Batch-Mode UTMOST Operation

 

Introduction

The new release of UTMOST (version 10.10) will feature a batch-mode working environment in addition to the regular, and more interactive, UTMOST options. This batch-mode capability is essentially command line driven and was added for two main reasons. Firstly, batch-mode UTMOST will allow the UTMOST user to speed up and automate the parameter extraction process in situations where an adequate extraction strategy has already been defined using the regular UTMOST Graphical User Interface (GUI). The user interaction is effectively eliminated, and relatively time-consuming parameter extraction procedures can be effected without the user having to monitor or oversee the extraction process. Batch-mode UTMOST does not currently perform the data measurement tasks. Secondly, batch-mode UTMOST commands are the means by which UTMOST parameter extractions can be incorporated into a Virtual Wafer Fab (VWF) experiment. In these situations the user wants to extract SPICE model parameters from characteristics created as a result of process and device simulations. This article will introduce the new batch-mode feature and demonstrate its usage with three examples.

 

The Batch-Mode Working Environment

In the new release of VYPER (version 1.4) the user is offered the choice of activating batch-mode or more interactive UTMOST executables. The interactive options are basically similar to UTMOST as it appeared in previous releases. If the batch-mode option for the MOSFET module is selected a window similar to that shown in Figure 1 will appear. The user can activate the batch-mode executable and enter commands one by one, storing all of the commands in an ASCII Command file at the end of the session. Alternatively, the user may already have a pre-existing Command file containing all required batch-mode commands. This file can be loaded and run automatically. All commands are editable once they are loaded so that changes can be made even after the commands have been loaded. Run-time messages, including notification of warnings and errors, will appear in the Protocol section of the screen.

 

Figure 1. The Batch-mode UTMOST window.

 

 

There is an extensive library of batch-mode command options available to the user. Commands to load an UTMOST setup file and to load measurement log files are mandatory. Most of the UTMOST settings and selections will be automatically loaded once the UTMOST setup file, stored by

the user during an inter active session, is loaded. This effectively cuts down on the number and variety of batch-mode commands necessary. There are batch-mode UTMOST commands to perform simulations, to perform fitting algorithms, to perform parameter optimization strategies, to manipulate model parameters, to select/deselect UTMOST routines, to select/deselect devices for any UTMOST routine, to select/deselect parameters for optimization, to select wafer die numbers, to load setup and data log files, to create postscript plots, to load/store SPICE libraries, to store SPAYN databases etc. System level commands are also accessible from within the batch-mode environment.

In the following sections of this article three UTMOST batch-mode examples will be described. These examples serve to demonstrate the usefulness of the UTMOST batch-mode option. Any lines in a batch-mode command file beginning with the "#" character will be treated as comments. Any lines in a batch-mode command file beginning with the "!" character will be treated as system-level commands.

 

Batch-Mode Example 1

The first batch-mode command file example is shown in Figure 2. The purpose of this example is to extract a scalable BSIM3 model parameter set from a measured UTMOST data log file, and store the resultant parameter set in a SPICE library file. The example proceeds as follows:

  • The working directory is defined and an UTMOST setup file is loaded. This setup file was defined and stored using UTMOST operating in the regular interactive mode. The default model in this setup file is BSIM3 and the setup file also contains the user-defined local optimization strategies which were developed for the devices under analysis. These local optimization strategies were associated with the ALL_DC1, ALL_DC2, and ALL_DC3 UTMOST routines.
  • Certain BSIM3 model parameters, namely TOX and XJ, are initialized prior to any parameter extraction or parameter optimization.
  • The measurement log file is loaded. This file was created and stored using UTMOST (interactive mode). Measurements were only taken for the BSIM3 routine. However, the general purpose ALL_DC routines can automatically access data measured by the BSIM3 routine.
  • Devices are selected for the BSIM3, ALL_DC1, ALL_DC2, ALL_DC3, and ALL_DC4 routines. By default, all devices for which BSIM3 data exists in the log file, will be selected for these routines.
  • The BSIM3 fitting algorithm is performed. Local optimization strategies associated with the ALL_DC1, ALL_DC2, and ALL_DC3 routines are then performed in order to refine the extracted model parameter set.
  • The plot option is activated and postscript files are generated which contain measured and simulated I-V curves obtained using the ALL_DC1 and ALL_DC4 routines. In this case ALL_DC1 was configured in the setup file to display multi-geometry IDS-VGS curves while ALL_DC4 was configured to display IDS-VDS curves.
  • These postscript files are plotted and stored.
  • The extracted BSIM3 model parameters are stored in SPICE format in a library file.

 

Figure 2. Batch-mode commands for Example 1.

 

 

Batch-Mode Example 2

The second batch-mode command file example is shown in Figure 3. The purpose of this example is to extract scalable BSIM3 parameter sets from data which was measured on many wafer sites using UTMOST controlling an automatic prober. Only selected wafer sites are selected for parameter extraction whereas by default the extraction would be performed for all existing wafer sites. The resultant parameter sets are appended to a pre-existing SPAYN database so that they can be used for worst-case model development. The example proceeds as follows:

  • The working directory is defined and the UTMOST setup file is loaded.
  • The measurement log file is loaded.
  • The TOX, XJ, and RDS0 parameters are initialized.
  • Seven wafer sites are selected in turn for parameter extraction. BSIM3 model parameters are extracted using the BSIM3 fitting algorithm followed by some local optimization strategies. Parameter sets are appended to a SPAYN database file after each extraction.

 

 

Figure 3. Batch-mode commands for Example 2.

 

Batch-Mode Example 3

The final batch-mode command file example is shown in Figure 4. The purpose of this example is to extract a single-geometry BSIM3 model parameter set from data which was generated using the ATHENA and ATLAS process and device simulators. This data was stored by ATLAS using the Standard Structure Format (SSF) and transformed, in this example, to the UTMOST data log file format. The extracted SPICE model parameters are stored to a library file but they are also stored in SSF format so that they can be read back into a Virtual Wafer Fab (VWF) database. This example could be easily embedded in a VWF split lot experiment so that the relationships between SPICE model parameters and process parameters could be determined for a process under development. Worst-case model parameter sets for a process under development could also be generated using this example. The example proceeds as follows:

  • The working directory is defined and the UTMOST setup file is loaded.
  • The TOX parameter is initialized and the device polarity and dimensions are set up.
  • The ATLAS data files are read in and they are converted to UTMOST format.
  • Local optimizations are performed using the IDS-VGS and IDS-VGS data in order to extract a BSIM3 model.
  • Measured (i.e. from ATLAS) and simulated (i.e. from BSIM3) IDS-VDS data is stored in SSF data files so that plots can be viewed with Silvaco's TonyPlot graphical utility.
  • An UTMOST postscript file containing measured and simulated data is also generated and plotted.
  • The extracted BSIM3 parameters are stored in SSF and SPICE library format.

 

Figure 4. Batch-mode commands for Example 3.

 

Conclusions

A new and very powerful batch-mode UTMOST option is presented and described in this article. This capability will be invaluable to UTMOST users who want to increase their model generation throughput because it speeds up and automates that parameter extraction process. This feature will also make it easier to generate the statistical model data bases needed for worst-case and statistical analysis tools like SPAYN. The UTMOST batch-mode option is also the means by which SPICE models can be extracted from experiments involving process and device simulation. UTMOST batch-mode commands can be included into a VWF experiment so that so-called process "corner" models can be identified. These models can be used to examine the sensitively of circuit performance to process fluctuations for a process which is in the early stages of development.