1. Nanoscale Dielectric Films by Plasma Oxidation
Alex Usenko NANOSMAT-5, Reims, France October 21, 2010

2. What is Corning® Silicon-on-Glass (SiOG) Technology?
Gate Driver
TCON
DC/ DC
DAC
Other Functions
Source Driver / DeMUX
IC Chip on Glass
Active Matrix
(display pixels)
SiOG
Poly-Silicon
Single Crystal
High Mobility
High Uniformity
Microscopic Crystals
Medium Mobility
Low Uniformity

3. Display Industry is Moving to OLED Quality
Future handsets will increasingly require the quality of an OLED display
Exceptional picture attributes (contrast, color, viewing angle)
Thinner, lighter form factor
…but OLEDS place higher demands on the display backplane quality
OLED
LCD

4. Computer, Screen - Alltogether

5. Silicon-on-Glass Process
Voltage
Si Substrate
Si-H → Si + H2
Anodic Bonding Step
Si Substrate H
Heat
Ion Implantation
Clean and Pre-Bond to Glass
glass
Separate Si Substrate
Thin and Clean
SiOG

6. New Process for Silicon-on-Glass Finishing
As-transferred → Plasma Oxidize → Strip Oxide
bottom interface of oxide would be smoother than top surface
if oxidized thickness equal to thickness of damaged part of silicon film, the damaged part would be removed

7. Why Plasma Oxidation Is Less Popular Then, Say, Thermal Oxidation?
Plasma oxide is, in general, inferior to thermal oxide; it has:
Some deviation from stoichiometrical composition (silicon-rich oxide toward Si-oxide interface)
Increased interface state density
Might have some porosity
But, plasma oxide still has advantages over the thermal one
Can be obtained at room temperature
Has low stress
Cheap
Thus, the plasma oxidation can be beneficially used in
Applications were passivation is not critical
Cost-sensitive applications requiring passivation

8. How Thick Oxide Can We Get by Plasma?
Plasma oxidation growth kinetics
published by
(1) Kraitchman
(2) Kimura
(3) Sugano
(4) Eljabaly
(5) Taylor

9. Experimental Tools Processing conditions Samples
high frequency MHz Nextral
low frequency 30 kHz Technics
Processing conditions
incoming gas: oxygen,
oxygen flow: 2-10 sccm,
pressure: 30 – 300 mTorr,
plasma power: W,
process time: minutes
Samples
Silicon wafers
Si3N4 films on Si
SiC films on Si
Technics 8800 plasma tool

10. Thickness and Composition of Oxide Film Converted from Nitride – Low Frequency Plasma
SIMS
Spectra

11. Thickness and Composition of Oxide Film Converted from Nitride – High Frequency Plasma
SIMS
spectra

12. Composition Profiles of Grown Oxide, Time Varies from 0
Composition Profiles of Grown Oxide, Time Varies from 0.5 to 10 Minutes
SIMS
30 kHz
plasma

13. Oxidation Kinetics In Low Frequency – 30 kHz Oxygen Plasma at Room Temperature
Thickness of SiO2 film (nm) converted from Si3N4 as a function of processing time (minutes). Pressure and power are fixed: 30 mTorr, 700 W,

14. Oxidation Kinetics In Low Frequency – 30 kHz Oxygen Plasma at Room Temperature
Thickness of SiO2 film (nm) converted from Si3N4 as a function of chamber pressure (mTorr). Time and power are fixed: 2 min, 700 W,

15. Oxidation Kinetics In Low Frequency – 30 kHz Oxygen Plasma at Room Temperature
Thickness of SiO2 film (nm) converted from Si3N4 as a function of plasma power (W). Time and pressure are fixed: 2 min, 30 mTorr

16. Depth Profile Of Composition of Plasma Oxide
Measured by VASE (varied angle spectroscopic ellipsometry)
15 nm thick
Graded composition
Silicon content 33% on surface (i.e., stoichiometric)
41% on interface (silicon-rich)

17. Surface Roughness Before and After Plasma
3.17 Å rms
Before
1.33 Å rms
After
Polishing Effect

18. Why Smoothing Happens?
Interface between film and substrate is smoother than initial surface; after oxide stripping sharp features disappear
Plasma erosion is more pronounced at peaks compared to valleys

19. Roughness after Plasma–how it depends on pressure
-- Area
- Section

20. Roughness after Plasma–How it Depends on Power

21. Roughness after Plasma–How it Depends on Time

22. Conclusion: Where Nanoscale Plasma Oxide Is Preferable?
In applications where surface passivation is critical, thermal oxide is still required
Plasma oxide is competitive in many applications like:
As sacrificial oxide (for example, polishing by oxidation/stripping)
As a mask (no warp due to high temperature processing)
When material or device should not be overheated (solar cell passivation, silicon-on-glass, etc.)
TFT gate oxide
Making hydrophilic surfaces (for wafer bonding – non-bondable Si3N4 surface can be turned bondable)