3D Device Simulation Using ATLAS/DEVICE3D

New developments in ATLAS have led to the introduction of three new 3D products under ATLAS: DEVICE3D, INTERCONNECT3D and THERMAL3D. These products replace the standalone THUNDER program. The new DEVICE3D product within ATLAS extends the capabilities of S-PISCES in modeling general non-planar 3D structures. The structural definition, models, material parameters and solution techniques are extensions to the 2D SPISCES syntax. DEVICE3D is integrated into the VWF allowing RSM's of 3D effects to be generated. An example of this is shown in Figure 1.

A completely new graphics program, TONYPLOT3D, is also being released. This program includes standard graphics libraries to take full advantage of graphics accelerators.

 

3D Structure Generation

DEVICE3D supports structures defined on 3D prismatic meshes. Structures may have arbitrary geometries in two dimensions and consist of multiple slices in the third dimension. There are two methods for creating a 3D structure that can be used with DEVICE3D. One is through the command syntax of ATLAS and the other through an interface to the structure definition and meshing program, DEVEDIT3D. DEVEDIT3D provides the ability to read in 2D structures from ATHENA and extend them non-uniformly to create 3D structures for DEVICE3D.

 

Narrow Width Effects in MOSFETs

DEVICE3D can simulate narrow width effects using structures defined in DEVEDIT3D. Potentially, a 2D cross section of field oxide bird's beak from ATHENA can be used as the input to DEVEDIT3D to provide accurate doping and geometry. Variation in the width of the device and doping under the field oxide can be defined as experimental variables in VWF. The combination of DEVEDIT3D and DEVICE3D running under the VWF is able to produce results for threshold voltage and other device parameters. Figure 1 illustrates the threshold voltage increase with decreasing device width and increasing field doping.

 

Figure 1. NMOS threshold voltage as a junction of device width and field implant.

 

Single Event Upset

A model for electron/hole generation by ionizing radiation is included in DEVICE3D. Users can specify entry and exit coordinates for an ion track through the device. The generation rate can vary with length along the track, distance from the track and time. Figure 2 shows the electron concentration after an angled alpha particle strike through a pn junction. DEVICE3D is able to simulate the transient current generated from the particle strike.

 

Figure 2. Contours of electron concentration generated by an angled alpha particle strike.

 

Flash EEPROM Programming

DEVICE3D includes features necessary for simulation of Flash EEPROM programming and erasing. Both hot electron injection and Fowler Nordheim tunneling models are available in DEVICE3D. Charge boundary conditions for floating gates can also be defined. A band-to-band tunneling model is included for use in erasing simulations. Figure 3 shows the electron current density in a 3D EEPROM device during programming.

 

Figure 3. Current density at the silicon surface of a 3D EEPROM structure.