Characteristics of Neutral Beam Generated by a Low Angle Reflection and Its Etch Characteristics by Halogen-Based Gases Geun-Young Yeom SungKyunKwan University
Problems of Current Etch Technology Scaling down of the device to nano-scale : increased volunability to processing damage - Physical damage - Electrical damage (Charging damage) DRAM Half Pitch Gate Length 2/32 SKKU
Charging Effects 3/32 SKKU
Trend of Etching Tools Development 4/32 SKKU
Researtch Status of Neutral Beam Etching Technologies 1) Gas dynamics or hyperthermal atomic beam (Heating of gas) - Caltech by Giapis in 2 (laser), PSI Inc. in 2 (laser), NEC by Nishiyama in 1995 (thermal heating), etc. Oklahoma Univ. in 2 (hyperthermal) 2) Ion-neutral scattering (charge exchange process) - Hitach by Mizutani in 1995 (ion removal by retarding grid), NTT by Matuso in 1995 (ion removal by magnetic field), etc. 3) Ion-electron recombination (surface neutralization) - IBM by Chen in 1997 (sheath recombination by ion and electron) - Tohoku University in 22 - Ebara Research Co. in 1995 (capillary hole) - Tokyo Univ. in 2 (focused fast atom beam) 5/32 SKKU
Neutral Beam Etching using Gas Dynamics PSI Inc. in 2 (laser) 6/32 SKKU
Researtch Status of Neutral Beam Etching Technologies 1) Gas dynamics or hyperthermal atomic beam (Heating of gas) - Caltech by Giapis in 2 (laser), PSI Inc. in 2 (laser), - NEC by Nishiyama in 1995 (thermal heating), etc. - Oklahoma Univ. in 2 (hyperthermal) 2) Ion-neutral scattering (charge exchange process) - Hitach by Mizutani in 1995 (ion removal by retarding grid), - NTT by Matuso in 1995 (ion removal by magnetic field), etc. 3) Ion-electron recombination (surface neutralization) - IBM by Chen in 1997 (sheath recombination by ion and electron) - Tohoku University in 22 - Ebara Research Co. in 1995 (capillary hole) - Tokyo Univ. in 2 (focused fast atom beam) 7/32 SKKU
Neutral Beam Etching by Ion - Neutral Scattering (Tatsumi Mizutani et. al, hitachi, 1995) 8/32 SKKU
Researtch Status of Neutral Beam Etching Technologies 1) Gas dynamics or hyperthermal atomic beam (Heating of gas) - Caltech by Giapis in 2 (laser), PSI Inc. in 2 (laser), NEC by Nishiyama in 1995 (thermal heating), etc. Oklahoma Univ. in 2 (hyperthermal) 2) Ion-neutral scattering (charge exchange process) - Hitach by Mizutani in 1995 (ion removal by retarding grid), NTT by Matuso in 1995 (ion removal by magnetic field), etc. 3) Ion-electron recombination (surface neutralization) - IBM by Chen in 1997 (sheath recombination by ion and electron) - Tohoku University in 22 - Ebara Research Co. in 1995 (capillary hole) - Tokyo Univ. in 2 (focused fast atom beam) 9/32 SKKU
Neutral beam etching by Ion-Electron Recombination (I) (Demetre J. Economou et.al, Houston Univ., 2) 1/32 SKKU
