1. 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

2. 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

3. 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

4. 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

5. 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 ( oC)
~1 mL
of Ti-Nx
5/24/2001

6. 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

7. 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

8. 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

9. 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