8.27 Sspd_chapter 6_part 8_caliberating athena for typical mosfet  (Page 21/4)

SSPD_Chapter 6_Part 8_Caliberating ATHENA for typical MOSFET FLOW

7.8 Caliberating ATHENA for typical MOSFET FLOW.

This section of the manual provides information on which parameters should be tuned in the input file to provide predictive simulations using a typical MOSFET process flow. We assume you are now familiar with the mechanics of making an input file and using the correct methods and models (see Section 7.7.3:“Choosing Models In SSUPREM4”). For example, incorrect use of the METHOD statement will invalidate the rest of the following section.

Calibrating an ATHENA input file for a typical MOS process flow involves using the device simulator, ATLAS, since electrical measurements from the MOSFETs in question often represents the majority of the physical data available for calibration. This can be thought as a paradox since ATLAS would also have to be correctly calibrated. The reason that this doesn’t present a problem is discussed below.

An important point to remember when using Technology Computer Aided Design (TCAD) is that the most critical task is to accurately model the process flow.

Note: For accurate MOSFET simulation, you should invest 90%of the time in achieving an accurate process simulation, while only investing 10%of the time in fine-tuning the device simulation.

The reason for this, especially for silicon technologies, is that the device physics, in general, is understood. For silicon, not only is the physics well understood, it is also well characterized, so most of the default values in ATLAS will be correct. Therefore, the calibration of an ATHENA process file does not involve the calibration of well known quantities such as diffusion coefficients. Instead, the calibration involves variables that are process and production line dependent. For example, the damage caused by an implant cannot be determined exactly, since it is dose rate dependent and can be influenced by beam heating of the substrate, which is dependent on the carousel rotation speed and the efficiency of the cooling system.

Note: If the process has been correctly modeled, the device simulation will also be accurate if appropriate models have been chosen.

If a simulated device exhibits electrical characteristics that are totally inaccurate, you may have done something wrong in the process simulation. Do not make the mistake of changing well known default values in the simulators to make a curve fit one set of results because this will lead to poor predictive behavior. Try and find the cause of a discrepancy.

7.8.1: Input Information

It may seem obvious but must be emphasized that an accurate process flow is vital for simulation accuracy, especially for Rapid Thermal Anneals (see Section 7.7.8:“Simulating Rapid Thermal Anneals (RTA) Notes” for details). Other process information required is an accurate cross-section of the oxide spacer. Modeling the spacer profile accurately ensures the lateral damage distribution due to the subsequent source-drain implants is correctly modeled.