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Example 41: Stress of Substrate Coated with Thin Film

General

• A SiGe substrate is coated with a thin Si film. The stresses are generated due to the mismatch of their lattices.
   

• Lattice mismatch ratio = (Thin film's lattice constant - Substrate's lattice constant) / Substrate's lattice constant
  When the ratio of -0.1%, the tensile stress generated in the Si layer is calculated.
  The lattice constant of Si layer is smaller than that in SiGe layer. The lattice mismatch ratio is negative.
   

• Unless specified in the list below, the default conditions will be applied.

 

• Obtain this session's project file. (Right-click and choose 'Save link as')




• Results will vary depending on Femtet version and the PC environment.

 

Analysis Space

Item	Settings
Analysis Space	3D
Model Unit	um

 

 

Analysis Conditions

The unit is [um] to cope with thin film.

Item	Settings
Solver	Stress Analysis [Galileo]
Analysis Type	Static Analysis
Options	N/A

 

Model

The SiGe layer is a 0.1 um-thick solid body. The Si layer is a 0.01 um-thick solid body.

 

 

Body Attributes and Materials

Body Number/Type	Body Attribute Name	Material Name
0/Solid	SiGeLayer	301_Silicon(single-crystal) *
1/Solid	SiLayer	301_Silicon(single-crystal) *

* Available from the material DB

 

The initial strain (axial) is set to -0.001 on the Initial Strain tab of SiLayer. This is equivalent to -0.1% lattice mismatch.

SiLayer shrinks by 0.1% during the simulation.

 

Body Attribute Name	Initial Strain
SiLayer	Axial strain/Isotropic/-0.001

 

Results

The gradation contour diagram of maximum principal stress is shown below.

The substrate warps due to the lattice mismatch. The tensile stress is generated in the Si layer.