Frank Greer, David Fraser, John Coburn, David Graves Fundamental Beam Studies of Radical Enhanced Atomic Layer Deposition (RE-ALD) SFR Workshop May 24, 2001 Frank Greer, David Fraser, John Coburn, David Graves Berkeley, CA 2001 GOAL: to evaluate film properties of RE-ALD deposited films by 9/30/2001. 5/24/2001

Motivation Current deposition technologies such as i-PVD and CVD are not sufficiently conformal for barrier layer deposition. Atomic layer deposition (ALD) has been proposed as possible alternative due to it’s nearly 100% conformality. Many different approaches and films reported1,2 TiCl4 + NH3  TiN Good resistivity reported Residual Cl% increases with decreasing dep. T (0.5% at 500oC, 1.5% at 400oC, 3.0% at 350oC) May lead to integration troubles with metals due to corrosion Key issue for integration Thermal budget Chemical stability of low-k films Mismatch of thermal expansion coefficients Lower temperature deposition using radical activation may allow for easier process integration with low residual Cl content. 1. Satta et al., MRS 2000 Spring Mtg. (D6.5) 2. Ritala et al., JES 147, 2000 5/24/2001

Step 2: TiClx (ab) + XH*(g) + N*(g) Radical Enhanced ALD1 Uses a volatile precursor and a radical source to deposit a film Reactants introduced in separate steps to achieve atomic layer control Products are nitride film and HCl Radical flux instead of heated substrate catalyzes precursor decomposition Potentially lower processing temperatures Low temperature processing questions: Precursor How and when is monolayer-like adsorption achieved without precursor condensation? Radicals Are radicals sufficiently reactive to remove ligands from precursors? Are radicals sufficiently unreactive to stop after one ML of reaction? Step 1: TiCl4 (g) Step 2: TiClx (ab) + XH*(g) + N*(g) TiN (s) + HCl(g) Precursor/Radical Inlet Wafer Heated (?) Pedestal 1A. Sherman U.S. Patent 1999. 5/24/2001

Future in-vacuo Auger Analysis Schematic of the Beam Apparatus in Cross-section (Top View) Quadrupole Mass Spectrometer (QMS) Load Lock Future in-vacuo Auger Analysis X = O, N , D Atom Source X Surface Reaction Products Analysis Section Rotatable Carousel Tuning fork chopper + + Experimental Diagnostics QCM - Measures mass change of film QMS - Measures products formed on film - Characterize beams Silicon-coated Quartz Crystal Microbalance (QCM) Ion Source TiCl4 Precursor Doser Main Chamber 5/24/2001

Experimental Procedure 1. Adsorption 2. Pump down TiCl4 3. Dechlorination 4. Pump down 5. Nitrogenation D ~1 mL of TiClx N ~1 mL of Ti-Dx Conventional ALD-like sequence Each step in process monitored in-situ with QCM Many cycles used to grow a film Resulting films removed for ex-situ XPS analysis Surface temp varied (32-135 oC) ~1 mL of Ti-Nx 5/24/2001

Precursor Adsorption Model Results 5x1014 6x10-5 8x10-3 135 9x10-5 80 1x10-4 32 Site Density (#/cm2) s(TiClx) self sticking s(TiN) initial Temperature (oC) Two uptake regimes (rapid ads. followed by slower ads.) Adsorption may not be confined to a single monolayer Data fairly well represented by assuming precursor adsorbs two monolayers of TiCl2 initial sticking ~ 100x self sticking contributes to uniformity self sticking decreases with inc. T coverage is more monolayer-like at higher temperatures TiCl4 Adsorption QCM 5/24/2001 1 L = 1015 Molecules/cm2

Dechlorination Results Exp. decay in Cl surf. conc. fit assumes D abstracts/replaces Cl kD+ClDCl = 3±1 x10-4 Much lower than previously reported value for H abs. of Cl on Au (~0.1 at 25oC)1 Fairly insensitive to T Calculated Cl density within a few% of ads. assumptions Suggests TiCl2 is appropriate surface species D Dechlorination Cl QCM Cl Lost Upon Exposure to Deuterium Cl loss due to abstraction by D atoms Cl Atoms/cm2 D atom Exposure (L) 5/24/2001

Dechlorination Results Residual Cl% can be controlled through TiCl4 and D dosages Increasing relative D exposure time reduces Cl content to detection limit of XPS! (<0.3%) Comparable thermal ALD process yields 1.5% Cl at 400oC1 Previously reported RE-ALD of Ti shows Cl “in the low percentage range”2 D Dechlorination Cl QCM Residual Chlorine vs. Relative D Exposure 100oC Results Cl Content (%) 1 Satta, A. et al. MRS 2000 Spring Meeting (D6.5) 2 Rossnagel, S.M. et al. JVST B 18(4) 2000. Relative D Atom/Cl Exposure 5/24/2001

Nitrogenation Results Nitrogen uptake does not saturate! ex-situ XPS shows N/Ti > 1 Initial uptake of nitrogen fit to linear model (sN = 8±4x10-3) Nitrogenation D QCM Uptake Upon Exposure to N atoms Milestones 2002/2003 2002  Study effects of surface preparation, type and temperature on film properties. 2003  Apply method to patterned surfaces for barrier film application. Explore DRAM capacitor applications. N Atoms/cm2 Nitrogen Atom Exposure (L) 5/24/2001