Paradee Leerungnawarat. Department of Materials Science and Engineering

Transcription

1 Paradee Leerugawarat Departmet of Materials Sciece ad Egieerig

2 Itroductio What is SiC? Why SiC? SiC has may advatages over Si. It is widely used for high power, high temperature electroic devices. Why High-Desity Plasma? It is very difficult to wet etch (practicality). Covetioal Reactive Io Etchig produces very low etch rates

3 Silico Carbide Crystal Structure 3C-SiC 6H-SiC 4H-SiC

4 Silico carbide properties Properties 3C-SiC 6H-SiC 4H-SiC Si Badgap (300 K, ev) Idirect Idirect Idirect Idirect Electro Mobility (cm 2 /V-s) room temperature, dopig~10 16 cm -3 Hole Mobility (cm 2 /V-s) room temperature, dopig~10 16 cm -3 Breakdow field (MV/cm) > dopig~10 16 cm -3 Thermal Coductivity (W/cm-K) room temperature, dopig~10 17 cm -3 Electro drift velocity (10 7 cm/s) Dielectric costat, ε

5 SiC Power Electroics The much wider badgap ad breakdow voltage for SiC relative to Si makes it attractive for high temperature, high power device applicatios. To date, high power MOSFETs, rectifiers, thyristors ad IGBTs have all bee demostrated i SiC, with far superior breakdow voltage ad o-resistace compared to Si. To make may of these devices, it is ecessary to have low damage, dry etch processes with high aisotropy.

6 Theoretical ad Experimetal Performace of SiC Ad Si Schottky Rectifiers.

7 Oe Applicatio: Via-Hole Etchig EMITTER FINGERS GROUNDING PAD 2-4 mil THINNED WAFER VIA FLIP-SIDE PLATED METAL Requiremets: High SiC Etch rate : High selectivity for SiC over mask material

8 Previously Reported Etch rates of SiC Reactor SiC Gas Coditio at highest ER ER Ref (Å-mi -1 ) RIE 6H CHF 3 /O 2 20 sccm, 200 W, 0% O SF 6 /O CF 4 /O NF 3 /O C SF 6 150W, 80 mtorr H,4H NF mtorr, sccm, 275 W ECR 6H CF 4 /O 2 500W, -100V, 17.5%O 2, 50 sccm C,6H CF 4 /O 2 650W, -100 V, 17%O 2, 50sccm H 20SF 6 /10Ar 750W, 250 rf, 2 mtorr, 30 sccm C,6H SF 6 /O W, 1 mtorr, 4 sccm H 10Cl 2 /5Ar 1000W, 150 rf, 1.5 mtorr, 15 sccm Cl 2 /5H W, 150 rf, 1.5 mtorr, 15 sccm IBr/4Ar 1000W, 250 rf, 1.5 mtorr, 15 sccm 1100 NF 3 800W, 100 rf, 1mTorr, 10 sccm 1600 SF 6 800W, 100 rf, 1 mtorr, 10 sccm 450 ICP 6H Cl 2 /Ar or /He 100 Cl 2, 750 W, 250rf, 5 mtorr Cl 2 /Xe 13%Cl 2, 750 W, 250rf, 5 mtorr 260 IBr/Ar 10%Ar, 750 W, 250 rf, 5 mtorr 800 ICl/Ar 66%Ar, 750 W, 250 rf, 5 mtorr 250 6H NF 3 /O 2 or Ar 100%NF 3, 750W, 250 rf, 5mTorr

9 High-Desity Plasma I this work we employ a form of high desity plasma (Iductive Coupled Plasma) ad several differet F 2 -based gas chemistries. HDP provides high io flux, low io eergy ad efficiet plasma dissociatio : low damage, high rate etchig. We examied the active plasma species by Optical Emissio Spectroscopy (OES) i order to uderstad the etch mechaism. We also examied several differet mask materials (Al, ITO ad Ni).

10 ICP Schematic Gas Distributio Plasma Alumia Chamber Sample ~ 2 MHz Power Supply Powered Electrode MHz rf source ~

11 Etchig Mechaisms e i e e i e i i e i s sput acc s s s sput diff abs s s des s abs s des s abs s sput s- Sputterig Chemical Reactio Io-Assisted Plasma Etchig Plasma Regio Substrate By products (Volatile products)

12 Keys to SiC Etchig Must break strog Si-C bods i order to allow etch products to form. Expect SiF x ad CF x to be the etch products (These are much more volatile tha SiCl x ad CCl x, ad hece F 2 - based plasma chemistries are favored over Cl 2 -based chemistries).

