Chalmers University of Technology

MNT 2016; Lecture 3

Numerical Simulation of Semiconductor Processes and Devices

Hans HjelmgrenMicrowave Electronics Laboratory

Department of Microtechnology and Nanoscience

or simply TCAD

Chalmers University of Technology

MNT 2016; Lecture 3

L3: Technology CAD

1. What is TCAD?2. Calibration3. Synopsys Sentaurus TCAD4. References

Chalmers University of Technology

MNT 2016; Lecture 3

1. What is TCAD?

Processsimulation

Devicesimulation

Compact model

extraction

CircuitSimulation

TCAD

Chalmers University of Technology

MNT 2016; Lecture 3

According to Wikipedia“Technology CAD (or Technology Computer Aided Design, or TCAD) is a branch of electronic design automation that models semiconductor fabricationand semiconductor device operation. The modeling of the fabrication is termed Process TCAD, while the modeling of the device operation is termed Device TCAD. Included are the modelling of process steps (such as diffusion and ion implantation), and modelling of the behavior of the electrical devices based on fundamental physics, such as the doping profiles of the devices. TCAD may also include the creation of compact models (such as the well known SPICEtransistor models), which try to capture the electrical behavior of such devices but do not generally derive them from the underlying physics. (However, the SPICE simulator itself is usually considered as part of ECAD rather than TCAD.)”

Chalmers University of Technology

MNT 2016; Lecture 3

(Almost) Everything that can be measured can also be simulated, but it is not always

the best choice since,• simulations can be extremely time-consuming,• there may be simpler alternatives, e.g. analytical

expressions, simple measurements,...• the uncertainty in the obtained results might be too

large,• or no measurements to check the simulated results

against.

Chalmers University of Technology

MNT 2016; Lecture 3

2. Calibration

C. V. Mouli, J. Vac. Sci: Technol. B, p. 354, 2000.

Check Software Supplied Models!

Chalmers University of Technology

MNT 2016; Lecture 3

Calibration is difficult and time-consuming

• Requires knowledge of the exact process flow, device layout, and how the measurements were done.

• A very accurate calibration is essential for some purposes, e.g. predicting simulations and positioning of the process window.

• It is of less importance for other purposes, e.g. failure analysis, education, prestudies, improved understanding.

• Constant recalibration due to process modifications, new measurements, and new simulation software.

• Many coefficients in TCAD simulators make it difficult to determine a unique solution. “Poorly understood parameters become candidates for tuning.”

Chalmers University of Technology

MNT 2016; Lecture 3

Always make a test with double grid

”If you haven’t tested the sensitivity of your simulations

to the grid, you haven’t simulated anything at all”

Chalmers University of Technology

MNT 2016; Lecture 3

Measurements are not always correct

• SIMS and SRP should be performed and interpreted accurately. – A too fast SIMS sputtering resulted in 700 Å instead of 1200 Å

emitter depth.• Exact process flow.

– Simulated oxide was 400 Å while measured was 700 Å. CV-measurements indicated 400 Å. The test wafers had not follow exactly the same flow as the ordinary wafers.

• The spreading in measured data can be significant, especially at high frequencies due to parasitics, wrong method (measuring something else), process variations, etc.

Chalmers University of Technology

MNT 2016; Lecture 3

Examples to start from

3. Synopsys Sentaurus TCAD

Chalmers University of Technology

MNT 2016; Lecture 3

Chalmers University of Technology

MNT 2016; Lecture 3

4. References1. B. A. Biegel, ”Accuracy counts in modeling TCAD’s future”, IEEE

Potentials, p. 19, 2000.2. M. Duane, ”TCAD needs and applications from a user’s perspective”, IEEE

Trans. Electron, p. 976, 1999.3. J. Mar, ”The application of TCAD in Industry”, SISPAD, p. 139, 1996.4. C. V. Mouli, ”Models and methods: Effective use of technology-computed

aided design in the industry”, J. Vac. Sci: Technol. B, p. 354, 2000.5. S. K. Saha, ”Managing technology CAD for competitive advantage: An

efficient approach for integrated fabrication technology development”, IEEE Trans. Engineering Management, p. 221, 1999.

6. M. E. Law, “Process modeling for future technologies”, IBM J. Res. & Dev., vol. 46, pp. 339-346, 2002.

7. I. Bork, V. Moroz, L. Bomholt, and D. Pramanik, “Trends, demands and challenges in TCAD”, Mat. Sci. Eng. B, vol. 124-125, pp. 81-85, 1005.