HINTS & TIPS

Q: What are the options for generating 3D structures for ATLAS device simulation?

 

A: Currently there are three options for generating 3D device structures.In all cases the prismatic meshing of ATLAS/DEVICE3D permits arbitrary shaped device regions in 2 dimensions (typically X and Y) and rectangular regions in the other dimension (typically Z).

  • definition though the ATLAS syntax.
    This limits the user to defining box shaped regions. Region definition is though statements such as:
		region num=1 silicon x.min=0  \ 
		x.max=1 y.min=0 y.max=1 z.min=0 
		\ z.max=1 
Mesh generation is handled though the Z.MESH statement which is analogous to the X.MESH and Y.MESH statement used in 2D ATLAS simulations. Electrodes and doping can be defined using the same syntax as 2D ATLAS but with Z.MIN and Z.MAX parameters to control the Z extent. Doping profiles can be read from the formats supported in 2D ATLAS: ssuprem3,athena,ascii.
 
  • use DEVEDIT3D to create a 3D mesh structure
    DEVEDIT3D is a 3D structure generation and meshing tool used to generate the mesh, regions, electrodes and doping used in ATLAS/DEVICE3D. It allows users to draw regions by hand in 2D and project them into the third direction. DEVEDIT3D contains all the sophisticated meshing options available to 2D DEVEDIT. These include: mesh constraints by region, mesh constraints by a user defined box, refinement on doping and other quantities, mouse controlled refine and unrefine boxes. DEVEDIT3D has both interactive and batch mode operation. This is the recommended approach for 3D power device simulation.
  • use ATHENA and DEVEDIT3D to extend a 2D process simulation to 3D
    A 2D process simulation from ATHENA can be extruded to form a 3D structure using DEVEDIT3D. In this mode DEVEDIT3D can be used to add extra regions and doping if required. This mode us commonly used for modeling MOS width effects in 3D (see Figure 1). An ATHENA simulation of the isolation bird's beak and field stop implant is performed. The 2D structure is loaded into DEVEDIT3D and extended in Z direction. The polysilicon gate is truncated in Z and aluminum source/drain contacts are added. The source/drain doping profiles can be read from analytical functions or other process simulation results. A worked example named mos2ex04.in is supplied with the Fall 96 release CDROM.

Figure 1. 3D device simulation of MOS width effect
can be performed on structures created ATHENA.

 

For devices with non-rectangular regions in the XZ plane such as pillar MOSFETs or cylindrically designed power structures DEVEDIT3D can also be used by drawing in the XZ plane and projecting into the Y direction.

The future release of Silvaco's 3D process/device simulator ODIN will provide a fourth option for 3D simulation problems. ODIN is based on tetrahedral mesh elements and will overcome the mesh restrictions described above.