Poly Fuse OTP Cell A CMOS compatible Poly
Poly. Fuse OTP Cell A CMOS compatible Poly. Fuse element used in an One Time Programmable circuit Johannes Fellner austriamicrosystems AG 08. 04. 2005 A leap ahead in mixed signal
Purpose Design an OTP Element in a Standard 0. 35 um CMOS Process Poly. Fuse element defined Programming within process specification High lifetime & reliability Implementation of the OTP Element into an IP-Block - 2 Infield programming option High programming yield copyright © 2005 austriamicrosystems AG -
Outlook 3 - Introduction into Poly. Fuse OTP - Programming Characteristics Cross Sections WAT Implementation Design Issues for IP Block Summary copyright © 2005 austriamicrosystems AG Reliability and Yield
Introduction Poly. Fuse used as an OTP base element Poly Silicon with Tungsten Silizide Low ohmic standard resistance (<100 W) High ohmic after programming (>10 k. W) copyright © 2005 austriamicrosystems AG - 4
Poly. Fuse Element Programming Features - Programming in standard - Current programming Infield programming possible 5 copyright © 2005 austriamicrosystems AG CMOS process
Programming Characteristic Imax Imelt Ilinear 6 tprog 0µs Iheat: Temp. is raising Imin Ialloy Iheat Vprog V Ilinear: Linear resistor characteristics Imelt: Tungsten Silicide is melting Iosc 1µs 2µs 3µs Imax: Maximum current of minimum resistance Imin: Local current min. Iosc: Oscillation because of Ialloybreak : No autonomous current pinch off copyright © 2005 austriamicrosystems AG Iprog m. A
Cross Section Typical Current Programmed Poly Fuse - Active Poly. Fuse region no longer has Tungsten included - High ohmic stable alloy Minimal lifetime drift of the resistance value Field Oxide Tungsten Plug Tungsten Silicide Poly Silicon approx. 40 nm Field Oxide Substrate 7 Local break of a few nm copyright © 2005 austriamicrosystems AG -
Cross Section Low Current Programmed Poly Fuse - Inhomogenious temperature gradient during programming Tungsten Plug Low ohmic resistor Lifetime drift to higher resistor values Field Oxide Tungsten Silicide Poly Silicon Field Oxide Substrate 8 Tungsten Plug copyright © 2005 austriamicrosystems AG -
Cross Section Low Current Programmed Poly Fuse - High energy is forcing the Tungsten seperation - Relatively high ohmic resistor - Break before Tungsten completely removed - Lifetime drift to lower resistor values possible Tungsten Silicide Poly Silicon Tungsten HALO Tungsten Field Oxide Tungsten Silicide Poly Silicon Field Oxide Substrate 9 Tungsten Plug copyright © 2005 austriamicrosystems AG Tungsten Plug
Reliability Investigations Lifetime Drift over Time - 2000 h Burn. In@125 °C HTOL Test JESD 22 -108 - 10 typical current programmed Poly. Fuses low current programmed Poly. Fuses high current programmed Poly. Fuses copyright © 2005 austriamicrosystems AG Lifetime Drift Investigated for
Yield Analysis Testchip with Geometrical Variations - Variation of size of programming transistor Variation of Poly. Fuse length and width Design Of Experiment (DOE) Run With of Stack: Tungsten Silicide - Poly Silicon Tungsten Silicide thickness variation Poly Silicon thickness variation Analysis 11 Programming within specified limits Variable temperature and supply specifications copyright © 2005 austriamicrosystems AG -
Process Control WAT Structure - Poly. Fuse Element Burning NMOS Transistor Measurements 12 Resistor of unprogrammed Poly. Fuse Resistor of programmed Poly. Fuse Current of Burning Transistor copyright © 2005 austriamicrosystems AG -
Design Issues IP Blocks with Poly. Fuses Designed - 32 bit 128 bit Optimized Programming Path Poly. Fuse Related programming transistor Special Test Function 13 to guarantee lifetime stability for infield programming copyright © 2005 austriamicrosystems AG -
Design Requirement - A programmed Poly. Fuse resistance must be larger than 10 k. W after programming - The resistance of a programmed Poly. Fuse is checked at 1 k. W during lifetime operation - This margin ensures properation of programmed Poly. Fuses over lifetime Requirement for Infield Programming 14 Testmode to measure the unprogrammed Poly. Fuse resistance (<100 W) copyright © 2005 austriamicrosystems AG Requirements For Lifetime Stability
Base Cell Principle Schematic 15 Poly. Fuse Element Programming Transistor Current Mirror Testmodes copyright © 2005 austriamicrosystems AG -
Base Cell Principle Layout 16 PROM Storage RAM Access LOADing Mode PROGramming Mode Optional Parallel Out copyright © 2005 austriamicrosystems AG -
OTP Block Principle Layout of OTP Block 17 32 bit and 128 bit Version 32 bit Parallel Out Address Decoder Autoloader at Startup Combination up to 2 kbit copyright © 2005 austriamicrosystems AG -
- Reliable Programming Conditions - Programmable over whole Process Range - Lifetime Stability - High Programming Yield - Process Control - Infield Programming Option 18 copyright © 2005 austriamicrosystems AG Conclusion
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