Atomic Layer Deposited HfTiOx composite film On Si (100) with Al

2

O

3

as buffer layer

Adam Kueltzo

Thornton Fractional North High School

July 30

th

, 2009 University of Illinois at Chicago Advanced Materials Research Laboratory (AMReL) Mentors: Dr. G. Jursich and Dr. C.G. Takoudis Departments of Bioengineering and Chemical Engineering

Motivation for Research

 An Al 2 O 3 buffer layer is applied to improve the quality of the interfacial layer between high-k films (TiO 2 and HfO 2 ) and Si substrate  To run experiments in the atomic layer deposition (ALD) reactor and to examine thin film growth rates  To analyze the resulting thin films on silicon using spectral ellipsometry, Fourier Transform Infrared (FTIR) spectroscopy, X-ray Photoelectron Spectroscopy (XPS), and Atomic Force Microscopy (AFM).

Hypotheses

 A self-limiting reaction between a titanium, hafnium, and aluminum precursor, an oxidizer (H 2 O), and the silicon substrate  Good film uniformity on the substrate and film thickness control (using a spectral ellipsometer)  Absence of organic compounds in the resulting film structures (using FTIR spectroscopy)  Stoichiometry of the high-k material and the bonding states of the elements (using XP Spectroscopy)

New High-k Dielectric Materials

 The past few summers work has been conducted with Hafnium and recently Titanium and Aluminum  C = k A t "High-k" stands for high dielectric constant, a measure of how much charge a material can hold.  Hafnium oxide has a k value of 20-25  Titanium oxide has a k value higher than 30

Why deposit multiple precursors on substrate?

 Enhances dielectric constant (k)  Aids in the size miniaturization of semiconductor devices

Atomic Layer Deposition (ALD)

 Uses pulses of gaseous reactants (precursor and oxidizer) alternately fed into the reactor  Allows for atomic layer thickness control  Film thickness depends on number of deposition cycles

ALD Process

 “One Cycle”  Precursor    Purge (N 2 ) Oxidizer (H 2 O) Purge (N 2 ) http://www.cambridgenanotech.com/

ALD Reactor Set-up Modification capacity of three metal precursor deposition compared with previous two Ice bath Hot wall reactor Operating Pressure = 0.2-1.5 Torr Moisture pulse = 0.05 s C

Detailed on next slide

Female Elbow (VCR) Union Tee (VCR) To ALD Reactor Female Elbow (VCR) Ti precursor vessel (existing) Al precursor vessel (added)

Acceptable Temperature Window

 ALD reactions usually occur between 200-400 °C in the reactor  Above 400 °C, the chemical bonds are not stable and the precursor may decompose

200 ° C 400 ° C

 Below 200 °C, the reaction rate may be reduced www.icknowledge.com/misc_technology/Atomic%20Layer%20Deposition%20Briefing.pdf

Properties of the Precursors

TDEAT Tetrakis(diethylamido)titanium C

16

H

40

N

4

Ti

-Molecular weight 336.42 g/mol -Appearance Clear orange liquid -Melting point < -20°C -Vapor pressure 0.5 torr at 90°C -Density 0.92 at 33°C -Viscosity 8.8 cSt at 34°C www.praxair.com



TDEAH



Tetrakis(diethylamino)hafnium Hf(N(CH 2 CH 3 ) 2 ) 4

Molecular weight 467.0 g/mol Appearance Pale yellow liquid Melting point -68°C Vapor pressure 0.2 torr at 90°C Density 1.25 g/mL at 32°C Viscosity 5.7 cSt at 30°C www.praxair.com



TDEAA



Tris(diethylamino)aluminium Al(N(C 2 H 5 ) 2 ) 3

- Molecular Weight 486.7 g.mol-1 - Physical State Low MP solid - Melting Point 28-31°C - Boiling Point 250°C - Vapor Pressure 0.2 Torr @ 100°C - Density 0.915 g.cm-3 @ 25 ° C www.aloha.airliquide.com

Experimental Conditions

 Reactor Temperature ~ 200 o C  Operating pressure .2-1.5 Torr  Precursor Temperatures (Hf 67 o C) (Ti 62 o C) (Al 100 o C)  Purge Gas (N)  Purge time after precursor pulses - 10 seconds  Purge time after oxidizer (H 2 O) pulse – 20 seconds kept at 0 o C to stabilize vapor pressure

Initial TDEAA Bubbler Configuration

70 60 50 40 30 20 10 0 80 Reaction temperature: 200 o C Plugs number : 5 90 100

Bubbler Temperature ( o C)

110 Ser i es 1 Ser i es 2 Ser i es 3

70 60 50 40 30 20 10 0 3 Reaction Temperature: 225 º C Precursor Temperature: 100 ºC 4

Saturated ALD Plugs for TDEAA

5 6 7

Number of plugs

8 9 10

Temperature window for TDEAA

3.5

3 2.5

2 1.5

1 0.5

0 125 Precursor Temperature: 100 ºC Plugs Number: 7 150 175 200 225 250

Reaction Temperature (ºC)

275 300 325

Growth Rate of HfO2 (at the Reaction T of 200 ºC)

140 120 100 80 60 40 20 0 0 25 Grow th Rate = 1 Å/cycle 50 75

Cycle number

100 125 150

Future Work

 Further validate the deposition rate of TDEAA - Thickness determination  Deposition of TDEAH and TDEAT  Apply TDEAA buffer layer to silicon substrate

References

Anthony, J.M., Wallace, R.M., & Wilk, G.D. (2001). High-k Gate Dielectrics: Current Status and Materials Properties Considerations. Applied Physics Review, 89 , 5243-5275. Brain, Marshall. (n.d.). How Semiconductors Work. [WWW page]. http://computer.howstuffworks.com/diode.htm

. Cambridge NanoTech, Inc. (2003-2007). Cambridge NanoTech: Atomic Layer Deposition Systems. [WWWpage]. http://www.cambridgenanotech.com/. IC Knowledge LLC. (2004). Technology Backgrounder: Atomic Layer Deposition. [WWWpage]. http://www.icknowledge.com/misc_technology/Atomic%20Layer%20Deposition%20 Briefing.pdf

. Intel® Education. (n.d.) Inside The Intel® Manufacturing Process: How Transistors Work. [WWWpage].

http://www.intel.com/education/transworks/index.htm

. Majumder, P., Jursich, G., Kueltzo, A., & Takoudis, C. (2008). Atomic Layer Deposition of Y 2 O 3 Films on Silicon Using G158.

Mutschler, Ann Steffora. (2007). Intel, IBM Embrace High-k Gates for 45nm. Electronic News. Peters, Laura. (2007). Behind the Breakdown of High-k Dielectrics.Semiconductor International. p. 30. Praxair Technology, Inc. [WWWpage]. http://www.praxair.com

Zant, P. V. (2000). Microchip Fabrication (4 th ed.). New York: McGraw Hill.

Air Liquide[WWWpage]. http://www.airliquide.com/en/semiconductors/aloha-advanced-precursors/high-k.html



Acknowledgements

EEC-NSF Grant #0926260  Mentors: Dr. Greg Jursich and Dr. Christos Takoudis  Doctoral students: Qian Tao and Manish Singh