Compact Model for ESD Protection in Nanoelectronics

1. Cracow Sep. 13-17, 2004 Nano and Giga Challenges inMicroelectronicsSymposium and Summer SchoolResearch and Development Opportunities Afternoon 11: Nanotechnology Tool Kit (3:00pm - 6:00pm), Wed., Sep. 15th, 2004 A Compact Model for Electrostatic Discharge Protection Nanoelecronics Simulation Jam-Wem Lee and Yiming Li Department of Computational Nanoelectronics, National Nano Device Laboratories Microelectronics & Information Systems Research Center, National Chaio Tung University 1001 Ta-Hsueh Rd., Hsinchu 300, Taiwan

2. Introduction • In nanoelectronics, whole chip ESD protection design is important for obtaining robust circuits; especially for the gigascale very large scale integration (VLSI) circuits • Conventional design methods basically rely on the testkeys verifications and encounter some unexpected results due to the ESD events are instantaneously transient behaviors • Such conventional design method does prolong the time schedule and trouble the circuit development cycle including ESD issues • Any efficient computer aided design (CAD) tools are necessary for researchers and engineers to design whole chip ESD protection circuit

3. Introduction A Design flow using conventional approach (the left figure), and the right one is ESD model which includes SPICE-added design methodology

4. Introduction • However, currently existing ESD models are based on the bipolar junction transistor (BJT) model, such as the Ebers-Moll, the VBIC, the MEXTRAM, the HICUM, and the Gummel-Poon models • These models exploring the pre-breakdown phenomena work under the normally operation regions, but they can not model post-breakdown behaviors • Simulations based on the conventional BJT-based ESD models for the pre-breakdown behavior is not enough for advanced ESD modeling • In this paper, a parasitic model specifying the device physics of the ESD operation is proposed

5. Introduction • By considering the geometry effect in the formulation of snapback characteristics, our model can be directly incorporated into electronic circuit simulation for whole chip ESD protection circuit design • Using an intelligent computational algorithm, the proposed model and corresponding parameters are calibrated and optimized with the measured data • With the developed ESD model, we can investigate robust enhancement problems and perform a SPICE-based whole chip ESD protection circuit design in nanoelectronics

6. ESD Model Formulation • We can construct the snapback current-voltage (IV) by using a current controlled voltage source (the breakdown voltage of parasitic BJT) VBCE, the series resistance caused by Rd and the external resistance contributed from measurement instrumentsRx. The IV formula is: • The current controlled voltage source VBCE is expressed as • where B is solved from the following equation:

7. ESD Model Formulation Equivalent circuit models for the conventional (right figure) and our (left one) proposed models

8. ESD Model Formulation • where R and C can be solved from the following two auxiliary equations • There are only six parameters Rd, n, Zs, re, Is and appearing in the model to be optimized. In the model, Rxis 50 ohm and Vt is 0.0259 V • The optimization of parameters is performed with the intelligent computational algorithm • In order to perform ESD robustness simulation on the whole chip design, ESD model which can satisfy different scale devices is needed

9. ESD Model Formulation • The parasitic BJT works under the two different region, they are normally operation (low current) and ESD protection (high current) regions. Those two regions reflect different device physics

10. ESD Model Formulation • Shown in the following, we can determine the geometry ratio as GR = Max{DW,DL} / Min{DW,DL} • The geometry ratio means that, when GR is equal to 1 that protection device has the highest efficiency • Contrary, a large ratio leads to the lower protection efficiency. Accordingly, the protection efficiency is proportional to (GR)ngr;where ngr is a number between -1 and 0 The non-uniform turn-on effect in the multi-fingers devices

11. ESD Model Formulation • Besides the geometry ratio, the channel length of the protection device should be also taken into considerations when constructing the multi-dimensional device model • The channel length will strongly affect the current gain b of the parasitic BJT • Taking b gain into consideration, the turn-on efficiency is Rd= (L)nl • Combining the previous two geometry related expression, the turn on resistance Rd is written as Rd = Rd0 * (GR)ngr* (L)nl

12. Results and Discussion • In this work, a 130 nm CMOS process with dual gate oxides is used in preparing the test devices • For the ESD damages are always occurred at the input/output (I/O) devices, therefore, the thick oxide devices are usually used in designing the ESD protection circuit • In order to obtain a better match with the realistic situation of the ESD protection circuit design, the I/O devices with a gate-oxide thickness of 7.0 nm and the gate length of 440 nm is firstly prepared in this experiment • Transmission line pulse (TLP) system is used in measuring the snapback IV characteristics and verifying the ESD robustness simultaneously

13. Results and Discussion The transmission line pulse system used in this experiment

14. Results and Discussion The optimized parameter for our model

15. Results and Discussion Comparison of the measured (dish line) and the simulated (solid line) results

16. Results and Discussion Optimization of the geometry ratio effect (ngr = 0.84)

17. Results and Discussion Optimization of the channel length effect (nl = -0.24)

18. Conclusions • An ESD equivalent circuit model for deep-submicron and nanoscale semiconductor device simulation has been developed • This model accounts for the snapback characteristics and can be directly implemented into nanoelectronic circuit simulation • Using the measured data, physical properties and geometry effects have been modeled and optimized in the proposed model • Simulation and comparison have demonstrated good accuracy of the proposed model • Mathematically, this ESD model is continuous and can be incorporated into SPICE-compatible circuit simulators to perform ESD simulation in nanoelectronics.

19. Thank you for your attentions!