Generation of Directional Neutral Beam by Low Angle Reflection Recombination by low angle forward scattering 1~3 retarding grid reflection plate 9 5~15 Neutral beam Ion beam 5~15 Reflection plate : Si Ion gun O 2, SF 6 neutral beam ion beam faraday cup or sample rf coil When the ion beam was reflected by a reflector at the angles lower than 15, most of the ions reflected were neutralized and the lower reflector angle showed the higher degree of neutralization. 11/32 SKKU
Experimental Low Angle Reflected Neutral Beam System Quartz Plasma Electromagnet RF Coil Φ4 Acceleration Grid Focusing Grid 6 inch 25 mm Deceleration Grid Ion Beam Flux Plate-type type Reflector 5 o Reflection Angle Neutral Beam Flux Substrate 12/32 SKKU
Ion Flux and Neutral Flux as a function of Acceleration Voltage Ion current density (ua/cm 2 ) 4 3 2 1 SF 6 SF 6 5 o reflection NF 3 NF 3 5 o reflection CF 4 CF 4 5 o reflection Ar Ar 5 o reflection Grid hole size:ø2 neutral beam retarding grid reflection plate ion beam rf faraday cup or sample coil 1 2 3 4 5 6 7 Acceleration voltage (volts) 13/32 SKKU
SiO 2 Etch Rate as Functions of Acceleration Voltage and Gas Flow Rates for SF 6, NF 3, CF 4, and Ar Condition : reflector angle: 5, rf power: 5W SF 6 gas flow rate: 7 sccm Condition : reflector angle: 5, rf power: 5W Va : 7V SiO 2 etch rate ( nm/min. ) 4 3 2 1 SF 6 NF 3 CF 4 Ar SiO 2 etch rate (nm/min.) 8 7 6 5 4 3 2 1 SF 6 NF 3 CF 4 Ar 1 2 3 4 5 6 7 Acceleration voltage (Volts) 2 4 6 8 1 12 14 16 Flow rate (sccm) 14/32 SKKU
SiO 2 and Si Etch Rate as a Function of SF 6 Gas Flow Rate Condition : reflector angle: 5, rf power: 4W, distance between reflector and sample : 4 cm, pure SF 6, Va: 4 V, Ve: -1 V 2 13 18 SiO 2 12 11 Si Etch rate (A/min) 16 14 12 Va: 4 V Ve: -1 V 1 8 1 12 14 16 18 2 22 24 26 Flow rate (seem) Etch rate (A/min) 1 9 8 7 6 Va: 4 V Ve: -1 V 5 8 1 12 14 16 18 2 22 24 26 Flow rate (sccm) 15/32 SKKU
Etch Rate and Etch Selectivity as a Function of Gas Flow Rate Using the Neutral Beam Etching System Condition : rf power: 3W, acceleration voltage: 4V, reflector angle: 5 o reflector material: Si 5 4 Si SiO 2 PR.7.65.6 Si/PR SiO 2 /PR Etch rate(a/min) 3 2 1 Selectivity.55.5.45.4.35.3 4 6 8 1 12 14 16 18 2 CF 4 flow rate (sccm).25 4 6 8 1 12 14 16 18 2 CF 4 flow rate (sccm) 16/32 SKKU
Etch Rate and Etch Selectivity as a Function of H 2 to CF 4 Using Neutral Beam Etching System Condition : rf power: 3W, CF 4 +H 2 : 15sccm, acceleration voltage: 4V, reflector material: metal, reflector angle: 5 o 45 3. Etch rate(a/min) 4 35 3 25 2 15 Si SiO 2 PR Etch selectivity 2.5 2. 1.5 1. Si/PR SiO 2 /PR 1 5.5 1 2 3 4 5 6 7 H 2 /(H 2 +CF 4 )%. 1 2 3 4 5 6 7 H 2 /(H 2 +CF 4 )% 17/32 SKKU
SEM Micrograph of SiO 2 Etch Profiles (Neutral Beam Etching) Condition : SF 6 2.5 sccm, rf power: 4 W, acceleration voltage: 4V, reflector angle: 5 o etch mask : Cr 18/32 SKKU
SEM Micrograph of Si Etch Profiles Condition : CF 4 15sccm, rf power: 3W, acceleration voltage: 4V, reflector material: metal, reflector angle: 5 o 19/32 SKKU
