C2. The size of a test session ranges anywhere
from 0 (empty session) to r.
C3. Any non-empty session is supposed to be a
unique session for any TSV within it.
Objective: Minimize total test time of all sessions.
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20. Experimental Results
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Test time comparison for a 20-TSV network

21. Experimental Results
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Test time comparison for resolution constraint r = 3

22. Experimental Results
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Comparison of number of sessions for r = 4

23. Conclusion
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•An ILP model is proposed to generate near-
optimal set of test sessions for pre-bond
TSV testing.
•ILP model always reduces pre-bond TSV
identification time compared to that of a
previous heuristic method.
•Future exploration can be possibly deriving
necessary and sufficient conditions to
generate globally optimal set of sessions.