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Advantage of RIE
RIE is a technology utilized to create microscopic ridges on the surface of the cell using plasma and reactive gases. The subtle ridges allow the solar cells to better absorb the sunlight reflected on the surface, therefore enhancing output and conversion efficiency.
RIE (Reactive ion etch)
100 mTorr Range - Physical(ion) and chemical - Anisotropic, controllable etch profile - More selective than sputtering
PLASMA ETCHING
α
Second bounce
First bounce
Third bounce
Second bounce
First bounce
The textured top surface reduces reflection from the solar cell and, when combined with a reflecting back surface, helps to confine or ‘trap’ light within the cell.
70 % transmitted 30 % reflected 3~5 ㎛
Cell Current ( mA )
Pyramids Slats
53.7˚ 45˚
Texture Angle ( o )
60˚
Poly-Si : Wet texturing (Roughness, < 3 um)
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Reflectance Reduction Mechanism
Surface texturisation & Light Trapping
Inverted Pyramids
SF6 3000sccm/Cl2 1800sccm/O2 3000sccm/RF 26.5kW/Pressure 250mTorr/Gap 12mm fixed/Time 50sec fixed RunOrder SF6 Flow Cl2 Flow O2 Flow RF power Pressure 1 2700 1800 3000 26.5 0.25 2 3000 1800 3000 26.5 0.25 3 3300 1800 3000 26.5 0.25 4 3000 1500 3000 26.5 0.25 5 3000 1800 3000 26.5 0.25 6 3000 2100 3000 26.5 0.25 7 3000 1800 2700 26.5 0.25 8 3000 1800 3000 26.5 0.25 9 3000 1800 3300 26.5 0.25 10 3000 1800 3000 25 0.25 11 3000 1800 3000 26.5 0.25 12 3000 1800 3000 28 0.25 13 3000 1800 3000 26.5 0.2 14 3000 1800 3000 26.5 0.25 15 3000 1800 3000 26.5 0.3 Post RIE Ref 11.24 11.61 16.40 13.59 13.74 13.89 17.58 13.60 12.10 14.81 13.84 13.69 11.34 13.79 19.65 Lifetime Decrease 0.90 1.17 1.73 1.08 1.66 0.91 0.57 1.90 1.30 1.61 1.40 1.59 0.84 0.61 0.14
•α : The path way of 2 light bounds at V- valley’s bottom corners. •α = 45˚ : The path way of 2 light bounds at all of area. •α = 60˚ : The path way of 3 light bounds at all of area. •Increasing of Pyramid texture angle + Number of bounds + Photo current. • Photo-current : Random texture << regular texture of pyramid at front and back side << the same size of pyramid at front and back side.
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Understanding about Plasma of 4th State of Matter
Ice
Water
Steam
Sun, stars, electric arcs, lighting, neon sign
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Effect of SDR
1. There is no affection with kinds of SDR solution type(Acid/Alkali). But initial wet texture surface will be affect to the reflectance after RIE. 2. Based on the SDR condition, it is possible to remain the residue after RIE. It means that the rinse process has a possibility to affect to the RIE process. 3. It is possible to show the difference of RIE process results according to the Wafer type and SDR status(Wafer preparation). Residue remain after RIE
Ex) Not enough Rinse Time
Normal status after RIE
Ex) Enough Rinse Time
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DOE in HQ
Datum Condition
Chemical, thus faster by 10-1000X Isotropic etch profile High etch rate Good selectivity Less prone to radiation damage
Higher Pressure
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Scheme of RIE Reactor
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Directional Etching by DC Self-bias
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6
(U-Mask)
Reaction
Film
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Plasma Etch Systems and Mechanisms
< 100 mTorr
Plasma Etching Reactive Ion Etching (Rຫໍສະໝຸດ BaiduE) Sputter Etch – Ion Milling
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Basic Steps in Dry Etching
Plasma
1
Generation of Etchant Species
Gas Flow
2
Diffusion to Surface
Ion Bombardment
3
Adsorption Byproducts
4
Diffusion into Sheath convection flow Boundary layer layer 5 Deposition
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JUSUNG RIE
5.April.2011
OUT LINE
1. Plasma & RIE technology
2. SDR effect 3. Effecting of RIE Parameter for Reflectance (DOE in HQ) 4. Cell Manufacturing in HQ 5. CIP(Continuous Improvement Program) & HW explanation of Jusung RIE
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3/45
Definition of Dry Etching(Plasma Etching)
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Boundary of DOE : Target Reflectance 11%
Gas condition : 2700~3300sccm(10%) of SF6 & O2, 1500~2100sccm(10%) of Cl2. RF Power : 25~28kW Pressure : 0.2~0.3Torr
-
Higher Excitation Energy
PHYSICAL SPUTTERING (and lon Beam Milling)
Physical momentum transfer Anisotropic etch profile Low etch rate Poor selectivity Radiation damage possible
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Texturisation : Light trapping
•Saw Damage Etch : Remove the Saw Damages (Micro-cracks) on the wafer. •Texturing : Textured surface (Pyramid or Random ridges) Reduce light reflection : Increase the light path way in the solar cell & light reflection from back side to inside again Light absorption Increase the Isc. •Reflectance of Si : ~30%@No texture surface, ~10%@Textured surface, ~3%@ARC deposition