Effect of Reflector Angle on Reflected Angle and Flux of the Neutrals Condition : SF 6 1 sccm(.6 mtorr), rf power: 4W, acceleration voltage: 4V reflector material: Si SiO 2 etch depth(a) 6 5 4 3 2 1 5 o 1 o 15 o 2 o SiO 2 etch depth(a) 6 5 4 3 2 1 1 2 3 16 18 14 1 8 12 6 Reflected polar angle θ r ( o ) 4 2 5 o 1 o 15 o 2 o 4 5 2 4 6 8 1 6 Reflected polar angle θ r ( o ) 9 Incident ion energy: 4V SiO 2 etch depth(a) 5 4 3 2 1 Incident ion energy: 4V 1 o 5 o SiO 2 etch depth(a) 5 4 3 2 1 1 2 3 15 18 21 12 6 3 33 1 o 5 o -1-8 -6-4 -2 2 4 6 8 1 Reflected azimuthal angle φ r ( o ) 4 5 Incident beam direction 24 3 27 Reflected azimuthal angle φ r ( o ) 2/32 SKKU
Effect of Reflector Materials on Reflected Angle and Flux Condition : SF 6 1 sccm(.6 mtorr), rf power: 4W, acceleration voltage: 4V reflector angle: 5 o SiO 2 etch depth(a) 7 6 5 4 3 2 1 Incident angle θ i : 5 o DLC Si Metal SiO 2 7 6 5 4 3 2 1 1 2 3 4 5 6 7 16 18 14 SF 6 + 1 8 12 6 Reflected polar angle θ r ( o ) 4 2 SiO 2 DLC Si Metal 2 4 6 8 1 Reflected polar angle θ r ( o ) 21/32 SKKU
C-V V Characteristics Before and After Neutral Beam & ICP Etch Capacitance (F) 1.2E-1 1.E-1 8.E-11 6.E-11 4.E-11 reference neutral 3 min ICP 2 min Capacitance (F) 5.E-11 4.E-11 3.E-11 2.E-11 reference neutral 3 min ICP 2 min 2.E-11 1.E-11.E+ -6-5 -4-3 -2-1 -6-5 -4-3 -2-1 Voltage (V) Voltage (V) <Big dot: 3um x 3 um > <middle dot: 2um x2um> Al(5A) Si 3 N 4 (5nm) SiO 2 (2nm) Si p-type, (1)1Ωcm 22/32 SKKU
I-V V Characteristics Before and After Neutral Beam & ICP Etch Treatment -ICP plasma power: 5 W, bias voltage: -1 V, gas: O 2, time: 2 min - Neutral beam power: 5 W, acceleration voltage: 4V, extraction voltage: -1V gas: O 2, time: 3 min, distance: 5 cm Current (A) 5.x1-7 4.x1-7 3.x1-7 2.x1-7 1.x1-7. reference neutral beam etching ICP etching -2-4 -6-8 -1 Voltage (V) <small dot: 1um x 1um> 5.x1-7 4.x1-7 reference neutral beam etching ICP etching 5.x1-7 4.x1-7 reference neutral beam etching ICP etching Current (A) 3.x1-7 2.x1-7 Current (A) 3.x1-7 2.x1-7 1.x1-7 1.x1-7. -2-4 -6-8 -1 Voltage (V) <middle dot: 2um x2um>. -2-4 -6-8 -1 Voltage (V) <Big dot: 3um x 3 um > 23/32 SKKU
SEM Micrograph of Poly-Si and Poly-Si/SiO 2 Etch Profiles (ICP Etching) condition : rf power: 7W, Bias voltage: -75V pure SF 6 5 mtorr, (Poly-Si) (Poly-Si/SiO 2 ) 24/32 SKKU
SEM Micrograph of Poly-Si and Poly-Si/SiO 2 Etch Profiles (Ion Beam Etching) condition : SF 6 2.5 sccm(.3 mtorr), rf power: 4W, Ve: -1V, Va: 4V, etch mask: Cr (Poly-Si) (Poly-Si/SiO 2 ) 25/32 SKKU
SEM Micrograph of poly-si and SiO 2 Etch Profiles (Neutral Beam Etching) condition : reflector angle: 5, SF 6 2.5 sccm(.3 mtorr), rf power: 4W, Ve: -1V, Va: 4V (Poly-Si) (Poly-Si/SiO 2 ) 26/32 SKKU
GaN and GaAs Etching as a Function of Flow rate, Additive Gas Process conditions Fixed power : 4W, Fixed acceleration voltage : 4V 35 45 Etch rate (Angstrom) 3 25 2 15 1 GaAs GaN Etch rate (Angstrom) 4 35 3 25 2 GaAs GaN 5 1 15 2 Cl 2 flow rate (sccm) <Cl 2 Flow rate> 5 1 15 Ar flow rate (sccm) <Cl 2 +Ar Flow rate> Total flow rate : 15sccm 27/32 SKKU
