Application of layers with internal stress
This presentation is the property of its rightful owner.
Sponsored Links
1 / 16

Application of layers with internal stress for silicon wafer shaping PowerPoint PPT Presentation


  • 84 Views
  • Uploaded on
  • Presentation posted in: General

Application of layers with internal stress for silicon wafer shaping J. Šik 1 , R. Lenhard 1 , D. Lysáček 1 , M . Lorenc 1 , V. Maršíková 2 , R. Hudec 3,4 1 ON Semiconductor Czech Republic 2 Rigaku Innovative Technologies Europe

Download Presentation

Application of layers with internal stress for silicon wafer shaping

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Application of layers with internal stress for silicon wafer shaping

Application of layers with internal stress

for silicon wafer shaping

J. Šik1, R. Lenhard1, D. Lysáček1, M. Lorenc1, V. Maršíková2, R. Hudec3,4

1ON Semiconductor Czech Republic

2Rigaku Innovative Technologies Europe

3Astronomical Institute of the Academy of Sciences of the Czech Republic

4Faculty of Electrical Engineering, Czech Technical University in Prague


Outline

OUTLINE

  • Theory

    • Radius of curvature and warp

    • Thin film stress

  • Experiment

    • LPCVD Poly-Si Films

    • Squared wafer shape

  • Multilayer stack design proposal

  • Summary & Acknowledgements


Application of layers with internal stress for silicon wafer shaping

RADIUS OF CURVATURE and WARP

What is the relation between R and w? Assuming wafer shape is close to model.

WAFER

D/2

(1)

w

Wafer diameter

Warp

Radius of curvature

For small angle φ:

R

Therefore, the Eq. (1) can be rewritten as

φ

(2)


Application of layers with internal stress for silicon wafer shaping

RADIUS OF CURVATURE and WARP

Wafer diameter


Application of layers with internal stress for silicon wafer shaping

ORIGIN of THIN FILM STRESS

  • Thermal expansion

  • Intrinsic

    • growth

    • misfit

    • phase transformation

  • Extrinsic

    • applied stress

    • plastic deformation

(3)


Application of layers with internal stress for silicon wafer shaping

THERMAL STRAIN and STRESS

Due to mismatch of thermal expansion coefficient between substrate ( ) and film ( ), after temperature ramp down a strain ( ) is built in.

DEPOSITION TEMPERATURE

ROOM TEMPERATURE

Compressive stressin layer

THIN FILM

SUBSTRATE


Application of layers with internal stress for silicon wafer shaping

THERMAL STRAIN and STRESS

Biaxial stress in thin film on thick substrate is related with strain:

(4)

Young’s modulus; Silicon (100) – 1.3·1011 N/m2

Poisson’s ratio; Silicon (100) – 0.28


Application of layers with internal stress for silicon wafer shaping

INTRINSIC THIN FILM STRESS

Thin film with residual stress on the top of silicon wafer deform wafer according stress value and stress type [S.Timoshenko, J. Opt. Soc. Am., 11, 233 (1925) ](compressive or tensile)

COMPRESSIVE STRESS in layer

THIN LAYER

w

(5)

WAFER

R

Young’s modulus ; Silicon (100) – 1.3·1011 N/m2

Poisson’s ratio; Silicon (100) – 0.28

Wafer thickness

Radius of curvature after film depo

Radius of curvature before film depo

THIN LAYER

TENSILE STRESSin layer

Therefore the warp is proportional to the residual stress and film thickness and inversely proportional to the wafer thickness squared.

WAFER


Application of layers with internal stress for silicon wafer shaping

THIN FILM STRESS VALUE

Example of residual stress in different depo and thermal growth layers are in tables. Values are just indicative as the intrinsic stress may vary with the process conditions.

Compressive stress

Tensile stress


Application of layers with internal stress for silicon wafer shaping

LPCVD Poly-Si FILMS

Heat treatment of poly-Si films can cause the atoms to move to low-energy positions. Poly-Si thickness (THX) is proportional to the depo time, which can impact the stress in poly-Si films.

Compressive stress [MPa]


Application of layers with internal stress for silicon wafer shaping

BACK SIDE LAYER

After depo of poly-Si (THX 1.5 m)and for wafer thickness 507mm the warp 110mm (R = 25.6m) was achieved.

Warp profile perpendicular to the facet

Wafer deformation map


Application of layers with internal stress for silicon wafer shaping

WAFER SHAPE

Circular 150mm wafer, thickness 378 mm, warp 181mm was squared to □ 100mm. Squared wafer keeps axially symmetrical shape.


Application of layers with internal stress for silicon wafer shaping

WAFER SHAPE

Squared wafer has spherical shape. Deviation from ideal sphere is within 1 m.


Application of layers with internal stress for silicon wafer shaping

MULTILAYER STACKDESIGN

  • To get low R we need to combine layers with high tensile stress on the front side and compressive stress on the back side.

  • All process steps have to keep high surface quality of the polished front side.

R < 10m

Layer with tensile stress

WAFER THX ?

Layer with compressive stress


Application of layers with internal stress for silicon wafer shaping

LAYER STACK AND WAFER THICKNESS

  • For designed stack we can calculate the wafer thickness to achieve expected radius of curvature.

  • As we can see in chart the wafer thickness 195mm would be needed for R ~ 2m.

  • That thin wafer is sensitive for handling and also it is affected by gravity sag.


Application of layers with internal stress for silicon wafer shaping

SUMMARY & ACKNOWLEDGEMENTS

  • Impact of thin film stress on wafer shaping has been reviewed.

  • Layers with internal stress uniformly shape silicon wafer w/o deterioration of high quality of the polished front side (surface RMS ~ 0.1 nm ).

  • Stress in thin film is supposed to be constant regarding to the film thickness, which is valid for most of dielectric thin films used in microelectronics, except of poly silicon.

  • Stress in poly silicon layer is reduced with film thickness due to atoms migration into low energy position.

  • The circular wafer keeps the original axially symmetrical spherical shape after squaring. The solid area can be build from squared segments.

  • Multilayer stack has been designed to decrease the radius of wafer curvature to R ~ 2 m.

  • For other than spherical shape photolithographyhas to be used. Suitable technology is available in semiconductor industry.

  • Research was partially supported by Projects MŠMT KONTAKT ME09028 & MŠMT ME0918.


  • Login