2. Characteristics of Nanometer Devices
Design trends
Increasing corners of operation (multiple frequencies,
voltage, power scenarios)
Increasing integration (SOCs, SIPs)
Permeation of high bandwidth serial/ differential
interfaces
Process issues
Process variations becoming key concern
Increasing wiring densities leading to complex signal
integrity problems
Dominance of new kinds of defects based on the metal
subsystem
3. Test Challenges – Increased
Parametric Variations
Source : “Parametric Failures in CMOS ICs- A Defect
Based Analysis”, Hawkins et al., ITC2002
4. At Least Test will Find It?
e- e-
L TARGET
L EFFECTIVE
Minor bridging defects etc.
Current vs. Speed Limit
Current
L EFFECTIVE = L TARGET - X
e- e-
X : Lot1
L TARGET O : Lot2
L EFFECTIVE
L EFFECTIVE = L TARGET + X
Source: Madge, et. al., 2004
Speed
6. Test Challenges - Cost of Test
Source : International Technology Roadmap for Semiconductors, 2001
7. Test Challenges – Power
Test power could be more than functional power
– more regions of the device operating than in functional mode
– switching of logic during scan shift
With increasing design frequencies & integration
– Can the tester supply the power required in the test mode
– Can the package support the power required in the test mode
– Will the part be able to withstand the power consumption during
high voltage testing
8. Test Challenges - Yield Learning
Defect sizes scale as quickly or faster than the device features
Difficulty in localizing faults increases one order of magnitude
every six years
Defective chips offer significant information on these failure
mechanisms
Yield learning is becoming increasingly important
To tune the manufacturing processes to achieve higher
profits
To reduce the time for volume production since product life
cycles are coming down
10. New Fault Models - Bridge Fault
Testing
Bridge fault testing detects shorts between interconnects
0
A 0
0
1
1 B 0
11. Bridge Fault Testing
Number of possible bridges in a design is exponential to
the number of nets
Bridge node pair extraction is done from layout based
on proximity analysis
Critical
Area
Analysis
Four possible bridge fault tests exist for a pair of nodes
Could lead to a large test vector count
12. High resistance bridging faults
Bridge Resistance Data*
Source: “Test challenges in nanometer”, Kundu et al., ITC2000
13. Delay Fault
DC tests (eg based on stuck-at, logic bridge model) are
no longer adequate
AC tests which ensure that the design works at the
rated speed are required
14. Delay Fault Testing
Delay fault tests check if any node in the design is slower
to rise or fall than it should
Requires design techniques to obtain high coverage
On-chip PLL based clocking
Support for multiple clock domains
Knowledge of device timing exceptions
Consume 2x-5x times the number of test patterns for
stuck-at fault testing
15. Small Delay Defects
Source: “Test Method Evaluation Experiments and Data”, Nigh et al., ITC2000
16. Small Delay Fault Testing
small delay test
0.4
0.1 transition test
0.3 0.3
0.2 0.5
17. Reducing the Cost of Scan Tests
Scan in 1 Scan out 1
Scan in 2 Scan out 2
Scan in 3 Scan out 3
Scan in 4 Scan out 4
Scan in 5 Scan out 5
Test time = length of scan chain x #patterns x (1/frequency of shifting)
Test volume = length of scan chain x #patterns x 2
18. Scan Compression
Scan chain group 1 Scan chain group N
Scan chain group 2
Scan in 1 C
E o
x m
Scan in 2 p p
a r
n e
d s
e s
Scan in N r o
r
19. Reducing Power During Test
Divide and conquer
Switch lesser logic while reducing test time
Prevent the functional logic from switching during
scan shift using data gating
Power aware ATPG patterns which prevent transitions
that don’t result in additional coverage
20. What is the Problem?
Design 1 Design 2
• Same Die Size
• Same Complexity
• Same Foundry
• Same Process
21. What is the Problem?
Design 1 Design 2
77% Yield 42% Yield
Interactions Between Design and Manufacturing
22. Scan based diagnostics
To enable effective use of scan patterns for yield
learning, the patterns should have
Capability to identify failures
– Requires high test coverage
Capability to isolate the failures
– Accurately map the failures to the physical location of the
failures
23. Scan based diagnostics
Layout
Defect mapping
suspect
coordinates
Physical
Failure
Analysis Failure
Diagnostics
Information
Defect
information
ATPG based
failure
diagnostics
Manufacture
Wafer
Failure
Information
Test
24. Economics
$$$$
Yield
Accelerated Yield Learning
Standard Yield Improvement
Time
25. Conclusion
Nanometer testing presents new challenges not seen
hitherto
Without a single-eyed focus on test, either of the
following scenarios are likely:
Low Test Quality : High escape rates of defective
devices
High Test Cost : Affecting profitability
Slow ramp to volume : Missing critical time-to-market
windows
The solution to these problems requires a tight
interaction between the test experts, silicon technology
experts and ATE experts
