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 Atomic Layer Deposited HfTiOx composite film On Si (100) with Al 2 O 3 as buffer layer

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 Hafnium oxide has a k value of Titanium oxide has a k value higher than 30 "High-k" stands for high dielectric constant, a measure of how much charge a material can hold. C = k  A t

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 )

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

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

Acceptable Temperature Window ALD reactions usually occur between °C in the reactor Above 400 °C, the chemical bonds are not stable and the precursor may decompose Below 200 °C, the reaction rate may be reduced 200°C400°C

Properties of the Precursors TDEAT Tetrakis(diethylamido)titanium C 16 H 40 N 4 Ti -Molecular weight 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

TDEAH Tetrakis(diethylamino)hafnium Hf(N(CH 2 CH 3 ) 2 ) 4 - Molecular weight 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

TDEAA Tris(diethylamino)aluminium Al(N(C 2 H 5 ) 2 ) 3 - Molecular Weight g.mol-1 - Physical State Low MP solid - Melting Point 28-31°C - Boiling Point 250°C - Vapor Pressure °C - Density °C

Experimental Conditions Reactor Temperature ~ 200 o C Operating pressure 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

Reaction temperature: 200 o C Plugs number : 5

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, Brain, Marshall. (n.d.). How Semiconductors Work. [WWW page]. Cambridge NanoTech, Inc. ( ). Cambridge NanoTech: Atomic Layer Deposition Systems. [WWWpage]. IC Knowledge LLC. (2004). Technology Backgrounder: Atomic Layer Deposition. [WWWpage]. Briefing.pdfBriefing.pdf. Intel® Education. (n.d.) Inside The Intel® Manufacturing Process: How Transistors Work. [WWWpage]. Majumder, P., Jursich, G., Kueltzo, A., & Takoudis, C. (2008). Atomic Layer Deposition of Y 2 O 3 Films on Silicon Using Tris(ethylcyclopentadienyl) Yttrium Precursor and Water Vapor. Journal of The Electrochemical Society. 155(8), G152- 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]. Zant, P. V. (2000). Microchip Fabrication (4 th ed.). New York: McGraw Hill. Air Liquide[WWWpage].

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