ALD Oxides Ju Hyung Nam, Woo Shik Jung, Ze Yuan, Jason Lin 1

Outline Materials: –Al 2 O 3 –HfO 2 –ZrO 2 –TiO 2 For each material: –ALD Chemistry –Physical Characterization –Electrical Characterization 2

Al 2 O 3 3

Chemistry Precursors: Trimethylaluminium (TMA, (CH 3 ) 3 Al), H 2 O Reaction: 2Al(CH3) 3 + 3H 2 O -> Al 2 O 3 + 6CH4 Composed of two half-reactions: –A) AlOH* + Al(CH 3 ) 3 -> AlOAl(CH 3 ) 2 * + CH 4 –B) AlCH 3 * + H 2 O -> AlOH* + CH 4 –(*: surface species) Figure: gspot.com/ 4

Deposition rate: on Si Found depositio 200 o C: ~0.99 A/cycle 5

Deposition rate: on Si Deposition rate decreases with temperature increase 6

MOSCAP Fabrication Process flow: Si substrate diff clean → Al 2 O 3 deposition → Al deposition → patterning (Karlsuss) → wet etch → FGA annealing Annealing treatments appear necessary Cycles Hysteresis (V) Befer FGAAfter FGA Hysteresis before & after annealing ∙FGA done at: 325 o C, 30 min 7

Dielectric Constant Dielectric constant is extracted from accumulation capacitance & measured dielectric thickness CyclesDielectric Constant (k) Extracted dielectric constant: ~6.75 ∙Deposition temperature: 200 o C 8

Fixed Charge Due to the fixed charge along the high-k/Si interface, flat band voltage (V fb ) shifts with Al 2 O 3 thickness. Fixed charge density can be estimated from V fb shift. From measured data, dV fb /dt = 3.5 x 10 7 V/m, Q f = x C/cm 2 (1.24 x q/cm 2 ) 9

Mobile Charge Mobile charge density was calculated from hysteresis Q mobile = C ox x V hysteresis 10 Cycles Hysteresis (V)Mobile charge dnesity (xq/cm 2 ) Befor FGAAfter FGABefore FGAAfter FGA x x x x x x 10 10

Temperature Dependency As deposition temperature increases, Al 2 O 3 becomes denser, and dielectric constant also changes. Temperature ( o C)Dielectric Constant (k) ∙ALD 100 cycles 11

Al 2 O 3 on Ge Al 2 O 3 was deposited on epi-Ge Growth rate was lower compared to Al 2 O 3 on Si: ~0.9 nm/cycle * epi Ge Si substrate Al 2 O 3 Metal (Al) Patterning + Etching FGA 12

MOSCAPs on Ge Hysteresis: high D it - annealing treatments appear necessary Dielectric constant: ~6.3, lower than Al 2 O 3 on Si Fixed charge: Q f = x C/cm 2 (3.09 x q/cm 2 ) Cycles Hysteresis (V) Befer FGAAfter FGA CyclesDielectric Constant (k)

HfO 2 14

ALD of HfO 2 - Chemistry Precursor : H 2 O Reactant :Tetrakis(dimethylamido)hafnium(IV) [(CH 3 ) 2 N]Hf The surface of Si can be either –H or –OH terminated, although –OH termination is more favorable Nitrogen is used to purge the precursor and the reactant between the steps Step 1 – 4 is repeated for in terms of cycles to achieve desired thickness. 15

Deposition thickness vs Temperature The deposition showed almost linear decrease with temperature until rapid decrease beyond 250°C. The samples were annealed at 300°C for 30min additionally to see if there are change in thickness due to densification, but found the change negligible. Future ALD process temperature was chosen as 200°C, as the standard recipe suggested. 16

Surface Roughness of HfO 2 films Surface roughness was measured using AFM to investigate the film quality in according to deposition temperature. On average, the films showed ~0.2Å(rms) in surface roughness, which is a comparable value to bare Si surface roughness. 17

Deposition rate of HfO 2 at 200°C Deposition rate of 0.99Å/cycle was observed for deposition at 200°C The thickness was measured by using ellipsometry (Woollam) Native oxide was also measured (7~10Å) to increase the accuracy of the film thickness. 18

MOSCAP Fabrication FGA Annealing at 300°C, 30min Forming Gas Annealing (FGA) 300°C, 30min Aluminum sputtering 2.5kw, 200sec(Gryphon ). HfO2 deposition at 200°C (Savannah) Diffusion clean (HF last) Si (WbDiff) MOS Capacitor was fabricated to measure the electrical properties of the HfO 2. Hydrogen in the forming gas should effectively reduce the interface traps between Si/HfO 2 interface, reducing the degree of hysteresis. 19

Capacitance – Voltage Characterization Dielectric Constant (k), doping type and concentration were extracted at 1MHz 20 Average Dielectric Constant : Average Doping Concentration: 1.5 x /cm 3 Hysteresis Range: 230mV-285mV Mobile Charge Range: 8x10 11 /1.4x10 12 /cm 2

Positive Vfb shift Fixed Charge Extraction Fixed Charge TypeFixed Charge Density : Negative : 2.94x10 12 /cm 2 Fixed charge type and density were extracted by normalizing each CV curve, and observing the direction and degree of V fb 1MHz 21

ZrO 2 22

ZrO 2 Chemistry Tetrakis[EthylMethylAmino] Zirconium. Zr[N(C 2 H 5 )(CH 3 )] 4 XPS confirmation for ZrO 2 deposition. Precursor temperature, pulse widths for precursor are ca refully examined. –Standard recipe will be available in the root of recipe folder. 23

ZrO 2 Capacitors Deposition rate at 200C, 100 cycles, ~87A oxide thickness 24

Deposition Rate Deposition rate at 200C, precursor line at 110C pulse time 0.5sec. 25

Deposition Temperature Deposition rate varies with deposition temperature, indication of ins tability of phase/property of the deposited film. Post deposition annealing and will largely influence the property. 26

TiO 2 27

ALD of TiO 2 Tetrakis(dimethylamido)titanium –[(CH 3 ) 2 N] 4 Ti Water –H 2 O Standard recipe is at 200°C 28

Physical Characterization (1) 0.38A/cycle 12A native oxide R 2 = ALD regime is confirmed, with 0.38A/cycle growth rate. 29

Physical Characterization (2) XPSAFM RMS: 0.36nm Ti:O ≈ 1:3 30

Relative Dielectric Constant (k) Depending on which pair of C-V considered, k = 7.6 to

Fixed Charge (Q F ) Al / Al 2 O 3 / TiO 2 / Si Al / TiO 2 / Al 2 O 3 / Si Al / Al 2 O 3 / Si Cannot be +Q F Still requires more study. Current belief is that the TiO 2 /Si interface is very defective. 32

Mobile Charge (Q M ) ΔV = 0.145V ΔV = 0.093V From hysteresis, estimate mobile charge density 4.7×10 11 cm -2 (Before FGA) 2.7×10 11 cm -2 (After FGA) 33

Thank you 34