1. PolyFuse OTP Cell
A CMOS compatible PolyFuse element used in an One Time Programmable circuit
Johannes Fellner
austriamicrosystems AG

2. Purpose Design an OTP Element in a Standard 0.35um CMOS Process
PolyFuse element defined
Programming within process specification
High lifetime & reliability
Implementation of the OTP Element into an IP-Block
Infield programming option
High programming yield

3. Outlook Introduction into PolyFuse OTP Programming Characteristics
Cross Sections
Reliability and Yield
WAT Implementation
Design Issues for IP Block
Summary

4. Introduction PolyFuse used as an OTP base element
Poly Silicon with Tungsten Silizide
Low ohmic standard resistance (<100W)
High ohmic after programming (>10kW)

5. PolyFuse Element Programming Features
Programming in standard CMOS process
Current programming
Infield programming possible

6. Programming Characteristic
Iprog mA
Vprog V
tprog 0µs 1µs µs µs
Ilinear: Linear resistor characteristics
Iheat: Temp. is raising
Imelt: Tungsten Silicide is melting
Imax: Maximum current of minimum resistance
Imin: Local current min.
Iosc: Oscillation because of break
Imax
Imelt
Imin
Ialloy
Iheat
Ilinear
Iosc
Ialloy: No autonomous current pinch off

7. Typical Current Programmed Poly Fuse
Cross Section
Typical Current Programmed Poly Fuse
Active PolyFuse region no longer has Tungsten included
High ohmic stable alloy
Local break of a few nm
Minimal lifetime drift of the resistance value
Substrate
Field Oxide
Poly Silicon
Tungsten Silicide
Tungsten Plug
approx. 40nm

8. Low Current Programmed Poly Fuse
Cross Section
Low Current Programmed Poly Fuse
Inhomogenious temperature gradient during programming
Low ohmic resistor
Lifetime drift to higher resistor values
Tungsten Plug
Field Oxide
Tungsten Plug
Tungsten Silicide
Tungsten Silicide
Poly Silicon
Poly Silicon
Field Oxide
Substrate
Substrate

9. Low Current Programmed Poly Fuse
Cross Section
Low Current Programmed Poly Fuse
High energy is forcing the Tungsten seperation
Break before Tungsten completely removed
Relatively high ohmic resistor
Lifetime drift to lower resistor values possible
Tungsten Plug
Field Oxide
Tungsten Plug
Tungsten
HALO
Tungsten Silicide
Tungsten Silicide
Poly Silicon
Poly Silicon
Tungsten
Field Oxide
Substrate
Substrate

10. Reliability Investigations
Lifetime Drift over Time
2000h °C
HTOL Test JESD22-108
Lifetime Drift Investigated for
typical current programmed PolyFuses
low current programmed PolyFuses
high current programmed PolyFuses

11. Yield Analysis Testchip with Geometrical Variations
Variation of size of programming transistor
Variation of PolyFuse length and width
Design Of Experiment (DOE) Run
With of Stack: Tungsten Silicide - Poly Silicon
Tungsten Silicide thickness variation
Poly Silicon thickness variation
Analysis
Programming within specified limits
Variable temperature and supply specifications

12. Process Control WAT Structure Measurements PolyFuse Element
Burning NMOS Transistor
Measurements
Resistor of unprogrammed PolyFuse
Resistor of programmed PolyFuse
Current of Burning Transistor

13. Design Issues IP Blocks with PolyFuses Designed
32 bit
128bit
Optimized Programming Path
PolyFuse
Related programming transistor
Special Test Function
to guarantee lifetime stability
for infield programming

14. Design Requirement Requirements For Lifetime Stability
A programmed PolyFuse resistance must be larger than 10kW after programming
The resistance of a programmed PolyFuse is checked at 1kW during lifetime operation
This margin ensures proper operation of programmed PolyFuses over lifetime
Requirement for Infield Programming
Testmode to measure the unprogrammed PolyFuse resistance (<100W)

15. Base Cell Principle Schematic PolyFuse Element Programming Transistor
Current Mirror
Testmodes

16. Base Cell Principle Layout PROM Storage RAM Access LOADing Mode
PROGramming Mode
Optional Parallel Out

17. OTP Block Principle Layout of OTP Block 32bit and 128bit Version
32bit Parallel Out
Address Decoder
Autoloader at Startup
Combination up to 2kbit

18. Conclusion Reliable Programming Conditions
Programmable over whole Process Range
Lifetime Stability
High Programming Yield
Process Control
Infield Programming Option