Use of Stress Evolution Model for Thick Stress Deposition in 3D

vsex09.in : Use of Stress Evolution Model for Thick Stress Deposition in 3D

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

This example is essentially a 3D version of the example vsex08.

Most commercial process and stress simulators consider deposition not as a physical process governed by a time-dependent model, but rather 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. More details regarding differences of the two models can be found in the 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

This example demonstrates how the stress evolution model can be applied to simulation of stresses generated during thick layer deposition process and compare the results with standard one-step model. The test structure used in this example is a quarter of a a 40 nm MOS transistor.

The input deck consists of five sections:


  • Formation of a test structure with one layer nitride stressor in Victory Process. The structure is shown in the first 3D plot.
  • 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 Victory Stress. The structure is shown in the second 3D plot.
  • Calculation of stresses using stress evolution model of Victory Stress and "looping" capability of DeckBuild
  • 3D and 2D visualization of simulation results for both models

The stress evolution simulation uses the same structure with 20 layers at each step while 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 3D plots which compare Sxx stresses for two models. The Sxx stresses are also compared in two cut planes: Y-Z (vertical plane which roughly corresponds to 2D simulation of example vsex08) and X-Y (horizontal plane just 1 nm under silicon surface). The first of 2D comparison plots is very similar to 2D simulation of example vsex08. It shows that the stress evolution model predicts higher stress level under the gate. This fact is even better illustrated in the second X-Y plane. The upper-left corner of this cut plane corresponds to the gate area.

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 .