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

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

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

Computer, Screen - Alltogether

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

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

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

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

Experimental Tools Processing conditions Samples high frequency 13.56 MHz Nextral low frequency 30 kHz Technics Processing conditions incoming gas: oxygen, oxygen flow: 2-10 sccm, pressure: 30 – 300 mTorr, plasma power: 100 - 700 W, process time: 0.5 - 120 minutes Samples Silicon wafers Si3N4 films on Si SiC films on Si Technics 8800 plasma tool

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

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

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

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,

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,

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

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)

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

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

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

Roughness after Plasma–How it Depends on Power

Roughness after Plasma–How it Depends on Time

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)