11/8/ Radical Enhanced Atomic Layer Chemical Vapor Deposition (REALCVD) SFR Workshop November 8, 2000 Frank Greer, John Coburn, David Frazer, David Graves Berkeley, CA 2001 GOAL: to determine the feasibility of using radicals to perform atomic layer deposition of Cu diffusion barriers at low temperatures.

11/8/ 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. Process temperatures used in ALD may be incompatible with new low-k dielectric films. Lower temperature deposition using radical activation may allow for easier process integration.

11/8/ Radical Enhanced Atomic Layer CVD (REAL CVD) 1 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? 1 A. Sherman U.S. Patent Wafer Heated (?) Pedestal Precursor/Radical Inlet Step 2: TiCl x (ab) + XH * (g) + N * (g)  TiN (s) + HCl (g) Step 1: TiCl 4 (g)

11/8/ Surface Reaction Products Atom Source Schematic of the Beam Apparatus in Cross-section (Top View) Quadrupole Mass Spectrometer (QMS) Main Chamber Analysis Section Rotatable Carousel + Experimental Diagnostics 1.QCM - Measures mass change of film 2.QMS - Measures products formed on film - Characterize beams Silicon-coated Quartz Crystal Microbalance (QCM) Ion Source + Tuning fork chopper X TiCl 4 Precursor Doser X = O, N, D Load Lock Future in- vacuo Auger Analysis

11/8/ Experimental Procedure Conventional ALD-like sequence –Each step in process monitored in-situ with QCM –Cycle used multiple times to grow a film Surface temp varied (32, 80, 135 o C) TiCl 4 ~1 mL of TiCl x 1. Adsorption 2. Pump down D ~1 mL of Ti-D x 3. Dechlorination 4. Pump down 5. Nitridation N ~1 mL of Ti-N x

11/8/ Precursor Adsorption QCM Results Two distinct uptake regimes –Initial rapid ads. followed by significantly slower ads. Adsorption may not be confined to a single monolayer Data fairly well represented by assuming precursor adsorbs two monolayers of TiCl 2 * Model fit allows estimation of: –Sticking probabilities –Active site (*) densities * TiCl x * * Suntola, T. et al Uptake Upon Exposure to TiCl 4 TiCl 2 Molecules/cm 2 TiCl 4 Exposure (L) TiCl 4 Adsorption 1 L = Molecules

11/8/ Adsorption Model Results initial sticking ~ 100x self sticking –contributes to uniformity self sticking decreases with inc. T –coverage is more monolayer-like at higher temperatures TiCl 4 5x x x x x x x x x Site Density (#/cm 2 ) s(TiCl x ) self sticking s(TiN) initial sticking Temperature ( o C)

11/8/ Dechlorination Results Cl loss due to abstraction by D atoms ex-situ XPS analysis shows ave. Cl conc. = 2.2% (0.6%- 3.8%) * D Cl Cl Lost Upon Exposure to Deuterium QCM Dechlorination Exponential decay in Cl/cm 2 fit assuming replacement of Cl with D k D+Cl  DCl = 3x10 -4 Fairly insensitive to T Calculated removed Cl density within a few% of ads. assumptions Suggests TiCl 2 is appropriate surface species Cl Atoms/cm 2 D atom Exposure (L) * Process not optimized for chlorine removal

11/8/ Nitrogenation Results N D Uptake Upon Exposure to N atoms QCM Nitrogenation N Atoms/cm 2 Nitrogen Atom Exposure (L) Nitrogen uptake does not saturate! ex-situ XPS shows N/Ti > 3 Initial uptake of nitrogen fit to linear model (s N = 8x10 -3 ) 2002  Study effects of surface preparation, type and temperature on film properties  Apply method to patterned surfaces for barrier film application. Explore DRAM capacitor applications. Milestones 2002/2003