13 Experimet 1. 4H-SiC 2. Al 3. Ni 4. ITO Mask with Apiezo wax ICP reactor 2 mtorr 15 sccm Etched depth measuremet Gas : NF 3, BF 3, SF 6 or PF 5 ICP source power: 750, 1000, 1250,1500 W Rf chuck power: 150, 250, 350, 450 W Optical Emissio Spectroscopy (OES) Stylus Profilometer(Tecor) Roughess Measuremet Atomic Force Microscope

14 Etch rate i differet ICP Power i four differet gases PF 5 Etch Rate (Å/mi) BF 3 SF 6 NF 3 250W rf, 2 mtorr, 15 sccm Etch Yield (atom/io) PF 5 BF 3 SF 6 NF 3 250W rf, 2 mtorr, 15 sccm ICP-Power (W)

15 Dissociatio Eergies ad OES Spectra 20 9 Itesity (Arb. U.) NF W ICP 5W rf 35mTorr F F F F F Chemical Bod Stregth (KCal/mol) NF SF Itesity (Arb. U.) 6 3 B 100 BF W ICP 5W rf 35mTorr SiF x F F F F Itesity (Arb. U.) SF W ICP 5W rf 35mTorr SiF x F F PF BF Itesity (Arb. U.) PF W ICP 5W rf 35mTorr P SiF x F F F Wavelegth (m) Wavelegth (m)

16 Etch rate ad dc self-bias i differet rf power 7000 Etch rate (Å/mi) PF 5 BF 3 SF 6 NF PF 5 dc self-bias (-V) BF 3 SF 6 NF 3 750W ICP rf-power (W)

17 Surface roughess data from AFM SiC Cotrol : RMS = 2.5 m PF 5 : RMS = 2.0 m BF 3 : RMS = 0.8 m 1500 W Source Power 250 W rf chuck power 1 miute SF 6 : RMS = 1.4 m NF 3 : RMS = 0.6 m

18 Surface roughess i differece gases RMS (m) Cotrol PF 5 BF 3 SF 6 NF 3 Surface may actually become smoother due to the agular depedece of io millig which leads to faster removal of sharp features o the surface. + 1 θ ER ICP-Power (W) 0 90 θ

19 Etchig i 10SF 6 /5Ar w ad w/o UV Etch Rate (Å/mi) UV w/o UV dc self-bias dc self-bias (-V) Etch Rate (Å/mi) UV w/o UV dc self-bias dc self-bias (-V) ICP power (W) rf power (W)

20 Etchig i 10Cl 2 /5Ar w ad w/o UV Etch Rate (Å/mi) UV w/o UV dc self-bias ICP power (W) dc self-bias (-V) Etch Rate (Å/mi) UV w/o UV dc self-bias rf power (W) dc self-bias (-V)

21 Surface roughess of SiC at 200 W rf chuck power w UV illumiatio w/o UV illumiatio RMS (m) 1.5 RMS (m) w UV illumiatio w/o UV illumiatio ICP power (W) 10SF 6 /5Ar ICP power (W) 10Cl 2 /5Ar

22 SEM: SiC surface, etches with SF 6 W/O UV With UV

23 Etch rate of differet metal masks 10NF 3 /5O W rf chuck power 750 W ICP power 2 2 Etch Rate (µm/mi) 1 0 SiC Al Ni ITO Etch Deposit Etch Rate (µm/mi) 1 0 SiC Al Ni ITO Etch Deposit ICP Power (W) rf Power (W)

24 Etch rate ad selectivity i various gas ratio Etch Rate (µm/mi) Etchig SiC Al Ni ITO -0.5 Depositio Selectivity Ifiite SiC/Al SiC/Ni SiC/ITO %NF 3 (Total flow NF 3 /O 2 is 15 sccm)

25 SUMMARY NF 3 achieved the highest etch rate up to 8000 Å/mi which is a result of its higher dissociatio efficiecy i the ICP source. With high O 2 additio to NF 3, very high etch selectivity for SiC over Al achieved due to oxidatio of Al. With very low O 2 cocetratio, Ni mask shows better performace. UV illumiatio ca icrease the etch rate of SiC i Cl 2 discharge but ot i SF 6 discharge. UV illumiatio ca improve surface morphology of SiC i SF 6 discharge but ot i Cl 2 discharge.