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

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

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

OTP Block Principle Layout of OTP Block 17 32 bit and 128 bit Version

- Reliable Programming Conditions - Programmable over whole Process Range - Lifetime Stability - High Programming Yield - Process Control - Infield Programming Option 18 copyright © 2005 austriamicrosystems AG Conclusion