UTMOST Provides Unique Characterization Capabilities

UTMOST (Universal Transistor MOdeling SofTware) supports the acquisition of semiconductor device electrical data from a wide range of measurement equipment, and the generation of model parameter sets from measured or simulated data, via parameter extraction and/or optimization methodologies. UTMOST extracts DC, AC, and transient device parameters for a very wide range of commercial and proprietary models for MOS, BJT, JFET, MESFET and diode devices. UTMOST will soon enter its tenth year of continuous development, and is in use at several hundred installations worldwide. The present version, UTMOST III, was introduced in 1992 and runs under the MOTIF Graphical User Interface.

 

Rich In Features

The development and customization that has taken place through the years means that UTMOST supplies an impressive array of features. Many of these are unavailable in other commercial parameter extraction software packages. Some of the capabilities and features of UTMOST are summarized below:

  • Support for a comprehensive range of measurement equipment (over 130 instrument drivers have been implemented) allowing the use of standard or customized parametric test systems
  • Step-and-repeat wafer probing capability with a very wide range of supported commercial probers
  • Complete graphical wafer and die description
  • An HP 4145 emulator with which measured data can be interactively analyzed
  • Extraction of device z, y, h, and s parameters
  • The use of macro modeling, employing SmartSpice and Skematix (schematic entry), to extract parameters describing complex devices for which no analytical model exists
  • Links to SmartSpice and numerous other commercial and in-house circuit simulators enables parameter extraction to be performed for device models that are not intrinsically supported by UTMOST itself. The supported commercial simulators include ELDO, HSPICE, PSPICE, SABER, and SPECTRE

The ability to use data from physically-based simulators such as ATHENA and ATLAS. (During 1994 UTMOST will also be available as a component of Silvaco's Virtual Wafer Fab)

  • Multi-target and multi-geometry optimization to ensure that models are valid over a wide range of biases and/or device geometries
  • The input and output of model parameters in a Spice library format thus simplifying the control, documentation and storage of model parameter sets
  • Over 300 pre-defined extraction routines
  • Graphical parameter sensitivity information and graphical error history during parameter optimization allow critical parameters to be identified
  • The ability to easily convert parameters from one device model to a parameter set valid for a completely different model, without having to re-measure the device characteristics
  • Log files organized so that the data acquisition and parameter extraction tasks can be separated, thereby decreasing wafer test time
  • The output of parameters in result files in a customizable ASCII format
  • A user-friendly file management system
  • Free training and assistance with customization
  • Availability on many platforms including Sun Sparc (SunOS and Solaris O/S), HP 300, 400, and 700 series (HP-UX 7.0, 8.0, and 9.0 O/S), DEC (ULTRIX and ALPHA), and IBM 6000

 

Enhanced Quality

A new release of UTMOST will be made in January 1994. This release is significant in several respects. Overall product quality has been enhanced, and new features have been added.

Silvaco has traditionally offered free customization of UTMOST. This service has been very popular, but it has also made version control, support, documentation and QA more complicated. Starting in January 1994 new versions of UTMOST will be released only once every six months. This will enable Silvaco to deliver a very stable, high quality product.

Comprehensive documentation, including extensive descriptions of parameter extraction techniques, is now provided in a set of three new UTMOST manuals. The information in the manuals is also available as on-line help. Manual updates will be circulated with every six-monthly release.

Diagnostics have been improved. In particular, a record of all error messages generated during a parameter extraction session is stored in a single file to aid in the identification of set-up problems.

 

BSIM3 Support Introduced

The emergence of the BSIM3 circuit model for MOSFETs has attracted a great deal of attention in the semiconductor industry. BSIM3 has some crucial attributes that overcome the limitations of previous models. Earlier models suffered from some combination of the following defects: they were unable to model MOSFET device characteristics accurately; they contained too many parameters, which made the extraction and management of model parameter sets over-complicated; they contained empirical parameters that precluded geometry scaling; and links between the statistical variations of the model parameters and process variations were difficult to determine.

The BSIM3 model is accurate down to sub-micron channel lengths, and uses a parameter set of manageable size that is related, as much as possible, to IC process variables. The January release of UTMOST contains the BSIM3 model equations and allows UTMOST users to extract complete sets of BSIM3 parameters using optimization-based parameter extraction procedures. This makes it possible to investigate BSIM3 capabilities and to extract preliminary model parameter sets (See Figure 1).

 

Figure 1. Measured characteristcs from an N-channel 50/1.2
device with modeled BSIM3 characteristcs extracted.

 

Improved Rubberband Feature

The Rubberband feature in UTMOST is extremely popular. It enables users to examine interactively the effects of changes in a model parameter, or group of parameters, on selected device characteristics. Users can extract complete parameter sets using this facility alone. Rubberband gives valuable insight, with the aid of graphics, into the relative importance of any component parameter in modeling selected device characteristics. It can help a user to define a parameter optimization strategy or it can provide insight into the behavior of the particular device model in use (See Figures 2 and 3). The Rubberband feature has been enhanced significantly for the January 1994 release. In particular, an advanced new equation solver has improved the speed of operation.

 

Figure 2. Rubberhand control screen.

 

Figure 3. Parameter extraction for an
NPN BJT using Rubberband facility.

 

Conclusions

UTMOST has always been a very versatile product that provides unique capabilities for device characterization. The enhancements in the January 1994 release make UTMOST even more powerful.