SUPREM Simulation

1. SUPREM Simulation ECE/ChE 4752: Microelectronics Processing Laboratory Gary S. May March 18, 2004

2. Outline • Introduction • Diffusion Simulation • Oxidation Simulation • Ion Implant Simulation

3. SUPREM • Except for a few simple cases, complications may arise in the calculation of diffusion and ion implantation profiles, and oxidation rates • Numerical methods have been developed to perform these computations in 1, 2, or 3 dimensions • Numerical simulations can be used optimize process recipes and test process sensitivity without costly and time-consuming experiments • One simulator: SUPREM (“Stanford University PRocess Engineering Module”) • Silvaco software version of SUPREM is called SSUPREM3 (1-D) or SSUPREM4 (2-D)

4. Caution • SUPREM is not infallible (although it’s pretty good), since its accuracy depends on the quality of models, parameters, and numerical techniques it employs. • SUPREM results should be verified experimentally at least once to ensure accuracy.

5. SUPREM Input Deck • Title card • Comment repeated on each page of the output • Comments • Initialization statement • Sets substrate type, orientation, and doping • Sets thickness of region to be simulated and establishes a grid • Materials statements • Process statements • Output statements

6. Outline • Introduction • Diffusion Simulation • Oxidation Simulation • Ion Implant Simulation

7. Flux • All diffusion simulators based on 3 basic equations • Flux: • where: Zi = charge state of the impurity • mi = mobility of the impurity • x = electric field

8. Continuity where: Gi = recombination rate of the impurity

9. Poisson’s Equation where: • e = dielectric constant • n = electron concentration • p = hole concentration • ND = ionized donor concentration • NA = ionized acceptor concentration

10. Solution • These 3 equations are solved simultaneously over a user defined 1-D grid • Diffusivity is calculated using: where the values of D0 and Ea are included in a look-up table for B, Sb, As in Si • Empirical models are added to account for non-standard diffusion (i.e., oxidation-enhanced, oxidation-retarded, or field-aided)

11. Example go ssuprem3 Title Pre-deposition of Boron Comment Initialize the silicon substrate Initialize <100>Silicon Phosphor Concentration=1e16 Comment Diffuse boron Diffusion Time=15 Temperature=850 Boron Solidsol Print Layers Concentration Phosphorus Boron Net TonyPlot -ttitle “Boron Predep” Structure outfile=predep.str Stop End example

12. Pre-Deposition Example

13. Outline • Introduction • Diffusion Simulation • Oxidation Simulation • Ion Implant Simulation

14. Oxidation • SUPREM can also be used to simulate oxidation using the Deal/Grove model • SUPREM uses Arrhenius functions to describe the linear and parabolic rate coefficients for wet and dry oxidation • Oxidation processes are accessed using the same command as diffusion processes: DIFFUSION • For oxidation, parameters DRYO2 or WETO2 are added • EXAMPLE: Diffusion Time=30 Temperature=1000 DryO2

15. Outline • Introduction • Diffusion Simulation • Oxidation Simulation • Ion Implant Simulation

16. Ion Implantation • SUPREM can calculate ion implant profiles • Simulated impurities can be implanted, activated, and diffused • SUPREM contains data for the implant parameters (Rp and sp) for most dopants; for unusual materials, the user must provide this data • SUPREM can also handle implantation through multiple layers (i.e., through an oxide) • EXAMPLE: Implant Arsenic Energy=60 Dose=5e15