Damage Analysis Etched n-gan, GaAs Process conditions Fixed acceleration voltage : 4V, pure Cl 2, Gas flow rate : 3sccm, GaN Photoluminescence GaAs PhotoReflectrance Room Temp. PL Intensity (a.u.) 1 1 1 As-received ICP treatment Neutral treatment R/R (arb. units) Reference ICP ethcing Neutral etching 35 4 45 5 55 6 65 Wavelength (nm) <GaN PL> 1.3 1.35 1.4 1.45 1.5 1.55 1.6 Photon energy (ev) <GaAs PRS> 28/32 SKKU
I-V V Characteristics of GaN LEDs after Neutral Beam Etching of p-gan Condition - Neutral beam etching : Power 4W / Bias +4V / CF 4 15sccm / 4min / thickness 6-65Å - ICP etching : Power 4W / Bias -4V / CF 4 15sccm / 15sec / thickness 75-8Å 1 8 Reference ICP etching Neutral beam etching 1 1 1 Reference ICP etching Neutral beam etching.1 Current (ma) 6 4 LogA (ma).1 1E-3 1E-4 1E-5 2 1E-6 1E-7 1E-8 Device Structure -15-1 -5 5 Voltage (V) -1-5 5 Voltage (V) p - contact : Cr/Au p - contact : ITO p - GaN P-GaN surface Hole size : 2μm Reference Multi quantum well n - contact : Ti/Al n - GaN Neutral beam etch ICP etch 29/32 SKKU
GaN Device Efficiency after Neutral Beam Etching of p-gan 12 <Reference (No pattern)> Hole patterns <Neutral beam etch (patterned)> Emission intensity (A.U) 1 8 6 4 2 42 44 46 48 5 52 Wave length (nm) Reference Neutral beam textured Emission at 2mA Emission intensities were increased about 22% in neutral beam textured GaN LED (OES analysis) 3/32 SKKU
Commercialization Alpha Version for 12inch Dia.. Silicon Nano Processing RF Matcher Plasma source Grid & Reflector Chuck Process Chamber Pump Control box Item Ion source Grid & Reflector Chuck Chamber & Vacuum system Gas 사양 - Source type : ICP - Power 3W - Density : 5.5E+11(4mTorr, 25W) Grid Reflector Wafer - Grid에 DC Bias 인가 - Grid hole size; 2, 3, 4mm -Gridgap;2,4,6mm - Reflector angle; 3, 5, 7 + Plasma + + + + -Chuck&reflectorgap;5,1,15mm - Grid material : Graphite + bias Control voltage Ground - Tilting(Manual, 45 ) & Rotating(Automatic, 15RPM) - Lift pin & Mechanical clamp - No Cooling & heating - Vertical type - Chamber pressure :.3mTorr with Ar 4sccm - TMP 42l/s - Gate valve : ø4, Step motor Operation(Pressure control) - Gas box type : IGS(1.25) - Gas line : 14 line < 설비구성 > < 설비사양 > 31/32 SKKU
Summary Using a low energy reflection of reactive ion beam, directional reactive neutral beam for chargeless etching was successfully fabricated. By using the neutral beam, nanoscale etching of silicon and silicon oxide could be achieved. No charging damage was detected by the use of the neutral beam while the conventional ICP etching showed a significant damage such as leakage of gate oxide, RIE-lag, etc. It is believed that, neutral beam etching technique is benificial for the nanodevice processing not only for the top-down devices but also for the bottom-up devices 32/32 SKKU