Use of Stress Evolution Model for Thick Stress Deposition in 2D

vsex08.in : Use of Stress Evolution Model for Thick Stress Deposition in 2D

Requires: Athena and Victory Stress
Minimum Versions: Athena 7.6.8.R , Victory Stress 2.4.8.R

Most commercial process and stress simulators consider deposition not as a physical process governed by a time-dependent model, but rather as a mathematical abstraction in which a new layer just appears on the top of the structure. In these simulators the stress equations are solved after a material layer or region has been already added to the structure and not during the physical process of deposition. This one-step approach couldn't accurately predict stresses built in the deposited layer and in adjacent areas.

In order to accurately predict stresses in thick layers the process should be considered as a series of deposition and relaxation steps to emulate mechanical quasi-equilibrium during this physical deposition process. This more accurate simulation could be achieved by using "stress evolution" or "stress history" model implemented in Victory Stress.

This example demonstrates how the stress evolution model can be applied to the simulation of stresses generated during thick layer deposition process and compare the results with standard one-step model. Detailed results of this example are presented in Simulation Standard paper "Simulation of Stress Evolution During Semiconductor Device Fabrication":

http://www.silvaco.com/tech_lib_TCAD/simulationstandard/2012/jul_aug_sep/jul_aug_sep2012.pdf

The input deck consists of five sections:


  • Formation of a test structure with one layer nitride stressor in Athena
  • Calculation of stresses in the test structure using the one-step model of Victory Stress
  • Formation of a test structure with multi-layer stressor in Athena
  • Calculation of stresses using stress evolution model of Victory Stress and "looping" capability of DeckBuild
  • 2D visualization and average stress extraction for both models

The stress evolution simulation uses the same structure with 20 layers at each step while the effect of new sub-layer deposition is emulated by changing the status of this new sub-layer from "non-active" with properties inherited from "air" to "active" material region with properties inherited from nitride and the intrinsic stress of 1 GPa. Then Victory Stress recalculates stresses in the modified structure after each deposition step.

The simulation results are shown in two plots which compare Sxx and Syy stresses for two models. In flat areas of deposited layer, both models produced similar and essentially uniform stress. In the single layer case non-uniform stress regions appear only near corners of spacer/nitride. However, in case of multi-layer stress history simulation a highly non-uniform stress field extends diagonally from the spacer/substrate corner to the top of the film. In other words, stresses are significantly higher where the layers are sharply bent. As the result the integrated stresses under the gate appear to be 1.4 - 2 times higher when the stress history method is used. The extracted averaged stresses are calculated and saved in vsex08_0.dat and vsex08_1.dat.

To load and run this example, select the Load example button in DeckBuild. This will copy the input file and any support files to your current working directory. Select the run button to execute the example.

Note: To run this example you have to enable System commands in the Options menu from DeckBuild: Main Control .