Every software package contains a full set of examples suitable for that version and are installed with the software. If you see examples here that are not in your installation you should consider updating to a later version of the software. These examples can be used by beginners and advanced users for product evaluation, teaching purposes, and self-training.
Required Modules
Victory Process
- 2D Diffusion & Implantation
Victory Device
- 2D Simulator
- 2D Chemistry
In this example, we demonstrate the Positive Bias Temperature Stress simulation due to electron trapping by oxygen related trap, and the role of hydrogen passivation in In-Ga-Zn-O (IGZO) TFT device. In Victory Process part, we simulate the hydrogen diffusion in etch stopper process. The partial pressure during the etch stopper process affects the hydrogen concentration in the IGZO layer. In Victory Device, we simulate the electrochemical reaction formula for explaining the positive threshold voltage shift by electron trapping as well as hydrogen passivation forming OH- (Hydroxyl) bond.
The hydrogen atom is a donor in a-IGZO material when it forms to make a OH- (Hydroxyl) bond as well as it passivates the neutral precursor state (electron trap site: O (neutral)). This neutral precursor trap can be an electron trapping state or passivated by hydrogen atom. We simulated the hydrogen passivation reaction and electron trapping reaction using chemical ion reaction/transport model in Victory Device.
Victory Process / Process simulation and hydrogen diffusion
Bottom gate SiOx etch stopper a-IGZO structure formation using Victory Process:
-To simulate hydrogen diffusion process, we used material/interface statement to modify a default hydrogen diffusion coefficient in Victory Process.
-Hydrogen in ambient of an etch stopper deposition process injects into IGZO and diffuses during the annealing process. The hydrogen concentration in the IGZO depends on the partial pressure which determines the hydrogen concentration in the ambient of etch stopper deposition.
Victory Device / Ion Reaction and Transport Simulation
After the hydrogen diffusion process and structure formation, initial hydrogen concentration is imported from Victory Process using
DOPING f.doping= “
This C-interpreter function reads hydrogen profile from the process structure.
After reading hydrogen concentration, we define each ion’s charge state.
In this example, IGZO is the neutral precursor state which is an electron trap. It will decompose to negatively charged state (IGZO-) by electron trapping and neutral passivated state (IGZOH) by hydrogen passivation. The overall hydrogen passivation rate is affected by hydrogen concentration, reaction rate of passivation, and hydrogen diffusion.
SPECIES formula= “H ” charge=0 name= “H ”
SPECIES formula= “In:Ga:Zn:O ” charge=0 name= “IGZO ”
SPECIES formula= “In:Ga:Zn:O ” charge=-1 name= “IGZO- ”
SPECIES formula= “In:Ga:Zn:O:H ” charge=0 name= “IGZOH ”
In this example, we only consider interface traps using INTERFACE command. User can add bulk traps using DOPING statement.
INTERFACE s.i x.min=-12.0 x.max=12.0 y.min=-0.21 y.max=-0.19 species.name= “IGZO ” concentration=8e11
INTERFACE s.i x.min=-12.0 x.max=12.0 y.min=-0.21 y.max=-0.19 species.name= “IGZO- ” concentration=1e10
INTERFACE s.i x.min=-12.0 x.max=12.0 y.min=-0.21 y.max=-0.19 species.name= “IGZOH ” concentration=1e10
Total amount of neutral precursor trap concentration at the front interface is 8e11 /sqcm. This trap will decompose to passivated state (IGZOH) and electron trapping state (IGZO-) depending on the hydrogen concentration.
For drift-diffusion simulation of hydrogen atom during applied bias and temperature, we need to define the diffusion coefficient. Other ion species is immobile. In this example, we assumed the same diffusivity over all regions.
MATERIAL species.name= “H ” species.ea=0.35 species.af=1e3 species.hop=1e-6
Next, we define the chemical reaction formula using REACTION command.
REACTION formula= “IGZO + H <=> IGZOH ” forward.rate=2e-17 forward.ea=0 reverse.rate=1e-15 reverse.ea=1.5
REACTION formula= “IGZO + e- <=> IGZO- ” forward.rate=1e-10 forward.ea=0.83 reverse.rate=1e-15 reverse.ea=1.5
PROBE statement measures occupation probability of each ion species and concentration at the front interface during stress time.
PROBE x=0.0 y=-0.2 material=IGZO ft.species= “IGZO ”
PROBE x=0.0 y=-0.2 material=IGZO ft.species= “IGZO- ”
PROBE x=0.0 y=-0.2 material=IGZO ft.species= “IGZOH ”
PROBE x=0.0 y=-0.2 material=IGZO species.name= “IGZO ”
PROBE x=0.0 y=-0.2 material=IGZO species.name= “IGZO- ”
PROBE x=0.0 y=-0.2 material=IGZO species.name= “IGZOH ”
The simulation starts to get the initial threshold voltage (Vth). Then, PBTS simulation proceeds with stress voltage of “Vgs=+20V + initial Vth ” to maintain the constant stress voltage.
ASSIGN command in the input deck performs 3 loops to calculate PBTS characteristics of IGZO TFT with 3 hydrogen conditions, low (Low), medium (Med), and high (Hig), in this order. The results show the hydrogen concentration dependence of the PBTS stability.
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